Compression vs. Boost?

sxysweed · #1 01-05-2010, 11:22 AM

Been doing some reading on the subject of compression vs. boost. Just a few questions though.

So, say you have a build running a JRSC on a D16A6. It's running say a 10lb pulley, will be fully tuned. X/Y/Z brands for I/H/E. Fuel is E85. Would it make more power on say 11:1 compression than on 9:1 compression?

Now, same setup and scenario, but we're running say 8lbs of boost. Which would make more power, the 11:1 or the 9:11 compression?

From my understanding where you raise cylender pressures to raise power output (and torque), the higher compression will make more power, on both 8lbs and 10lbs of boost, right?

Found a short thing on Team Integra, and it suggested that you would have higher dynamic compression on say like 8lbs and 11:1 compression than on 10lbs and 9:11 compression, and thus make more power.

Okay, so with all that said, say I'd be running a JRSC Setup or a small turbo where turning up the boost will only blow hot air and wouldn't return more power, would I want more compression (like say 11:1 vs 9:1)? Keep in mind this would be running on E85 which is 105(?) octane fuel.

The numbers may not be all that correct, but it makes it easy to think about.

MugenSI · #2 01-05-2010, 04:24 PM

Compression vs. Boost - Honda-Tech

Good quote from the thread

Quote:

This has been a long debated issue. It all depends on the type of fuel you are running and whether you have the ability to map out your timing.

In the end I truely think its a matter of prefference. Nutty tuner like me believes in the 10:1 minimum principal. However, I have seen both schools of thought work. For a full blown racecar I really don't see the advantage of running lower compression ratio if you have the choice to run alcohol or super high octane race gas. Octane is a whole seperate issue in itself.

For street application running high compression with boost is probably not the best idea. Chances are you are going to detonate or have to run extremely retarded timing to the point of running the EGT too high under boost.

Super charged application..... you can run higher compression and more timing than turbocharged application with the same compression ratio. You will not believe how much timing a roots style blower can take... scarry.. It all has to do with efficiency of the blower. Less efficient more timing, more efficient less timing. On twin screw style blowers they are very efficient compared to standard roots blowers.

si_killa · #3 01-06-2010, 11:16 AM

Its simple.

More compression=more power, which requires less boost to achieve your h.p goal and vice verse, less compression requires more boost to attain your power goals.

E85 is like gods piss, you can run a assload of timing and be safe =)

MugenSI · #4 01-06-2010, 04:30 PM

Quote:

Originally Posted by si_killa

Its simple.

More compression=more power, which requires less boost to achieve your h.p goal and vice verse, less compression requires more boost to attain your power goals.

E85 is like gods piss, you can run a assload of timing and be safe =)

BUt with higher compression, the tuner has alot less room for error compared to less compression

esotericimage · #5 03-01-2010, 06:05 PM

Quote:

Originally Posted by MugenSI

BUt with higher compression, the tuner has alot less room for error compared to less compression

that is correct!

HPC.DERF. · #6 03-02-2010, 08:23 PM

im running about 12 to 1 compression on my turbo car..

i've never seen a turbo car as responsive as mine with similar mods and make the kind of power im making on low boost..

car made 425hp on 7.9 psi

**Turbogixxer** · #7 03-02-2010, 09:21 PM

Quote:

Originally Posted by HPC.DERF.

im running about 12 to 1 compression on my turbo car..

i've never seen a turbo car as responsive as mine with similar mods and make the kind of power im making on low boost..

car made 425hp on 7.9 psi

There is a SAE paper that shows compression with boost is only good if you have a flat style piston. Most people say it "spools" faster because of the increase on non-positive pressure loads.

HPC.DERF. · #8 03-03-2010, 12:37 PM

my pistons only have a 1.5cc dome which is pretty close to flat.. between that and the head i have the compression is right around 12...

and from having the same turbo kit back to back on 2 diff motors with the only thing changed being the compression this motor spools a lot faster

**neo** · #9 03-03-2010, 04:16 PM

My BMW has like 12:1 compression and TWO turbos stock....

I trust BMW engineers.

**Turbogixxer** · #10 03-03-2010, 05:46 PM

Quote:

Originally Posted by neo

My BMW has like 12:1 compression and TWO turbos stock....

I trust BMW engineers.

BMW engineers wrote the paper lol

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