Hi Folks,

I bought a 1989 IROC with a stock 5.7 350 motor. I have read Stock Horsepower ratings of 230, 240, and 245. Now, which is the real rating?

Thanks!

 

Depends on the combo. and the year and a few other minor things, your 89 should be 230. the dual cat option boosted it to 240 and I believe the 91-92 years got 245. Due to better computer.

 

Your '89 IROC with the 2.77 gears and single cat is rated at 230 HP.

The 90-92 5 HP increase is mostly due to the bump in compression from 9.3:1 to 9.7:1, in my opinion. We *could* say its because the speed density computer is better than the maf computer, but that might make some people upset.

 

i dont believe the ratings... these cars have put down 220 at the wheels bone stock... thats a solid 250-260 hp on motor

but the dual cats are said to increase power 10% somehow.... which makes no sense to me... why have 2 restrictors than one?

and 90-92 cars i believe had a slightly different cam profile (narrower LSA and possible duration differences) and lighter pistons i believe.

 

lots of little differences for the hp change over the last few years of the thirdgen. to orrs comment, think of it this way, have all 8 cylinders breathe through one cat or give 4 cylinders each, there own cat. does that help make sense?

 

Compression stayed at 9.3:1. https://www.thirdgen.org/1991-chevy-camaro

 

The tech data is wrong then. I have visually seen for myself the difference in pistons between 87-89 350's and 90-92 350's. The 90-92 350 pistons have a smaller dish, and the circumference is flat instead of stepped. This means the piston has a smaller area and so the compression goes up. I wish I had pics to show the differences.

 

I thought the L-98's had 9:1 C/R and it was the 305 LB9 that had the 9.3 C/R ( 58 cc vs 64 cc head on the 350)

 

My 92 350 pistons are Mahle flat tops, not dished, with 4 valve reliefs.
My 92 Helm's manual states compression to be 9.75:1.

 

Not everything you read on the internet is true

 

The technical data has been fixed thanks to the great admin, JT.

 

Thank you for your help!!