so ive got a 2.1kb 3" pulley 7.25" crank pulley. I am calculating 17.7 LB of boost. I am getting 13 psi can I lose that much boost due to headers and free flow intake?
04 cobra motor boost lost due to headers and big intake
- Thread starter LT1BIRD
- Start date
What kind of boost gauge are you using? Factory? Aftermarket? And did you recently add the 3" pulley and/or 7.25" crank pulley? If so, how much boost were you seeing before those mods?
Check your bypass is closing completely. I had a similar issue, I was bleeding off 4-6 PSI and was because the bypass arm was getting caught on the fuel rail fitting.
You will be down 1-2 PSI with headers. That is what I saw on my 2.8h.
You will be down 1-2 PSI with headers. That is what I saw on my 2.8h.
hey bud! its an aftermarket boost gauge... not new.... i had the 4" pulley on before with the 7.25 balancer.. but I just remeasured it and its really a 7.00 inch.. that brings down the boost to like 16.5lb .... on the 4" pulley I was getting 7-8LB so not to far from the 8.7 it should be.. so losing 3 psi from headers and intake.. does anyone have similar loses? i dont think the belt is slipping (6 rib) as i watch the boost and it seems somewhat stable... 12 psi quick.. then goes up to 13 around redline...
did you ever actually make that much boost or are you calculating/estimating how much you think you should be making? wording makes it a little unclear - an observed drop of that much boost is definitely different than what you're actually making vs what you guestimated you should be making
Headers are usually good for a 1-2psi drop.
Not sure what your actual engine setup is, but that’s typical for C headed 4v cars with our cams.
A good intake would raise boost, as you are able to get more air to the rotors.
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Not sure what your actual engine setup is, but that’s typical for C headed 4v cars with our cams.
A good intake would raise boost, as you are able to get more air to the rotors.
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im making 13psi but calculating 16.5 based on my pulley setup.. ok, so lets say i lose 2 psi for headers and full 3" exhaust no cats. i guess im not that far off then..?? maybe losing 1 psi due to intake or belt slippage 
The calculated is always just an estimate. Engine set up and weather can affect boost levels. I can see a 1 or 2 psi drop depending on the weather.
that sounds good... thanks for the help guys!
Oh, and using the cowl as the intake is awesome.
Yes! I never seen this before. Pretty cool.
im making 13psi but calculating 16.5 based on my pulley setup.. ok, so lets say i lose 2 psi for headers and full 3" exhaust no cats. i guess im not that far off then..?? maybe losing 1 psi due to intake or belt slippage
Shoot I bet cats and headers is 3 psi combined.
Most people going to headers ditched cats way prior it seems.
Are you taking elevation into account?
My car made 15psi at sea level. Didn’t realize until a year later, I was only seeing 12.5 at 3800’.
Im now pullied for what is usually 23/24 and I see 19/20.
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Heck, I just want to say he's got one hell of the nicest looking engine bays I've seen!
thanks guys! at the last nmra show here in FL it did win best engine.. I was kinda shocked with so much competion.. but honered! well back to my psi drop issue.. i did have a 7.25" damper pulley.. I just dont have mics that big so hard to meaure... do it should have the 17.5lb of boost based on the KB formula.. I know its a ton that goes into it. its just down on boost. Im at sea level in FL but summer hot...im sure the DA is 2500ft...... the 6 rib setup is probably just not holding well... I have a new american racing solutions damper coming tommorw(killer customer serivice)... mine is stock and weak.. If i see a change.. ill swap the whole setup over to 8 rib.. ive got most of the parts now.. been collecting them when i started to up the boost. If i can get to 15 psi ill be happy.. im not sure the damper pulley has enough wrap on it but not sure how to fix it without some custom pulley brackets! see the pic
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Let's see the whole car. What is it, 60's coupe/Fastback ??
@Black Gold 380R
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