Just bought the C4 and using SOTP method it seems quite a bit quicker than my 95 T/A.

Other than the C4 having 4 bolt mains (which wouldnt affect HP/Tq), what if any are the differences between the two engines?

Is there a real 25 HP difference between the two in stock form or was that just GM protecting the Vette's image?

 

I have heard that the less horsepower ratings were from a more restrictive exhaust and intake( they suck from factory) . That is the only diff. I am aware of asides the 4 bolt...... I had a buddy with one that was stock and while my z was stock both were m-6's His was noticbly faster through all rpm ranges-- when I added CAI and LT's we ran toe to toe until 100-ish then he'd start to pull,maybe due to gearing and weight. Of course his car is built to hell now , doubt that I could handle his car anymore...

 

Also, the C4 weighs less, a little over 3000lbs vs. the ~3500lbs that the Z weighs.

 

C4 is actually 3300-3400lbs, C5 Z06 was the only "modern" Vette at 3000lbs. Yes, the C4s do make more power, the exhaust manifolds are significantly better flowing (equivalent to shorty/mid headers for f-bodies), and then they have true dual exhaust all the way to the back. Add on that the air intake is much better flowing, and you're easily looking at a 20-30HP jump over an f-body LT1. The 92 C4 LT1 M6 I used to have made over 270RWHP bone stock, and that was with worn lifters and a miss due to old plug wires.