Please educate a newbie (myself) on the world of Rajo's. What is the main difference between my stock 21 engine and a Rajo engine?
RAJO is like a Fronty - overhead valves.
Scott, Rajo heads (like Frontys and Roofs) have the valves in the head, using rockers to open them. Stock engines like yours have the valves in the block. I can email you a PDF file that shows many of the period aftermarket heads from the various manufacturers.
An overhead valve conversion, coupled with an increase in compression ratio and better carburetor and better exhaust should easily double the horsepower of a stock Model T.
This will also mean your brakes are now completely inadequate and your crankshaft will last half as long. Fuel mileage will also go down.
An overhead (Rajo, fronty, roof) will allow more power and speed from your model T. Since most T's go fast enough, the greatest gain is in hill climbing ability. I have a Rajo equipped Mercury speedster, it gets excellent fuel economy. The brakes work exactly the same as before the Rajo. I don't worry about the crankshaft as most people I know have not broken one.
I totally agree with you. It is quite possible to get more power/hill climbing ability and burn LESS gas. The T came with a notoriously inefficient combustion chamber and as such wasted a lot of gas. Most of the overheads burn the gas more efficiently.
In my opinion and it's only my opinion, the best thing you can do to a T engine is raise the compression ratio. It will get better fuel mileage and run cooler.....assuming you drive it that same.
Scott, it seems to me that most of the members on the Forum who post about their broken T cranks have stock engines or engines not modified with overhead valves.
Lugging a T engine is bad for the crank. The increased horsepower you get from overhead valves reduces the need to lug the engine. You can just zip up those hills!
Brakes are always an issue with a T but careful driving helps. Seems to be an overstatement to say your brakes will be completely inadequate. There are easy ways to improve the T's braking capacity but you still have to be careful. There are people who get in accidents with bone stock Ts because of the brakes.
The increased compression and improved combustion chamber efficiency should improve mileage, but hey, the idea is to increase horsepower and have fun. If you are going to spend the $$$ on a Rajo or Fronty head, gas mileage should not be a concern.
What I like about the overhead valve conversions is that the increased horsepower makes driving in the hills a pleasure. In Northern California we have some great mountain roads that are a blast to drive in a T with lots of extra power. While you can chug up these roads in your stock T, I will take the extra power of a Rajo any day.
Plus an overhead valve looks really cool, sounds great and will add several thousand dollars to the value of your car.
Check out the Northwest Vintage Speedster website at nwvs.org. There are lots of great articles on their website regarding Model T performance. I am amazed at the amour of speed equipment that was made for the humble T. I am a speedster guy through and through and have been since I was 9 years old. I just wish I could afford more of the stuff. For now, I will have to make do with my Rajo BB and BBR equipment.
Increased compression from a overhead or flat head will add to the compression braking effect when slowing down.
Increasing compression may be nice? However, milling heads, especially overhead valve heads, has ruined many hundreds of such heads. Be a bit careful when looking to buy any overhead valve setup that the casting has not been cut down to the point the casting is severely weak and nearly worthless. I have seen a few where the milling got into the spark plug threads. Some of these after-market heads had castings that (shall we say) lacked adequate quality control. I have heard a few people tell of milling an overhead valve head and think "a little more" a few times. And once too many, finding a big hole where there is supposed to be something pressing the head-gasket against the block.
That is my "two cents".
Drive carefully, and enjoy, W2
Increased compression is better achieved by buying a set of pistons that are made to achieve the desired compression. Most of the overhead conversions will only have 4.5 to 1 compression if you use stock style pistons.
Only mill the head to achieve flatness.
Royce, do you have any published information on overhead compression ratios that you can post? It would be very helpful to see the differences between the various brands and models.
some heads can be milled considerably without comprising the integrity of the casting. depends on the particular design. also whether your using a pressurized cooling system. i must preface this by saying that i have been advertising a B head that has a fair amount of decking to the point that it has opened into the water chamber in a couple of places. however with a good gasket and non-pressure system should perform just fine. i do agree that milling should normally be done at a minimum and use piston choice to achieve increased compression when possible.