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I am seeing a lot of threads on members wanting to go higher on their boost, but not many inputing how much is safe? A guy here in Knoxville is running a 2.80 upper and a lower pulley kit as well. How safe is this? Anyone care to give some input?
 

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The Ubiquitous Jimmy V.
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How safe is it?
That's a though question. We have strong motors. Tunned properly 14 even 15 lbs boost is fine..
Guys running more then 15lbs really don't expect there motors to last as long as stock.If they are they are kidding themselves.
Even with lower boost levels the tune and your maintanance also driving habits have a lot to do with the motors longevity.


jim v.
 

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More boost is definatly hard on the engine, but i think, obviously the real motor killer is detonation. If the guys running high boost have good fuel, they are pretty safe.

Take a look at this though, I wonder how much HP these high boost cars are really putting out before you subract out the parasitic loss of the blower? Could be that the high boost 500 rwhp cars are putting out 650-750 with the extra 150-250 going to turn the blower.

I decided to put up a web page on the above subject, my humble opinions...
http://users.erols.com/drfunky/pages/BoostHP.html

For those who don't want to click , Here is the info:

From Eaton's website, power consumption versus blower speed:


Notice the curves don't go past 12,000 RPM, and the highest boost shown is 10 PSI.

I have calculated blower speed at redline for the available pullies. Most of these diameters were supplied by others and haven't been measured by me. If you have any of these and think the Diameters I have in the chart is wrong, let me know.



What happens when you run the Eaton at these higher speeds and boost levels? I attempted to add a curve, extrapolated to 16000 RPM and 15 psi of boost, Please ignore my crappy ability to draw a smooth line with a mouse:



At 15 pounds of boost and 16,000 RPM if my crappy extrapolating is even close to right, the blower is consuming 160 HP!

Actually, I don't think I made a steep enough line, I think the power consumption is even higher.

What do you think the power consumption curve would look like at 19 psi and 21,000 RPM?

Can the blower possibly be adding more power to the engine than it takes away to turn it?
 

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JT said:
More boost is definatly hard on the engine, but i think, obviously the real motor killer is detonation. If the guys running high boost have good fuel, they are pretty safe.

Take a look at this though, I wonder how much HP these high boost cars are really putting out before you subract out the parasitic loss of the blower? Could be that the high boost 500 rwhp cars are putting out 650-750 with the extra 150-250 going to turn the blower.

I decided to put up a web page on the above subject, my humble opinions...
http://users.erols.com/drfunky/pages/BoostHP.html

For those who don't want to click , Here is the info:

From Eaton's website, power consumption versus blower speed:
SNIP
At 15 pounds of boost and 16,000 RPM if my crappy extrapolating is even close to right, the blower is consuming 160 HP!

Actually, I don't think I made a steep enough line, I think the power consumption is even higher.

What do you think the power consumption curve would look like at 19 psi and 21,000 RPM?

Can the blower possibly be adding more power to the engine than it takes away to turn it?
JT,

I've actually simulated a lot of this on desktop dyno with interesting results. What I've done is take the Eaton specs for blower HP loss, translated that into efficiency numbers (with 0 HP loss being 100% efficient, and loss of 1/2 HP being 0%, more or less, with the midpoint of the RPM curve as the data aquisition point), and extropolated them out to various boost levels, and pluged those numbers in whenever I reduce the blower pulley diameter in the software (look for a longer thread on desktop dynoing the car soon). Anyhow, that only tells part of the story, however, as I'm sure you know, because when the Eaton spins higher it puts out a ton more heat. Since desktop dyno doesn't have the ability to add in a heat index, I simply used the temps listed in the latest 5.0 mag to extrapolate the increased heat and modeled it by reducing the efficiency of the intercooler accordingly. What I have found is fairly surprising. Using the 2.93 pulley (2.51 ratio, blower efficiency 60%, IC efficiency 75%), the numbers at the engine are around 516 HP @ 6,000, and 521 TQ @ 4,000. This translates into (roughly) 438/443 at the rear using 15% loss, which is almost exactly what I'm seeing on my car. Using the maximum pulley diameters, with no other mods (3.3 ratio, blower efficiency 50%, IC efficiency 65%), the numbers at the engine are around 526 HP @ 6,000, and 553 TQ @ 4,000. This translates into (roughly) 447/470 at the rear using 15% loss, which is close to what people with these mods are showing. So it seems, with no other mods, changing from a 2.93 upper with the stock lower to a 2.8 upper with the 9" lower gains you a whole 9 RWHP and 27 RWTQ. Not very much, and I think that's the point, The surprising part is, if you change the TB at this point from the stock (357 CFM flow) to something that flows 450 CFM, you go to 551/574 at the engine (468/489 RW), which is pretty illustrative of another problem, intake flow. So, just for giggles, I popped in a completely fantasyland TB with a flow of 1150 CFM, and got 599/615 at the engine (509/523 RW) :jawdrop This tells me that the intake is a definate restriction to that amount of boost. If you take it further, you get some really nice numbers by raising the rev limiter to 8,000 (which I was told the engine SHOULD support), porting the heads/enlarging the valves, and popping in a set of cams speced for the heads. However, it may just be easier to pop a Rayjay 300B turbo, intercooler, and 450 CFM TB on there, as with NO OTHER MODS, that makes 696 HP @ 5500 and 710 TQ @ 5,000 :eek: :jawdrop

Now, be advised that all of this is assuming I have the correct cam specs (couldn't find them, but I ran iterator tests of about 200,000 different cam profiles until I got HP/TQ curves that matched our dyno results), and the head numbers aren't too far off (using the 4-valve head/ported base spec, as I can't get flow numbers on our heads and Dyno2000's "Stock 4-valve" profile absolutely will NOT support the HP numbers we are seeing on the stock heads).
 

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I think you've hit on an interesting "point of dimenishing returns" with our engines. That is, while higher boost produces more power, at some point the parasitic losses overtake the gains.

I sometimes wonder if those guys running oversized lowers and undersized upppers are really getting their money's worth. At some point I guess you have to find a larger and/or more efficient blower, like the Kenne-Bell.

I think most street cars will settle on 3.1 or 2.93 uppers soon as that seems to be the best "bang for buck".
 

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Holley Blower boost bat man:cool:
 

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If you want "Safe Boost" stay stock!
 

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I've wondered if there should be an index to 'Most informative threads' or 'So now you Know' or somesuch?
I would nominate this one (JT's and NetWG's, and Jim's posts).
JW
 

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jhwalker said:
I've wondered if there should be an index to 'Most informative threads' or 'So now you Know' or somesuch?
I would nominate this one (JT's and NetWG's, and Jim's posts).
JW
Thanks for the complement, JH. Actually, a lot of info from the threads I found most informative is in the FAQ (link at the bottom of my sig). This info isn't in the current version, but will most likely be in the next version :)
 

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JW I was thinking the same thing. Like a freq ask tech section. What ya think. It be easier for me and more informative for the members.

Rick
 

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jhwalker said:
I've wondered if there should be an index to 'Most informative threads' or 'So now you Know' or somesuch?
I would nominate this one (JT's and NetWG's, and Jim's posts).
JW
JW,
Thanks for the kind words. Makes me feel better about spending time drawing HP curves and the like.

JT
 

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I'm going to work on my belt slipping problem but mine makes 20psi up to about 5400rpm then the belt slips and it holds at 17psi until I shift.:jawdrop
 
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