Milling 1920s head for higher compression question

[Mark Gregush]

Has anyone milled, for example, a 1920 head, more than just clean up, to boost the compression, say 1/8"-1/4"? If so, how did it work out? The casting looks like it had enough meat there to do so. That is a big empty space over the valves and pistons. T guys do, up to 3/16". So was wondering?

[Minibago]

One consideration to make is that the plug should be a long reach plug to ensure combustion happens well into the chamber not up in the plug orifice.

 

We already have inefficiencies of firing over the valves instead of over the piston. Just be sure your clearance is good.

I am not an engineer but I would also be concerned about increasing the compression too much with poured bearings and splash feed lubrication.

Here in Australia a chap (sadly now passed on) manufactured aluminium heads with about 5 to 1 compression but the improvement was more in the swirl design of the combustion chamber (a la Riccardo) and the moving of the plug to over the piston. At the same time reducing the thread to 14mm for the use of modern plugs.

 

[John McEwan]

I would worry about bending con rods from too much compression. These rods are like ice block sticks.

[Mark Gregush]

Model T rods are even smaller, running on a 1.25 diameter crank journal with splash lubrication and pored Babbitt bearings, rods and mains (which are 1.25 too), and people increase compression to about 5.5/6.0 to 1 with stock engines (in good repair, a stock T engine is about 50-55 pounds compression at 4.65:1 with 3.75" pistons). My 1921 T with overhead conversion using 1928 Chevrolet head, was around 75 with stock rods/mains/pistons. Model As with 40 HP, splash lube, stock Babbitt rods and mains, can go even higher, but most guys keep them around 5.9:1. Babbitt is not a concern, esp if using good tin based Babbitt. Not talking about huge increase, that is why I am asking the question, to see if anyone had done it, and how much of an improvement they saw.

I wondered if anyone made a high compression head, thanks for that information.

The pre-1928 Chevrolet's used longer reach plugs for just that reason, because of where they mounted, to get the spark out of the pocket.

Everything I have read says, that on the side valve engine, the plugs should be over the valves. Although, one of the new Model A heads that a guy is working on, the valves, while not over the pistons, look kind of in between. That could be the design of the combustion chamber.

Edited August 20, 2021 by Mark Gregush (see edit history)

[Minibago]

I think that side valves have the spark plug over the valves due to no overlap (sometimes an underlap) on the valve timing combined with no swirl in the combustion chamber so over the valves is the largest concentration of combustible vapour. Ralph (our greatly missed head manufacturer) also recommended a regrind of the cam shaft lobes to provide the aforementioned overlap. What is the grind? Not sure, the instructions were, “take it in to Clive (Clive Cams in Ferntree Gully Melbourne) and ask for Ralph’s recipe” the redesigned head introducing a swirl combined with the valve timing overlap provides a fuel air mixture worth igniting. Increasing the compression ratio on it’s own may not make the improvement you are looking for.

[Mattml430]

1 hour ago, Minibago said:

I think that side valves have the spark plug over the valves due to no overlap (sometimes an underlap) on the valve timing combined with no swirl in the combustion chamber so over the valves is the largest concentration of combustible vapour. Ralph (our greatly missed head manufacturer) also recommended a regrind of the cam shaft lobes to provide the aforementioned overlap. What is the grind? Not sure, the instructions were, “take it in to Clive (Clive Cams in Ferntree Gully Melbourne) and ask for Ralph’s recipe” the redesigned head introducing a swirl combined with the valve timing overlap provides a fuel air mixture worth igniting. Increasing the compression ratio on it’s own may not make the improvement you are looking for.

I did Ralph’s grind on my cam and raised the piston height by .020”

Clive does is a 53 Chrysler grind for our 6 cylinder dodge engine. Quite possibly different for the 4. 
Goes really nicely. 

[Minibago]

Ralph’s 1915 4 cylinder was fitted with his taller first and second gear set, his head and reground cam and went like a cut cat. 

[Minibago]

Just a further thought, the flywheel on the DodgeBrothers Four cylinder is very very heavy, a result of this is a tendency to break the crank shaft.

Another of Ralph’s recommendations was to machine an inch off the outer ring on the flywheel, of course it goes without saying that crack testing the crankshaft is a very good idea.

[Mattml430]

20 minutes ago, Minibago said:

Just a further thought, the flywheel on the DodgeBrothers Four cylinder is very very heavy, a result of this is a tendency to break the crank shaft.

Another of Ralph’s recommendations was to machine an inch off the outer ring on the flywheel, of course it goes without saying that crack testing the crankshaft is a very good idea.

Yes your right we also took some weight off the flywheel I forgot about that. That was another suggestion from Ralph. 
I took 3.5kg of it and then had it re balanced. 
I think it was 26.5kg and I took it down to 23kg. 

Edited August 20, 2021 by Mattml430 (see edit history)

[aunty norm]

I had my cam ground to a Ralph special grind ! 

Work well on my 1937 dodge!

Ralph will be sadly missed!

[nearchoclatetown]

Have any of you talked to Cled? I think he had his four going over 80 mph. 

[Minibago]

Not on a public road tho’

[Minibago]

2002 on the salt pan.

Aluminium body and slightly modified mudguards / wings / fenders.

Among other things.

I don’t think slightly higher compression will do it. 😂😂😂😂

 

[nearchoclatetown]

All true, but he's pretty crafty and I am sure has secrets. 

[Minibago]

Yes he does, he has been a leading supporter of the Dodge Brothers cars for many years here in Australia, sadly he has not been well these last couple of years.

[Mark Gregush]

Great information and more food for thought.

[John McEwan]

On 8/20/2021 at 7:36 PM, Minibago said:

Just a further thought, the flywheel on the DodgeBrothers Four cylinder is very very heavy, a result of this is a tendency to break the crank shaft.

Another of Ralph’s recommendations was to machine an inch off the outer ring on the flywheel, of course it goes without saying that crack testing the crankshaft is a very good idea.

Can anyone give a report on the results from machining the 1” off the flywheel on the early Dodges?

[Mark Gregush]

I posted this question over on the Dodge Club Facebook page, one person replied that they had done the 3/16 and lightened the flywheel; https://www.facebook.com/groups/dodgebros/

Sorry I can't seem to post a direct link to my question here.

[dwollam]

I took .125 off the head and block combined, mostly off the head, on my 1922 DB Screenside. That doesn't really raise the compression much but every little bit helps. Kinda like trimming an 1/8" off the top of a 5 gallon bucket! I did in fact have it going 62.7 mph by GPS so it doesn't run too bad. Everything else is stock.

[22touring]

Guys, I know this is a little bit off-topic, but I really want to ask you this.  There is an old story which circulated within the DB community, to the effect that trying to explore the acceleration potential of a Roof OHV cylinder head on a 3-main motor will blow out the bottom end big time.  The story goes that this happened once at some antique car meet; not sure if it was a DB get-together or some other kind of meet.  Have you ever heard this?  Do you think it is true?

 

WTH, since I'm going totally off-topic here anyway, did you guys know that F. Scott Fitzgerald had Nick Carraway, the narrator of "The Great Gatsby", drive a DB 4-cyl. car because he wanted to enhance the narrator's credibility? 

[nearchoclatetown]

I won't say a 3 main bearing engine is the strongest to hotrod. But if you follow land speed racing Rich Fox put a Y block Ford ohv head, like a 312, on a 3 main engine and set a record at Bonneville. The engine is in Speedy Bill's museum in Lincoln Nebraska. Morten and Brett made heads for them back in the '20's and '30's. I think Frontenac, owned by Louis Chevrolet, built heads for 3  main engines too. There's a fairly famous sprint car from N.Y. with a 3 main engine too. Can't think of the car's name, it's maroon. And there's an Aussie named Cled Davies that went about 85 mph a few years ago with one in his race car. 

Edited August 27, 2021 by nearchoclatetown (see edit history)

[jari12]

1 hour ago, nearchoclatetown said:

I won't say a 3 main bearing engine is the strongest to hotrod. But if you follow land speed racing Rich Fox put a Y block Ford ohv head, like a 312, on a 3 main engine and set a record at Bonneville. The engine is in Speedy Bill's museum in Lincoln Nebraska. Morten and Brett made heads for them back in the '20's and '30's. I think Frontenac, owned by Louis Chevrolet, built heads for 3  main engines too. There's a fairly famous sprint car from N.Y. with a 3 main engine too. Can't think of the car's name, it's maroon. And there's an Aussie named Cled Davies that went about 85 mph a few years ago with one in his race car. 

The NY sprint car you mention was called the Dundee Dodge. Pictured here.

[MikeC5]

The Model T guys have the parts availability to do it.  You can get an extra stout crankshaft made for the T-block and also reproduction Rajo overhead valve conversions, etc.  None of this stuff is cheap but it is available.   I would be hesitant to spend the money hopping up a DB 4 without a new, full-fatigue life crank.  Especially with the 3 main bearing blocks.  Maybe these guys know some tricks and could help:  http://www.fastfourspecial.com/press.html  

[nearchoclatetown]

They only use fast four blocks, 5 main bearings. 

[dwollam]

Biggest problem with the 3 main engine is the starter/generator drive chain. That's what lets go at high speed and destroys engines. That's the big advantage of the 1926 B 3 main 6 volt separate starter and generator and then of course the C and D engines with 5 mains and the so called fast four engines (also D).

[Mark Gregush]

Re the chain; In your opinion, with the 1920 engine, what RPM range would be ok? This question was not about high speed, just comfortably going a bit faster than 35 and still having some reserve power for the hills, not freeway speeds. The chain, while, does carry a load, not like the load from turning a cam shaft used on many types of engines. Would this be more about wip than load?

If I did the math right, has the disadvantage of the lowest ratio rear end made by Dodge at that time. But at least it is better than my 1948 Ford F2, which generally I keep under 45, otherwise the 6 is really turning the RPMs. 

Edited September 4, 2021 by Mark Gregush (see edit history)