High Compression Head
 

So recently I've been showing interest in the possibility of purchasing a high compression head in the future... with this interest comes an internal conflict. Obviously the high compression head will increase power but what the are the negative affects of doing this or are there any (such as increased bearing wear). If increased bearing wear is a prevalent problem then is it advised to only up grade to 5:5:1 head as opposed to purchasing the 6:1 head that will clearly provide much more power for only $30 more.

Re: High Compression Head
 

Don't worry about the bearings. I run a 6.8 with other modifications with no problem. Others use higher compression with babbitt. Jim Brierely runs Bonneville with babbitt mains.

Re: High Compression Head
 

the casting on ford type heads give a lil boost , but they are restricted on air . I ran a 6-1 for years , then changed from stock casting to a lion 3 . you need a big bucket to carry the difference . the stock casting 6-1 will not hurt your stock motor .

Re: High Compression Head
 

The easiest upgrade is the 5.5 head. It is acceptable to run the stock head studs with the 5.5. I have run a 5.5 head for over 20,000 miles without incident. It provides extra power when climbing hills. I am very happy with the 5.5. One item to consider when installing a head with a higher than 5.5 compression ratio is you will need to install Grade 8 head studs.

Re: High Compression Head
 

I would go with the 6.1 at least. I have been running 5.9 brum since 2003 and love it, would really like the 7.1. I personally believe buying a 5.5 is throwing your money away. the reason is if you drive a correct built engine at 6.1 or close you will really notice the 5.5 is ok but you get the best bang for the buck with a little more uuummmmppphhhh. have fun modelAtony tony white Lafayette, LA

Re: High Compression Head
 

if your motor is tired say goodbye

Re: High Compression Head
 

If your engine is in good condition you will have no problems with a High comp Head
If not you shorten its life
Might be worth dropping the sump and inspecting things 1st

Re: High Compression Head
 

HIGHER compression DOES put on extra load, especially, on ROD BEARINGS!!--Like, put on 60 LBS of GUT & your FEET begin to HURT.
Bill W.

Re: High Compression Head
 

other than the bearings i put an HC head on a engine and not long after the blow-by was terrible... it must have blew a piston...

Re: High Compression Head
 

Check the clearances of the bearings, adjust as necessary. Install the HC head and enjoy. There are three things to watch for; 1) spark setting, you don't have to lower the rod as much. 2) the slow idle sound goes away (or at least changes). 3) hand cranking it harder.

Re: High Compression Head
 

If you want to see performance difference between the 5.5 head and the 6.1 head go to Snyders web site click on HC head then look for the dyno testing results. You will see there isn't much to gain with the 6.1 head compared to the 5.5 head. I have two As....both motors are fairly fresh rebuilds. The one with the stock head has 60 pounds of compression in every cylinder. The one with the 5.5 head has 90 pounds of compression in every cylinder. I sure you will get differences of opinion on this but this is what I found.

Re: High Compression Head
 

Bearing loads from the higher compression are not the problem. The potential for bearing failure is from inattentive drivers who just yank the spark lever completely down and leave it there. Either install a distributor with mechanical advance or learn to advance/retard according to load and speed.
Don't run it too retarded either or it will overheat.

Re: High Compression Head
 

Glad this was brought up. I decided to change my oil pan gasket and found a small amount of coolant in the oil. Time to change the head gasket, which means its time to upgrade to a high compression head (been wanting to for a few years now). I have the same dilemma 5.5 or 6. I have a stromberg, header with glass pack, and just recenty installed an electronic ignition. The only thing that concersn me is that the motor is older. With the pan off and a flashlight in hand everything looks to be in great shape. I'd love to go 6-1 because it seems like that is definitely the better option for the price. Sounds like I should be safe with that, is the 5.5-1 any safer?

Re: High Compression Head
 

'motor is older' ! Whatever that means, if it means that the engine is worn out, you can expect 'some' things/unintended consequences...the higher the head compression is , that you put on. That is, worn out rings...expect blowby. Worn /loose bearings...expect shorter life and noise...etc. With what you say you have, I'd first thing check compression and thereby ring conditions...dry then wet tests...etc.
Also, with what you've said about blown head gasket, I'd check for deck problems, i.e.- valves seating/good condition; cracks and uneven deck surface. Think of increased compression maybe worsening an already existing problem that caused blown gasket ?
Do you know just how old/worn your engine is ? Maybe if real worn, the cam gear (fiber)may not like...more power, etc. Good luck :)

Re: High Compression Head
 

Older as in I haven't gone through the internals. The car was "rebuilt" in the 80s by my father. He said he did a head gasket sometime in the past, but it could've been 30 years ago. I replaced the cam gear after that decided to lose a few teeth on me in the middle of the road about 3 years ago. I don't put many miles on it or drive it hard. I'm guessing its the head gasket because there is some, but a very small amount of coolant in the oil. It also looks like after blowing out the coolant that there is some oil in the coolant. This is pretty minimal, but I want to get it corrected.

I'll definitely run a compression test then.

If I have a faulty head gasket won't that also mess with the compression readings?

Re: High Compression Head
 

Not necessarily. You could have a minor, slow seepage of coolant when the engine is cold, but when it's fully warmed up, everything expands enough to seal up and hold compression. If it's bad enough to show low readings on a compression test, you would likely be blowing water out the radiator big time.

Re: High Compression Head
 

A couple of thoughts: First, the cam gear is totally unaffected by a high compression head. It does not take any more effort to turn the cam no what the compression.
Second, the bearings don't know nor care if the cranking compression is higher ie: if a compression test showed 60# with the stock head and 90# with the new head, it will not affect the bearings. This is because combustion pressure is a lot more than compression pressure, by several hundred pounds more.
Now, what is supporting all that pressure? Oil! There is always a film of oil between the crankshaft journal and the bearing (whether Babbitt or insert) that prevents metal to metal contact, which would mean a rapid death! But if you let pre-ignition or detonation occur (which is like hitting the top of the piston with a sledgehammer) you can squish out that film of oil and damage occurs. Same thing if the oil supply is insufficient. Bearing surface area is plenty to support the extra load of higher compression as well. So a high compression head won't kill an engine by itself, it has to have help.

Re: High Compression Head
 

I always say that the high compression head is the best "bang for the buck" at improving performance. As to the bottom end, I have a Brumfield 5.9 on one car that is all babbitt, and a 5.5 on another where the mains are babbitt and have around 45,000 miles on the two cars with out a problem.