Planning for 408 - Possible Solid Flat Tappet cams
The car Will be mostly for fun on the street, so it has to have torque and not be a dog until high rpms. For max rpms I put 6200 for cam specs for that cam from jones cams. Should I be Revving this 408 higher? No advertised duration from jones cams. I did request a street cam from them and not a race cam. This is not a single purpose drag car. Car weight 3000 lbs.
My stroker experience is none. They are just naturally more RPM limited, based on piston movements after TDC. 6200 RPM seems like it is high for that IF you are road racing/ autcrossing.... not that it can't run there but will be naturally rolling off and so the cam needs to be more duration to get there RPM. Pushing the cam to work at that RPM range will raise the bottom end of the RPM range and there is the issue of concern for me.
If the RPM range is 3000 to 6200 with a bigger cam, then the usable RPM
ratio is 2.06. If the RPM range is dropped 500 RPM at both ends with a smaller cam, that is 2500 to 5700 RPM; usable torque range
ratio is 2.28. To get to that RPM range
ratio with the bigger cam, the lower RPM now has to be 2700 RPM with the big cam. But you are off the torque curve of the big cam at 2700.... You don't have a torque converter to allow the RPM's to rise up.... you are stuck with the narrow RPM range
ratio.
That will make a difference with that 4 speed, and hard running like on autocross. Trust me, you will find corners and speeds where 2nd gear will be too low and 3rd gear will be too high... So the real reason to stay smaller is to get a bigger RPM range
ratio, with your intended use and the 4 speed.
Just an experience: I had a 1.6L rally car with a solid 2500 to 6500 RPM range (2.6 RPM ratio), that was hands-down a much better rally car than a higher HP 1.9L with a 3700 to 7500 RPM range (2:1 RPM ratio). Both 4 speeds... the bigger engine would get into spots where you could not find the right gear and RPM combination.... the RPM range ratio did not work with the gears. I revved it past 7400, sometime to 8200, just so the RPM drop going into 3rd did not kill the torque. The smaller engine with the smaller cam was never in that kind of situation.
Hope that helps.
