The Stovebolt Site Forums The Shop Area Engine Shop 235 Timing

I have a totally rebuilt 1953 full pressure 235 in my ’41, it is stock except 0.020” over on the bores and a 848 head.

Today is the third or forth time I have played with the ignition timing. I removed the lower flywheel cover and painted a nice white stripe right over the “ball”. I have made adjustments to make the timing 2 degrees BTDC; 5 degrees BTDC; 10 degrees BTDC; and 12 degrees BTDC. After each adjustment I shut off and restarted the truck and took it for a short drive including a “foot to the floor” ½ mile run in high gear starting at about 30 MPH. I found no discernable difference in starting or performance and could hear no pinging across all of the adjustments.

During the engine’s reassembly I checked the’41 flywheel before I installed it and found by measuring and a simple calculation that the “ball” is 5 degrees of rotation ahead of the U/C mark. Before I installed the cylinder head I found when the U/C mark is aligned with the timing window pointer the # 1 piston is exactly at the top of its stroke. All of this makes me sure the timing marks are correct.

Shouldn’t I expect some noticeable difference in a full 10 degrees change in timing?? Where are you guys running the timing on your 235’s??

With today's fuel about 10 degrees seems to work best on most of the 216s and 235s I time.

I found working on our '40 this summer that these engines will run with lots of advance. I learned that to much advance would give a slight surge at a steady speed. It also would cause it to run a bit warm when driving at highway speeds in hot weather. I backed the timing off a bit and it performs great and runs much cooler at highway speeds. No matter how much I advanced the timing I didn't have an issue with hot cranking or pinging.

Thanks guys. I think I'll stay with 10 degrees for now.

YEP....we went through a whole bunch of scenarios even with our Langdons HEI we found that just timing to the BB was best and it was at this point our vacuum was almost at its highest. Learning both timing methods was of great value to us. The factory specs are for timing at the BB. Never tried to time after the BB (ATDC) yet another scenario I guess. Steve

Dave:

It is interesting that you have referred to “today’s fuels” in your note. I’m wondering what the difference is between gasoline of the 40’s & 50’s and the gasoline of today.

I’m thinking that it is essentially the octane rating that should affect the timing and spark knock (pre-ignition). Was the octane rating of the older gasoline’s lower or higher than today’s? I remember something about the older fuels being measured by one method and, I think, modern gasoline octane rating is an average of the old method and a newer method all if which rates today’s gasoline at a higher octane that it would have been rated in the 40’s.

Hey Kip,
I am not up on the changes, I am only going by my experience.

By the late 1950's/early 1960's, even "regular fuel" engines had compression ratios in the 9's, so gasoline needed lots of anti-knock compounds. Some of the super-premium gas was well over 100 octane, and I've seen stock compression ratios of 10.5:1 or more on some of the factory hotrods from the early 60's. Other than buying 100 octane aviation gas or a few "off-road only" brands of racing gas, I can't imagine running those engines without some sort of fuel additive, even on unleaded "premium".
Jerry