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Thread: Gasket matching

  1. #1
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    Gasket matching

    Anybody done gasket port matching on a Magnum? HTF do you line up the gaskets for scribing with the bolt holes at an angle? Guess work could end up 1/8" off in the vertical axis easy. Almost seems like it would have to be bolted up on a block to do accurately, and mark positions of the gaskets for alignment... or am I missing something?
    I have new heads and intake not yet installed, and want to do it off the motor.

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    Member JGC403's Avatar
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    It would probably be best to set the heads on the block, because there is a notch in the intake manifold gaskets that fit with the head gaskets. The head gaskets hold the intake manifold gaskets in place.

    It wouldn't take long to put new head gaskets on, set the heads on, the dowel pins will hold them in place and put a bolt or 2 in just hand tight to ensure they won't fall off while your moving stuff around. Then spread some Dykem Blue around the ports, set the intake gaskets in place and scribe away.
    No replacement for displacement!

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    Quote Originally Posted by JGC403 View Post
    It would probably be best to set the heads on the block, because there is a notch in the intake manifold gaskets that fit with the head gaskets. The head gaskets hold the intake manifold gaskets in place.

    It wouldn't take long to put new head gaskets on, set the heads on, the dowel pins will hold them in place and put a bolt or 2 in just hand tight to ensure they won't fall off while your moving stuff around. Then spread some Dykem Blue around the ports, set the intake gaskets in place and scribe away.
    Thanks - I was afraid that was the case. It wouldn't be a big deal to do it on a block on an engine stand, but I wanted to at least port the heads ahead of time to install on the motor still in the daily driver Jeep. I could do this if the intake bolts were perpendicular like they used to be (I could do it in my kitchen!), but with the angled bolts there's no way to position the gasket accurately enough even on one side.

    So, what do they do if you order pre-ported heads from a place like Hughes? Do they use a dummy block, give it their best guess because it's not their car, or is there some scribing template that takes out the guess work?

    Oh well... I was considering fully rebuilding a JY block instead of rebuilding just the top end of mine, and this is one more reason to go that route if I don't come up with another solution.

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    9 months later... matching gaskets between Edelbrock heads to M1 2bbl on a donor block:

    First, I had to figure out where the combustion chamber side of the heads would end up after zero-decking with the final gasket in place. From the stock deck height it worked out to .023, so I used some .020 shims (close enough for porting) to temporarily mount the heads with 4 studs each, just snug:
    P1010026.jpg
    Here's the math:
    Stock deck height: 9.585
    My target zero deck height for my piston compression height and rod length: 9.568 + .040 gasket = 9.608, giving the difference of .023 above stock deck. You want the intake runner to be a little smaller (like .015) all around than the head port, so that .003 difference won't matter...

    Then I used donor Felpro .060 gaskets to figure out how the intake and head ports line up - first positioned on each head, and noticed the Edelbrock ports match the gaskets as perfectly as you could expect:
    P1010035.jpg

    Carefully set the intake in place, making sure the gaskets didn't move from the sharpie line I had traced onto the heads for reference, and bolted it snug, making sure the end gaps were parallel, traced with a sharpie and scribe:
    P1010031.jpgp1010030.jpg

    Then I removed the intake and taped the gaskets back on the intake, using the scribe line on the gaskets for alignment, and got this:
    P1010034.jpg
    No sir, I don't like it. Almost a .14" overhang on the roof. Sure, I could just grind away on the runner roof until it matched, but there are a couple problems with this: along the entire length of the runner, there's only a .024" difference in height, so the bottom of the runner would end up bigger than the top, slowing the air velocity. Also, because the air has to turn down in the port, most of the air-fuel mixture flows along the roof, making the roof transition the most important part. I found out Cometic makes a .188" thick gasket. A little trigonometry tells me that would move the intake port up (at a 48* angle) .137" relative to the head port, which would line the roofs up almost perfectly.
    This solves one additional problem and creates another: the front and rear end gaps were too tight for the Mopar end gaskets - the gap with the .060 gaskets was only .125, but should be about .20 compressed. The .188 intake gasket, however, overcompensates, and ends up with a gap about .10 too tall. My solution here is to get .1" plate aluminum and mill it to fit and bond to the bottom of the valley cover of the intake. This has a side benefit of creating an extra airgap, increasing the thermal isolation of the intake.
    Of course I could have just bolted them on and cranked up the boost and nobody would ever see it... but that's not how I roll.
    Last edited by carlmon; 07-10-2016 at 04:07 PM.

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    While I'm waiting for that fat gasket, I'm getting irritated by those giant choke points in the head ports caused by the push-rod holes:
    P1010036.jpgP1010038.jpg
    That dam push-rod bulge chokes the 1.14 width down to 0.88"! Unacceptable! So I'm going to make push-rods with gaps in the middle so they won't interfere with the ports, fill the holes and grind them flat.


    Kidding! You can't do that. But what I could do is measure the location of the holes and determine the metal is .1" thick - plenty of material to mill the intrusion down .080", safe to do on a milling machine. I may cut until I see air, and sleeve the holes with thin wall brass tube to reseal them, for an extra .020 width. If Edelbrock was really cool, they would have made the push-rod holes 3/8 x 5/8 oval so you could get another 1/8" width in that port (you don't need as much fore and aft clearance). I guess I could fill that hole and cut an oval hole myself, but there are limits to my disorder.


    Those choke points will still be there after I'm done with them, choked down to about 1" from 1.14' - so there's no reason to gasket match that side of the intake runner. It would actually be better to leave it as is to reduce the flow that hits the intrusion, and maximize the opening on the other side (narrow the wall between the port pairs) - won't be able to get it up to the full 1.14", but every bit helps at the choke point.


    I'll update this when the fat gasket comes in- don't want to grind anything until I've triple checked alignment with the actual gasket. Then I'll go to town on the heads and intake while the machine shop works on the block.

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    proper write up, very interesting! thanks!
    98 ZG 318 limited: np 242 swap,dana30hp swap,aussie locker, shift kit, optima red, 170lbs reduction, 5.9 vents, kn air filter, air ram, 1.7 HS RRs, SCT 93 oct tune, magnaflow muffler 12255, magnaflow hi-flo cat, spectre air hat, 2x52mm tb, 5.9 efan swap, ngk fr5-1 plugs, mopar perf wires, new cap 'n rot, maxxperf coil, iat relocation, roof lights, pirelli scorpions on masitaly 16x7 rims ET=0, ome HD coils +2",rubic exp +2"shocks, skyjacker ss, rubic exp adjustable front arms, jks rear+procomp front trackbar, prothane engine n tranny mounts, prothane sway bars bushings, drilled n slotted rotors, aeronautical front brake lines, purple led into front grill, hella h4s 100/55w, osarm h3s 55w.
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    Got the Cometic .188 gasket in:
    p1010040.jpg
    Now that's a gasket! My trigonometry worked out perfectly - notice the gasket scribe marks on the roof of the head and the intake are almost exactly the same, which means the roofs line up perfectly:
    P1010045.jpgP1010047.jpg
    A tiny amount of grinding the roofs will match both to the gasket for a very smooth transition. The floors will remain untouched - it's actually desirable to slow the floor air a bit so it can make the short radius turn at the front of the valve bowl. The lateral port location on the Cometic gasket is slightly more favorable than the Felpro, with the dividing wall a little narrower at 0.2" - the dividing walls will be ground to match to relieve some of the pressure on the push rod choke point.
    Also, notice the larger gap at the bottom:
    P1010041.jpg
    This was .125 before - now it's about .30 as expected, to be filled with .1" aluminum plate and Mopar end gaskets.

    The guy at my machine shop suggested I need to mock-up the rocker arms and push rods before I grind away the push-rod port intrusions. With higher spring pressure for supercharging, apparently I need larger diameter push rods, so need to test fit, and do any clearancing on the holes before removing the excess metal on the port side... which also means I need to buy my rocker arms now. I want to use full shaft rockers for maximum stability, but the only ones I could find for the Edelbrock heads were pair-shafts (not full shafts) from Jesel ($1100) and Hughes ($640). Sounds like a no brainer, but I know one local guy who said the Hughes version pulled the studs out of the aluminum heads, and he had to have them repaired. Looks like the Jesels have the same type of mounting, which is why I want full shafts... so I'm kind of stuck for the moment. I suspect the full shaft rockers made for the stock Magnum heads would fit, except they would use different thread bolts for mounting the bases, and larger bolts might not clear the shaft. My only solution might be to make custom threaded inserts to make existing full shaft kits work. Anybody know something I don't, please let me know!
    Last edited by carlmon; 07-19-2016 at 01:40 AM.

  8. #8
    RallyJeep GO
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    Stud / pedestal rockers like the Harland sharps (which are paired) and others should work. You might need to drill / tap the heads for a larger stud for more strength though. Stock magnum rockers use 5/16" studs, IIRC. 3/8" is common and IIRC, you can get rockers with 7/16" studs as well.

    What are you running for valve springs in terms of seat and open pressures?
    1998 ZJ 5.9 Limited - Deep Slate
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    Hughes and Harland aluminum paired 'shaft' setups still have a split trunnions, which is where aluminum rockers usually break. At least the Jesel ones have full width trunnions, but they're twice as much $. Theirs, and full shaft rockers are much stronger since there is no gap in the rocker arm to accommodate a stud. If a full shaft kit would fit with minor customization I'd go that route. I know it's overkill, but that's my middle name. There is no penalty for overkill, but underkill can come back to bite you.

    Don't know about the springs yet - depends on the cam specs, but the springs that came with the Mopar/Eddie heads are far too wimpy. They are the springs from the Eddie 61779, which is weird since Eddie makes the 61775 with heavier springs specifically for hydraulic lifter on the Magnums, and these are Mopar Magnum specific heads. Anyway... I won't be running high RPM, but the boost will require heavier springs on the intake valves, and I might be able to use these wimpy springs for exhaust. We'll see what the cam manufacturer recommends.

    Oh... and drilling/tapping the heads is an iffy proposition - as it is, the intake stud holes pierce the intake ports, so those studs have sealant on them. Also, they have 7/16-14 studs with helicoils. That's why I was thinking I could make custom inserts - remove the helicoils and convert the existing aluminum oddball helicoil thread to 3/8, or whatever a full shaft mount comes with. This is what Hughes did to get their smaller paired studs to fit, and I'd have to do just as much work to keep theirs from pulling out as I would to fit full-shafts. I'm sure it would actually be easy if I had a full shaft set here to look at, so maybe I'll just order one to try. Have my eye on a chro-moly arm set from Comp that's almost as light as aluminum, but stronger and lots of spring clearance, and more overkill.

  10. #10
    RallyJeep GO
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    I'd figure out what your spring pressures will be before going crazy. My valve springs are 145 lbs on the seat, 304 lbs at .512" lift (max lift for my cam with 1.7 rockers) and I've spun it to 6k plenty of times with the basic 5/16" stud Harland Sharp rockers. No signs of fatigue on them or anything and I've spent plenty of sustained time in the 4000 - 5500 rpm range.
    1998 ZJ 5.9 Limited - Deep Slate
    Mods: Big trans cooler, 231 swap, Indy MA-X heads prepped by IMM, Comp 20-744-9 cam, 1.7 HS roller rockers, 52mm TB, Airgap manifold, DT headers and full 3" exhaust, SCT tune homebrewed by me, Martin Saine valve body, B&M tranny pan, magic suspension made from unicorn tears, power steering cooler, lots of lighting mods

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    Porting update time:
    As I mentioned I might in post 5 above, I decided to sleeve, or 'tube' the pushrod holes. When I ran the calculations, the airflow that I need for the expected power demands a 2.05"^2 choke point, which means I need to open the port right to the edge of the holes, and in some cases, due to casting variances, I actually broke through... but that's the whole reason for tubing.
    You have to ream the holes with a proper reamer first. The pushrod holes AND the head stud holes (which also had to be tubed) were .544", so I got some thin-wall 9/16" tubing and reamed the holes to .5626". AFTER the porting, the tubes will be permanently installed and sealed with JB Weld. Of course, you only have to do the holes near the ports, so only 6 holes per head - circled so I don't screw up and ream the wrong holes in this pic:
    P1010067.jpg

    After measuring, establishing best port alignment, scribing gasket marks, reaming, and test fitting the tubes, I opened up the mouths of the intake bowls with a mill. Pros that have done porting for years do it by hand with a die grinder and burrs, but the mill let me take off down to .001" accuracy to keep them as even as possible without worrying about slipping and gouging something (like my finger!). I started with the dividing walls between the port pairs, and then opened the pushrod side to 0.988" (originally 0.88"):
    P1010050.jpgP1010051.jpgP1010052.jpg
    In the first pic you can really see how much the pushrod holes protrude into the port, and really limit airflow - by far the tightest choke point, now opened up by 12%...

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    ... but once those were opened up I could see how much the head stud holes protruded deeper in the port... photos of before, and after milling one side for comparison:
    P1010070.jpgP1010083.jpg

    And another angle looking down the bowl:
    P1010087.jpgP1010088.jpg

    You can really see what a speedbump that casting hump is for fast moving air (especially supercharged air).
    I used a ball mill because that deep in the port the wall curves toward the valve - the ball mill leaves smaller grooves that are easier to clean up. After removing most of the meat, I cleaned up the small remaining bump with sanding rolls to the point you can't feel any bump now - sorry, no pics yet after the hand work.
    Up next is deshrouding the valves, and general cleanup of the combustion chamber, and mild bowl smoothing (the bowls came pretty well prepped out of the box).

    I should mention opening up the choke point and aggressively enlarging the ports is a terrible idea unless you've done the math. For a street motor you're better off having a port that's too small than too big. I did the math here, and opened the choke point exactly enough to barely support the maximum expected airflow, and apart from moving the stud speedbump I didn't enlarge or alter the port design. I haven't remeasured their volume yet, but I expect they will be only 2 or 3 cc's bigger than out of the box, so should flow better without reducing air speed.

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    Got the head porting done and tubed. Intake ports ended up 181cc, about 5cc metal removed from the casting. I took them in for flow testing - very happy with the results!
    IMG_3864.jpg
    Pre-porting:
    .100 ......200...... .300 ..... .400..... .500 ..... .600
    62/52 119/105 175/142 225/169 251/185 260/190
    Ported
    70/52 130/105 202/142 262/167 282/175 288/188

    More flow across the board, even at lower lift it's still around 15% more flow, probably due to deshrowding the valves by widening the combustion chambers (I punched them out to a full 4" width). At max lift (.530 with my cam and lifters) it's about 288 - about 25 CFM higher than out-of-box, but I especially like the low-mid numbers - the flow at .400 lift is a massive improvement.

    This should be a very good match for the M1 2bbl, that flows 270 before porting, and I expect it will meet or slightly exceed the head flow with the enlarged plenum and porting. Should be an awesome setup for a supercharged street niner.
    Last edited by carlmon; 10-17-2017 at 04:58 PM.

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    Member JGC403's Avatar
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    Nice write up and nice increase in flow. You are correct in thinking that the center divider and the roof are the most important areas to have aligned. I have and old Mopar Performance book that confirms that. But not for the reasons you are thinking. I don't agree with this statement:
    "Also, because the air has to turn down in the port, most of the air-fuel mixture flows along the roof, making the roof transition the most important part."
    Most of the fuel is at the bottom of the port not the top. Fuel tends to fall out of suspension and go toward the floor, plus the injectors are pointed at the floor of the port inside the head, past the intake manifold transition. Even with a Carburetor the fuel has even more time to fall out of suspension and move toward the floor since the air/fuel mixture has the entire port of the intake manifold and the head to travel instead of just in the head like with the fuel injector.
    No replacement for displacement!

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    Thanks! About the roof flow: I may have been looking at it backwards - you WANT faster flow at the roof, because that's how you get more air to flow into the cylinder, but that doesn't mean it happens. You avoid killing the speed by making the roof transition smooth. In contrast, you want the floor flow to be slower so it can make the tighter turn into the front of the valve, and making it slower by inducing turbulence there also helps keep the fuel suspended. And you want the entire column of air making the turn in unison, so the roof flow has to be faster than the floor, just like the outside tires have to roll faster in a turn.
    If I had just bolted the intake on with a standard .060 gasket I would have given up the advantage of raised ports the heads came with - essentially free power by raising the intake! Even if you don't go medieval on the ports with a die grinder, it pays to get the roofs lined up. You can always stack multiple gaskets to get the right lift, if you can't find the right one.

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