how is the stock exhaust port in stock form in your opinion?
The exhaust port took a lot of work actually for a 474. It might not be quite as bad with a 450. The port layout isn't bad, it's just smallish all the way through the port. Overall, the exhaust port got noticeably bigger. The Z head probably got just as much cut out of it. Yours especially for a 490 with +1's.
I'm thinkin about goin bigger bore than the 474 kit. Now do you think just going bigger bore is better or do I go stroker? I know I've got to get bigger cams. One of the builders over on ltr450hq goes bigger on the valves. If I go to 100mm do you think I should get the bigger valves or stay with what I got?
I'm not familiar with the LTR or it's quirks, but bore vs stroke when you're only talking 20ish cc's, I don't think you'd really tell the difference in either route. However 100mm is a a lot of piston, and makes a pretty wide combustion chamber, which is a little more prone to detonation, and might take a little more timing to make it really run. A high compression, dome piston can make matters worse and hurt combustion efficiency. You can't get by with quite as much compression per octane number either. You tighten your tuneability range that way.
The stroker is a little less headache (as strange as that sounds), but stroke limits rpm potential. If it's just a couple mm, then it won't make much difference, and if you already were staying within the 10,500 rev limit, the stoker won't hurt you a bit. The down side to the stroker, is they usually use a shorter rod ratio which wears pistons and cylinders faster, (but helps fight detonation) or you end up needing an expensive stroker piston.
Technically, you could (if it's all setup right, and doesn't bring on some combustion problem) get a little more horsepower from an all bore build, because you COULD turn it 12,000 rpm and still have a decent life span from it, if the valvetrain can handle it.
I would prefer +1 valves all the way around even for a 474. I would definitely go with +1 valves for anything bigger! To be honest, I think this head that I'm working on would benefit from +1 valves. Peak flow still isn't getting as high as the Z head. I know that a different valve seat profile can get it there, but it may have to give up some low lift flow to get it, and this is doing better than the Z heads at low to mid lift. With +1's you can gain across the board.
To run 490+ cc's with stock valves would shorten your rpm range. It creates a catch 22. It limits high rpm power unless you add bigger cams, which limit low end power. You can pick up better overall power with bigger valves.
I wouldn't waste your time doing any of it without porting though, especially on the exhaust side. A 490 would be really stuffed up trying to breathe through the stock exhaust port. The exhaust side especially has to completely change to make it worth the bigger valves.
Ice Cube Z490
Custom CFM Motorsports +6mm 13:1 JE 2-ring Piston, +5 Hotrods Crank
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