high comp + boost theory
#11
Re: high comp + boost theory
Originally Posted by trevor72
It is all about cylinder pressure. How you go about making it is up to you. I'm not sure how less boost and more compression would make less power.
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.
#13
Re: high comp + boost theory
Originally Posted by cloud
is there a noticable differance in power going from 9.1 stock compression to 8.5 with vitaras out of boost
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.
#14
Re: high comp + boost theory
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.
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.
#15
Re: high comp + boost theory
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.
cliffnotes, lower compression raises the knock threshold for your tune on pumpgas other than that who cares.
either or will work.
#16
Re: high comp + boost theory
Originally Posted by 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.
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.
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.
#17
Re: high comp + boost theory
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.
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.
#18
Re: high comp + boost theory
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.
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.
#19
Re: high comp + boost theory
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.