Don Terrill’s Speed-Talk

I've been told, and have read from multiple sources, that 2618 piston/rings dont last very long for a street setup compared to 4320 pistons due to the looser P/W clearances needed to allow the 2618 slugs to expand to operating temp. I'm running .0045" for P/W clearances which is only a thousandth from the minimum spec recommended by JE.

My main question would be, would using a oil pan heater in conjuction with a block heater to tighten up the clearances before starting the engine, reduce the wear associated with having loose cold clearances? I've been told the block heater themselves can heat coolant up to 120 degrees in cold climates, and I live in Florida, and I know this is a far cry from piston opperating temps, but would it maybe work?

Would this be an overall way to allow for greater engine longevity in general? I'm just kinda gandering at possible way's to produce the most service life out of my build and this is one of them I was thinking. Or am I just kinda over thinking it like usual.

I have a friend who got 70k miles out of a 2618 piston setup and as far as I know the engine was still fine when he pulled the motor and sold the car. I know alot of things are to account for, like machining quality, tune quality, maintainance, etc.

its not just clearance which is a issue at warm up due to larger coefficient thermal expansion with 2618, it is the low silicon with 2618 which is less good for wear protection.

i'm also curious in what sort of street miles people have gotten out of a 2618 alloy piston in a street type application. i know people have done 100,000 miles with aftermarket 4032 before and OEM use that alloy when they do forged, would also last atleast that long one would hope.

My old junk301 had 1/8" over, 283", 290/315 hp, Badger steel-strutted cast pistons in it in a worn out stock bore SJ 327 block.

Musta had .007" on each side. Sure, she knocked, hammered, and smoked, but boy would it rpm! I think that I remember stuffing a .015" feeler gauge down one side....

My Machinist had me install the pistons backwards to put the pin offset at a better angle. But it did add to the starting noises... Cold, more slap! But once hot, fine by me!

pdq67

This 2618 v 4032 "debate" is flat out goofy. Or, more accurately, marketing.

4032 pistons are cheaper. Why? Beats me...the forgings are the same price and they cost more to make. The thermal expansion argument was absolutely valid....in 1986. But we were pretty stupid in 1986. The piston to wall clearance is a matter of application and skirt design. In any use where you can destroy a 4032 piston, you can destroy a 2618 piston.

At least with the ones I made I never was concerned about skirt wear, becasue it was never a problem. You might see a difference in ring groove life, but I can't see it as being an issue.

The world is chock full of race engines using 4032 and street cars using 2618.

Well I guess there's a reason I asked the question here instead of going off what "google experts" have to say. Although the general consesus remains that 2618 pistons are not ideal for 100k+ mile service intervals. But I'd like to experiment with ways to maybe push the envelope of the 30-60k mile service intervals I've been seeing people talk about.

Mark O'Neal wrote:This 2618 v 4032 "debate" is flat out goofy. Or, more accurately, marketing.

4032 pistons are cheaper. Why? Beats me...the forgings are the same price and they cost more to make. The thermal expansion argument was absolutely valid....in 1986. But we were pretty stupid in 1986. The piston to wall clearance is a matter of application and skirt design. In any use where you can destroy a 4032 piston, you can destroy a 2618 piston.

At least with the ones I made I never was concerned about skirt wear, becasue it was never a problem. You might see a difference in ring groove life, but I can't see it as being an issue.

The world is chock full of race engines using 4032 and street cars using 2618.

just say you are building a NA street engine the price for the two was close enough to not be an issue. what type of scenario or specifics with application would make you recommend 4032?
really short skirt and compression height does that help steer you one way or another?

does noise inherently mean higher wear? e.g if you did two cold starts a day with 50miles a day driving which one would last longer and by how much would you think all else equal non race application, pure street.

Personally don't see what the issue is . Big deal if it makes noise on initial start up. Maybe use coatings to get around scuffing?

Both materials have pluses & minues...That is why pistons are available in both types.

2618 is stronger & will take more punishment. 4032 expands less, wears better, & can be fitted tighter. 2618 expands more, requires greater bore clearance, but once up to operating temp, should be as quiet as 4032 pistons.

Many OEM's have been using 2618 for quite some time. Certainly the high horsepower stuff. The forgings, piston and skirt designs, machining tolerances have all changed since the 80's. There is really no reason to not use it. Piston to wall clearances on a well made 2618 boxed slug aren't much different than a 4032 slug. Unless you call .0005" a big difference. I run .0022 p/w clearance ( bore to piston .0043 or so) with no cold slap and excellent wear. Cannot compare today's forgings with the past. 2618 OR 4032.

Naively, I'm thinking that the block material has to have a first-order impact on the issue. The clearance you have to run on an aluminum block piston is different from the clearance you have to run on an iron block piston. My motor is running a coated aluminum piston against an etched aluminum bore. Next motor would probably run an aluminum piston against a nikasil coated aluminum bore. In both cases, when a shop sees the specified clearance, they'll call to reconfirm the numbers as the required clearance is very low compared to most iron-block motors. The pistons slap and other such wear issues that are caused by large clearances are probably not an issue for me.

Bradley67 wrote:Many OEM's have been using 2618 for quite some time. Certainly the high horsepower stuff.

can you give some examples?
thanks

Bradley67 wrote:Many OEM's have been using 2618 for quite some time. Certainly the high horsepower stuff. The forgings, piston and skirt designs, machining tolerances have all changed since the 80's. There is really no reason to not use it. Piston to wall clearances on a well made 2618 boxed slug aren't much different than a 4032 slug. Unless you call .0005" a big difference. I run .0022 p/w clearance ( bore to piston .0043 or so) with no cold slap and excellent wear. Cannot compare today's forgings with the past. 2618 OR 4032.

There it is. There is almost no difference in the clearance, the material is irrelevant, now that we all have ovularity turning machines.

And now they have those that will fit in your garage, instead of just the big machines that were all we had when I first started.....so you guys can experiment.

When we cam ground them we just tapered from the bottom to the ring land and put in .009 a side cam....no matter what the application was. Now they are very specifically shaped.

digger wrote:

Bradley67 wrote:Many OEM's have been using 2618 for quite some time. Certainly the high horsepower stuff.

can you give some examples?
thanks

Manley - 4.6L Ford

Mark O'Neal wrote:There it is. There is almost no difference in the clearance, the material is irrelevant, now that we all have ovularity turning machines.

And now they have those that will fit in your garage, instead of just the big machines that were all we had when I first started.....so you guys can experiment.

When we cam ground them we just tapered from the bottom to the ring land and put in .009 a side cam....no matter what the application was. Now they are very specifically shaped.

For true, Mark. Look at an old ForgedTrue or Venolia and they have to be run with huge P/W clearance.

mark... I used to work in a machine shop in the early seventies they had a old Van Norman piston grinder, never saw it used but the old guy there used it and always talked about taper and a,b,or c cam grinds on the pistons do you have any information on this???? just would like to know thanks