Details are:

.030 on the bores, scat 4340 forged crank, scat 5.850 billet h-beam rods, SRP/JE flat-tops,Speed-pro file-fit rings; plasma moly top ring, iron second ring, LT oil rings.

Planning on spraying 300 on this bottom end (two stages @ 150 each). What top ring gap have you guys been running on this sort of combo. I already have them cut to .012, with the expectation that they will open up about .005 after break-in for a total gap around .017. My question is do you think this is too tight with spray? What have you guys seen out there..

Thanks,
Dave C.

 

there should have been a sheet with the rings telling you how much to gap it for nitrous and/or heavy nitrous use. Usually a .00X for X.XX bore

 

Yes. I saw the "recommended" gaps for different uses, but the recommended .025 gap seemed a little big to me (considering it would end up being .030 after break-in), and I wanted to get some input from members who've put together something similar. Last thing I want to do is put too much gap in there, and have it unload the top ring.

Dave C.

 

I believe that the LAST thing I'd want to do is to put them in with too little gap and experience the trauma of having the ends of the rings butt together, possibly break the rings, and probably take out the cylinder walls. I suspect that the manufacturer's recommendation of .025 is made with the expectation that elevated cylinder temperatures stemming from use of laughing gas could cause increased thermal expansion of the rings. I gap top rings in Stock and Super Stock motors at .017 and we certainly don't build the kind of heat that nitrous is capable of generating.

Good luck

 

heavy boost and nitrous motors need A LOT of top ring end gap

over .025 is NOT un-common. What is un-common is a .005 increase in gap during break-in, i've never had an engine shop tell me that

 

Sounds like good advice to me, as does going with the ring manufacturer's numbers. I like to use their cylinder wall finish recommendations also. They want your rings to perform at least as well as you do so you'll keep buying their product for your next engine.

Yeah, moly is pretty tough stuff. I don't recall rings wearing in enough to increase the gap .005.


My $.02

 

Do NOT go by the ring manufacturer's specs. ALWAYS go by the PISTON manufacturer's specs. The composition and design of the piston will DRASATICALLY affect the required ring gap.

My mild 383 blower motor using KB hypereutectic pistons uses MASSIVE .032" top ring gap. Hypers with rings close to the piston face throw MASSIVE heat at the top ring. Ask me how easy it is to butt a ring gap closed using a .026" top ring gap with these pistons. Go ahead- ask me!

ALWAYS ALWAYS ALWAYS follow the PISTON manufacturer's recommendations. Takes about 15 minutes to call their tech support line. Time well spent. Do not go by "gut feel" or experience with other motors. You will be wrong almost always.

 

In so far as the ring gap increasing through break-in, I'll have to stand by that. Every .001 increase in bore (the walls are going wear, not the rings, since the rings are a helluva lot harder material than the cyl walls. - I should have been clearer in my original post ) will increase the circumrence by about .003 which will translate into an increase in ring gap.

At any rate, thanks for the input. I'm giving JE a call now just to be sure.

Dave C.

 

Let us know what JE says, as I am building a new motor this winter.

Rich Krause

 

ring gap does open up quite a bit on a real street motor.

I usually gap on the small side of the reccomended gap(by the piston manufacture). Because this is a real street engine it will open ~.003 easily.

 

OK.

Called JE, and they recommended something a bit different than Speedpro. On these particular moly rings, with their forged pistons, they recommended 18 to 20 for the top ring and 20 to 22 for the second. .012 initial (and the tech confirmed that they WILL open up somewhere between .003 and .006 in a street motor)was way too small, even for N/A with my compression target and I'm planning on spraying the everyloving crap out of this thing, so I'm going ot open them up on the high side.

I'm going to go with .020 on the top and .022 on the second.

Good call Damon The JE tech was WAY familiar with this setup, and was quick on the answer, and I didn't have to wait on hold forever. Cool

Thanks fellas..
Maybe when I get this thing running, I can finally turn some decent numbers like you do..

Dave C.

 

Hey Jordan, I have been following your progress for while know and glad to hear that you are doing well with your racing. Do you still find time to build engines on the side .. also I see that you have not updated your other site for a while know (with the z/28) anything new with the car etc …


Jim

 

yea, I do stuff on the side still.

My car is now powered by a t88.. just made ~650rwhp on 12psi/pump gas looking for 900+rw on race fuel when I go back to dyno.

I need to update my site.. bad. just SO much work to redo it the way I want, and so little time

 

Thanks, just trying to help avoid making a few of the same mistakes I have.

Until the first time you rip the top ringland off the piston from too small a ring gap you don't give a hoot about ring gap specs. Then you blow up a motor you poured your heart and soul (and MONEY) into 100 miles down the road. THEN YOU GET REAL **** ABOUT IT. Like I am.

 

cool hope to see some udate pictures of your set-up soon


Jim