I've heard that you can lose 1 or 2 psi when running the OBX header.
I'm making just hair over 15 psi on my auto meter boost gauge @ fuel cutoff.
I remember making 17 psi when i first installed the gauge w/out OBX on.

note: I checked the bypass its fully closing ( i adjusted the screw a lil, no diff)
checked the ic boots, no visible cracks or holes.
I had the pulley belt changed out no problems with it but it was time, now i here a whine coming from the pulley area... but no change in boost.
Does 15 psi sound normal with a 19% pulley and the obx?

 

Why would you lose boost from a header? I can see back pressure being an issue but its not like its an NA car. And the OBX header is only .50" larger in diameter....

 

Pretty simple, really. Boost is just an indication of air not being able to get through/out of the engine. Since the header and cat cause restriction in the airflow, it contributes to boost. The less restrictive the intake, head, exhaust system and so forth are, the less boost you will see. I know when I swapped my stock header back in place of my RMW temporarily, my boost went up significantly. That speaks well for that particular aftermarket header. I imagine the OBX does the same thing, to an extent.

 

so basically not as much back pressure to boost against,
but is 15 psi w/ a 19% pulley normal?

 

Your theory is backwards. Boost is indicated on the gauge through the vacuum system. In a turbo car you want NO restrictions whatsoever. On an NA/SC car you want a happy medium. For boost...the intake and head have everything to do with it. The higher cfm you can obtain...the higher you can boost. Not lower it....

 

So i should have gained boost not lost?
i def lost boost directly after the change but didn't feel slower. Actually felt a little stronger 3k and up.
maybe someone can chime in that has the same setup as me as to what boost numbers they are pulling.

 

I'll have to agree to disagree.

 

How so? It's document physics... I will just chalk it up as you are from Arkansas and dont know any better....lol

 

You gained TQ from the effectiveness of the header. As far as boost goes...all cars react different. No one car is the same....

 

Yeah, we're pretty dumb here in Arkansas. But I do have an above-average number of teeth.

 

I am not aware of a correlation between Header and Boost.

 

The Roots style supercharger stacks air into the intake manifold faster than can be consumed. Boost is created in the intake manifold after the SC, unlike some other superchargers which compress the air before discharge downstream. The rate at which air can be moved through the head and out the exhaust system does indeed affect the amount of boost allowed to be formed within the intake manifold. Changes to camshaft profile or valve timing, head flow & valve size, header configuration, and cat back, can alter boost for a given SC rpm and particular vehicle. However, comparing boost among Eaton 45s in other vehicles is not good for evaluation purposes even with good controls, unless it is an extreme outlier number indicating a problem.

From the data I’ve collected and seen shared from others, 15 psi at WOT on the street in moderate ambient temps, with a 19%, would indicate healthy flow capability.

Low and no back pressure are good for all vehicles, there is no such thing as “good” or “happy” back pressure; only that less is better.

 

Just to throw it out there, via an autometer gauge I get 13psi max at WOT with my mods.

-Cody

 

Hmm. Sounds like someone may have read a book or two this subject

 

Ok, cool so I just ran another test yesterday and it seems like i'm almost @ 16 psi at 85F 1400 ft above sea level. I'm guessing i have nothing to worry about then. car feels strong def in the midrange. Thanks guys

 

Welcome. Sorry for the semi-highjack, but it was germane to the question at hand.

 

Your wrong hes right. Sorry. In short any restriction you do away with before the supercharger will increase boost. Any restriction you do away with after the SC you will loose boost. But still make more power.