I picked up a set of Autolite 24's to do my tune up tomorow. Should I go back and swap them for 25's. I have H/C/I/full exaust but all motor, no bottle, no blower, so will 24's make me go slower?
I would just stay with the 24's. they are the colder temp range of the two plugs if I remember right. If you've got aluminum heads, I would definately stay with the 24's. I don't think it would make a huge difference either way, so if you choose to swap back to 25's I don't think you will be hurt.
if you're still running the thumper e7 heads i'd stick with the stock/stock replacement plugs. have you milled the heads at all? what's your c/r. i think the 24's are the stock type plug but i'm not sure.
The reason I picked up the 24's is the colder range, I just don't know how much colder of a plug they are. I work in a shop as an assistant auto tech, and talking to the tech I work under he told me that "the colder plug will take more temp to clean itself, too hot of a plug they tend to wear out by burn up, too cold the foul due to carbon buildup, so since your engine has considerably more air and fuel flowing through it, and is driven hard, a colder plug might be a good idea." Which I have noticed my plugs which are now 25's tend to get a little brunt up a little early for thier age. I think I will try the 24's for this cylce.