Why does my Bone stock 96 3100 GP seem faster than my modded 95 GP 3100

[blackbombshell95]

I have a BONE STOCK (129k miles)1996 Grand prix coupe with a fresh headgasket job with resurfaced heads.

And for some WEIRD REASON it feels faster than my (93k miles)1995 Grand Prix coupe.
The 96 even seems to shift harder too.

My 1995 has a ffp pulley/dog bones. 62mm TB, Custom Cold air box w/ K&n filter. 2.5'' cat-back. B&M Trans pressure thingy. Plugs and wires. This is obviously not including the nitrous kit.

What could be the cause of my 1996 grand prix to feel faster than the 95? The previous owner said he got the 96 GP to run a 16.3 in the 1/4 bone stock. The fastest I could get my bone stock 95 to run was a 16.9. And I managed a 16.2 once with those mods.


Possible causes?????
The 95 GP has been painted several times so the weight of the paint might be building up?
The 96 has 1.6 roller rockers and the 95 has stamped 1.5. But they are rated at the same HP?
I dyno'd my 95 3100 with the mods above wtih NO nitrous @ 133whp(heat soaked). Does that seem right for the mods above? The 95 is pulling no ecu codes and seems to run like mint.
The 96 just had the heads resurfaced and the CR was probably bumped up a bit but enough to make it feel stronger than the 95 3100?
The 2.5'' catback is too large for the 3100 engine?

The 96 feels particularly stronger in the lower rpm range between 2k and 4k rpms.
Even my Girlfriend who knows nothing about cars says that my 96 is faster than my 95. LOL

[FastGT31]

many modifications without tuning can be bad. if you havent had it tuned for the modifications i would do so to maximize the performance they will give you. best way to settle whether or not it truly is faster, take both to the track and have the gf drive one and race her. then switch vehicles incase one driver is better than the other. just cause it FEELS faster doesnt really mean it is.

[blackbombshell95]

I plan to take it out with my brother and do a side by side run

[SappySE107]

Your stamped rockers are 1.6. Same cam specs and same actual lift at the valves.

[Ortie666]

its deafanatly the paint!!

[Superdave]

any dead bodies in the trunk?


tune it.

[MMGT1]

If it isn't tuned yet, you're in for a surprise!

[blackbombshell95]

If it isn't tuned yet, you're in for a surprise!

U wanna come and tune my 1995 GP obd 1.5? lol

[1988GTU]

Simple way to tune it...


Swap all your mods from the one car to the other and DHP it.

[Rhedalert]

I'll tell ya right now, I went from my stock '95 engine management system to an OBD2 system from a '97 model year. Without doing ANY OTHER modifications the car drives, and even sounds completely different. It is much quicker than it ever was. A '94-95 "obd 1.5" is good for a stock engine, stock everything. THATS IT.

[blackbombshell95]

U know what Rhedalert, i think that just might be the ticket! IIRC i've heard of a few other obd2 96 gp 3100's running 16.3's stock while i'm seeing the 94 and 95 guys running 16.7's to 16.9's.

Now I need a write-up/ list of parts i'll need for a obd 2 swap. Can I use a 96 GP 3100 as a donor car for the obd2 swap? I think i've read somewhere that I have to use a 97 or newer?

[Rhedalert]

I used a '97 harness only because that's what I found first. '96 Harness is identical, so is the PCM. I'm actually using a '96 van PCM. You also will have to modify is since the firewall connector wiring is different in a few ways. Not only did GM change the PCM, they also changed some of the power distribution to the accessories, inside AND under the hood. The #1 fuseblock under the hood is also wired different. I spent about a week's worth of evenings figuring out what changes I had to make. Fun times.

[blackbombshell95]

Care to PM me a parts list of what i will need if and when you get a chance? Thanks

[PCGUY112887]

Could also be that you are used to the way the car drives when hitting the nitrous.

[Azrael]

I wouldn't be too surprised with the tuning being the cause. With OBD I and II, GM knew they'd be using them for several years each. With OBD 1.5 it was only used for one, maybe two years. Which ones do you think they spent more time/money on?