Compression/head gasket selection. 360

Small Block Mopar Engine

Will a thicker head gasket cause problems?

  1. Yes

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  2. No

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  1. jtn2655

    jtn2655 Member

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    I'm building a 360 for the street/ occasional track day, Edelbrock Performer RPM aluminum heads (63cc chamber) KB 107 pistons (+5.00cc), block bored 30 over, xtreme energy hi lift cam 231/237@ .50
    edelbrock RpM Air Gap intake, holley 750 carb and summit racing 1 5/8 headers.

    Just got block back from machine shop and was running through my compression calculator. With a .050 fel-pro Gasket I will be at approximately 10.54:1. If I step it up to a .060 head gasket it will bring me down to 10.3:1. I will run on 93 octane. Will the thicker head gasket cause any problems?
     
  2. dartfreak75

    dartfreak75 Restore it, Dont part it! FABO Gold Member

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    I am building dang near the exact same build except for the cam and intake. Mine also came out around 10.5 check the dynamic compression with that cam you may be ok the way it is with the felpro thats what I'm using also. I'm at a high elevation 2400 that along with my cam put my dynamic compression at 8.3. Which is right at the top for pump gas. From what iv read 8.5 is about the highest dcr you want to go for pump gas. Dynamic compression is what you have to watch more that static compression when your calculating for pump gas.
     
  3. yellow rose

    yellow rose Overnight Sensation

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    Are you at zero deck? Above the deck? Below the deck? If so, how much?

    I don’t ever trust what the piston manufacturer says about some or dish volume. If you don’t pour the cylinder you won’t know exactly what you have.

    Also, some of those online calculators don’t ask for the gasket bore size. That makes a big difference.

    My point is you don’t have too much CR to run on pump gas with what you have. And, you CR is probably a bit lower than what you think it is.

    If you post your gasket bore and where the piston is relative to the deck I can get you a bit closer on CR. But, to know for sure you’d need to pour a cylinder.
     
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    • dartfreak75

      dartfreak75 Restore it, Dont part it! FABO Gold Member

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      The gasket bore on those are 4.180 I doubt he is above the deck unless he milled the deck. Mine are .012 under with the factory height block I didnt mill my deck height any.
       
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      • rumblefish360

        rumblefish360 I have escaped the evil Empire State! FABO Gold Member

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        Simple question, simple answer, been there and done that.
        my answer is;
        No!
         
      • AJ/FormS

        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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        Yeah it will do nothing for you except slow you down,lol

        I have ALMOST the exact same engine specs, except mine is bored .040, and I run a Hughes HE3037AL cam (230/237@.050); and have been running it since 2004,with the pistons averaging .005 ABOVE deck, with the .039 FelPros, and at an SCR of 10.95 or better. The Quench averages to .034 with one a lil tighter at .032.
        This engine runs funtastic!...
        on 87E10,
        in a streeter,
        for well over 100,000 miles,
        at 32* PowerTiming, all in by 3400.
        I have run it with more timing, and all-in sooner, but found that my butt-dyno did not know the difference, so I run it easy. This same 32* at 3400 got my race-weight 3467# 68 Barracuda, to 93mph in the 660, at 900ft, on a Hot July afternoon...... with 3.55s and a Commando 4-speed/GVod, splitting gears, yes;still on 87E10.
        We (my 16 year old son and I), drove 30 minutes to the track, ran the number, bought the Tee shirts,had lunch, watched the dragsters; then went home.
        I took that engine apart every winter for the first 5 years, and never saw a sign of a problem traceable to too much pressure. The last time it was apart was winter of 04/05
        My point is ; don't WASTE the pressure potential. Mine cranks about 177 to 180 psi. (It has run 185psi on 87E10 with a different combo; 11.3Scr and MP292/108 cam).

        BTW
        The KB TOP ring-gap factor of .0065, is, IMO, too tight.
        My engine ran hot, could not be cured of that in the usual ways, and would lock up almost every time I shut it off. Sometimes I would have to wait 30 minutes before the Dakota mini-starter could crank it up.
        I took the engine out and opened the gaps up to the "street/towing" spec of .0080 factor, which worked out to .032 on the top ring. For the Second ring,I used the published KB spec + .002 so .028 .. That instantly solved the problem.
         
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        • dartfreak75

          dartfreak75 Restore it, Dont part it! FABO Gold Member

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          I just filed my rings this morning I used the .008 gap factor I set mine to .032 end gap
           
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          • AJ/FormS

            AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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            That is the first time I have heard it said like that, and is what I did. First the math, then the pour. The pour can't lie.
             
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            • MOPAROFFICIAL

              MOPAROFFICIAL FABO Gold Member FABO Gold Member

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              Like was mentioned, you have a rough idea of what the static compression should be or around. Run the static against the cams intake closing and get an idea of the dynamic/effective compression.
              On 93 octane you should be fine if stay under 200psi
               
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              • AJ/FormS

                AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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                Yeah I have heard that combo-number several times since I joined in 2014.
                 
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                • Wyrmrider

                  Wyrmrider Well-Known Member

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                  let's have the deck clerance
                  without that detail plan to open up around the valves and stick a .028 gasket in it
                  going to.060 quench is not a good idea
                   
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                  • AJ/FormS

                    AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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                    I initially ran an .028 gasket at the 11.3 spec with pistons down a bit. At the first regularly scheduled winter teardown, I found the fire rings migrating towards the valley, both sides all holes IIRC. That's when I shaved the decks,again, and installed the .039 FelPros, cuz I had heard those were THE ones to run.
                    I wish I could recall what brand those .028s were, but cannot. I'm sorta thinking they were Orange,but not sure whatsoever; that was year 2000. They were NOT blue, but mightabin black.

                    Now that I think of it, that engine was set up for the 292/108 cam. But I didn't like it, pulled it out and sold it in late summer. Swapping a Hughes HE2430AL (270/276/110 advertised) in it it's place. Ima thinking the pressure was pushing 190 with that small cam, so I probably overdid it for the .028s
                    Yeah, the Wallace is predicting 192psi........
                     
                    Last edited: Oct 4, 2020
                  • yellow rose

                    yellow rose Overnight Sensation

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                    I just ran your numbers as best I can with what we know, and I get a CR of 10.4398 just as it sits.

                    That’s making two big assumptions. The first assumption is the valve notches are only 5 cc’s. I doubt they are that small. The other big assumption is deck clearance. I did your math, which I will outline below at a .0000 deck clearance. If your piston is below deck (which it probably is) that will make the above number lower than what I’ve posted. And, if the piston is above the deck (highly unlikely) then the above CR will be higher than what I’ve posted.

                    Here are the number I have.
                    Combustion chamber 63 cc
                    Piston volume. 5 cc
                    Head gasket volume 11.270 cc
                    Deck clearance .0000 for 0 cc
                    Swept volume 748.293

                    So the math is:
                    Chamber cc+ head gasket cc+ piston cc+ swept volume

                    That is divided by:
                    Chamber cc + head gasket cc + piston cc

                    That means it looks like this:
                    63+11.270+5+748.293=827.563 and
                    63+11.270+5=79.27 and then it’s...

                    827.293/79.27=10.4398 CR

                    Again, that’s assuming a .0000 deck clearance AND 5 cc piston notch volume.
                     
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                    • Wyrmrider

                      Wyrmrider Well-Known Member

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                      aj did you use something like (btw there is no "like") spray Hylomar?
                      retorque the heads?
                      tks and your analysis is spot on
                       
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                      • AJ/FormS

                        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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                        @Wyrmrider
                        Q; did you use something like (btw there is no "like") spray Hylomar?
                        A; No;headgaskets went on dry.

                        Q; retorque the heads?
                        A; Yes;broke the cam in with the outersprings; then retorque the heads,install inner springs,
                        and reset the lifter preload.

                        Q; and your analysis is spot on
                        A; re post #6/ and the tight gaps?
                         
                        Last edited: Oct 5, 2020
                      • AJ/FormS

                        AJ/FormS 68 B'cuda fb, Form S clone ... 367/A833/3.55s FABO Gold Member

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                        Additional information, to those that might like to know;
                        The KB spec on those 107s is 1.5 to 2 thou skirt clearance at below 4.10inch bore, and 2 to 2.5 over that. So 4.040 is pretty close to the changeover point. Anyway, I didn't tell the machine shop what to do, and when I got the block back, it was at 2.5. Not knowing any better, I was a little miffed, but it was too late to argue about it, so I put it all together.
                        So now with the tight gaps, and the unsolvable overheat, I didn't know; was it the rings or the skirts.
                        What I didn't mention in the previous post, is that, when I tore the engine down. I also had the cylinders honed out a tad more, for additional skirt clearance,at the same time. I used a different machine shop this time, who claimed the holes in the now re-seasoned block were no longer straight. Not having the tools to prove otherwise, I trusted him to do his thing. When I got the block back, the clearance was 3.5thou pretty much every one the same from what I remember. I was again miffed, more than before, but, c'est la vie, I said and assembled it.I checked the KB catalog, and saw that .0035 skirt was NOT excessive,and so the machine-shops were no longer the bad-guys in this story.
                        With the new specs, that stoopid iron hunk-a-junk instantly settled down.
                        It had more power, used less fuel, and wonder of wonders, it ran "cold". I was no longer miffed at anybody. I was ecstatic.
                        But on cool mornings, I could hear the pistons rattling just a tad, telling me the piston skirts had NOT been the problem. So, I installed first a 185 stat, then a 195 stat; and the engine seemed to like it. That Hi-flow 195 ended up running 205 at the stat-house.
                        The little Hughes 223/230/110 cam eventually went to over 30 mpgUSg on point to point hiway travel. And, with a lil tuning, it would idle down to 500rpm, pulling itself in first gear (manual trans), on a flat,level, hard, surface.
                        Then I knew I had made the right cam choice. This was now a sweetheart of a combo. I never again missed the 292/108 cam.

                        Oh yeah, I took it to the track one time. I had a hard time with my shifter that day,and out of 4 runs, only one was any good. On 245/60-14s and with 3.55s, she hit 106 mph at 12.9 and change @3650 pounds and 900ft. Badaboom! The Wallace Calculator says 106 takes 335hp. I was a happy man to be in the 12s. I mean what's not to like about a 12 second streeter that hits over 30 mpg on the hiway, and spins those skinny 245s forever?
                        Wonder of wonders.

                        Well, I better tell this part;
                        That fuel-mileage was made in DOUBLE-overdrive lol. I was using the Mopar od 3+1box, and the GVod behind it, so with 3.55s the final drive ratio was 1.966, and with 27" tires; 75=1830/85=2080,. I used a Holly 600 (1850), that I especially tuned for this run. When we got to our destination, the 750DP went right back on.
                        BTW: Swapping 4-speeds on a 4-post drive-on hoist, takes less time than swapping chunks, even having to drop the exhaust, and the overdrive unit separately. My record for dropping it all, is 17 minutes.
                         
                        Last edited: Oct 5, 2020
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                        • MOPAROFFICIAL

                          MOPAROFFICIAL FABO Gold Member FABO Gold Member

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                          I set hypers at .003, have for 20 years.
                           
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