5.5 or 6.0 High Compression Head?

[Ruth]

While I'm sure this has been asked a thousand time, I just can't find an answer.

Which head would be a better choice for me. I have a '30 town Sedan. I'm not a racer or speed demon. The old girl could just use a bit of help going up hills.

I value all of your opinions. Which head would be recommended, the 5.5 or 6.0. Engine is bone stock and in good condition.

Thanking you all in advance, Ruthie.

[Dodge]

Compression is your friend, I would go with the 6-1

[TinCup]

I run the 5.5 Snyders head and it is all that I need. It is the only non stock item on my motor. I can easily pull long grades and the car will run 60 if I let it. Higher compression also means more stress on your mains.

[Dick M]

There are two things to consider. One, the higher the compression ratio, the more strain on your engine. You say your "old girl" is bone stock meaning that you have a babbitted engine. Is the additional benefit of the higher 6.1 compression head worth putting the heavier strain on your engine? The second thing to consider is: will you have to upgrade your head studs to grade 8? The 5.5 head does not require this upgrade. I would go with the 5.5 head because it will be easier on your engine and you will not be required to change your head studs. JMO

[Ruth]

Thanks for the quick responses. Yes she still has babbitt bearings.

[Greg Jones]

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I have both the 5.5 and the 6.0. I would recommend the 5.5.

FWIW, both heads came from Snyder's and both required milling for flatness. Keep that in mind. The 6.0 out of the box looked like it had been dragged down a highway for a few miles, looked like they tried to surface it with a belt sander or angle grinder. It was nasty and I almost sent it back, but my machinist worked his magic on it. I love Snyder's so am not bashing them, but hopefully the machined surface is a little better on that head.

[1929]

My rebuilder will not put more then a 5.5 head on a Babbitt motor, I put the 6-1 head because I have inserts.

[Henry's Lady's Man]

I use a 6-1 on my 30 Town Sedanwith great results. Bonnie pulls uphill quite nicely now. I combined it with a B camshaft for better breathing, in and out.
Yes, I have babbitt also. My understanding is that you go a bit easier on the advance... I run my advance lever at 9:00 (about halfway down). The reason is, the gas burns faster now with h/c. So too much advance would bang on the babbitt harder. Diesel engines from the late 1800's had babbitt as well, and had 8-1 or 9-1 compression so I think you're just fine; though listen to everyone here. I'm sure someone will beg to differ.

[Henry's Lady's Man]

Originally Posted by Greg Jones

I have both the 5.5 and the 6.0. I would recommend the 5.5.

FWIW, both heads came from Snyder's and both required milling for flatness. Keep that in mind. The 6.0 out of the box looked like it had been dragged down a highway for a few miles, looked like they tried to surface it with a belt sander or angle grinder. It was nasty and I almost sent it back, but my machinist worked his magic on it. I love Snyder's so am not bashing them, but hopefully the machined surface is a little better on that head.

Also, I bought the Snyder 6.0, and had to ream out the water outlet to make room for the impeller/propeller. It kept hitting; so they need to check these out better, IMHO.

[BRENT in 10-uh-C]

Folks, sometimes we all get sidetracked in the forest simply because we seemingly start focusing on one tree. The original Ford produced high compression head was approximately 5.3 compression. For years, the Brumfield's head was a 5.9 which is very close to the 6.1 compression. Brumfield equipped engines ran MANY miles on babbitt. If THAT was not enough proof, consider how long diesel engines used babbitt for bearings with their much higher compression ratios.

The bottom line is do not get hung-up on this babbitt and 6.1 compression discussion. If you have a tired & worn engine, it is likely going to fail whether it is a 5½.1 or 6.1 compression ratio head. As the original poster suggested, their engine in good condition will benefit with a minimum of 6.1 compression, ...and maybe even more compression too!

[Big hammer]

Originally Posted by Dick M

There are two things to consider. One, the higher the compression ratio, the more strain on your engine. You say your "old girl" is bone stock meaning that you have a babbitted engine. Is the additional benefit of the higher 6.1 compression head worth putting the heavier strain on your engine? The second thing to consider is: will you have to upgrade your head studs to grade 8? The 5.5 head does not require this upgrade. I would go with the 5.5 head because it will be easier on your engine and you will not be required to change your head studs. JMO

I asked my engine rebuilder about grade 8 studs, he chuckled and said their not needed. I went with the 6.0 head! I am very happy :-)

[CarlG]

I would put new studs in with any new head -- regardless.

[TerryH]

FWIW I had the 5.5 head installed about 10 years ago on my Town Sedan, and I really like it. Of course they did not even have the 6.0 then......I also have the Mitchell OD and really like the combination, as I do a fair amount of freeway driving and touring here in S. California. My feeling is there probably is not a whole lot of difference between the two; either one will give you more power, especially helpful on grades. The Town Sedan is the heaviest Model A and really benefits from this easy modification. Good luck with your decision!

[Synchro909]

The claimed compression ratio is only half the issue. What CR you actually get depends on how much over size your bores are. I run a 5.5:1 head on my Phaeton but a recent compression test gave me 95-99 psi on all cylinders. That equates to well over 5.5:1. The bores are 0-060" over from memory.

[Terry, NJ]

With an oversize bore your CR will be even higher. Just boring the engine will result in a higher CR with a stock head. I asked someone who knows more about these things than I do what the increase was and IIRC it was a .038 just by boring it .040. Not much, but slightly more!
If you multiply 14.7 PSI (Atmospheric Pressure) X the CR, 4.7 you get 79.09 PSI ( I did this 3 times and two different answers, I got this answer twice, so it wins!, But it looks wrong to me!) In any event, The CR is a multiplier of atmospheric pressure. But it's more important that the numbers be equal within ten LBS. There is also an increase due to the heat generated with compression.
Terry

Originally Posted by Synchro909

The claimed compression ratio is only half the issue. What CR you actually get depends on how much over size your bores are. I run a 5.5:1 head on my Phaeton but a recent compression test gave me 95-99 psi on all cylinders. That equates to well over 5.5:1. The bores are 0-060" over from memory.

[CYB4]

I have the Snyders 5.5 head on my stock engine for about 1000 mls with the usual studs, no problem at all. Uphills the car is stronger, it runs now real 103 kmph topspead.

[Joop]

That is about 64 miles per hour.


,,

[George Miller]

Originally Posted by BRENT in 10-uh-C

Folks, sometimes we all get sidetracked in the forest simply because we seemingly start focusing on one tree. The original Ford produced high compression head was approximately 5.3 compression. For years, the Brumfield's head was a 5.9 which is very close to the 6.1 compression. Brumfield equipped engines ran MANY miles on babbitt. If THAT was not enough proof, consider how long diesel engines used babbitt for bearings with their much higher compression ratios.

The bottom line is do not get hung-up on this babbitt and 6.1 compression discussion. If you have a tired & worn engine, it is likely going to fail whether it is a 5½.1 or 6.1 compression ratio head. As the original poster suggested, their engine in good condition will benefit with a minimum of 6.1 compression, ...and maybe even more compression too!

plus 1

[Ruth]

Thanks all for the info. One more question came to mind. beside compression ratio is there a difference in combustion chambers and if so, which head is better?

Thanks again.

[Henry's Lady's Man]

The two Snyder heads (5.5:1 and 6.1:1) do have slightly different shapes for combustion. I have only experience with the 6.1. I would suggest you repost it as a separate question or contact Snyder's. They probably get the most feedback.