maggie boost question Please help
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 838
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From: Elgin Il
maggie boost question Please help
my car is only seeing 7/12 to 8 pounds of boost regardless of pulley size, i mean i went from a 3.1 to a 3.0 and the boost stayed the same, on the dyno you could see the increase in power and torque off the line and across the band, but the peak #s were the same. something is restricting the boost from increasing, at first i thought it was the cover on the air filter(shroud over the blackwing) so at the track today, i ran 1 time with it on 11.04 @125, then with it off 11.01 @124 1/2 then a few times with a new filter, around the same times, but the 1 thing that stayed the same was 7 1/2 to 8 # of boost, could it be a blowoff valve issue? if so is it a piece that i could replace, or would it have to go to maggiville, any ideas on whats going on here?
Race Director
Joined: Apr 2005
Posts: 10,179
Likes: 2,306
From: Wesley Chapel, FL Las Vegas, NV
my car is only seeing 7/12 to 8 pounds of boost regardless of pulley size, i mean i went from a 3.1 to a 3.0 and the boost stayed the same, on the dyno you could see the increase in power and torque off the line and across the band, but the peak #s were the same. something is restricting the boost from increasing, at first i thought it was the cover on the air filter(shroud over the blackwing) so at the track today, i ran 1 time with it on 11.04 @125, then with it off 11.01 @124 1/2 then a few times with a new filter, around the same times, but the 1 thing that stayed the same was 7 1/2 to 8 # of boost, could it be a blowoff valve issue? if so is it a piece that i could replace, or would it have to go to maggiville, any ideas on whats going on here?
That where I am on my setup. I'm pulling 5.2 psi. I can pulley up another 2 psi but without going to a larger TB it's not going to give me anything.
When you change the pulleys you are turning the blower faster. But if you can pull in more air it has nothing to compress so psi boost is not changing.
Last edited by Vega$Vette; Oct 20, 2007 at 07:31 PM.
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 838
Likes: 0
From: Elgin Il
already have the 90mm snout and a ported Ls2 thottle body, belt slip isn't the case as i just changed to ECS heavy duty tensioner last week.i will check to see if a hose is interfering with the bypass valve controller, thanks, Matt.
Melting Slicks
Joined: Sep 2004
Posts: 3,178
Likes: 13
From: N. County/San Diego
my car is only seeing 7/12 to 8 pounds of boost regardless of pulley size, i mean i went from a 3.1 to a 3.0 and the boost stayed the same, on the dyno you could see the increase in power and torque off the line and across the band, but the peak #s were the same. something is restricting the boost from increasing, at first i thought it was the cover on the air filter(shroud over the blackwing) so at the track today, i ran 1 time with it on 11.04 @125, then with it off 11.01 @124 1/2 then a few times with a new filter, around the same times, but the 1 thing that stayed the same was 7 1/2 to 8 # of boost, could it be a blowoff valve issue? if so is it a piece that i could replace, or would it have to go to maggiville, any ideas on whats going on here?
Remember, if you take away restriction your boost will drop, so 71/2-8 lbs sounds about right, I wouldn`t expect to see much of a difference between a 3.1 and 3.0 pully.
You can either pully down to a 2.9 or consider milling the heads slightly to recover the lost boost.
I`m currently in the process of upgrading to a hotter cam and ported Edelbrock 215 heads, I had to mill the heads to recover the lost boost due to the less restrictive combo so I speak from first hand experience.
Obviously the combustion chamber cc on YOUR heads will determine your requirements. Maggies love compression and a 2.9 pully is about the max you want to go and still be able to control (I have alky) IAT temps.
Safety Car
Joined: Jul 2005
Posts: 4,275
Likes: 4
From: Vancouver WA
If he changes from a 3.1 to a 3.0 without changing anything in the motor, then he should have gained about 1 psi of boost.
If you change something in the motor (heads, Cam, and/or exhaust) and the boost goes down, then you are moving more air thru the motor, and should make more power. Providing your not blowing it all out thru valve overlap.
If you change something in the motor (heads, Cam, and/or exhaust) and the boost goes down, then you are moving more air thru the motor, and should make more power. Providing your not blowing it all out thru valve overlap.
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Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 838
Likes: 0
From: Elgin Il
If he changes from a 3.1 to a 3.0 without changing anything in the motor, then he should have gained about 1 psi of boost.
If you change something in the motor (heads, Cam, and/or exhaust) and the boost goes down, then you are moving more air thru the motor, and should make more power. Providing your not blowing it all out thru valve overlap.
If you change something in the motor (heads, Cam, and/or exhaust) and the boost goes down, then you are moving more air thru the motor, and should make more power. Providing your not blowing it all out thru valve overlap.
Thread Starter
Burning Brakes
Joined: Oct 2004
Posts: 838
Likes: 0
From: Elgin Il
Safety Car
Joined: Jul 2005
Posts: 4,275
Likes: 4
From: Vancouver WA
Loosen the 2 scews that holds the valve onto the blower case, and move it back and forth until it just barely touches the tab on the by-pass valve shaft. Whatch and make sure it doesn't start to push on the tab when you tighten it up.
Racer
Joined: Mar 2006
Posts: 464
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From: silverdale washington
I would just unplug it let it try to make boost all the time. Your vacuum should drop about 8" at idle or so give or take a few " depending on your setup. It is normally shut, and has to have vacuum to open the valve. Hence when you get on it the vacuum drops to nil and the valve shuts and it makes boost. If you unplug it then unless its misalgined now it is definitely shut. You can pull the tb and snout or just tb and look and see if it looks like it seals. Thats where I would start. I also made less boost than most due to camshaft selection, however mine will make it just higher in the rpm band. If it appears to be sealing try completely removing the intake. Only maf & tb. That should tell you if its your air intake.