Which head to use?

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Model T Ford Forum: Forum 2013: Which head to use?
Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Everett on Monday, June 03, 2013 - 04:58 pm:

High head, or low head...that's the question!

If all factors about it are the same, for a speedster (stock components and 35 MPH cap) which head would be better?

Weigh in, please.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Everett on Monday, June 03, 2013 - 05:11 pm:

Although I've had both heads for years, I never noticed until now the difference in depth of the chambers between the high head on the right and the low on the left.

Assuming both are straight, no cracks, and ready to mount, which should be used?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bob Gruber- Spanaway, Wash. on Monday, June 03, 2013 - 05:13 pm:

Low one will give a couple more HPs.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bill Everett on Monday, June 03, 2013 - 05:14 pm:

High head on the left, low head on the right.




Top of pagePrevious messageNext messageBottom of page Link to this message  By Kerry van Ekeren (Australia) on Monday, June 03, 2013 - 05:19 pm:

The low head will give you a little more compression but the high head will give you a little more water. As for a little more torque, the low head is the more desirable one.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Nathan Bright on Monday, June 03, 2013 - 06:30 pm:

Low head will give better performance. If your engine tends to overheat you want to use the high head since it has a larget waterjacket. If you have an extra 50 bucks, you can mill your high head to give you the best of both worlds. Take off at least .125 up to .250. the more the better but make sure your pistons dont hit the head.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Monday, June 03, 2013 - 06:34 pm:

Most low heads won't give any measurable difference in power or torque than any high head - the difference in compression ratio is very small - 4:1 compared to 3.8:1 Only the 09/10 heads had noticeably more compression = 4.2:1 and thus some more power. See Tom Carnegie's dyno testing results at the Tulsa T club's website: http://mtfctulsa.com/Tech/head_dyno_testing.htm
1911-16 low head gave even lower power at certain rpm's than a stock high head.

For some real difference get a Z or Prus head. Prus heads weren't around when the Tulsa tests were done. Here's a dyno results comparing a Prus and a Z head by Tom Graham: http://www.mtfca.com/discus/messages/257047/324600.html?1354029640 - even more high end power with the Prus than with the Z head. Interesting enough the old Waucesha Ricardo head with only 4:1 compression ratio shows the best torque and hp of all at the lowest rpms, below 1000:

carnegie torque


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Monday, June 03, 2013 - 08:54 pm:

It's clear by that graph that the low head DOES provide a measurable increase in low-end torque. Looks about 10% or more. That's Huge! Also note that the high head has an abrupt spike at 900rpm whereas the low head is smooth and remains above the high head torque until 1300rpm. That's just where you want the torque for a cruiser. Horsepower takes over at about 1100rpm.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Monday, June 03, 2013 - 09:27 pm:

Those spikes may be due to crappy test technique. They were subjective readings of an analog pressure gauge. These graphs may be useful for spotting trends, but I wouldn't look at them with too critical of an eye.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Ken Kopsky, Lytle TX on Monday, June 03, 2013 - 10:48 pm:

True but the data has been published to show the results of different designs. Removing the spike and placing the point at the trending apex would give a better perspective. Even so, the low head shows better low end torque than the high head, all other things being equal. And it is measurable and significant. That's the point I'm making.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Nathan Bright on Tuesday, June 04, 2013 - 12:21 am:

im confuzed... what kind of head is the black "ford?" also, this shows that a milled high head is better than the z head at low RPMs... really?? thats hard to believe! im not sure what is the "best" head in this graph... the top three all have good characteristics. What range of RPMs do model ts operate at normally? I was gonna buy a Z head but now im wondering if if i should just mill the mess out of my high head.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Tom Carnegie on Tuesday, June 04, 2013 - 12:50 am:

The "Ford" is out of the service bulletins or some such book.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Mark Gregush Portland Oregon on Tuesday, June 04, 2013 - 01:02 am:

With a stock rear end 35 MPH is about 1400 RPM, 30 is about 1200.


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