13.5+:1 compression ratio pistons F4i

[JamesWolak]

We have been running the 12.8:1 wiseco pistons on our motors for awhile now. We have had decent results with them but i am unhappy with the geometry of them and they require a decent amount of prepping to get them the way i like. All and all i can't complain about them too much but i am looking to bump our compression ratio up and do some dyno testing over the summer.

I am looking to find a piston around 13.5:1 for the F4I. I have searched in the past with no luck. Did a quick search today and found some for the RR motor http://www.jepistons.com/cat/j...onda/cbr_600rr.shtml (http://www.jepistons.com/cat/je/power/street/honda/cbr_600rr.shtml) I dont think the RR pistons can be swapped with the F4is but i am not 100% positive.

I know i could get some custom pistons but i like parts "off the shelf." This allows me to order a set of pistons and get them next day. You know for when you find out somethings fawked up 13 days before comp and need to have them next day AMed to your house. http://fsae.com/groupee_common/emoticons/icon_rolleyes.gif I also could shave the head/run thinner head gaskets but we allready have issues blowing head gaskets and i hate having to machine blocks.

Also if anyone is running some 13.5+:1s and could share your opinion with me on them i would appreciate it.

[Whis]

You could try longer rods, but that doesn't fix your geometry problem... Or different cranks, but that does other weird stuff, really weird stuff that takes a lot of thinking through.

[JamesWolak]

Originally posted by Whis:
You could try longer rods, but that doesn't fix your geometry problem... Or different cranks, but that does other weird stuff, really weird stuff that takes a lot of thinking through.

Lol. I knew someone was going to bring up rods and cranks. I am just trying to keep it simple with some off the shelf parts.

[Whis]

Well. Since I know nothing about the F4i, that was all I could give you... Sorry. Yeah, we're running a single and it was really easy (expensive) to get parts to make our engine like what we wanted. Sorry dude man.

[Wesley]

well... I know leaving the middle layer of the MLS head gasket bumps it up to about 12.5 with no reliability issues - we've been doing it for a while.

Alternatively, you could weld up the combustion chambers, but that's fairly involved in terms of maintaining port geometry..

[Superfast Matt McCoy]

Originally posted by Wesley:
well... I know leaving the middle layer of the MLS head gasket bumps it up to about 12.5 with no reliability issues - we've been doing it for a while.

Alternatively, you could weld up the combustion chambers, but that's fairly involved in terms of maintaining port geometry..

With the stock pistons, you can't take more than one layer off without your pistons and valves getting together like two high school kids in an under-the-bleachers makeout fest. With the higher comp pistons you might not even get away with one, but like Wes said it is a pretty reliable solution and it's definitely worth checking.

Seems like we found a particular brand of spark plugs that upped the cylinder pressure a little. Once you're at 12.8 it doesn't take much to get higher.

Personally, I would get some used RR pistons off eBay or something and bust out the micrometer. I'm pretty sure the camshafts are identical, so if the wrist pin height, bore, and combustion face shape are the same, you're probably good to get the aftermarket 13.5's.

Then you can come back here and say "Matt, it totally worked!" and I can know for future exploits with my two F4i's.

[Mikey Antonakakis]

Yes, this would be quite interesting to know...

[JamesWolak]

Yeah.

Like i said gaskets really aren't a choice and neither are spark plugs. We have had run ins with both of these and have found what works.

I guess i will call JE and see what they say the differences are with a RR motor pistons.

[Marty J]

We went with customs from JE last year.. i dont think the RRs work, pretty sure the combustion chamber is different so the combustion face is different... If you want off the shelf the Wisecos were the only thing i could find... But in the end i just had JE make up a set with the highest dome they could and then I hand finished everything for clearence. ended up with 13.7:1

[JamesWolak]

Marty. How long did it take for JE to make these?

Also check your inbox

[Marty J]

As far as how long it took to get the parts from JE... It took a damn long time. But there was a reason. They apparently hadn't made f4i pistons in that size before (or at least that what they told me) so we had to make a combustion chamber mold and all that good stuff... If you do decide to go that way PM me and ill hook you up with the guy at JE that I worked with which should speed things up. When everything was finally straightened out it only took them a 3 or 4 days to pump out the final part.

Ill go ahead and answer your PM here in case other people have the same question... (my FSAE philosophy is that it should be more about having fun and learning than winning so I'm pretty free with our information)


Marty,

You responded to the post i made about 13.5:1 pistons. Was hoping that i could get some more information about your experiance with the 13.7:1s you guys had made.

I have had some issues with pre-ignition from hot spots on the 12.8:1 wisecos. Along with a few other things i think it has to do with the surface of the piston.

How does the surface look on your pistons? Is there any way that you can share some pictures with me?

I understand that you might not have this info or are willing to share it but i have some questions regaurding your setup:

Are you running these on a turbo or NA setup?
Are you knock limited or are you reaching MBT?
What fuel are you using?
What are your max EGTs?

I was working the pistons and and building the engine at absurd hours so i didn't think to take pictures after i reworked the domes, but i may be able to find a picture of them fresh out of the box so you can see what i started with... have to look for them though.

We Haven't had any pre-ignition issues but that was a major concern of mine. By rounding off all sharps in the combustion chamber and on the piston head (being careful to limit the amount of material you take off to maintain compression) you eliminate major hot spots.

I modeled the dome work after EYDYNs roller wave pistons (i've done the same om my personal Integra engines to great success) if you arn't familiar, check them out (http://theoldone.com/components/pistons/index.html) they are known for running silly high compression ratios on pump gas engines

-Car is NA.
-MBT most places in the map with some exceptions at low RPM when the restrictor doesn't put such a damper on dynamic compression.
-100 Octane Gasoline baby (powered by dead T-Rexs... f**k corn)
-dont remember what peak EGT was but I feel like it was somewhere around 1650... cannot quote me on that though.



Problems- Had to rework the spark plug reliefs because we were bending them if they were turned toward the exhaust valves.

-worst part is, the car has a hell of a time crank starting with a regular motorcycle battery... damn thing is though to turn

[Luniz]

We are running a 600RR engine on which we have machined the head so that we get a compression ratio of sth like 14:1 and did not encounter any problems so far. Obviously, 100 octane rocket fuel is required, but apart from that, no issues so far.

[JamesWolak]

GT100 is still supplied at comp?

Marty i will be PMing you for that contact at JE.