Need some engine advice....

[Nate S]

His plan is to replace the .080 head gasket with a .110 to get to 9.65:1 cr. Does everybody agree that should be enough to take care of the problem?
And another option I guess would be to pay him extra to replace the pistons to get a quench, or would that also mean a cam change? Is a quench really that important for what I am doing with the car and worth the extra cost since it is already put together and making good power without one? Or would this be another debate similar to running ported vs manifold vs no vacuum advance?

9.65 with that cam will be fine. Probably need pump 93. Ask about intake spacing while you’re talking. It might not line up very well without some shims.

As for quench. It’s basically equal to another 1/3 of a point of compression, maybe 1/2. Where you are that’s about 10 horsepower. I wouldn’t lose sleep over it. Good analogy to the ported / manifold vacuum. Either will work and some people get pretty opinionated about it.

 

[hunt2elk]

9.65 with that cam will be fine. Probably need pump 93. Ask about intake spacing while you’re talking. It might not line up very well without some shims.

As for quench. It’s basically equal to another 1/3 of a point of compression, maybe 1/2. Where you are that’s about 10 horsepower. I wouldn’t lose sleep over it. Good analogy to the ported / manifold vacuum. Either will work and some people get pretty opinionated about it.

For some reason he is using 78.5cc for the combustion chamber # instead of the 76cc that is wrote down on the sheet. His math shows it has 10.27:1 compression right now instead of the 10.53 that we are getting.

 

[Nate S]

For some reason he is using 78.5cc for the combustion chamber # instead of the 76cc that is wrote down on the sheet. His math shows it has 10.27:1 compression right now instead of the 10.53 that we are getting.

Maybe the “spec volume” is 76 and he cc’d them to 78.5? So 10.27 sounds believable. On my phone so I can’t just drop the number in and tell you. Might want only a .100 gasket so as to not drop too far.

 

[33 IMP]

Wallace has a calculator "hp change for compression change." If its correct you will lose next to nothing , percentage wise, going down to 9-1. I wouldnt want to be too conservative, dropping only a half point, but then i'm used to the crap 10%alc 91 in california. I would want to make sure i only had to do this once.

 

[PRHeads]

https://www.dragzine.com/tech-stori...ormance-squished-between-the-piston-and-head/

 

[33 IMP]

Refering to my post #107 in this thread, and just for giggles.......
I measured a trw 2295 i have laying around ( i have some custom ross and some shelf ross laying around too, but no access right now) and the piston head above the top ring land is about .020 smaller than the skirt size, to allow for heat expansion. And the top ring is about .350 down from the deck.
So.... i calculated the bore space at 4.35x.350 down, then subtracted the (kinda assumed, but you know how that works) piston head space, 4.33x.350, and came up with .047 cu.in. (roughly, the calculator gave me seven digits behind the decimal point). Converting this to cc's to make it clearer, that is more than 7 cc's. My take-away from this is that this can be a significant space that wallace takes into account, but doesnt really tell the calculator user why it is significant.

 

[PRHeads]

i calculated the bore space at 4.35x.350 down, then subtracted the (kinda assumed, but you know how that works) piston head space, 4.33x.350, and came up with .047 cu.in. (roughly, the calculator gave me seven digits behind the decimal point). Converting this to cc's to make it clearer, that is more than 7 cc's.

You have the decimal place off by one.
It’s .7cc.

A cylinder 4.35 x .350 is 85.25cc
A cylinder 4.33 x .350 is 84.47cc

The difference is .78cc.

 

[33 IMP]

Oops. Thanks Dwayne!

 

[wyrmrider]

lowering compression with thicker gaskets seems to work
but it takes more throttle to get the same power
so more heat and EGT and gas mileage suffers
still the gaskets are a quick and dirty "fix"
I helped design the KB quench dome pistons and they do work- lots of test builds, miles and dyno time
our customer (fleet)had been having us welding up the open chambers
later Chrysler had us set up a PER for warranty work on these engines
and
It's not about a few hp
you can make a little more hp with an open chamber head with good gas
It's about gas quality sensitivity, advance, driveability below max hp
you need both quench and squish
new heads with better combustion chambers and spark plug locations are the answer except for a restore buid, and there custom pistons or the KBs

 

[PRHeads]

I helped design the KB quench dome pistons and they do work

 

[Nate S]

lowering compression with thicker gaskets seems to work
but it takes more throttle to get the same power
so more heat and EGT and gas mileage suffers
still the gaskets are a quick and dirty "fix"
I helped design the KB quench dome pistons and they do work- lots of test builds, miles and dyno time
our customer (fleet)had been having us welding up the open chambers
later Chrysler had us set up a PER for warranty work on these engines
and
It's not about a few hp
you can make a little more hp with an open chamber head with good gas
It's about gas quality sensitivity, advance, driveability below max hp
you need both quench and squish
new heads with better combustion chambers and spark plug locations are the answer except for a restore buid, and there custom pistons or the KBs

Sounds super cool. The level of detail you can go into when it’s professional design work is awesome. Any data or charts you can share?

 

[wyrmrider]

Nate this was in the late 60's and 70's
before PC to take notes
Work was funded by Municipal transit bus companies on Propane Mopar 440's
Then CNG
Then some work on 440 and 360 Motorhomes
By the time Chrysler figured out to make a clean 440 it went out of production
Thank the smog mafia
better converters and EFI would have made it work
There is no way to make a late 440 live when worked hard without pistons
head change really help to but you then need pistons too

 

[Nate S]

Nate this was in the late 60's and 70's
before PC to take notes
Work was funded by Municipal transit bus companies on Propane Mopar 440's
Then CNG
Then some work on 440 and 360 Motorhomes
By the time Chrysler figured out to make a clean 440 it went out of production
Thank the smog mafia
better converters and EFI would have made it work
There is no way to make a late 440 live when worked hard without pistons
head change really help to but you then need pistons too

What an interesting perspective that gives. Thanks for sharing.

 

[69 GTX]

If it were me, I'd want the dish pistons. and a .040 head gasket. But it depends on what he will do.

 

[hunt2elk]

If it were me, I'd want the dish pistons. and a .040 head gasket. But it depends on what he will do.

After all the reading I have been doing lately, I agree. Would it just be a piston change, or would the cam also need replacing?

 

[wyrmrider]

depends on the cam that exists
all stock cams need to go they date from the 60s- over 50 year old designs kept for smog
pick your intake duration based on torque curve, rpm range you need for your build/ application
exhaust with headers or modern exhaust ports do not need the long durtion of older designs
now try and keep the valves on the seats as long as possible to keep the valves cool-
and try and hold down overlap to keep the intake charge from blowing out the exhaust
reversion, etc
intake close based on compresson and fuel
naturally all the points change from a motrhome to a street build to a race car with open headers
you need to know piston deman at each degree to do it right
you CAN have too much lift too early
which can happen using a short rod cam in a long rod engine
by was tis post all oer the plae..

 

[69 GTX]

I would think You could keep the same cam. By using the dish piston you won't loose as much compression because it will be a better burn. My old 440 with the open chamber heads would rattle back in the 80's if I wasn't running premium (100) with the old 6 pack flat tops from Speed Pro at 10.5 If you lower the compression to about 9.5-10 with a good piston with a 0 deck and D shaped dish you wont be giving up hardly any performance. I really like the Icon pistons. But again if he wants to just stack up the head gasket to lower the compression that will work but it'll be a lower compression because it won't be as efficient. And it'll cost him the least. Make sure he checks the intake to head ports if he does that.

 

[hunt2elk]

Motor is out and need to build a crate to get it back to CA.
Talked to Brian for quite a bit yesterday. He plans on taking it apart to check the bearings because it had run so much with the detonation and to also see if he can find anything else amiss. He is being really decent, admitting that he made a math error, not having enough room between the cylinder and piston, and having to high of compression. He states that pretty much every build he does is not built with a quench. Claims that the effect of quench is nonexistent above 3000 rpm and also can make more power without it.
Bottom line is that he will build the motor back however I want it, which I am very pleased about.
So now my question is, if it were you, would you have him put in dish pistons and a thinner head gaskets for quench? The cam will probably also have to be changed to bleed off some compression. He was talking of getting that down to 170 or so.

 

[Kern Dog]

YES, go with the dished pistons! The quench and reduced compression ratio allows you to have a better burn and less risk of detonation. If this is not a race engine, you'll be spending more time below 3000 rpms cruising than above it racing.

 

[451Mopar]

The "D" style dish piston, about 0.040" quench distance, and true 10.0:1 compression (or less) piston.
The cost of the pistons is partly offset by the cost of what the thicker head gaskets would have cost (Cometics are not cheap)
https://www.cometic.com/applications/automotive/chrysler/b/383--383ci63l-v8
Cometic 0.120" head gasket $228.43 each (or $456.86 a pair)