08-21-2015, 04:17 AM | #1 |
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81A heads?
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?
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08-21-2015, 05:07 AM | #2 |
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Re: 81A heads?
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. |
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08-21-2015, 07:33 AM | #3 |
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Re: 81A heads?
Chambers need to be cut a bit.
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08-21-2015, 07:36 AM | #4 |
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Re: 81A heads?
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. |
08-21-2015, 07:39 AM | #5 |
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Re: 81A heads?
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. |
08-21-2015, 08:54 AM | #6 |
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Re: 81A heads?
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08-21-2015, 12:27 PM | #7 |
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Re: 81A heads?
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. |
08-21-2015, 12:51 PM | #8 |
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Re: 81A heads?
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.
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08-21-2015, 12:53 PM | #9 |
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Re: 81A heads?
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. |
08-21-2015, 02:51 PM | #10 |
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Re: 81A heads?
Interesting stuff. Thanks guys. It will be interesting to see what Ol Ron comes up with.
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08-21-2015, 06:54 PM | #11 |
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Re: 81A heads?
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. |
08-21-2015, 06:56 PM | #12 |
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Re: 81A heads?
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?
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08-21-2015, 11:22 PM | #13 |
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Re: 81A heads?
81As on a stock bore 239 is 6.5:1. .080 over is still just 6.8:1
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08-22-2015, 09:50 AM | #14 |
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Re: 81A heads?
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. |
08-22-2015, 08:27 PM | #15 |
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Re: 81A heads?
btt
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08-22-2015, 09:13 PM | #16 |
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Re: 81A heads?
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! |
08-22-2015, 09:28 PM | #17 |
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Re: 81A heads?
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. |
08-22-2015, 10:20 PM | #18 |
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Re: 81A heads?
Before I made my own heads on our dragster,the ones that it went best on were 8Rt cast iron truck heads.
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08-22-2015, 11:18 PM | #19 |
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Re: 81A heads?
In the short these heads will not improve compression any more than the stockers on the engine now?
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08-23-2015, 12:23 AM | #20 |
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Re: 81A heads?
Thanks guys for the interesting reading.
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