valve size question


New member
I have a 60 over wisco piston 4.500 rod jr race car heavy duty dual valve springs ported polished 28 mm mikuni carb on alky 5hp billet arc flywheel stock size valves whats the est hp? and how much would I pick up going to big valves and what size vales should I go to?
You left out one of the most important factor's which will determine how much power you can make, the cam. If you have a modern .400 + lift cam and are willing to turn it up hard, you should be around 16 to 18 HP at peak. At a .060 over bore with a stock stroke you won't see all that much added power going with bigger valves, once you get around .100 over and stroked then big valves really start helping more. You do need a good Limited Mod style port job though. Jon
i am running they dyno 121 cam I think its a 430 lift cam and I try to turn it as hard as it will every time I hit the track anywhere from 8500rpm to 9000 plus
and thanks jon borgen
That is a big cam, .438 intake lift. Where it's really big is in duration 280 degrees at .050 lift. You will have to turn that cam hard to get everything out of it. Dyno recommends 9600 for target max rpm. It was designed for 16 CI JR dragsters and all you have is a 13 CI engine, it's not gonna have a lot of bottom end with that kind of duration on a small motor which will make it even more important for you to turn it hard. Any stroker will help with power because of the added engine size but the biggest ones are harder to install because of rod hitting the block , cam to rod clearance, they need more work done to fit them in without parts crashing into each other. Your 4.500 rod won't work with any stroker crank. Jon