Recently installed a mild cam/headers but the car will only trap 102-103 mph. Mods in sig

I'm running shorty headers but I've seen others running shorties that aren't this hindered. I have the Hooker's and have read that you need to open the collectors up a bit, is this holding me back? You thoughts?

Stock programming - idle adjusted shift points, etc... most of the easy common stuff. No fuel or spark tables though, i'm still a rookie. Could this be it?

Only pulling 240 g/ps of air into the MAF, swapped it out with a buddies Granatelli unit and jumped to 320+. Same ET's and MPH although I only got 1 run in with the swapped MAF.

Stock 1.5 rockers. Is my MPH lost in the rockers?

I've adjusted and re-adjusted them. No ignition issues that I can see/feel either in Datamaster or driving.

Bad coil? Even though I can't see/feel it could this be a cause?

Where oh where is the MPH that everyone seems to think I should have?


EDIT: The cam specs are: .226/.236 .501/.526 with 1.5 rockers

 

That cam is way too big for stock programing. You will never get the most out of the cam until you reprogram it to better work with the cam. Get it programed and I think you will be quite surprised.

 

You definetely need tuning... it's really pointless to do a cam or any other major mods without tuning. Most of your power is lost in the wrong air fuel ratio.

As for the GPS values, you can only use values from a stock, unmodified MAF for reference. Other MAFs won't work due to different calibration and/or size.

 

I'll third the tuning opinion, heck Ive seen 218/224 cams run like crap with a bad tune. Youre basicly changing the motors breathing cycles with the cam , why would you keep the stock stuff in there?

 

Fair enough. Ion, you've checked my Datamaster logs just a lil while back. I was trying to find the shortage of air before I went with tuning, should I try another stock MAF sensor first to see if there is a difference?

Also, should I wait to have a tune done until I add 1.6 rr or will I be ok to have you tune it now the way it sits? I'm not sure how much is involved in tuning, if any, for 1.6 rr's versus stock 1.5's.

I'm just not that great with my tunercat yet that I can't tune.


Ion, thoughts? Should you tune it now with 1.5's or wait till I add the 1.6's?


Thanks! I guess I didn't realize that tuning would affect me this much.

 

The 1.6s wont make a big difference enough that the ECM wont be able to correct for.

 

Thanks again for the replies!

I'm hoping that the tune will get me 2-3 MPH more putting me near the 105-107 mark. Is this feasable with my setup? Asking for too much possibly?

 

Very Possible, I hit over 110 with home ported heads and a cc305 in my ol 93.

 

Tuning will help you out immensely, but I'd also look at getting a better header. The Hooker shorties aren't exactly the best thing out there.

 

Did you change your valve springs?

That cam has way too much lift for stock valve springs.

-Dave C. '97 Z28

 

Yes, I used cmotorsports EX612 kit.


I went with the coated Hookers because of a great GP price and my fairly strict emissions testing here. I'm hoping that the LSA of 114 will help pass e-check, if it doesn't i'll consider longtubes after I find a place out of my county to register the car in.

 

Did you reuse the stock seats for those springs or did you have to buy some? If so, which ones did you end up buying?

 

Stock seats I believe, can't remember now. I'll have a look at my receipt tonight. No machine work necessary on these springs.


Also, could running too low of tire pressure affect my MPH? I run the car full weight too, no reduction whatsoever with 3/4 of a tank of gas usually. I run it as it's driven on the street, I have no interest really in stripping the car down.

 

springs should have been set at a 1.8 inch seat height. At 1.8 inchs those 612 springs will be 135 lbs seat pressure which is what you want. I believe the Combination motorsports ones are made to work with stock seats and provide around 135 lbs of seat pressure.

If you have not checked out your car out on tuner cat or turbo link then you NEED TOO. 1.6 rockers and headers can set off your knock sensor and even the LT4 knock module may still read false knock. If its pulling 15 degrees of timing (max) then its sapping quite a bit of power. Plus you need to tune out your air fuel and timing with the new cam..

 

I trapped 103mph with mildly ported heads, stock cam and boltons.. I would get that thing tuned as soon as you can.