measuring piston to deck clearance on 440 source dished piston

[Paul_G]

Where do I measure from? I know it right over the wrist pin center of the piston. The 440 source dished pistons sit below the hole in the dish, .012" above the hole at the pad. Should I use the above the hole in the pad area for my height measurement? If so Summits compression calculator puts this combo at 12.2.

 

[68-500]

Above the bowl. Should be a flat high area on the OD of the piston top. If your .012 out of the hole. And are running a closed chamber cylinder head I would recommend a minimum .050 head gasket.

 

[BSB67]

……..012" above the hole at the pad.

Someone has cut the deck quite a bit to be proud 0.012”.

 

[Paul_G]

Someone has cut the deck quite a bit to be proud 0.012”.

You betcha! I am rebuilding the 505 stroker I had built for me 6 years ago. That machine shop screwed me 6 ways from Sunday.

I am using a different piston with a bigger dish. Trying to get the compression down to something managable on pump gas. The machine shop that has the heads right now, Trick Flow PP240's, is replacing valves and having to mill them quite a bit. He cc'd them, one head, the one that burnt a groove across the center two cylinders that the first shop welded up, CC'd at a little over 70 CC. The other one was still stock at 78CC.

Using Summits compression calculator, it puts the compression on the 70cc repaired head, with the old pistons, at 12.03:1. the stock head at 78cc is, 11.06:1. No wonder it detonated itself to death in 5000 miles. I was keeping the timing around 30°. It was probably still detonating I just could not hear it. They built it for 10.5:1. At least that what I paid them for.

 

[Paul_G]

With the new pistons I bought, they have a 27cc dish, 440 source #5074. With the heads both being 68cc now I am going to need a thick head gasket. I can get Cometic up to .120".

Using a .095" gasket puts the compression at 10.83:1. The .120" gasket brings it down to 10.3:1

 

[beanhead]

Where do I measure from? I know it right over the wrist pin center of the piston. The 440 source dished pistons sit below the hole in the dish, .012" above the hole at the pad. Should I use the above the hole in the pad area for my height measurement? If so Summits compression calculator puts this combo at 12.2.

Yes you measure to the highest point/"top of the pad".

 

[68-500]

If the pistons are a true .012 out of the bore I would .050-.060 hg. And have the chamber in the heads and the dish in the pistons enlarged to get to the desired cr. More than .050 quench distance your opening the door to detonation again.

 

[Paul_G]

The chambers in the head are pock marked from the detonation. Smoothing that out and enlarging the chamber might do it. Last I talked with the machinist he was going to mill the good head to match the other one. I am calling bright and early in the morning. If he has not cut the good head yet I want to discuss getting a new bare head and swapping the guts from the cut head to it.

 

[BSB67]

You betcha! I am rebuilding the 505 stroker I had built for me 6 years ago. That machine shop screwed me 6 ways from Sunday.

I am using a different piston with a bigger dish. Trying to get the compression down to something managable on pump gas. The machine shop that has the heads right now, Trick Flow PP240's, is replacing valves and having to mill them quite a bit. He cc'd them, one head, the one that burnt a groove across the center two cylinders that the first shop welded up, CC'd at a little over 70 CC. The other one was still stock at 78CC.

Using Summits compression calculator, it puts the compression on the 70cc repaired head, with the old pistons, at 12.03:1. the stock head at 78cc is, 11.06:1. No wonder it detonated itself to death in 5000 miles. I was keeping the timing around 30°. It was probably still detonating I just could not hear it. They built it for 10.5:1. At least that what I paid them for.

Boy, that’s unfortunate.

No good way to open up the one chamber verses milling down for the rest?

 

[33 IMP]

I'm not sure tf will sell a single bare head.
Frankly, I'd run the .125 gasket, and not worry a minute about quench. Nice to have, not essential. I'd much rather have a pump gas compatible engine, which to me is about 9.5 to 1 (without a 250° at .050 cam. 10.5 with that much cam)

Note: mopar built millions upon millions of engines with no quench whatever..

 

[68-500]

If you run .060+ hg. May as well just throw the Trickflows in the scrap bin and use some 346 or 452 open chamber cylinder heads.

 

[RemCharger]

The TF heads are sold individually.

 

[BSB67]

What is hg?

 

[33 IMP]

If you run .060+ hg. May as well just throw the Trickflows in the scrap bin and use some 346 or 452 open chamber cylinder heads.

I agree. Just throw away that extra 80 cfm airflow that you purchased. A 500 inch engine has no need for more air than 361.
Or, you could keep that .040 quench, 11 to 1 compression and watch it detonate itself to death, again.

 

[33 IMP]

What is hg?

Head gasket.

 

[Cranky]

Measure the dish too and go from there but I'm thinking you do have too much static compression....and depending on your cam....what is your compression gauge reading....if the engine us fully assembled??

 

[68-500]

He’s building a 500ci inch engine with all custom parts. Why would he build a non quench combustion chamber? I guess just throw $10k out the window to build something thats just meh, instead of great. Personally If it where me I would sell the 240’s and buy some 270’s, really on 500ci 270’s are really to small. But if he puts a big ole .100 hg on it.Build a 2025 engine to 1968 smog technology, It seems like a waste of a lot of great parts.

 

[33 IMP]

Why would he build a non quench combustion chamber?

Maybe cause he's got a butchered block without enough deck height, and a set of pistons with too much compression for pump gas?
I guess those millions of mopar engines with no quench all must be garbage too, hunh?
I seem to remember Kern Dog trying alp kinds of things to get his stroker not to detonate. He finally solved it. HE STUCK FAT HEAD GASKETS IN IT.
I agree, the 270s would probably be a better choice.

 

[33 IMP]

I just re-read op's first post. Apparently he's got new pistons with more dish. If so, it's a matter of doing some measuring, and calculating, to get the compression where he wants it.
Quench is nice if you can get it, and at the same time get the c.r. you want.

 

[68-500]

Not sure what KD had going on with his engine. We’re discussing Paul G’s engine. Im just saying the engine is apart the only factory parts left is the block and it not a budget 383,440 with mostly factory parts. Why not do it right? As to the millions of non quench Mopars, junk no but if its apart being build for more than stock power why not build a closed chamber quench engine? Everyone says get Stealths or Trickflows then we throw out the quench because we got to much compression instead of buying the correct pistons.