Drive Spacer
 

Ok I know this has been discussed before on this forum. Im considering a 1 inch drive spacer my boat slips a little out of the hole. Im getting tired of backing out of the throttle a bit coming up on plane just so my rpms dont go high. I would like to know what the best spacer is and how much I should pay for it. My drive is bravo 1 x drive 05 heat stock 496ho, only thing I have done is a 25 pitch powertech ofx 4 blade prop which has extra cup. What will this do for me?? Higher speed, better bow lift, no slip, etc. Any help would be appreciated!

Thanks Garret

Garret,
The extra prop shaft depth will allow your current prop to come onto plane with less slip, it will have a lower slip % in mid range cruise, and quite possibly more top end.
It's a win win. Imco has a good one.
I would look at the online performance catalogs like Teague, CP, etc. for availability and pricing.
Regards,
Steve

Thanks for the reply Steve. I talk to Eric at EB Marine today he said a drive spacer would do good so i think Its a no brainier? I told him my rpm and top speed from this weekend Which was 2 people Half fuel going 59mph @ 4700 rpm and he said I need to step down 1 pitch on my prop. I have like 20% slip l cant achieve 4950 or 5000 like i want to with my ofx 25pitch. Do you also think If I got my Prop turned down to 24 pitch I would gain around 250 rpm? Also If I added a 1 inch spacer with the prop going down further would that make it hard to achieve 5000 rpm?

Thanks Garret

Just to add, I put a 1" spacer in my '03 heat and it definitly helped going on plane, I don't blow the prop anymore and I gained 3mph at cruise (3300-3500rpm). I stayed the same maybe 1 mph slower at WOT but it cut my rpm back 350. I am going to have a prop worked next to get the 500EFI back to 5100-5200rpm.

I have a new to me 1999 heat with the 502 and everything is stock. This past weekend was my first time to use the boat and I experienced what I now think was slip, not too much getting to a plane, but cruising about 3500 RPM's. Would the drive spacer help with the slip or is changing the prop with a spacer be a better option. I don't know what pitch the prop is, but I'm sure it is what came on the boat from the Nordic.

Garret, when you change one thing, it does affect other things.
In this case slip % and RPM/speed. You'll have a better data base if you change one thing at a time. Run the spacer and check mid-range and WOT rpm, speed, and slip %. From there you can make a more educated estimate on your propeller needs. I am not familiar with your prop. Some designs work better than others when it comes to repitching up or down. I would find some Bravo 1s in 24" and 26" to test, as well as your current prop. You may be better off swapping your propeller than having it reworked.
It does sound like you are currently over pitched, and can use some extra RPMs. BTW, be aware that some designs are not the exact pitch they are stamped, so that's why it helps to try different designs and brands. Around here (generally hot and humid) Mag HOs and 502 Mags run the best with 26" B1s when we get them set up properly.
Regards,
Steve

The pre-step pad vees had a much lower X dimension and are usually OK as is, unless you add a lot of HP.
You may need to add a little extra cup to your current prop to get rid the slip.
Welcome aboard!
Regards,
Steve

When you say "add a little extra cup", is that modifying my prop or getting a new prop with different specs?

Cup is a reference the "bend" in the trailing edge of most propellers. It is designed to add holding power for carrying weight, lifting the bow, and generally reducing slip.
Increasing the cup does add pitch to a propeller too, so it tends to reduce RPM.
If your current propeller is in the correct RPM range for your motor, then I would have it modified. If it isn't (either too low or high), then I would do some prop testing with other props.
Regards,
Steve