prop sugg. on a 84 272 ls w/ 5.7 twins?
 

I have an 84 formula 272 with the twin chevy 5.7's, right now trimmed out I am at 47 mph gps at 4900-5000 rpm's. thats with just enough fuel and three adults and a child on board with just the essential equipment. I am running a set of cleavers 21p, not sure they are cleavers but they are 21p.both right hand drive. I have alpha 1 drives. I have heard that thses old v's like the 3 blade round ears props.
I would like more top speed (like everyone else). I am not a drag racer so hole shot isn't too important.
any input?

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

If your gears are a 1.47 then you have some serious slip issues. I am coming up with 30%. This is unbelieveably high and means that your efficiency is only at 70%. You should be 1/2 of that at 15% worst case scenario. I would try to find some 21 Mirage Plus propellers and test them.
If you can reduce the slip then the speed will follow.

Julie

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

Thanks Julie

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

You sure you don't mean 57 on GPS??? I have a customer with that exact boat and props. I built some modified 350's for it and we were getting 64 on GPS with those same props and gears at around 5300 RPM.

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

positive it was 47 and my engines are bone stock so if you got 64 with built engines I am not too far off of where I should be I would think. I am sure with more practice and ideal conditions i could get mid 50's. I plan on heads cam and intake over the winter.estimated 400 ponies per, then I will probably bust my drives. all in good fun though. The only other thing i can think of is my props aren't at all polished anymore they look like brushed aluminum now, I don't know if that makes a difference. I will post a pic and let you see.

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

here is a pic of the props, the only markings on them is 21p and a couple numbers.

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

My friend has the same boat, stock power, his is counter rotating. I dont think you gain speed with that, just handing. He runs Mirage 21 and sometimes will switch to 23. His are not Mirage plus. He has runs a best top speed of 59 mph GPS and with the 21 somewhere around 55.

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

Flatout,

Those are Mercury canned cleavers. Old style props which will produce decent top end but performance can leave alot to be desired.

Julie

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

thanks julie

ok new #'s
 

I did some work and some testing today, I adjusted my throttle cables so now I am getting full throttle. they were off before thats why I had a hard time matching rpm's. I got a best of 52.8 on the gps this time at a solid 4800 rpms. now as soon as I trimmed down the rpms dropped off like nobodies business. trimmed all the way down I was only getting abot 4100-4200 rpm's. I would like to see 60-65 mph which is what everyone else with this boat has done.
My drives are Alpha ones does that limit me? is there any shorty lowers or any performance upgrades for them?

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

MUCH BETTER!!!!!!!!!!!

You still have 19% slip though. You should be at 15% at a minimum with the 3B Cleavers. You are running right were you should be with the 5.7 L motor at the 4800 RPM at WOT. I think you should try to test some Mirage Plus 21P props and see if they bite a little better.

Julie

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

Can anyone give me some pointers on swithing the gears around in the drives to make the port drive turn LH? I have no Idea how to tear apart a drive though I am very mechanically inclined do most of my own work on my trucks and hot rods. Is it something I should take to a shop?

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

You have to buy a counter rotating alpha drive. they are very hard to come by.

Re: ok new #'s
 

This may sound like a stupid question, but I had a friend that made this mistake last week...
Are you sure your gps is reading mph and not knots/hr?
Your boat should go 60mph with 21p at 4800 engine rpm.
53knots is about 60mph...

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

Just installed a counter rotating drive on my 1986, 24ft Daytona. Went from 20p aluminums to 23P Mirage. Runs straight and handles much better. GPS at 61MPH at 4400 rpm. Have stock 260hp 5.7 w/ alpha I drives. Got a new drive on Ebay for $1600. Now need more power.

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

to make an alpha counter rotate you switch to a counter rotating lower.......you do not have to change the whole drive...............doug

Re: prop sugg. on a 84 272 ls w/ 5.7 twins?
 

Thanks guys I will start searching on ebay for a counter rotating lower.

Re: ok new #'s
 

your alphas arnt going to limit you ......they are actually faster than a Bravo due to a smaller gearcase and less mechanical drag from smaller/lighter gears and shafts.......there are no shorty lowers available only a VERY rare "Alpha SS" drive from Mercury that is 2" shorter than a stnd Alpha.....from what I understand (Ive never seen one) you cannot modify a stnd Alpha into an SS they are their own animal ( I could be wrong though)........my very knowagable drive guy said Merc did offer a hardened upper gearset fothem but now the new ones have all been brought up to that spec.......you can have aftermarket nosecones installed and a Simrek drive shower is definatly a high performance modification......they run hot!!!! ........change drive oil often and watch the level.....if it gets even a little bit down you are in trouble