383 PISTON HEIGHT

[Garys1969RR]

Did the 68 383 have a positive deck height? I've heard of that, never saw one. Now a guy is wanting a piston for one, and he says it's slightly positive. Is that also true for the 69 383? Wish they had one for the 440.

 

[Mebsuta]

My 68 383 did with the original pistons. I think the 69 383 I had did too. 68 and 69 had the same compression height if it was a 10-1 engine.

Still have both. The 68 is apart and the 69 was rebuilt and that's what's in my car now. When the engine was rebuilt many years ago, replacement flat-top piston were available with the original compression height, so I think it still is positive deck, although I haven't had the heads off to look in many years.

A lot of people say they were not, but the two engines I am familiar with did. The compression height for 68-69 piston is 1.932 or 1.934 depending on who is measuring. Those are no longer available.

 

[silversedan]

68, only big block with positive deck height, I have one from my 68 road runner.

 

[Garys1969RR]

My 68 383 did with the original pistons. I think the 69 383 I had did too. 68 and 69 had the same compression height if it was a 10-1 engine.

Still have both. The 68 is apart and the 69 was rebuilt and that's what's in my car now. When the engine was rebuilt many years ago, replacement flat-top piston were available with the original compression height, so I think it still is positive deck, although I haven't had the heads off to look in many years.

A lot of people say they were not, but the two engines I am familiar with did. The compression height for 68-69 piston is 1.932 or 1.934 depending on who is measuring. Those are no longer available.

There is a guy looking for original 383 pistons for a 68, on parts wanted. In case you are willing to sell some. Do you still have some used ones left? His name is 69 Chargerman

 

[65-440]

I've heard some engines were as much as .100" in the hole ....

 

[Garys1969RR]

Yep, I have a 77 440, it's at .160 down. No torque at all. 7 to 1 C Ratio at 5200 feet. Way low on power. The blower helps.

 

[CompSyn]

Did the 68 383 have a positive deck height? I've heard of that, never saw one. Now a guy is wanting a piston for one, and he says it's slightly positive. Is that also true for the 69 383? Wish they had one for the 440.

I have a stock 69 Roadrunner 383 engine. The pistons measure at 1.932". The stock steel shim head is around 0.020". The stock uncut 906 heads CC'd at 91 CCs on the money.

Hopefully within the next couple weeks I'll be able to measure the piston in the bore, but I've read on a factory blueprint deck of 9.980 the piston sits .0025-.003 in the hole.

I've never heard of a factory production line 383HP to have pistons sitting above the deck. I'll be sure to post what I find on mine.

That said, when all the numbers above line up, a stock 68/69 383HP would have around 9.2:1 compression; a bit short of the optimistic factory 10:1 rating...

 

[PurpleBeeper]

In the old Direct Connection engine book it said that 68 & 69 HP 383's had stock pistons that stuck out of the block slightly. It was in a reference to using the 915 closed chamber heads which would cause piston-to-head clearance problems (with stock shim head gaskets) for just those two engines.

 

[69Bee]

Speed Pro L2315F pistons come with a 1.920" piston compression height. Stock advertised block height (never usually is), is 9.980", and will result in a theoretical deck height of 0.012". I am building one now, and squared the block for a height of 9.963". This should result in a zero'ish deck height. With 0.039" head gaskets, CR will be 9.2 to 9.9 depending on the heads.

 

[Dipstick]

In the old Direct Connection engine book it said that 68 & 69 HP 383's had stock pistons that stuck out of the block slightly. It was in a reference to using the 915 closed chamber heads which would cause piston-to-head clearance problems (with stock shim head gaskets) for just those two engines.

^^^^^^^^^
This

Page 53, "The '68-'69 383 has a positive (above block) deck height which does not have enough piston-to-head clearance to allow the use of small chamber heads."

 

[CompSyn]

In the old Direct Connection engine book it said that 68 & 69 HP 383's had stock pistons that stuck out of the block slightly. It was in a reference to using the 915 closed chamber heads which would cause piston-to-head clearance problems (with stock shim head gaskets) for just those two engines.

It may be that Direct Connection was referencing the NHRA Blueprint spec of .021" above the deck? But up until this point I've never heard of any stock production 383HP with pistons above the deck.

I've followed a guy in the moparts forum who's measured two stock 69 383HPs and said they were both .0025-.003 in the hole...

It'll be interesting to see where mine falls.

 

[moper]

Take it apart and measure. Chances are none are where they are supposed to be going by blueprint specs. Most 383s need a serious decking to get to blueprint deck height. Problem with that is on the older equipment it meant removing the ID pad. Modern equipment can do it without removing the ID pad.

 

[BSB67]

Did the 68 383 have a positive deck height? I've heard of that, never saw one. Now a guy is wanting a piston for one, and he says it's slightly positive. Is that also true for the 69 383? Wish they had one for the 440.

The debate seems to rage on. I have seen only a few originals. They were all close but slightly under the deck. At least one person that I know has claimed that he has measured one motor slightly positive. I suspect that everyone could be right, and what explains the difference is simply the factory variances in decking, among other things.

 

[1778ppr]

Piston “Zero Deck Height” for big blocks (not RBs) would be 1.932”. I was curious about the positive deck height on 1968 383 HP (road runner) engines. I own one and a 1969. But, have not had the ’68 apart. I have 906 heads and standard size 383 pistons. The standard size 383 pistons do not fit inside the open chamber of the 906 heads. So, if the block is blue print deck height, the head gasket is .020” compressed, and the piston compression height is more than 1.952” there will be mechanical interference between the piston and the head. I’ll try and get a pic of what I’m describing posted.

 

[BSB67]

Piston “Zero Deck Height” for big blocks (not RBs) would be 1.932”. I was curious about the positive deck height on 1968 383 HP (road runner) engines. I own one and a 1969. But, have not had the ’68 apart. I have 906 heads and standard size 383 pistons. The standard size 383 pistons do not fit inside the open chamber of the 906 heads. So, if the block is blue print deck height, the head gasket is .020” compressed, and the piston compression height is more than 1.952” there will be mechanical interference between the piston and the head. I’ll try and get a pic of what I’m describing posted.

I know what you are talking about.

The pistons were 1.932, but the blueprinted deck was a bit shorter causing the 0.022" proud piston. Back in the day, the 383 A Body guys running SS/H had to relieve the edges of the piston tops because they couldn't mess with the head.

 

[fratzog lover]

If you measured all the unrestored 383's out there, they are probably all over the place. Mopar certainly didn't have time to blueprint deck heights. My 68 (disassembled in 1980) was 30 in the hole.

 

[chtampa]

The debate seems to rage on. I have seen only a few originals. They were all close but slightly under the deck. At least one person that I know has claimed that he has measured one motor slightly positive. I suspect that everyone could be right, and what explains the difference is simply the factory variances in decking, among other things.

I rebuilt a couple that I had back in the 70's and the parts book gave you a choice of positive or zero deck height for pistons. I actually went with the zero because the trick back then was to run 67 440 heads to have the closed chamber.

 

[mopar 3 B]

^^^^^^^^^
This

Page 53, "The '68-'69 383 has a positive (above block) deck height which does not have enough piston-to-head clearance to allow the use of small chamber heads."

Unless you use a thicker head gasket.

 

[Garys1969RR]

Yes, that's what I thought. They must have been referring to using the .020 thick gasket, which would put piston to head clearance at .017. And that's not enough. A .040 gasket would give you .037, just right.

 

[BSB67]

Unless you use a thicker head gasket.

That reference is likely from the Mopar manual written in the mid 1970s. There was no 0.040" Felpro gasket. The 0.020 was the go to high performance standard. The high performance aftermarket gasket was a shim gasket too, with a coating.