Gear ratio help needed?

[DaveW]

Hi there
Here's my dilema, I've got an XTB-21 running a 200Xri Merc. I'm turning a 22" Lightning ET to 7100rpm and getting around 74mph or so out of her. I have a CLE case with a fat shaft.
I don't know what gear ratio is in the the box, but I have just blown it up and looks like I'll be needing a new gearcase.
I've picked through all the XTB owners details on the Ally owners site, and feel I was missing out on speed.
The numbers on there vary from low of 72mph with a 22" Tempest on a TM case (200 Mariner @5850) to a high of 86 on a 200 ProMax with a TM case spinning 6750rpm. There are also quite a few over 80 running either CLE's, coned boxes or SM's.

My questions are: What do you think the ratio was in the box I blew, and what should it ideally be. Keep in mind I'll need some prop recommendations too.

Of all the props being run on other XTB's and 200hp motors there is only one 22" (the Tempest). The majority are 26" Trophys, 27" Tempest, a 26" Chopper, a 28" Chopper 2, and a 27RX.

Can you understand my confusion?

Thanks in advance from Australia!

 

[Mr. Scary]

Most likely, your gear ratio was 1.87:1 as that was a standard gear ratio in an 200 XRi. Did you have a low-water pickup nosecone on it? If not, there might have been some speed opportunity there because you would have been able to raise the motor up quite a bit and still get water pressure.

 

[DaveW]

Thanks for that!

I had a CLE on it with low water pickups, added separately only in the last couple of years.

I also forgot to mention I have a hydraulic jack plate and can raise her up as high as water pressure allows, hence my speed question.

 

[Jimxb02]

If you do the math on what you have ---- (rpm/1.86 X 22" / 1056 X 92% =) you get about 74 MPH. So you probably had a 1.86 gear case.

If that was a stock 200EFI you were beyond the peak power point at 7100 RPM.

I would get another low water pickup case with 1.86 gears and go with a 24 or 25 pitch prop. You should then see 80+ mph speeds.

Jim

 

[RedAllison]

Forgive me if you've answered these questions elsewhere:

Do you still have the stock metal reeds and is your oil injection connected? If so you're on borrowed time with either @ 7100!

I think you're just burning more gas than you should by propping so low. Like Jim said, the port timing and power curve on that motor is MUCH lower than 7100. I'd prop it for mid 6s and for a fishing prop I'd say you'd probably be happiest with something like a 25" Trophy or Quad IV OT style. You'll be giving up a lil holeshot by no longer having a 22"er (I bet your boat RIPS out of the hole now as it is!) but I think you'll be happier in the long run.

I too agree, you should find yourself in the 80+ range once dialed in.
RA

ps
Oh yeah, I agree with Sam... 1.87s for sure!

 

[john4utvols]

I would get the 1.75 gears, you will be suprised.

 

[froggy]

Dave,

Stick with the 1:87 gears and the CLE case. I ran my XTB with a 28 pitch prop (it was powered by a carbureted, 2.4 liter, Merc) to 6800 RPM time after time.

As was stated earlier, you are burning too much gas with the low pitched props. Also, you are jeopardizing the integrity of your oil pump at the high RPMS.

Get a new Merc Chopper II in 26P and pick and grin!

froggy

 

[DaveW]

Sorry, should have mentioned some other things:
Oil injection was one of the first things removed - I'd read the stories

I also had reed issues (lost the tips off quite a few with luckily minor damage only to the top of one piston) and she now has carbon fiber ones in it. This confused me a bit too as they are supposedly high performance and I lost at least 2mph with them in???

Currently my hole shot is sorta good - it gets bow high very fast and comes down like a rocket, there's a pic below of her just before planing (plus I love this shot!)

I do tend to run fairly heavy (full fishing load) but still think there's more in it.

Froggy, what sort of speeds where you hitting with those numbers?

And John why 1.75 over 1.87?

Thanks heaps for the advice all, since I've got the only Ally Bass Boat in Australia I don't have too many knowledgeable people down here to talk to about it

 

[froggy]

Dave,

I would hit 81 - 82 mph with two fishermen and a fishing load. Empty, the boat would run 85 - 86 mph. The hole shot, though not dragstrip quality, was good, even with the livewell full. Incidentally, I had one of the first CLE cases and put my stock 200 gears in it. Without the CLE, I would blow out at 78 MPH everytime. My RPM's were limited by the stock, diaphragm, fuel pump. You should do better.

Good luck with the Ally down under!

froggy

 

[DaveW]

So I'm theoretically missing a fair bit - especially when you consider I run in salt water and should be a little faster anyway.

The only other variable I can think of is my setback - I have a 3.5" plate, then the jackplate adds 5.5" giving 9" total, how does this compare with yours?

 

[john4utvols]

Dave, 9 to 10" setback is fine.
The reason I say 1.75 is one of my good friends boat is a xb2002 with a pro max 225 we were having trouble getting above 92mph, So we starting doing some work first thing we done was swapped from 1.87 to 1.75 this alone picked us up to 98 ( reason being we were able to get more rpms out of the same prop) plus its hard to believe the hole-shot was better. I could prove the hole-shot by racing the same boat with a 280 with the same pitch prop, we would beat him out of the hole every time. Now we moved the rpms up to7400 and let Jc mod the SM case and are now hitting 105. I can also justify a SM case with jc extended nose cone is faster on top end than a 200 modified. We broke the skeg off the SM during the winter, so we made a decision to go with the 200, this was a mistake with the same gears the boat lost 3 mph. This is my opinion. John

 

[froggy]

Dave,

Your setback should be fine. When I bought my XTB 21, in 1985, it came with a 6" hydraulic plate. I was having a terrible time getting to Darris' advertised (yes he used to advertise it) top speed so I called Darris. Darris recommended a 4" setback so I changed out the 6" hydraulic to a 4" manual (conveniently provided by Allison) and lo-and-behold lost 4 mph.
Rather than change back, I moved my batteries back as far as they'd go and got the 4 mph back.

In summary, your setback should be far superior to what I had and should help you carry "real world" fishing loads with ease.

Try a 26P Chopper II. Incidentally, you will need to get your engine up some to run this prop, but I think you'll like it.

froggy

 

[DaveW]

Thanks heaps - sounds good.

The other battle down here is prop availability just to try them, it's not like I've got a few mates who I can swap props with as I'm the only person I know with low water pickups and a hydro jackplate!

Prop cost is another beauty - A new Lightning ET or similar is in the $2300 range (roughly $2100US)!

I've got a great mechanic who races F1 Powerboats and he helps where he can but even to borrow a prop is hard.

Hopefully I'll find out about my gearcase today and then the experimentation can begin!

Thanks to everyone for their help and any other suggestions would be appreciated!

ALLY OWNERS ROCKS!

Dave