ZDOG

iTrader: (13)

if you give up a point in compression approxamatly how much more boost can you run? for example: stock ls1 is 10.1 and lets say good tune 8psi on good pump gas. if you lower it to 9.1 what could you raise boost to? also your losing power dropping compression right? so what are you gaining with the additional boost if any? t.i.a.

Pro Stock John

iTrader: (34)

I was told that a full point drop in compression would require 1 lb increase in boost to make up the difference.

But to answer your question... well let's see if there are any generalizations that apply.

Seems like 9psi intercooled is the average safe max that I see in this section.

Let's drop the compression to 9:1... Well I do see folks running 12-15psi with 9:1 and even lower compression. So it 'appears' to me that folks are able to run a few more lbs of boost with a point or more of compression drop.

ZDOG

iTrader: (13)

so its like a one to three ratio in a sense?
thanks

nick y

iTrader: (1)

i run 18psi on 94 no alchy and got ZERO KR!

compresion @ 8.37

30th t/a

iTrader: (51)

damn i was going to post this exact question yesterday...haha...anyway

i see people with bone stock motors and turbos making 570-580rwhp on 11psi and 600rwhp on 12ish. the question was going to ask was with my stock heads, stock cam and stock ls6 intake and 8:5.1 compression plus a forged bottom end....what boost am i going to need to hit 600rwhp?? i was guesing 13-14psi....and i want that on straight 93. what do you guys think?

my other question was what how much boost should my t44s put out?

Valkyn

iTrader: (8)

Im kind of a FI newbie, so can someone tell me why instead of running a bigger SC/turbo for more boost, people just dont up their compression ratio?

Like running 12:1 compression with 10lbs of boost, instead of going with more boost on lower compression?

DocT

High Compression engines + boost = BOOM

DocT

gotta keep the boost at a minimum on higher compression engines;5-6lbs of boost on a 10:1 or 10.5:1 is considered fairly safe by most people here, but to run much higher boost, you'll need to lower the compression (and forge bottom, build heads to handle load).

Valkyn

iTrader: (8)

Wouldnt 8:1 compression and 15lbs of boost make the same power as 12:1 compression and X (10?) lbs of boost?

brad8266

iTrader: (23)

No, it is not a linear relationship. High compression is bad with boost because high compression causes hotter cylinder temperatures, and air that is compressed like the air from a super/turbo charger is also very hot. When you take the combination of hot boosted air and add it into a cylinder with high compression, it tends to preignite and detonate due to the extremely high temperatures. That is one reason that high comp and blowers dont go well together. To keep tempertures down you need to sacrifice one, either boost or compression ratio.

ZDOG

iTrader: (13)

so sacrifice compression because boost pays back more right????

Pro Stock John

iTrader: (34)

Perhaps high compression + boost = builds heat faster than low compression + bigger boost

Not sure.

brad8266

iTrader: (23)

Exactly, lets be thoretical here now. Say at 10.5:1 CR you can only run a max of 8PSI safely, this would in theory be a 54% power increase for the motor. Any more boost and it will become unsafe to the motor. Now lets change heads and get dished pistons and get down to 8.5:1 CR. We would lose some HP if we were running naturally aspirated, but we are boosted here. So with that CR we can run lets say 15 PSI boost. Now we have an increase of slightly over 100% in HP. So by reducing CR to allow for more boost you can run a ton more boost safely, whereas with high CR you will detonate very early at low boost. Losing HP by dropping CR should not even be an issue because if you are going low CR then you obviously are planning to go boosted, so the hp loss N/A by going low CR is not revelant.