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Thought we'd pull the dizzy and check it on the Sun machine. Does anyone know of a timing curve that works pretty well on a stock engine using currently available gasoline? Thanks.

Andy

Well, to sort of answer my own question ... With the initial timing set at 4deg btdc at 650 RPM the total timing was 20deg btdc at 3200 RPM. Admittedly I have VERY limited experience in Dodge flatheads, but this looks much different than a typical OHV engine. How can these things run with such limited advance? I can't imagine that the combustion is that efficient, so what gives?

Good question.I'm interested in input on this topic, from the experts with our M37's. I know there is a lot known from guys who have been involved on the performance side of the flat head design. Just need to get the question to the right guys. I think Some graphs have been posted in the past, but I'm not that good at searching them out yet.

My understanding is that 4 degrees BTDC is the correct setting. Charles at M Series Rebuild is the source of this information.

I know that RMS has done a lot of research on these engines (as well as other flatheads), and I'm sure there are other people out there who have a lot of experience and knowledge about these engines and their design parameters.

Hopefully the experts will be along soon.

Hi Guys,

if I understand the question right you want to know why flatheads and overhead valve motors have different ignition advance needs....right? Well.......compared to an overhead valve engine, flatheads don't need as much initial timing advance. That's because the air/fuel mixture is much more turbulent when it gets to the combustion chamber than it is in an overhead valve motor. On an OHV motor the mixture has pretty much a straight shot into the combustion chamber, where on a flathead it has to travel a much more difficult path that has lots of turns and bends before it gets to the combustion chamber. With a more turbulent mixture it ignites easier and burns a bit quicker....so less ignition advance is needed.

regards,
bob

I'm set at 10* btdc, and the truck is running great. We are at 8000' though. I might try a little more advance and see how it goes

Bob,
What you said is parallel to the limited info I've dug up on flatheads. It just amazes me that the turbulence created by the design is good enough to make up for the short comings of the combustion chamber. Seems that the flame travel would be pretty poor compared to a modern chamber design, but I guess if it's mixed up well enough it will burn plenty quick. Anyone on here have any flathead racing experience? I need to find someone who runs the Jr. Dragsters, I was told those 5hp briggs could be tweaked up to 40hp for a run, talk about a hand grenade!

Andy

Hi Andy,

I wouldn't say it makes up for the shortcomings of the combustion chamber, as turbulent flow doesn't necessarily relate to efficient flow. And the more efficient the process, the more power you'll make. The turbulence gives you a nice fast burn, but having more airflow and a slightly longer burn time makes more power. The time to combust is what it is and is addressed with timing....no big deal.....but twice the airflow with more advance needed sure would be nice. That's why people "relieve" the block between the valves and the combustion chamber....to gain some airflow at higher revs, albeit at the loss of a bit of compression ratio. Certainly not needed on the old workhorse M37's motor, although I'm sure a few have tried it. Actually, with this forum being as old as it is......I'm sure some have messed with the airflow on the 230. Hopefully they'll join in the discussion and summarize for us.



regards,
bob

I do as zgjethro and run 7 to 10 degrees. The reason the specs are 4 and 20 total is these engines were designed to run on 70 octane or worse fuel. When you get into the 50s and look up the flathead 230 car engine specs they change. compression ratios got higher as well. after WW2 the quality of fuel started to go way up. dont be afraid to run at 10 it will unlikely ping and will run nice. There are at least 127 different blends of fuel in the US market so that will determine where the ideal setting is.

Here's the timing curve for a dizzy we just rebuilt:

Distributor RPM / Camshaft Degrees
250 / 0 (start point)
500 / 3
750 / 5
1000 / 7
1250 / 10
Advance ends here, no point bounce until over 3000 Distributor RPM!

Anyone actually have specs??

Just so you know, the advance curve is lined out in the TM. (Engine Clutch manual) No graph, just the numbers.

just me,
Is it in this one?

http://www.steelsoldiers.com/upload/M37 ... clutch.pdf

If so I must have missed it.


Andy

I saw it just last week in one of my manuals. I went through them last night and couldn't find it again. It was in a weird area and I WILL search it out and find it. Damn it, I know I wasn't seeing things!

just me wrote:I saw it just last week in one of my manuals. I went through them last night and couldn't find it again. It was in a weird area and I WILL search it out and find it. Damn it, I know I wasn't seeing things!

Section 123b of TM9-8030 gives an advance spec of "18deg to 22deg at 2,250rpm".

The Chrysler Industrial Engine manual gives tabular advance curves for the civilian distributors, but none of those are the same model number as the military.

Elwood,
I'll have to check out the Industrial manual. I'm curious to see how they compare. I'd like to find the curve for one of the higher compression motors of the '57-'59 passenger cars and see what it looks like.

Andy