Running a milled head with domed pistons opinions please

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Model T Ford Forum: Forum 2013: Running a milled head with domed pistons opinions please
Top of pagePrevious messageNext messageBottom of page Link to this message  By Nathan Bright on Sunday, May 19, 2013 - 12:55 am:

Hello, so as stated before I have domed pistons. Im looking to add a couple extra ponies by milling a head. I have access to both a low and high head. I know i can run a stock low head with domed pistons but can/should i mill it down? or would i have better luck milling down a high head to retain the higher capacity water jacket? I also would like to use groove the head using the Somender Sing groove principal. How deep should these be?

thanks for the info

-Nathan B


Top of pagePrevious messageNext messageBottom of page Link to this message  By Cameron Whitaker on Sunday, May 19, 2013 - 01:24 am:

You really have to be careful when running domed pistons. They can run very close to the head, and in at least one engine I've seen, they've actually been just touching the head, and the head was not milled.

I believe that the general rule-of-thumb is that if you're running domed pistons, don't run a high-compression head, just a stock head.

Here's my 2 cent's worth. I wouldn't run domed pistons. Instead, I'd look into a new Z-head with stock-style pistons. The combustion chamber is a much better design, and I've heard of anywhere from a 30-50% increase in horsepower with one. In fact, I've heard of the increase being comparable to a Rajo head!


Top of pagePrevious messageNext messageBottom of page Link to this message  By Seth from NC on Sunday, May 19, 2013 - 01:35 am:

Lol the problem Cameron is a Z head is $300, and then if you already have domed pistons new flat ones are another $80, plus rings and you're out $500 when you add all the tax and shipping. Whereas it can be a lot more realistic to spend $75 to have a head milled some X amount you specify to a shop. Course if it wasn't for the money all is speedster guys would be running Rajo heads and (insert favorite unaffordable speed item).


Top of pagePrevious messageNext messageBottom of page Link to this message  By Terry Woods, Katy, Texas on Sunday, May 19, 2013 - 02:02 am:

Nathan, Check out the MTFCA Tulsa website. Click on technical. Then click on Accessory heads. They state that a stock high head with stock pistons can be milled .125 and a Z or Waukesha head can be milled .050, if using stock pistons. Also they give dyno figures.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry Ostbye on Sunday, May 19, 2013 - 02:05 am:

First off a Z head gives you a huge increase in HP and torque but nothing like Rajo head.

As for Nathans question, Milling your head will increase compression but you need to measure piston to head clearance with model clay and make sure you leave ample room so the piston doesn't hit the head.

As for what I've done personally. I have milled a low head to 284 CC's with stock pistons and it did help a little bit but when I changed over to a Z head I literally yelled Holy S**t before I got out of my drive way. Since then I have done many other things to gain power, speed and better braking to make the car more driver friendly and safe to drive in today's traffic.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Jerry Ostbye on Sunday, May 19, 2013 - 02:05 am:

First off a Z head gives you a huge increase in HP and torque but nothing like Rajo head.

As for Nathans question, Milling your head will increase compression but you need to measure piston to head clearance with model clay and make sure you leave ample room so the piston doesn't hit the head.

As for what I've done personally. I have milled a low head to 284 CC's with stock pistons and it did help a little bit but when I changed over to a Z head I literally yelled Holy S**t before I got out of my drive way. Since then I have done many other things to gain power, speed and better braking to make the car more driver friendly and safe to drive in today's traffic.


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Sunday, May 19, 2013 - 03:27 am:

i would use the high head because i know i would break something and would not want to break the low head, But that is just me.

About those grooves in the head? Some people laugh at those http://oldschool.co.nz/2011/forum/index.php?/topic/30955-fabrication-cock-ups-lo ls-and-general-wtf/page-21 as seen in that thread... Warning it might hurt your eyes. Did warn you.


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dare - Just a little South West . on Sunday, May 19, 2013 - 05:10 am:

Domed pistons will give you moore ooooompf cheaply.
Having said that, you have to be aware that milling the head beyond the point where a piston can stop and reverse direction ( stretching a little at the top of the stroke ) will cause more drama.
Plasticene - the stuff that kids play with is your friend for finding the squish area when your piston is at top dead centre.
You will need a little room, not a lot, but a little.
I have taken my heads down a fair bit as well as the block for cleaning up pitted areas, all of this adds to the compression, which on a cold day, will cause sore arms when cranking it over.

Good luck, you do have two choices or three, do nothing, used domed or use a Z.

David.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Nathan Bright on Sunday, May 19, 2013 - 09:04 am:

is the combustion chamber different from low to high heads? Okay.. So lets say that i do the squish test with my current high-head and i hypothetically have .500 of clearance. how much should i leave? Also, im not looking for more drama, just some cheap speed, so if this is going to threaten the life of my crank im not interested at all! this car hasnt been apart in 25+ years so all i really know is it has cast iron domed pistons.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Nathan Bright on Sunday, May 19, 2013 - 09:06 am:

kep.. Your link is broken. Id like to see that info though. How deep can you make those grooves before you bust into the w/j?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Nathan Bright on Sunday, May 19, 2013 - 06:08 pm:

I guess im asking mainly how much clearance should be between the top of the cyl and bottom of the head.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Doug Money - Braidwood, IL on Sunday, May 19, 2013 - 06:45 pm:

Nathan, one thing to consider, what compression ratio do you have with both high compression pistons and shaved head? How will your 25+ year old babbitt feel about it?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris from Long Beach & Big Bear on Sunday, May 19, 2013 - 06:45 pm:

Nathan, Sometimes folks on this web site tell you what you are doing wrong and not how to fix your problem. If you have an eighth of an inch on top of the piston with no gasket in position you will have about a quarter of an inch and that is enough.

The problem is the domed pistons. They are really not the best solution to power and that is what your web site poster's are trying to tell you. Domed pistons distribute the burned gasses all over the piston and the gasses get surprised when the exhaust valve opens and then they have to turn around and change directions before they can escape. This takes time and the exhaust valve can close before all of the gasses are out at high speed. The result is bad breathing and lower power at higher speeds. In other words it is a bit of 80 year old technology and there are better ways to do it today. A piston with a dome on the far side and a wedge on top aiming at the valves would be better than a full round domed one with gap all around. But you have domed pistons so the best way for you to go is to mill the head and use those pistons with at least an eighth of an inch of space on top of the piston.


Pull the head bolts and put some children's soft modeling clay on top of each piston and crank the engine over a full turn by hand. Then measure the thickness of the clay and only remove metal from the head in the amount that will leave at least an eight of an inch or perhaps a quarter of an inch of space, you decide.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Nathan Bright on Sunday, May 19, 2013 - 07:48 pm:

Thanks frank. I appreciate when you post. ALWAYS value your opinion. Do you think my babbitt will hold up to a shaved head?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Donald Conklin on Sunday, May 19, 2013 - 08:13 pm:

I wouldn't trust kids Play Dough(sic). Use modeling clay.
Checking valve to piston clearance didn't work out. Expense!!!!


Top of pagePrevious messageNext messageBottom of page Link to this message  By David Dare - Just a little South West . on Sunday, May 19, 2013 - 08:20 pm:

Check your gapping with no head gasket, then if you don't have piston strike, your good to go with the head gasket in.

David.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Les Schubert on Sunday, May 19, 2013 - 09:16 pm:

Nathan
You talk about 25 year old CAST IRON pistons. I personally have never head of such a thing in my 40 years in the hobby. This doesn't mean they don't exist. The dome pistons we are talking about have a smoothly rounded dome that extends about 1/2-3/4" above the deck unlike the ordinary T piston that has a beveled edge "pop-up" about 1/4" above the deck. I just want to be sure we are all on the same page!!!
I have dome pistons with a low head (and cam and Stromberg OF and aluminum intake) in my '13 and I really like it
High heads can be milled 1/8" (and some 3/16"). The issue is not piston contact, it is head deck thickness.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Frank Harris from Long Beach & Big Bear on Sunday, May 19, 2013 - 09:47 pm:

Nathan, I have a Joe Gemsa engine running nine and a half to one compression and it is stamped by Joe himself at nine and a half to one compression ratio. Yes it has a babbited T crank. You must remember that diesel engines used to have babbited bearings. It is the small journals and weak casting of the lower end that fail on the model T engine. When you get a built engine you don't abuse it, you treat it with kindness and don't horse it around.




gemsa


Top of pagePrevious messageNext messageBottom of page Link to this message  By Nathan Bright on Sunday, May 19, 2013 - 10:19 pm:

Oh i am not worried about the quality of babbitt, im just wondering if my babbitt that is who knows how old can stand those compression ratios. Im sure new babbitt can take whatever you throw at it. I just dont want to beat my old babbitt out.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Verne Shirk on Sunday, May 19, 2013 - 10:29 pm:

About 1997 dad & I put some domed pistons in a 1920 T engine. The reason we did was that we had to bore it to 0.080" O.S. (I think it was 0.080"...maybe it was 0.100" O.S.). They only had domed pistons above 0.060". We didn't really want to bore it that much but it was either sleeve the engine or go with bigger pistons. Sleeving was expensive (like $400) compared to boring it bigger and getting domed pistons (like another $20 or so). The supplier (I think it was Langs) told us to use a high head because of clearance. Some years prior to that, we had bought a disassembled T speedster with a partially rebuilt engine. That car came with some high compression pistons. They had a very rough top to them. On the engine we were rebuilding we remembered those rough pistons and were kind of reluctant to get the newer domed pistons. It turned out, they were machined quite nice. We put them in and the car performs great! We have had no problems with it. No overheating, no rod problems, and no crank problems. We run an original '15 T radiator and even a couple of summers ago ran without a fan on 100+ degree days!!! The engine sounds great...kind of like an early big bore low RPM engine...very throaty! Now, I can't say I can build another engine and get the same results. I guess that is why some people post, "results may vary". I can't tell you how much clearance we have above the pistons. I've heard you want to have at least "the thickness of two nickels" or you will run into problems with carbon knocking. Now, on another T engine we did regular T pistons and a Haibe High Power head. I'm still sorting it out yet. I have not ruled out too much compression as a cause for its overheating.


Top of pagePrevious messageNext messageBottom of page Link to this message  By Nathan Bright on Sunday, May 19, 2013 - 11:17 pm:

thanks verne, great info! Les- I havent removed the head and put a magnet on them but they are certainly domed as i can look at it through the spark plug holes. I also took a metal rod and felt the top of the piston. Its not a flat-top piston.


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Sunday, May 19, 2013 - 11:26 pm:

Link not broken for me. Maybe it does not like international links?


Top of pagePrevious messageNext messageBottom of page Link to this message  By Roger Karlsson, southern Sweden on Monday, May 20, 2013 - 03:31 am:

Kep, you've got to be registered at that forum to see it, so I did.. Here's the picture they were bickering about, ridges in a modern four valve head supposedly aimed at reducing knocks to be able to advance timing even more. Noone there actually knows whether it makes any positive change, but lots of opinions :-)

ridges in a head


Top of pagePrevious messageNext messageBottom of page Link to this message  By kep on Monday, May 20, 2013 - 03:58 am:

So i saw where they filed a crowsfoot looking thing in the head with them meeting near the sparkplug/valve area. Not sure if it helped much.

Nice animation on this link http://forums.focaljet.com/duratec-tuning/561265-somender-singh-grooves-duratec. html But that does not apply so well to our flatheads. Still interested in how you make this work.


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