Good evening everyone,

I am in the middle of an engine overhaul on a 1973 240z. I am having to replace the original head, because it was warped beyond salvaging. I picked up an E88 head from a guy, but it appears to be from a 260z and it has larger exhaust valves then my original head. I was told, today, that I will have clearance issues with the exhaust valve hitting the cylinder. Can anyone verify if this information is correct? If so what are my options can the exhaust seats be replaced to accept the smaller valves? Any other options? I was also told that this particular head does not flow the exhaust as well as the smaller valve E88, is that correct?

Thanks in advance for any help you can offer, I did check the search function, but didn't find an answer.

Craig

The L26 block was the same bore size as the L24. You should have no clearance issues for the larger exhaust valves. That is only a problem when using the later 280Z heads that had bigger intake valves.

As far as exhaust flow differences (if any), I don't think it will be significant for a normal street motor.

Arne is right. The exhaust valve wont be a problem. The L24 and the L26 had the same 83mm bore size.

The head will lower your comp ratio a bit. If its the last E88 head, they had a combustion chamber size 47.8cc. If you had an E31 with 42.7cc it will drop the comp ratio from 9.1:1 down to 8.5:1 if you run it with a 1mm headgasket. You could notice that, depends on your driving style.

You can calculate it using this website. Note the E88 data is for an Australian head so you need to correct the combustion chamber to 47.8cc to suite the emmision design.

Engine Design Utility

Chas

The L26 block was the same bore size as the L24. You should have no clearance issues for the larger exhaust valves. That is only a problem when using the later 280Z heads that had bigger intake valves.

As far as exhaust flow differences (if any), I don't think it will be significant for a normal street motor.

Yes, the L26 shares bore diameter with the L24, but the L26 is notched from the factory for exhaust valve clearance!

I thought the same as you Arne, before I was corrected on this.

Arne is right. The exhaust valve wont be a problem. The L24 and the L26 had the same 83mm bore size.

The head will lower your comp ratio a bit. If its the last E88 head, they had a combustion chamber size 47.8cc. If you had an E31 with 42.7cc it will drop the comp ratio from 9.1:1 down to 8.5:1 if you run it with a 1mm headgasket. You could notice that, depends on your driving style.

You can calculate it using this website. Note the E88 data is for an Australian head so you need to correct the combustion chamber to 47.8cc to suite the emmision design.

Engine Design Utility

Chas

No, the exhaust valve will be a problem, on a stock-bore L24. Refer to my above post.

I believe notching was recommended to allow more room for the exhaust to breathe around the valve. I notched my block on both sides.

You can eliminate the problem with a simple notching of the block (for the exhaust valve).....a better solution is to get an early E88 or E31 head.....they aren't that hard to find and will give you a better performing engine (higher CR). IMO

True the earlier head would be better, but in most cases the head needs some work-as in valve guides or seats, so you might as well upgrade to the bigger exhaust valve.

You can eliminate the problem with a simple notching of the block (for the exhaust valve).....a better solution is to get an early E88 or E31 head.....they aren't that hard to find and will give you a better performing engine (higher CR). IMO

The bigger exhaust valve ain't going to do that much for performance. If you want performance, buy an early head, install the L28 hardened seats, L28 valves and notch the block......or better still, bore .040 over and you won't need to notch the block. The late E88 heads are just plain poor as far as performance is concerned.

First let me thank everyone for their response, this forum is a wealth of information. Second let me ask a couple of more questions, if I go with .040 over pistons, does that take care of this problem? Third can I regain some of the performance by shaving the head?

Thanks again,

Craig

ZWolfe......Yes, if you bore.040 over, you won't have to notch the block. Notching the block is not difficult either, as long as you don't go deeper than the ring or back under the head gasket. The late E88 head is probably the worst performance choice you can make for an L series engine IMO. The early E88 and E31 heads used brass valve seats which are incompatible with unleaded gas. If you go that route, you'll need to have hardened valve seats installed. If you do go that route, you can install L28 valve seats and L28 valves and pick up a nice combo for your L24 block. If you do go with the bigger valves, you'll have to notch the cylinders for clearance of the bigger exhaust valve. If you bore .040 over, no notching is necessary.....you'll have enough clearance for the larger exhaust valve.

You could have the combustion chambers welded & reshaped and have the steel valve seats installed at the same time. Thats what I did...

Thanks guys for the additional info. I just dropped $100.00 on this head, I hate to start over looking for another head. This appears to have steel guides and seats in it already, is that the way the 260 came? I was planning on shaving it .030, port matching the intake and exhaust and polishing the combustion chambers. Will any of that help, or am I just putting lipstick on a pig?