High Compression Pistons?

[ShionS14]

I was wondering how you would figure out if you had a cam with long duration and high lift, and you had high compression pistons, if the valves would not hit the piston? and how would you solve it? does anyone make a high compression piston that has the valve cut on top of it? i hope this makes sense to ya'llthanks

[SimpleEnigma]

The only time you would really have a problem with something like that is if your cam timing or duration is set such that the valves are still open when the piston passes through TDC.

Piston shape is important to the compression ratio, but unless you had domed pistons i dont think you have to worry about your valves making contact with the piston, as long as the cam timing is set correctly and you dont break your timing chain

[ShionS14]

devious do you have any insight for me?

[deviousKA]

The ka24de does have limited valve to piston clearance. How long of duration cams and how much lift are you planning to run?

For instance, a "hot" oem cam setup 248/248 at base setting (with cam gears) combined with early 89 ka24e pistons (.020" over the 34mm compression distance) yeilds less than .015" exhaust valve clearance. That is with a fresh timing chain assembly, any slack in chain retarding the cam timing will obviously provide less clearance.

This is very slim on that particular setup (to slim), but using different pistons can give a lot more room. Late 89-90 240sx or stanza ka24e pistons are .040" lower in the area that the exhaust valves come close (.020" lower than the 34mm compression distance). I would suggest an exhaust valve to piston clearance of at least .030".

As with any custom high compression and cam setup you will want to verify with your engine assembled with one of the piston tops covered in .070" or so worth of modeling clay. This adds another step to the assembly process but is a must. If you find that clearance is minimal after all of your desired components, best course of action is advancing the exhaust cam with an adjustable cam gear. If that does not do the trick with just a minor degree adjustment, you will need to flycut your piston tops. Custom pistons can be ordered/designed with valve relief/flycut, or the pistons added dome volume can be positioned away or around the valves.

What are your desired specs or parts that you want to end up with (compression ratio, cam lift/duration)? I may be able to give you a better idea of whats necessary.

[ShionS14]

well as soon as my head gets here i am going to give it off to port pros and have them port polish, 3 angle valve job install new springs retainers etc. after that they are going to flow bench it and send the numbers off to comp cams to tell me what cam would be best for my head flow. i am not wanting to go to radical but a little bit more aggressive than what pdm and jwt sell. compression, i was thinkin 10.5:1 but am not sure what pistons to use to get to that number since the ka24e pistons bump up to 11:1 so i probably should have waited and asked this question after i got my specs down. and then i will also get an e-mange or maybe a standalone(dont know if i want to attempt an ITB setup or not)

[PandaS14]

Regarding cams, I've got a little more info on the crower ones.

Unfortunately, they never tested or even made any of the cams that they listed. They've got one set of turbo cams ready for production (testing was just finished up), but no N/A grinds. I talked to the guy who did the testing for them and they just pulled numbers out of their asses that they thought would work, and listed them in their catalog. some of the lifts were so big that they would have hit the head. So as of now, JWT and PDM are still the best ones out there.

And the worst part is, they have no intention of making or testing a N/A grind.

[ShionS14]

well i just lost a whole lot of respect for them, do the guys at enjuku know they did that?

[PandaS14]

the guys at Enjuku just listed the specs crower had in their catalog supposedly.

[ShionS14]

well at least they didnt post it knowing that crower just pulled those numbers out of there ***