fe3tcourier

because there is less fuel and air to explode...

high compression is over rated. it just forces your octane level up if you want to not retard it to manifold/turbo melting levels. if you can get e85, and be bothered making it work, then high compression is a goer. if not, lower = better.

moral of the story, its hard to have your cake and eat it to

meaning

if you want big power on pump gas, you need to suffer the lag.

cloud

is there a noticable differance in power going from 9.1 stock compression to 8.5 with vitaras out of boost

fe3tcourier

someone else will have to tell you for sure, but unlikely.

take short look back in time and see that old school econobox engines ran as low as 7:1 compression to be suitable for low octane fuel with their primitive chamber/piston designs and they were still primarily limited in output by the rpm, not torque. if i wanted to run very high boost on pump gas safely with no aids, i'd consider going as low as 7:1 on a modern engine. my first choice for moderate boost would be 8:1 and light boost 10 - 15psi would be 9:1. on 10:1 you'd best keep it under 10psi on pump gas for good reliability and ease of tune. thats not to say thats the be all and end all, but its a good starting point for a noob.

marcj

You need to do more research on how turbos work.. the whole concept is to use the turbo to compress air, dense air = more efficient combustion.

What you're wanting to do is run the motor at stock (or higher?) compression for daily driving because you're worried 9:1 @ low rpm's wont accelerate quickly.. if you want low rpm acceleration on the fly, use a smaller turbo, such as a ball bearing T28 from a nissan. If you want top end power use something bigger. Basically, you're not running efficiently if you want high compression + low boost.

alcohaulin_hatch

if you want a good explanation there is an excellent thread on evans tuning website.

cliffnotes, lower compression raises the knock threshold for your tune on pumpgas other than that who cares.

either or will work.

Inquisition

This is only true to a point. Compression ratio, like boost, just increases your VE. Turbos are neat because you can have a shitty engine, just increase the boost, and you will make more power because you are just going to shove my air into the engine. NA on the other hand it is very hard to increase air flow so it's all about taking whatever air you can get, and combusting in a manner which yields the most power. Combining both ideas will yield the highest efficiency. Realistically if I want to make 300whp and run 93/94 octane, I know 9:1 compression I have plenty of margin for error(given my turbo setup doesn't suck). So I increase my compression to 10:1, I still have room for error but not a ton. Now I'm at 11:1 and I'm entering the "if you ---- up, I'm going to turn your pistons into scrap metal" zone. At this region you are making the most power most efficiently but are running a low margin of error. It's all about what your priorities are. Racing super competitively, where winning counts for something, you want to run close to a 1.0 safety factor. Granted if something goes wrong, you're fucked. But if things go right, you have a chance to win. Running with a large safety factor, sure you may finish every race, but your chances of winning are decreasing.

With a D-series engine, I would run 9.5:1-10.0:1 compression, and a T3/t04e 50 trim .48/.60. If you were talking about a B-series engine, I would suggest 10-10.5:1 compression with a similar turbo.

xxguyxx

i have a 11:1 Stock prelude type s motor in my prelude, t3/ t4turbo on 6lbs. runs awesome. its been boosted about 3 months now.
i spent a lot of time tuning it so it doesnt knock. but its all the the tuning. i have plenty of power in the lower rpms and turbo spools a lot faster on this car compare to my other car lower compression (9:1) same turbo. high compression low boost is all in tuning the ignition timing.

Oscar

Here's a thread comparing 10:1 compression to 9:1 compression, on a boosted gsr.
http://forums.evans-tuning.com/viewt...hp?f=15&t=1612

The graph is no longer up, but they talk about it.

It's a 15whp difference, running ~9psi on both setups.

evo_lucian

Not a honda but i am currently supercharging a my toyota 4age with 10 c/r . basically i had two options high boost + 8:0 gze pistons or low boost + 10 stock pistons. The latter seemed more attractive and unavailability of the forged pistons helped influence me too. 8psi + 10 c/r + good intercooling + good fuel and timing management = fun *** car to drive.

lastresort576

idk if it was mentioned, but make sure u do a turbo ring gap, and not a N/A gap.