Pump Gas and DECR

[Goldmember72]

Hey everyone, I am close to going back together with my 72 440. I am pretty close to making my decision on the head gaskets but thought this would be the place to find out what others suggest based on their experience. I am using KB184 pistons .083 in the hole (4.340 bore), cam intake closing point 37 degrees. I have clayed the step head to combustion chambers and CCd the combustion chambers (3462346 heads). Quench is .052 to .058 with a .020 head gasket and combustion chambers 88 to 89 cc's. That puts me at 168 cylinder pressure and a dynamic effective CR of 8.32. It is my understanding 165 absolute cylinder pressure is a max for 93 octane. Our local 100% gas is 91 which is what I plan to run. Going up to .039 head gasket is 160 cylinder pressure and 8.0 DECR but this adds .019 to my quinch which from what I understand anything over .060 doesn't have much value. I will be using a 165 thermostat and evens waterless coolant. I want to get all the DECR I can but also want to be able to use 91 gas that is available several places at least here on Oklahoma. My local elevation is 1200. I am thinking play it safe and go with the .039 head gasket but would really like to hear what has worked out for others. Any help is appreciated.

 

[Kern Dog]

It looks like your math is way off. First, you have a 4.340 bore? A .020 over 440?
Pistons .083 in the hole and a .020 head gasket add up to .103 below deck. There is no way that you can gave .052 quench since the piston is double that distance away from the head. You have maybe 7.2 compression with this combination.
What is DECR?
I have 175 cranking compression with my 10 to 1 440/493 and mine runs fine on CA 91 octane.

 

[Goldmember72]

It looks like your math is way off. First, you have a 4.340 bore? A .020 over 440?
Pistons .083 in the hole and a .020 head gasket add up to .103 below deck. There is no way that you can gave .052 quench since the piston is double that distance away from the head. You have maybe 7.2 compression with this combination.
What is DECR?
I have 175 cranking compression with my 10 to 1 440/493 and mine runs fine on CA 91 octane.

Yes, I have a 4.340 bore, I am .020 over, the .083 is to the top of the part of the piston under the valves. the step part of the piston goes up another .140 which is where I clayed to determine the quench.DECR is Dynamic Effective Compression Ratio that takes into account the closing position on the intake cam lobe and altitude along with static compression ratio, rod length and the other normal calculating factors. My stroke is factory at 3.75 and rod length 6.786. Using the calculator at Wallace Racing the effective stroke is 3.45 inches. I guess I didn't make my inquiry very clear. I am sure your intake cam lobe closing point is much higher than my 38 degrees and you may be running aluminum heads. I am very confident my math is correct. Thanks for the reply anyway.

 

[Goldmember72]

My piston, the .020 over step head KB184

 

[Kern Dog]

Maybe the guys in your area use some different terms in respect to engines. I have not heard of the DECR term, only the Dynamic C/R.
.020 over 440 to use 400 pistons and rings?
I have ran the 292/509, a Comp Cam XE 285HL, the Lunati 316/326 solid and the 284/528 solid. The car wanted to knock with them all regardless of the point of intake closing. I finally went with thicker head gaskets to lower the squeeze from 10.9 to 10 to 1 and the problems went away. I went about it a bit backwards though, I should have pulled the engine and put in dished pistons to lower the C/R but retain quench. I still may do that someday.

 

[PurpleBeeper]

Your math is well beyond me, but I do know that you will run HOTTER with Evans coolant, which won't help your detonation issues. Evans is basically DexCool coolant concentrate (no water added to make it 50/50) and water transfers heat much better than ethylene glycol... my 2 cents

 

[moper]

A few remarks based on the OPs info - The step pistons like that are really involved to get to be effective. Was the block square decked? Was it align honed? Was the crank indexed and stroke corrected? The rod lengths equalized? On the 346 heads - were the chamber depths and volumes equalized, and made smooth? These are the steps you need to take, to get those pistons to provide effective squish, which is really what quench is. If all these steps were not taken, the readings will vary cylinder to cylinder. Plus - as you note quench gets less effective very quickly as the distances between the parts increase. It's really powerful at .030. It's good at .040. It's doing something at .050. It's doing nothing at .060. That's why all the blueprinting work has to be done. Honestly I've built one engine with those pistons. It is cost prohibitive to do it in most cases when you can just buy better aftermarket parts including heads.
I'll add, nothing wrong with open chamber heads either as long as the desired result can be reached using them. The only thing I read as a "must have" is pump gas friendly. With the setup the OP has, and assuming the blueprinting was either not done, or only some of it was, the tune will be more critical than any of the actual measurements. I've run open chamber heads at 185psi before, and they ran on 10% ethanol blends of super (91) out of the pump. I've also had engines that I was tuning that were pingers with 150psi. So it's about the package and execution (tuning). I think you'll be ok with what you have, and I'd just not worry about quench.

 

[not so famous bob]

A few remarks based on the OPs info - The step pistons like that are really involved to get to be effective. Was the block square decked? Was it align honed? Was the crank indexed and stroke corrected? The rod lengths equalized? On the 346 heads - were the chamber depths and volumes equalized, and made smooth? These are the steps you need to take, to get those pistons to provide effective squish, which is really what quench is. If all these steps were not taken, the readings will vary cylinder to cylinder. Plus - as you note quench gets less effective very quickly as the distances between the parts increase. It's really powerful at .030. It's good at .040. It's doing something at .050. It's doing nothing at .060. That's why all the blueprinting work has to be done. Honestly I've built one engine with those pistons. It is cost prohibitive to do it in most cases when you can just buy better aftermarket parts including heads.
I'll add, nothing wrong with open chamber heads either as long as the desired result can be reached using them. The only thing I read as a "must have" is pump gas friendly. With the setup the OP has, and assuming the blueprinting was either not done, or only some of it was, the tune will be more critical than any of the actual measurements. I've run open chamber heads at 185psi before, and they ran on 10% ethanol blends of super (91) out of the pump. I've also had engines that I was tuning that were pingers with 150psi. So it's about the package and execution (tuning). I think you'll be ok with what you have, and I'd just not worry about quench.

whole combination sounds screwy to me. I`m no expert, but I like quench, mine is .037-.039 with steel rods.

 

[451Mopar]

Are you using 0.050" cam timing numbers for the closing point?
I'd run the 0.020" head gasket. You can put a thicker gasket in later if there is a need to do so, but giving up the quench with the thicker gasket might not make any difference to control pre-ignition, and you just gave up compression.
I don't have time right now to run the numbers. What is the static compression ratio, ans cam specs?
I did a 360 with the quench dome pistons, and as mentioned, it takes alot of detail and extra machine work to set them up. On my engine, the block decks were way off originally, front to back and side-to-side. The heads I used were not the original heads, and one head the chamber was 0.010" deeper than the other. Both needed to be milled to set the quench pad to Zero clearance without a head gasket. I think I took 0.040" off one head, and 0.050" of the other head, and the intake side of the heads were milled too. With all the milling, the intake sat so low, that I only needed a little RTV on the end rails (no room for end seals.)

 

[Kern Dog]

OP did a Keyser Soze.......POOF, he is gone!

 

[Goldmember72]

A few remarks based on the OPs info - The step pistons like that are really involved to get to be effective. Was the block square decked? Was it align honed? Was the crank indexed and stroke corrected? The rod lengths equalized? On the 346 heads - were the chamber depths and volumes equalized, and made smooth? These are the steps you need to take, to get those pistons to provide effective squish, which is really what quench is. If all these steps were not taken, the readings will vary cylinder to cylinder. Plus - as you note quench gets less effective very quickly as the distances between the parts increase. It's really powerful at .030. It's good at .040. It's doing something at .050. It's doing nothing at .060. That's why all the blueprinting work has to be done. Honestly I've built one engine with those pistons. It is cost prohibitive to do it in most cases when you can just buy better aftermarket parts including heads.
I'll add, nothing wrong with open chamber heads either as long as the desired result can be reached using them. The only thing I read as a "must have" is pump gas friendly. With the setup the OP has, and assuming the blueprinting was either not done, or only some of it was, the tune will be more critical than any of the actual measurements. I've run open chamber heads at 185psi before, and they ran on 10% ethanol blends of super (91) out of the pump. I've also had engines that I was tuning that were pingers with 150psi. So it's about the package and execution (tuning). I think you'll be ok with what you have, and I'd just not worry about quench.

Thank you, this is the type of response I was looking for. The block was square decked, rods re-sized, the 345 heads do have some variance in the combustion chambers thats for sure. You are correct in stating to get the quench correct this is not a cost effective build. My goal was to retain as much of the original parts (externally) as possible and still build back some performance above the 1972 rating. I have learned more on this build than all of the previous builds, as this was the first time I didn't just replace what I had to with the basic factory type or equivalent parts. I will go much further into detail in the planning stages in the future. I went deeper into the factory heads then I had intended to money wise and know I could have most likely came out with more power and not much more money into it. Thanks again for informing me based on your experiences that the tune will be a bigger part of being pump gas friendly from this part forward.

 

[Goldmember72]

451Mopar,
Yes, the intake closing point is at .050 as I degreed in the cam: Intake opens 4* BTC and closes at 37*ABC, Exhaust opens 46*BBC, Closes at 0* ATC, Duration @ .050 222/226, LSA 110*, ICL 107*. Static CR is at 9.295 with .020 head gasket and 8.949 with a .039. I did make an error on my rod length though when I started this, it is 6.768

 

[451Mopar]

451Mopar,
Yes, the intake closing point is at .050 as I degreed in the cam: Intake opens 4* BTC and closes at 37*ABC, Exhaust opens 46*BBC, Closes at 0* ATC, Duration @ .050 222/226, LSA 110*, ICL 107*. Static CR is at 9.295 with .020 head gasket and 8.949 with a .039. I did make an error on my rod length though when I started this, it is 6.768

Those numbers don't seem to add up? a 222 intake installed at 107 cl should have intake closing at about 31 degrees ABDC?

 

[Goldmember72]

Here is my cam card, I may have not typed it in correctly. I was at work and trying to do more than one thing at a time.

 

[451Mopar]

Sorry, my bad. My good computer died Monday, and I was using a spreadsheet from my old computer that is layed out different.
Did you count in the 3.5cc valve relief volume?
My numbers are close to what you have, but slightly lower compression ratio.
Here is what I was using:
Bore = 4.340" (0.020" over)
Stroke = 3.750"
Rod Length = 6.768"
Block Height = 10.718" (0.007" less than spec @ 10.725") This makes the piston your 0.083" below deck height.
Piston - KB184:
Compression height = 1.992"
Valve relief volume (includes the step volume) = 3.5cc dish (add to chamber volume.)
At this point the quench dome should be 0.057" above deck height at TDC.
Head gasket:
Average Bore Diameter = 4.410"
Compressed thickness = 0.020"
Volume = 5.007cc
Quench dome above gasket = 0.037"
With your 0.052" quench clearance, the Head serface to quench area of the head would have to be 0.089" deep. This actually sounds about right for a stock, unmilled head?
With the 88cc head volume, and 0.083 below deck, 5.007 head gasket, and 3.5cc valve pockets, I get 116.63cc above the piston for a compression ratio of 8.79:1.
If the heads were milled to 85cc, that is 9.0:1 compression.

The reason your dynamic calculation is high, is you need to enter the intake closing point that is closer to the real closing point, usually the advertised duration is a bit closer, but I would guess your intake seat closing is closer to 64 degrees? This puts effective compression ratio around 7:1, and maybe 140 cranking psi?

I would try to equalize the quench distances, then mill the heads to get a tighter quench distance and raise the static compression ratio a bit. The cam does look good nice for the combination, but I don't know why they want so much lifter pre-load? I usually use 0.040" pre-load.

 

[Goldmember72]

451Mopar,
Thanks for your help. I still have the degree wheel on and set. I will re-check the seat spec tomorrow hopefully. Its going to be a late one at work tonight. Yes, I accounted for the 3.5 offset on the positions. The block and heads were surfaced, approximately .010 on each. They sunk the valves a bit on the valve job and installed hardend seats on exhaust. I am not real clear on why thay sunk the valves though. Maybe you or someone could enlighten me on that. After surfacing the heads it put my cc's right back where they were. Thanks again.

 

[Goldmember72]

Sorry , on my phone and auto- correct made some changes to my last post. I am sure you get the point.

 

[451Mopar]

If your degree the cam, get the 0.006", 0.010", 0.020",0.050",and 0.200" duration numbers.
I think the 0.006" duration is what many use for "Advertised" duration (although this could really be any thing, I know some used 0.004, and others 0.008" too.)
Many solids are rated at 0.020" to account for the valve lash. Might be a good number to use for the DCR calculation too? The 0.050" is current industry standard rating. The 0.200" durations can be found in some lobe master profile catalogs and can give a comparison of how agressive the ramp rate is between the 0.050" and 0.200" durations.
Not sure if you done the degreeing before?
For the duration measurements, you don't even need to worry about crank position.
You can just rotate crank to where the cam first reaches the checking tappet lift (like 0.006"). Take the degree wheel measurement, or just set the pointer to zero. Rotate through max lift to the same tappet lift on the closing side, and record that degree wheel measurement. If you zeroed the pointer at the first measurement, it duration should be the same as the second measurement (if the degree wheel reads degrees 0-360?) If not you have to do some math to find the difference from starting point to end point, and/or reading from a 0-90-0 degree wheel.

 

[Goldmember72]

I got some of the numbers today but failed to get the same positions on the closing side of the intake lobe. Intake open at .006-28.5, .010-24, .020-7, .050-4 all BTC, .200-36 ATC. I totaled up from 0 (TDC) forward, open .006 to closed .006=270.5. If I worked the math correct after I got to work that would mean the on the closed side at .006 would be 62 ABC. I will verify that and the point on the closed side tomorrow. I came up with 241 .006 open to closed on the exhaust. using the 62 instead of the 37 for intake closing point makes a big difference. The KB calculator show to use the intake closing point at .050 plus 15 degrees which is 52 not the 62 I came up with at .006. I do have a question on the 3.5 cc value on the pistons. From the KB it looks that value is to be -3.5 and getting the correct does make a difference. Are you adding or subtracting that? Again I do appreciate all the help.

 

[451Mopar]

Your right, I added the -3.5cc when I should have subtracted it from the head volume (109.63cc volume above piston), so 9.29:1 compression with 88cc head. That sounds better. I was thinking the step volume was less than the valve relief volume.

The 270.5 duration for the 0.006" numbers is right, and the correct open/close points for 107 centerline. That must be the Hughes SEH2226BL-10 cam. Those have fast ramp rates. The -36 ATDC 0.200" number should give a closing point of -2 ABDC (2 before BDC) and 142 duration @ 0.200". The 270-222-241 duration numbers are near or better than many hydraulic roller cam profiles. Most Flat tappet hydraulic cams with 142 @ 0.200" are [email protected]" and [email protected]" advertised, because they were designed for a smaller diameter lifter. Cam lobe profiles like the Hughes ones require the larger diameter 0.904" lifter.
Compare "advertised durations" to something like the Comp Dual energy 269@? advertised, [email protected]", and 129 @ 0.200". That is a difference of 13 degrees duration when the valve is open 0.300" (0.200" tappet * 1.5 Rocker ratio) or more (where the head is making good air flow.)

With the correct 9.29:1 static, and 62 degree closing point, I get dynamic compression of 7.33:1, estimate cranking PSI 146?