did these changes make my car slower?
before 1988 iroc, 5 speed, 3.73, 24lb injectors, zz4 crate motor, lt4 hot cam, stock tpi, fuel pressure 50lbs, would run 13.3

 

Just adding parts without matching the rest of the intake system could be the issue. Either that or the shifting was a little off.

 

or you made a mistake in installation with a vacuum leak.

 

I would look for vacuum leaks. Then tuning issues. Car should not be slower.

What did the rest of the run look like, and how was the weather? Similar 60 foots? Did you shift the same rpm as before or go higher like that motor would want with SLPs?

 

there is no vaccum leak and the problem is nothing obvious. The car is just simply slower. Even feels a little slower.

 

May not appear to be obvious but you never know. Double check everything from the install. What is your current fuel pressure and did you shift at the same rpm as before with stock TPI?

How much timing are you running? Still running stock base with these runners? Was the base port matched to the runners?

 

no port match. Went to the track and tried shifting everywhere. tried fuel pressure everywhere. Fastest et at 5000 rpm shift. Car went 13.3 stock tpi???? whats going on? 10 degrees of timing (same as before) been over everything. my old 60 foots were low 1.8 and now best of high 1.8. My fastest times are with no burnout( mickey thompson drag radial) soo confused. I feel like i wasted $600. What do i do now?

 

sell it.

(the car)

 

buy a base and throttle body and youll be good

 

I think the SLP runners have a bigger diameter than what the stock GM TPI base inlets are, if so, you have a step mismatch, might adversely affect air flow.

also, you indicate you took all the emissions gear off. did you disable the AIR, EGR and canister purge in the chip? if not, your ECM might be having issues, that could affect your optimal tune.

 

What was the weather like when you went a 13.3 compared to now? Weather plays a HUGE factor. Also you mentioned your 60' being almost a tenth slower. That can add up to at least 2-3 tenths on the big end. What was your mph with the new runners? Higher, lower, the same? Since the slp's flow better at high rpms your going to need to add fuel up top in your tune to really reach their full potential. Same track? There's alot of variables that can really add up.

 

I bet the turbulence caused when the air is hitting the much smaller intake runners is part of your problem. when I added my edelbrock runners and intake, I port matched at every transfer (plenum to runner, Runner to intake) and definitely saw and felt an improvement.