I just installed a set of RB headers and presilencer in my '90. They do give a noticable power increase over the straight-pipe I was running(as well as some extra sound), but they seem to have caused a more noticable flat spot as well through the rpm band. I used to have a small flat spot between maybe 7.1k and 7.2k rpm, but now it seems I have more of one between maybe 6.1k to 6.4k rpm. Has this happened to anyone else? If so, is there any way to correct it besides a standalone or something to that effect, or am I just the lucky type of person to have this happen? I have a port-matched intake which seemed to even out the flat spot before I got the headers, but that's pretty much a one time deal. What could I do now? Any info or help would be great.

 

when I put them on, I noticed a jump in power right at that rpm. I thought they were just tuned for that rpm, but maybe not. Does it still pull hard after that? If not it could be a non-working VDI.

 

It still seems to pull fine after that spot, it's just more noticable a flat spot than before and at a lower rpm. I suppose I'll look at the VDI tomorrow but I'm pretty sure it's fine. Is there anything else I should maybe check? I'm at a loss right now, I think my brain is slightly disfunctional. Hopefully tomorrow thought processes will return to normal as well.

 

when u ported the manifolds did u change the vacuum hoses? and if you did, did u remember to swap the resistor pill for the pressure sensor?

 

Uhhhh.... what ?

 

I think it is a bead shaped piece of plastic with a small orifice in it which you insert inside the vacuum hose before installing it between the intake manifold and boost (manifold pressure) sensor. It delays quick changing vacuum readings to the ECU like how a heavy flywheel makes the car smoother but less responsive.

 

Oh. I'll check into it. Thanks guys.