Very good advice

 

Thank you sir, you are an honest and respectable adversary.

 

my only statement is......... if u want low end power buy a V8 hehe.

I am a person who would choose a car by its trap speed, not its ability to tow. There will be a point where an engine will make max power w/ A boost + B timing + C static compression ratio but you will alway be limited to this power by octane level in your gas.

To me, if a car with lower static compression but more boost and timing would run a higher trap speed then a car w/ higher static compression but less boost/timing.. but car 1 is slower putting around town I would still choose car 1 over car 2. why? because when im putting around town i am doing exactly that, putting around town, not racing.

"It's up to the individual to choose which way they want to do it, but it's not fair to only feed them ONE side of the argument." I totally agree.



[Modified by DIRep972, 1:43 AM 10/12/2002]

 

When I built my motor I lowered my compression to 8.5:1. I've been around turbos for a while (not hondas) and have never seen these kinda of compression numbers (>10:1) on a properly built turbo motor.

Let's say for a minute that no one here is gonna drive round ever day on race gas. Do all you high compression guys think you have secretly discovered the way of making boosted HP and no one else ever tried running higher compression and less boost and timing.

Even on conservative factory motors CR is lowered and they arent even trying to run 15+ psi. You can do all the math you want but at the end of the day there arent any situations where high CR and boost work well. IMO

 

Here's my take. A 1 liter engine running 14.7psi of boost (numbers for argument's sake) will have twice as much air in it's combustion chamber as running at atmospheric. Thus, it can have twice as much fuel put in and make twice as much power (approximately).

But, we must look at compression -

((boost/14.7psi atmospheric)+1) * compression ratio = effective compression ratio

so, 14.7psi of boost on a 10:1 N/A engine will yield a compression ratio of 20:1. So, let's see what it will take to lower our effective compression back down to the 10:1 of the N/A engine.

((5/14.7) + 1) * ~7.5:1 = effective compression ratio of 10:1

SO, you could have a compression of 7.5:1 running 5psi of boost and have the same effective compression ratio as 10:1 N/A. But, here's the trick. the compression ratio has been lowered by 25%, correct? HOWEVER, the air in the chamber has been increased by 34% (5psi boost/14.7psi). SO, you are getting 9% more air in each combustion chamber at the same effective compression ratio! You will also be able to run more aggressive timing, out of boost, which could make up for some of the turd-effect...

Lower compression + more boost will make more power IN BOOST. The only time this is an issue is when 'driveability' comes into play, because the power/efficiency will be much less out of boost, but who really gives a ****, since we aren't driving Insight's and who races a honda under 4k-5k (where a turbo would be spooling) anyway?!?!

Anyone have any thoughts?

 

Anyway...I guess that didn't really adress the original question...
In light of my last post, I'll rephrase it in the form;
"what's the highest effective compression I can run on pump gas?"

It depends on the octane (and if you live in a metro area, as it's different in some places, 93 octane is not always the same) as well as operating temperatures and timing, since you are concerned about detonation, really. I would go with the 9.5:1 pistons. For a while I thought higher compression would be better, but that's because I didn't know what I was talking about

you could totally run 10psi on 9.5:1 pistons on premium gas, with very little timing retard. I think you could go up to 12-14psi, really...though, I can't seem to really find a straight answer on what the maximum effective compression vs. timing for pump gas is...

err...maybe that all meant something?

 

great info you guys.

i really bit off more than i could chew with this post. i appreciate all of the input and i must say that there are some really knowledgable (sp?) guys on the board.

Thanks again,
Brian

 

boosted hybrid was sucessfully running an 11.0:1 comp. turboed setup...you can get faster spool on a larger turbo with higher comp., and cooler intake charge with the larger turbo since you get get more flow at less boost. i know he was also runnign water/alcohol injection, though. and i don't want to hear any of this "water/alky injection is a band-aid" nonsense. it cools the intake charge, period. is an intercooler a band-aid?

anyway if you are interested in higher compression you can talkt o boosted hybrid, i know it worked for him.