Attention: Owners with Z head experience!!!

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Marshall V. Daut
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Attention: Owners with Z head experience!!!

Post by Marshall V. Daut » Thu Oct 03, 2019 10:07 am

'Sorry, Guys, but I have to post this question again. It got buried deep in my engine thread last week, so I guess no one saw it. I'm sure SOMEONE out there in Model T Land can answer it. I have a gut feel for the answer, but I'd like to run the question past Z head owners anyway.
We will be mounting the new Z head on my friend's T engine next week and I'd like to know what expected compression readings might be. The head is 6:1 CR, the pistons are 0.030" oversize, new rings, the valves have been re-lapped, and the camshaft seems to have good lift, although I suspect it is just a standard re-grind. With an original cylinder head, a good psi reading should be 55 or so. With the Z head in place, what should we expect to achieve with the engine cold and no manifolds (immediately after installing the head as a test) and then when it's been warmed up? Should the numbers go up as much as 5 psi once the engine is warmed up? I hope to see numbers in the 70-75psi range. Too high optimistic? Too low pessimistic?
I contacted the Z head manufacturer, but he didn't have the answer. I hope to provide him with one after you guys have chimed in. Thanks in advance.
Marshall, the Continually Frustrated One

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Ruxstel24
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Re: Attention: Owners with Z head experience!!!

Post by Ruxstel24 » Thu Oct 03, 2019 10:19 am

Marshal, I don’t have a direct answer to the PSI spec. But my opinion is that you won’t see a “true” reading until the rings and everything seats in...maybe 500-1000 miles.
Also there’s variations between engines...eg head gasket thickness, bore size, etc.


Burger in Spokane
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Re: Attention: Owners with Z head experience!!!

Post by Burger in Spokane » Thu Oct 03, 2019 10:26 am

I run a Z-head, but have never taken the numbers, like you are asking for. I can tell
you that my free starts stopped and the old dog scoots up hills like it never did before
though !
More people are doing it today than ever before !

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DanTreace
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Re: Attention: Owners with Z head experience!!!

Post by DanTreace » Thu Oct 03, 2019 12:45 pm

Put a used 'z' head on the '26, changed out from stock iron. When first start, hard knocks!!, shut off right away. But after blueing the combustion chambers, and removing some alum that allowed the pistons to strike, got great performance! Seat of the pants noticeable.

100_0389 (640x427).jpg
So, for any high compression head, safe way is to mount w/o gasket, and roll the crank around for all the pistons to rise and be sure the head won't rock on the block. Then add gasket and good to go.
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Re: Attention: Owners with Z head experience!!!

Post by Tim Williams » Thu Oct 03, 2019 2:40 pm

Not to Hijack the thread, but switching from cast iron pistons to aluminum one will I run into a clearance problem with the Z head? Again my apologies for asking this question on the thread. I current do not have clearance issues with the cast iron pistons.

Tim

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Thorlick
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Re: Attention: Owners with Z head experience!!!

Post by Thorlick » Thu Oct 03, 2019 5:16 pm

I've been running on a Z head for over 15 years. I had no problem with hitting my aluminum pistons until about the second time I had the head decked (due to warping when it ran low on water due to a gasket leak). I found that if you put the head in place without tightening the head bolts and without a gasket or spark plugs you can spin the crank. Spin it and if it hits you will hear a klunk. Now spin it with your hand on the head, you can feel the strike. You can go to TDC or BDC and use a feeler guage between the head and the block to get a "feel" (pun intended) for how much material to remove.

If I found a strike I would put the bluing on the inside of the head. After spinning the piston striking will show a blue spot on the offending piston and there will be a holiday in the even blue of the head's combustion chamber. I gently reduce the area in the head with a stone, a bur, or an abrasive disk and then repeat the procedure. Keep repeating until it doesn't strike the head anymore, ie. there is no knocking when you spin the crank and you cannot feel the head move. Now when you put in a head gasket you will be ok. I creep up on the problem removing tiny bits at a time. Once you remove the aluminum you are not going to put it back! I doubt you can remove enough to create a leak in the head thereby trashing the head, but each bit you remove will weaken the head. I believe that in a Z head the raised horse-shoe areas are fairly thick and this is where the piston will strike so you should be ok grinding there. At least I have never had a problem doing this adjustment.

You get about the most compression obtainable on your Z head this way. Be aware that if you are extremely close the buildup of carbon can cause a knock. This will require pulling the head off for "de-coking" (cleaning off the built up carbon).

IMHO, TH
Terry Horlick, Penn Valley, (Northern) CA
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Re: Attention: Owners with Z head experience!!!

Post by DanTreace » Thu Oct 03, 2019 5:56 pm

Tim

To add what Terry posted, the 'z' head has a thick squish area, and this head is cast alum, so the casting determines the combustion chamber, could be varying depths of the chamber at the squish ledge.

So, you should check before securing the head, by not using a gasket first and check. In my case, the used 'z' head may have been decked, my block was decked and new Egge pistons, stuck up like most do anyway.....but did hit, and I did the grinding away of spots on the squish ledge. No issues from years of running.
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Mark Gregush
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Re: Attention: Owners with Z head experience!!!

Post by Mark Gregush » Thu Oct 03, 2019 7:23 pm

other ways to check are; balls of aluminum foil place in several locations on the pistons or modelling clay.
I know the voices aren't real but damn they have some good ideas! :roll:

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Re: Attention: Owners with Z head experience!!!

Post by Oldav8tor » Thu Oct 03, 2019 8:35 pm

My compression readings on a broken-in engine with aluminum pistons varied from 80 to 75. The dyno showed 25 hp at 1600 rpm
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Re: Attention: Owners with Z head experience!!!

Post by Tim Williams » Thu Oct 03, 2019 9:40 pm

Thanks guys for the information. I will check when I put the aluminum pistons in.

Tim


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Marshall V. Daut
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Re: Attention: Owners with Z head experience!!!

Post by Marshall V. Daut » Fri Oct 04, 2019 11:21 am

Thank you all for your input so far.
Yes, I had planned on test fitting the head with and without the gasket once we have put the pistons in next week. The suggested 75-80 psi figure was about what I had thought might be achievable and desirable. I know it's not all about raising the compression in the cylinders. The head's combustion chambers and how the flame travels across the piston contribute to better performance, too. I had hoped we'd realize more than a 5 HP gain with this head, however. The head's accompanying instruction sheet claims a 7 HP increase. Does that 2 HP difference rally matter? Probably not when we're talking such low HP figures. 5 HP does represent a 25% increase, but I was hoping for more. We don't expect to end up with a 427 Corvette when all is said and done. We'd just like to feel more confident when taking the car out on the road that we won't be a hinderance to traffic. We were a road hazard before tearing into the engine with an average of 30 psi in the cylinders.
I'll come back later this coming week with the results of our labor, assuming it doesn't rain the day we're down on the farm and we can take the T out for a spin to gauge any improvement in performance.
Marshall


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Re: Attention: Owners with Z head experience!!!

Post by Burger in Spokane » Fri Oct 04, 2019 11:30 am

What do you mean by a "hindrance to traffic" ? Are you actually unable to keep up in regular
30-35 mph city/residential traffic ? Or are you trying to not annoy the Mario Andretti wannabees,
and pseudo-stunt drivers that create a reckless menace to people that DO drive safely ?
More people are doing it today than ever before !


Topic author
Marshall V. Daut
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Re: Attention: Owners with Z head experience!!!

Post by Marshall V. Daut » Fri Oct 04, 2019 11:44 am

'Nothing worse than being in front of some punk in a hurry to get to McDonald's to get his Oh! so important Bic Mac and fries in the next 30 seconds. In a Model T, the problem is compounded. My friend's Model T will never see the big city, as he lives in the country. But the paved road in front of his farm is a fairly busy artery for big farm trucks and semi-trucks on their way to or from Burlington. We have had these guys come up behind us WAY over the speed limit and pass us going around a blind curve. I know that going 5-10 miles an hour faster with the new cylinder head won't solve this kind of problem, but it will give my friend a little more confidence that he can move quicker to get off to the side of the road and let these guys pass.
Marshall


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Re: Attention: Owners with Z head experience!!!

Post by Scott_Conger » Fri Oct 04, 2019 11:53 am

Marshal

I was out of town and just saw your question: my response to you on your other thread provides you with exactly what you want to know regarding your head. That said, I am glad that Tim posted his results for you, but in the future, knowing the compression ratio and atmospheric pressure, it's simply a math problem.
Scott Conger

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Marshall V. Daut
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Re: Attention: Owners with Z head experience!!!

Post by Marshall V. Daut » Fri Oct 04, 2019 1:17 pm

Scott -
Yes, thank you. I did see your post with mathematical CR equation. Good information! I was looking more for actual real-life experiences where guys used a compression gauge to check the psi readings in their engines. Using your calculations would be an interesting mathematical exercise - if I could add 2 + 2 and not end up with 5 half the time. :) I'll try your recommendation and see how that compares to the actual readings we obtain from this engine. So many variables to take into consideration, such as valve sealing quality, lifter adjustment, cam lift/duration and ring end gap, that aren't taken into account with theoretical calculations. And it will be interesting to compare actual gauge readings with the engine cold after first being re-assembled next week and then again after the engine has warmed up, and even later when the rings have seated themselves. I was certain other guys with less than optimum professionally rebuilt engines like ours could provide the range of figures I was hoping to receive.
Thanks again for taking the time to explain the calculating procedure, Scott. I'll give 'er a whirl - as long as my wife checks my figuring afterwards!
Marshall, the "F" student in math class


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Re: Attention: Owners with Z head experience!!!

Post by Burger in Spokane » Fri Oct 04, 2019 1:45 pm

Ah, .... so you have those same stunt driver, can't be bothered to get up early enough
to get to work on time without speeding, my hair appointment is more important than
your life types in Iowa too ?

I guess I have a mild advantage, offering up a nice overhanging flatbed in which the
stunt drivers and inattentive texters can mash their windshield against. At least from
a direct rear approach ....

But to your point, I live on "the South Hill". There is no approach from town that is not
steep, and in most cases, long too. The Perry District sits in a bowl, about half way up to
the top, and Altamont Drive, while steep, is curvy and stair-stepped, making for easier
T driving at reasonable speeds. Before I did the Z-head and express gears, I backed traffic
up every time, having to go down to low pedal well before I crested any of the steep sections.
With the Z-head and express gears, I have the power to push my heavy TT up those steep
sections without low pedal, and the express gears allow me to get a good run at the hills,
again, the Z-head giving me more power to get up to those speeds.

I have clocked my TT at 48mph twice. On flat ground, and to be fair, it was wound out.
But 35-40 is comfortable, and hills are no longer an issue. Express gears are 5:1. When I
get the O/D in it, comfortable flat ground speeds should raise new issues like wheel and
tire balancing, that are not on the radar of a vehicle that normally does not exceed 40.
More people are doing it today than ever before !


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Re: Attention: Owners with Z head experience!!!

Post by Graybeard77 » Fri Oct 04, 2019 2:42 pm

I haven’t checked the comp. on my engine since I put the Z head on. Have over 1,000 miles on it and has really made difference in the hills. Drove to St. Louis, Mo. Last Friday on old Rt. 66. My for-dor is heavy but only in low once. Best money I spent on my 26 T. Improved my mileage also. Clyde.

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