high boost/power clearances
 

I was seeing what you guys are running for piston to cyl wall, ring end gap, and oil clearances on your high boost, power engines. Looking for input in the 800-900 hp range. I am using arias pistons. I was thinking of 4.5-5.0 thou on piston to cyl, and 24 on first ring, and 27 on second, and close to 1.7 oil clearance. Anybody with experience with this power range see anything wrong with these clearances?

Re: high boost/power clearances
 

sounds good can probably get away with .0018 oil clearances and .0055 p2w but thats on cp i dont know arias..

Re: high boost/power clearances
 

I run a 5 thousands pwc w manleys and slightly tighter end ring gaps, its funny because every one said I'd get a ton of piston slap, its quite as a mouse

Re: high boost/power clearances
 

^ yeah, how much power, and what bore are you? mine is 82mm, and I want to go 4.5, but I wanted to get some input from people that have made this power, and if I should go bigger on wall clearance. You say you are tighter on ring end gap? what are you running? Also if I get the tops of the pistons coated and the skirts, does this change what I should run for clearances?

Re: high boost/power clearances
 

im sure i will get a WTF but here it is... pwc for 81-85 mm bore on high boost motors (45+) 6-8 thou. when i have ran them tighter after a couple hot laps it would seem like the piston was siezing in the bore.(hard to crank over with starter and by hand) as far as ring gap same deal i have buit engines for people that have wanted the ring gap as high as 40 thou. with out blow by issues. as for oil clearance i would call 1.7 on the tight side on a steel rod i would be looking for about 2.5 (you can get away with loose ,tight on the other hand will eat itself!)on alum. rods i like to heat the rod up to about 150 degrees F and i am looking for about 2.6 -2.8 at this temp because the rods will swell more once they are warm. take it with a grain of salt but this is what i do to keep motors together!

Re: high boost/power clearances
 

on those engines where it was hard to turn over after dyno pulls, did you ever get the chance to disassy and inspect those? how much drop in oil pressure with oil clearances up at 2.5? I've heard of people running p/w that loose before, what is the longevity with wall clearances that loose? Just trying to get some insight on the topic, thanks!

Re: high boost/power clearances
 

6-8? Crazy. I wouldn't go much over 5. Just so you know Arias told me to gap the top ring more because it sees more heat. I'd give em a call but your numbers (24 on first ring, and 27 on second) sound good to me

Re: high boost/power clearances
 

^ I've been told 4.5-5.0 on wall clearance. I just want to make sure it's not too tight for the boost and horsepower goal. I don't have experience at these power levels, so I'm gauging input from people with experience before I final assy. thanks for the input. and on oil clearances, 1.6-2.0 thou ok. I know another member said 2.5, anybody run these oil clearances?

Re: high boost/power clearances
 

Mine is set at .005" p2w oil clearances are between .002 - .0025 oil pressure is fine there

Re: high boost/power clearances
 

what pistons and bore are you?, and what did you end up doing for ring end gap? thanks for the input.

Re: high boost/power clearances
 

Arias shelf pistons. 83mm bore ring gaps I believe are .023 and .026 or near that

Re: high boost/power clearances
 

Sorry for bringing this back up but my question is, how do you guys get .0025 or more on your oil clearance? of course w/o cutting the crank or boring/honing the the BE of the rod? thanks.

Re: high boost/power clearances
 

by using thinner oem honda bearings...

Re: high boost/power clearances
 

You do not want to open up the big end of the rod to get more clearance. That is how you spin rod bearings and destroy an engine.

Re: high boost/power clearances
 

.0025 clearance. Acl race bearings

Re: high boost/power clearances
 

The thinest honda bearing is about .058-.0588 w/c are the red bearings. Using those still not enough to get that much clearance to .0025 maybe .0020-.0021 at best.

Re: high boost/power clearances
 

I've used them before but not thin enough to get to that clearance you guys are getting:mad:

Re: high boost/power clearances
 

the .025 numbers we are talking about are ring end gap. oil clearances are in the thousandths .0025

Re: high boost/power clearances
 

Yes, I meant .0025 my bad.:hammer:

Re: high boost/power clearances
 

i've used acl std bearings and king race bearings and they seem to fall into the .0014" to .0017" range. I haven't used acl race, are the acl race bearings thinner? i havne't had that much clearance with aftermarket bearings unless race ones are thinner. Or do you polish the shit out of the journals to get more clearance? When I called king on the race bearings for thickness, the dimension they gave matched in the "green" bearing zone of a oem honda one.

Re: high boost/power clearances
 

Yes the acl race bearing is thinner than a STD. Acl STD are equivelant to Honda green

Re: high boost/power clearances
 

You will probably have to turn the crank then to get clearance if you can't use an "x' bearing. Polishing is not how to get clearance either. Polishing just finishes the surface of the journal. If you were to try to "polish the shit" out of it, you would end up with a journal that's neither round nor straight. It'd probably look good though, lol.

Re: high boost/power clearances
 

There is nothing wrong with resizing the rods. If done properly. Hell we resize oem rods with 0 failures. My race motor rods are resized. The key is finding a bearing that is close, then getting the final specs with a rod hone.

Re: high boost/power clearances
 

No, there isn't anything wrong with resizing rods, but resizing them for bearing clearance is a bad idea.

The inside diameter is smaller than the outside diameter of the bearing shells. This press fit is what holds the bearing in place, and keeps it from spinning in its bore. There is only about a .0005" or so range that the housing bore diameters can be in. If you have to go looser to acheive a desired bearing clearance, you could lose some of that press fit and risk spinning a rod bearing. Too tight, and you lose some of the eccentricity that produces the wedge of oil between the journal and the bearing.

Re: high boost/power clearances
 

Ive learned a lot about clearances blowing up engines and scraping the shit out of pistons making them clap like hell and leak like a son of a bitch over the years. 800-900hp needs more than .005 of PW clearance...i dont know what it is but a lot of piston companies though they know what they are doing...don't rate our pistons the right way. at 900hp, we make a **** load more power per piston than a 900hp v8....that means a lot more heat...some guys get away with the typical clearances, maybe their tuning is unworldly...and godly...great for them...I know what i run and it aint .0045 thats for sure.