Fuel's Winter Project: Build It Before It Blows

[BruceH]

A .06 cc depression (what Diamond values the shallow exhaust valve relief in my pistons) would bring about 12.7:1. It isn't going to tax e85 imo. Plus it would give you a bunch of off boost power.

How about 12.7:1 with about 20psi and 327 cubic inches of mod motor? Since you are staying e85 no matter what go for the most compression you can.

 

[JoshK]

Man that sounds like fun Bruce!

 

[05stroker]

A .06 cc depression (what Diamond values the shallow exhaust valve relief in my pistons) would bring about 12.7:1. It isn't going to tax e85 imo. Plus it would give you a bunch of off boost power.

How about 12.7:1 with about 20psi and 327 cubic inches of mod motor? Since you are staying e85 no matter what go for the most compression you can.

That was my thinking with my current build at 302 CI. Time will tell...

 

[JoshK]

I really enjoyed the 11:1, so it is hard to say enough is enough. Man does that apply in more ways than one.

 

[Doug M]

Yeah dude, Just stop

 

[JoshK]

Yeah dude, Just stop

 

[jodadejss06gt]

Holly shit, 12+ on a mod running strong boost! I'm in for the results lol.

 

[roberts]

Did I just read stock heads on a big bore build? Why spend thst much money josh might as well get ported heads

 

[JoshK]

Well at 12.7:1 it probably won't take a lot of boost.

I will run ported heads if you buy them for me Travis

 

[JeremyH]

12.7:1. It isn't going to tax e85 imo. Plus it would give you a bunch of off boost power.

How about 12.7:1 with about 20psi and 327 cubic inches of mod motor? Since you are staying e85 no matter what go for the most compression you can.

I totally disagree with this train of thought on a boosted street car even with e85, even though you have had short lived success with it Bruce. Why have higher cylinder temps and pressures all the time when you don't have to or need it. Out of boost cruising who cares what power it makes, your not using any of it. And boost is instant getting on the throttle when driving. A point of compression is good for maybe 10-15hp and a 1lb of boost is good for 20-40rwhp depending on setup (30-40rwhp for a turbo car) as you know, so its not going to be some crazy difference with all that compression.

Did I just read stock heads on a big bore build? Why spend thst much money josh might as well get ported heads

Yeah stock 3v heads have lots of low end velocity and flow from the factory. No point on a turbo car unless you want to spend some money. Is 10-20hp worth $2k+ for heads? If so get them lol

 

[gray1622]

13:1 Sounds awesome.....

 

[retfr8flyr]

Yeah stock 3v heads have lots of low end velocity and flow from the factory. No point on a turbo car unless you want to spend some money. Is 10-20hp worth $2k+ for heads? If so get them lol

I totally agree. I had one of the best head porters around tell me that, with an FI setup, the only thing you needed on the 3v was a little bowl and short turn radius cleanup. He said a full port job was only worth another 10-15 HP, for all that money spent. Now NA is another story and fully ported is the way to go, because you need all the help you can get but with FI I feel the money is better spent elsewhere.

 

[jodadejss06gt]

^^^^THIS!!!!

 

[dysan]

I totally disagree with this train of thought on a boosted street car even with e85, even though you have had short lived success with it Bruce. Why have higher cylinder temps and pressures all the time when you don't have to or need it. Out of boost cruising who cares what power it makes, your not using any of it. And boost is instant getting on the throttle when driving. A point of compression is good for maybe 10-15hp and a 1lb of boost is good for 20-40rwhp depending on setup (30-40rwhp for a turbo car) as you know, so its not going to be some crazy difference with all that compression.

This may be a good point when dealing with a turbo or boost controlled centrifugal where it is easier to change the amount of boost but with a blower like my Edelbrock, the more boost I make the hotter the IAT temps get so being able to make the power I want with less boost is a huge plus for me. There is no way I could be as competitive at the track if I was running 15-18psi of boost and having the computer pull timing on each run compared to just 9psi of boost and having the car be dead nuts consistent.

 

[JoshK]

That's my thinking as well. The combined compression will be the same either way for say 800hp, so why not let the engine do its share and rely less on the turbo to do all the work? Especially if E85 is going to be the only fuel the car ever sees.

I am making a conversation to help with the decision. Not decided either way for sure yet.

 

[jodadejss06gt]

Get to reading Josh!

http://www.xcceleration.com/cr-boost 101.htm

 

[JoshK]

Get to reading Josh!

http://www.xcceleration.com/cr-boost 101.htm

So maybe zero deck the block to huh, lol

 

[jodadejss06gt]

haha I just thought you might like to read some more about it. Don't know how much good it will do though. I will use 93 probably more than I'll use e85 on my engine, so if I have to get pistons, I'll probably try to stick with something around stock cr.

 

[JeremyH]

That's my thinking as well. The combined compression will be the same either way for say 800hp, so why not let the engine do its share and rely less on the turbo to do all the work? Especially if E85 is going to be the only fuel the car ever sees.

I am making a conversation to help with the decision. Not decided either way for sure yet.

Doesn't quite work like that more air with boost means more fuel which helps keep things cool during combustion. I look at it this way, only time I'm out of boost is at idle and easy easy driving at low rpm in which case it doesn't matter what power I'm making im not getting on the car or trying to be fast. Boost it there as soon as I want it when I put my foot in it. Lower static compression means lower cylinder pressure and temps all over, for me that means more forgiving and reliable, no brainer for my street car. My motor has been getting abuse for 4 years now. Hitting rev limiters, no lift shifting, banging away on the 2step at 6500rpms lol. And even that time I put 87 octane in not thinking when switching back from e85 and full boosting..oops. That could have been deadly with a higher compression motor.



Just my opinion and what I have had great success with on a street car, my 9:1 compression 281 with moly rings and stock heads does quite well. A track setup or max effort setup, sure go for it. I think I would be happy with stock 9.8 or 10:1 if it was an e85 only car but that's the max I would personally ever want to run based on what I have had success with it.

 

[BruceH]

Jeremy, have you ever had overheating issues? It just doesn't seem to be a concern with mod motors.

I can't see why a person would hold themselves back with a lower compression motor if they didn't have to. Just a few years ago the thought was to turn off the knock sensors while keeping compression low as a safety measure. It certainly works and lower compression is going to be safer. If it's needed is another discussion.

Higher compression on it's own isn't going give a whole lot of hp just like you said and I've experienced the same with n/a builds. Higher compression with boost is additive. Why not have the equivalent of more boost but not have to use more boost? Especially if using a fuel like e85?

I understand your thinking and it works but imo it's just not needed with a s197 and e85.

The first motor I built for my Whipple setup had 9.4 compression. It was noticeably less powerful with the same boost level when compared with the stock 9.86 motor it replaced and it showed on the baseline dyno prior to bumping the boost for a built motor.