Lets say I will be running E85, a 4" thick FMIC and meth. What kind of compression ratio do you think I can get away with. Motor will be dyno tuned by one of the best in the midwest.

I'm just leaving my options open right now as I don't know exactly what I want to do. I don't want to be limited to the 3 E85 stations around here, but I also want a killer setup.

I need to let me head porter know how far to mill the heads, so pretty much anywhere from high 8's to about a 9.5 compression ratio are my choices.

 

easy 10:1 on 100+ octane E85, intercooler, & meth.

 

I would do 9.5:1 max because you may not go E85.

 

I'd want to know the whole combo before hazarding an opinion. And inject a 50/50 water/meth mixture, not straight meth. Cam specs will be one of the things I would need to know before expressing an opinion. Also, the max CR you CAN run is not always the best. Blown and NA motors are quite different. If you have a big blower, a higher boost/lower CR combo has been shown to be superior many times. i have seen it myself, more than once.

Rich

 

The short block is BGauthier's old block. Specs can be seen here.
http://www.blown383lt1.com/

Cam specs can be found here.
http://www.blown383lt1.com/camspecs.pdf

Heads are Brodix track 1's being ported my Ron and should be around 235cc intake runners. I haven't milled them yet as I don't know what compression ratio to go with.

Intake will be a Holley EFI single plain with an elbow and a monoblade.

Head gaskets will be Cometic MLS. Probably .027" compressed thickness to keep head milling to a minimum. I know quench isn't really a concern on blower motors, but it'll be around .0455".

And turbo is a TC78 header kit from RealQuick with a 4" thick intercooler.

Car will be 99% street and will be running a 24X LSX ignition with D585 truck coils.

Built A4 tranny with 2800 triple disc stall, 12 bolt with probably a 3.08 gear.

E85 is limited to around 3 stations around here and I'll be running 80lb injectors so I'm not certain E85 will be an option. Fuel pressure will be upped to keep duty cycle down if I do run E85.

Fuel pumps are dual walbros and hopefully the stock fuel lines will be able to keep up.

I think that's the major details to this build. If anything else is needed, just let me know. Thanks for the help.

 

What blower/turbo will you be using?

Rich

 

why only a 2800 stall?

 

I will be building him a custom built turbo kit:

1.75" primary tube headers
TC78
3.5" DP
3" cold side piping
31x12x4 A2a ic

 

Thank you. I can't wait to see this thing.

I got a good deal on it and I wanted it to be streetable with my current combo.
Also, I was told with the power level I'll be at with the new combo, it'll feel more like a 3200 stall.

 

Build it around 8.5:1 and use as much boost as you can w/o detonation.

Rich

 

Thats it?

I really don't plan on pushing more than 15 psi so I figured at least a 9.0:1 would be alright.

How did you figure on a 8.5:1? Is there some calculation you used for octane rating.

 

Experience. More boost v. more compression, the choice is clear. You will gain enxt to nothing from the hgiher CR and lose more than you gain woth more boost and timing.

Rich

 

Some guys over on ls1tech are going beyond 10:1 compression ratio with E85 and they are running 20+psi. They report faster spool up times and more power down low when out of boost.

I honestly don't know what to do. I don't want to leave too much on the table, but I also don't want detonation.

 

It's a blown engine. The static CR means next to nothing as far as power production unless you are building a grenade like a blown alcohol or fuel car or are limited in air flow from your blower. You are limited by pump gas. You gain less (by far), from increasing the CR than you do from increasing the boost. This is true as long as you blower/turbo is able to flow enough air w/o getting outside of it's efficient range. You need someone who understands turbos to size the blower - I don't know enough about that to tell you anything specific about the right turbo/housing to use.

Low compression/high boost/good heads/relatively small cam is the way to make a blown street car. It's not the same as an NA car! There are a lot of variables in the tuning mix. These include timing, intercooler efficiency, blower efficiency, need for excess fuel to cool the charge (mixture) etc. So it's hard to speak in more than generalities. Your CR is not related to the size of your ****, unless it's your ewang. You can go on the 'net and brag about your CR or drive a fast car that won't rattle itself to death on pump gas.

I will say it once more, then go ahead and build what you want.

If it's a fresh build, size the turbo or blower according to the hp you can reasonably expect. Use a "low" CR and have it tuned with the fuel you plan to use. A big cam is not needed, good heads are needed. Keep the intake charge cool.

Here's a chasis dyno graph of an LT1 built according to those rules with 7.5:1. 26psi from a centrifugal. Would be a 100-200hp more with a turbo. This was a cludge, the exact setup isn't the point - it's the low CR.



Rich

 

How much power you trying to make? I run the tc78 on a stock 5.3 with just a cam in it, twin procharger interoolers, no meth, and iats stay fine. We ran the same setup in my buddies car but with a 3" 30x12 fmic with at 14.5lbs, 26 degrees timing.

I'd think on 10lbs you'd make 600rwhp through the auto. I'd build it 10.0:1 at minimum 9.5:1, especially if you are planning on running e85. It's weird most the lsx guys run more compression and do fine, while the ltx guys always try to run less and less compression, even if they have a good top end.