BuickMike

Hi all,

I've been doing some research and am still confused if there is any difference in factory camshaft between the 87-89 and 90-91 LB9's with a 5 speed? My son got the drivetrain out of an 89 IROC 5 speed with a 3:42 rear gear that he is going to be swapping into his 85 S10 for a budget build. I know the 90-91's were rated for more HP, but was not sure if that was only due to the exhaust change and going to speed density, or if they had a different cam profile? I have a good stock camshaft from a 91 L98 in a Corvette that he can have and I'm guessing that's the same cam that came in the 90-91 5 speed LB9's, but I see mixed information on whether the 87-89 cams had less lift / duration or not. Thanks for any info.

LiquidBlue

I seem to recall later TPI cars getting "hotter" cams. think you are on to something. have you tried looking up the GM part number for the different years?

ughmas

Not sure off the top of my head but according to 3rdgenformula.com the different years had some slight cam variances in lift and duration, 87 being the smallest lift, but not sure if this contributed to the higher HP. I think the dual cats made the most difference according to the data - also not sure if this translates directly to camaros

LiquidBlue

you can get some formula data over here : https://www.3rdgenformula.com/90/90technical.htm

DynoDave43

iTrader: (11)

I saved this from TGO years ago. I believe it to be a pretty good reference piece, but cannot vouch for it.

BuickMike

Thanks for all the replies! I checked out the differences on 3rdgenformula and it looks like in 90 the M5 cam got a hair less lift / duration, but narrowed the LSA a little too. Looks like all it did was make peak HP at 200RPM higher. The 89 IROC we pulled the motor from only had 1 cat, however it was a botched up job on an aftermarket cat that was way too small and that was only 2". Looking at the Y, it appears it was once a dual cat setup.

LiquidBlue

What kind of Buick do you have Mike?

TransamGTA350

iTrader: (2)

If the 89' was a 305TPI/5-speed with 3.42 rear, then it would have the bigger cam (same as the 350TPI). The 88'-89' had the largest lift and duration of all of the TPI cams. The 90'-92' cam was slightly smaller, but tighter lobe separation angle. At the end of the day, probably pretty much a wash between the 88'-89' and the 90'92' cams. I would not go through the effort to swap from one to the other. The horsepower bump in 90' had more to do with going to speed density fuel injection and getting rid of the mass airflow sensor, which was a bit restrictive.

Kevin91Z

iTrader: (1)

DynoDave43 posted the correct info. There is only a tiny difference between the 89 and 91 camshafts, not enough to be worth swapping. The HP difference was from the dual cats and slight bump in compression.