gears and rpm query

MilesnMiles · Post by **MilesnMiles** » Thu Aug 14, 08 6:24 pm

Having fitted my 3.91's i've calculated that i'll be hitting 5,500rpm thru the lights. My question is, for racing should that bethe postion i.e top of rmp/power band at the finish?

Anonymous · Post by **Anonymous** » Thu Aug 14, 08 6:59 pm

All depends on the motor Miles , don't wanna be pulling more than 5500/5700 with hydraulics , probably not worth the risk if the heads can't flow anyhow.

I go through the traps around 5700rpm , got hydraulic lifters so don't wanna spin any faster.

I am interested to know too.

Dave-R · Post by **Dave-R** » Thu Aug 14, 08 7:25 pm

You can rev as high as you like on hydraulic lifters if they are the right kind and have minimal preload. I used to hit 6500 on every shift no problem.

You are best hitting your shift rpm at 30 feet past the finish line.

Your shift rpm from second to third is down to where your power curve is at.

db · Post by db » Thu Aug 14, 08 10:23 pm

How do you keep all this stuff in your head Dave

Pete · Post by **Pete** » Thu Aug 14, 08 10:29 pm

Shifted Julie's 440 with 509 cam and roller rockers at 6500 no worries.

I don't rate the stamped rockers much, but the lifters don't seem to be a problem. I did have to back some of the pre-load out, though.

I regularly took my 340 Duster to 6200, sometimes 6500. It makes more noise than power then but it is fun!!!

At the Nats was shifting the 500 at 7200rpm, so don't worry too much

Pete · Post by **Pete** » Thu Aug 14, 08 10:31 pm

And Dave is right, the 2-3 shift is earlier than the 1-2 shift, well in our cars it is

Dave-R · Post by **Dave-R** » Fri Aug 15, 08 8:46 am

The gear ratios are not evenly spaced so the 1-2 shift has to be much higher to prevent the rpms from dropping too much into second.

Use lifters with a real circlip rather than the stock wire clip. Then only use 20 thou max preload. In some cases you could actually use zero lash but no need normally as with the correct springs for the cam you shouldn't get any pump up.

Use desktop dyno to see where your power curve is at. Your ideal 2-3 shift rpm will probably be about 1000rpm past peak HP but that depends on how steep your power curve is.

Jeff · Post by **Jeff** » Fri Aug 15, 08 9:18 am

Dave wrote:
Your shift rpm from second to third is down to where your power curve is at.

3rd? Don't get to 3rd!

Pete · Post by **Pete** » Fri Aug 15, 08 9:21 am

Gay gears or not enough power

Jeff · Post by **Jeff** » Fri Aug 15, 08 9:24 am

My gears have little white bobby socks.

Dave-R · Post by **Dave-R** » Fri Aug 15, 08 12:18 pm

Jeff wrote:My gears have little white bobby socks.

So does the driver.

Jeff · Post by **Jeff** » Fri Aug 15, 08 12:21 pm

YEAH? And you love it!

Dave-R · Post by **Dave-R** » Fri Aug 15, 08 12:51 pm

It's not the same since you cut your hair short.