[budsthe3]

Hi all, I'm trying to get some opinions on a good RPM to shift my new motor safely at. I was thinking maybe around 6k.
Here's my combo:

496
4 bolt mains
Scat 9000 cast crank
Square port aluminum heads
Howard's hydraulic roller cam
234/243 dur, 634/643 lift 112 LSA
2600 - 6500 range
Scorpion roller rockers
Edelbrock rpm air gap
Quick fuel brawler 850 mech sec
Accel HEI
TH400 3000 converter
3.73 rear, 28" tire

 

[GuysMonteSS]

What are you doing with it ?? Street or strip ??
6000 RPM sounds like a safe limit to me for a street car.
If you're racing it and looking for every last little bit you can wring out of it,I have read that some will rev them a couple of hundred RPM's past the point of max power as the shift point.
Guy

 

[budsthe3]

What are you doing with it ?? Street or strip ??
6000 RPM sounds like a safe limit to me for a street car.
If you're racing it and looking for every last little bit you can wring out of it,I have read that some will rev them a couple of hundred RPM's past the point of max power as the shift point.
Guy

It's a street car that will see occasional track time. I meant shifting at the track, sorry

 

[GuysMonteSS]

It's a street car that will see occasional track time. I meant shifting at the track, sorry

Just my opinion Bud,but since it is your street car and not a dedicated strip car,I would set the rev limiter at no more than 6000 RPM.
Guy

 

[p40]

what is your cam rpm good for if its 6500 shift at 6000

 

[68Chevele]

62-6500rpm should be no problem with the stuff you have listed there. At the track try different shift points to see where the car ET's the best.

 

[Kirk's67SS]

I have Howard Roller Cam and Roller Rockers in my 468 BBC
I Shift at 6,000 rpm for my Car's Perf at the Track / see My Sig

 

[bradley67]

Try 5,700 first to second and 6,500 second to third. This also depends on how much the rpm falls back on the 1st to 2nd shift. Caveat - Don’t miss second to third shift!
Sometimes, depending on the whole combo - short shifting your first shift point puts you back in the torque band to pull the vehicle faster thru that big transition from 1st to 2nd.
As said earlier try different shift points to see what it likes.

 

[68Chevele]

Try 5,700 first to second and 6,500 second to third. This also depends on how much the rpm falls back on the 1st to 2nd shift. Caveat - Don’t miss second to third shift!
Sometimes, depending on the whole combo - short shifting your first shift point puts you back in the torque band to pull the vehicle faster thru that big transition from 1st to 2nd.
As said earlier try different shift points to see what it likes.

Just like my peanut port engine, just because it will turn 6500 doesn't mean it will make power at 6500. The little heads were happier shifting at 5800 and then legging it out in high gear FTW.

 

[pannetron]

Since you didn't mention con-rods, push rods or valve springs, I wouldn't rev it over 6K I bet that cam makes killer mid-range torque so maybe even shift at 5500.

 

[budsthe3]

Since you didn't mention con-rods, push rods or valve springs, I wouldn't rev it over 6K I bet that cam makes killer mid-range torque so maybe even shift at 5500.

Forgot to mention the rods, they are forged I beams. Not sure about the pushrods, valve springs match the cam but am not sure about them either. This is a crate motor.

 

[-SS454-]

will depend on your springs/valvetrain. 6000 should be safe, 6200-6500 you could very easily start seeing valve float.

Have you considered putting it on a chassis dyno to find out where it makes it's power and when the power falls off?

 

[GuysMonteSS]

will depend on your springs/valvetrain. 6000 should be safe, 6200-6500 you could very easily start seeing valve float.

Have you considered putting it on a chassis dyno to find out where it makes it's power and when the power falls off?

Good idea !!!
Guy

 

[budsthe3]

will depend on your springs/valvetrain. 6000 should be safe, 6200-6500 you could very easily start seeing valve float.

Have you considered putting it on a chassis dyno to find out where it makes it's power and when the power falls off?

That's a good idea. I'm not aware of any in my area, I'll have to search

 

[77 cruiser]

Generalization I used to see a lot was 10-15 % above peak HP rpm. Too bad you don't have a dyno sheet.

 

[bracketchev1221]

I think with the bigger inches the motor will tail off before 6500 even though the cam is rated there. I don’t think that engine will need to go past 6500 ever. Start at 6 and increase it 200 every run until it stops getting quicker.

 

[BillyGman]

If you'll be racing the car, keep in mind that in the lower gears, (especially first ) the engine revs so quickly that if you set your shift light at 5,500 RPM, by the time you complete the shift, the motor would've hit 6,000+ rpm before the the revs drop down when it actually hits the next gear.

 

[68Chevele]

Those aluminum sq. port heads are going to need more duration and rpm to make them perform at their peak. I would advance the cam a few more degrees to help out the low end a bit.

 

[cv67]

Are those the generic 325cc heads out there?
Id say 5800 it will last a long time...6kis no problem