Hello everyone. I am building my spare engine. It is 4g63 block and my biggest question is what compression ratio would you guys recommend. My plan is to use Wiseco pistons and their only option is 9.0 compression or 10.5 compression there is nothing in between. This engine will be use with e85/race gas only no pump fuel at all but it will see 40+ psi boost on big turbo. Would you guys do 10.5 or 9.0 compression ratio? My current motor is 10.5 and see a lot of boost and it is working good so far for last 4 years. Thanks!

 

I would go 9:1. Much easier to tune and tuners don't freak out with the higher compression. I built an all e85 motor that was 12.5:1 and every tuner I talked to wouldn't touch the car. There really isn't much different between the 2 really but lower compression will keep the car happy and you would be able to run more ttiming and boost.

 

Thanks a lot for help. Why higher compression is harder to tune? Isn't higher compression more responsive on throttle? Lower compression motor will need a little more boost to make same power as higher compression on little lower boost. Am I correct or wrong? Thanks!

 

The margin for error on high compression is much smaller - it's more sensitive to ignition timing and knock, which makes the tuner's job more difficult (and dangerous). If it's E85 ONLY, I'd go with the higher compression in this rare instance. But the car would be limited to a minimal boost level on 91 octane with hugely diminished ignition timing.

 

Thanks a lot for your opinion. This engine will be E85 engine only. I was so much on the side of going higher compression but I just watched a video from dsport magazine that is very interesting. According to this video high boost high compression motor will lose power vs same boost lower compression application. My current motor is 10.5 compression 40psi boost and low timing for known reason, but now I am building spare motor and I am lost what to do with compression ratio.
Here is youtube link to this video if you would like to see.

 

Yeah I have been through all these debates in the past when I built my 12.5:1 2.4. I will tell you driving a low compression 2.4 to my high compression 2.4 obviously with different boost levels I didn't notice a difference in response. But as stated less room for error. I know e85 doesn't knock as much as pump gas but its a tuner thing. My original engine builder had no issues with it but when you start adding forced induction into the mix it creates problems.

 

Higher compression does not improve turbo response, but certainly does increase power off-boost. It will feel stronger as the turbo comes on, because it is. All of the theory in the world kind of goes out the window against real-world experience. Curt Brown's 16G power record (499 whp) was made with a "high compression" motor (they say it was above 9.0:1 but don't give specifics), and the English Racing team was using 11.0:1 compression on their DSM that set all kinds of records, which is not a happy accident. High boost and high compression ratio both do the same thing, the only difference is the location that they do it. The key to making more power with it is to best control the combustion, to make the best peak torque at TDC. This is why tuners don't like high compression; the timing window to take advantage of that increased cylinder pressure and burn rate is much smaller than the lower compression & lower cylinder pressure motor. Any donkey can tune it when the margin for screwing up is low, but this separates the pros from the average joes. As long as timing is where it should be, and there's no knock - you'll make the power.

 

If you are building an engine I'd recommend going to a 94mm crank. A forged eagle crank is inexpensive and will make good power. 9:1 is a nice target for compression. If you are going for 1000-1100whp , lower then 9:1 compression will be easier on parts and tuning.

 

Will 94mm crank make it 2.1L? What rods should I use with it? I was thinking to go standard 88mm crank and standard length rods but maybe I am wrong.

 

Very will put my man. Curt also ran a 2.1 or so it was rumored.

 

Yes but most people call it a 2.2. A crank is so inexpensive and worth it IMO. 94mm crank in a 63 block is a proven recipe. You can use 150/153/156 rods. 153mm rods would be ideal but plenty of people have used 150mm or the longer 156mm rods with less then ideal compression height.

A set of Carillo rods with a bolt upgrade would be my choice for a long running street engine up to 1000whp or so. They are strong and lightweight. Past 1000whp , An Aluminum rod would be recommended.

CP makes a nice piston, but an upgraded trend pin would be a good choice.

 

Yeah I agree with you on this. Mate it with a 156mm or 162mm and that spells fun.

That would make a 2.2 with a 156mm or 162mm. The 162mm would be a long rod 2.2

 

Ok so if I get 94mm crank and 156mm rods what pistons will I need to use?

 

Which setup and compression will make the most power on boost. I know I know it all depend on tune etc but my original plan was to do 88mm crank standard lenght rods and wiseco pistons 10.5 compression but this is exactly same setup as I am running now on 6466 turbo and I dont how I am feeling on building exactly same setup again. Thanks for any input guys

 

Lower compression = can make more power due to more boost.
high C/R is more responsive with less peak power due to less boost.

Goes back to the same thing everyone asks: "What do you plan to do with the car?".

One of the most fun I've had was 350whp from a small turbo and meth injection on a 1.8L with 11:1.
That car just seemed to move at any RPM. Revving to 8200rpm helped.