My Buddy has a 91 Trans am with a 406 SBC. The current cam is a hydraulic roller .554 intake and exhaust .050" Duration intake/exhaust 254 Rockers are 1.6 . I am not sure what the rest of his cam specs are.

We set the rev limiter to 6800 and it is hitting it right after the 1000ft. The trans is a TH400 and the rear gear is 4.10's.

Should we change the cam and spin it to 7300ish or put a 3.90 rear gear?
The motor has billet mains and all forged internals.

Just looking for some opinions

Thanks

Tire size?

how did you come up with your 6800 rev limit?

The tire is a 28".

It made good power up to 6800 NA and didnt hit the limiter before the traps. Once we started to spray it was hitting the limiter.
Also stopped making power on the dyno at 6800

whats the tranny feel like.hows the stall?

If the engine stops making power at 6800 on the dyno, setting the rev limiter at 6800 is too low. Bump the rev limiter to 7200 and try again at the track. You should be at your shift point just before you cross the finish line and taking it higher as you cross is very common for a proper setup. The rev limiter setting should be just before where the valves start to float, not where your peak power is.

If you can find the cam specs, they should give you an RPM range of the camshaft. Do the valve springs match the requirements for the camshaft?

The .554 lift and 1.6 rockers bothers me. Is that the cam specs or how much lift with the 1.6 rockers. Either way, are the heads set up for that much lift without getting coil bind or having the bottom of the retainers hit the top of the valve guides?

like alky said, you can take it over 6800 if that is indeed where the peak is. however, this being a nitrous car i would drop the gear down to 3.90's or even down to 3.50ish depending on how well the car acted to the 60'. you will find your timeslip wont change all that much when you drop the gearing... the engine wont seem to care. if it spins sometimes or goes up on the bumper taking gear out will help.

Nitrous can give people fits when it comes to gearing as you will pick up mph, but typically run the same RPM as NA. Actually any type of power adder typically does this.

If you motor can rev to 7200, just bump it up and try it out there. As you bottom end is super solid, a few more rpm should work - assuming you don't get valve float. A lot easier than changing gears...

I guess we will try and up the limiter first. We found the build sheet with the cam info.

Int.open @.050 22
Int close 52
Exh open 58
Exh close 16
Int C/L 105
Int Duration 254
Exh C/L 111
Exh RAR 1.6
Exh Valve Lift .554
Int RAR 1.6
Int Valve Lift .554
Int lobe lift .346
Exh lobe lift .346
Spring pressure meets the Cam card 145
Open pressure meets the cam card 340

So the .554 lift is with the 1.6 rockers based on the lobe lift numbers. Are the heads and springs capable of that much lift?

That cam has a lot of duration and lift. It has requires very heavy spring pressure. It probably has an RPM range into the 7000's.

Exh RAR 1.6
Exh Valve Lift .554
Int RAR 1.6
Int Valve Lift .554

looks like its .554 at the valve using a 1.6 rocker arm ratio.

How much you spraying? Power adders add mph and only way to get more mph is more rpm. If you are spraying a decent shot you will see a bigger rpm increase requirement. Changing cam for that is the wrong idea to have. Cam sets powerband, you gear and tire to match. You need less gear on spray. Simple as that. You probably wont have enough rpm to make up for the difference. Hard to say

6800 gives 138 mph. 7200 gives 146 so you may cover if the shot is small

Your valvetrain needs to be pretty serious to hold off float above 7k with a hyd roller. Revving out may not be safe

So far we sprayed it with a 150 but ran Into the rpm issue. We plan on doing a 200.

I'd gear down

Or stuff a taller tire under the fenders and keep the gears you currently have. I was able to squeeze a 29.5 under the fenders with a few typical modifications.

raise the rev limit

where the heck are you racing on Dec 25th ?!

LOL

Merry Christmas

Florida !!

Thanks for the help guys !