s i 442

Its in a 69 455. Is it high or low compression?

Troys Toy 70

Not sure on 69. A 70 with a v notch, which it looks like you have, but the picture is a little fuzzy when I blow it up; is high compression.

I'll wait to see what others chime In.

edzolz

Appears to be the low compression version but can't tell how deep the dish is. If it is approximately .060 deep, it is high comp.

MDchanic

Typically Olds used a single U-shaped notch in the piston crown to denote a low-compression piston, a single V-shaped notch to denote high compression, and a double notch to denote "ultra-high"-compression (as in the W-30 and Toronado).

The 1969 CSM, however, depicts a single U-shaped notch for low compression, and a double V-shaped notch for all high compression, so, since you have a single V-shaped notch, I really can't say.

Have you measured the volume of the dish?

- Eric

joe_padavano

The "V" notch would indicate high compression on a factory piston, but that sure looks like a soup-bowl in the top of that piston. Light angle and shadows can be deceiving, however. The remains of the FelPro blue head gasket also prove the motor has been apart at least once before, so do we know that's a factory piston or not?

joe_padavano

The double V-notch is for the flattop 400 piston. The HC 455 piston was a single V-notch. Of course, if that's not a factory piston, all bets are off.

MDchanic

Which is what I've always thought, but I checked the '69 CSM before posting, as the dish did look deep, as I hate to say anything without at least some justification, and I found this:




- Eric

MDchanic

Incidentally, here are 1968 and 1970 for comparison:







- Eric

joe_padavano

Eric,

That illustration appears to be in error. For one thing, all 68-69 400 motors use the same flattop HC pistons. That illustration shows a dished HC piston for the 400. Here's the same illustration from the 1968 CSM:



Also note that both the 1968 and 1970 CSMs show a single V-notch for the 455 HC pistons. Also, the parts book shows the same P/N for the 455 HC pistons for all three model years (1968, 1969, and 1970).

joe_padavano

I have a pretty good idea of what happened. In 1968, the 400 HC used flattop pistons. The 10.25:1 350 HC used the 6cc dish pistons. The 10.5:1 RamRod 350 motor used flattops, but that motor was not released in time to make the CSM printing, thus it is not shown on the chart.

For the 1969 model year, the 400 LC motor was dropped, and someone added the W-31 to the chart using the illustration formerly used for the 400 HC piston. Unfortunately, they then incorrectly labeled the former 400 LC piston as the 400 HC and for some reason used the same figure for the 455 HC piston. DOH!

MDchanic

That is a darned plausible explanation, Joe.

So we're back to saying what should be correct if we follow the standard pattern:
That's a high compression piston, but check the dish volume to be sure.

- Eric

joe_padavano

Yet another example of why I hate to let tech editors touch my technical documents at work.

s i 442

Ok, this is a 69 block "39M" still standard bore, I measured that, could that block or those pistons come with the 1970 W30 and the "F" heads? The engine had non air alternator brackets on it also but im sure its a Automatic crank. Dish depth is .141

MDchanic

So, a presumed 2.90" by 0.141" = 6cc volume = high compression.

- Eric

s i 442

Yes 2.90 wide by .141 deep.

MDchanic

Just as we thought, before being deviously derailed by the CSM.

- Eric

joe_padavano

Not from the factory. Production "F" heads didn't exist when that motor was built.

Once again, the remains of the FelPro blue head gaskets are NOT factory. The heads and head gaskets have been replaced.

s i 442

So a 70 W30 only used a 70 block even if built in the last 6 months of 69?
Anyway Im keeping the 455 and going to build it and buy a Cutlass to put it in!

joe_padavano

1970 model year cars, which were built from mid-1969 to mid-1970, ALL GOT 1970 VINs. There is no fuzz whatsoever on that. The VIN derivative on the block MUST match that 1970 VIN by law. The year in the VIN derivative stamp is the MODEL year, not the calendar year. Sorry, but I really don't understand why this still seems to confuse people.

s i 442

Thank you Mr Padavano for your info and helping me with my questions.
Im going to keep the engine and build me a sweet little 455 for cruise night, then buy a Cutlass to put it in next!.

edzolz

Not so. 2.90 is inches measurement and .141 is inches measurement so the answer is in cubic inches. Also the formula for a cylinder is V=pi/r2/h. The conversion from cubic inches to cc says this is 14.XX cc's.

MDchanic

Crap. I just re-did it and got 15.2cc.

Don't know how I got that one wrong - the arithmetic is pretty simple.

Either way, still high compression for a 455 (nominal 14cc), if I'm not mistaken.

Thanks for the correction, though.

- Eric

joe_padavano

Your math is right but the formula you typed is wrong. V= pi x r^2 x h, not divided by. That does yield about a 15 cc dish. That is correct for a 10.25 factory piston for a 455.

edzolz

Your right, been retired too many years. Forgot how to state a formula.

Donaldbabineau

If aftermarket, it may be high compression 68-70 if recession depth is 0.12". Low compression would have no notch and would be 0.324". (Mahler, 2009)

Donaldbabineau

If aftermarket, it may be high compression 68-70 if recession depth is 0.12". Low compression would have no notch and would be 0.324". (Mahler, 2009)