larger throotle body = less boost???

i have a dual 52 mm BBK throttle body on my 1993 Camaro Z28 with an ATI psc-1 procharger system and my boost never reached 9 lbs under full throttle, it tends to stay around 5psi (ON MY BOOST/VAC GAUGE) from a rolling 50mph start. does a bigger throttle body lower boost pressure??? aka. should i switch back to a stock throttle body to reach higher boost levels on the ati setup???

Read this: http://web.camaross.com/forums/showthread.php?t=283782&referrerid=10136

Good info on page 2.

It's only going to allow you to move more air into the engine, I can't see how it would hurt you.

i have a dual 52 mm BBK throttle body on my 1993 Camaro Z28 with an ATI psc-1 procharger system and my boost never reached 9 lbs under full throttle, it tends to stay around 5psi (ON MY BOOST/VAC GAUGE) from a rolling 50mph start. does a bigger throttle body lower boost pressure??? aka. should i switch back to a stock throttle body to reach higher boost levels on the ati setup???


Don't know how up on FI you are, so I apologize if you are already aware of a lot of this, but it may help some other, less knowledgeable readers as well.

Boost is resistance to air flow. A larger throttle body will only decrease boost pressure if the original throttle body was a restriction. The 9 psi rating of the P1SC is based on a stock motor with a stock intake/exhaust setup; it will flow x amount of air per a given rpm, not counting restrictions. When the airflow encounters restrictions (whether in the intake, heads, or exhaust tracts) it creates back pressure; this is boost. Since you have headers and a larger throttle body, your engine will flow better than stock, this will reduce boost pressure per a given rpm. You should still be flowing the same (or a little more) air, it just isn't backed up in the intake tract to the same extent is was before. You should actually be making a little more power than before because you have a more efficient air pump. If you are not making the same or a little more power, you may have a little belt slippage. I hope this helps.

that helps alot. thanks guys

What you guys are saying about making a more efficient air pump is correct. You will lose a little boost when you flow more air through a motor. You should not be losing 4#'s of boost with a larger throttle body and headers. I have a cam, longtubes with 4" exhaust, throotle body and a bunch of other crap. I have a 12# pulley on and I see about 10#'s at about 6000rpm. I think you have a problem if you are losing 4#. Check your guage connections or restrictions in the hose. Does the car still feel the same? Do you feel a loss in power?

You guys have this all wrong. You measure boost in the intake manifold plenum. ANY restriction UPSTREAM of the plenum (throttle body, MAF) will decrease boost. Any restriction DOWNSTREAM of the plenum (heads, exhaust) will increase boost.

Think about this, hold the throttle 2/3 open. How much boost do you make then? Not much, right? Isn't this a restriction, though?

Mike

If you have a bypass or blow off valve, could it be malfunctioning? That sure seems like a lot of boost to be losing, modified or unmodified.

Ken R.

where is your gauge reading the boost from? what is the source?

You guys have this all wrong. You measure boost in the intake manifold plenum. ANY restriction UPSTREAM of the plenum (throttle body, MAF) will decrease boost. Any restriction DOWNSTREAM of the plenum (heads, exhaust) will increase boost.

Think about this, hold the throttle 2/3 open. How much boost do you make then? Not much, right? Isn't this a restriction, though?

Mike

Thanks for keeping me honest, Mike. You are absolutely right and I stand corrected. :bow: Brain fart on my part. :o I was thinking that any time you remove a restriction, airflow will go up and boost will go down, but as you stated, changes to upstream and downstream flow will have the exact inverse effect on manifold pressure. When downstream flow increases, boost decreases and when upstream flow increases, boost increases and, conversely, when upstream flow decreases, boost decreases and when downstream flow decreases, boost increases. I apologize for any confusion.

I just realized you've posted this here as well. If you'll notice, EngineerMike and myself are trying to explain the same thing to you. THREAD FROM LT1TECH.COM (http://lt1tech.com/cgi-bin/ultimatebb.cgi?ubb=get_topic;f=2;t=000174)

I can't say for sure what the problem is, but switching back to the stock throttle body would deffinately be a step in the wrong direction (assuming your 52mm throttle body is in perfect working order).

You guys have this all wrong. You measure boost in the intake manifold plenum. ANY restriction UPSTREAM of the plenum (throttle body, MAF) will decrease boost. Any restriction DOWNSTREAM of the plenum (heads, exhaust) will increase boost.

Think about this, hold the throttle 2/3 open. How much boost do you make then? Not much, right? Isn't this a restriction, though?

Mike

If he's measuring from the intake pipe the smaller throttle body would show higher boost pressure on the gauge.

If he's measuring from the intake pipe the smaller throttle body would show higher boost pressure on the gauge.

I agree!

Totally depends on where you are measuring from. Either way, any restritction is bad, before or after the plenum :)

-Shannon