High Compression Head

German guy

German guy

Senior Member
Any comments regarding the Snyder's 5.5:1 head to replace my stock version? I have read a number of comments on this site recommending 6.1:1 or even 6.5:1 but also several claiming that they add significant stress to rods, and bearings. There seems to be a level of disagreement regarding that issue and I would rather err on the side of less stress and slightly less compression while still improving performance so that I can make it up the steep hills in my area in 3rd gear. My concern is a few posts stating that there have been machining issues with the 5.5:1 heads. Are they all made by one manufacturer? Is the one from Snyder's particularly problematic? Overseas shipping and customs duties makes returning defective parts expensive. I will appreciate any input.
 
There is no actual data I know of that indicates the increase in stresses as a result of running a 5.5:1 or 6:1 head. There is an increase in stresses, but the number of Model A's running these heads indicates the increase in stresses is not deleterious. To the contrary, the benefits of running a hi-compression head are very favorable, and include higher gas mileage, lower operating temperature and more power. I have been running hi-compression heads with babbitt bearings for many thousands of miles.
 
Diesel engines of the Model A era ran compression ratios of 14:1 to 16:1 on babbitt bearings.
 
Increasing hp output does increase stresses in the engine
This is a fact and cannot be disputed
Yes diesel engines do run a much higher cr but the bearing design is much different than the Model A

What damages the A engine is detonation or pinging
This is the uncontrolled combustion in relation to crankshaft position and it will damage the crank/rods and bearings

Any of those heads mentioned will increase the hp and all of them will require less ignition timing advance

J
 
If your engine is in good shape, the higher compression heads won't hurt it. If you are cruising down a level highway at the speed you did with your stock head, then the stress on the engine is about the same. I would recommend the 5.5 head based on its combustion chamber design, but I don't know about any fit up issues.
 
I also run a high compression heads and I've done many thousands of miles with them. I have learned that the higher you go, the more fussy these old girls get about their timing - ignition timing, that is. What did you think I meant??
I suggest finding out (ask here) how much advance is allowable with whatever head you choose and obtain a distributor with auto advance limited to that figure. It is too much advance that will spoil the high compression experience. Get it right and you'll wonder why you didn't do it years ago.
 
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with the roads in Germany/France go with the 6-1 head.

It doesnt make a difference compared with the 5.5 head. a little more output.....
 
Gutentag German guy! As John Neilson says, use less timing and all will be OK. Early Miller's and Offies ran babbitt at Indy, and that is stressful but they survived foe 500 miles of full throttle racing!
 
I have both 5.5 and 6.1. Honestly I cant tell much difference. My 5.5 is in a pickup, the 6.1 in a sedan. The pickup will run circles around the sedan, but its lighter. I would not hesitate to use the 5.5.
 
The Snyder's 5.5 head works well for me. A Centrifugal advance distributor such as the Model B ford unit or the new Super B+ to give better timing control is also good.
 
butch chase said:
The Snyder's 5.5 head works well for me. A Centrifugal advance distributor such as the Model B ford unit or the new Super B+ to give better timing control is also good.
Click to expand...

I googled "Super B+ distributor" and didn't find anything. Can you give more details?
 
Bruce of MN said:
I googled "Super B+ distributor" and didn't find anything. Can you give more details?
Click to expand...


It’s a new product being made by a small shop in Missouri. Supposedly it has the same performance as the original B dizzy but without the maintenance headaches. Casting looks like a Mallory. No info available online yet.
5b19e09bba92d9a94446a95b1578cf14.jpg
 
The Super B + is a new distributor from Mean's Garage in Missouri. its built from all new components and has an advance range like the Ford Model B, hence the name. Looks like Mallory, All service parts are locally available.
6 of our club members are running them with good results. Easy starting and good acceleration.
See post 12 for contact info. There's also a Ford Model B distributor Facebook group that has photos.
 
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Thanks for the additional info regarding the Super B+ Distributor. I sent an e-mail to them for pricing, information regarding installation, and if any special modifications are necessary.
 
As noted, timing is important.

Before making expensive modifications, try retarding the spark on uphill runs, advance downhill. You may find the standard 40HP engine up to the task after all.
 
I drove a Babbitted Model A engine coasts to coast and back three times on the great race, plus thousands of miles just driving, with an 8/1 Thomas head on it. No damage to anything. Often drove 70mph and more. Any compression increase theoretically shortens bearing life on any engine, but driving habits cause more bearing failure then anything. Do not lug these engines and with good bearings done correctly they will last many many miles. Most engine failures in these cars are caused by bad machine work or incorrectly driving the car.
 
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