As I attempt to nail down final specs for my slugs... I'd like to know what the CF's truly experienced high-performance engine builders think about the various forged piston alloys available.

I may be missing a couple (or more), but it seems 2618's (no, low or high silicone) and 4032's are the most common forgings out there for the BBC. Of those, my understanding is that "no-silicone" T-61 2618's are most preferred for racing applications since they are not as brittle as alloys containing silicone, but that higher silicone 2618's and 4032's have lower expansion coefficients which allow tighter piston/cylinder wall clearances preferable in a street mill.

If I'm on the right path so far, what do you guys think about using 4032's in a 10-10.5:1 CR, 550-600 HP, moderate solid roller, street/occasional road course 496 BBC mill? Imposed redline likely 7000'ish. Might spray it with 100+ shot, eventually.

FWIW: Yes, I intend on having the domes thermal coated. Considering expansion/accumulator grooves. Not sure about friction coating the skirts yet. And no, I'd rather not tear it down every winter...

Thoughts???

Thanks, in advance, as I'm hoping the usual suspects chime in here...
Charlie

 

I think either will be fine...really. I've always used 2618 for serious race stuff..just like everyone else. Piston design has come a long way and they can do a much better job with controlling noise etc with the looser clearances typically run with 2618. We recently did a 632" motor. The difference between the first shelf JE pistons and the next set of Diamonds that we had custom made was huge. In fact the diamonds weighed 40 grams less. They had an interesting skirt profile. They make no noise on cold startup and seem to be working great.

My 540 has 4032's in it. They are basic SRP's with no coatings etc. They have been in there 7+ years now with no problems. I run them at .0045 clearance which is a lot more than JE/SRP requires..but I feel good there. interestingly they are also dead quiet at startup. My car spends a lot of time running around with no air filter and you would expect it to have ring/piston/bore/issues. None so far. Lots of miles and lots of screaming down the track. I think the 4032 material is helping in that regard.

I have my old 427 with the GM/TRW's in it. Those things are bricks. The motor has been honed a few times and the tightest hole is .007..loosest is .0095. Sounds like a diesel when cold....but runs like a ****!

Biggest thing to watch for is pin clearances. Many pistons come very tight. It's good to spend a little time with a hone to loosen them up some.


JIM

 

Thanks, Jim. 7 years, eh? I'm really leaning toward 4032's (likely custom Arias or possibly some "worked" SRP's) and looking for this very kind of confirmation.

What do you think about thermal coatings with occasional shots of giggle gas? I've seen some references that say the coating may not be the best idea in the event that the additional heat isn't for short durations only, whatever "short" means. I had thought the coating would be even more desirable for longer hits...

 

I think coatings are generally a good idea. Not sure if they are all that necessary. Lots of fast stuff runs without them.I'm talking serious N20 race stuff here. But if they manage to stick well...then they could give some insurance. There might even be a HP or two in them from what I've seen in extreme race environments. How much help they give a street motor with relative cool temps and carbon buildup is open for discussion I suppose. Years ago I did the VHT spray bomb treatment on my 427 pistons. I tore it down a year or two later and was impressed to find most of the coatings still there. Actually pretty surprised.

Coated bearings show promise, but it seems some of the most serious folks are running without them. And these are the folks you would expect to use them. I think if the oiling system os good....it doesn't matter. *Might* help if something bad happened...but you probably have issues anyway.

I've yet to see the coatings last too long on piston skirts. might be good for race stuff with vacuum pumps...but I figure limited value in anything that puts any real street miles on it. Guess they don't hurt anything though.

Whose coatings are you looking at? Swain?


JIM

 

Yeah, I believe Swain to be the choice, given their long track record. (FYI, Jet-Hot is getting into coating engine components, too.) I'll probably end up doing the domes and I've just about talked myself into sending in my valve springs for the oil shedding treatment too, tho we share similar thoughts about the skirts on a street engine. I kinda figure the 4032's with tighter clearances ought to give me enough of a leg up against scuffing the walls.

Appreciate the feedback. IMHO, as it's been said before, some of this hi-po street stuff takes more thought than hard-core racing, and it makes me want to step back and do some head scratching (like I'm going thru on the cam, again) every once in a while.

 

Boy. looks like we generated a whole lot of interest in this one huh???

I agree.....building a really nice street motor to run really hard is tough stuff. You end up with a slow race motor that has sorta street manners, or a fast street motor that has sorta street manners. Lots of compromises. Anything you can do to shed heat etc is good stuff. buying good parts and having excellent machine work is paramount. The cam has the biggest bearing on manners...that's why I encourage people to get really good heads...evne if they seem big. I'd rather run a great set of heads with a flat tappet than a poor set with a roller.

JIM

 

I went through the same thoughts on my build. I will be spraying a 150 shot once in a while, mostly street use and ended up with Mahle pistons. Skirt coating is standard, Low expansion forged which I liked for a street engine and great uniformity in weight and size, price was very competitive. Limited choices though.

 

I can't comment on alloy types. I've just entrusted Wiseco to make the call. Swain Tech did my original 383 JE pistons with the triple coating

Top thermal, bottom oil repellant, moly skirts. The top still had a coating on the last refresh. That even with some bad preignition from a low octane sold in the high test pump.

I am a believer in the gapless rings. I've managed to get sub 3% leak downs after a 500 mile breakin period.

 

Glad you brought up the gapless rings, gkull. Apparently not too many guys run (or admit to running) them, but I've given some thought to it. Haven't heard enough to gather what the exact consensus is on them. It's good to hear you're on the satisfied customer list. Do you happen to have any input about increased vacuum claims?

 

I can tell you this. The lack of blow by and very low leak down % tells you that they really seal well. I've help mount some of the motors down at the race on the dyno stand. Some of the big blocks setup for large amount of N20 with their wide end gap rings just pump out crank case vapor when under load. Then you get these serious road racing motors with gapless rings and the pipes are glowing on the stand and very little vapor is coming out. Or even the dry sumped motors have to have an manifold air adjustable bleed because they start drawing up to 20 inches of vacuum in the block. Max hp is reached at @ 15 inches of vacuum below the pistons.

I think that most N/A race motors are using gapless these days.

 

When I get my 383 assembly built it is going to Swaintech. Everything I can find says that they are the way to go.

That and they are around the corner from the first college I went too.

 

I gotta say that very few race motors I know of use gapless. I think the concept is good...but seems like more people have issues than do well with them. Sounds like you hit it right!

ML67 went through a couple of version of the gapless sucking oil in his 540 until he hit a combo that worked too.

I think dynamic running conditions are a lot different than static leakdown tests would indicate. Again, not saying they don't work...but you don't see OEM's or most of the race teams I know of using them. Even in cases like the Engine Masters deals where every half a HP counts...you didn't see them much..if at all.

JIM

 

Jim are you running 1/16th first and second rings. Most small block forged pistons use these tiny rings for less friction the down side is they don't last very long. In a motor that is going to be refreshed annually it's not a big deal. Anyway I've had better luck following what all these roundy rounders are doing.

I think that the gapless rings are also used because many of these dry sumped motors are running Methanol. They want to minimize the amount of water in the oil before the motor comes up to temp enough to boil the water off.

Engine master motors often don't last through the dyno run periods. My friends have entered a few and they say lots of motors blow at the events. So a one shot wonder using 5 weight oil @ 30 psi with springs on the verge of float is not my idea of a street motor. I've seen rods and piston skirts that looked like swiss cheese.

 

Just a little article - I know don't believe half of what you read!

http://www.racetep.com/totalsealframe.html

 

Don't let me stop any debate over rings...

I just wanted to interject that SRP tech has recommended 0.004" piston/wall clearance for my build using their #212157 4032's (496 BBC, 10.2:1 w/118cc Edelbrocks). Also, I've learned that JE/SRP now offers coating options for their shelf-stock pistons. They obviously understand the lure of such one-stop-shopping.

Now, where were we? Rings. Still listening...

 

The skunkWorks

Rounded machining edges.

The thread that 69 NOX RATT put up just recently on his new valve
covers, there is a picture of a piston on it, thats the way one should
be, all the sharp machining edges were rounded smooth on the dome,
machining edges rounded smooth in the valve pocket, that kind of
work would do worlds more for someone then any coating.

 

Yes I have 1/16th" rings with std tension oil rings. For sure there is power to be had with lo-tension stuff....or going to .043 or less....but hey, this is a street weenine motor.

I can see benefits possibly with alcohol for fuel during cold start up.

Gapless always had trouble sealing at high rpm when they used 2nd ring gapless it seems. It got somewhat better with the top ring being gapless. I believe there was the issue of *lifting* the top ring when you had a gap on #1 and not on #2. Same reason ring mfgs want you to use larger gaps on #2 than #1 these days. I've tried it both ways, never had an issue with either one. Just for the record my current ones are set up *old school* with a smaller 2nd gap.

BTW- I've used the SRP rings which are Speed Pro's I believe and they did excellent...just like you would expect Speed Pro's to do. Currently I have Mahle brand rings in it. They were out of Speed Pro's/SRP's when I ordered. I actually went out on a limb. These were bought from Competition Products and came in a Howards box. Howard's buys them in bulk and reboxes them...just like SRP. When I opened box the packaging all said Mahle just like I was told and the instructions were from Mahle. Anyway, they are working perfectly too..no issues.


I know some folks who've done well in the E/M Challenge. I can tell you they don't use gapless in their race stuff either. You're right...borderline street stuff there, but I know one of the motors was built for a '57 Chevy and will end up there after the E/M deal was done this year.


Interestingly, they also did some back to back testing with coatings. This was on a then 850HP LS-1 type race motor. Mega RPM. They had run it for a while without coatings. Then tore it down and had every coating known to man put in it. Oil shedding, pistons, rods, crank etc . When all was done..they found no benefit at all. They did regular dyno testing, they did step acceleration testing etc. Nada!

They still do use pistons that are coated on top as insurance..but not for power. Their E/M engines didn't use coatings either....and they placed #2 or #3 this year I beleive.


JIM

 

Jim, I was trying to find a real answer on Gapless rings. It is only in the last two years of the gapless top ring when these local race engine builders jumped on them.

I just don't mind trying something new. I do know how much blow by I got before and how by 10K miles I was putting out blue smoke. So I will have to rack up some miles this summer as a real life test.

 

All of SRP's "small dome" series pistons for BBC's now have "CNC machined domes with radiused valve reliefs [to] provide optimum flame travel". From the example pic, they look ready to go.



Arias and others also offer such blending, but typically as an extra.

FWIW, I'm only considering any coatings for durability, as I'm not looking for additional power.


Back on the rings, does anyone have a handle on just under what conditions accumulator grooves actually become beneficial?

 

This is good to know guess I'm living in the past from my trw stuff.