Launch and shift rpm.

[Ed Carpenter]

My step dad bought a dragster. It's has a transbrake. The torque convertor is a 5500 stall. What should he leave at? The car has a 355 in it. 13 to 1, roller cam, ported heads 2.15 1.60 valves, 750 cfm carb etc what would the best shift point be on this combo. I think he needs to turn it harder than he is. He is shifting at 6500. 4.88 gear if that helps. Also the car came with 16X33 tires on this thing. I feel that is to big for this combo.Thanks Ed.

[Bill Baer]

Well Ed It depends on what he’s trying to do with it. For bracket/super class racing you need to observe the rear tires at launch and 60’ times and if necessary chip it down to get a consistent launch and 60’ times. However if the 60” time and reaction times are consistent just “let it eat”.
As far as shift point goes that depends on the camshaft and design and airflow capacity of the cylinder heads you could try shifting it higher or lower until you figure out the max rpm for HP which could be anywhere for 6000-9000 but I wouldn’t try any more than 7500 or so unless you know what valve train is good to. And don’t be surprised if changing the shift point doesn’t make a big difference and if turning it harder doesn’t make it faster why do it?
As far as the tires being to big, again for bracket or super class racing as long as the car has acceptable reaction times then they can’t be too big!
However if your looking for the best ET and don’t care about consistency the car will go quicker with a smaller and lighter tire (lower rotating mass/weight) but it won’t be as consistent as the Big “O” tires.