T head aluminum piston projects, Wisconsin and Locomobile

[alsfarms]

I am at the start of a aluminum pistons for a Locomobile and also a Wisconsin project. I bring this question here hoping that someone, who has experience with T head aluminum pistons, will respond. My question is how much dome is good to boost the compression from 4:1 to about 5:1. I realize that many considerations should be involved. Here are a few considerations:

1- engine oiling

2- crankshaft strength

3- crankcase stability

4- combustion chamber configuration 

5- ignition type

6- bore and stroke 

Please share your experience.

Al

Edited December 13, 2023 by alsfarms
Clarity (see edit history)

[Mark Gregush]

You might get more response if you put what make and year you are working on in the title per the STOP and READ at the top of this section. 

Edited December 13, 2023 by Mark Gregush (see edit history)

[Rusty_OToole]

Have you tried Egge Machine? They have been around since 1915, they may have made pistons for your car when it was new. https://egge.com/

[1906 lozier]

Alsfarms; first off, why would you want to raise compression. The original engineers did extensive development before the cars were ever put on the road. second, I have seen more than one brass era  Buick engine blow the cylinders right off of the block from doing this same thing. and they are not Tee head engines. I have a customer that did exactly what you are asking about on a 1912 Pullman and he blew the jugs off of it from only adding 1/4 inch to the top of the pistons on a 4.5 inch bore. Don't do it please. you will not see a difference in performance, and if you do add compression and it blows, you will have a very expensive repair bill.

[alsfarms]

I have seen the same issue with a couple of fellows who put domed pistons in an American-LaFrance speedster engine. I would be very nervous to mess with anything the uses an aluminum crankcase. The Locomobile crankcase is manganese bronze, strong, stable and etc., you could say....over built. Mercer was cutting edge on small CID T head engines and high compression. If I don't get comfortable with a dome I absolutely will go with lighter aluminum pistons, even though Locomobile did not engineer or use aluminum pistons. Some things are better with current technology or we would still be using candles for light.   🙂

Al

[AHa]

I second 1906 Lozier's sentiments. In the early 1900s engineers were dealing with inferior metals and made concessions accordingly. The marvelous Mercer is a case in point. The compression of the T head motors was increased to something more like 7 to 1 but what most people do not know is that many were blown apart. One reason there are so few existing today is the motors didn't last. Increasing compression in a brass era car is a sure recipe for disaster.

 

Most early cars rely more on torque than HP. Increasing compression will not change that. Most early cars capture HP at a much lower RPM than modern cars, which again, thwarts efforts to increase compression.

[AHa]

Aluminum pistons are really the only choice if a motor needs to be bored. Cast Iron Pistons are almost impossible to find. One just needs to remember the motor was not designed for aluminum pistons. These old motors cannot be treated, or mistreated as the case might be, like a newer motor. They should not be revved up like modern motors.

[alsfarms]

I agree that these old engines should not be over rev'd.

Al

[AHa]

Just remember, if a motor has 15 thou. of wear in the walls of the cylinder and you bore it to twenty, you have increased the pressure on the crank, crankcase, and cylinder bolts already. I like to say the engineering that went into brass cars has been lost to time. We can see what they did, but they worked with inferior metals and casting processes. They  made allowances for these limitations and tested the engineering. We don't know how much stress the crankcase and jugs will take until we have broken through that threshold but that is a very expensive thing to learn. Moreover, most people who do learn it are embarrassed and won't admit the mistake so others can't learn. It is a real testament to the engineers of the day that the cars have lasted these 100 years but many have had new crankcases and jugs cast, and new cranks machined.

[PFindlay]

On 12/12/2023 at 8:47 AM, alsfarms said:

My question is how much dome is good to boost the compression from 4:1 to about 5:1.

I was curious about this last year when I had to go with aluminum pistons in my 1910 Knight engine.   There are several online calculators that will allow you to play with the variables to see the change in compression.  One I used is at Summit racing: https://www.summitracing.com/newsandevents/calcsandtools/compression-calculator

 

You'll need to enter the volume of your combustion chamber which may be complicated for a T-head, but if you are just playing around you can estimate it as best you can.  It's not a variable that will change so close is good enough for now.  You may find that it would take a significant increase in the dome to boost the CR that much. 

 

Peter