showvette

I had my machine shop file the rings for the LS I'm building. They filed the top to .022" and the 2nd to .023". It's a 10.5" compression engine with a 3.902" piston. I plan on spraying between 150 and 200 through it.

Frank

Black00SS/65SS

iTrader: (2)

the piston wall to bore clearance also has to be increased to compensate for the extra heat you will generate. This as well as guidelines for increasing ring gap should have come with your pistons and rings. Was 5he machine shop aware of your nitrous plans for the engine?

showvette

Yes. Hone was done at 3.904", I believe. They had the pistons and knew I planned on a 200 shot.

Frank

ckpitt55

iTrader: (4)

only 0.002" clearance on forged pistons AND nitrous on top of that?

most forged pistons I've seen recommend 0.004" clearance at minimum - at least mine did - and that's before any power adders come into play. you're probably looking at 5 thou minimum for a 200 shot

Black00SS/65SS

iTrader: (2)

Precisely, all the engines ive honed we used to run.0055 as a minimum piston clearance and usually went .006. What pistons are you running?

showvette

I wasn't exactly sure on the bore hone. My machine shop had my pistons and he knew I'm running nitrous. He explained that he was opening the bore up with that in mind. He also explained that opening the bores would make more noise. That part is right. Now, back to the ring gap?

Frank

showvette

3.902" Probe forged flat tops.

Frank

ckpitt55

iTrader: (4)

Well you need to be sure. What I'm trying to convey here is that the bore sizing details are not irrelevant - do not overlook them. Case in point: the first shop I took my block to did a torque plate hone and sized my bores for the pistons. Great. I get the block back and measure everything. Pretty inconsistent in taper, o-o-R, and sizing. Some bores were less than 0.003" clearance when the documentation I gave them clearly stated 0.004" minimum. Had I not measured the bores I would not have caught this problem. Second shop took out the taper and opened them all up to 0.005"-0.0055", which I verified by measuring again.

If you're not going to measure yourself, I'd ask him what he cut them to at the very least. Most places' definition of "good enough" will not match up with yours, so it's not a bad idea to cover your *** a bit especially with the coin involved. You'll be building yourself a new motor if he cut them too small.

Find out what your bores were cut to first. If you don't need any changes, then size your rings. For a 150 shot - shoot for 0.006" x bore for top, and then a couple thou looser than that on your second ring. Maybe size them a tad bigger than that if you're going to be spraying closer to 200. If your pistons came with any sizing guides though I'd follow their recommendations.

KCS

iTrader: (20)

Pistons are sold in bore sizes, not piston diameters. So your Probe 3.902" pistons are for a 3.902" bore and the piston major diameter will be smaller by however much clearance Probe recommends. Another .002" sounds excessive for a 200 shot, but it should be okay.

The ring gaps are big for that bore size and application, but it won't hurt anything. I usually like the second ring gap bigger than the top, but by more than just .001". If I were you, I'd just leave it alone and run it.

showvette

This project has been through the "bore size nightmare" already...LOL I 'm building this thing myself because my "engine builder" screwed me. He had everything for 6 months and nothing was getting done to it. He kept blaming it on his machine shop taking too long. After the parts came . My machinist knows we have the capability to spray up to a 250 shot. He also told me specifically that opening up the bores to where they need to be for nitrous that it would make a little noise when I first start itfrom the "machine shop", I had the opportunity to check them out. The bore looked like it had been done with a ball hone, and the decks were whiz wheeled, instead of machined, and the cam wouldn't fit in the block. My fiancée owns a race parts business, so we had bought all the parts through her, so he had all the parts to do the job. After seeing the block, I gathered everything up and took it to my machine shop. The bore size was still 3.900", they chewed up the cam bearing bores by using the wrong driver, and the decks were a mess. I took them my pistons with the single intent of having the bores fitted to the pistons. My machinist knows we have the capability to spray up to 250 so he set the bore size accordingly. They do a lot of race motors. He also let me know ahead of time that opening up the bores for the nitrous will make it have a little more noise when I first start it.

Frank

ckpitt55

iTrader: (4)

yikes, best of luck Frank

-Chuck

showvette

This is off of Probes web site. I also just called their tech line and he suggested a .022" gap.


Q: What ring end gap should I run?


A: A proper ring end gap is essential for achieving maximum power output. Too large of a gap can allow combustion pressure to escape past the rings. Too small of a gap can cause the rings to end butt and damage the rings and cylinder walls. Both conditions will reduce the performance level of the engine. The proper end gap increases with the power output of the engine. Please use the following formula:


Top Ring: Multiply the bore size by .004 (ex. 4.000 x 0.004 = 0.016)

Second Ring: Add .003" to top ring calculation (ex. (4.000 x 0.004) + 0.003 = 0.019)

For power adders, increase gap by 0.005"

showvette

BTW, the block has now been decked properly and the cam bearing put in correctly...LOL I also found that my crank that I was told was trashed had never been cut either...And it's in perfect shape. My machine shop checked it and told me they wouldn't cut a crank in that good of shape. Luckily, I was able to swap my bearings for a standard set.

Frank

LS1-450

iTrader: (33)

Sounds like you're now in good hands. A shop that has the respect of racers to build their engines isn't gonna steer you wrong. Enjoy it!

showvette

I just talked to my machine shop. They told me to leave the rings at .022" and .023" for the bottle. This is primarily a street car and a show car. It's only going to get hit with spray on a very rare basis...

Frank