Prop size after engine mod.

[LarsVIP]

Hi,

I have a 1989 VIP 1850 BR with a 4.3L V6 2BBL running with a HighFive 19" prop.
Last summer at WOT with light load it hit 40MPH @ 4.500 RPM.

This winter I have upgraded the intake and carb. to 4BBL to get more power, this should take it from 175 to about 200HK.

I took it for a test run and with about 3/4 open trottle it hit 4.500 RPM and 40MPH, but with WOT the RPM dropped as if I had hit the RPM limiter.

Any advise for prop size and number of blades?

I'm thinking of a 21" with 4 blades...

 

[jestor68]

Re: Prop size after engine mod.

Shouldn't hit any limiter until past 5000 rpm, since the top rated rpm is around 4800.

Not sure what you mean by rpm dropped at full throttle? Dropped to what, from what?

Rev limiters don't cause rpm to "drop" per say; they simply cut the ignition off and on really fast so the motor can't go past a certain point. It sort of sits there and "stutters" at that set rpm(if it's working right).

Perhaps you're just over fueling after a certain throttle setting, and dumping more fuel into the motor than it can handle, causing it to "bog".

 

[Sea Rider]

Re: Prop size after engine mod.

Is that a factory recommended conversion, or it's your personal conversion ? If the latter, probably a incompatible upgrade ?

Happy Boating

 

[steelespike]

Re: Prop size after engine mod.

Unless the VIP is a real tub I think last years 4.3 should be pressing 50 mph.
I don't think the high 5 is the best choice for top end with your motor.It should deliver
amazing grip and hole shot but 5 blades is a lot of drag.
Imo you you should be turning 4800 with a 19" prop(not a high 5)
Perhaps even over revving. You may want to varify the tach is accurate and speed by gps.
Your numbers do seem reasonable but for the lack of rpm and speed.
Also you may have a motor issue. Check that the throttle is not opening too far.
Check the timing is set right and advancing as it should.
It's also possible the changes may require a different advance curve.
If your looking for top end a 3 blade is a better choice.You need to be sure
of the motor before any prop change.

 

[MikDee]

Re: Prop size after engine mod.

Hi,

I have a 1989 VIP 1850 BR with a 4.3L V6 2BBL running with a HighFive 19" prop.
Last summer at WOT with light load it hit 40MPH @ 4.500 RPM.

This winter I have upgraded the intake and carb. to 4BBL to get more power, this should take it from 175 to about 200HK.

I took it for a test run and with about 3/4 open trottle it hit 4.500 RPM and 40MPH, but with WOT the RPM dropped as if I had hit the RPM limiter.

Any advise for prop size and number of blades?

I'm thinking of a 21" with 4 blades...

Well, That was last summer, it's Spring now,,, IMO, apparently you did something wrong on the 4bbl install? Don't be lookin to reprop till ya get that fixed!

By the way, who advised the high five prop

 

[jestor68]

Re: Prop size after engine mod.

The High Five is recommended (by Mercury) for V-6 power stern drive runabouts where tow sorts are a priority.

I'm waiting for him to say what rpm it went to before it hit the wall.

And lets not forget that we're talking about a 25 year old motor that he's trying to hop up.

 

[MikDee]

Re: Prop size after engine mod.

Chances are the secondary butterfly lockout linkage is messed up, and not letting them open.

 

[not enuf toys]

Re: Prop size after engine mod.

This winter I have upgraded the intake and carb. to 4BBL to get more power, this should take it from 175 to about 200HK.

with no cruel intentions at all ~ 25 hp with intake and carb? most likely not.

I don't remember the ratio, but its something like 50 hp for a 1-2 mph increase

I run a high five 19 pitch and the hole shot is amazing. I did however loose 3-5 mph on the top end.

what are you ultimately looking for? good hole shot for pulling or top end? if top end you have the wrong prop on there. a 19 3 blade would suit you nicely

I carry two props with me - the 5 blade 19, and a 3 blade raptor 21

the 3 blade has great top end but the 5 blade is much more fun!

 

[Lager]

Re: Prop size after engine mod.

I would be wondering why my engine lost power after 3/4 throttle ?

 

[jimmbo]

Re: Prop size after engine mod.

with no cruel intentions at all ~ 25 hp with intake and carb? most likely not.

I don't remember the ratio, but its something like 50 hp for a 1-2 mph increase

QUOTE]

It's 5hp per 1 mph difference. As for the 25hp increase, not likely. A 4.3 is pretty small for a 4 bbl to be of much use, Unless it is a small(less than 400CFM) 4bbl.

 

[LarsVIP]

Re: Prop size after engine mod.

Thanks for all the replies, I don't know where to begin, but perhaps I should start with getting the engine running with more than 4.500 RPM...

What I'm looking for, is to be able to fit a prop with higher pitch to get a higher crusing speed, instead of sailing close to WOT all the time.
The High Five was on the boat when I bought it and it gives an amazing hole shot even with the boat fully loaded, but as I now can understand it comes with the cost of top speed.

Now as I could find out, the engine comes in two versions one with a 2BBL carb with 175HK and one with 4BBL carb with 195HK as I recall, so instead of replacing the engine, I thought this upgrade should give a good boost in power, if it's 20-25HK I don't know, but I hope ;-)

Regarding the upgrade, I used these parts from Michigan Motorz:
4.3L - 4 bbl. V6 Edelbrock Performer 90? Intake Manifold
Edelbrock 1409 Marine Carburetor (600 CFM)
Edelbrock 1409 Carburetor Calibration Kit - 4.3L V6
4.3L Delco Voyager EST Marine Electronic Distributor Kit


When the engine hits 4.500 RPM then it "stumbles" and drops 1-200 RPM when giving more throttle and I can feel the boat slowing down, so the wall is at about 4.500RPM.
I have set the timing with a timing light as a 4BBL stock engine.

 

[steelespike]

Re: Prop size after engine mod.

It seems you should solve your 4500 rpm problem.
I think its safe to say your modifications haven't caused a problem.
You need to check the rev limiter. When both setups experience the same 4500 rpm cut off it would seem it is the rev limiter cutting in.
Other possibilities something in the exhaust creating a restriction as the rpm approaches 4500.A loose internal part or maybe a rubber elbow or connector collapsing.Many years ago we had a car that shut down at the same rpm every time. Running but apparently
strangled.Found a loose plate in the muffler that completely blocked the outlet at the same rpm.
Have you checked that the timing advances as it should?Has the timing been set using the proper procedure?
As far as your cruising speed it seems to me that the high five would make a low rpm cruising speed
very easy to maintain with little fuss.
Increasing pitch makes the motor work harder hole shot takes longer it will fade more as you add weight. Increasing pitch may lower rpm but will strain the motor more and may require more throttle for a given rpm. As you increase pitch it makes it harder to maintain an even cruisiing speed.
If we knew your actual wot rpm it would be easier to say try a 21" 3 bld. ss prop.
Assuming a 1.61 ratio I think a 19" 3 blade should run close to 50 at 4800 rpm.
A 21 may be a little sluggish compared to the high 5 but could run over 50 if the boat isn't a
slug. If a 1.84 ratio it would be slower.