Just curious, do any of you know what the compression ratio was used in the C-35 Rajo head when running standard T pistons. The head in question is the Rajo 8 valve with two intake and 3 exhaust ports all on the passenger side.
I checked the NWVS site and Speed Secrets book and can't find anything about the compression ratio.
Later Model T stock compression ratio was just under 4:1? I'd bet the Model C-35 compression ratio isn't much more when using stock T pistons/crank.
I've heard the C-35 head was Racine Joe's effort to develop a high production, bolt-on head; in lieu of the B and BB heads that could easily tear up the drivetrain.
I think the advantage of a C-35 head is not an increase in compression, but the ability for better breathing due to the overhead valves. Of course, the compression could be increased if the head was milled (typical on a lot of these) or high compression pistons were used.
Way too many people mill these (and most) model T over-head-valve heads WAY TOO much. Many heads have been ruined by cutting them. The small gain in performance by milling that last 1/8 inch is only useful in full racing conditions, and destroys the head's reliability and life expectancy.
For that matter, even the second 1/8 inch milled is a waste. Only the amount needed to make the head seat properly is useful in any real way.
Okay. That IS my opinion. But I am right.
Drive carefully, and enjoy, W2
The original T overheads were low compression, as the gas available in those days would not allow higher ratios. Even the B model Rajo probably is no more than 5:1. The C-35 is close to that, I bet. These heads gained performance through far more efficient flow, or breathing. All of them could benefit from higher compression with modern gas, but milling is not the way to do it. Special pistons are the way to go. A well built flathead will keep up with the overheads until they really begin to open up and breathe at higher RPMs. By then you are going faster than most guys want to drive a model T. The big thing about overheads is they just look cool.