Shift Rpm

[sstock]

Hey guys, JMS has my chip calibrated for a 5500 shift.
I make peak power at 4900 (stock cam). I'm inclined to think that 5500 might be a little on the high side, was thinking of moving it down to 5200. What are you guys thoughts on this. I had read somewhere that the shift should be 500 rpms over peak to make sure you are still making good power in the next gear. Anyone?

Later
Steve

 

[Lightning Struck]

Where is your torque peak?? I remember you saying it's at 3800??

 

[sstock]

yep 3800

 

[Lightning Struck]

You want your RPM after the shift to be right around that RPM... I personally would have it land just under your torque peak, so that you go through the peak.. So I would do the calculation to find out at what RPM the shift needs to take place to drop the RPM to around 3800RPM..

If that is about 5500RPM then you need to look at the torque under the curve(Excel can really help here).. I know this seems like alot of work just to pic out a damn shift RPM...

<edit> What I meant by saying look under the curve is you want the most power available... I'm almost positive this is going to be on the top end.. I'm pretty sure on this logic, but I'm sure someone else will chime in

 

[Bad as L]

Steve
Why dont you give it a try first, you can usually get a little more rpm out of a small cam when it has boost on it and you have fresh valve springs and a little more lift now. Also a better breathing set of heads will take some pressure off of the cam. Could be worth a try.

But if it seems like that last couple hundred rpm is taking too long then deffinately change it.
Dale

 

[Marshall Werst]

Steve,

Do you have the stock valve springs..... I do and the valves start floating around 5200-5300 rpms....

 

[sstock]

No, the springs are fresh svo jobs. No float here.
Dale I ran the 5500 shift last season and seamed OK but the last 500 r's were pretty slow with those stock GT-40 irons. Revs a lot faster now. Talked to JMS today and told them the scoop and gave them the dyno info, they said to leave the shift as it is because the brick is so heavy. They said they have played around with this combo and because the vehicle is so heavy you have to keep it in the powerband, a 5200 shift will drop the revs too low in third and slow the truck's ET. They are going to fatten up my program a bit no charge. These guys are great and always willing to help. BTW, I can't wait to get my hands on the EEC tuner but the slush fund just bought a couple of Terrier pups

Later
Steve