Downeaster
Junior Member
Will be buying a high compression head from Snyder's. They have a 5.5 to 1 and a 6.1 to 1 available. Other than the difference in price. What are the pro and cons between the two heads. Which one would you buy and why?
High compression head
- Thread starter Downeaster
- Start date
John LaVoy
Well-known member
We just finished the article that will appear in the next Model A Times regarding the new head. You get about 4 more horsepower with the new one. for the short version.
Aerocraft
Well-known member
In my opinion, it would depend upon the condition of the engine. If it is a fresh overhaul, the higher compression probably would work well. If the engine has an unknown history, is noisy, or has some other question about its condition, then either the 5.5 head or no change might be best. It's your call. Gar Williams
John LaVoy
Well-known member
the 6-1 is the newest one we have dyno tests on both and the new one is about 4HP more.
TerryH
Well-known member
The Snyder heads are very good, and either will offer a big improvement over a stock head, especially if you are driving one of the heavier models, such as a Town Sedan and also if you plan to install an overdrive. The 6 to 1 version has not been out very long, so feedback is just starting to surface. You might want to wait for the article in the next Model A Times as they have done a test and should have up to date info. The 6 to 1 version might be slightly harder on your bearings, so if your engine is older or in unknown condition, the 5.5 might be the way to go.........and it still offers significant improvement.
Boston Bruce
Senior Member
I have had the 5.5 Snyders head on my 1930 coupe for about 6 years now with no problems. I used the "modern" gasket with the built in silicone seal and torqued the head to 65 lbs. using new studs. I don't want to get into a discussion about the amount of torque you use, but no leaks or problems so far. 
This summer I put the new 6.0 head on my Station Wagon -- same gasket and same torque. Pulls the hills much better than when using the old standard head.
This summer I put the new 6.0 head on my Station Wagon -- same gasket and same torque. Pulls the hills much better than when using the old standard head.
Jim Parker Toronto
Well-known member
MAP, you asked "How are you sure to get the new version of the head?" If you ordered one from Snyders, (the only maker at this time) I am sure that it is what you ordered. Being new to this forum, and maybe the hobby, Snyders is one of the good ones! You can trust them and they are nice people to deal with.
Pa Joe
Senior Member
My engine is at the rebuilder right now and I've been asking the same question of people including my engine builder (with a great reputation) and people that have been in this hobby for years. And the general concensus is that with babbit bearings the 5.5 is the best choice. My builder also mentioned that at one time (dont know when or if the problem has been rectified) there was problems with the castings of the 6.1. Now, I'm fairly new to Model As, so maybe different opinions on the barn, but that's the info I got
BCCHOPIT
Well-known member
Is that at the wheels or crank?
Bob Johnson
Well-known member
If you assume that the top of the piston is flush with the block deck at TDC and that you have a standard bore then you would have 149.4 cc for 5.5 and 137.0 for 6.0. That would include the 9.6 cc due to the 0.050 head gasket. Thus 139.8 cc for 5.5 and 127.4 cc for 6.0 without including the volume due to the 0.050 head gasket.
Bob
MikeK
Well-known member
Who's general consensus? Not Larry Brumfield, who made 5.9 heads for years. Not anybody that used Winfield and various other 'power' or 'high-speed' heads way before insert bearings were adapted to A's. Not anybody that realizes bearings with clearances that are large and sloppy and rocking on too big of a shim stack will fail with a stock head. Not anybody that knows too much advance will soon destroy any type of bearing, with even a stock 4.22 head.
Seems like this "consensus" only developed after the introduction of the conservative Snyder 5.5. Marketed as a "safe" limit for babbitt because much of the market was engines with old, sloppy, poor, overshimmed babbitt, and lots of A owners have no clue about ignition advance and will lug and run in a way that would kill any type of bearing. Some people will believe anything a vendor tells them to promote their product as best.
Henry went with 4.22 because octane was rotten, about half of what gasoline is now. Many other manufacturers at the time had ratios well over 6 on their poured babbitt engines.
Larry Brumfield
BANNED
Actually, very few of the engines fitted with a Regular Brumfield Head 5.9 are a 5.9 ratio. Most are 6 to nearly 6.2 to 1.
The same type result applies to Snyder's heads or any head, including the various Brumfield Super Heads, for the reasons I'm about to explain:
There's hardly an engine block out there that has not been resurfaced, usually multiple times. Consequently, any pistons used of original length rise above the block surface at top dead center and this raises the compression ratio. Moreover, even when the engines were BRAND NEW the pistons rose above the block surface .031" and most people don't even put that into their calculations.
Next, add in the bores greater than standard if it applies.
And last but certainly not least, I hardly ever see anyone calculate the compression ratios correctly because they goof when they determine the volume of the various gaskets; which due to its odd shape cannot be accurately determined mathematically very easily. They also don't take into account the gasket's volume while under compression and they routinely guess at the distance the gasket compresses. Even measuring a used gasket is not completely accurate because a properly made gasket has a certain amount of resiliency.
I solved this problem by modifying an engine block with plugs welded in to occupy and seal over the cylinder bores. Then resurfaced the block smooth. To simulate various deck heights and bores I used thin metal disks of the appropriate sizes/thicknesses (made out of sheet metal and mic'd) laying where the pistons would be (and used the .031" standard bore disks to figure standard B-F Heads and B-F Super Heads). Sometimes I had to do this part mathematically which I could do anyway but I like to make things. After the head and gasket are installed and torqued and re-torqued to specs, the true volume can be measured by pouring a low surface tension liquid through the spark plug holes (without any worry of seepage because there are no pistons). The compressed gasket's volume is measured along with the combustion chamber at the same time.
I used the above method for several years to make Brumfield Super Heads in any ratio desired (for a person's particular engine) but it got to be more trouble than what I was charging and it's really not necessary. So I changed to standard B-F ratios with the Super Heads. People would call and say something like, "My bore is .060" over and my pistons stick up .061". I want you to make me a head with the compression ratio as close to 7 to 1 as you can get it and no higher."
Well what if the standard ratio offered comes out a little over with your engine? Are the bearings going to fail?
The same type result applies to Snyder's heads or any head, including the various Brumfield Super Heads, for the reasons I'm about to explain:
There's hardly an engine block out there that has not been resurfaced, usually multiple times. Consequently, any pistons used of original length rise above the block surface at top dead center and this raises the compression ratio. Moreover, even when the engines were BRAND NEW the pistons rose above the block surface .031" and most people don't even put that into their calculations.
Next, add in the bores greater than standard if it applies.
And last but certainly not least, I hardly ever see anyone calculate the compression ratios correctly because they goof when they determine the volume of the various gaskets; which due to its odd shape cannot be accurately determined mathematically very easily. They also don't take into account the gasket's volume while under compression and they routinely guess at the distance the gasket compresses. Even measuring a used gasket is not completely accurate because a properly made gasket has a certain amount of resiliency.
I solved this problem by modifying an engine block with plugs welded in to occupy and seal over the cylinder bores. Then resurfaced the block smooth. To simulate various deck heights and bores I used thin metal disks of the appropriate sizes/thicknesses (made out of sheet metal and mic'd) laying where the pistons would be (and used the .031" standard bore disks to figure standard B-F Heads and B-F Super Heads). Sometimes I had to do this part mathematically which I could do anyway but I like to make things. After the head and gasket are installed and torqued and re-torqued to specs, the true volume can be measured by pouring a low surface tension liquid through the spark plug holes (without any worry of seepage because there are no pistons). The compressed gasket's volume is measured along with the combustion chamber at the same time.
I used the above method for several years to make Brumfield Super Heads in any ratio desired (for a person's particular engine) but it got to be more trouble than what I was charging and it's really not necessary. So I changed to standard B-F ratios with the Super Heads. People would call and say something like, "My bore is .060" over and my pistons stick up .061". I want you to make me a head with the compression ratio as close to 7 to 1 as you can get it and no higher."
Well what if the standard ratio offered comes out a little over with your engine? Are the bearings going to fail?
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Regarding cc's per compression ratio, I have an old Weiand head advertised 7:1 CR head with a combustion chamber that measures 135 CC's, no flycut. I measured my stock 31 head and it was as I recall 272 cc's and I read/heard somewhere that the 28-9 heads were a few cc's smaller around 268. My pistons had a .040 popup, which you really need to measure for an HC head, so I had .025 machined off the pistions because of no flycut on the head. Larry is right about the difficulty of measuring the gasket volume. I muliplied 6" X 3" X .050 for ball park figure of gasket volume. (The 6" is about the length from the valve side to the cylinder side, 3" wide is a compromise figure because of the wider shape of the gasket around the bore and valves, and narrower in the middle. The .050 is the thickness of a compressed Best gasket--I have taken a few off and measured them. Measure your gasket, it may be different.) Then mulitply by 16.387 to change the cubic inches of the gasket volume to cubic centimeters. Add this to the chamber cc's. Here is a link to a compression ratio calculator that is fun to mess with. http://www.csgnetwork.com/compcalc.html However, it is designed for OHV engines so put in -0- in the gasket thickness and gasket bore and add the gasket cc's calculated as above to the number for the combustion chamber cc's. Should give you a figure pretty close. A few cc's or CR points one way or the other is not going to make much difference but Larry's method of actual measurement is surely most accurate. (Be sure you are at TDC on the compression stroke. Use the timing mark.) And Larry is building to manufacturing specs, the rest of us can be a little sloppy.
Re comments about babbitt for HC heads, the 53 Chev std transmission was the last production engine with babbitt bearings and splash lube to the rods and it was a 7.1 CR with much higher bearing loading per horsepower than the Model A. I think the comments on other posts re thick shim packs is correct and the next overhaul I am going to strip the shim packs down to a few shims to around .010 and I would suggest that anyone rebuilding an engine from here on do the same. You will probably have to do it yourself because the rebuilders will charge extra for the extra work, and probably not want to do it anyway, so buy a mic and do it.
Re comments about babbitt for HC heads, the 53 Chev std transmission was the last production engine with babbitt bearings and splash lube to the rods and it was a 7.1 CR with much higher bearing loading per horsepower than the Model A. I think the comments on other posts re thick shim packs is correct and the next overhaul I am going to strip the shim packs down to a few shims to around .010 and I would suggest that anyone rebuilding an engine from here on do the same. You will probably have to do it yourself because the rebuilders will charge extra for the extra work, and probably not want to do it anyway, so buy a mic and do it.
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Larry Brumfield
BANNED
I beg to differ with you in how people look at it. The average Joe will focus only on the numbers and many make a big issue out it. I can tell by their comments and the expression on their faces. That's why I had to become more accurate with measurements even though as you say it may not make much difference.
"Well what is yours? Mine is 6 to 1."
"Well mine is closer to 6.3" (with a half-*** grin of knowledge that mine has a drastic difference in power)
Quite often it's the exact opposite with even as much as nearly a whole compression ratio point less due to air flow differences and combustion chamber design.
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