Zajicek HC Head
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Topic author - Posts: 451
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Zajicek HC Head
I am interested in acquiring a High Compression head and the Z head by Steven Zajicek has been recommended. I'd like to hear from folks that have personal experience using one before I purchase. Have also heard the Prus head is an alternate choice, but again would like to hear from people that have used either head. Like to know the good, the bad and the ugly about either one. Thanks
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Re: Zajicek HC Head
I recently installed a new z head. It did require massaging of the chambers for piston clearance.
Andy
Andy
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Re: Zajicek HC Head
Hi Andy
What type of messaging did you have to do? Did you get a satisfactory boost in power?
What type of messaging did you have to do? Did you get a satisfactory boost in power?
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Re: Zajicek HC Head
I installed a used one on my friend Clay's coupe. Did not look like any fitting was done in the past to clear the pistons. He really likes the extra power it give the 26 coupe it's on. I suggest changing the title to "Z" head as that is what most people will know them as. Not many will even know about the Zajicek part.
I know the voices aren't real but damn they have some good ideas!
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup
1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup
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Re: Zajicek HC Head
I installed a Z head when I had the engine rebuilt. I looks great and I'm happy with the performance. Definitely better than a stock engine. This is the results of a dyno test done soon after assembly:
Dyno Results
RPM Torque HP
1200 96 21.93
1400 90 23.99
1600 87 24.98
1800 74 25.36
2000 68 25.89
Dyno Results
RPM Torque HP
1200 96 21.93
1400 90 23.99
1600 87 24.98
1800 74 25.36
2000 68 25.89
1917 Touring
1946 Aeronca Champ
1952 Willys M38a1 Jeep (sold 2023)
1953 Ford Jubilee Tractor
1946 Aeronca Champ
1952 Willys M38a1 Jeep (sold 2023)
1953 Ford Jubilee Tractor
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Re: Zajicek HC Head
I have a Z head on the 14 touring and a Prus on the 15 Speedster. Both are an improvement on the Ford head but I prefer the torque characteristics offered by the Prus. I think the combustion chamber shape is better and it gives more useable torque and better mileage. JMHO
Tony Bowker
La Mesa, California
1914 Touring, 1915 Speedster, 1924 Coupe.
La Mesa, California
1914 Touring, 1915 Speedster, 1924 Coupe.
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Re: Zajicek HC Head
Only “seat of the pants dyno" to go by here.
Installed Prus head on my ’26 runabout 2 years ago. No modifications were needed. Can maintain 35 mph on hills I used to have to shift into Ruckstell. A noticeable improvement in performance all around. Engine runs cooler. No problems with ignition knock. Head weighed in at 12 lbs. The cast iron head weighed 28 lbs. Even adds an additional quart coolant capacity. Like Tony B. noted, gets better mileage as well. My engine does have an EE crank. A happy camper.
Installed Prus head on my ’26 runabout 2 years ago. No modifications were needed. Can maintain 35 mph on hills I used to have to shift into Ruckstell. A noticeable improvement in performance all around. Engine runs cooler. No problems with ignition knock. Head weighed in at 12 lbs. The cast iron head weighed 28 lbs. Even adds an additional quart coolant capacity. Like Tony B. noted, gets better mileage as well. My engine does have an EE crank. A happy camper.
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Re: Zajicek HC Head
I just installed a P head on my 26 roadster pickup. Everything fit fine, no problems with clearance. The only trouble I had was getting a head gasket, but forum member helped me out. I live up a long steep hill, and I am very happy with the improved performance. I haven't checked specific fuel consumption, but I haven't had to refuel yet, and I would have with the old head. I'm very happy with the improved performance.
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Re: Zajicek HC Head
The pistons hit the head with no gasket. I put it on the mill and raised the chamber .030" then blended the radius. It may not have needed so much in every hole but I wanted to keep them the same. If I had to do it again I would probably have gotten the Prus head, the machining appears more accurate. If available, a Ricardo head is probably the best combination of compression and breathing for a touring engine.
This isn't my first rodeo, I've had to massage 5 or 6 Z heads. Pistons hit on all of them. The instructions that come with the head specifically tell you to check for this.
Andy
This isn't my first rodeo, I've had to massage 5 or 6 Z heads. Pistons hit on all of them. The instructions that come with the head specifically tell you to check for this.
Andy
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Re: Zajicek HC Head
While they did not test the Prius head -- I don't think they had one readily available when they did the testing. But they do have some great information on the Z and other heads installed on the T. See the Model T Ford Club of Tulsa technical page at:
http://mtfctulsa.com/Tech/index.htm
and recommend you review their sections on :
Power, Torque and Model T Performance at: http://mtfctulsa.com/Tech/power_and_torque.htm
Dyno Data at:
http://mtfctulsa.com/Tech/DynoSummary.htm
Model T Accessory Heads at:
http://mtfctulsa.com/Tech/heads.htm
Other items are interesting also -- but those are related to your question.
Respectfully submitted,
Hap l9l5 cut off
http://mtfctulsa.com/Tech/index.htm
and recommend you review their sections on :
Power, Torque and Model T Performance at: http://mtfctulsa.com/Tech/power_and_torque.htm
Dyno Data at:
http://mtfctulsa.com/Tech/DynoSummary.htm
Model T Accessory Heads at:
http://mtfctulsa.com/Tech/heads.htm
Other items are interesting also -- but those are related to your question.
Respectfully submitted,
Hap l9l5 cut off
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Re: Zajicek HC Head
Similar experience, the Prus head performs best for me. Now my test is sorta garage like, but when measuring one chamber of each, the Z and the Prus, the Prus held less, so the chambers proved more compression possible.
Now the results of the Tulsa more scientific tests showed the Z head to be 203cc. But my test showed 250cc.
Anyway, was running this Z head on my '27 and thought it was giving good results, but when changed over to the Prus (no other engine changes), the T ran much smoother and got 3-4+ mph at cruise speed.
IMO, the Prus is CNC machined chambers and all match each other. The Z chambers are as cast. The Prus is also made of high grade alum, and then subject to vacuum impregnated sealer like they do all modern alum heads, i.e. less worries of corrosion on iron block.
Note Z at 203cc in a chamber
Prus head below, Z head above, see chamber differences in shape
Prus measured 210cc, Z measured 250cc in my garage tests.
Now the results of the Tulsa more scientific tests showed the Z head to be 203cc. But my test showed 250cc.
Anyway, was running this Z head on my '27 and thought it was giving good results, but when changed over to the Prus (no other engine changes), the T ran much smoother and got 3-4+ mph at cruise speed.
IMO, the Prus is CNC machined chambers and all match each other. The Z chambers are as cast. The Prus is also made of high grade alum, and then subject to vacuum impregnated sealer like they do all modern alum heads, i.e. less worries of corrosion on iron block.
Note Z at 203cc in a chamber
Prus head below, Z head above, see chamber differences in shape
Prus measured 210cc, Z measured 250cc in my garage tests.
The best way is always the simplest. The attics of the world are cluttered up with complicated failures. Henry Ford
Don’t find fault, find a remedy; anybody can complain. Henry Ford
Don’t find fault, find a remedy; anybody can complain. Henry Ford
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Topic author - Posts: 451
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Re: Zajicek HC Head
A lot of good information has been posted on this subject and I for one sure appreciate all the input. The consensus seems to be that the Prus head is a slightly better option than the Z. One thing about the Z that I am concerned about is the need by some to "Massage" the head some to not come in contact with the pistons. At the same time, I am wondering about the higher compression of the Prus causing issues with the head gasket or crank, any more thoughts on this?
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Re: Zajicek HC Head
the compression ratio difference,as recorded in other threads about this subject, is minimal. Neither head approaches 6 to 1 compression ratio.
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Re: Zajicek HC Head
Years ago I had a Z head, which I ran for awhile and sold with the car it was on. I liked it and thought it was quite an improvement but that was just observation, no tests.
I also had a Waukasha Ricardo head I ran for awhile and sold probably on Tbay. I couldn't see that it did much, if anything, more than the stock head with .080 planed off it.
Then I had a Lizard head which I ran a while, took off and cut in half with a chop saw and threw it on the scrap heap.
Then I found a Haibe High Power head that I liked so much I took it off and kept it when I sold that T. Later I found another one that was cosmetically a little nicer so I sold the first one. I would like to have a Prus head to try but haven't got that done so far. My take on it just from looking without having them side by side is that the Prus head is closer to the Haibe or Giant Power combustion chamber shape.
Anybody have a comparison of those two?? I'm going to put the Haibe on my 27 coupe if I ever get time to work on it. I'm sure it will be better than the stock head. I don't want to go real fast anymore anyway, just go up the hills a little better. I'm working on a Ruckstell to put under it when I get time, fat me up a hill in a coupe is all it wants.
I also will, of course be running either a U & J, Stromberg OF, Zenith S4BF or a Cyclone prototype carb that I've been wanting to try for several years. Probably the OF.
I also had a Waukasha Ricardo head I ran for awhile and sold probably on Tbay. I couldn't see that it did much, if anything, more than the stock head with .080 planed off it.
Then I had a Lizard head which I ran a while, took off and cut in half with a chop saw and threw it on the scrap heap.
Then I found a Haibe High Power head that I liked so much I took it off and kept it when I sold that T. Later I found another one that was cosmetically a little nicer so I sold the first one. I would like to have a Prus head to try but haven't got that done so far. My take on it just from looking without having them side by side is that the Prus head is closer to the Haibe or Giant Power combustion chamber shape.
Anybody have a comparison of those two?? I'm going to put the Haibe on my 27 coupe if I ever get time to work on it. I'm sure it will be better than the stock head. I don't want to go real fast anymore anyway, just go up the hills a little better. I'm working on a Ruckstell to put under it when I get time, fat me up a hill in a coupe is all it wants.
I also will, of course be running either a U & J, Stromberg OF, Zenith S4BF or a Cyclone prototype carb that I've been wanting to try for several years. Probably the OF.
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Re: Zajicek HC Head
TonyB wrote: ↑Wed Jun 03, 2020 1:05 pmI have a Z head on the 14 touring and a Prus on the 15 Speedster. Both are an improvement on the Ford head but I prefer the torque characteristics offered by the Prus. I think the combustion chamber shape is better and it gives more useable torque and better mileage. JMHO
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Re: Zajicek HC Head
I prefer the P head after running a Z head for several years . The guys running a Scat crank don’t have to stop & wait on me at the top of the hills now
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Re: Zajicek HC Head
My car had a Z head when I inherited it. Unfortunately it cracked the year Pop passed away from the heater malfunctioning in the garage.
I put THE Jensen head that Kevin Prus told me he used to make his mold.
I also honed and ringed it/touched up and adjusted the oversized valves at the same time.
Aluminum early intake, Stromberg OF and a Thomas distributor is the extent of the mods and I can tell a difference between the Z and this head, even before the OF, with an NH, it was stronger. The OF was the cherry on top.
I put THE Jensen head that Kevin Prus told me he used to make his mold.
I also honed and ringed it/touched up and adjusted the oversized valves at the same time.
Aluminum early intake, Stromberg OF and a Thomas distributor is the extent of the mods and I can tell a difference between the Z and this head, even before the OF, with an NH, it was stronger. The OF was the cherry on top.
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Re: Zajicek HC Head
Had the Z head installed on my engine by the rebuilder. Ran it for two years and replaced in with the Prus head. Like this set up better. The Z head is on mt project engine now, but if that turns out well I will get another Prus head for that as well.
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Re: Zajicek HC Head
There used to be another aluminum High Compression Head available, made by Ralph G. Reeder, in Dickinson, Texas.
I have always wondered if he was friends with Ralph Zajicek or if they worked together to design those heads.
It had Ford years cast in it, on the driver's side in back and I have one in my attic yet.
It took me a long time to find out who made it and I have never tried to use it.
I have always wondered if he was friends with Ralph Zajicek or if they worked together to design those heads.
It had Ford years cast in it, on the driver's side in back and I have one in my attic yet.
It took me a long time to find out who made it and I have never tried to use it.
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Re: Zajicek HC Head
I had the honor of having dinner with Ralph's widow one night. We talked at great length about her husband and his rather significant contribution to the Model T world. She said that he was very proud of his work on the high compression head, but she also said that he was a tool and die maker by trade. His proudest achievement was in the medical field. A surgeon came to him and said that he wanted to pioneer a new type of surgery that he would call laproscopic. That is where the surgeon makes only two or three small incisions to perform surgery. Very common now, but unheard of not long ago. Ralph designed all of the instruments that the surgeon used. Much faster recovery time for patients. That was his proudest achievement.