how much boost is normal?

ThunderDave

Registered User
I bought a 91 super coupe back in July and until now, I thought the car ran like it was supposed to. The boost gauge read 8-9psi at the maximum boost. I added a 5% overdrive pulley and the maximum boost rose to 14-15psi. I've been told since then by other sc owners that I should have had 14-15psi to begin with, before the 5% pulley was added. Is this correct and if so, what could be the problem with not having that much boost before. Any help would be very much appreciated.

David
 
12 psi is normal and the gauge isn't always accurate. Yours sounds about right with the 5% pulley. Check the small hose from the boost/vacuum gauge that attaches to the intake manifold adaptor right next to the ACT sensor. The rubber boot will sometimes crack and leak a little, which would cause a lower boost reading.

David
 
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My 90 AOD w/ fresh head gaskets and no cats w/ stock pulley will hit 9-10 MAX. I am going to order a 10% overdrive pulley for it and try to get at least 14 psi out of this sucker. The heads have been milled and ported but I don't think that would lower that boost that much? It used to get 11-12 psi w/ cats and stock heads.
 
maybe the reason urs doesnt produce enough boost with-out the OD pulley is because maybe your exhaust has been worked on?
am i right folks? backpressure relief causes boost to go down. am i right or am i right?
 
I'm surprised a 5% OD would give you a 75% increase in boost. It should give you a couple more psi, but not 6 psi more. Did you fix anything else while you were installing that 5%? Sounds like maybe you had a vacuum/boost leak before, since 8-9 is a little low. Unless you have a very free flowing exhaust.
 
boost

Thanks for all the input guys. The only mods on the car that I have done is is remove the air silencer box, k&n filter and flowmaster original 40 series muffs. The car ran strong before I changed the muffs with the boost around 9 psi, but is much better now with the o/d pulley and getting about 14 psi. Dave McGlaughlin who some of you might know told me he was getting 14 psi on the sc he used to have with the stock pulley. Sounds impressive to me. Maybe each one varies depending on setup, mods and enigine/ supercharger wear. I'll check those vacuum connections and see if I can find a leak. Thanks again for the help.

David / super91coupe
 
I'm surprised a 5% OD would give you a 75% increase in boost. It should give you a couple more psi, but not 6 psi more.

That's what I thought was kinda wierd. That is a huge jump up in boost for just adding a 5% pulley. I'd say 1-2lbs. is more common with that. :confused:

Thomas
 
boost

Ok guys, after checking it again on the way home this moring, max boost was about 12 and then right before shifting at near red line it jumped a little, maybe 12 1/2- 13. So I guess it's where it should be with the 5% pulley. And according to some of you, it was where it should have been with the stock pulley. So I have found out what I wanted to know and I guess the car and boost are right. Thanks!

David
 
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