Set up for a 27 ZR with a 525 EFI
 

I just repowered to a 525 EFI from a 496 HO. I am now struggling with getting the right X dimension and prop size. Started with an XR with an IMCO lower/ Bravo 1 28p. Boat only ran 73 at 5400 RPM (guessing ~26% prop slip). I had power left but the REV limiter kicked in. Next, I added a one inch IMCO spacer. Boat ran 73 again, but did take the RPM down some. Still hitting the REV limiter but the throttle/ trim was closer to WOT. But I still have a big prop slip problem (24%)
Is anybody running a 27 ZR with a 525 EFI? If so, can you tell me how you are set up/ what speeds you getting? Don't know whether to go for a bigger spacer or try a 5 blade prop next. The rooster tail is still showing that the blade tips are surfacing a bit (tail is actually throwing to the right a bit).
If it helps, the hole shot is very good and the cruise at 3500 RPMs is 41 MPH (GPS). At about 68, the boat is starting to fall off the pad and by 73, it's a hand full to control.
Any help is appreciated!
Thanks
Barry

I was running a 28b1 on my Donzi and the boat didnt like it. Spinning 6500 it ran 92mph. The handling and performance of the boat sucked. 5 blade round ear 28 pitch herring 5800 rpm 95 mph. Totally different boat. With the 5 blade I've made some pretty hard turns over 90 mph. With the b1 I think the boat would roll over...

Black Baja,
Thanks! different hulls, but i think the same result. I can't seem to push through 73 mph with the Bravo 1. The boat keeps falling off the pad. And you are one of many now telling me to check out the performance with a 5 blade. That will be my next step, in fact looking for one now in the "wanted" forum.
For the 27 ZR, Donzi's performance stat sheets showed 81 mph with the 525 efi optional package and they ran that with a 26p Bravo 1. I'm hitting the rev limiter (5400 rpm) with the 28p. But, I still don't know if it's because the blades are breaking the surface (they are) or becuase i still don't have enough prop. Going to try a 5 blade and see what happens.
Thanks for the data!
Barry

Please keep up with this thread.Im very interested in the out come.Thinking this will be my next up grade as well.

Tokima3,
Glad to help. There weren't any responses for a 27 ZR so it was a lot of trial and error. After the 1 in spacer and 28 p four blade, I tried a 5 blade. Because of hitting the rev limiter, I went with a 29p which should have and did knock the rpm's down 500. That solved the rpm problem, but the performance was the same. I only got 73 on gps. Hole shot wasn't any better and cruise about 42 mph on gps.
Next step was to change the spacer to a two inch. That solved a lot of problems for me. I started with the 28p, 4 blade and got to 75 mph before running out of lake. Water was very choppy and it was a very windy day. Higher speeds were definately obtainable if I had had more room to run. Notably, the hole shot was great and cruise improved to 45.6 mph.
Next, I tried the 29p 5 blade. It was a pig getting out of the hole and still only ran about 73. A lot of that was due to the prop finally being fully submerged. I'm either going to sell it or have it worked to a 27p and use it for a back up prop.
I also ran a 27p 3 blade just to see what the extra bow lift would do. Again, only got 73 mph, but that was in part because I was too busy holding on to the boat! It was a wild ride, and I don't recommend it.
I'm very happy with the 2 inch spacer/ 28p b1 4 blade. All my test runs were in fresh water and I believe that when I get it back in the Gulf, I'll see 80 mph.
And as an added note, I had 4 adults and a child with a full tank of gas, on yet another windy, choppy day and still had good performance. Good hole shot, 45 cruise, and hit 73 mph.
All in all, a vast performance over the 496 ho where I only got to 64 at WOT. Were you seeing the same with your 27ZR? If so, you may want to consider looking at a 1 or 2 inch spacer to see what that does to your performance first. That's an easy change to guage what your performance change will look like when / if you change to the 525. You can re-use the spacer with the new set up. I have a 1inch IMCO with about 30 minutes run time for sale! Hope this helps and good luck! Barry

hey thanks for all the great info
.Im running a stock 496 with factory set up. I did replace the 12 in tabs with 16 in tabs. With only the wife and I was able to hit 67.2 on the g p s. That was running down Sarasota bay in a light chop. I felt I needed to stop there as we were experiencing a tremendous chine walk. So I have no idea if anything further would be possible for me. I m guessing the spacer would help though. If you would like you can either p m me a price or go ahead and post it up here for your 1 in.
thanks again for the info
Todd

Todd,
is that a 496 or a 496 ho? If you got 67 on a 375 hp 496, I don't think you need any help with the spacer. If it was the 496 ho, then we were pretty similar in speed. I had real high prop slip numbers until I added the spacer.
I'll post it in the swap shop soon. Or if you want to test it first, shoot me an email at [email protected] and we can work something out.
Barry

Barry
sorry....496 ho.if you would nt mind .when you put it on up for sale .put something on this thread. I don't get the opportunity to get on here much.hopefully it e mails me..thanks again
Todd

30p Bravo 1. If hole shot was good then remove any spacers added after.

Todd,
Copy all and I'll make sure to post the spacer on this Donzi thread. Although, I thought about it, my boat came with a 26p B1. If that is what you were running, your prop slip numbers are real good and I doubt that your X diminsion is off like mine was. Which means you probably don't need a spacer at all.
Break, for Thirdchildhood - is your 30p B1 recommendation for me? I'm all ears on any advice you have. The 28 B1 is doing well for me, but i think i'm going to take the prop in for re-cupping. There are no dings, dents, scratches or anything, but it's about 5 years old now and probably could use some attention. That should be like adding some pitch but if you ran a 30p B1 on a 27ZR, can you tell me what kind of performance you got?
Thanks! Barry