Safe RPM range?

[dnyhuf]

Re: Safe RPM range?

Sooo... those with bass boat hulls and a 200gt will get best results all around(great hole shot and max speed), propping for the rev limiter? Can most that are propped at say 5500 see increased performance if they prop for the limiter?

 

[Texasmark]

Re: Safe RPM range?

An example of what D said I experienced in a used boat. I bought the boat and it was way, way, under propped. The WOT rpm's were way above what I wanted to run on a day to day basis. My boat has a pad.

So I went to the prop calculator and figured I needed a prop with 4" more pitch to get my rpms down to where I wanted. Well, as D said, more pitch put more work against the transom.....and for the speed, the torque curve on the engine was probably shot with the orig prop.

My 4" increase in pitch caused a disproportional speed increase brought on by just what he said.....the boat went fast enough to be farther up on the pad which significantly reduced drag....so going faster meant more rpm's (cause the load on the engine had actually decreased) and I was still way too high in rpm's. I went up 3 more inches with a 3rd prop and finally got my rpm's down to where I wanted them.....course the boat was hauling arse by this time.

HTH

Mark

 

[dnyhuf]

Re: Safe RPM range?

Well I will rephrase then. With the info provided by the obviously talented and respected Dhadley, could one say that the majority of performance hulled bass boat's with a 200GT that's propped to 5500, see a performance gain in hole shot, and lose little, if any, top end if propped for the limiter? This is assuming no other setup changes such as jackplate, etc.

 

[Texasmark]

Re: Safe RPM range?

On the hole shot, if you want to change that without affecting anything else, port your prop. It lets the prop ventilate when the water pressure against the exhaust is high (dead in the water). The exhaust gas over the blades allows them to slip which lets your engine develop it's rpm's (hence hp) rapidly and holes are much improved. Once underway, the water pressure moves from behind to along the sides of the prop which seals the holes off and you don't know they're there.

Works really great for water skiing.

Mark

 

[dnyhuf]

Re: Safe RPM range?

Thank you for the info TexasMark. The Raker props mentioned earlier are ported. I thought that with the info provided by Dhadley concerning the 200GT and WOT RPM'S, it may give those that have that motor more options when propping. In my case the drop from a 22p to 20p made quite an improvement to hole shot without losing any top end. With no Jackplate or other means for help in setup at this time, being able to prop toward 6700 gave me the oppurtunity to improve one variable(hole shot) w/out effecting another(top end). Just thought that others in the same boat(pun intended), may be able to take advantage of another tool. Thanks for all the great input from all that have responded. Yes, I know I'm rambling ( perhaps one of the first signs of growing old).

 

[LubeDude]

Re: Safe RPM range?

1996 Stratos 295, 19 1/2', 200 carbed Johnson Limited Edition. Some say that this engine is actually a 225.

I,ve had this boat for only this last season and have done so much screwing with it, (Jack plate hight, Props, tuning etc),That I think that I'm totally confused right know.

At this moment in time I have a 13 3/4" X 25P Renegade 4 Blade and am running 68 GPS @ 6,100 and 2 3/4" below the pad. I have been tuning for the 6,000 RPM mark cause I guess I'm just plane Sceeeerrred! Next prop to try next spring is a 13 3/4" X 25P 4 blade Trophy. I love the High Five props also and am looking for one in 25P to try. You loose a bit of top end, but they are the most awesome prop as far as holeshot and handling that there is on a Bass Boat! You can pull trees around in the lake and reposition stumps with them! IMHO. Right now I'm prop poor with five SS props.

Just make sure if you are running at or near the 6,000 RPM band to rejet #2 Cylinder 2 steps richer.

 

[Texasmark]

Re: Safe RPM range?

Interesting dny. I have 2 props I run on my boat: 24P XP at 5600 and 50; 21P (same brand) at 6400 and 48 on a 3 cyl Merc. I too experience a much better low end and slower speed operation (controllable boat position) with the 21 yet doesn't cost me much top end.

Mark

 

[dnyhuf]

Re: Safe RPM range?

Just make sure if you are running at or near the 6,000 RPM band to rejet #2 Cylinder 2 steps richer.

First I've heard of this. What is the reasoning?

 

[dnyhuf]

Re: Safe RPM range?

So....why rejet 2 steps richer on #2 cylinder if propping for 6000? Recommended RPM range is 5000-6000.

 

[steelespike]

Re: Safe RPM range?

I have the books in the shop, I'm in the house. I remembered that stroke at like 2.5 and the 3 came out with the 307 or 309 (forget which is Ford and which is Chevy) when emission controls kicked in......but it may have been 3 and 3.5.

Anyway it was short and fast. Had a friend with a '58 4 door Bel Air 283, 2 BBL with a 2 speed Powerglide........Mom's car. Another friend had the, just out, '59 Biscayne 348 with 3 deuces and a 3 speed stick. The latter was from California and had the typical attitude.

The Bel Air smoked him big time. The ribbing went on for weeks. Grin

Mark

The 348 was based on a truck engine and I don't think it was a great factory performer.But am surprised it couldn't whip a 283 power glide.
I had a friend with the 409 4 spd version in a 62 Impala hd top.
Speaking of short strokes he ran against a Falcon with a built up 260 V8
3 spd. (claimed 10,000 rpm.)Killed the 409 off the line but caught him at about 100.
Speaking of small 60s V8s I think Buick holds the record for small.
I think it was a 212 aluminum V8. And I believe it is still in service in English Rover autos.Ford had a 229,and Studebaker a 221.Which I think someone
set a speed record with an all Studebaker car some years agops I'm raving about the "good old days"!!