Identify exhisting prop

[Wimperdink]

I'm running a 1985 bayliner capri 2.1 with volvo penta and i'm having trouble with holeshot and speed... In wading through the hundreds of posts about props i've decided to get a lower pitch prop. my operating range rpms are 4400 to 4800 and i'm running 3100 at wot. It was taking forever to plane until I got the smart tabs on... now its planing fine but extremely slow top end of 27 mph (was at 25 before tabs) and wot rpms are 3100. Anyway I've pulled the prop and its a Michigan with stamped number SMC 347 . Can anyone tell me the pitch of this prop from that part number. thanks <br /> Any size/pitch/blade# recommendations would be appreciated too

 

[Dunaruna]

Re: Identify exhisting prop

Hi wimperdink, welcome to iboats!<br /><br />That 2.1L is working overtime, you need something around 15 x 15 or 15 x 17. I just did a google on the michigan wheel SMC347 - zero hits, sorry.<br /><br />Before you start repropping, do a thorough tune and carb clean, you may find some horses there, then prop to suit WOT.<br /><br />Aldo

 

[05GlastronSX]

Re: Identify exhisting prop

obviously you need to go DOWN in pitch. you are lugging your engine really bad and i would NOT run the engine anymore until you change your propeller or unless you want some serious damage done to your engine. I dont know the current pitch of your prop but it looks to be WAY to high. now, as for selecting a new prop, what do you mostly like to do? also, what do you want? good handling? good top end? good holeshot? you could look into a SS prop if you want one one of the three i have mentioned, but if you want decent overall performance without the stumping pulling hole shot or eye blistering top end, i think a regular aluminum prop would work OK. i also would recommend a 3 blade propeller unless you are really into a great holeshot and different handling characteristics.

 

[Boomyal]

Re: Identify exhisting prop

Like Aldo says, check that everything else is working well before leaping to a prop. I would also take your's to a prop repair shop to determine it's measurements. You need a known baseline to work from if indeed your problem is prop pitch.<br /><br />The fact that you only get 3100 rpm makes me suspicous that something else is going on here. What is the likelyhood that such a grossly improper prop would have been put on the boat?

 

[Dunaruna]

Re: Identify exhisting prop

Found it - an SMC347 is an alloy 3 blade, R/H rotation - 14 x 19.<br /><br />Waaayyyyy to big, that's what I'm running on a 22ft V8!!!!!!!

 

[Wimperdink]

Re: Identify exhisting prop

I've done a complete tune up, Cleaned carb, and adjusted timing and i've got 150 - 152 psi on all 4 cylinders. I bought the boat used from a hillbilly up north so who knows... it might have been a friends prop and the price was right. Anyway Thanks folks. Dun I appreciate the prop sizing info.. there's 14 x 17 's all over ebay so that will be my first try.. or would a 15 x 15 be a better bet? i'll keep this one as an emergancy spare.<br /><br />Id like a good all around solutions, some skiing some cruising.

 

[Wimperdink]

Re: Identify exhisting prop

p.s. 05GlastronSX this is a heavy boat with an underpowered 4 cylinder (105 hp) The only blistering that will be going on is from the sunshine.

 

[Dunaruna]

Re: Identify exhisting prop

14 x 17 is still too big, me thinks you need a 15".<br /><br />But before you do that, remove the top timing belt cover and check the cam timing (don't confuse that with ignition timing). You could be one or two teeth out.<br /><br />The 19" will be o/k as a spare, especially for freshwater trolling.<br /><br />Aldo

 

[Wimperdink]

Re: Identify exhisting prop

Been there done that... #1 at tdc on compression stroke and top cam is lined up on notchs perfectly. would you reccomend a 15 x 15?<br /><br />That would also explain the 19 pitch as the previous owner only used the boat for fishing

 

[Dunaruna]

Re: Identify exhisting prop

Assuming everything is 100% o/k, yes - 14 x 15 (I mistyped the first 15 x 15).<br /><br />You would be going down 4" in pitch, that will raise your WOT RPM's by about 800 - approx.<br /><br />That's only going to take you to around 4000RPM, still too low, but better!<br /><br />You still may have another problem.

 

[Wimperdink]

Re: Identify exhisting prop

Great... I appreciate the help. Going prop shopping.. Ya think the extra rpms will help top end as well or will I just get better holeshot and maintain top end? Once again Thanks all for the input.<br /><br />p.s. ugh michigan wheel doesnt make a 14 x 15 prop for my long shaft. (git your mind out of the gutter) smallest they make is the 14 x 17. for the long shaft. they make a 14 x 15 in the short shaft version.

 

[walleyehed]

Re: Identify exhisting prop

Dunaruna, we may see more rpm rise due to the fact the engine will be up near it's max torque range and will gain more than 800....it "may" show 1000 even 1200 gain if going through or getting close to the torque peak.<br />I agree with a 15P though...

 

[Dunaruna]

Re: Identify exhisting prop

Originally posted by walleyehed:<br /> Dunaruna, we may see more rpm rise due to the fact the engine will be up near it's max torque range and will gain more than 800....it "may" show 1000 even 1200 gain if going through or getting close to the torque peak.<br />I agree with a 15P though...

I was in the middle of typing a similar reply when a customer interupted me and I lost the post before I could "add reply". Damn pesky customers <br /><br />I would also add - <br /><br />That's a small power plant, don't expect miracles.<br /><br />Aldo