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This kind of performance is not achieved by duplicating YouTube porting video clips. Remember when you hurt the low lift flow you profoundly injure all but wide open throttle high rpm performance. You can turn an OK performer into an unhappy and unpleasant to drive engine / car.




Ed
I will disagree with the above statement simply because it is possible to achieve excellent cylinder head performance with hand porting. The Key with hand porting is only remove the minimum amount of material to get the job done. The big disadvantage of hand porting is that it is an incredibly time consuming operation that will result in many hours of labor The main advantage of CNC type porting is a reduction in porting time especially in a production environment so this is why shops use CNC equipment to port heads.


Not my work, but here is home port job that addresses the bowls that most critical area for flow in the 4.6 head



Of course if you hog out the ports, velocity and therefore performance will suffer.

In this exhaust port, the gasket area has ben marked so it is not removed. the goal is simply to blend the walls and knife edge the divider.


Even Accufab Racing will finish port their heads by hand. I would suspect that the initial CNC port is done to speed up the process.

"Accufab does its own porting, starting with a CNC program and finishing by hand. The intake ports are not radically changed. The floor of the port is simply cleaned, while the roof and bowl are opened around the backside of the bowl. This makes more of an oval shape relatively deep in the intake port to keep the cross-sectional area the same throughout the port."
 

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I will disagree with the above statement simply because it is possible to achieve excellent cylinder head performance with hand porting. The Key with hand porting is only remove the minimum amount of material to get the job done. The big disadvantage of hand porting is that it is an incredibly time consuming operation that will result in many hours of labor The main advantage of CNC type porting is a reduction in porting time especially in a production environment so this is why shops use CNC equipment to port heads.


Not my work, but here is home port job that addresses the bowls that most critical area for flow in the 4.6 head



Of course if you hog out the ports, velocity and therefore performance will suffer.

In this exhaust port, the gasket area has ben marked so it is not removed. the goal is simply to blend the walls and knife edge the divider.


Even Accufab Racing will finish port their heads by hand. I would suspect that the initial CNC port is done to speed up the process.

"Accufab does its own porting, starting with a CNC program and finishing by hand. The intake ports are not radically changed. The floor of the port is simply cleaned, while the roof and bowl are opened around the backside of the bowl. This makes more of an oval shape relatively deep in the intake port to keep the cross-sectional area the same throughout the port."
Hey that's my porting! I stared at it for a little while wondering why it looked so familiar lol. Probably the 40+ hours I spent staring at the heads. I took a bunch of pictures when doing my porting but am by no means an expert. I didn't try to radically change the ports just clean up what ford provided, smooth the short side bowl radius, and knife edge the dividers on intake and exhaust. I also opened the bowls up to i think 80% of the valve seat and blended the ports to match up with what the machining left behind. Not sure what if any improvements it made though since it was a full motor rebuild and swap from b to c heads.
 
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What you intuitively think about porting and air flow dynamics will only get you so far in personal porting exercises and importantly fall miles short of what an average commercial porting job will produce. If you are buying expensive pieces for the rest of the engine why would you elect to skimp on the important head port purchase check point.

People who are short of cash for properly ported heads should consider a few check points
  • Don't begin projects without a plan,
  • Don't begin projects without a budget,
  • Don't overlook how good OEM heads are right out of the box,
  • Don't do something just to do something — that's stupid!
Some of you might remember a moderator and site member named Broke 7. His real first name is Allen. Allen has a 3650lb 03/04 Cobra that i,s basically stock with 9:1 compression, Whipple and all cabin internals, radio, heater etc., but with a straight rear axle. Allen is not an automatic car and street drives his car periodically to local shindigs.. Allen has a T-56 and a set of Stage ! Comp cams with, I belive 0.450 and 0.474 lift and a duration somewhere in the low 220's. Allen's car regularly runs 8.80's and 8.90's at over 160 mph with the OEM Cobra heads and computer.

I am going to be so bold as to suggest if you are not running high 8's at 160 mph you have a long ways to go with the basic components that Ford gave you. Save your money learn how to use what you have in an optimized way before you go blowing a lot of money on expensive parts you don't know how to use any better than what you already have (that actually works pretty well). You will have more fun, learn more about your car and making power and importantly enjoy your toy more. This is especially true if you do it without blowing a lot of money on high dollar hot rod parts that are not needed — especially if your performance target is slower than high 8's and 160 mph.

A monkey with a machine gun is not particularly threatening unless he discovers where the trigger is, what it is used for and importantly how to aim the gun. Both KB and Whipple have been very upfront with power potential for these engines with just blower replacement. You have awesome equipment learn how to use it before you start modifying stuff you don't need to.


Ed
 

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Hey that's my porting! I stared at it for a little while wondering why it looked so familiar lol. Probably the 40+ hours I spent staring at the heads. I took a bunch of pictures when doing my porting but am by no means an expert. I didn't try to radically change the ports just clean up what ford provided, smooth the short side bowl radius, and knife edge the dividers on intake and exhaust. I also opened the bowls up to i think 80% of the valve seat and blended the ports to match up with what the machining left behind. Not sure what if any improvements it made though since it was a full motor rebuild and swap from b to c heads.
I think you did a great job with the porting and there is no doubt in my mind that the heads will perform well. You mentioned that you did not radically alter the ports and that is the correct thing to do. Accufab Racing does not radically alter the ports of their heads either nor do they "gasket match" the intake or exhaust ports on their heads and it works for them.

Finally, it is certainly labor intensive to hand port a set of Modular 4V heads as noted by the 40+ hours of labor on your part, but that did not deter you and hopefully it will inspire other hard core Mod Motor enthusiasts to do the same.
 

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What you intuitively think about porting and air flow dynamics will only get you so far in personal porting exercises and importantly fall miles short of what an average commercial porting job will produce. If you are buying expensive pieces for the rest of the engine why would you elect to skimp on the important head port purchase check point.

People who are short of cash for properly ported heads should consider a few check points
  • Don't begin projects without a plan,
  • Don't begin projects without a budget,
  • Don't overlook how good OEM heads are right out of the box,
  • Don't do something just to do something — that's stupid!
Some of you might remember a moderator and site member named Broke 7. His real first name is Allen. Allen has a 3650lb 03/04 Cobra that i,s basically stock with 9:1 compression, Whipple and all cabin internals, radio, heater etc., but with a straight rear axle. Allen is not an automatic car and street drives his car periodically to local shindigs.. Allen has a T-56 and a set of Stage ! Comp cams with, I belive 0.450 and 0.474 lift and a duration somewhere in the low 220's. Allen's car regularly runs 8.80's and 8.90's at over 160 mph with the OEM Cobra heads and computer.

I am going to be so bold as to suggest if you are not running high 8's at 160 mph you have a long ways to go with the basic components that Ford gave you. Save your money learn how to use what you have in an optimized way before you go blowing a lot of money on expensive parts you don't know how to use any better than what you already have (that actually works pretty well). You will have more fun, learn more about your car and making power and importantly enjoy your toy more. This is especially true if you do it without blowing a lot of money on high dollar hot rod parts that are not needed — especially if your performance target is slower than high 8's and 160 mph.

A monkey with a machine gun is not particularly threatening unless he discovers where the trigger is, what it is used for and importantly how to aim the gun. Both KB and Whipple have been very upfront with power potential for these engines with just blower replacement. You have awesome equipment learn how to use it before you start modifying stuff you don't need to.


Ed
Here is something else you may want to think about: If you have a set of C heads like I do and have no desire to purchase a set of 03-04 Cobra 4V heads , then your choices for port work are limited because that shop in Michigan that you speak so highly of won't even touch a set of C heads. Additionally, even if I bought a pair of 03-04 Cobra heads, that shop in Michigan won't even offer to sell or ship a pair of their ported heads to California residents such as my self. Fox Lake Racing did do C head porting, but they recently went out of business. There is a certain three letter company in California that does offer C head porting services, but as a matter of policy, I choose not to deal with that company.

Furthermore, I still strongly disagree with your assertion that a do it yourself hand port job is vastly inferior to a commercial equivalent. In my opinion, one can only know for sure what 4V mod motor cylinder head port job is vastly superior only after a flow bench cylinder head port shoot out is held.

One thing we might agree on is to utilize as many factory parts as possible. For example, I already have a set Manley 300M billet I beam rods in my possession (that many people have mentioned that I don't need ) and other fancy parts for my 1000+ Teksid build. However, the plan is also to re use my original 2001 Cobra Teksid block, C heads, 01 Cobra intake manifold, crank, factory fuel rails, production type returnees fuel system and more. Again, many people are saying that my plan will not work and I say bull crap to that.

By the way, how many of you remember this car?
175620

Way back in the late 1990's this car was running in the eights at over 150MPH with a small Vortech S Trim at 15 PSI and a lot of factory Ford parts including the intake and B heads! The car did have an aftermarket Electromotive engine management system that allowed it rev past 8800 RPM.

175621
 

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Here is something else you may want to think about: If you have a set of C heads like I do and have no desire to purchase a set of 03-04 Cobra 4V heads , then your choices for port work are limited because that shop in Michigan that you speak so highly of won't even touch a set of C heads. Additionally, even if I bought a pair of 03-04 Cobra heads, that shop in Michigan won't even offer to sell or ship a pair of their ported heads to California residents such as my self. Fox Lake Racing did do C head porting, but they recently went out of business. There is a certain three letter company in California that does offer C head porting services, but as a matter of policy, I choose not to deal with that company.

Furthermore, I still strongly disagree with your assertion that a do it yourself hand port job is vastly inferior to a commercial equivalent. In my opinion, one can only know for sure what 4V mod motor cylinder head port job is vastly superior only after a flow bench cylinder head port shoot out is held.

One thing we might agree on is to utilize as many factory parts as possible. For example, I already have a set Manley 300M billet I beam rods in my possession (that many people have mentioned that I don't need ) and other fancy parts for my 1000+ Teksid build. However, the plan is also to re use my original 2001 Cobra Teksid block, C heads, 01 Cobra intake manifold, crank, factory fuel rails, production type returnees fuel system and more. Again, many people are saying that my plan will not work and I say bull crap to that.

By the way, how many of you remember this car?
View attachment 175620
Way back in the late 1990's this car was running in the eights at over 150MPH with a small Vortech S Trim at 15 PSI and a lot of factory Ford parts including the intake and B heads! The car did have an aftermarket Electromotive engine management system that allowed it rev past 8800 RPM.

View attachment 175621

Jan,

Your experiences with Livernois' reluctance to sell you product or services has to do with the California CARB regulations regarding using non-OEM components on a street driven car. It Is not an unwillingness on the part of Livernois to ship heads to you . It is an unwillingness on their part to get into a tussle with California over selling non-CARB compliant parts that you will use on a daily driver. Being a California resident, you already knew this.

If you want to buy race car parts for use on a race car you will have no problem. The rub is non-CARB compliant components on daily drivers. Do not conflate the sale of race parts and the sale of CARB compliant daily driver parts. You are smart enough to know the difference and the conflation only adds to the confusion you like to spread and it is not welcome here — don't do it.

Ford has evolved the Modmotor port design over the years on both the intake and exhaust sides of the head. The particular program that Livernois uses for the Stage III port they offer requires a specific casting. Different castings and port shapes may not allow the port to be created in the casting or may allow the port to be created but the casting is, in Livernois opinion, compromised from a reliability or performance standpoint. They have made a business decision not to go there. That is their call. If you don't like it, you have the option of going elsewhere.

You are certainly entitled to your own opinion and if you want to believe that a hand ported cylinder hear without flow testing for either ultimate flow performance or port to port flow matching is the optimum solution for you, again that is your call and you are entitled to it. Head shops invest in flow testing equipment for a reason and as luck would have it, that reason is port to port consistency, head to head consistency, customer to customer and job after job consistency.

The ability to measure flow performance, provides for improved head port development providing progressively better and better performing ports. The absence of performance measurement denies those sorts of development benefits. It is sort of like going to the track and racing your car but not getting a timeslip. Without knowing your short times, your ET or your MPH it is impossible to tune the car as well as the racer who gets a timeslip to see how his tuning efforts performed. No different when you port heads.

I find it interesting that after arguing that hand porting without any sort of measurement can be equivalent to a professionally ported head using CNC machinery and flow bench development, you return to argue,
one can only know for sure what 4V mod motor cylinder head port job is vastly superior only after a flow bench cylinder head port shoot out is held.
You can't have it both ways. You need to pick one model and hang your hat on it. Flip flopping only adds to your own mismessaging and a reader's confusion.

While I recognize you predilection to argue, about almost anything, the forum is intended to try to help the reader and not confuse him or the discussion with minutia, speculation or inconsistency. You have a preference for all the above. Please attempt to manage the logical mayhem, that you so often find yourself awash in, and refrain from allowing it to spill over onto this site.


Ed
 

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Jan,

Your experiences with Livernois' reluctance to sell you product or services has to do with the California CARB regulations regarding using non-OEM components on a street driven car. It Is not an unwillingness on the part of Livernois to ship heads to you . It is an unwillingness on their part to get into a tussle with California over selling non-CARB compliant parts that you will use on a daily driver. Being a California resident, you already knew this.




Ed
Honestly, I did not know that a modified Cobra 4V cylinder head was a part that a particular shop would consider too risky to sell or ship to California. In fact, this is the first time I've seen a shop that won't sell or ship a set of ported cylinder heads to California. I've always assumed that it was the usual parts such as "off road" exhaust systems that eliminate the cat converters, aftermarket engine management systems, performance cam shafts, etc that retailers would not ship or sell to California. Now can add ported heads to that list. learn something new everyday.

Finial thing I'll say is that I don't see how CNC porting is somehow vastly superior to hand porting in terms of improving cylinder head air flow, velocity and thus performance because I have not seen the CNC porting superiority hypothesis supported by any experiments that I could find. Also consider the following:

"Myth #1. CNC is “better”

"This one depends on the piece in the machine. If your making billet heads, the accuracy of the CNC is worth talking about, because you’re making something from scratch and making a batch of them ensures that they will all be the same. But when it comes to CNC machining a factory cast cylinder head, talking about the accuracy of the machine is a moot point. I say this because the factory head is cast, which means there will be some variation from head to head because of the imperfections that come from the casting process. That’s where the words “core shift” comes into play, because when we get cast heads back from the CNC shops there is not one that is exactly the same. In fact, in the head there is no ports that are the same. You can even see where the CNC did not touch the casting in one port but did in the others. That’s because the CNC machine does not know where the ports are, just where they are supposed to be. Meanwhile, a hand knows the center of that port every time. So, what does this mean?

While a CNC is better than a hand at many things, when it comes to porting your factory cast cylinder head it is really just faster, meaning it’s faster than any human could grind and sand your head. So, instead of waiting weeks or months to get it back from the machine shop, someone with a CNC could rip through it in a few hours and have it on the floor ready for machine work. Talking about consistency machining an inconsistent part makes no sense except to market it as the best option. However, because there are cylinder head guys out there who do such a poor job hand porting, seemingly haven taken lessons from a blind person with a hammer and a chisel, they help perpetuate the myth that CNC porting is more accurate or “better”

And I suspect that for the reasons stated above, Accufab Racing will first CNC port a set of 4V Modular Ford heads and then finish port them by hand.

We will agree to disagree on this one Ed and if you need to find me, I'll be in the garage porting my Cobra C heads because that shop in Michigan won't touch my C heads anyway.
 

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Honestly, I did not know that a modified Cobra 4V cylinder head was a part that a particular shop would consider too risky to sell or ship to California. In fact, this is the first time I've seen a shop that won't sell or ship a set of ported cylinder heads to California. I've always assumed that it was the usual parts such as "off road" exhaust systems that eliminate the cat converters, aftermarket engine management systems, performance cam shafts, etc that retailers would not ship or sell to California. Now can add ported heads to that list. learn something new everyday.
You are obviously not knowledgeable about the California Air Resources Board (CARB) regulations regarding modifications to motor vehicles driven in California.. That is not unusual for a non-manufacturer or most end users. The CARB restrictions are designed to prevent modifications to daily drivers that have not been certified by CARB authorities as not diminishing the vehicle's ability to meet the EPA emissions levels the OEM built it to meet.

Some aftermarket manufacturers like KB and Whipple have taken the time and spent the money to have their products certified by CARB as being compliant. Once the certification is successfully completed the manufacturer is authorized to ship a CARB compliance label / badge with each product. The label is to be affixed to the vehicle it is installed on per CARB regulations. This compliance certification is product and vehicle specific.

Manufacturers who choose to ignore the CARB requirements, in California, could potentially be held accountable for their non-compliance. The experience is both expensive in terms of time, lawyers and the potential fines that can be assessed. Livernois is taking prudent steps to avoid being drawn onto one of those unpleasant, unnecessary and expensive confrontations,



Finial thing I'll say is that I don't see how CNC porting is somehow vastly superior to hand porting in terms of improving cylinder head air flow, velocity and thus performance because I have not seen the CNC porting superiority hypothesis supported by any experiments that I could find. Also consider the following:

"Myth #1. CNC is “better”

"This one depends on the piece in the machine. If your making billet heads, the accuracy of the CNC is worth talking about, because you’re making something from scratch and making a batch of them ensures that they will all be the same. But when it comes to CNC machining a factory cast cylinder head, talking about the accuracy of the machine is a moot point. I say this because the factory head is cast, which means there will be some variation from head to head because of the imperfections that come from the casting process. That’s where the words “core shift” comes into play, because when we get cast heads back from the CNC shops there is not one that is exactly the same. In fact, in the head there is no ports that are the same. You can even see where the CNC did not touch the casting in one port but did in the others. That’s because the CNC machine does not know where the ports are, just where they are supposed to be. Meanwhile, a hand knows the center of that port every time. So, what does this mean?
You are smart enough to know that the flow performance is not a result of using CNC machining techniques alone. The CNC machining technique guarantees precise duplication port to port and head to head. If the basic porting program is poorly conceived the resulting flow characteristics will also be poor. The use of CNC equipment will not alter those fundamentals.


While a CNC is better than a hand at many things, when it comes to porting your factory cast cylinder head it is really just faster, meaning it’s faster than any human could grind and sand your head. So, instead of waiting weeks or months to get it back from the machine shop, someone with a CNC could rip through it in a few hours and have it on the floor ready for machine work.
While you observation about the speed with which a head can be completed is correct, that is only one reason the CNC prepared head is a better choice for the head porting service. The precision and consistency with which the CNC port can be formed and shaped eclipses anything a hand ported head can match. CNC shaped ports can be dimensionally reproducible down to less than a thousandth of an inch. Hand ported heads can have variations of 0.060" or more for radii and port cross section. Those are huge differences in precision and reproducibility and most importantly port flow.

Once a preliminary port design is finished a port can be inspected on a flow bench to find opportunities to further enhance the air flow. After discovery on the flow bench, a second port is built on the CNC reflecting the progressively more subtle porting changes used to further enhance flow. This type of successive port shape and volume development produces flow rates that are simply not possible to duplicate with a hand ported equivalent.

Tha said the tool, no matter how high its quality, is no better than the man using it. If you are not schooled in the optimization of the machine performance or the dynamics of fluid flow it will take you longer to achieve the same results — if you achieve them at all. It is not the tool it is the knowledge and skills of the man/men using them.


Talking about consistency machining an inconsistent part makes no sense except to market it as the best option. However, because there are cylinder head guys out there who do such a poor job hand porting, seemingly haven taken lessons from a blind person with a hammer and a chisel, they help perpetuate the myth that CNC porting is more accurate or “better”
I gave you credit for being smarter than that statement would imply. I am going to assume you are being argumentative just to be argumentative.

If you were to apply the same logic to machining a block deck or cylinder bore or main bores then none of the cast blocks (which are 100% of what Detroit manufacturers and sells) would be finish machined in a CNC machine center. Instead we would have men with files smoothing off the deck surface from the raw castings for improved gasket seal. If that sounds foolish then rethink your usage logic.

Again the value that the CNC machining center brings to the process aside from reduced manufacturing time is precision and reproducability part to part and production run to production run. The flow performance is not a result of using the CNC machining center (although the consistency and reproducability are). The flow performance is the result of a good understanding of fluid dynamics, hours of painstaking port development work on a flow bench and modifications to a test mule until the port approximates the best flow possible across the entire lift curve and within the physical constraints of the actual casting.


And I suspect that for the reasons stated above, Accufab Racing will first CNC port a set of 4V Modular Ford heads and then finish port them by hand.
The reason that a shop would use hand porting to finish a port is only because the port shape precluded a CNC cutting tool getting to the point in the port that needed attention — assuming you are capable of generating the code. There is nothing that a hand porting job can do that a CNC machining center can not do more precisely and better.


We will agree to disagree on this one Ed and if you need to find me, I'll be in the garage porting my Cobra C heads because that shop in Michigan won't touch my C heads anyway.
As always everyone is entitled to their own opinions. However, they are not entitled to their own facts and you are no exception. I do think it is excellent you are willing to invest the time and effort into doing your own porting. I also believe that better results are commercially available that would free you up to engage with other facets of your build. It is the age old trading money for time model and plays out a little different for everyone. You have obviously decided what is best for your build and I wish you success.

Because to do live in California you might want to become more knowledgeable about CARB before you attempt to get your finished car smoked out here.


Ed
 

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If you have a clutch that slides a bit on the gear change the impact on the crank snout is measurably reduced. That's the good news. The bad news is the clutch, which is already a consumable, becomes even more consumable. Another aggravating issue is the actual rotor pack rpm when you finally release the clutch in the next gear. Because we can not manually shift like an automatic the real rotor pack rpm is more like 20,000 rpm or higher when the clutch re-engages, which means even more damage to the crank snout,


Ed
So what if your blower belt is "slightly loose" but not so loose to where it would cause belt slip during WOT? What I mean is on the gear change instead of the crank snout taking a brunt of the load the blower belt slips a very minimal amount reducing the force on the snout. So the belt would be a consumable now?

I am noticing some belt dust but no boost loss from what I can see...
 

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So what if your blower belt is "slightly loose" but not so loose to where it would cause belt slip during WOT? What I mean is on the gear change instead of the crank snout taking a brunt of the load the blower belt slips a very minimal amount reducing the force on the snout. So the belt would be a consumable now?

I am noticing some belt dust but no boost loss from what I can see...
Your post ended with the comment I was going to start with, Wings (BTW give me a first name and I'll use it in the future).

On high powered cars there is a magical spot in the traction / torque transmission matrix that is right on the edge of breaking the tires loos but does not. It represents the maximum acceleration the tires are capable of producing without going up in smoke. When you go down the track after the run you will see two black tracks from the rear tires. Those tires are on the verge of but not breaking loose. The phenomena is called, not surprisingly, black tracking. Watch the Fuel cars on FS-1 when they broadcast the NHRA events. They will periodically show arial views and you can see the black tracking.

The rough analog of the phenomena is a belt tension that is just enough to preclude belt slip on acceleration and still produce the target boost. One of the characteristics of this will be belt dust around the blower drive on the front of the engine. Although one system has been optimized another is still essentially unmodified. The minuscule slip that produces the belt dust is insufficient to protect the crank snout so system #2 gets a failing grade.

Think of the dynamic as if you were the crank snout. As you come up in the rpm the crank is turning clockwise and there is a counter clockwise tug on the crank snout to drive the blower. When you change gears and the blower's rotor pack has to suddenly slow down the torsional load on the crank snout goes from the normal counter clockwise rotation instantly to a clockwise loading where the crank snout has to absorb the higher rotor pack inertia to slow the rotors down.

It is the counter clockwise to clockwise loading variations that eventually twist the crank snout off. With the original Eatons and early small 2.2 / 2.3 L KB and Whipple compressor the loading was still relatively small compared to the 3+ liter compressors both companies were beginning to introduce. Few if any folks (I can't recall anyone but I could be wrong) experienced snout failures with the original 'small' compressors that KB and Whipple offered.

Not so once KB & Whipple began offering their bigger compressors, now it was a different story. The bigger blowers because of the higher levels of stored kinetic energy were capable of applying much greater torsional twisting force to the snout of the crank. Enough in fact to eventually begin breaking snouts.

Your question about using belt slip as the pressure relief valve for the crank snout while good thinking and instinct, is an extraordinarily fancy balancing act. If you are not using a blower bigger than 2.3 liters you are 99% safe. If you are using one of the original 2.9 // 3.0L blowers you have entered the grey area. If you are using a 3.3L or larger compressor you are out on the thin ice. It is not a matter of will it happen but more a matter of when.

If you street drive the car and don't competitively run the engine up to 7500 / 8500 rpm prior to shifting, you will probably will dodge the bullet. If you do run the engine up to 7500 / 8500 rpm you are back out on the thin ice again. A clutch that slides on a gear change is a big help and also a big maintenance item. Even mild slippers are not well suited for anything outside of racing and don't forget they should be maintained between rounds. The other consideration with slippers is they usually use counter weight to lock up the clutch. That means high rpm shifting is going to be challenging.

Years ago at one of the NHRA meets a car pitted next to us that used a sprag on the blower snout. Because he was pitted right next to us I got a chance to talk with him and check out his sprag gizmo. The spray would lock when turned clockwise driving the blower and it would free wheel when turned counter clockwise. The idea was to allow the blower to free-wheel on gear changes. The focus at the time wasn't crank snout protection. Chryslers have snouts that are over 1.5 inches in diameter. The focus was blower belt life.

The particular car was big on lockup clutches and at the top of each gear the clutch was locked tight. Before his sprag gizmo, a gear change slowed the rotor pack and would use a blower belt every two, maybe three passes. The correct fix that they later embraced was not allowing the clutch to lock up and sliding through the gear change. From the outside you could no longer hear the gear changes and the engine sounded like it went to high "C" and just stayed there the whole quartermile.

I have toyed with the idea of using a sprag on our blowers for some time now to take the load off the stock crank snout. I need a good solid kick in the pants to get motivated to do something about this again. :) For the time being, if I were you, I would use organic clutch linings and stay away from grabby linings like the ceramic and sintered iron alternatives. The idea of using the blower drive belt sip as a pressure relief valve is admirable and good thinking but pretty fancy when it gets to real life implementations.


Ed
 

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If you street drive the car and don't competitively run the engine up to 7500 / 8500 rpm prior to shifting, you will probably will dodge the bullet. If you do run the engine up to 7500 / 8500 rpm you are back out on the thin ice again. A clutch that slides on a gear change is a big help and also a big maintenance item.
Awesome explanation thank you for taking the time to do that. That's a very good analogy about the tires on the cusp of breaking loose, great visual.

My blower is a 3.4 Whipple and I thought I was doing myself a favor by taking off the Metco 4# lower and going to a stock "caged" 4# lower. I had the Metco 4# lower paired with a 2.3 TVS. Im now regretting the move to the 3.4 after reading this thread and chatting with you and learning about the torsional twisting force (which is the real problem). I shift at 6,500 and never go any more than that, my tuner and I agreed with that so I don't go past 6,500. I guess my next play would be wait and see if VMP creates a 3.0 with a removable inlet, turbo, or a Whipple 3.0 (not ideal because no removable inlet). The car is mainly lives on the drag strip with a rare drive into town once in a while. Im actually in California too, im up in Humboldt County and race out at Samoa dragstrip.

I'd love to see that sprag setup that actually sounds very interesting. Do people still do that? That's kind of an interesting idea to incorporate inside of the blower if that's even possible.

Thanks again for taking the time to enlighten me.

Oh yeah and my name is Justin.
 

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1965 SPF 427 Cobra, & 2022 BMW M850
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There is a small pressure relief valve, so to speak, built into the blower drive, Justin. That pressure relief is the belt tensioner. After a gear change, the taught drive side of the belt goes slack as the blower tries to twist the crank instead of the other way around. At the same time the previously slack side of the blower drive belt, managed by the belt tensioner, goes taught.

Once this "reverse" sort of operation begins the blower will pull up against the belt tensioner in it's attempt to spin the crank. When it does this it will tighten the tensioner arm spring just like we do when we put on a new belt. OEM and aftermarket tensioner springs can be of differing strengths. Tensioners like the ThumpRRR tensioner can be reassembled with the spring clocked even tighter than ThunoRRR ships the tensioners.

The upshot of all this is there is some relatively easy relief, not a fix, but at least some aspirin for the headache. Beyond the aspirin, this fall or the next time (this fall would be good :)) you freshen the engine, take the time and effort to have the crank studded. Studding is not a 100% fix, there have been two possibly three cars that still broke the crank. Allen Garrett (Broke 7 on the site here) broke his crank snout despite being studded but it took him multiple years of racing to do it.

The silver lining is that even if you break the snout the stud keeps everything together, instead of the snout falling in the pan. Allen believed the stud saved him from some additional damage that would have otherwise occurred. When I originally did the stud modification I used a 9/16" (0.5625" diameter) ARP 8740 stud. Check out the Crank Tech I & II write ups in the TToC. In later years I discovered that GM uses a 5.185" long 16mm (0.630" diameter) bolt on the Gen IV 7 liter LS7 engines.

The ARP replacement bolt for the GM LS7 is a very nice off the shelf alternative that only requires a little adjustment in hole depth to work with our engines. Best part is, it is an off the shelf item not a custom piece. ARP recommends torquing the stud to 235 ft lbs on a stock LS7 crank. The ARP torque specs page for fasteners shows a torque spec of 244 ft lbs. for a 16 mm fastener made of 8740 steel.

175624


I would use the 244 spec on my engine. The higher spec will play to your advantage because of the OEM press fit of the damper on the snout. Request the shop to use a thread forming tap when they drill and tap the crank snout. The thread forming tap produces smoother stronger threads. They are like the rolled threads on the ARP bolt.

An OEM snout is only 1.25" in diameter. The length of the press fit in the damper is only 0.700" that provides a press fit of 0.7/1.25 or only 0.56 diameters! This is inadequate for both a damper and blower drive. I ended up going to a billet crank with a custom 1.400" diameter snout that was 0.700" longer than stock. The revised snout provided. a full diameter of press fit and on a much larger crank snout with a crank made of decidedly stronger steel.

The billet approach is a ~$3K fix for the problem. That is a lot of money, however it approximates the cost of the rebuild after a snout failure soooo ... Something to think about down the road.

For right now the short way home (and least cost) would be the ARP LS7 snout bolt, ARP part# 234-2504 torqued to 244 ft/lbs.


Ed
 
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