New engine, new prop

[skargo]

I have a 78 Nova 210 with a 5.7 engine I just swapped in pace of the old engine which had a crack in it. This is a GM performance 260hp with the truck/rv cam grind, VERY similar to the engine it replaced.

I have been on the water everyday for the past 9 days. Yesterday, on the way out I tagged something, rock or stump. Can't really see damage on my SS 19p prop, except for some slightly rough edges but I could not get it above 4100 rpms.
I swapped on a 4 blade aluminum 20p prop today. It won't reach 4K rpms, but it is quicker at other RPMs. At just under 4 grand I was hitting 37mpg SOG on my GPS.

I took a guess, as I was switching from 3 to 4 blade and SS to aluminum.
Should I be looking at an 18p in a 4blade?

I am taking the drive in tomorrow to get it resealed. It has been picking up small amounts of water and is leaking drops of gear oil out of the small "weep" hole. I am going to have him check the shaft and make sure the drive is OK.

 

[45Auto]

Re: New engine, new prop

Would it go above 4100 before you hit the stump or rock?

Would the original engine reach the correct WOT RPM with either of your props?

If the performance of your new engine is substantially less than the old one with the same props, you may want to get the engine installation checked.

 

[skargo]

Re: New engine, new prop

Would it go above 4100 before you hit the stump or rock?

Would the original engine reach the correct WOT RPM with either of your props?

If the performance of your new engine is substantially less than the old one with the same props, you may want to get the engine installation checked.

The engine went to 4500 rpms easily before I struck whatever I struck. I never went WOT before as I am still in the break in period.

 

[steelespike]

Re: New engine, new prop

Why not have the stainless 19 repaired.I wouldn't make any prop changes until the motor is fully broken in and you determine that the rpm drop is from your props run in with what ever.
If you read the stickies at the top of the page and the helps on the prop store page it will help you understand prop selection better.We'll be glad to help with any confusion from what you have read.
Usually when going to a 4 blade you would lower pitch 1 inch if your your original prop was right.
going from ss to al creates a more variables.
I think you should get the ss repaired and see if your back to your original numbers.

 

[skargo]

Re: New engine, new prop

I will drop the prop off today.

 

[45Auto]

Re: New engine, new prop

Hard to imagine a prop with no visible damage being the cause of losing more than 400 RPM. I've hit stuff hard enough to break 2 gimbal rings about a year apart with no loss in performance.

Won't hurt to have it fixed and check again before doing anything else, though. maybe you'll get lucky!

 

[skargo]

Re: New engine, new prop

Hard to imagine a prop with no visible damage being the cause of losing more than 400 RPM. I've hit stuff hard enough to break 2 gimbal rings about a year apart with no loss in performance.

Won't hurt to have it fixed and check again before doing anything else, though. maybe you'll get lucky!

Thanks. I dropped the boat off today for my drive issues. i am going to drop the prop off tomorrow, and we will see what happens.
I am with you, seems weird to lose that many RPMs.