'05 Regal 1800 4.3GL prop selection

[gozfast]

I need a little help to get started. I currently have the Volvo/Penta 4.3GL with the SX drive, labeled with a 1.66 gear ratio. It now has a Volvo brand stainless prop marked as 14.25 x 23 but my max indicated rpm is 4900. I really don't believe the 4.3 could spin the 23 pitch that high. Possibly the installed prop was re-pitched, but since I'm the third owner I don't know the history, so I don't have a reliable baseline. I'd like to get a "really good" stainless replacement but honestly don't know where to start. Unfortunately, I don't have a place that will let me test various props, so I need to pick the right one first time. I know the stepped hull on the Regal boats is a little faster than most and doesn't seem to fit well with the normal calculated prop selectors. The engine is stock with only some cold air ducting. My priority is to max my top speed without totally killing the holeshot and keep it at the spec'd 4600 max rpm. Does somebody have any real experience with a stepped hull Regal 1800 and a carburated 4.3GL that could help?
gozfast Posts: 1 Joined: Thu Sep 04, 2014 8:53 am

 

[Maclin]

What is the top MPH at the 4900 rpm's now? Speedo or GPS...?

 

[gozfast]

Speedo showed ~55 mph, but I'm not sure I believe that. Unfortunatly I didn't have the GPS on at the time and I didn't want to hold it over the max RPM for too long. Previous runs at lower speeds showed the speedo reading about 1 mph higher than the GPS number.

 

[YoungMind]

GPS speed will help make sure that your combo is operating at peak performance.

Also, if you want to make sure the prop is right take it to a prop shop and have them calculate the pitch. That will tell you whether it was tweaked by a PO or not.

 

[SkiDad]

Ken at propgods.com - he will be able to help you fine tune a prop. Your numbers seem to be close. I'm not sure why you want to go faster - that is pretty darn fast for an 18' boat w/V6 - you have to be careful at those speeds especially if you have kids.

 

[redmen62]

I'd recommend going with a 14.5x21. It's a little bigger and has a little bit shallower of blades so it will push a little more water with every rotation, and the larger diameter will slow down your engine RPMs a little bit

 

[steelespike]

Using a pretty normal 13% slip 4900, 23" prop, calculator says 55.9.

 

[gozfast]

If I understand the replies, It seems to show that I do not have a re-pitched prop and it is a actual 14.25 x 23. So since I don't see a prop with a greater pitch than 23 that fits the SX drive, I need to go to a larger diameter. If I go down to a 21 pitch on the 14.5 will that drop me 300 RPM or should I stick with the 23 pitch at the 14.5 diameter? Does anyone have a prop brand and type they would recommend with my previous priorities of maxing my top end without totally killing the holeshot? Something that's a good value but doesn't need to be cheap either. Ideally I'd like to test, but don't have a local place that will let me do that. Maybe I'd order a couple of sizes if I could return the one I don't use. Any suppliers that do that? And Mitzysman, I've never understood the concept myself of not wanting to go faster. You should see my other toys.

 

[steelespike]

Are you worried about the 4900 rpm. In my mind 100 rpm is the plus or minus error range.
At 55+ speed I would say your about there.According to my info the 4.3 is rated for 4400 to 4800.
Why do you want to lose 300 rpm?How is your hole shot? I would expect a little sluggish.

 

[gozfast]

No Title

The carbureated 4.3GL is rated for 4200-4600, a little lower than the fuel injected model. I didn't know how much safe margin I had but I'm probably past the peak HP at 4900. With the drive trimmed down the holeshot is totally acceptable to me. The outdrive has one of those wings installed by a previous owner, so I don't know if that makes a difference or not. The currently installed Volvo prop is in really good shape but I wanted a spare anyway and didn't want to leave anything on the table. I thought the 14.5 x 23 Stiletto Advantage II with the vented hub might be worth a try. Any other better recommendations? Would the 21 pitch be a better choice at that diameter? Oh, and by the way, the boat will probably see a V8 in the future.