daqcraig

I am in the process of repowering my 342 Baja. It had twin 7.4 L MPIs 310 HP with 3B 23 Pitch props.

I am going to twin 496 mag HOs with 425 HP and stainless headers. New motors and new X drives as well. I am hearing everything from 24 to 28 pitch.

Also what is the significance of going to a four blade from a three blade. I understand I am gaining about 100 ft lbs for torque. Anyone know the straight skinny on what the boat would get the best top end speed? I only care about cruising,etc. and the hole shot does not matter to me. Thanks

cbeastwood

Stock props are 26's I believe. Better would be a labbed 26, as my engines hit 4,800 rpm and don't come close to the rev limiter. I think if you went to 24's you'd be hitting the limiter and going no faster.

Headers will get you about 3-4 mph on this boat. Probably closer to 3. I don't think they're cost-effective on this boat.

I'm seeing about 67-68 mph tops in freshwater, 70-71 in saltwater. With labbed props I'm guessing another 4-5 mph because you would be using the whole rev range...

throttleup

I would try the props you have now. The limiter on the 496 HO is much higher than your old motors. The additional rpm potential of the new motor will make up for about 3" in prop pitch.

After you have a couple runs with the props you have now you will have some good baseline numbers to work with.

cbeastwood

Throttle Up,

Not trying to hijack his post, but what if I went back to 24's on my stock 496's - do you think I could add a few mph given I'm hitting about 4,800 rpm with the 26's. Or should I have them labbed?

throttleup

The 24's will be to small.

You are close on RPM and you could get there without lab finishing or down pitching the props. You may have a couple more mph there. It would help to get the rpm close to the 5000 rpm level with your motor.

JaayTeee

A 98' 342 most likely has the drives
installed pretty low.

Your best top speed will probably be with the three blades.

The props you have will be pretty close, you'll just be
able to spin them faster.

bbladesprops

First of all, daqcraig never told us what rpm he is turning the props with the 7.4's. In therory, you may be able to run the existing propellers. The increase in HP is worth at least 2 inches in pitch. That means add 400-500 rpm to the current rpm you are at with the 23 and that is where you will be with the 496 HO's. You have a new rev limiter at 5150.

My thoughts are a specifically Labbed 25 Mirage + will give you the best top speed and a set of 25 Revolution 4's would be the best all around propellers for the best cruising speeds.


cbeastwood, no brainer, Lad the current propellers with the correct recipe and you will be there!

daqcraig

The 23 P props with the 7.4 MPI Wot Rpm was 4300. I didn't see what difference that made since I am installing new 496 mag Ho motors with new Bravo 1 X drives. The engines will also have stainless headers.