5.5 head

Ordsgt

Ordsgt

Senior Member
After blowing a head gasket I decided to replace the head also. Part of the reason was a friend blew his head gasket and took the old head to machine shop to get a clean up cut and found the head was cracked. He went through 4 heads before he got a good one and the machining bill was over $400. Well I thought to avoid all that and just get a Snyder 5.5.Well its on and running and what a difference 10 hp makes. Very pleased I went this route
 
There is no doubt that extra bit of compression really helps. I found the main benefit was the extra low down grunt. Now, if you improve the carburettor, you won't know yourself. Even a B carb with an enlarged inlet manifold will wake up the car. A downdraught (like a Stromberg or Webber) does even more.
Who says original is best?
 
Compression ratio is only part of the picture. The combustion chamber design is important too. It effects breathing and combustion efficiency. In my opinion, the combustion chamber for the racing flat head Harleys had the best design.
 
I have a 5.5:1 head on my Coupe and a 6:1 head on my Victoria. The 6:1 head has a noticeable increase in torque over the 5.5:1 head. To use the full travel of the spark advance lever, special tuning is necessary. Here is what I did to regain full travel of the spark lever.
 

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Curious...For those that converted from a stock head to a 5.5, how many of you used your original studs. I'm debating changing the head for performance and would like to keep the original studs. Thank you!!!!
 
Rebuilders recommend changing out the studs on a rebuilt engine. The latest ones I bought were not straight and it made putting the head on difficult. However, after a few miles and a few re torquing, they straightened out so the head was easy to remove next time. The straightening indicates to me that there is some yielding in the steel. If you do change out the studs make sure the tapped holes in the block are clean down to the bottom. I use some anti seize except if the holes go into the water jacket, in which case I will use a sealant.

The high compression heads are more efficient so more of the fuel is converted to torque and less to heat. So, if you drive your car at the same speed as before the coolant temperature will be lower.
 
When I had blown a head gasket before on this car I replaced all the studs and nuts with harder ones, they were grade 8. I ran a tap through all the stud holes before installing the new studs. This time when I put the new head and gasket on it was a dream as the studs and nuts were like new despite being in the car 2 years ago. All the work to put a new gasket on before it just felt better to put all new studs. I considered the money spent on the studs was worth it
 
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As a matter of interest, what is the general opinion on maximum advance for a 5.5:1 head. I run a max of 22° for a 6:1 but I realise a 5.5:1 would be more.
 
Just a side note. Don't use a tap to clean up the head stud holes. Use a thread chaser.
The thread chaser will clean out the threads. The tap will cut material out of the stud holes.
There are three grades of taps. Each one has a different tolerance of depth cutting.
The taps most of get from the hardware store, Snap-on, Matco ect. cut a deeper thread
than the taps that are used in engine manufacturing.
 
Bob Bidonde said:
I have a 5.5:1 head on my Coupe and a 6:1 head on my Victoria. The 6:1 head has a noticeable increase in torque over the 5.5:1 head. To use the full travel of the spark advance lever, special tuning is necessary. Here is what I did to regain full travel of the spark lever.
Click to expand...

I don’t agree with this. Actual timing and dwell measurement will help in significantly finding your ignition sweet spot considering elevation p, fuel quality and other things.
 
I do what Bob does by timing my engine with the spark advance 3 or 4 notches down. I have a 6.5 head. I still change my timing to match conditions but at a lower position of the spark lever. With the higher compression ratio the spark advance does not have to change with RPM as the burn rate increases with increased engine speed. I will retard the ignition one notch when lugging or driving in town and advance one notch when cruising on a level road with reduced throttle. I start the engine with the lever 3 or 4 notches down. I love to listen to a low idle and can get a really low idle with the lever all the way up and the throttle cracked.
 
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Dodge said:
Just a side note. Don't use a tap to clean up the head stud holes. Use a thread chaser.
The thread chaser will clean out the threads. The tap will cut material out of the stud holes.

D.I.Y. chaser... notch a fastener to resemble a pie missing one piece and it will clear the threads without damage.
Click to expand...
 
Dodge said:
Just a side note. Don't use a tap to clean up the head stud holes. Use a thread chaser.
The thread chaser will clean out the threads. The tap will cut material out of the stud holes.
There are three grades of taps. Each one has a different tolerance of depth cutting.
The taps most of get from the hardware store, Snap-on, Matco ect. cut a deeper thread
than the taps that are used in engine manufacturing.
Click to expand...

I purchased a set of thread restorer taps and dies from Amazon (https://www.amazon.com/Lang-Tools-2581-26-Piece-Restorer/dp/B00DTEFSWY/?tag=atomicindus08-20) and they’ve worked just fine. Not horribly expensive - about $50 if I remember correctly.
 
Now, advise you to get your intake bored out to 1.250 and bolt a B carburetor on it. Or get a downdraft Carb. on it. The A engine is starved for gas with the A carb.
Terry
 
California Travieso said:
Bruce,

I like your approach to the problem. Approximately, how many clicks up from full advance did you place the stop on your car? From Bob’s diagram I would assume it would be 4 to 5 clicks up for a 6.0 compression head.

David Serrano
Click to expand...

The underside of the device is flush against the bottom and the top is filed to give the 28 degrees using the Nurex timing strip as mentioned in my post. I never looked to see how many clicks.
 
Synchro909 said:
As a matter of interest, what is the general opinion on maximum advance for a 5.5:1 head. I run a max of 22° for a 6:1 but I realise a 5.5:1 would be more.
Click to expand...

A little different setup as I have a Phillips Auto Advancer (original NuRex) but I have my total advance set @ 28° BTDC with my 5.5 head. I have it so I can retard the timing with the original advance control if that is too much on hills
 
Ordsgt said:
...I replaced all the studs and nuts with harder ones, they were grade 8. I...the studs and nuts were like new despite being in the car 2 years ago.
Click to expand...
New grade 8 studs have a much higher yield rate than the originals which were probably grade 5. They all rely on some stretch for their holding power. The grade 8 stretches less so it doesn't fatigue as fast. Most newer cars torque the heads 90-100 ftlbs and at 55 lbs the grade 8s should last many rebuilds. Has anyone tried 55+ lbs with the new bolts? My 289 HiPo would blow the gaskets at the stock torque but 5 pounds extra and the problem was cured.
 
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