Zajicek HC Head

Discuss all things Model T related.
Forum rules
If you need help logging in, or have question about how something works, use the Support forum located here Support Forum
Complete set of Forum Rules Forum Rules

Topic author
SurveyKing
Posts: 449
Joined: Thu Jan 10, 2019 8:36 am
First Name: Daniel
Last Name: Snell
* REQUIRED* Type and Year of Model Ts owned: 1909 Touring, 1924 Touring, 1925 Roadster Pickup, 1921 Touring
Location: Boerne, Texas
MTFCA Number: 31662
MTFCI Number: 23677
Board Member Since: 2014

Zajicek HC Head

Post by SurveyKing » Wed Jun 03, 2020 8:39 am

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

User avatar

AndyClary
Posts: 605
Joined: Sun Jan 06, 2019 11:15 am
First Name: Andrew
Last Name: Clary
* REQUIRED* Type and Year of Model Ts owned: 1914 Runabout 1926 Coupe. Mercury Speedster #1249
Location: Usa
MTFCA Number: 24057

Re: Zajicek HC Head

Post by AndyClary » Wed Jun 03, 2020 9:23 am

I recently installed a new z head. It did require massaging of the chambers for piston clearance.

Andy


Topic author
SurveyKing
Posts: 449
Joined: Thu Jan 10, 2019 8:36 am
First Name: Daniel
Last Name: Snell
* REQUIRED* Type and Year of Model Ts owned: 1909 Touring, 1924 Touring, 1925 Roadster Pickup, 1921 Touring
Location: Boerne, Texas
MTFCA Number: 31662
MTFCI Number: 23677
Board Member Since: 2014

Re: Zajicek HC Head

Post by SurveyKing » Wed Jun 03, 2020 9:47 am

Hi Andy
What type of messaging did you have to do? Did you get a satisfactory boost in power?

User avatar

Mark Gregush
Posts: 4956
Joined: Sat Jan 05, 2019 1:57 pm
First Name: Mark
Last Name: Gregush
* REQUIRED* Type and Year of Model Ts owned: 1925 cutdown PU, 1920 Dodge touring, 1948 F2 Ford flat head 6 pickup 3 speed
Location: Portland Or
MTFCA Number: 52564
Board Member Since: 1999

Re: Zajicek HC Head

Post by Mark Gregush » Wed Jun 03, 2020 9:52 am

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! :shock:

1925 Cut down pickup
1920 Dodge touring
1948 Ford F2 pickup

User avatar

Oldav8tor
Posts: 1929
Joined: Sun Jan 06, 2019 11:39 am
First Name: Tim
Last Name: Juhl
* REQUIRED* Type and Year of Model Ts owned: 1917 Touring
Location: Thumb of Michigan
MTFCA Number: 50297
MTFCI Number: 24810
Board Member Since: 2018

Re: Zajicek HC Head

Post by Oldav8tor » Wed Jun 03, 2020 12:31 pm

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
1917 Touring
1946 Aeronca Champ
1952 Willys M38a1 Jeep (sold 2023)
1953 Ford Jubilee Tractor

User avatar

TonyB
Posts: 663
Joined: Fri Jan 04, 2019 11:15 am
First Name: Tony
Last Name: Bowker
* REQUIRED* Type and Year of Model Ts owned: 1914 touring
Location: La Mesa, CA
MTFCA Number: 32
MTFCA Life Member: YES
Board Member Since: 2005

Re: Zajicek HC Head

Post by TonyB » Wed Jun 03, 2020 1:05 pm

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.


BobD
Posts: 276
Joined: Sun Jan 06, 2019 3:08 pm
First Name: Bob
Last Name: Doris
* REQUIRED* Type and Year of Model Ts owned: 1926 Runabout, 1930 Sport Coupe
Location: Prescott, Arizona
MTFCA Number: 32538
Board Member Since: 2017

Re: Zajicek HC Head

Post by BobD » Wed Jun 03, 2020 1:12 pm

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. :)

Screen Shot 2020-06-03 at 9.54.54 AM.png


Randy SR
Posts: 30
Joined: Sun Jan 06, 2019 11:44 pm
First Name: Randall
Last Name: Schultz-Rathbun
* REQUIRED* Type and Year of Model Ts owned: 1926 roadster pickup
Location: Brush Prairie, WA

Re: Zajicek HC Head

Post by Randy SR » Wed Jun 03, 2020 5:17 pm

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.

User avatar

AndyClary
Posts: 605
Joined: Sun Jan 06, 2019 11:15 am
First Name: Andrew
Last Name: Clary
* REQUIRED* Type and Year of Model Ts owned: 1914 Runabout 1926 Coupe. Mercury Speedster #1249
Location: Usa
MTFCA Number: 24057

Re: Zajicek HC Head

Post by AndyClary » Wed Jun 03, 2020 5:50 pm

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

User avatar

Hap_Tucker
Posts: 365
Joined: Sun Jan 06, 2019 4:58 pm
First Name: Hap
Last Name: Tucker
* REQUIRED* Type and Year of Model Ts owned: 1915 cut off touring; 1918 touring; 1922 Speedster
Location: Sumter, SC
MTFCA Number: 100
MTFCA Life Member: YES

Re: Zajicek HC Head

Post by Hap_Tucker » Wed Jun 03, 2020 6:40 pm

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

User avatar

DanTreace
Posts: 3299
Joined: Sun Jan 06, 2019 10:56 am
First Name: Dan
Last Name: Treace
* REQUIRED* Type and Year of Model Ts owned: '23 cutoff, '25 touring, '27 touring
Location: North Central FL
MTFCA Number: 4838
MTFCI Number: 115
Board Member Since: 2000
Contact:

Re: Zajicek HC Head

Post by DanTreace » Wed Jun 03, 2020 8:45 pm

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
444582.jpg
444582.jpg (120.71 KiB) Viewed 5840 times

Prus head below, Z head above, see chamber differences in shape
Prus below Z above.jpg

Prus measured 210cc, Z measured 250cc in my garage tests.
Prus 210cc Z 250cc.jpg
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


Topic author
SurveyKing
Posts: 449
Joined: Thu Jan 10, 2019 8:36 am
First Name: Daniel
Last Name: Snell
* REQUIRED* Type and Year of Model Ts owned: 1909 Touring, 1924 Touring, 1925 Roadster Pickup, 1921 Touring
Location: Boerne, Texas
MTFCA Number: 31662
MTFCI Number: 23677
Board Member Since: 2014

Re: Zajicek HC Head

Post by SurveyKing » Thu Jun 04, 2020 9:50 am

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?


Wayfarer
Posts: 97
Joined: Fri Jan 03, 2020 10:04 pm
First Name: Cory
Last Name: Woerth
* REQUIRED* Type and Year of Model Ts owned: 26 engine on a stand, Canadian '23 center door
Location: Colorado Springs CO
Board Member Since: 2020

Re: Zajicek HC Head

Post by Wayfarer » Thu Jun 04, 2020 10:58 am

the compression ratio difference,as recorded in other threads about this subject, is minimal. Neither head approaches 6 to 1 compression ratio.


StanHowe
Posts: 979
Joined: Mon Jan 07, 2019 5:42 pm
First Name: Stan
Last Name: Howe
* REQUIRED* Type and Year of Model Ts owned: 2
Location: Helena, MT
MTFCA Number: 19133
Board Member Since: 1999

Re: Zajicek HC Head

Post by StanHowe » Thu Jun 04, 2020 2:06 pm

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.


rofirestone
Posts: 59
Joined: Sun Jan 06, 2019 9:41 pm
First Name: Roy
Last Name: Stone
* REQUIRED* Type and Year of Model Ts owned: 1915 Touring--1925 Tudor
Location: Poca, W V
MTFCA Number: 23830
MTFCI Number: 18986

Re: Zajicek HC Head

Post by rofirestone » Thu Jun 04, 2020 5:24 pm

TonyB wrote:
Wed Jun 03, 2020 1:05 pm
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


rofirestone
Posts: 59
Joined: Sun Jan 06, 2019 9:41 pm
First Name: Roy
Last Name: Stone
* REQUIRED* Type and Year of Model Ts owned: 1915 Touring--1925 Tudor
Location: Poca, W V
MTFCA Number: 23830
MTFCI Number: 18986

Re: Zajicek HC Head

Post by rofirestone » Thu Jun 04, 2020 5:29 pm

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👍

User avatar

Ruxstel24
Posts: 2345
Joined: Sun Jan 06, 2019 11:25 am
First Name: Dave
Last Name: Hanlon
* REQUIRED* Type and Year of Model Ts owned: 24 Touring car
Location: NE Ohio
MTFCA Number: 50191
Board Member Since: 2018

Re: Zajicek HC Head

Post by Ruxstel24 » Thu Jun 04, 2020 6:51 pm

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. :D


Gonenorth
Posts: 130
Joined: Tue Jan 08, 2019 6:04 pm
First Name: Kevin
Last Name: Whelihan
Location: Danbury, WI
MTFCA Number: 30688
Board Member Since: 2008

Re: Zajicek HC Head

Post by Gonenorth » Fri Jun 05, 2020 8:31 pm

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.


J1MGOLDEN
Posts: 945
Joined: Sun Jan 06, 2019 5:39 pm
First Name: James
Last Name: Golden
* REQUIRED* Type and Year of Model Ts owned: 1926 Model T Roadster
Location: Bowie, MD
MTFCA Number: 14294
MTFCI Number: 13562

Re: Zajicek HC Head

Post by J1MGOLDEN » Sat Jun 06, 2020 4:48 pm

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.


Mike Thomas
Posts: 26
Joined: Sun Jan 06, 2019 10:50 am
First Name: Mike
Last Name: Thomas
* REQUIRED* Type and Year of Model Ts owned: 1925 Coupe
Location: Centerville, Iowa

Re: Zajicek HC Head

Post by Mike Thomas » Sat Jun 06, 2020 10:50 pm

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.

Post Reply Previous topicNext topic