View Full Version : Prop question

08-12-2012, 07:12 PM
Getting very close to finishing my boat, looking for advice.
21 gt
volvo 280 no trim
383 sbc 400 (+?) honest horsepower
rpm to ~ 5500 / 5700

Solas 21 or 23?

My buddy has a Michigan I can borrow, 14 x 24, I think.
Bigger diameter of Solas better for beamier boat?

Any guesstimates? I would think 18 info might or not apply the GT is probably another 500 lbs.

Rounded keel with short strakes, if it makes a difference.

Thanks for any advice!


08-12-2012, 07:42 PM
John, that looks real nice. I hope me, you and Ralph get to go for a ride soon.
I can't really say what prop would be best for a GT, but I do know it takes a lot of power to spin a 23" Solas above 5000. I've got two of them(23"Solas)so if you'd like to see if works for you, I'll let you try it out. If Ralph's works for you, that'd be more like a 21" Solas. Ralph also has my Ultra, which you're welcome to try.

08-12-2012, 08:26 PM
Thanks Mike, I hope to be ready in two weeks, but you know how that goes!
Have to clean up wiring, no big deal, mount new exhaust tips, am going to rebuild the K5 cylinders just because, and start her up!
And put one more set of bunks under the bow, and buff and wax hull, and....
Talk to you soon!

08-12-2012, 09:23 PM
I am not a big fan of running over 5K, I did with my 383 in the 22 when I put it together and was considerably slower at higher RPM's. 5600 gave me 62+ propping down to 5000 gives me 65.5, it is about torque not HP with these boat engines. I went from a 3B 21" to a 4B 23" to get my best performance so far, I plan on trying a 4B 24" to see where that puts me. Pushing a heavier you need to get on top of the torque band, a 16 or 18 not as important.


08-12-2012, 09:24 PM
One thing I would modify your throttle linkage.



08-12-2012, 10:03 PM
I did the throttle linkage after I saw the thread, I also changed my shifter to a pull configuration, originally I had turned the carb around, the cable interfered with the cooling system.

08-13-2012, 08:50 AM
There is a breather on the passenger side and I installed one @ the fill cap. I used K-N filter type. I have to take updated pictures.
When you say another hole, do you mean further back? Not a tremendous amount of material there.
I know my friends run usually their Volvos in the highest hole. I guess that's what makes the 280T unobtanium.

08-16-2012, 12:47 PM
MOP here is the linkage - simple
Fixx here are the breathers

08-16-2012, 12:56 PM
I think what fixx might be getting at is the breathers should be plumbed back to the intake.

08-16-2012, 01:24 PM
I know several people who run open systems, I figured the theory would be a boat being under load most of the time would have very low vacuum rendering a PCV inoperative. Do most people on here run them? I had considered a PCV with a Honda Fanboy type oil trap. Worried about oil fumes / detonation.
Thanks for any advice,

08-16-2012, 02:54 PM
The guys who do the machining on my engines saw my PCV hose to the carb and told me motor oil has a horrible octane rating, and your nuts for giving the motor a source of it. My oil gets hot enough so moisture isn't a problem, and the oil gets changed long before it's corrosive.

09-17-2012, 09:19 PM
Splashed the boat for the first time today. Tried Ralph Savarese's 21 Michigan repitched to 22.5. Not even 100 yards was at 5000+.
Back to dock and we put on a Solas 23. 5000 rpm and 62 on iphone gps. I am very very happy.
I now have a like new 21 Michigan I was planning to have repitched for sale!

My GT21

Ralph's 18 in the Great South Bay

Now to get it tuned right, maybe try the middle hole, on accelleration it goes a little ways before it bites.

09-17-2012, 09:31 PM

Bobby D
09-19-2012, 12:57 PM
Congratulations your boat sounds assume.