Hello again. Past threads I have read seem to tout the Z hi-comp head as a winner. Does the extra compression wreak any havoc on stock engine parts? I'm just trying to gain a little more horsepower, not building a racer. My 26 motor runs well and has aluminum pistons now. Thoughts? Concerns? Thanks, Howard

I had one on my stock 1926 express. It made a huge difference on hills. As soon as I can afford one for my new T, I plan to get another one.

Mike

Howard,
I've got a Ricardo Waukeshaw head on my Speedster, and performance is excellent, considering what the rest of the engine is. Have had no problems with it at all, just better performance.
Bob

Howard,

With today's fuel, it is a shame not to have one. If you use the extra power all the time, of course you will have accelerated engine wear, but if you drive your car reasonably - nothing but a win-win situation IMO. Your car will run cooler, as will the exhaust valves and the manifold, and it will use less fuel.

Seth

The Z head is a copy of the old Haibe High Power. If you can find one of those, they are as good or better than a Z. If you can't, my choice is the Z. Stay away from the Lizard, also known as the Yapp Crapp. If you want one that leaks water like a sieve because of the core shift problem they couldn't solve, I have one for sale. I have a Haibe and think it runs better than a Waukesha Ricardo but it is a pretty subjective evaluation. "You can't go wrong with a Z and it won't hurt your T." I would have made that the sale slogan if I had developed them.

You can not use a high compression head with domed pistons.

You can not use a high compression head with an old tired engine.

One of our club members got about 5 miles on his new high compression head before the rods started knocking rather badly.

From everything I have researched so far “everyday for 5 years, every book I have read over and over, as well as post after post on these boards” I have come to the conclusion that it is best to stay away from any high compression anything and I personally would recommend keeping the Ford Model T engine 100% stock or as stock as you can get it, unless you are building a racer for speed.

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MY ANALYSIS:

FACT: There are a lot of crankshafts being broken everyday – most can be tracked back to bad alignment problems. The best of the best Model T Mechanics have stated that there are 3 things that cause crankshafts to being broken and they are alignment, alignment, and alignment. BUT… you would think there would be another factor and that would be:

#1 Increasing compression not only increases your power but it also increases the forces and stress at the crankshaft. This would be similar to revving up your engine to move up a hill “a BIG no-no” that will lead to a broken crankshaft. This would add more stress to an already old, week, small or even smaller under sized crankshaft from the forces caused by the high compression heads or pistons. This added force can not be good and in my theory could lead to a crankshaft fracture.

&

#2 Installation of newer modern 4th main bearings “that ford had at their disposal back in the 1920’s” that they opted out of in favor of Babbitt. These newer modern bearings do not allow for ware like the Babbitt does forcing the transmission to run 100% true to fit where if it were aligned “right on” and stayed that way “run a wheel over a curb or pothole and the pan will take a bend causing miss-alignment” it would not be a problem, but if there were any miss-alignment at all one would think the Babbitt would confirm to this ware lessoning the stress on the crankshaft allowing a kind of self fix and the newer modern bearing would force the crankshaft to bend over and over causing the fracture.


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This is just my opinion that goes into a little more detail then you asked, but it is on the subject and should be kept in the back of your head. I am in no way a professional mechanic yet and I am still learning and have a long way to go. Others here will probably trash my analysis but that is fine, this is my theory and I stand by it.


Travis E. Towle
Topeka, Kansas

785-554-8238 cell
1-800-579-6477 home office

Z head YES YES YES. I have been able to get over 50hp with a Z head.
Seth and James are on the money.

Stan, The would be the slogan to use. IIIIII like it!!

Howard; My opinion is that if it takes 15 Hp to power a 'T' at 30 MPH with a stock head, it will take 15 Hp to power the same 'T' 30 MPH with a high compression head. The forces on the engine only increase when the engine is using the extra power the head makes available.

As Seth has indicated, the fuel mileage will increase and the engine will run cooler.

Sincerely

Jim Weir

Jim and/or Seth - Have to show my ignorance here; I certainly understand why the increased power and better gas mileage with higher compression (and more effecient shaped combustion chamber), but why would the engine run cooler? Thanx for anyone who could explain this to an old guy that's still trying to learn.

Howard;

I've run a high compression head for over 15 years on my T, and my father's car had a high compression head for many many years; he had one on it before I was born. Other then the head the engines were completely stock. I never had any problems with anything as a result of the head, period, and I was never hesitant to take my car and drive it 100+ miles a day on a week long tour. I've been driving Ts for a little over 35 years. I drive in the Sierras and coastal mountains of California as well as the Rockies on occaision. I avoid in-town driving when I can. I do not baby my T, but I don't run it into the ground either.

I had the exact same concerns when I installed a 6.5:1 head on my '15 with babbit. I adjusted my rod and main bearings when I put the head on so they were in close tolerance; that's very important to do. I run coils on magneto and use both Ford Faithful and mag post oilers; nothing fancy. I've got Ruckstells and external brakes on both of my T's.

The 3 best things you can do to improve the tourability (is that a word?) of a T is:

1 Rocky mountain (or other) external brakes
2 High compression head
3 Ruckstell axle

If you tour in the mountains I'd put the Ruckstell in front of the head.

Most people that tour regularly keep their cars in good repair; you just don't go out on a 400 or 500 mile week long tour an a tired engine that you don't know is in good repair. I figure you're probably going to tour or you probably wouldn't be considering the head. As long as your bearings are adjusted properly when you put the head on(that's an afternoon job) you'll be pleased. You'll probably be kicking yourself for not installing it earlier.... I know I was.

Harold,

The higher compression assures that the combustion process is completed before the exhaust valves open. The stock 4:1 compression was just that to deal with the low octane fuel available then. Modern fuel allows higher compression and the engine's thermal efficiency rises with any increase in compression ratio. To cruise at 30 mph with a high compression head, the throttle will not have to be open as far. If an engine burns less fuel to make the same amount of power, it will run cooler.

Seth

Well that certainly makes sense! Thanx Seth,....harold

A high compression head causes the engine to run cooler mostly because it's also a high expansion head. The higher expansion ratio means that the exhaust gases are cooler.

Harold, the Z head also holds a little more water (I seem to remember a quart??) than the stock head, so it will cool that much more.

I put a Z head on over a year ago, and have not regretted it a bit! I would recommend you check your rod bearings (at least), and tighten them up as a precautionary measure before using the Z head.

IMHO, the best upgrade (with Rocky Mountain Brakes a close second) you can make on your T.

Bob

Yeah Bob; I did know about the increased coolant capacity; that makes sense too; thanx,....harold

Skinned knuckles reprinted an article from a garage owners' magazine from the 1930s in which they claimed high compression would improve fuel economy, and be easier on the bearings. When owners complained of no better economy, they admitted using the extra power to get more performance.

www.SkinnedKnuckles.net

Can't find the article in the past issue list, so have asked the publisher to identify it.

rdr

A typical stock Model T engine will have a compression ratio of 4:1 and produce a compression reading of 40 to 55. A 40 psi engine can still run well, but slow more on hills and will have a lower top speed. A 50 psi engine, without domed pistons, is normally healthy enough for a high compression head.

On the plus side, a high compression head will raise the compression to about 95 psi, which is just about double a stock engine compression reading and provide a noticeable power increase. On the minus side, the engine may be difficult to start, almost impossible to crank by hand, will use more oil and smoke a lot more. The engine will also lose the relaxed Model T sound produced by 4 good coils and sound more like it is laboring to make a hill, even when it is idling. Corrosion can also be a real problem with the aluminum head in a few years.

The domed pistons will raise the compression to about 75 psi on a good engine for about half the cost and also provide less strain on the rod and crankshaft bearings.

I've had only one experience with a high compression head & it was all for the better. I installed the head on a then recently re-built T (my first T a 23 roadster with a serial # '25 engine). In literal language terms it turned the motor from a chugger to a thumper. In performance terms it climbed hills in high gear which were only climbed in low gear.
Edward R. Levy
P.S. During my ownership of the vehicle (18 years) I adjusted the Rod bearings twicw & the Mains not at all)
Edward R. Levy

Howard:

Happy Thanksgiving to All !!

Two negative responders out of the whole bunch...... I too have a Z head on a '26 Runabout. I also run a Anderson style timer with coils, standard rear gears, and all synthetic lubricants. No problem whatsoever with bearings, starts easy in cold weather either hand cranking on magneto or with the starter.

Starting problems have a few causes : Poor fuel mixture, low compression, poor spark, wrong timing, maladjusted or weak coils. Don't blame a cylinder head for that.

The Z head combustion chamber is designed to swirl the mixture for a more complete burn, with the added compression results in a extra perky engine.

Shaving a standard Ford head will raise compression a bit, but will not afford the same mixture burn

Actual compression readings are less that reported above " in theory ".

Travis & Jim :
If there were so many negatives with the "Z" head, why are so many T owners happy with it's results ?
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Bob Jablonski

Bob,

I am a speedster owner without the benefit of a Z head. I have never been around another T, so I've obviously not had the pleasure of enjoying a T with a Z head.

But I know what it would do for my car and you can bet that obtaining one will be high on my list of priorities!

Happy Thanksgiving to everyone, regardless of where you call home.

Seth

Seth:

Happy Thanksgiving to you & your family.

If you do get a "Z" head, lets say from a white bearded fat guy in the short term, will the great state of Louisiana change your plate to read " 25 HP " ?????

Harlon Zaijacek sells the "Z" head, may even have a vendor listing on this website. He and his brother before him have been advertising in the Vintage Ford over 15 years that I'm aware.

Go find some other T's

Thanks Bob!

No, I imagine that Louisiana would look the other way if I was to fit a Z head since lies and corruption tend to prevail in Louisiana anyway. LOL!

I know how to get a Z head for sure, it's just mighty hard to consider that priority when there are so many other things needing to be done in order to pass "tech inspection" by the MTFCA in order to be allowed to tour next summer............

Seth

95 psi sounds high for a high compression head with regular pistons, but perhaps in the right neighborhood if combined with domed, high compression pistons.

The Tulsa club did some research on various Model T heads, including measuring the combustion chamber volume and calculating compression ratio. Both the Z and Reeder heads CR were 5.3:1 (below the often quoted 6:1) compared to original head CRs of 3.8:1 to 4.2:1 depending on vintage of the original head.
An increase of compression ratio from 4.0:1 to 5.3:1 should raise compression by about 33%, not double it.

http://clubs.hemmings.com/frameset.cfm?club=mtfctulsa Click on "Technical", then on "Model T Accessory Heads".

Raising the CR from 4.0 to 5.33:1 would increase the cranking compression 1.33 to the 1.4 power (the k for air - air is far from a perfect gas) - not just 33%. This would be exactly the case if the intake valve closed at bottom dead center and no heat was lost during the compression process.

Jim Golden is in the ballpark regarding that compression figure as far as I'm concerned.

Seth

Seth, why would raising compression ratio with domed pistons cause a different compression pressure than raising compression ratio with a high compression head?

The Tech sheet for the 2008 is I believe the same check sheet we use for every National tour, its for your family's safety and the other T'ers. The cost of the week is cheap, if you make National tours like we have for years, you pay for T and driver, and Pass. so much, then there are extra meals, goodies you purchase while there etc. Motels, or camper chgs etc. Fuel to get there, flats etc. that's life. THIS will be the 100th anniv, of the Model T, when its over there will NEVER be ANOTHER. Ive been a member since 1966, club started in 1965, I was the only member of our club for 10 yrs before starting a chapter in 1976, we hosted 3 Natl tours with 6 members, and families, I still have the 26 TT I bought when I was 16 in 1956, , so you have 2 choices ENJOY the festivities, or stay at home, and belly-ache later I wish I'd gone. We will be there John and Karen Danuser Fulton Mo

1.33 to the 1.4 power is 1.49. So given the assumptions Seth stated if compression pressure is originally 50 psi and the CR is raised from 4.0 to 5.3 (33% increase) then the compression pressure should go to 75 psi, not the 95 psi Jim Golden suggests.

Anyone have actual compression pressure with a stock head and a high compression head on the same engine? Or even compression pressure on an engine? There's too much speculation and not enough data.

Jim didn't do the math, he just measured the compression.

Something that hasn't been mentioned in this thread is cranking the engine with a high compression head. I am running a lizard with a 6.5 ratio, and I have to depend on the starter now. Even after it is warmed up I can just barely turn it over with the crank.

Jim, What head did you measure 95 psi compression with? Z, Reeder, Lizard, or ??? Had it been milled? Do you know what the compression pressure was with a stock head?

Just looking for information so I can learn. Thanks.

That was a Z head, but the unknown factor is how much the block was shaved on the top, if at all. Theoretically though 14.5 psi at sea level Times 6.5 Equals 94.25 which is close to the 95.

Some of our older club members could not hand crank the engine after the Z head was installed.

Guys,

We've had this discussion before, at length, and I guess since I haven't messed with model Ts for twenty years or more, it was taken as just more BS from a newbie.

Jim Golden measured cranking compression with a Z head and reported some 95 psig which I said was in the ballpark.

The CR is calculated using the FULL swept volume, but the full swept volume is not compressed because the intake valve is open well after BDC.

The volume in the guage adds to the volume in the combustion chamber.

Some of the heat of compression is lost to the cylinder walls, the piston top, and the combustion chamber.

All three of these things will lower the calculated number.

What's the point in arguing about it anyway - it is just a dang model T engine that is doing great if it reaches 10hp/litre!

Seth

Adding a Stipe Cam along with the High Compression head will make you a very happy camper indeed!

Thanks Jim for the information. Data is always useful.

I'm reading this with great interest. I like having neat products available from fine suppliers. I've never read or heard anything bad about the Z head.

But, I'm not sure that it's the end all, be all that some proclaim it. This spring, I bought a car that had been rebuilt with aluminum pistons, a "touring grind" cam and a Z head. My "seat of the pants" experience with the car did not give me the impression that it had as much power as the other engines in our stable. Most of our engines have plain aluminum pistons, Stipe .280 cams and stock heads milled .125".

I'm guessing that in the right engine, the Z head can be just great. But, without a top shelf cam, the engine will still strangle itself. I'd love to see a dyno test with an engine with a Z head and a typical used or reground cam vs. a Stipe cam and a milled stock head. Of course, we all know that the Z head with a Stipe cam would be the best performer of all. But, I wonder where a guy's best bet is when he's only got enough money in his budget for either the cam or the head, but not both. I didn't own that car with the Z head long enough to do any further experimenting.

You know the Z head will ADD to the performance of the engine, so that is the first place to put the money for better performance if you have a less than $500 budget for more power. I'm assuming here that we are talking about engines that already have aluminum pistons. Cams, albeit not the Stipe, are cheap. A touring grind cam from Chaffins is about $60.00 A Carnegie Brothers cam will do wonders for an engine for about the same money. The Z head will cost about $325 delivered to your door. Add a good head gasket and you are still at $350. While a Stipe is probably the best cam I can say from personal experience that the Carnegie cams will give you more overall zoom than a stock cam and do it using the same cam bearings and lifters you have now so the cost of installing one of them is less than $100. That's where I'd put my money. The Montana 500 rules will not allow any other head than Ford script high type. But you can whack as much as you want off it. Most of the cars have at least .125 off them, some even more. Those cars will run with the big dogs all day long but I think they would run even better with a Z head. My racer sure did. I had a 500 engine with a good cam, shaved head, decked block, etc., but when I put the Z head on it there was a definite boost in power and speed. If I only had, say, a hundred bucks or so to play with, I'd chisel an eighth of an inch off a stock head, put a Carnegie cam in it and go play. Remember here that one goal with a 500 car is to go DOWN hills really fast as well as going UP hills really fast. Going down, the cam will control the speed as much as it does going up. Suck, Squeeze, Bang, Blow, Suck, Squeeze, Bang, Blow.

Bill Stipe offers a reground T cam for $85.
http://www.specialtymotorcams.com/pages/camshafts.html

Hi Folks,

I'm stuffed, but I guess them's the rules for Thanksgiving. Hope everyone else ate well too.

I had started another thread, big gulp intake manifold, but didn't get any hits. I figured it was closely related to this one. Regardless of the head, wouldn't the motor run more like Lance Armstrong with bigger lungs pulling more air? The question I was asking was wouldn't you also need to exhaust more if you were breathing better with the high volume intake manifold in order to realize better performance? It makes sense that a larger intake would help performance, but I'm just wondering whether I need the improved exhaust as well.

Thank you all for such great and well-thought responses about the Z head. My motor is good and tight so I'm not going to worry about the bearing stress from the extra CR. I think the Z head will fit down the chimney just fine. Santa best get the hint. Thanks all, Howard

I have aluminum heads on both my Model T's. This is the single best part that can be added to a Model T. Anybody who has not tried this and is saying it is bad is simply not well informed.

Since my cars are 1913 and 1915 I could not use the high "Z" head as it would not fit under the coil box. Be sure you get a low head if your T came with one originally.

Royce

Thanks to improved fuels today, high compression will provide more power/economy at all rpm from every T engine.

Consider the T intake and exhaust to be a balanced system which is optimized for the rpm range of the engine. If you want power at higher rpm, you need to improve the breathing. That means all these: carb, intake manifold, valve lift/duration, exhaust manifold and muffler.

A better carb than the stock style puddle carb will give better economy and smoother running by itself, but not necessarily more power.

rdr

If you want the benefit of the improved design combustion chamber a Z head offers, but want to stick with a lower compression head, try the Ricardo head. I have one on a heavy wood bodied T pick up and its the strongest running T I own. With a 250 Stipe cam, a high volume intake manifold, a modern core radiator, an NH straight thru carb and a Ruckstell, I drive the mountain roads from Folsom to Soda Springs at least once a year. I tried it with a stock T outfitted with a Ruckstell and I didn't have enough power nor cooling capacity. Only made it about half way up before deciding to turn around for home. I have a Z head I will be installing on the pickup and will post back if I notice a difference between the two.

I would be leary of installing any type of high compression head on a engine that hasnt just been gone thru.To much to ask of old babbit and unknown parts.
I would also think that alot more power would kinda take away that "T" feeling of being able to just clear the hill.

If you live in the flat country you will probably see little use for a little more power. Here in Northern California we have some pretty fair hills and mountains. An aftermarket head is not an insane amount of compression, but is a big assistance with the hills. Compression doesn't break crankshafts, people do.

Andy Clary

Andy,

I live in northwest Louisiana which is flat by most people's standards. A high-compression head would be important to me so that my car would accelerate that much better which might be a good idea around here with all the impatient drivers. It also would cool my engine somewhat, saving me the expense of a $700+ radiator which my car could really use.

I'm not disagreeing with you at all, especially regarding your final comment!

Seth

I live here in Snuffy Smith land and the hills can be very steep,my coupe wouldn't go up in high on most ,i even installed a new Warford which helped a lot but i put a Z head on and rarely need the Warford,my engine was rebuilt three years ago by Ron Miller so i know it is in good shape,i do wory about the crank though,the head adds about +-seven HP.so a thirty percent increase in power.
Rick

Rick,

You aren't using the benefit of the head for 35% more power, you are using it for 35% more torque since you are stating that it allows you to pull the hills in high gear.

It is true that you are adding 35% pressure to the babbitt bearings and you are twisting the crank 35% more, but having 35% more torque at 1000 rpm is not at all the same thing as having 35% more power at the peak power point of some 1600 rpm.

In my not so humble opinion, you can breathe easy and stop worrying about the crankshaft. If you do that, you are likely to enjoy your car more. Just listen for loose babbitt and take up the slack when needed.

Drag racers like Dr. Noel are the kinds of guys that need to worry about their crankshafts, not you. (IMNSHO)

Seth

That is one good license plate. Maybe some of the impatient drivers might not be so quick to judge if they see that.
I once had a devil of a time getting up some hill east of Placerville, so much so I was in low or maybe even Ruckstell low for a bit. A woman driver came up behind me and honked. There was no place to pull so she must have been thinking I was taking my time gazing at the scenery. She was driving some older model import and didn't have a clue how hard it was getting up that hill.

The loads on the rod and main bearings are from a combination of the power/torque producing forces of the gases on the piston tops acting through the rods, and the inertal loads due to the rods and pistons accelerating and de-accelerating twice every revolution. I haven't done the calculation for a Model T engine but I suspect the inertial loads are greater than the power producing forces at higher engine speeds. So an increase of X% in torque/power at higher speeds won't increase loads on the bearings by a corresponding X%. The increase in bearing loads will be a considerably lower percent.

Power = Torque X Speed
Torque = Power / Speed
(appropriate conversion factors needed depending on units used)
An increase in torque at a given speed will also result in an increase in power at the same speed. An increase in power at a given speed will also result in an increase in torque at the same speed. So the shape of the power curve and torque curve are directly related.

I agree that for most Model T driving and hill climbing in particular an increase in torque/power at moderate engine speeds is more important than the peak power/torque. Higher compression ratio should help across the engine speed range, while improved breathing generally provides maximum benefit at higher speeds. Benefits of a different camshaft vary depending on the particular profile. With a reground Moel T camshaft there has to be a compromise between amount of lift (better breathing) and duration (too much decreases mid-range power/torque).

LOL! Maybe I should have said, "The loads on the bearings on the crankshaft will rise 35% due to the gas pressure component."

You are correct David. I stand corrected.

See Wade, I'm no expert at all, so Rick Goelz has even less to worry about!

Seth

Someone asked about crank starting with a high compression head. I normally do not use the starters in my Model T's unless I happen to stall the car in an intersection with oncoming traffic coming my way. I find that it is no big deal but I must say that I am a big strong guy. There is more effort required to hand crank your car with the high compression head. If you are near your physical limit cranking with a stock head this might be the time to install a starter.

Royce

Royce - If I remember correctly from years ago when I had a Model A, I'm pretty sure the crank (hand crank for starting that is) is slightly longer due to the Model A having a larger 4-cyl engine. By the hand crank being "longer", I mean a slightly greater distance between the axis of the portion of the crank that you grip with your hand, to the axis of the crank which coincides with the axis of the engine crankshaft. How about adapting a Model A hand crank to a "T", or, modifying a Model T hand crank to approximate the larger size of the Model A hand crank for engines with high compression heads? More leverage, hence easier to crank the engine over, no?

Harold,

I've cranked a Model A and can say that it is a whole different animal than cranking a T. Before you change anything just give it a try. Most people of average strength are not going to have a problem hand cranking a T with a high compression head. If you are elderly, disabled or have arthritis you probably need to think about adding a starter.

Royce

The crank for our '29 Model A has the same throw as the crank for our '16 Model T.

The front bumper on an A makes the A harder to crank than a T without a bumper because the A has a front bumper. Consequently you have to lean over to crank an A rather than stand directly next to the crank as you can on a T without a bumper.

Our A has a 5.9 compression ratio head, and I've hand cranked it a couple of times when the engine was warm. Not too bad but not something I'd want to do everyday, primarially because of having to lean over the bumper. Our T doesn't have a starter so I always hand crank it and see no reason to add a starter.

Years ago while in high school I drove the family Model A (original 4.2 CR head) frequently. A broken bendix spring meant the starter wasn't working for a couple of months. I hand cranked it to get it out of the garage, but when I made a stop I always looked for a grade to park on so I could coast and "bump" start it instead of hand cranking. One time I was out with my sister who didn't know how to drive a manual transmission. We made a stop at the local McDonald's which had a flat parking lot. So instead of hand cranking I persuaded my sister to sit behind the wheel with her foot on the clutch, and the transmission in 2nd gear. I pushed the car to get it moving then told her to lift up with her left foot. She did, the engine started, and she was headed across the parking lot yelling "what do I do to stop!". Eventually she pushed back down with her left foot before hitting another car.