PROS and CONS of a high compression head

[marc silva]

I am finally starting the re-build of an engine. Do I put a high compression head on or not? Is it really harder on the lower end? I drive it like a wuss anyway but I want it to "go" when I step on the gas if I need to. Opinions please. Thanks for all your wisdom as usual.
Marc

[tpowel2]

Good question, I would like to know the same thing.

[colin1928]

Hi Compression Head do make more Horse Power
Every Horse power made in combustion chamber is transferred through the piston then the con rod then crankshaft
so if you go from 40 hp to 60 hp you add 50% Load and wear to these parts

[freak]

That said, I have one and it's been running fine for 10's of years.

[TerryH]

Most high compression heads do not add 20 hp; using Snyders 5.5 or 6.0 will probably net you around 10 more hp. As for extra wear and tear on the engine, yes if you drive hard and push it all the time, and aren't careful with timing and spark advance, you can do some damage. Many, many of our local club members have them, and they are probably the single most effective way to give your A a significant power boost without compromising the car. I have a Town Sedan, which is one of the heavier Model A's, and it certainly helped.
Terry

[Gary WA]

Sponsored Links (Register now to hide all advertisements)

What is so different with the timing and spark advance as with a stock head vs high comp head. Is the timing set different with HCH? thanks. Just finished stock eng today with High Comp Head. Ready to fire up tomorrow. What changes should I make prior to starting?

[Mike V. Florida]

You need to relearn the sweet spot for running the engine.
you should run cooler with better gas mileage.

I know of or read that anyone has said "Damn, I wish I left the original head on the engine."
The only problems I have ever heard of come from those that refuse to follow the instructions that come with the head to the letter.

[Mike V. Florida]

Originally Posted by Gary WA

What is so different with the timing and spark advance as with a stock head vs high comp head. Is the timing set different with HCH? thanks. Just finished stock eng today with High Comp Head. Ready to fire up tomorrow. What changes should I make prior to starting?

HC heads don't need as much advance as a general rule.

[tbirdtbird]

let us know how you make out

[H. L. Chauvin]

Hi marc,

Humble & serious response for you to maybe try:

A. If you presently drive a 1939 pick up & you want to know how it feels to drive a 2014 V-6 SUV, you could read & ask questions how it feels to drive this SUV for 10,000 years & never know for sure.

B. However, if you find somebody with a 2014 SUV that would let you try it, you could save 9,999 years plus 364-7/8 days of reading & asking questions -- not counting a leap years!

C. So, if you could possibly find a Model A owner in your area with a high compression head installed, you could actually "feel" the actual difference to decide if it fits your above mentioned term "Go".

D. In my opinion, your term "Go" will translate into your wanting a higher compression head in any language, foreign or domestic.

Just one opinion on how to "feel" the difference & get your project going.

[Marco Tahtaras]

They are a great addition. They don't do a good engine any harm. However owners ARE more likely to cause harm primarily due to improper use of timing advance. The low compression on the stock engine is very forgiving of misuse. The higher the compression, the more critical the proper use of timing becomes.

[Pete]

Originally Posted by tbirdtbird

babbitt can withstand to 7:1 compression

Would you believe 10 to 1 turning 4800 on mile dirt tracks.
Ed Winfield did it many times. He was almost unbeatable.

[colin1928]

Very true Pete but Ed like you Stripped down his engines after almost every event

[montanafordman]

I can think of one downside - with a high compression head (and also other common mods like lightened flywheel, b carb etc) you wont be winning the slow driving car games like you would otherwise.

[gwhite]

Originally Posted by tbirdtbird

babbitt can withstand to 7:1 compression

Citation, please?

[PC/SR]

gwhite: Weiand 7:1 head, carbs, cam, more speed stuff, no pressure oil except center main, babbitt bearings no problems. Personal redline is 4000 RPM. The limitation of the stock Model A babbitt engine is not compression but RPM.
Put on the HC head and enjoy. You will learn to use the timing lever as never before, and become a better driver because of it. Set initial timing in the normal manner. Play with timing to find your sweet spot. Advance and retard as you drive and learn how the engine responds. The engine is more responsive to timing adjustments. Half advance at full throttle for starters, more at cruise, full retard descending hills, for example. As you get used to using the timing you will start to keep your fingers on the lever and adjust it as you drive. It becomes kind of fun and part of the Model A experience.

[mleder]

PC/SR : With my A stuck in the garage till this hard winter ends I can't try out your suggestions right now however I would like a little further explanation on the full retard for descending hills. Are we talking mountain country hills ? regular rolling hills ? and what will I notice hear or feel by using full retard? Thanks, waiting for winter to end in Minnesota to end.

[Pat Martone]

Maybe it is me, but I've not heard about many blown head gaskets from people using a stock head, but I have heard of lots of blown head gaskets from people using HC heads. (BTW - I'm using a Snyder 5.5 head.)

Also, I would like to learn more about the advantages of using a full spark retard when descending hills. I was thinking that with the wheels trying to speed up the engine (engine braking), you would want to keep the spark advanced. I welcome an explanation. Thanks.

[Chris in CT]

Hi Marc,
I'd like to underline what Marco and others above have said about learning to properly adjust your timing lever. As the compression goes up, the more sensitive your car will become to timing setting. In particular, you will want to retard your timing when the car is under load, such as climbing a hill. Since you are going to the trouble of installing a higher compression head, you might wish to consider one of the aftermarket centrifugal timing devices for installation in your valve galley. Set it and forget it is not a good idea with higher compression heads or lightened flywheels.
Happy Motoring!

[John LaVoy]

We have had high compression heads (5.9, 5.5, 6.1) on various engines with no problem. The timing suggestions are important. When you say you drive it like a wuss, I'm hoping that is saying you lug the engine. Lugging will damage the bearings more than anything else you can do. You need to keep the crank turning and downshift when necessary to do that.