Maximum milling of a low head

[Les Schubert]

I’m trying to help out a friend. He has a T race car and he can’t run a “after market” cylinder head. So he is going to run a low head and is wondering how much he can remove (I suppose more realistically how much he needs to leave to maintain good integrity)??
So I said I would ask for your opinion.
Thank you

[Kevin Pharis]

Is filling the head an option…? Seems like there would be much more benefit to creating some squish area and creating a “crows foot” shape chamber…

[Harry Lillo]

Kevin,
I have thought about this in the past; obviously you have done so as well.
At a recent swap meet a fellow had a spray cast setup I almost bought to
try this out. I wasn't sure it would stand up to the repeated combustion cycles.
Do you have any thoughts as to how one might do so?
Harry Lillo
Calgary

[Kevin Pharis]

I’ve never worked with iron spray welding before… so don’t want to comment on this method. But I always imagined a little patience and a lot of brazing rod might go a long way at the M500…

[Kerry]

I run a low head that has .080" off it, it didn't clear HC pistons but stock height aluminum pistons it just fitted.

[Craig Leach]

I have heard tails from old dirt track racers running ford flatheads that brazed up heads to get more compression. And I have seen a set of
two piece flathead V8 pistons that you could change the rings on by unbolting the top of the piston without having to remove the rod.
Why cant the crows foot pattern be cast into the piston for a high compression piston to use a stock high or low head?
Just thinking a set of $200 pistons Vs $400 heads. Then maybe I've just been around to many diesel engines.
Craig.

[Les Schubert]

Kerry
That is exactly what I was looking for!
Thank you

[Wayne Sheldon]

I am curious what speedster group or meet wouldn't allow an after-market head? Frankly, maybe it sounds like my kind of group? I have been involved with speedsters for over fifty years now, and been involved in the rules and debates about how far is too far for a long time. The only group I know that strict is the Montana 500 crowd! (If it is them, maybe best to not admit it?) I know they have strict limits on alterations.
Generally, milling the head buys very little in speed or performance. And the cost in reliability can be a lot! Sudden splits in the head and head gasket failures can knock a car out of the running in just a few moments.

I wish I could get back to really working on my cars. I have one nearly ready to run that I used an overly milled low head on. The head was that way when I got it, so I figured I might as well chance it and see what happens. Quick examination found too little left of the mating surface to the block. Several areas where water passageways had enlarged due to loss of material. Closer examination found no immediate threats to blowing out combustion chambers (that can happen if heads are milled too far!), and hopefully enough for the head gasket to seal and hold? The car has been nearly ready to run for ten years now, and I still haven't heard it run.

Proper shaping of the combustion chamber wasn't understood until the 1920s, and even then not well understood until after model T production ended.

One of the most interesting, most bizarre, speed alterations I ever saw for a model T? And I have threatened to try this myself! I saw the head, broken, in another fellow's junk pile. A common high head, with steel plate shaped and brazed inside the combustion dome to pinch down the combustion chamber, and shape it slightly hoping I think to expedite the exhaust? It appeared to have holes drilled in the tops of the combustion domes to allow water to cool the steel plate. It would need to have that otherwise the steel plate would get red hot! The apparent failure of the head looked to be that all the brazing and alterations probably warped the head, and whoever tried this didn't mill the head after. It had split in several places, and appeared nearly ready to break into two pieces.
Still an intriguing idea?

Fifty years ago, I also parted out a really messed up mid 1920s Chevrolet. When I pulled the engine apart, I discovered that someone way back when had brazed 3/4 inch thick steel caps onto the top of every piston! Must have bumped the compression a bunch! But I doubt the balance worked out very well. It was a really sloppy job of it.
People did some really crazy things back in those days.

[TXGOAT2]

As far as modified pistons, weight is a critical factor in pistons, and anything that increases the surface area of the top of the piston can be expected to increase the amont of heat the piston will absorb from combustion. Uneven section thickness in the piston head could cause heat control issues, too. If you're going to radically modify a stock cylinder head, you might do as well to start with a high head, since they are much more plentiful. I'd keep in mind that the head has a water jacket, and the pistons do not. Piston cooling in a high speed, high performance engine can be a challenge. 100 year old heads can be expected to have internal corrosion, besides normal casting irregularities. I'd be cautious about shaving a scarce one very much.

[AndreFordT]

On the 1926 touring I took 0.10" off the head.
No problems with the HC pistons but three year later I found this:


Good luck
Andre
Belgium

[Les Schubert]

Andre
I’m not sure what the picture is supposed be be showing!
Please explain.

[TXGOAT2]

There is a small hole in the head about where the center of the bore is. The picture with the spark plug out shows a pool of water in the cylinder before the head was removed. I'd guess this head had a flaw in the casting that eventually failed. Persistent detonation could also cause such a hole, though a piston will usually fail first.

[Jerry VanOoteghem]

Many years ago, a friend of mine took about .100 off a low head. Ran great until the entire combustion dome broke loose and pushed up into the coolant jacket. Apparently, there were reinforcing columns cast into the head to support the combustion domes. They had long before rusted away. Also, internal corrosion had already reduced the wall thickness of the head's seal face by some significant amount. Then there's also the normal variation due to core shift that you'll see in any casting. (I know you already know that Les.) So, I think the answer to the question, "How much?" is, "it depends..."

[Rich P. Bingham]

As kids, we grew up with the legend of the "hot rod Lincoln" and flathead V-8s with "shaved heads" that went like scat when dropped into Model As.
Do the math. Even removing a massive amount of material from a head surface makes for a negligible increase in the compression ratio. There's no need to "shave" a head any more than is necessary to true up irregularities.There are better ways to raise compression and blow out the bottom end !

We are now in a phase of the Model T saga where we have to consider that after a century, corrosion in cast iron items may begin to be the cause of failures unlike what we have been accustomed to dealing with.

[AndreFordT]

Les,
as Pat said. A few years after I installed the milled head the engine started to smoke a lot and was running on 3 cylinders.
As I took out the sparkplug I found water in the cylinder. The head off the engine showed the holl. I think it was corrosion. With a few taps with a small hammer the hole went bigger.

Changed the head with a good one with less milled off .
I still don't know if the problem had to do with 0.10" milled off head.

Andre
Belgium

[speedytinc]

The milling had nothing to do with the leak.
Excessive milling typically presents as a long crack in the piston side of the combustion chamber.

[Dan McEachern]

Read Rich P. comments again.

[Wayne Sheldon]

I have never been in favor of milling heads or blocks any more than is necessary to true up the mating surfaces for a reliable head gasket fit.
Many times, the joke is that a couple guys are milling the head shooting for some perceived notion of maximum performance. The head is set up in the milling machine or surface grinder, and the conversation goes like this;
"Take another pass!"
"Take another pass!"
"Take another pass!"
"Oops."
"$#!+."

[speedytinc]

The cavity above the valves it so large/deep on stock heads, serious milling is futile.

[AndyClary]

My experience is that the shaved head makes no real difference. If you have to run a stock head, a low head with the available high compression pistons runs pretty good.

Andy

[Kevin Pharis]

My rememberer is telling me that an early low head (‘15 ish) was slightly higher compression than the later design. Was sumpin like 4:1. Assuming the bore/stroke is unchanged;

Cylinder volume;
44.178”

Gasket displacement according to my big valve profile;
@ .040” = .756”
@ .050” = .945”
@ .080” = 1.512”

Target combustion chamber volume including gasket displacement, but excluding piston top displacement;
4:1 = 11.044”
4.5:1 = 9.817”
5:1 = 8.835”
5.5:1 = 8.032”
6:1 = 7.363”

All this nonsense basically says that cutting .080” off the head would raise a 4:1 head to about 4.8:1 on an otherwise stock engine

[ModelTWoods]

One might google, milling a T head MTFCA, and see what posts appear. It seems like the topic has come up, before on this Forum. If I remember correctly, someone said that they had milled and run a high head with .125 milled off. A well known T guy in south and central Texas, claimed to me that .150 could be removed from a high head. Of course a low head is different, so I wouldn't expect the same to be true for one.

[TXGOAT2]

I'd say mill a low head only to clean up surfaces, and use high compression pistons. Most T engines have oversize bores, so you'd get a little boost from that. A well-tuned intake/camshaft combination can substantially increase the effective compression ratio by increasing volumetric efficiency. If you can get more air/gas into the engine, the compression pressure will be higher. If a Scat crank is allowed, by all means use one. The engine responds to compression pressure, not compression ratio.

[Cordes_jeff]

I have taken as much as .200 off a high head. I've also blown the combustion chamber out of a head. It's all just play time and what the operator is comfortable with.

[David Greenlees]

Les, I milled .125" off of an early low head over 30 years ago used it on several cars on which it traveled a lot of miles, and it has been run fairly hard since then without any issues at all. Not having a chassis dynamometer in the shop or available nearby, we use a local hill for quantifying changes on clients' and our own vintage racing cars. In back-to-back tests at the same temperature on the following day, while approaching the hill at the same speed at wide-open throttle and maximum ignition advance followed by retarding it the same amount at the same spot both times while climbing, the extra power was noticeable. The car was able to climb over the top in high gear without lugging. Previously it required changing down to low, about 75' from the top of the hill.

We have also used this low head to diagnose an engine noise that turned out to be piston slap on an engine with a high compression alloy Sherman "Super-fire" head. After changing to the milled low head, the piston slap caused by the shape of the Sherman combustion chamber disappeared, and further investigation turned up excessive piston-to-wall clearance which was causing the knock.

[MWalker]

I have taken .125" off a few low heads without any problems. Key to doing this is using modeling clay to determine how much clearance is available. You don't know how much has already been removed.