head gasket for E31 with 280 valves

[bob m]

I am rebuilding an E31 head using 280 valves. The stock 280 head gasket does not give enough clearance to properly unshroud the valves. Is there an aftermarket head gasket that has a larger bore than the stock 280? I am going to use the head on an F54 block and will champher the bores as well.

I know several people have used this combination and I would appreciate any knowledge they gained from their experience.

Regards

Bob M

[Phred]

Bob,

I have used the stock 280 Datsun gasket #11044-N4221 without any problems, even with modified heads. Just to double check, I just laid one on a modified E-88 head which has 44mm Int. & 36mm Exh. valves. There's plenty of room. Don't unshroud the valves (Grind the chamber) beyond the stock gasket. There's nothing to be gained except lowering your compression. If you're experienced with a die grinder, you can scribe the gasket line on the face of the head. Grind out to the line, and then you can slightly undercut the chamber at the side of the chamber where the valve is closest to the edge of the chamber.This will allow flow around the edge of the valve. Believe me, I've messed with these heads on the flowbench and there is little to be gained. You could gain more flow by working on the valves and seat area. E-31's are good heads, unless you're building an all out race head, don't carve it up. Also be very carfull relieving the top of the block. This will help flow on an engine with a big cam. But its mostly for valve to block clearence. Measure how far down the top ring is, and lay a piece of tape .050 above that. Do not go any lower. This also takes some experience with a grinder to make a nice smooth, conservative, properly radiused cut. Good luck.

Phred

[bob m]

Thanks Phred, I appreciate your information. I want to end up with a fun sports car I can use on Sundays. I have had the car since 74 in stock condition (lowered,5 speed,exhaust)and enjoy driving it. I am working with a speed orientated machine shop and want to make this head breath as much as possible. There is about .040 clearance from the edge of the combustion chamber to the gasket which does not seem to leave much room to unshroud the valves. Has this worked for you? It should have 10.25:1 compression with this setup before decking the head and block so I am not adverse to lowering the compression. I have not decided on a cam but am considering a 260/280 cam reground for this motors specs. I am going to use the SUs with Ztherapy needles and jets.

Any other suggestions?'

Regards

Bob M

[jmortensen]

I have an E31 and L28 combo and I took out about 1/8" (it was a lot) around the edge on the intake side of the chamber to unshroud the intake valve when I matched it to the Nissan L28 headgasket. I took some out of the exhaust side as well. Sounds to me like you have an L24 gasket, not an L28 gasket. But that is just guessing. I'm with Phred though, something doesn't add up.

I did also notch the block to match the head so that there was an open space around the valve when it was all the way open. I didn't use a flow bench, just common sense. I don't know exactly what the results were, but I can say for sure they were better than before.

I wouldn't have thought that undercutting the chamber before the head gasket as Phred suggests would do much good. It might increase the flow at lower valve lifts, but at full open the valve is past the headgasket into the bore. Again, I've never used a flowbench, so maybe I'm just plain 'ol wrong on that one.

The other thing I concentrated on were the triangular wedges between the valves. I cut those down A LOT. I also polished out the circular machining marks around the valve seats, and took down all the sharp edges, including the triangular patch of spark plug threads that stick into the chambers. I also took down the walls where the chamber meets the deck of the head farther away from the spark plug. On the E31 there are 2 sharp ridges there with some pretty poor casting. I polished out all the crappy casting and took the sharp ridge out.

My only suggestion would be go big on the cam. I have a 490/280, and the head got shaved a bit so I believe I'm in the 11:1 range, and I have to run 95 octane to keep it from pinging. I'd go at least 280, maybe a little bigger if you can find it.