Horsepower difference ?

[onetinsoldier]

Heres a dumb question...........the first ZR1's had 375 hp , then it jumped to 400 hp, what change or addition made the difference in horsepower gain ?

[WARP TEN]

Originally Posted by onetinsoldier

Here's a dumb question...........the first ZR1's had 375 hp , then it jumped to 400 hp, what change or addition made the difference in horsepower gain ?

The '93 to '95s were rated at 405 HP. I believe the gains were due to some better porting and exhaust also with some chip tweaking but Marc and others could say more definitively. --Bob

[onetinsoldier]

I believe you are correct, porting and some change in cam grinding , gave it the 30hp gain . I know chevrolet used to retard cam timing years ago for emissions and hp reduction to meet standards.

[rkreigh]

improved intake port alignment. Bit better heads and cams, improved exhaust and header/cats.

405 hp blocks also had 4 bolt mains and all of them were made in 1993

[Hib Halverson]

>Mild port/polish on intake and exhaust ports.
>better blending of the ports just above the valve seats
>Three-angle valve seats
>"Sleeve spacer" between the head and injector housings to improve alignment
>Revised cam timing but cam profiles remained the same
>Revised calibration
>New exhaust manifolds...which actually cost 5-hp but went to production to solve a problem with the engine ingesting debris if the cat converter substrate failed at high rpm.

[WARP TEN]

Originally Posted by Hib Halverson

>Mild port/polish on intake and exhaust ports.
>better blending of the ports just above the valve seats
>Three-angle valve seats
>"Sleeve spacer" between the head and injector housings to improve alignment
>Revised cam timing but cam profiles remained the same
>Revised calibration
>New exhaust manifolds...which actually cost 5-hp but went to production to solve a problem with the engine ingesting debris if the cat converter substrate failed at high rpm.

Always glad to have your wisdom around, Hib. I had forgotten all the details and especially about the cat debris ingesting problem. --Bob

[Matt B]

Originally Posted by Hib Halverson

>Mild port/polish on intake and exhaust ports.
>better blending of the ports just above the valve seats
>Three-angle valve seats
>"Sleeve spacer" between the head and injector housings to improve alignment
>Revised cam timing but cam profiles remained the same
>Revised calibration
>New exhaust manifolds...which actually cost 5-hp but went to production to solve a problem with the engine ingesting debris if the cat converter substrate failed at high rpm.

That last point sounds really bad!!

[A26B]

Originally Posted by Matt B

That last point sounds really bad!!

That's because...... IF & When it does......... it Really is!
Referred to as catalyst reversion. Occurs during engine de-celleration, i.e. lifting throttle with clutch engaged at high rpm.

All that's left of the Oil Control Ring lands, is that short section on the left end.

[Hib Halverson]

Originally Posted by WARP TEN

Always glad to have your wisdom around, Hib. I had forgotten all the details and especially about the cat debris ingesting problem. --Bob

Some of that info came from GM press info that was distributed in the 1993 long lead book.


The rest of it came from a conversation I had many years ago with Graham B.

[tiegsd]

Originally Posted by Matt B

That last point sounds really bad!!

Oh wow. Have to assume that happened to a few cars until someone figured out what was going on?!