propshaft height for 105 Chrysler race motor

[RTM]

I`m running a 105 Chrysler on a Desilva F runabout. As it is now the propshaft is 3/4" below the bottom. Prop is a 2 blade Johnson mfg. brass 9X18-20 cupped. Its very difficult to get on plane, and turns about 6100rpm at 62mph. I`m thinking it needs to come up 3/4" inch to 1 1/2" above the bottom. With the 250lb. chrysler the boat is stern heavy but runs flat with engine at verticle.

[Mark75H]

As far back as the Chrysler racing unit puts the prop, if you go up you are probably going to have even more trouble getting on plane.

But you never know if you don't try ... I guess there is no reason not to try, but you are in unknown territory with your rig

[RTM]

(needs to come up 3/4" inch to 1 1/2" above the bottom.)

After rereading my post I meant to say I think the motor needs to come down 3/4" so the propshaft is 1 1/2" below the bottom of the boat.

[Powerabout]

another blade on the prop would help

[JohnsonM50]

I agree with powerboat on that, 2 bladers are pretty fast but not as efficient as a 3 or 4 blader. Youll also find that to maintain desired RPM as you add blades youll need less pitch. Take off: One 3 blade cleaver I use goes right up with little slip, the rest are typical spin till it grabs. All my 2 bladers are harder to start & less than 70% efficient while my two 3 blade cleavers are about 90%. That means better mileage, better handling, less wear & tear & when you really find a good one more speed [the best part] Im thinkin your rig has alot of potential. I hear them Chryslers aint slow.

[Bill Gohr]

Isn't that gearcase a 1 to 1.07 overdrive ratio? So I'm thinkin that a 17 is too tall, as well it is probably too low. I myself would run it a little higher and a 3 blade is a must, probably in the 15 range. I have several of those wheels for sale right now what diameter and rotation are you using.

[Aeroliner]

I have a Chrysler racing unit forsale with a new case and used gears and shafts. If anyone is intrested let me know at aerolinerboat@aol.com

Alan

[RogerH]

Here's a comparison. I don't have the boat where I can measure the distance below the bottom, but I had to LOWER the motor to get it to come up on plane better. Also I was running a three blade prop. I didn't keep this boat long enough to get it tuned, so can't be a lot of help. The Chrysler's are a bit heavier as you noted. The Chrysler units also have three different final drive ratios. I seem to remember the prop shaft being about 1.5" below the bottom, and it performed well at that depth.
The boat is actually a TerrilCraft - a DeSilva copy by Wade Terril.

[Mark75H]

Although it is rumored that there are 3 ratios for the Chrysler, only 7% overdrive appears in the parts list and I have never seen other than 7% over in a Chrysler

[brichter]

Although it is rumored that there are 3 ratios for the Chrysler, only 7% overdrive appears in the parts list and I have never seen other than 7% over in a Chrysler

I hope I can at least clear up part of the debate on what ratios exist.
These pictures show three gear sets that I have for the Chrysler racing gearcases.
From left to right: 18:19 overdrive; 14:15 (7% reduction) ; and the standard 15:14 (7% overdrive) The pinions are at the top of each picture.

This proves at least 3 ratios existed for these units.