Headgasket for Kb399 and 302 Heads

[72DMag]

Looking for some advice or a way to measure the clearance between the dome of the kb399 318 pistons to the cylinder head. The dome on these 318 pistons for those that don't know isn't on the quench pad it's in the valve area. Looking for high compression and with the pistons off they fit in the 302 heads. Would the .039 felpro gasket be enough?? Should I get clay and just set the head on the block to see how much room I have or has someone else on here ran this combo? Thanks

 

[rumblefish360]

Should I get clay and just set the head on the block to see how much room I have

This is exactly what I would do. IF he piston can simply be moved up and down past the TDC spot without a gasket, the clay will tell you the clearance and point to a head gasket thickness.

 

[72DMag]

@rumblefish360 thanks. i should also mention block is stock height and with dial indicator i got .194 out the hole at the dome. Looking for .040 clearance to be safe. Thanks!!

 

[Max1196]

Or play doe.

 

[rumblefish360]

Where does the low flat area sit?
(Not the outer most flat area.)

 

[72DMag]

Sorry for late response!! Life has been little crazy.

@rumblefish360 the flat part of the piston is basically zero deck at .005 in the hole. When I did the putty on the 302 heads with the dome of piston. There was plenty of room. closes thing was the spark plug. With the head bolted on and NO headgasket I got .188 clearance measuring the puddy from tip of spark plug to the dome.

I dont see a reason why that wont work. My concern at this point is valve lift. On intake with piston at TDC I got .353 when the valve hits piston. On exhaust I got about the same. Fyi these are stock valves in the 302 heads.

The cam I wanted to run is a hydraulic roller and I was going to use solid roller lifters. The cam has 468 lift on intake and 475 lift on exhaust with 1.5 ratio rockers. Duration at .050 is 230 on intake and 234 on exhaust. Valve timing events are as follows. Intake opens 7 btdc and closes 43 abdc. Exhaust open 45 bbdc and closes 9 atdc.

I'm far from a cam expert but I'm afraid there might be no room for that lift with these heads and the kb399 pistons. Sigh can someone more knowledgeable confirm that?

I know you guys like pics so I attached a bunch. Yes the bench in background is a mess

 

[Rat Bastid]

If I’m following what you are saying, you can’t measure P/V clearance for maximum valve lift at TDC. The valves are nowhere near max lift at TDC.

Max lift on the intake will be at where ever you degree the cam. For example, if you install the cam on a 106 Intake Lobe Centerline you will be at max lift at 106 degrees After Top Dead Center.

Max lift on the exhaust is After Bottom Dead Center.

Always, ALWAYS degree the cam. Always.

 

[72DMag]

@Rat Bastid No cam has been bought or installed. Taking measurements to predict what cam lift and duration will work using valve drop test at TDC.

I did forget mention cam I am considering is 108 lsa and installed at 108 intake center line.

 

[rumblefish360]

Rat B nailed it. As the piston is traveling up or down, the valve is at max lift when the piston is far away. As the piston rises, it will start to come close to the valve and hence why you check it with clay and a few rotations. That’s the only way to know for sure unless you have someone that used the same or larger cam. Take note of the timing events of the valves.

For the first time ever I ran into piston to valve clearance when I installed 1.6 rockers on a Hyd cam at .546 @ a 1.5, 582.4 w/1/6 rockers in my 340 with 10.5-1 replacement pistons. Small dome on them.

While I always go for the extra lift, it is t really needed in most cases, but it is grabbing as much as possible as to not leave anything on the table. Ether you can or can’t! But don’t sweat it if you can’t.

 

[72DMag]

Thanks!! I'll reach out to comp cams. I did a similar measurement for them so I could get max lift on a 383 cam I built with old school trw dome pistons.

Predict piston-to-valve clearance before ordering a cam with a valve-drop test

I think I'm good on all other clearances and should be fine with an .039 head gasket. I do see why Keith black states these dome pistons can't be used on magnum heads or closed chamber aluminum heads. I think the 302s are as closed chamber as you can get.

Doing a quick check that puts compression ratio roughly at 11:1.

 

[Max1196]

Rat and Rumble have got it covered. The "overlap", both valves open at the same time, is the factor in question. BUT that amount has nothing to do with the total lobe/ valve lift. the piston is long gone away from the valves at max lobe/ valve lift.

 

[Rat Bastid]

Thanks!! I'll reach out to comp cams. I did a similar measurement for them so I could get max lift on a 383 cam I built with old school trw dome pistons.

Predict piston-to-valve clearance before ordering a cam with a valve-drop test

I think I'm good on all other clearances and should be fine with an .039 head gasket. I do see why Keith black states these dome pistons can't be used on magnum heads or closed chamber aluminum heads. I think the 302s are as closed chamber as you can get.

Doing a quick check that puts compression ratio roughly at 11:1.

View attachment 1716012657

I get what you are doing. Valve drop at TDC. But you don’t use max lift because it doesn’t happen there.

You have to know the valve drop at TDC for the cam you are using at the installed intake center line.

If you know what lobes you are using, Comp lists valve opening for all their lobes in the lobe catalog.

If you have those numbers you can drop the valve at TDC and see what you have.

Of course, you will have more clearance than that due to head gasket thickness and lift loss due to rocker arm flex. That’s a whole ‘nother conversation.

 

[Hysteric]

I dont see a reason why that wont work. My concern at this point is valve lift. On intake with piston at TDC I got .353 when the valve hits piston. On exhaust I got about the same. Fyi these are stock valves in the 302 heads.

That's more than I have by at least 100 thou with the same heads milled to 60cc and a block nearly zero decked for stock low comp pistons. Bolt it together with some plasticine or clay and turn the motor over a few times and that will tell how much clearance you really have. You can move the cam ICL around if you need to to get the required clearance.

That's the clearance with a Ferrea 1.9 valve . Tried Edelbrocks with 60cc chamber and the 2.02 valve will not clear those piston notches. The pistons are Enginetech cast stockers and that notch has been clearanced at least another 50 thou to get what I wanted. Cam is of unknown origin that measured 222/231 110 with 465 lift @ 1.5 rocker ratio. Don't forget you lose a little lift with the lifter angle as well.

 

[Hysteric]

Would the .039 felpro gasket be enough??

IMO I would go with an MLS gasket and get it the same size as the bore to reduce crevices and increase comp and the thickness you need for adequate clearance.