What Propeller was specified for the 1980 Coronado

[1980Coronado]

Re: What Propeller was specified for the 1980 Coronado

http://cgi.ebay.com/ebaymotors/14x1...5416067QQptZBoatQ5fPartsQ5fAccessoriesQ5fGear

BTW a Prop shop can add or subtract up to 2" of pitch.

I was looking on E-bay but decided since I didn't know what prop would work best that I should probably deal with someone who will take a prop back if it didn't work. I'm working with Discount Inboard Marine and OJ props on this so it will interesting to see what direction they think we should go. They told me not to worry about the 30 day guarantee, they're going to work with me until we get it right. I'm going to go through the ignition and check timing to rule out an engine performance issue and then report back to them. Then we'll make a decision on what to try next. I don't think many people are calling and asking for props for these old boats anymore, so they don't have any direct experience to draw from.

 

[Tahorover]

Re: What Propeller was specified for the 1980 Coronado

If you have a quadajet you should check your welch plugs:
http://www.hotrodders.com/forum/leaking-quadrajet-138013.html

 

[1980Coronado]

Re: What Propeller was specified for the 1980 Coronado

Its a Rochester 4 Barrel Model 4MV Carb.

 

[Tahorover]

Re: What Propeller was specified for the 1980 Coronado

Its a Rochester 4 Barrel Model 4MV Carb.

Better known as a Q-jet or Quadajet.

 

[1980Coronado]

Re: What Propeller was specified for the 1980 Coronado

Better known as a Q-jet or Quadajet.

Ah...now I see the name quadrajet in some of the notes in the service manual....thanks for educating me on the lingo. I'll have to check into the welch plugs...something more to learn!

What are the symptoms of leaking plugs?

 

[Tahorover]

Re: What Propeller was specified for the 1980 Coronado

Symptoms vary greatly with the severity of leakage. My experience is with a automobile since all are boats are Chrysler powered. At first the q-jet would only leak at high vacuum situations and later it would still run slightly rich with the mixture screws turned most of the way in. After spending hours trying to find the GTOs lost power, I slapped a vacuum gauge under the windshield wiper and went for a cruise. With steady throttle on the freeway I was getting a 2"Hg swing on the gauge.

 

[1980Coronado]

Re: What Propeller was specified for the 1980 Coronado

Ok....good to know....something to keep in mind for sure. I haven't noticed any performance issue with the engine. It accelerates without hesitation, idles well, starts well, runs strong.....I don't expect to find anything wrong other than the prop is just too much for this setup. Since I don't know when the plugs etc. were changed last it can't hurt to go through it and replace the ignition parts. I would think the plugs might show signs of a rich mixture if the q-jet was dumping fuel....haven't had any of them out to check yet.

Nice Goat BTW

 

[1980Coronado]

Re: What Propeller was specified for the 1980 Coronado

Update:

Took the day off Friday to help Dad splash his 28' cruiser up at Wawasee, then headed off to my boat on lake George. Took the new prop off (4 blade 14 x 16) and put the old 3 blade "14" x 14 back on. Took it out for a run and noticed that it was running rough. Hooked the tach up and could only get 3700 rpm out of it at about 39 mph. Went to Napa, bought all new ignition parts....plugs, points, condenser, rotor, and cap. Installed the new parts yesterday, reset the timing and wow......now the old prop is turning 3900-4000 at 41 mph and the engine sounds good. While the plugs were out we ran a compression test and found all cylinders were at 130-140 psi on an engine with almost 1100 hours. So.....after a fresh tune and using a digital tach it appears that I do not have a prop issue and I wasn't over revving the engine. I didn't put the 4 blade back on to check it, but since I only gained 200-300 rpm with a tune-up, I figured the 4 blade would have gained the same amount which would still be too low.

One interesting thing I found was someone had installed Champion plugs in the boat but they were not the correct number according to the manual. It could be that the number listed in the manual (RV8C) has been replaced by Champion, but we bought AC Delco plugs that matched the number in the Mercruiser manual (AC-MR43T). Doubt that this had much to do with the performance issue, the points were worn badly and the gap wasn't set correctly by whom ever did the last tune-up.

I guess the question now is which prop to buy. The prop on it now is running fine, but it needs replaced. It's pitted and worn, and was reworked by the previous owner. The diameter was reduced from 14" to about 13.6" based on my measurement, and the pitch was taken down from 15 to 14. I'm considering just going with the standard 3 blade in a 14 x 14.

edit: went with OJ recommendation of a 13 x 16 4 blade....supposed to give 300 more rpm than the 14 x 16 4 blade...we'll see

 

[Dave Bortner]

Re: What Propeller was specified for the 1980 Coronado

Just stumbled upon your question through a Google search. My 1973 Coronado works best in Minnesota (about 900 feet elevation) with a 14 X 16 cupped 3 blade, or an Acme 13 X 15 four blade. Engine is 454 350 hp Crusader, about 4300 RPM with the Acme prop.

 

[1980Coronado]

Re: What Propeller was specified for the 1980 Coronado

Thanks for the info Dave...I tried a 14x16 cupped 4 blade from OJ props and my rpm was less than 3500. Then I put the old prop back on (3 blade 14 x 14...a reworked prop less than 14" diameter) and tested it and was only getting 3700 rpm.......after scratching our heads and digging into the ignition, we found the points were not gaped properly by the previous owner and were burned. After fixing that problem with a complete tune-up and ruling out compression issues, the RPM came up to 3900-4000. I never put the 14 x 16 4 blade back on it, but logically I should have gained roughly the same 200-300 RPM with it......so that still puts me in the low end of the RPM range (3800) with the 14 x16 4 blade. OJ says that the 13 x 16 4 blade will run 300 more rpm than the 14 x 16....that should get me close to 4100 rpm which is perfect. Comparing your boat to mine...you have 350 Hp....20 more than me...so... not sure that's enough Hp to change much but? 4300 RPM is over the 4200 recommended max WOT for my Mercruiser 454 MIE 330. I figure with the 13 x 16 I should be running somewhere between 40-45 mph at 4100 rpm which makes sense with your numbers. By increasing your 13 x 15 to a 13 x 16 I'd expect the rpm to drop by about 200 RPM....so that gives me confidence that the prop I have coming will work well.

 

[Tahorover]

Re: What Propeller was specified for the 1980 Coronado

I figure with the 13 x 16 I should be running somewhere between 40-45 mph at 4100 rpm which makes sense with your numbers. ll.

That is over 32% slip, 20 to 25% is more the norm from my findings:
http://www.rbbi.com/folders/prop/propcalc.htm
20%=49.7 MPH
25%=46.6 MPH

 

[1980Coronado]

Re: What Propeller was specified for the 1980 Coronado

That is over 32% slip, 20 to 25% is more the norm from my findings:
http://www.rbbi.com/folders/prop/propcalc.htm
20%=49.7 MPH
25%=46.6 MPH

My numbers are a SWAG. I didn't put the 14 x16 back on after the tune-up and I'm relying on my speed-o not a gps reading....so..? I don't know where the speed would have been with the 14x16, but the rpm would not have been where it needed to be even after the tune-up. Would you agree with my logic that the rpm gained by the tune-up would have been the same for both props (old 14x14 3-blade and new 14x16 4-blade)? I can't see getting a 300 rpm gain for the 14x14 and then suddenly getting a 600 gain with the 14x16 (4blade).

Ultimately the speed may jump up over 45, I just can't say for sure until I try it. I'm basically going with the recommendation of Eric Johnson at OJ prop, who says their tests show a 300 rpm gain between the 14x16 and 13x16. If my somewhat educated assumption is correct, the 14 x 16 would have run no more than 3800 rpm (probably less) after the tune-up, but I don't know what the speed would have been.....I can make an assumption that I would have gained another 3 mph maybe...so lets call that 45 mph on my speed-o (just as a point of reference). If I jump up another 300 rpm, the speed could increase a couple of mph...so maybe 47-48 mph is where it would end up....I guess we'll see. This has been an interesting learning experience...I love tinkering with stuff I'm not really looking for the speed as much as I am just trying to keep the rpm within the 3800 to 4200 rpm. 47-48 mph would be moving pretty good for that tub.

Honestly the prop I have on there right now shows good numbers in the calculator link you provided, but it's all pitted and has been reworked multiple times. It wouldn't kill me to just leave it on. My original assessment that I was over revving the motor was incorrect. I'm still going to replace the old pitted prop, it needs to be retired.

 

[Tahorover]

Re: What Propeller was specified for the 1980 Coronado

. 47-48 mph would be moving pretty good for that tub.

MY B-I-Ls 1963 Coronado can do over 55 and it surprises many!

 

[1980Coronado]

Re: What Propeller was specified for the 1980 Coronado

Update:

I installed the OJ 13 x 16 (4 blade) and I'm pleased with the boats performance. I used a digital tach and a hand held gps to test the boat with a full tank of gas and just me in it. The lake was a little choppy on Sunday so I know my speed is probably a couple of mph slower than if I had smooth water. RPM was close to max between 4100 & 4200 and I was able to touch 44 mph even with the chop and waves from other boats...On smooth water on a long run I'm guessing I could get to 46 mph, but that's not really that important to me. I'm able to plane it easily when loaded which is important.

Tahoe....I know your going to say that's a lot of slip, but I don't think I can improve on it substantially enough to justify trying another prop. 4200 rpm at 45 mph is 29%....however, when you take into consideration the type of hull and the lower rpm range allowed by the engine, I don't think it can really be improved much. When you look at some of the other data points speed vs rpm the slip is in the 20-25% range.......When you go full throttle the nose comes down and pushes more water....so the slip goes up as you reach the upper end. I could probably get more top end out of it with a different prop, but then it would struggle to get up out of the hole. I feel that for how we use the boat the prop is a good match. It comes out of the hole well with a load, and allows the engine to get to max rpm without a load. I think I'm done tinkering with it!