truck

If there ws a book called Forced Induction for Idiots I would buy it, although I doubt I could find it.
Now, the way I understand this is: The lower the compression the better. Am I right? At 6 to 8 psi do I want the lowest compression I can get? The more room in the cylinder the crap you can cram in there. Right?
Lingenfelter Vette has 9.5:1
Lightning 8.5:1
Top Fueler 6.5:1
<img border="0" alt="[Banging Head]" title="" src="graemlins/gr_banghead.gif" />
Thank you for you time, I think I need some sleep.

00blkws6

I am no expert but I would guess around 9.0-1 would be desired for boost applications. You will lose power n/a, but for detonations sake....
I will take the lower compression and add more boost!

smokinHawk

iTrader: (48)

There is a point were it will loose streetability.
the lower the CR the less throttle response. Also the higher the CR the easier the engine will spool the turbo.
i think 9:1 is a good number. BUt some have gone 8.7:1 and 8.5:1 in order to make more power on top.

AlienDroid

for mid level boosts 9:0 would be good, like SmokinHawk said, low compression motors feel like slugs at low rpm even with a turbo.

smokinHawk

iTrader: (48)

my 92 stealth had 8.0:1 compression, and untill the turbo kicks in felt like a 4 cylinder. no pep at all then the turbos would rool in and pull you back
my TA when it was NA with the CR at 10.5:1 would slam you back at about any rpm then pull you back.
the throttle "jumpy" respose is due to high CR. My bike at 11:1 CR will pull a whellie when you jump the throttle, cause its high CR.
if i had the $$ i wuld have got a high CR 422, and maybe some juice for those 9 sec runs.
but turbo is cheaper power then cubic inches., least compared to a 20 grand 422.

restoman45

iTrader: (2)

im pretty sure top fuelers have 12 to 1, at least that is what the pit guys have always told me...it souunds reasonable too if u look at the engine when its apart, they use flat top pistons, and the head chambers aretnt too big...anyways as far as compression goes, i think 9 to 1 is all around teh best, u can run tons of boost, and still have reasonable compression for throttle response...9 to one is the best.

JimmyKash

Actually top fuelers are in the 5-6:1 range but they also run nitromethane which affects what compression ratio you use

F8L Z71

I agree that a good comp. for a boosted car in the 8-12lb range is 8.5-9.0. Almost all the Mustang guys run this comp. All my blown motors were either 8.5 or 9.0 and I had really good luck with them.

Unless you plan on lots of boost I would not go below 9.0.

talonis

I'm planning on running 6# of boost, and was considering 9.5:1. Is that too high or a good ratio to be at for that sort of boost?

truck

9.5:1 and 6 to 8 psi was also what I was looking at running. I was leaning towards a Vortech unit, the kit does not come with an intercooler so keeping down detonation is going to be a big issue for me. I will have ported heads and probably a stock or a very small cam.

jacs

How much boost can be ran on an engine with 9 to 1 cr and forged internals???

And about how much hp will that be?, what can you run safetly all the time?

Sorry dumb questions, just starting to read about FI

Oh yeah, about how much does it cost to get to that cr, and how is it done?

<small>[ September 25, 2002, 06:51 PM: Message edited by: jacs ]</small>

Dave

for a given octane rating of fuel, lower compression will allow the use of higher boost for more peak power, but for street use, peaky power is vexing. Higher CR and less boost for street driving. <img border="0" alt="[Burnout]" title="" src="graemlins/burnout.gif" />

talonis

Yeah, I was thinking of putting on some 6L heads and a .067" head gasket to take the CR down to about 9.5:1 and then putting on a water-alcohol injection system to keep the temps lower.

MIGHTYMOUSE

iTrader: (59)

just want to remind everyone that cylinder pressure kills, not 'boost' so the psi is relative depending on the individual combination.

i will likely be running mid teens in boost (but with a smaller turbo) to get 600rw.. could do the same at about 10psi with a larger one, but i prefer the qualities of the smaller for my 6 speed sreet car.

my compression is 8.75:1 and plan on running pump gas at all times.. this is another factor to dropping compression...

9.5 is a good number, my first lc motor was that but.. you know at some point you will want MORE! so i say 9.0 is a nice middle number.

you really dont need to drop the compression untill you get above 8 psi Or 500 rear wheel on pump gas in my opinion.. it can be done safely with the proper tune and fuel set up.

i imagine you could squeeze 600rwhp from 9:1 on pump gas but you would have to be pulling some good timing and have the best pump gas u can find.

using a thick head gasket is definitely NOT the way to drop compression.. it would just make another weak point in the heads already not so great clamping.

scottywheels

I went with all forged internals and upgraded to 12 psi on the d-1 ans my CR is 9.2-1 and we are tuning it on 94 OCT and it will make over 600 rwhp