Piston Identification?

[Madman Stephan]

Can someone have a look at this picture and let me know any information what-so-ever about this piston? It's linstalled in a 360 with a .030" over-bore. I'm especially interested in the little notch on the right side of the piston.

Thanks!

[bbeckwith]

Stephan,

The photo is too dark to see much, so I adjusted the gamma in paint shop pro and now I can see the piston but cant make out any serial numbers on the top if there are any. The notch on the right side should indicate the piston is installed with that notch facing toward the front of the motor.

Bruce

[bbeckwith]

see if I can attach gamma corrected photo by re-naming it.

[moraycen]

That notch does just mean front. I would be more likely to wonder about where it looks like a valve hit it?


Ray

[dwc43]

Yeah, that's what I was thinking. That valve hit it real good.

[powerwagon]

has five valves per cylinder yeah, the notch just shows ya which way to face the piston, but that big dent in it, should tell ya what to DO with the piston-get some new ones.

[dwc43]

I agree, get new ones now, before it's too late.

[MoparMarcIdaho]

I didnt even look at it but if theres a dent in it dont reinstall.

[moraycen]

???????I'd be looking at those valves to?????????
Ray

[dewme5]

looks to good to be valve contact. is that the only piston that way? or, are they all that way? the pistons could have been clearanced for that application. The center 4 notches are just what the piston manf. wanted. But, that one might be just what that engine needed.

[moraycen]

dewme5 might be right that valve mark doesnt look it was hammered in.
Ray

[Madman Stephan]

Yeah, all the pistons look exactly like this one, so it's not a problem of valves hitting. All the valves are okay and show no damage. I was told that this engine had a VERY high compression ratio, somewhere in the 13:1 range. I've always run it on 94 octane with a bottle of fuel injector cleaner to increase octane. There's never been knocking of any kind.

When you look at the piston tops, they have a lot of notches and grooves, and I've never seen any like these in the past. So I was wondering if these were purchased this way, or if they might have been modified to increase the compression.

The engine has X-heads but I have no idea if they've been shaved or not.

Thanks for the help!

[dwc43]

I'd say that they have been moded to match the milled heads if it has a real 13 to 1. Fuel injector cleaner wont raise your octane. Only stuff like 104 will and then it will only raise it by about one point, so it aint worth the money. Race fuel is the only way to go, cause other wise you would have to take a lot of timming out of it to not damage that engine.

[Madman Stephan]

On a typical application like this, what should the timing be at?

[dewme5]

well, you don't cut into a piston to increase compression ratio.

The pistons might be sold as a 13:1, but you couldn't run them off of 94 octane. You've got the head off, so why don't you go ahead and measure everything to find out what you have.

the 3 C's of engine building.. Cam, Carb, and Compression. if you don't know for sure what you have, the others are going to be off to, and it's a losing battle the whole way.

beware of octane boosters. they have a sorts of misleading advertising. "raises octane by 7 points".. yeah.. .1, .2, .3......, .7 NOT 7. So, you go from 94 to about 94.7 big deal right?

[dwc43]

Originally posted by Madman Stephan
On a typical application like this, what should the timing be at?

Small blocks run 34 to 36 total timming if they are built right. If you have over 10 to 1 cr you need race fuel or the timming will need to be set way to low to make power so it will survive.

[powerwagon]

I've rebuilt motors before, but i've never seen a notch like that, if he's runnin 13 to 1, then was the notches put in to lower the compression ratio a little? If so, then why only one side of the piston, seems like that would mess up balancing a little, right? And if it was cut in there, how come its only on one side, what about the valve on the other side? I guess im the only moron who's lost on this?? I try to get as much info as possible off this website, cuz im fixin to do a performance rebuild (I've done a few motor rebuilds now, but none for performance, all out of necessity ), so i like to learn as much as possible. I know quite a bit about all that stuff, but i love learnin more.

pw

[MoparMarcIdaho]

Intakes are bigger than exhaust so they will be more prone to getting hit by the piston.Took apart a 440 a while back and the previous idiot that had just installed the high lift cam had it about a quarter turn off and it kissed all the intakes,after replacing all the valves with manley stainless ones and another new cam she runs sweet.

[dwc43]

Yeah, it's for intake valve clearance not compression relief.

[jelsr]

The extra notch makes me wonder what these were in before this engine. Looks like a canted valve notch like a BB Chev or Cleveland Ford. If for in line valves they would have to be pretty small diameter being that far off center.

[powerwagon]

i feel dumb now, cuz i knew that the intake valves were bigger than the exhaust valves. Thanx for the info guys, i appreciate all the help.

[jelsr]

Hey powerwagon, are these eyebrows in the same sequence as the valves? They should be on the inside for the two end cyl's and to the outside on the two center cyl's. Don't know if the pistons will work in a Poly but the eyebrow looks about right. They will have the eyebrow on the same side all the way through, none toward each other. Haven't worked on a Poly forever so can't remember the pistons but remember the intakes had a good angle and sat higher than the exhaust. Since the LA's open on center the eyebrow in the picture would clear a 2-1/2" or bigger valve? How about some of you Poly people, is this even possible?

[aDjUSTER]

If you recall the big trick in rebuilding the small block was to swap the pistons from the left bank to the right bank. In other words the small notch on the side of this piston is to be installed towards the front normally. The swap would put this notch towards the rear of the block. The reason for the double eye brows facing each other was to allow for the pistons to be installed in either configuration IMO.

[drag-n-cuda]

Madman Stephan,
Is this an LA or poly sb? 13:1 with what looks to be flattops would be extremely difficult to achieve without very small combustion chambers. Have you cc'd them and have they been angle milled? I'm thinking angle milled for the different location of that one relief.

drag-n

[pishta]

look like stocker low comp 340 pistons to me that hit a valve, nothing special. As noted before, getting 13:1 on a flat top is next to impossible as the hi-compression 340 pistons were a little popped up with one set of reliefs themselves.

[Madman Stephan]

Drag-n,

It's an LA block. I was told that this engine was a 13:1 when I bought it, but never really believed it. It was a good deal and the engine ran, so I couldn't pass it up.....

As far as being "angle-milled", yes it is. The heads' combustion chamber walls are about 1/8" high (on the lower side) and about 1/4" (on the high side).

PIshta,

All of the pistons look like the one in this picture, there has been no evidence of valves hitting them.

[340duster1]

Looks like some sort of chevy piston due to the location of the and angle of the valve reliefs. Possibly a .030 over 327 piston mill to be a zero deck. You could confirm this by measuring the piston pin size. It is smaller that the mopar one. The 5th valve reilief appears to be machined in due to the shape of the cut. This is to provide piston to valve clearance on a zero deck 360. I am surprised there is not one cut for the other valve. The cam must have a large LSA.

I just built a zero deck 360, the comp ratio with a 62 cc head worked out to 11.4:1. And that was a magnum head. So if you are using an x head there must be a serious amount of angle mill to them. Make sure you use a .040 thick headgasket when you reassemble it.