Re: high comp + boost theory
 

you will make much more power with low compression and lots of boost than with high comp and low boost.
in a way boost is like adding displacment to an engine without expanding the bores or lengthening the stroke.
you force more air and fuel in a smaller place(turbo honda) than sucking n/a air in a big place(v8).
thats where we detonate......
pistons with a 10.1:1(STATIC) COMP RATIO are running like 20.1 comp ratio under 18lbs boost(numbers are guesses but you get my drift)
pistons with a 8.0:1 (STATIC) cr are only running like 14.1 cr under 20lbs of boost.
find a happy medium that gives you a good cr under load and a turbo that moves enough cfm of air at your desired boost pressure.

thats pretty much the secret to top end horses

Re: high comp + boost theory
 

i knew this must have been done thats why i asked
i know how a turbo works and all that
since this is just a minor build (pistons rods 300hp) in the mean time and to learn off of before i do my full build in the future i thought about this

no i see that there isnt that much gain on the lower end
ill still do more research towards this before i make up my mind
but it was just a thought

Re: high comp + boost theory
 

Overall, high comp+boost > low comp+equal amount of boost. But that is given enough fuel to avoid knock on the high comp motor...

Re: high comp + boost theory
 

May be its me but i think the OP is looking for better spool time and off boost response as opposed to max power.

Re: high comp + boost theory
 

that was obvious....

Re: high comp + boost theory
 

He won't get it by just raising static compression. Squeezing the air/fuel mix more doesn't magically give the charge greater volume. You need to increase the volume of spent gases moving through the turbine to make it spool faster. The only effect of increasing compression is off-boost performance and having to use higher octane fuels.

Re: high comp + boost theory
 

I always thought squeezing the air/fuel more does create more heat and turbos spool from not just the spent gases but also from the heat expansion from those gases (why its hard to get performance out of rear mounted turbos without heatwrap on everything) But you may be right, I cant seem to find any reliable source that talks about static CR vs spool times

Re: high comp + boost theory
 

Ok well I may have slightly underestimated how much the spool time will be affected. But the slightly quicker spool will be negligible, and NOT worth the extra risk needed to prevent detonation. And whatever power is gained will probably be lost because you've got to retard the timing so much to keep detonation in check, and you'll also be dumping buckets of fuel into the cylinders to keep things cool.

Re: high comp + boost theory
 

Uhh, come again? You're confusing some things here, the only reason why a ring gap would change is if you're using cast or forged pistons.


For the OP, since I take it you want to try rockin' that 16g you could do one of 2 things...
1. You could swap the 7cm^2 housing from the 16g back over to the 14b's 6cm^2 housing if you like the spool response of the 14b, or...
2. Lean spool. Yes, I said it...lean spool. All newer Evo's run this on the stock setup, basicly it runs a bit leaner (and therefore hotter) in the first few thousand rpm's to get the turbo spooling faster. I wouldn't recommend it on a high c/r build, but if you do a vitara setup you shouldn't have a problem. At a throttle point over 50% my afr's will stay near the 14:1 mark into boost and around 13.5:1 up until near 4-5psi. After that the turbo is spooled up enough to drop to the standard (in my case) 11.3 afr until I hit my 23psi max. With a 16g6 and a 10.5cm^2 hotside on my 2 liter I start to spool by 2300 rpm and hit max boost by 3300rpm. If I disable lean spool I don't start hitting boost until around 3200 and peak isn't until 4000 or a hair later.

Re: high comp + boost theory
 

i considered the 14b/16g Frankenstein but quickly turned away
my buddy had it oh his zc and said that it lost top end power compared to the normal 16g

but the running lean... ill have to do some research
so i guess the boost makes up for the restarted timing to prevent knock