Final Engine Compression Ratio?

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nm9stheham said:
Hey wyrm... did you end up having a catalog listing for these pistons?
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I do have old trw and SP catalogs but we sold our house we had since 1955 and moved in december- everythings in boxes I did find a box of Mopar shop manuals and DC engine/ chassis etc books
I can take a look for the others this weekend but evidently the domes have been cut so he still would be better off doing the cc in the car the way I suggested if he wants to run pump gas
sorry about that
and when he does find out his true compression he will have to run a much bigger cam than what his chassis or driving style wants
if handy with a grinder he might get 5cc out of the heads
super thick gasket or get one of those shims
any other ideas
 
OK, wyrm.... yeah moving can be dangerous to your ability to find your treasure trove of stuff! I thought I had fond +10 cc net on those pistons but wanted to see if there was some confirmation of that.

BTW, OP, is the engine out of the car and on the stand? Doing the displacement test is not all that hard on the stand if you can rotate the engine 45* to get one bank of cylinder vertical. You don't need the plaxiglass then but you do need a graduated burrette. And.... you need a dial indicator to be able set the piston down in the hole a precise amount.... many folks forget that. If you are off .030" in how deep you move the piston down, then you are off 5 cc's right there. So it needs to be done with great care or it will give worse results.

Edit to add: And if you don't have a graduated burrette, but have a gram scale, then you can use that. 1 cc of water weighs exactly 1 gram.... so you can use the gram scale to figure out how much water is added to the hole. Use 1-2 drops of dishwasher detergent in the water to break the surface tension around the cylinder wall. Level the block deck with a bubble level, set the piston down a precise amount from TDC using a dial indicator, pack a bit of grease around the top edge of the piston and wipe out the excess, then fill where it is visually perfectly level with the deck; visually sighting across the deck with a light behind it works pretty well. Weigh water before and after fill, and the number of grams added is the number of cc's. The number of cc's that the piston has been displaced downward can be computed from the precise distance it has been dropped from TDC, and the final number worked out.

Hmmm the catalog volume and some estimate of the amount milled off would be a lot easier LOL.
 
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NM if you post the part number I find my catalog and look it up for you. I'm pretty sure I know where that catalog is.
 
Hey YR....4007042. Check out the OP's pix in post #22 & #23; the fire notch is almost all milled off.
 
billsdartgt said:
it may just find its way back in the motor so I can be done with it, at least no break-in needed.
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If you can verify that's what it is, you can run the numbers through the Wallace dynamic compression calculator and see what the DCR is. At least that would tell you before you put it back together.
 
after some behind the scenes discussions I think I found a cam, a couple of other things to check tomorrow then will send my friends at Summit some more money.

Stay tuned....
 
after some setback and delays went ahead and did some checks, I originally found a thread on here with cylinder info volume but can't find it now. - here's where things ended up, with online calculators I come up with around 10.8 on static and 8.4 on dynamic. Curious where this engine will end up with the 292 cam with 247/254 duration and 508 lift performance wise now

info and details:

TRW 11.5.1 dome pistons, unsure if they were milled as has been referenced based on cc value and what I have read on here Im gonna say yes
X-heads - measured volume 68.5 ( this was average - none at 68 and none at 69)
piston 1" down - 205cc's - (+/- about 1 cc)
stroke - stock
Bore - 4.030
Head gasket bore 4.180
head gasket thickness - specs say .049 - .054 - I measure the inner rind and got .054
deck clearance - .01 - this is a bit of a guess but I just don't know and with two different sets of heads everything still aligns well
IVC @ 50 with the cam degreed in @ 106.5 centerline.
 
billsdartgt said:
after some setback and delays went ahead and did some checks, I originally found a thread on here with cylinder info volume but can't find it now. - here's where things ended up, with online calculators I come up with around 10.8 on static and 8.4 on dynamic. Curious where this engine will end up with the 292 cam with 247/254 duration and 508 lift performance wise now

info and details:

TRW 11.5.1 dome pistons, unsure if they were milled as has been referenced based on cc value and what I have read on here Im gonna say yes
X-heads - measured volume 68.5 ( this was average - none at 68 and none at 69)
piston 1" down - 205cc's - (+/- about 1 cc)
stroke - stock
Bore - 4.030
Head gasket bore 4.180
head gasket thickness - specs say .049 - .054 - I measure the inner rind and got .054
deck clearance - .01 - this is a bit of a guess but I just don't know and with two different sets of heads everything still aligns well
IVC @ 50 with the cam degreed in @ 106.5 centerline.
Click to expand...

Rough math I get 10.58 but I’m tired. So I could be off a bit.

That should work real well with the 292 cam.
 
Thanks, seems like some of you guy's have better math skills than the online calculators, Im guessing it should put out at least 400ish HP, should get the Dart moving, still will need to address the convertor and transmission later on but right now just trying to get it all back together.
 
billsdartgt said:
Thanks, seems like some of you guy's have better math skills than the online calculators, Im guessing it should put out at least 400ish HP, should get the Dart moving, still will need to address the convertor and transmission later on but right now just trying to get it all back together.
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I’ll run the numbers again tomorrow. The wife stacked up honey do’s a mile high and beat me like a slave today so I’m spent.
IIRC it’s a stock 360 stroke right?
 
Was the 1" down actually 1.000" or very close? And was it with the piston moved 1.000" down from the TDC position, or with the flat area moved 1.000" from the deck? Just shooting for best accuracy.

If so, I get a net dome volume of +4 cc at an effective deck height of 0.000" per your 1" down measurement (as I first interpreted what you did). The pure cylindrical volume with no net dome or eyebrow works out to 209.0 cc for a 4.030" cylinder.

With that, plus a compressed head gasket thickness of .051", 3.58" stroke, 4.03" bore, 4.18" gasket hole, and an added 1 cc for the crevice, I get 10.75 static CR.

If you moved the flat of the piston down 1.000" from the deck (.990" actual movement from TDC), then I get 10.46 SCR.

For DCR, the IVC at the .050" lift angle is not what is used. The IVC angle is put in as either the advertised duration IVC, or an IVC based on the .050" lift plus a number like 15 to 20 degrees. (Comp's method IIRC). Using the 292 advertised, an LSA of 110 and an ICL of 106.5, I get a DCR of 7.9. If I use the .050" IVC + 15 degrees, I get a DCR of 8.31. So that brackets your DCR range.

I have not bothered to work it out at any elevation as you look to be near sea leve.
 
nm9stheham said:
Was the 1" down actually 1.000" or very close? And was it with the piston moved 1.000" down from the TDC position, or with the flat area moved 1.000" from the deck? Just shooting for best accuracy.

If so, I get a net dome volume of +4 cc at an effective deck height of 0.000" per your 1" down measurement (as I first interpreted what you did). The pure cylindrical volume with no net dome or eyebrow works out to 209.0 cc for a 4.030" cylinder.

With that, plus a compressed head gasket thickness of .051", 3.58" stroke, 4.03" bore, 4.18" gasket hole, and an added 1 cc for the crevice, I get 10.75 static CR.

If you moved the flat of the piston down 1.000" from the deck (.990" actual movement from TDC), then I get 10.46 SCR.

For DCR, the IVC at the .050" lift angle is not what is used. The IVC angle is put in as either the advertised duration IVC, or an IVC based on the .050" lift plus a number like 15 to 20 degrees. (Comp's method IIRC). Using the 292 advertised, an LSA of 110 and an ICL of 106.5, I get a DCR of 7.9. If I use the .050" IVC + 15 degrees, I get a DCR of 8.31. So that brackets your DCR range.

I have not bothered to work it out at any elevation as you look to be near sea leve.
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I got a 4 cc dome too. I only go half and inch so I don’t need over 200 cc’s.

I need to do the math again and see where I went off the rails last night.

All this is predicated on a 1.000 inch downfill.
 
I went a true 1” down, confident in the reading. The one calculator I was using Online asked for the IVC, that’s why I reposted here since y’all seem to have more info than the generic calculators. The one crappy thing I don’t know is the flow of the heads LSA on my cam is 108
 
OK, since you got the same +4 cc net dome, then we will run with that number and a deck-clearance of .010". The gives me the 10.46 static CR number. I'll note again that I include 1 cc for the crevice volume down to the top ring.

That works onward to the 7.9 to 8.3 DCR, depending on exactly what IVC angle I use. The big point there is that the IVC angle at .050" lift (50 degrees ABDC) is not what you use in the calculators. I ended up with 65 to 72 (depending on the assumption on low-lift the cam profle).

BTW, I use a free canned program ... from Pat Kelley. I find it easier to put in valve timing values. If I want to get altitude effects, I take the output of that program and plug it into the Wallace Dynamic calculator, where you can add in the effects of altitude. Once you get the process down and some realistic numbers under your belt, you can run through this in a few minutes.
 
As i mentioned I saw somewhere on this site that had the cylinder volume, and as mentioned at 1" it was 209cc's, I figured the 4 cc dome, using the calculator below with straight numbers it appears fairly close, curious if the HP calculator on same website is reasonably close to. At least one thing, detonation shouldn't be to hard to avoid. Pretty funny that of the several calculators that technically should be the same end up close - but not exactly even when the same data is used. I did read somewhere about adding to the IVC but no where did I find that in the calculators - thanks for the replies and info - optimistically the engine runs out well and at least manageable on the street, and of course able to do a burnout.

The Free & Accurate Horsepower Calculator
 
billsdartgt said:
As i mentioned I saw somewhere on this site that had the cylinder volume, and as mentioned at 1" it was 209cc's, I figured the 4 cc dome, using the calculator below with straight numbers it appears fairly close, curious if the HP calculator on same website is reasonably close to. At least one thing, detonation shouldn't be to hard to avoid. Pretty funny that of the several calculators that technically should be the same end up close - but not exactly even when the same data is used. I did read somewhere about adding to the IVC but no where did I find that in the calculators - thanks for the replies and info - optimistically the engine runs out well and at least manageable on the street, and of course able to do a burnout.

The Free & Accurate Horsepower Calculator
Click to expand...


I just ran my numbers through there and it shows mine making at least 50 HP more than it will. I’m pretty sure.
 
yellow rose said:
I just ran my numbers through there and it shows mine making at least 50 HP more than it will. I’m pretty sure.
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for mine it was around 400, if this engine only kicks 350 seems something will be bad off I would think - the stockish X heads are killers for sure though
 
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