Anyone running aournd 10:1 compression and low boost versus lower compression and high boost. I am thinking of having a big cube motor built for forced induction but thinking of going 10:1 compression and around 8-10 lbs of boost, for better low end power with d1sc. I know I can probably make more peak power with low compression and higher boost, but will I get more under the curve with higher compression and lower boost and also less worries of belt slip, its mainly for street versus drag strip. Any thoughts? Thanks

 

I replied to your PM

 

Thanks Scott. I sent one back. I really appreciate your help

 

Going from 10:1 to 9:1 you most likely won`t even be able to tell the differance from the lower compression. But you definatly will tell the differance from the extra boost and timing you`ll be able to run with the lower comp. I`m runing 8psi with 10:1 comp. And the car runs differant everyday, one day it`ll run great the next it`ll run like crap it all depends on the weather, 10*F change in temp. can mean the differance between runing great and pinging like a dinner bell.

 

MYTURBOT/A
thanks for the input. (Pining like a dinner bell) Thats funny

 

I am speaking from experience and research and listening to people on this forum as well as others.

First advice is if you have some time read the book "Maximum Boost" by Corky Bell...while it is not the most Comprehensive book it is a very good book to familarize yourself with if you plan on living in the world of forced induction.

My current setup is a Twin Turbo setup. My CR is 9.67:1...which is about .67 higher than I would like to be. When a Turbo setup is done correctly for the street..it will make boost at approx. 30% of max rpm and maintain boost throughout the rpm range. IMO Turbos that make a bunch of boost and then drop off are useless. You can have Hi Compression with boost..but the more boost you push the Higher Octane you will need and the greater your I/C Efficiency will have to be.

It is far better to have lower compression and be able to push more boost. For Example, I have to use 104 octane to push 16lbs of boost. I could probalby make more power running lower compression (9:1) with less boost (12lbs) and 91 Octane.

With my ATI D1 Procharger setup I ran 13lbs on 10.0 Compression on 91 Octane and made 610/545 rwhp/rwtq max RPM 6200...if I plotted the graph to 6700 RPM it would have been more like 650 rwhp....However with a Dyno Tuned 12.9 Air/Fuel and Stock Internals...that quickly send 4 pistons to their death. You could run 9lbs on stock internals with 10:1 CR and you would be ok on a good tune with no greater than a 11.5-12 Air/Fuel.

If you have a chance to design your motor for FI I would recommend a CR between 9-9.3:1. Then you can run enough boost to make the killer power on 91-93 octane or with a little additive or alky/water injection.

 

I didn't have luck with 6psi and 10.6:1 comp........#7 head gasket popped.........

Had a lot of nasty blow by after that happened..........

 

I'd do with the lower compression, the difference in a point of compression is supposed to be 3% and frankly once you play with boost you will want the option to make more power so to me it's more strategic to go lower.

 

Hey everyone thanks for all the input. It really helps, I just love this forum ShinobiZ. I remember from the other forums your old setup. I will be running a forged 408 iron block with this setup. Thanks again everbody

 

And I was about to ask the same "?". I am looking into a Turbo setup, and new bottom end to support it. End result, I want around 700 or so RWHP. So, I am looking at 8.5 - 9.0:1 CR and some dial-a-boost! Thanks for the good info guys...off to bookstore for some good reading.

 

Yes everybody has given some great info. Great site

 

Im glad the info I gave yo was correct,.....like I said if you are going to stay at that boost level then high 9's would be ok, but if you are going to run 15-20 like me and PSJ then I would go 9.2-1 or mower. and that is running 112 oct about 21-25 total timing.

 

Thanks for the info Scott. I will most likely stay under 12lbs of boost. I am not wanting to deal with all the belt slip problems of higher boost, and I havent seen any cog set-ups for C5's

 

the + cubes will take care of low end power anyway.

 

Thats what I am hoping

 

here is a calculation that can predict approximately what compression ratio and boost will do to temperature within the combustion chamber.

for example, if your design temperature is for a 90 degree F day and your intercooler is 85% efficient, @ 10# boost, 10:1 CR:

A roots blower which is 55% efficient will run at 1090 degrees F
The screw type and centrifugal which are 70% efficient will run at 1048 degrees F

The limiting temperature for say 91 octane is 1075 degrees F. this is only a guideline as the onset of detonation depends on cylinder design also.

Lower compession ratio will allow more boost but if you are looking for driveability more than drag racing, stay with a small cam and a higher Compression ratio, this is way more fun on the road, in my opinion.

 

You need to go do some more research dude.

 

Question does a procharger make more hp than a vortech supercharger? what is the limit of pounds for a stock motor? Would I beable to get 600hp on a stock motor with headers and tuning? thanks