High compression heads - Worth it?

[kimlinh]

I'd like to know what everyone's experience with high compression heads has been. I'm sure the extra power is nice but does it come at the cost of shortened bearing life. For engines with the original splash lubrication is the extra bearing load noticeable in shortened bearing life. Also how much performance difference do you notice between stock heads and a 5.5 or 6 to 1 head. My car runs very well but it could use a little help staying out of the way of modern cars when climbing hills. I don't drive on interstate highways so top speed is not a problem.

[Phred]

Assuming the bottom end of your engine is in sound condition, the short answer is:

YES

[Terry, NJ]

Around here, there are lots of hills, some fairly steep. I hate being the first one in a long line, poking up the hill, wishing I had a 3rd gear between second and high, so I'm ready for anything. In addition to HC heads, there is the old bored out intake manifold and a model B carb. (Boosts your output about 4HP , or 10%) and Aries muffler. All together, these mods give you about over 50 HP. Check it out, Google Piriano's Model A
Terry

[eagle]

My A is bone stock and I see no need for a HC head. I have the heaviest body, a Fordor, and do just fine with stock. I drive 50 mph all the time and would no matter how much power I had.

[captndan]

You must have two Model A's. One stock and the other with a HC head. Then you will know for sure.

[WHN]

Sponsored Links (Register now to hide all advertisements)

If you have a good running stock Model A they can be great drivers. Around town, on tours, off interstates, stock works great. No extra stress on 90 year old parts. If your not into the "mine is bigger or faster than yours", stock could be the way to go. Enjoy.

[Licensed to kill]

If you run a HC head I suspect you will lose that unique model a sound.

[29spcoupe]

I have a stock engine except for the HC head and a model b carburetor and ported out manifold. Performance is much better at the lower rpms, don't notice much of a difference at higher rpms. Much better on hills. John

[Dick Steinkamp]

Originally Posted by Phred

Assuming the bottom end of your engine is in sound condition, the short answer is:

YES

Which of his questions are you answering?

[harleynut]

You will lose the Model A sound.....no doubt. I have two As one with a Snyder's HP head and one without. One has 65 pounds of compression and one has 90 pounds of compression. The only difference I see is the higher compression helped a small difference on hills. I live in Pa and it's all hills. I asked the same question at Snyder's and they told me no problem with the Babbitt bearings if there in good shape. My opinion is if that's all your changing is the head, it's not worth the time and trouble of changing the head. Besides that, I like the Model A sound. My two cents.

[Marshall V. Daut]

Do a search using "high compression" or "cylinder head" as your key words. You will come up with more information and advice than you ever wanted to read. It's all there, so there's no need to reinvent the wheel here in a re-hash of the same input. People's opinions and advice from those threads will undoubtedly NOT have changed.
Marshall

[glenn in camino]

I have 2 model As with 5.2 police heads that have lots of power. They sound like Model As and run really well.

[Jim Brierley]

The 2 quickest and easiest way to get more power are higher compression and bigger carb. If you are going to drive it much, change the head and enjoy it. The Model A bearings, etc., are more than adequate to handle the extra power with no wear or other problems.

[wingski]

Guys, isn't a high compression head just one that has been shaved so the combustion chamber is smaller?

[Bob C]

Originally Posted by wingski

Guys, isn't a high compression head just one that has been shaved so the combustion chamber is smaller?

No, the combustion chamber has a different shape.

Bob

[TerryH]

I added the 5.5 head after I bought my car, and can honestly say it sounds the same to me. To me, the HC head works very well with an overdrive or a higher geared rear axle, allowing you to "pull" those higher gears and easier. If you are just driving around town, you won't notice much. For hilly country, second OD is wonderful and works very well.

[quickchange]

Hi comp head is like sex , once you try it you want more,

[Ernie Vitucci]

Good Morning all...I run a Snyder 5.2 or so head and a B Carburetor and a B Cam in the Distributor, a Mitchell Overdrive and that is all. I do have an oil filter and an air filter. I change 10-30 oil every 500 miles and lube 31 fittings at the same time. the old girl runs well and is quite reliable. I run 40 mph in 3rd gear and 55 in 3rd over on flat ground. The key is to drive gently and you can go anyplace you want. Ernie

[H. L. Chauvin]

Hi Kim,

FWIW: One humble opinion heard on one (1) vintage, very inexpensive method to increase an original Model A Engine's performance.

Model A racing engine re-builder, Mr. Ron Kelley, explained to me about many of his past experiences with testing horsepower on Model A engines on his "calibrated" dynamometer, most of which he recorded on printed charts in the past indicating horsepower and overall engine performance.

He said most never realize that one of the most effective horsepower gaining methods at the "least" cost to a Model A owner that he observed and tested is simply trying to increase the velocity and volume of the fuel mixture.

This method is related to what racing engine re-builders refer to as porting; i. e., smoothing engine interior surfaces adjacent to the where the fuel mixture is flowing.

Some Model A owners never understand and consider that smoothing the interior fuel passages to increase fuel flow is similar to one barely depresses a Model A accelerator where the carburetor butterfly throttle opens ever so slightly; hence, more of the fuel mixture is entering the combustion chamber at a more rapid rate which means the Model A engine's rpm's are increased.

This fuel/liquid/ air faster flow hydraulic engineering theory is not any different than that of using "Manning Charts" to determine the flow of fluids for designing engineered storm drainage.

For example, for fluids, because of interior surface friction, one can observe that:

A. Water flows faster in a new, clean concrete culvert than in an exterior drainage ditch full of thick grass.

B. Water flows faster in a new, ultra smooth PVC pipe than in an old very rough interior surfaced cast iron storm drain pipe.

Mr. Kelley further explained that while re-building stock Model A engines that he sees today, he observed several minor things can be done to increase engine performance only by slightly increasing fuel flow.

He recommends trying to provide smooth uninterrupted surfaces, (which causes turbulence and reduces fuel mixture velocity), where the fuel mixture flows such as:

1. Start by verifying that the interior of the carburetor venturi is smooth as opposed to having some of the earlier 1950's reproduction venturi's which had an internal lip which should be removed.

2. Verify that the carburetor to intake manifold gasket interior hole is enlarged where it does not protrude into the intake manifold thus causing turbulence. (Also, an old sagging Model A manifold with non-aligned openings at the engine block does not help to increase engine fuel flow.)

3. With a Dremel tool, smooth out the cast iron interior surfaces of the intake manifold and the engine's cast iron intake and exhaust ports. Smooth out very rough surfaces, protruding cast iron fins at corners and sharp corners; however, never cut deeply into the thin cast iron inside the engine ports such that one cuts into the engine's water jackets.

4. Remove and round off the sharp bottom lip on all valves and slightly round off the sharp top lip found on valves.

5. Insure there is no carbon build-up on the top surface of the engine block which can reduce valve opening size and fuel flow.

Just hope this can help someone some day.

[ursus]

Not apparently mentioned yet is that a high compression head will result in improved combustion efficiency hence better gas mileage.