Check my work-Chime in please

[DesertRat]

67 273 build data with 10.5 CR Egge domed pistons. CR Data gathered: Combustion chamber volume 62.5 CC measured. Bore 3.665 Stroke 3.31 Head gasket compressed .028 Head gasket bore 4.14. Measured cylinder volume with piston 1/2" down in cylinder = 84 CC. Rod length 6.123 Intake closing point ABDC 49.5 degrees. If I am missing data, just ask, my crank & pistons are in and ready to install cam & time it, dont want to "screw-the-pooch" so to speak.
TIA, DRrayer:

 

[RustyRatRod]

I come up with 8.2 DCR. That's gonna be pushin it for pump gas.

 

[AJ/FormS]

bore of 3.665? My brain hurts. I thought the stock bore was 3.630? A 3.635 bore would make a 273 actually a 274.8 Hmmm, Ima thinking a 30 over hole should be 3.660?
Oh I get it it's a .035 overbore. But why? What am I missing?

I musta done something wrong cuz I get a Scr of 9.64, and a Dcr of 8.47.

I get a swept of 572.22cc, and a total chamber of 66.237cc; which is head of 62.5, gasket of 6.176, and deck clearance of 2.439 pop-up

 

[Double M]

273 standard bore is 3 5/8" (3.625). I see many places where people round it off to 3.630. Why, I don't know!?

Russ.

 

[AJ/FormS]

Yeah that does it . the math says 273.29 cid
I knew that . I just forgot it. Sheesh!

How did I get the 2.439 pop-up? Well at your bore size the 1/2 inch down fill volume should be 86.439cc. Since you were only able to get 84cc in there, your piston is too big and therefore must be a pop-up; equal to the difference.

 

[RustyRatRod]

Well 8.4 DCR is even worse for pump gas.

 

[AJ/FormS]

With the closed chamber heads, and the really,really tight quench (you better check that closely), I think it will be fine. The .039 gaskets would add about 2.6cc, making the total chamber volume 68.238, and the Scr of 9.386, and the Dcr to 8.25.
Or you could keep the .028s and close the intake a lil later;51* would change the Dcr to 8.39, 53* would be 8.31.

But you have got to check the piston to head clearance!

 

[moper]

How did I get the 2.439 pop-up? Well at your bore size the 1/2 inch down fill volume should be 86.439cc. Since you were only able to get 84cc in there, your piston is too big and therefore must be a pop-up; equal to the difference.

x2.
What are the cam's LSA, exhaust opening event, and lift on both?

 

[frosty_the_punk]

This is what i came up with.

Effective chamber = 66.28
62.5 minus 2.4 plus 6.18
(Head chamber - pop-up piston + gasket volume)

Swept volume = 572.74cc (using Pi x radius squared x stroke)

Compression ratio = 9.64:1

(572.74 + 66.28 ) / 66.28 = 9.64


Using wallaceracing.com calculator with your stroke and rod length I get a DCR of 8.47:1 at sea level.

I wouldn't be worried!
Just be sure to check all your piston/valve tolerances before final assembly.

 

[DesertRat]

Below are the cam specs for the cam "on the shelf". The bore number comes from the stock bore + .040 overbore. FWIW I come up with 8.471 dynamic as well. I want to push the envelope a little bit but also want to buy gas for the car so I am asking myself "is it too close to the line"? No point in spending the money to build a 273 if you are not going to make it run like the 67 commando's ran back in the day-right! Looks like I could buy a thicker head gasket or a cam with a little more duration. The Lunati #60402 (old number) fits the bill and takes the same lifter/spring/valve height setup I already have. If I leave it like it is, will the engine run?
Once again group-thanks for the help!
"Nervous as a cheerleader on game day"-----DRrayer: except the seahawks!

 

[nm9stheham]

Hold the phone everyone.......the data given is not complete enough. You can't just calculate CR from the apparent 2.4 cc's measured above-deck volume, because there is also below-deck volume at TDC. The reason I say all of this this is because the Egge dome volume in not 2.4 cc's, (which is the flat-top .500" down-in-the-hole volume minus the measured down-in-the-hole volume). There is some volume info that we are missing.....

DR, how did you measure how far down in the bore the piston was when you did the in-block cc-ing? Did you use a dial indicator or a caliper or? And did you measure from the flat top of the piston for the .500" or where? This accuracy and where you measured is critical to your results. (And did you seal the edges of the piston top with clay when cc'ing .500" down in the hole?)

How far down below deck is the flat part of the piston when at TDC? We could work from the Egge compression height number but any block decking info would be missing from the equation.

Your cam closing number looks incorrect. I am getting 56* ABDC; that is based upon the advertised cam specs.

 

[DesertRat]

Hold the phone everyone.......the data given is not complete enough. You can't just calculate CR from the apparent 2.4 cc's measured above-deck volume, because there is also below-deck volume at TDC. The reason I say all of this this is because the Egge dome volume in not 2.4 cc's, (which is the flat-top .500" down-in-the-hole volume minus the measured down-in-the-hole volume). There is some volume info that we are missing.....I thought that might be the case.

DR, how did you measure how far down in the bore the piston was when you did the in-block cc-ing? Did you use a dial indicator or a caliper or? Dial indicatorAnd did you measure from the flat top of the piston for the .500" or where? From the top of the dome.This accuracy and where you measured is critical to your results. (And did you seal the edges of the piston top with clay when cc'ing .500" down in the hole?) I sealed the piston with lubriplate at the edges of cylinder.

How far down below deck is the flat part of the piston when at TDC? That is hard to determine, I could choose what I think is the flat part and dial indicate it.We could work from the Egge compression height number but any block decking info would be missing from the equation. No, I am all about doing the work at this point.

Your cam closing number looks incorrect. I am getting 56* ABDC; that is based upon the advertised cam specs.

My CR calculator asks for intake closing # + 15 degrees. Per Lunati tech support my cam closing given on card is at .050.
Thanks for input. I will get the missing information soon but how do we use it in the overall callculation? Have to add the below deck volume to the overall cylinder volume which reduces the static and dynamic CR. BTW-this is precisley why I asked for input-Thank you.
DT

 

[nm9stheham]

OK.... that must be the KB calculator; they work from the .005" lift and add 15*. I don't consider that the most accurate way.....

OK, so let's be clear on how you measured the .500" below deck number. Did you move the piston down until the top of the dome was .500" below the deck surface, or did you move the top of the dome down .500" from it's position at TDC?

 

[DesertRat]

OK.... that must be the KB calculator; they work from the .005" lift and add 15*. I don't consider that the most accurate way.....

OK, so let's be clear on how you measured the .500" below deck number. Did you move the piston down until the top of the dome was .500" below the deck surface, or did you move the top of the dome down .500" from it's position at TDC?

I put top of dome @ TDC and moved it down 1/2" or 500 thousandths.

 

[nm9stheham]

OK, can you move the piston back up to TDC, and then measure the CC's down in the block at that point? That will complete the data needed to figure this out. We can crosscheck this to the info given in the past for the Egge pistons.

And yeah, I expect the SCR and DCR to be lower with this info.... the Egge pistons are the lowest compresssion height of the available 4bbl 273 pistons.

 

[AJ/FormS]

Good call nm9

Furthermore, specking out a bigger cam may not be the answer. It is the ICA that is important. The real, installed, intake closing point. A one size or maybe even a two size bigger cam (longer duration),can have the exact same, or very nearly the exact same, ICA if they tighten up the LDA and add the duration in the overlap period. Be vewey,vewey kewful

 

[DesertRat]

OK, can you move the piston back up to TDC, and then measure the CC's down in the block at that point? I can measure the distance in thousandths from the block deck to the top of the piston flat. I cannot CC it as the dome will be above the deck at that point. Also, only part of the piston is flat, less than 1/2 of it, the rest is above the deck. That will complete the data needed to figure this out. We can crosscheck this to the info given in the past for the Egge pistons. I would like some clarification of how this calculation figures into the overall volume.

And yeah, I expect the SCR and DCR to be lower with this info.... the Egge pistons are the lowest compresssion height of the available 4bbl 273 pistons.

In the windstorm may be a day or 2 before I get back to it.

 

[DesertRat]

Good call nm9

Furthermore, specking out a bigger cam may not be the answer. It is the ICA that is important. The real, installed, intake closing point. A one size or maybe even a two size bigger cam (longer duration),can have the exact same, or very nearly the exact same, ICA if they tighten up the LDA and add the duration in the overlap period. Be vewey,vewey kewful

They made all this work in 1967. And with a .019 metal head gasket! Was it because the fuel was better quality than it is today? This build is not that complicated and not that far from the original 235 HP original commando release so I am having a hard time understanding all the concern. Not criticising, just want to learn a little something here!

 

[frosty_the_punk]

Hold the phone everyone.......the data given is not complete enough. You can't just calculate CR from the apparent 2.4 cc's measured above-deck volume, because there is also below-deck volume at TDC. The reason I say all of this this is because the Egge dome volume in not 2.4 cc's, (which is the flat-top .500" down-in-the-hole volume minus the measured down-in-the-hole volume). There is some volume info that we are missing.....

DR, how did you measure how far down in the bore the piston was when you did the in-block cc-ing? Did you use a dial indicator or a caliper or? And did you measure from the flat top of the piston for the .500" or where? This accuracy and where you measured is critical to your results. (And did you seal the edges of the piston top with clay when cc'ing .500" down in the hole?)

How far down below deck is the flat part of the piston when at TDC? We could work from the Egge compression height number but any block decking info would be missing from the equation.

Your cam closing number looks incorrect. I am getting 56* ABDC; that is based upon the advertised cam specs.

what measurement is missing? As far as i can see it's all there.

A perfect cylinder of 3.665" diameter is 0.500" height = 86.359cc (86.36)

This cylinder has a dome to reduce chamber volume, but it also may be slightly down the bore at TDC, not to mention it has ring lands, valve recesses etc that will add to the chamber volume. all of which mean that when the piston is moved .500" down from TDC and then a plate is put over the deck the measured volume is going to vary from the theoretical perfect cylinder volume of 86.36cc. the difference, be it negative or positive is added or subtracted to the effective combustion chamber volume.

In this case, the volume of that cylinder is a measured 84CC.

86.36cc - 84cc = 2.36cc (for simplicity sake we call this 2.4cc)

That's a measured volume, not guessed or taken from a parts book advertisement.

What numbers are we missing? We have calculated both the above deck volume and the below deck volume at the same time using the .500" method and come up with a final number of positive 2.4cc.

subtract that 2.4cc from the cylinder head chamber volume and you have the total chamber volume. 60.1cc.
factoring in gasket volume and cylinder's swept volume, all the numbers are there. right?

Having the advertised numbers, I also got a IVC at 56 degrees. bringing my calculated DCR to 8.15:1 at sea level.

 

[frosty_the_punk]

OK, can you move the piston back up to TDC, and then measure the CC's down in the block at that point? That will complete the data needed to figure this out. We can crosscheck this to the info given in the past for the Egge pistons.

And yeah, I expect the SCR and DCR to be lower with this info.... the Egge pistons are the lowest compresssion height of the available 4bbl 273 pistons.

How can he measure the area below the deck at TDC with a dome top if part of the piston is protruding above the deck?

It can't be done. This is exactly why the .500" method exists.

did you mean to suggest measuring how far down the flat part of the piston is from the deck height?

That can be useful, but the CC's are already measured using the .500" method. I guess it can't hurt to cross reference though.

 

[AJ/FormS]

They made all this work in 1967. Was it because the fuel was better quality than it is today? This build is not that complicated and not that far from the original 235 HP original commando release so I am having a hard time understanding all the concern. Not criticising, just want to learn a little something here!

Hey DR, this was in response to your previous post of just sticking a bigger cam in it.
Yes they used to have higher octane gas available at the pump. But our concern at this time in history, is to be sure the effective Dynamic Compression Ratio (Dcr) does not get too high for todays gasoline. Part of this Dcr is determined by the closing point of the intake valve. By empirical data it has been determined that at sea level the Dcr needs to remain below a certain value to prevent detonation. This value is not written in stone and varies with many factors. But generally needs to remain below about 8.2 +/-.2. Further if the Dcr gets to be to low the giddy-up factor goes soft. With a small displacement engine, therefore,the Dcr needs to be particularly carefully chosen to have both a strong off-the-line-performance yet to stay out of detonation.
Now, I'm pretty sure you know most or all of this. But what you may not know is that just throwing a longer duration cam into it, does not automatically preclude a later opening intake valve.
Here are some examples of imaginary cams that all have the exact same ICA of 56*.
Cam #1 is 252*, on a 114LDA, installed at 110, ICA of 56*
Cam #2 is 258*, on a 110LDA, installed at 107, ICA of 56*
Cam #3 is 264*, on a 106LDA, installed at 104, ICA of 56*
All the cams are fictitious, and are for illustration only. Notice each cam is about one size bigger on the intake duration. Notice also that the LDAs are decreasing, as are the installed centerlines. YET all have the same 56* ICA .
Point being; your statement "Looks like I could buy a thicker head gasket or a cam with a little more duration" sounds good, but it's not quite right.
What you really might need is; to buy a thicker headgasket or a cam with a little LATER CLOSING INTAKE.
So that is where I came in with "be vewey, vewey, kewful.
I hope that clears it up. My wife tells me all the time how senseless my humor is, so I apologize for my senseless humor, and once again, I'll try to keep it in check.

 

[frosty_the_punk]

for what it's worth, I've had no problem with DCR in the mid-high 8's running on 91 octane. (iron heads, open chambers)

yours is 8.15. IMO it's not even questionable.

edit: is the lunati cam card you posted for the cam you have or the cam you're thinking of upgrading to? (to bleed off some DCR.... either should be fine really)

 

[RustyRatRod]

for what it's worth, I've had no problem with DCR in the mid-high 8's running on 91 octane. (iron heads, open chambers)

yours is 8.15. IMO it's not even questionable.

edit: is the lunati cam card you posted for the cam you have or the cam you're thinking of upgrading to? (to bleed off some DCR.... either should be fine really)

Plus he will have quench working for him. Good info Frostamous. Thanks.

 

[DesertRat]

for what it's worth, I've had no problem with DCR in the mid-high 8's running on 91 octane. (iron heads, open chambers)

yours is 8.15. IMO it's not even questionable.

edit: is the lunati cam card you posted for the cam you have or the cam you're thinking of upgrading to? (to bleed off some DCR.... either should be fine really)

The cam card I posted is the cam I own and am ready to install. I choose it because it has a little more lift that the commando solid cam and close to the same duration specs, just a hydraulic version of same. Hoping for a slight increase in overall performance from the engine using this cam and the LD4B intake.
I was also hoping for a little more DCR than 8.15 but I need to build the engine and I am tired of thinking about it. If 8.15 is the number, that is how the engine will get built and I will worry about DCR on the next engine I build

 

[nm9stheham]

What numbers are we missing? We have calculated both the above deck volume and the below deck volume at the same time using the .500" method and come up with a final number of positive 2.4cc.

subtract that 2.4cc from the cylinder head chamber volume and you have the total chamber volume. 60.1cc.
factoring in gasket volume and cylinder's swept volume, all the numbers are there. right?

Having the advertised numbers, I also got a IVC at 56 degrees. bringing my calculated DCR to 8.15:1 at sea level.

You are correct, sir,, and thanks for taking the time to lay it all out for everyone. I was trying to separate out the positive above-deck and negative below-deck displacements to enter separately in to a calculation. But, in the end, it does not matter if they are entered separately in 2 places, or combined in 1 place. The net effect is the same.

Doing it both ways (with an estimate of the above deck dome volume at TDC), I ended up with 9.64 SCR and 8.14 DCR. If DR thinks that is a bit too much, a .039" head gasket yields a 9.34 SCR and a 7.89 DCR. This is using the advertised intake closing angle for the cam, which Lunati measures at .006" valve lift. So the only question is what calculator is better: using advertised closure angles or estimating off of .050" lift angles.

You could deck the block or heads at this point DR, or try to find steel shim head gaskets to get it up, but you're gonna find it to be pretty good at these numbers. Focus on the things like piston-to-valve clearance and consistent piston deck heights and piston-to-deck clearances and such.