High comp head versus high comp pistons

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Model T Ford Forum: Forum 2012: High comp head versus high comp pistons
Top of pagePrevious messageNext messageBottom of page Link to this message  By Ted Mumme on Saturday, July 28, 2012 - 08:02 am:

G'day everyone . Does anybody have any experience that shows better results(better performance) using high compression pistons instead of a high compression head? Does one perform better than the other? I am considering this from a racing point of view.
Cheers
Ted


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dare - Just a little South West . on Saturday, July 28, 2012 - 09:36 am:

G'day Ted right back at ya !, l see this is posting # 1 ....WELCOME to the MTFCA.

This topic has been discussed many many times, if you type in you title into the Keyword search, just above in the blue symbols you should find many different views.
Send in some pics of what you have.

cheers David.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Hap Tucker on Saturday, July 28, 2012 - 10:02 am:

Ted,

G’day and as David said, welcome aboard.

I actually recommend the Google Search over the forum search. If you start your Google search with MTFCA forum … and then type what ever else you want it will only look on the MTFCA forum. And it gives you a couple of sentences as a summary. I used:

mtfca forum high compression head verses high compression pistons and got

http://www.mtfca.com/discus/messages/179374/241057.html?1318653933

http://www.mtfca.com/discus/messages/118802/119035.html?1262433161

http://www.mtfca.com/discus/messages/80257/96868.html?1246331139

etc.

Recommend you also see the Tulsa Model T Ford Technical site. They have done a lot of research, dyno testing, and comparing how the cars climb a steep hill. They used the same engine/car for many of the test so it is more of an apple and apple comparison. See: http://mtfctulsa.com/Tech/index.htm and read the engine related ones especially Power and Torque at: http://mtfctulsa.com/Tech/power_and_torque.htm
For top end speed – Horse Power is needed for climbing hills Torque is needed. They have some great observations including “We estimate that for every 150 to 200 pounds the weight is reduced, the maximum percent grade [the T will climb in high gear] will increase by about one percentage point.”
For heads see: http://mtfctulsa.com/Tech/heads.htm and note that the compression ratio depends not only on the head but also is the bore stock or oversize – see: http://mtfctulsa.com/Tech/head_design.htm It discusses why in theory doubling the compression ratio will double the horse power but in reality that never happens because in general increasing the compression ration causes a decrease in air flow efficiency. So even if the high compression pistons gave the same compression ratio as a high compression head – there could be a difference in performance based on how the two engines breathed/moved the air. Frank Fenton had a great summary of how doing a combination of things works much better than trying to do a single “one large thing.” But I cannot locate that posting at the moment. So as a substitute I will refer you to the 1928-1931 Model A Ford dyno testing that compares heads, carbs, etc. Not T but a similar idea – you need the package to work well together.

The old saying is still true, “Speed cost money – how fast do you want to go?” If I won the lottery – one of the items I would want to purchase would be an overhead valve conversion (and some much better than stock Model T Brakes). Chaffin’s had a great reproduction Rajo see the posting at: http://www.mtfca.com/discus/messages/118802/120255.html?1263620016 and his advertisement on the MTFCA forum were still being listed a few months ago but when I looked today I did not see one listed. And of course there are original period heads etc. that become available on e-bay and swap meets etc. See the North West Vintage Speedster site at: http://www.nwvs.org/ and click on their Technical link http://www.nwvs.org/Technical/Technical.shtml which includes a great overview of many of the heads at: http://www.nwvs.org/Technical/MTFCA/Articles/1804OHVs.pdf And a 1928ish four cylinder Chevy, Olds, etc head can also be mounted on a T block using an adapter plate.

Good luck with your project and welcome aboard.

Respectfully submitted,

Hap l9l5 cut off


Top of pagePrevious messageNext messageBottom of page Link to this message  By Keith Gumbinger, Kenosha, WI on Saturday, July 28, 2012 - 11:17 am:

In my 4 Model T's, I have one with the high domed pistons, 1 with a Z head, and 1 with a Chaffin (Reeder) high compression head.

In my experience the Z head is the best as it gives more power than the others. Further, I would not use the domed pistons again as the low rpm power from them is lacking.

Just my opinion and experience, others may vary....

Keith


Top of pagePrevious messageNext messageBottom of page Link to this message  By Bud Holzschuh - Panama City, FL on Saturday, July 28, 2012 - 04:57 pm:

Ted

I have been thinking about this for some time as I am about to do some engine work myself and would like a small increase in power.

I first thought the z head was the way to go as its had many good reviews. But I am concerned bout increasing compression with those old heavy steel pistons and the possible extra stress on the crank.

Slightly higher compression aluminum pistons though, might give me a few extra HP and offset some of that stress on the crank with lower reciprocating weight.

I'm just a fair shade tree mechanic, NOT an expert by any means. I would be interested in hearing opinions from those who have had more experience in this area. Does this reasoning make sense? Might it help keep us out of the "two piece crank" club ??

Cheers
schuh


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