81A heads?

[Bassman/NZ]

What's the story with 81A heads when used on a 59A engine? Better chamber design? Higher compression? Do the valves clear, or do the chambers have to be cut?

[JWL]

This is an interesting question. According to the Service Bulletin information the standard 81A heads have 79 to 81 cc combustion chambers. I know there have been some recommendations that these heads can give a boost to the 59A engines. However, I fail to see that based on this Ford factory information.

There was a "high altitude" head with a 81AS designation which could be a viable option for elevating the compression ratio but my sense is these are more rare than the 30 year old virgin.

[Kube]

Originally Posted by Bassman/NZ

What's the story with 81A heads when used on a 59A engine? Better chamber design? Higher compression? Do the valves clear, or do the chambers have to be cut?

Chambers need to be cut a bit.

[scooder]

I've cc'd 81A heads, both iron and aluminium. Result 80cc. The 59AB head has about 76cc. Then 8BA went back to 80cc.
All stock uncut heads that I measured.
Based on this, swapping a 59AB head for an 81A would be a step in the wrong direction.
Martin.

[scooder]

As kube said, the early heads need a clearance cut for the valves if installed on a 59 up block. So you now have even bigger chambers, less compression.
Martin.

[Ol' Ron]

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Having a bit of trouble believing this. I've used several sets of 81A heads and found them to be much smaller in volume. I have a set in the shop I used on an 8BA engine for several years. Yes the valves have to be clearance at the top of the chamber, but the amt of material is negligible. Because of this I have recommended this swap. 'll check them again.

[scooder]

I'd love it if you check what you have there Ron. I've measured quite a few 81A heads and they all come in at 80cc +-1cc.
81AS heads are a bunch higher compression as JWL said they be rare.
Martin.

[rotorwrench]

The Chart that was on the HAMB list them at 80cc on one side and 78 or 79 on the other depending on whether it was A or B design change. There is only a slight difference at 4cc from the 59 series and a modest skimming of the parting surface would likely get it there as long as the piston clearance was still good.

[Bruce Lancaster]

81AS is listed in the bulletins as 60 CC, I think the highest compression head Ford cataloged.
S means I think that it was strictly over the counter, not used in production. Probably S stands for "service" or "special."
The only cataloging I have found says somethink like "natural gas and high altitude"
It was apparently discontinued before WWII and so was hard to find when stock car types discovered it. Ron has a baxkground in the Danbury flathead racing, I bet he has some of those!
Canadian bulletins rated all the heads for both 221 and 239, listing it as producing 8 to 1 on a 239 motor.
There were also a couple of bigger CC S heads designated for 239 use originally.

[Bassman/NZ]

Interesting stuff. Thanks guys. It will be interesting to see what Ol Ron comes up with.

[Ol' Ron]

Well I forgot about this until I just opened up the Barn, so I went out in the shop and after much diggen found them. After sanding down the paint I found so many numbers and letters that I have to photograph them. Just put a light layer of white paint on them. Will dig up my CCing mesuring stuff tomorrow.
To B honest the chambers do look big, unfortunately these heads were clearanced for a hi lift cam and have been milled. on all heads I use I always increas the angle at the end of the transfer area to 45 or better. Will try and remember to check them out tomorrow.

[47 flatbed]

I was hoping that this was an upgrade for my 59ab also. I pulled these heads off my 39 3/4 ton truck. Intresting I would have figured there would've been th 81t heads?

[Binx]

81As on a stock bore 239 is 6.5:1. .080 over is still just 6.8:1

Lonnie

[Ol' Ron]

OK, here's a picture of the combustion chamber. You can see the clearance for the valve lift and the small dome circle. I think the heads were milled 20 or 30 thou. for piston to head clearance. The chamber measured 74cc, now add 15 cc to this ( fudge factor for gasket and valve eye brows , etc and you come up with a CR of 6.4 on a 239 engine

You might ask, where did the fudge factor come from??
well after spending many days and months checking compression ratios on a varity of heads and engines I found that adding 15cc o a stock engine was pretty close to the real thing. now if you've relieved the block in some way you'll have to do it the old fashion way
So I guess I was wrong, don't like to do that. Pobody's nerfect.

[Ol' Ron]

btt

[scooder]

Ron,
Thanks for taking the time to do that. Those heads look (compared to mine) to have had a fair cut in the valve eyebrow area. As they've lost the curvey swoopy shape, and I'd hazard a guess at more than a 0.030" shave. I base this on the fact that mine have the dome area that starts about 0.015-0.020" from the gasket surface. To clarify, if I shaved 0.015" off my heads, the dome would still be full diameter, not the small diameter that yours have.
I've assembled a 99A block with a 4" crank using sock 3 3/4" pistons, which obviously had the piston popping out of the block. With a new un torqued head gasket, the stock 81A with its deep "counter bored" dome actually clears, only just (a couple of thou if I recall correctly) but clears! There deep.
If I shave them for 0.040" squish, with 3 3/4" crank and stock pistons, I'd need to cut 0.080"+ (if I recall correctly, I'm away from my notes) off them.
Martin.
Ps. Your a lot closer to perfect than I'll ever be, my short term memory is really really bad, so I get it wrong a lot!

[Ol' Ron]

I try different things, especially when we were racing, however, the engine on a short track is not as important as the driver and the cars handlng. And especially the tires. You need just a good engine. I didn;t figger this out for several years. Get on the throttle sooner, and drive in deeper. That's the key.
PS these heads breath very good.

[Lawrie]

Before I made my own heads on our dragster,the ones that it went best on were 8Rt cast iron truck heads.
Lawrie

[47 flatbed]

In the short these heads will not improve compression any more than the stockers on the engine now?

[Bassman/NZ]

Thanks guys for the interesting reading.