[BlownBlu97]

seriously debating on switching my current setup to turbo and selling the KB. My motor was rebuilt 3 yrs ago and has only about 6k on it but the builder set it up at 8.2:1 compression which I feel is way to low. I was thinking of going turbo because it will make much more controlable power and well sounds SICK. On the other hand, instead of changing my entire system, I thought of dropping the engine and bumping the compression to 10:1 and see how it does. I could make more power with less boost and I bet it would be an animal.

Any thoughts? Will the stock crank and rods handle 20+ psi tossed at them on race fuel with that kind of compression?

 

[WantedDOA]

Bumping the compression will not make the car feel that much faster.

If you had a really heavy car then the bump in compression would be much more noticeable.
Have you ever done your own calculations on what the compression ratio is??

 

[BlownBlu97]

no I have not, how would I do that? I have a feeling it is less then I think. I have 21cc Ross dish top pistons, the block is bored 20 over and the heads are stock.

 

[just4me]

why not both. Compression really helps build power. And on a turbo setup, it will decrease spool time.

I have a whipple 2.3 at 23 psi on pump/ race gas mix and my compression ratio is 9.5:1. I run 16 psi on straight 91 octane and it does just fine. Kick the compression and watch your torque go sky high. Mine peaked at 767 at 5000 rpm on a mustang dyno.

 

[showme cobra]

im doing a teksid build and my comp will be about 10.2:1 with my 3.4 crusher at 25 lbs of boost

 

[stangfreak]

Let me say one thing. Today I saw my friend do a pass on his car at the "local" track here on 14lbs of boost. After I saw that pass, I didn't want to go in the car for a ride. twin 62's turbo 400 setup. OUT RIGHT STUPID. It was actually scary seeing the car go.

so um, yea, lol turbo's

 

[03yllwcobra]

Do BOTH!! I upped my compression to 9.5:1 when I was doing the turbo but to be honest with you I wish i would have went with 10.5:1 quicker spool more throttle response definitely the way to go!

 

[BlownBlu97]

If I were made of gold I would do both LOL. I figure switching to a turbo setup will be int eh area of 12K to do right. I can sell what I dont need for around 6K tops. I bet to just pull the motor and up the compression to say 10.5:1 and leave the KB will be around 3,500 and I bet it will be an animal too and I dont have to go selling things and recreating the wheel. Again it is a street car. Maybe I'll even go to a 11:1 compression like a boss.

 

[stangfreak]

11:1 is too high imo. The tune will have to be spot on and there will be no room for error with that much compression.

 

[BLK_03]

Changing the compression on your current setup will make power and you WILL feel it. Going turbo will cost CONSIDERABLY more.

It just boils down to how much you want to spend. Your crank and rods will do just fine with the higher compression and whatever boost you plan on running. You could spray on top of it and still be fine.

 

[eschaider]

... My motor was rebuilt 3 yrs ago and has only about 6k on it but the builder set it up at 8.2:1 compression which I feel is way to low. I was thinking of going turbo because it will make much more controllable power ... I thought of dropping the engine and bumping the compression to 10:1 and see how it does. I could make more power with less boost and I bet it would be an animal.

Any thoughts?...

BlownBlu97,

If your comment about making more controllable power implies you have uncontrollable power right now then raising compression, as you suggest at the end of the post, with a twin screw will only aggravate an already troubling problem.

Higher compression on a turbo and higher compression on a twin screw do different things to the engine. Because the twin screw sees boost immediately and the turbo sees boost later in the power curve the twin screw loads all internals as hard or harder for a longer period of time. That means increased susceptibility to detonation and a significantly decreased safe operating window for boost, timing and fuel. Smaller mistakes will have bigger price tags.

While the engines can be run at higher compression ratios and reduced timing you are decidedly narrowing the elbow room you have available in the event of a whoops. If you are not racing the car competitively or using a turbo you may end up paying a higher price than you thought for the higher compression when something goes bump in the dark.

All of this doesn't mean don't do it but it does mean go in with your eyes wide open and pay attention to the details all the time not just during the selection / build process and don't bite off more than you can chew. BTW if you run ethanol, the anti knock qualities allow much higher compression and you surrender nothing in terms of safe operating window. You will however surrender gas mileage.

Ed

 

[BlownBlu97]

the reason I mentioned a traction issue is because I run a street tire so I dont chew up the bumper. I drags she go's good and hooks well. I totally hear you about narrowing the window of the fudge factor. Now I have a E85 station right down the road from me so that is not a problem. I could care less about MPG if it provides me some added insurance.
I think I am going to go to a 10.0:1 ratio and just keep the blower because my setup works. I have a 2.8 with the Todd Berry Behemoth intake and twin 75mm tb and going turbo will really hit the wallet.
I have Ross pistons and hell fire rings in it now, should I stick with the same brand?
What will be needed to do this? Different CC piston? Milling the heads? or both? he motor was balanced and already has all ARP fastners in it.

 

[torchred04]

the reason I mentioned a traction issue is because I run a street tire so I dont chew up the bumper. I drags she go's good and hooks well. I totally hear you about narrowing the window of the fudge factor. Now I have a E85 station right down the road from me so that is not a problem. I could care less about MPG if it provides me some added insurance.
I think I am going to go to a 10.0:1 ratio and just keep the blower because my setup works. I have a 2.8 with the Todd Berry Behemoth intake and twin 75mm tb and going turbo will really hit the wallet.
I have Ross pistons and hell fire rings in it now, should I stick with the same brand?
What will be needed to do this? Different CC piston? Milling the heads? or both? he motor was balanced and already has all ARP fastners in it.

If the piston and pin weight changes you need to rebalance the crank. Leave the heads alone and just have the cc on the piston changed so you will need a new set of 8 pistons. If the weight changes at all you need to rebalance the crank so just remember that.

 

[BlownBlu97]

cool deal, thats my winter project. Wont break the bank and should give me a noticable boost in performance. I figure a $3K bill to do the work.

 

[03Steve]

(Budget x 2) + 10% is what I typically end up spending when it comes to this hobby, lol

 

[4vMn12]

budget x 2 then 1.4x my experience, amount to add for tools,equipment, supplies, (SKY Is the limit) I'm Don and I have an addiction.... ....

 

[torchred04]

If you haven't already add some ARP 2000 3/8" rod bolts to your stock rods they will be much stronger with those. Have them checked for roundness as well.

 

[BLK_03]

What's a budget?

 

[eschaider]

(Budget x 2) + 10% is what I typically end up spending when it comes to this hobby, lol

Words of wisdom ^

What's a budget?

Words of brutal experience ^

I would give some thought to pistons of a more robust nature for where you are about to go. If you will be using E-85 then the sky is the limit for compression. I mean that literally.

We have a race only alcohol motor (non ModMotor)that runs 12.5:1 compression and 40+ psi of manifold pressure and 42˚ of timing (bigger bore than mod motor) and we wear out parts, we don't blow them up or burn them up. Ethanol is slightly different than methanol but it has a very similar tolerance for high compression without knocking. The power increase will be, lets say impressive.

You will need a thick crown piston 0.250 or more if you can and skirts of comparable dimensions. Use stainless (or tool steel) top rings, get the top ring down at least 0.275 (try for 0.300) and you will have a ride extraordinaire.

Ed

 

[BlownBlu97]

Now speaking of E85, I have 80lb motorsport injectors and a Glens Performace sumped tank fuel system with twin walbro external pumps and push lok hose/fittings. I should be fine to run E85 through it right?