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

[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.

[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 A26B

That's because...... IF & When it does......... it Really is!
Referred to as catalyst reversion. (snip)

"Catalyst reversion"...LOL
More like "catalyst regurgitation."

I don't remember what Graham called it but he did explain that because of lower pressure in the cylinder, the engine sucked pieces of the cat substrate past the exhaust valve. I'd imagine, if that happens, the damage sometimes had to be more severe than just a broken oil ring. GM wouldn't have spent the money to redesign the exhaust manifold if it hadn't spent too mucy money on warranty for that.