how much boost??

**nyls1346** · 02-06-2012

i currently have a 3.0" pulley making 11psi and im thinking about going to a smaller pulley its a ported gen 3, how much boost do you think ill pick up per inch

thanks

**dpzelenak** · 02-06-2012

.5-1.3 psi more maybe?

**matt5112** · 02-06-2012

How much timing?

What AFR?

mod list?

More boost might be a waste.

The traditional rule of thumb was one PSI per tenth of an inch.

**gtpsleeper** · 02-06-2012

With a roots blower more boost isn't always a good thing...

**matt5112** · 02-06-2012

moar heat.

efficiency in that range is 50% or less which means not only does the blower take more and more power to turn it, but it also generates more heat.

**nyls1346** · 02-06-2012

i am running e85 so it will react a little different than gas but im currently running 16* of timing and my original plan was to get on the dyno and dial it in and add more timing till i hit my peak torque and back it down a couple degrees

I also have a spare ls1 throttlebody and maf, i was thinking about slapping on, you think that will effect my boost level

**gtpsleeper** · 02-07-2012

Originally Posted by nyls1346

i am running e85 so it will react a little different than gas but im currently running 16* of timing and my original plan was to get on the dyno and dial it in and add more timing till i hit my peak torque and back it down a couple degrees

I also have a spare ls1 throttlebody and maf, i was thinking about slapping on, you think that will effect my boost level

while e85 is different as a fuel... it has nothing to do with the efficiency of the blower??? you will see peak performance (depending a little on flow mods) at around 12-14 psi... anything past that will be inefficient and will not net you any gains on e85 OR regular 91....

plus on e85 (and any fuel for that matter) timing>small pulley/pig rich... ESPECIALLY on e85....

**SnowFlake** · 02-07-2012

When you reach a certain point in the efficiency of the blower you'll actually lose power going to a smaller pulley. Before you start losing power, you lose gains, quickly. Going from a 3.8 to a 3.4 could give you 20whp... but going from a 3.4 to a 3.0 might only give you 5-10whp, depending on your setup of course.

**BillBoost37** · 02-07-2012

Mod list please. Because a 3.0 doesn't generate 11psi on a stock motor.

**gtpsleeper** · 02-07-2012

^^^ why not???

**BillBoost37** · 02-07-2012

Because ...unless he's in the Rockies.. a 3.8" pulley usually averages 8psi. Now factor in that it's winter and air is colder and denser for most of us. Call it 9psi at wot. Drop down to a 3.4" on a stock motor and you'll have plenty of restriction against flow. This creates plenty of boost backing up in the lim. Most guys see about 15psi on a 3.4 with an M90. He's talking 11psi on a 3.0 and what would he have if he went lower. Well there isn't much lower for him to go and how long can you strap a 3.0 onto a stock engine before the kaboom happens. Not tooo long.

Hence... I asked about mods to best understand the setup and the goal.

**gtpsleeper** · 02-07-2012

misunderstood what you were saying Bill sorry...

hes gotta be camed/heads to see that cuz Im ICd with rockers and see 12-15 (depending on the day) Im guessing

**BillBoost37** · 02-07-2012

Yup, that's what I meant.

I was rockered, cammed and heads, still saw ~15psi at the top end with a 2.9"

**gtpsleeper** · 02-07-2012

well and im genV too so if hes genIII itll be different but still... well see what he says...

**FoSHO99** · 02-07-2012

Add some timing, if you can get up 3-6* over stock on the current pulley and you are heading to a dyno anyway, then pulley down and run both configurations to compare at the dyno. I'm guessing you have larger injectors and at least headers if you're running a 3.0 now on ethanol...

**nyls1346** · 02-08-2012

i bought the car with these mods headers,cai,exhaust,3" pulley and there seems to be a mild cam in there but i dont know the specs, i measured the lift as close as possible with a dial indicator on the rocker arms

i ported the blower and opened up the lim, added 60lb injectors, and switched to e85 now
i was making about 13psi before i ported the blower and lim

btw whats your take on swapping the tb and maf, will i see much gain

**nyls1346** · 02-08-2012

the lift numbers were .510/.475

**gtpsleeper** · 02-08-2012

Im not sure what cam has those numbers... are you running a ported genIII?

**gtpsleeper** · 02-08-2012

stock rockers?

**nyls1346** · 02-08-2012

ya not sure on the cam but yes i ported the gen3 blower and opened the lim..
like i said, before i ported the blower i was making about 13psi and now im at 11psi
and the rockers look to be stock
those lift numbers might be a little low because i measured it from the top of the valvespring retainer and i guess its possible the hydraulic lifters compressed a little when i was turning the engine over by hand