High Comp. Head question

Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration
Model T Ford Forum: Forum 2005: High Comp. Head question
Top of pagePrevious messageNext messageBottom of page Link to this message  By Steve on Wednesday, September 19, 2007 - 09:42 pm:

A recent posting had a question about wether to buy a high comp. head and everyone said "yes".

So it's unanimous, more compression is good. So what is the difference between an aftermarket high comp. head and a stock head that is milled down to raise the comp. ratio?

I have heard of stock head's getting up to an eigth of an inch taken off! How would that "new" comp. ratio compare to the manufactured head's?

Steve


Top of pagePrevious messageNext messageBottom of page Link to this message  By bobster on Wednesday, September 19, 2007 - 09:50 pm:

Steve, the difference is that the "new" HP head (like the "Z" head) has a "Ricardo-style" combustion chamber that uses the gas vapor more efficiently, boosting the compression ratio to @ 6:1.

I'm not sure of the numbers, but a milled high-head doesn't come close to that ratio (somewhere around 4:1 ?)

Bob


Top of pagePrevious messageNext messageBottom of page Link to this message  By David_Cockey on Wednesday, September 19, 2007 - 09:55 pm:

A good "high compression" head should also improve the engine breathing. More mixture in means more power.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Royce Peterson on Thursday, September 20, 2007 - 06:45 am:

An aluminum head weighs about 1/2 as much as well as providing more efficient combustion for more horsepower while using less fuel.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck - SHVLA on Thursday, September 20, 2007 - 07:43 am:

Steve,

Milling the head an eighth of an inch will raise the compression on a high head (some 1917 and later) from the original 3.98:1 to no more than 4.5:1.

The popular Z head will raise it to 6:1 which not only adds power and fuel economy, it will make the engine run cooler under the same loads.

Modern gasoline is "octane-high" for stock, low-compression T engines and excessive heating of the exhaust valves, seats, and ports is a result of that.

In my opinion, a high-compression head like the Z is the single best improvement you can make to the T. All Z head owners would probably agree.

Seth


Top of pagePrevious messageNext messageBottom of page Link to this message  By Michael Pawelek on Thursday, September 20, 2007 - 08:14 am:

Steve, Note the design of the combustion chambers in the three examples below.
Top is "Z" head.
Middle is "Ricardo".
Bottom is "Ford".
roifvapr8tq9[4th[ert[w9tjv4t9093tmb


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jim Weir on Thursday, September 20, 2007 - 08:54 am:

Steve; The Ricardo style head has an area over the piston that is quite close to the top of the piston. When the piston is transitioning from the compression to the power stroke, the mixture is forced out of that area to increase the turbulence in the combustion chamber. This increase in turbulence or swirl, leads to more complete, and controlled combustion partly by reducing the stagnant or boundry layer of unburned mixture.

So in my opinion the Ricardo type head or 'Z' head will ad more power than a poorly designed head of the same compression ratio.

Sincerely

Jim Weir


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthony J. Marino on Thursday, September 20, 2007 - 02:43 pm:

Will a high compression Z head work with high dome aluminum pistons?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mike Walker, NW AR. on Thursday, September 20, 2007 - 02:55 pm:

No -- You can use one or the other, but not both.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Anthony J. Marino on Thursday, September 20, 2007 - 03:21 pm:

Could a comparable 'Z' head compression ratio be achieved with a stock/un-milled Ford head and 'high dome' aluminum pistons?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry VanOoteghem on Thursday, September 20, 2007 - 03:36 pm:

Anthony,

Read Jim Weir's post above. Just getting the compression ratio up is only half the story.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Tillstrom on Thursday, September 20, 2007 - 03:50 pm:

For $315 you just can't come up with an easier add on for the horsepower and hill climbing ability you get with a Z head. A buddy of mine has a very nice depot hack that was a bit weak on the hills. We drilled new dowel pin holes in a stock Ford cam gear and advanced the cam by 1/2 a tooth. This made a big difference in grunting power for the car. The next move was a Z head and it made a huge difference.

My 27 touring has a 3:1 gear so it was a bit weak on any hill. I added a Z head and it was a different car. This spring the fiber timing gear installed by the previous owner shredded itself. I installed a new aluminum gear from TTP (which appears to be 7075T6 aluminum) except I made a new timing mark on it and drilled the new dowel pin holes in it.

Having driven the car without the head and without the modified valve timing and then driven it with both mods I can say I will probably never install a stock head again and if I ever need to change a timing gear it will automatically be advanced 1/2 tooth.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris on Thursday, September 20, 2007 - 04:02 pm:

The Z head has a wedge built into it much like the 49 Cadillac overhead valve engine and also Oldsmobile engine did. They just had a slope and the Z head has a V-shaped cut out for flow and lower material around the edges.

A high compression domed piston pushes all of the gasses equally all over the combustion chamber on the exhaust stroke and the gasses are confused thus they must wait for the valve to open before they get their marching orders. The Z head pushes it towards the exhaust valve for better volumetric efficiency even before the exhaust valve opens.

One could suppose that you could install a Z head and then make a piston with the reverse shape in the top of it so as to raise the compression ratio even higher. 10 or 11 to one and higher are possible. A set of custome made cylinders would cost in the range of $1200 and up if you really want to scare people, including yourself.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul Vitko on Thursday, September 20, 2007 - 08:05 pm:

Interesting post on the timing gear half tooth advancement Gary. What happens to the top end?

I have two Ts with the Z. Nothing needed to be done with the 22 but about four hours were spent with a router increasing the squish clearance to thirty five thousands on the 26. Have no Idea if the block was decked or if it was the combination of parts used and the Z came from another engine used. The squish is even in all cylinders now.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Tillstrom on Saturday, September 22, 2007 - 06:46 pm:

I can say I don't see a difference in top end on my car (will still run 50 MPH+). Ralph did say his hack went from 45 to 43 after changing the cam timing. He also said he wanted the bottom end rather than the 2 MPH he gave up.

99% of all my driving is at 30-35 MPH. The only time I will run faster it to keep up with traffic. This afternoon I was in heavy traffic on a four lane road with a speed limit of 40 so I had to pick it up a bit until I turned.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck - SHVLA on Saturday, September 22, 2007 - 07:05 pm:

Gary,

You can bet that I'll do the same as you do. I run 3:1 gears and no auxiliary gears, so grunt at low speed means everything - and my car goes faster now than I want to drive. Paul is a speed demon in his T so he probably would never advance the cam - but he has some serious brakes, so I guess it is OK for him to speed as long as noone is riding with him and the insurance policies are paid up. :-)

Please allow me to ask this question:

How difficult a pull is it (hand-starts) with a Z-head and cam timing advanced? Advancing the cam will add to the cranking and low speed compression ratio. I've gotta be able to hand-crank the old thing and I already have one hernia I refuse to have fixed.

Thanks in advance,

Seth


Top of pagePrevious messageNext messageBottom of page Link to this message  By Paul Vitko on Saturday, September 22, 2007 - 08:32 pm:

Thanks Gary,
I prefer up to forty seven MPH slower would be fine but with coastal 101 traffic I can create a hazard with slow speed. So I live with the cards I am dealt with!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tim Moore on Sunday, September 23, 2007 - 12:59 am:

Seth;

What does SHVLA after your name mean? I have always wondered.

Tim Moore


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck - SHVLA on Sunday, September 23, 2007 - 07:16 am:

Tim,

Shreveport, Louisiana

Seth


Top of pagePrevious messageNext messageBottom of page Link to this message  By Noel Denis Chicoine, MD on Sunday, September 23, 2007 - 04:58 pm:

Seth, I've not advanced the camshaft, but have a Z head. I was worried about difficulty starting on crank also, but it hasn't been a noticeable difference. I don't get as many free starts, though. I almost always start my T by hand. It usually only takes 1 or 2 quarter pulls. I've shown a number of young ladies how easily they can start a T. On battery, all you have to do is pull it over center. You really don't need any speed. I need to pull faster if I try to start on Magneto. I don't think you'd do any more damage to your hernia with a Z head than with a stock head. Besides, you should get your hernia fixed now before you get old(er) and have a harder time healing. The laparoscopic mesh repairs are usually pretty slick and work well. Why put up with it?
Noel


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck - SHVLA on Sunday, September 23, 2007 - 05:24 pm:

Noel,

I mostly hand-crank except for that first (cold) time then I prefer the starter, but it is very easy with maybe 4.2:1 CR now. By the time I take it apart, I will use a Z and just pull a little harder.

Older.

The hernia is no big deal really, but I do agree that the sooner the better. Thanks.

Seth


Top of pagePrevious messageNext messageBottom of page Link to this message  By Gary Tillstrom on Monday, September 24, 2007 - 11:22 am:

Seth,

My car has a 12 volt battery (until it dies and gets replaced with a 6 volt) so I crank it by hand to save the starter from damage. Very seldom will I use the starter. I didn't see any real increase in difficulty as far as effort after I advanced the gear. I ran with the head and stock timing for about a year before the fiber gear came apart. The replacement gear was aluminum and I re-indexed it.

I have a PDF that was in one of our news letters a few years ago with a good picture that explains how to redrill the index holes (not rocket science). Shoot me an email and I'll send it to you. Gary


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth Harbuck - SHVLA on Monday, September 24, 2007 - 11:43 am:

Thanks Gary, I'll do that!

Seth


Posting is currently disabled in this topic. Contact your discussion moderator for more information.
Topics Last Day Last Week Tree View    Getting Started Formatting Troubleshooting Program Credits    New Messages Keyword Search Contact Moderators Edit Profile Administration