Changing Heads Original / High Compression
 

For those of you that have changed Heads can you tell me if changing from original to high compression requires longer bolts? If so how much difference in thickness is the two?

Thanks for your time.

Re: Changing Heads Original / High Compression
 

They should be the same.
Good Day!

Re: Changing Heads Original / High Compression
 

When I changed, I replaced the original head studs with high tensile ones. They are the same length.

Re: Changing Heads Original / High Compression
 

Dave in MN & Synchro909 Thanks to you both for the information!

Re: Changing Heads Original / High Compression
 

In general the previous comments are correct but what type of high compression head are you using?

Charlie Stephens

Re: Changing Heads Original / High Compression
 

5.5:1 recommended by one of the parts dealers over the 6:1.

Re: Changing Heads Original / High Compression
 

Did he say why the 5.5 over the 6?

Re: Changing Heads Original / High Compression
 

Easier on the Babbit.

Re: Changing Heads Original / High Compression
 

What vender was that, just out of curiosity?

Re: Changing Heads Original / High Compression
 

I would check the credibility of this source before making your purchase... It seems foolish to purchase a lower compression head when a higher compression can be purchased at the same price. If the babbitt is of concern, a higher compression of any sort shouldn't be installed; the engine should be rebuilt at that point.

Engine rebuilders such as Antique Engine Rebuilding don't even offer the 5.5:1 head anymore for their rebuilds because it doesn't make sense to install the 5.5:1 over the 6:1.

Re: Changing Heads Original / High Compression
 

If you have a stock distributor with no electronic or centrifugal advance the 5.5 *might* give you a little more wiggle room with where you run your spark lever.

I pay more attention to mine after going to the 5.5 but it still seems forgiving and it tells me when it's too far advanced (usually runs halfway down).

I can only assume that going to 6:1 would mean you have to pay even more attention to the spark advance or go to an automatic advance setup.

Re: Changing Heads Original / High Compression
 

Cape, I had 5.5 and then went to 6.1. It made a big difference. If i were you I would go directly to the 6.1, have it checked for straightness and go with grade 8 bolts.

With the 6.1 over a 4.2 and 5.5 you really have to play more with the spark lever especially on hills, no matter how small.

Re: Changing Heads Original / High Compression
 

Good Morning all...I agree with old31, however if the engine is not 'a fresh rebuild', it is a good idea to drop the pan and check the clearances on the mains and rods as you are going to ask them to work a bit harder. Definitely install an oil filter, I use the one from Snyder's that attaches to the valve cover. Even if you run your oil over 500 miles, don't forget to lube all 31 or so zurk fittings each 500 miles to keep down the wear on all the moving parts...Ernie in Arizona

Re: Changing Heads Original / High Compression
 

When I fitted a Winfield 7:1 alloy head, the original studs proved too short and I tried to get a set the length of the stud that holds the distributor cable. That proved impossible so I had to get a new high tensile set made. Unfortunately, only metric stock is available, but the end result was great as they fitted more accurately and the head slipped effortlessly on.

Re: Changing Heads Original / High Compression
 

Duh!

Re: Changing Heads Original / High Compression
 

Most of the vendors suggest changing out the head bolts to Grade 8 when installing a high compression head because they are less likely to stretch out of torque specs. Makes sense, more compression=more pressure on the hardware.
Worth spending the $40 for the "hopefully" easy replacement. Even if you have to wait on your next Social Security check to cover the cost. Chap

Re: Changing Heads Original / High Compression
 

The grade 8 studs also have tighter tolerance threads which I think means more than the added strength. I have had some grade 5 s that were very loose fitting in the block.

John