More speed please!

[racinrc14]

Boat: 1977 Glastron SS-V 189/Mercruiser 888 (Fresh 302 Ford, mild cam)

Current props: Merc. 14.5 x 19 = wot 4600+ rpm 38 mph
Merc. 14.5 x 21 = wot 4600+ rpm 42 mph

I limit the rpm with the throttle so I don't hurt my newly rebuilt motor. I am aiming for a max 4200 rpm. I would like a little more speed for the evenings when we are just cruising. I love the all around performance of the 21" prop, but more speed would be nice. I don't mind changing props at the lake, so I was considering buying another prop for cruising and was wondering what other folks might suggest. Pretty good sale going on here at iboats, would be buying it from the website. I'll be staying away from stainless due to cost and indecision on final prop size.

 

[ramster]

Re: More speed please!

You need to turn that motor 4600-4800 rpm at WOT, that is without holding back on the throttle. Propping it 4200 rpm WOT is lugging the motor and more damaging than high rpm. At your current 4600 rpm, is that with the throttle pushed all the way? Or, are you holding back? Also, are you trimming it up to the max rpm you can get? I think with a V-8 you should see close 50 mph, need more info before trying guess what prop is best.

 

[steelespike]

Re: More speed please!

Check out the Turning point Hustler;ss performance at al prices.
You ask for more speed for cruising? Are you looking for more spoeed at a given rpm?4 blade props usually stay on plane at a lower rpm but generally sacrifice a little top end.

 

[hwsiii]

Re: More speed please!

Racin, Ramster is 100% right about over propping the boat and Spike is definitely right about the props.


H

 

[wca_tim]

Re: More speed please!

depending on where you wind up with your max rpm at full throttle for your other two props, a laser 2 in 19 or 21 would probably give you the best top end. (3 blade) the others are right on with the 4 blades as well.. solas makes a good 4blade stainless for cheap (titan, i have one in 21 that is a lot better prop than I thought it would be when I bought it).

 

[hwsiii]

Re: More speed please!

Tim, can you give me some information on the blade geometry of that Titan, and the HR as well if you know.


H

 

[racinrc14]

Re: More speed please!

Ramster,
I am holding back on the throttle to keep the rpms from running away. The Merc. manual for my combo says max cruise 4200 RPM, but I'll double check this when I get home later.

I haven't checked my boats' speed with a gps, but a friend has a boat that outruns mine and his speedo (checked with gps) is fairly accurate. His speedo reads about 43mph when cruising next to mine with the 21 on at around 4600 RPM. I don't think there is much more throttle left, maybe up to around 5100 wide open and trimmed up.

All the stainless props I see are over $250, which is way out of my budget. I can get aluminum props here on Iboats for $150 or less.

 

[Dhadley]

Re: More speed please!

When you changed cams the OE spec for rpms went out the window. You'll have to balance the new rpm requirement between what the cam is made for and what the outdrive is designed for.

If the spec on the new cam is (for instance) 5000 +/- then you'll have to be careful with the drive, perhaps upgrade some components to safely run the rpm the cam (engine) is now made for. If the new cam makes it's best power at 4200 then the drive should be OK and you'll now be looking to max out at 4200 or so, not the 4800 with the stock cam.

 

[hwsiii]

Re: More speed please!

Racin, my data shows your motor's factory specs call for 3,800 to 4,200 RPM and a gear ratio of 1.5:1 with a base boat weight of 1,600 # please verify this , but Dhadley is right when you changed cams everything changed about the motor's RPM, so they are not as relevant as they once were.
I also find that if the gear ratio I have is right that you have a prop slip of 31% for both props and I find this hard to believe. I either have the wrong gear ratio or your tachometer is wrong. I also find you ought to be able to get about 47 MPH out of your setup.

Boat and Motor

Prop Picker

Prop Slip

I need more information to do a more comprehensive analysis of your boat and motor so if you will please fill out the following information I will be able to help more.

Iboats Boat and Motor Info
1. Year, make and model of boat
2. Length, width and base weight of boat, look for boat decal on back of boat
2a.What is the recommended HP for your boat
3. Number of people and gallons of gas normally on boat
4. What do you use the boat for
5. Is it a Deep Vee and if so how many degrees of deadrise
6. Year, make and model of motor
7. HP and gear ratio of motor IMPORTANT
If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing and turn the motor until the tape lines up with each other, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor
8. Manufacturer?s recommended Wide Open Throttle (WOT) range
9. Anti-ventilation Plate height above keel of boat if it is an outboard in inches
10. Is it a bass boat or does it have a pad bottom
11. Does it have a hydrafoil, dolefin or trim tabs
12. Make, model, diameter, pitch and whether SS or aluminum prop
13. WOT RPM and speed from your current prop and how much gas and how many people were in the boat for the test data and is the speed by GPS. If you do not have a tach you can buy a Tiny Tach for $ 50
14. Are you at sea level or a higher elevation, give us the elevation in feet
15. Has your motor been tuned up lately and have you checked that the carburetor butterfly is opening all the way, checked compression, and looked at the plugs and checked spark, all of the foregoing could be the reason your prop is not attaining full RPM
16. How long has this prop been on the boat and why, at this time, do you think it is the wrong prop
17. Does the prop show any damage that you can see
18. What problems are you trying to cure or what are you looking for the boat to do that it is not doing the way you think it should or to your expectations
19. If you are trying to attain a better cruising speed and fuel savings or trying to attain a faster speed I will want you to take your boat and run it with 1 or 2 people and give me the RPM and speed readings starting at 3,000 RPM in 500 RPM increments all the way to WOT.

REMEMBER, The numbers I give you will be NO better than the information you give me

The only thing I ask of you is to come back and give me a report of WOT RPM and speed for my database.


H

 

[ramster]

Re: More speed please!

I think 4200 rpm is low for any V-8, Ford or Chevy. If the motor specs say 4200 max, I would think it's because the motor was tuned to make peak power at that rpm, not because the bottom end won't take it. You put in a little more cam so your peak power may well be around 4600-4800 now. If you can run right up to 4600 holding back a little with the 21", I would get something like a Turning Point Hustler in a 23", probably the best AL prop going, at a cheap price. That should keep you around 4500rpm my guess. I would feel safe running that motor at 4800 rpm all day long. I have a 305 Chevy bone stock except for the addition of a 4 barrel, and I run that wide open quite a bit, up to 4900 rpm.

 

[racinrc14]

Re: More speed please!

Ok, that's a lot of information, but here is what I found:

1. 1977 Glastron SS-v 189
2. 18'9" bow to stern, beam width (as measured) 86.5", Base weight 2155lbs unloaded
2a. Came from factory with 188HP Mercruiser (302 Ford v8 sterndrive).
3. Rated for 8 persons, normally loaded with 5 persons with combined weight of 800lbs. Normally carrying 20 gallons fuel, 30 gallon tank.
4. Recreational use, mostly cruising and tubing.
5. Modified shallow vee, keel to rubrail 32.5" at transom.
6. 1978 Ford 302 V8, factory spec except cam. Cam (Summit K-4400) rpm range 1500 - 4000 (nearly stock specs).
7. I am assuming the motor makes it's rated 188hp and I believe the gear ratio in the lower unit to be 1.65 to 1. (stamped on the outdrive).
8. 4200 rpm max recommended WOT as per manual #2.
11. No hydrofoil
12. 14.75" x 21"P Merc. Aluminum 3-blade.
13. Observed 44MPH @ 5150 RPM WOT with two persons (425lbs), and 15 gallons on board, trimmed for simultaneous max RPM and MPH.
14. 613 ft elevation
15. Fresh motor, with correct carb operation.
16. Recently purchased boat, rebuilt motor, prop came with boat.
17. Had current prop re-conditioned while engine rebuild was in progress, no damage noted.
18. I believe the WOT rpm too high, and WOT speed too low.
19. Not concerned with MPG.

 

[hwsiii]

Re: More speed please!

Rain, I show your reommended RPM should be between 4,200 and 4,600 RPM and a gear ratio of 1.71:1, please verify this. I am using the 1.65:1 gear ratio you gave me, but please look on the motor and see if it has a reommended RPM on it. I believe its hould probably be loser to 4,600 but I am not sure. I find your prop slip to be at 34% and that is exeedingly high to say the least.
Before we pik a prop let's make sure your tah is working orretly, beause I do not beleve it is right at all. If you an borrow a mehani's tah to hek the RPM while atually running the boat to verify the RPM. You an try turning the swith in the bak a few times to to lean the ontats and see if that makes it work. While you are testing the tah give me the WOT RPM and speed and then let me know what it is.


H

 

[ramster]

Re: More speed please!

If your spinning a 21" over 5000, and you want to stick with aluminum, you need a good quality prop like a Solas, or a Turning Point, in a 23", those props have decent cupping and are more efficient than OEM props.

 

[racinrc14]

Re: More speed please!

Ok, I'm planning on going out this Friday so I'll take my dwell/tach with me to verify. If I pull the top cover off the upper gear housing and count the teeth on the driven and drive gears, will that give me the correct ratio?

 

[hwsiii]

Re: More speed please!

If you don?t know the ratio, you need to pull the plugs out and put a piece of tape across the prop and the lower unit and then cut it between the prop and the housing and turn the motor until the tape lines up with each other, it is easier if two people do this, so one can watch the prop while the other counts the revolutions of the motor.


H

 

[vegasphotoman]

Re: More speed please!

Interesting thread......I have the old 302 too (1978) but OMC stringer 800 drive...

Hi RacinRc, read your post on my thread......researched yours....any pics of that glastron of yours lurking on the threads?

yeah mine has the somewhat confusing 2 different firing orders, our motor has water in it too, but our boat had at the least, 2 to 3 foot of water in it for a long period of time (thats why everything wood was mulch and the eng had greasy water lines on it all up the sides of it)

I worked at a Ford dealership as a heavy line tech for over 10 years, never did I see a 302 with cracked heads or blocks...an Intake leak sounds viable to me (your engine) they are fairly bulletproof motors. and on a boat probably have alot less run time on em compared to car engines (for sure)
actually a v8 boat motor would be a great place to get a replacement engine for a car! if ya think about it, just switch the marine stuff out (water headers etc)
on mine I believe the oil got contaminated from being submerged in water....or sunk in a few feet of water.

does anyone know WHY there are 2 HP ratings for the same engine? or is one for the 351 and one for 302? (maybye the intake manifold is shared for the motors) so it is stamped with both firing orders...or like it was said reverse run motors for dual drives...