Records are meant to be broken - Fastest Allison XB 21 Ever!

[Tim Powell]

Can you get lower ratio gears for those new LU's ?

Yes, depending on model:

250R - 1.75 only
300R - 1.60 or 1.75
450R - 1.60 only

The 1.6 works great in the 450, however it does not work well in the 300R. By the time you pitch down to get the RPM up you end up not having enough wheel to run the same speed as 1.75 with a big wheel. It pulls the engine out of the power band and turns it into a turtle. Overall performance is better with the 1.75 on the 300R. There is a 500-600 rpm difference between 1.6 and 1.75.

[Hammmerhead]

Yes, depending on model:

250R - 1.75 only
300R - 1.60 or 1.75
450R - 1.60 only

The 1.6 works great in the 450, however it does not work well in the 300R. By the time you pitch down to get the RPM up you end up not having enough wheel to run the same speed as 1.75 with a big wheel. It pulls the engine out of the power band and turns it into a turtle. Overall performance is better with the 1.75 on the 300R. There is a 500-600 rpm difference between 1.6 and 1.75.

Interesting. Im wondering now if my SHO with a 1.62 sporty might benefit going to a 1.75.

I assumed you would be on the limiter with the 450 and having to run something crazy like a 34.

[Tim Powell]

Interesting. Im wondering now if my SHO with a 1.62 sporty might benefit going to a 1.75.

I assumed you would be on the limiter with the 450 and having to run something crazy like a 34.

Not sure where I will land, Basically from 300 HP 31 to 500 HP 33 you drop 700 RPM on paper, the 500 HP wheels are stiff! I could turn a 300 HP 34 a little easier than this 33. At some point I expect to hit a wall with the load I am carrying.

[MET]

Thanks Tim, I didn’t already feel inept enough at driving my boat!

Appreciate the reality slap!

That’s awesome piloting!!!

MET

[Hammmerhead]

Not sure where I will land, Basically from 300 HP 31 to 500 HP 33 you drop 700 RPM on paper, the 500 HP wheels are stiff! I could turn a 300 HP 34 a little easier than this 33. At some point I expect to hit a wall with the load I am carrying.

In my younger days I ran a 1.24 gear in an Imco drive and ran a 30 and a 32. Didnt know what taller gear you could pack in a modern sporty.

[Tim Powell]

Thanks Tim, I didn’t already feel inept enough at driving my boat!

Appreciate the reality slap!

That’s awesome piloting!!!

MET

Our last ride down Guntersville still has me rolling LoL

[Tim Powell]

In my younger days I ran a 1.24 gear in an Imco drive and ran a 30 and a 32. Didnt know what taller gear you could pack in a modern sporty.

nice! The V8 sporty will hold a 1.60 or 1.75 and the 3.0L will do 1.62 and 1.75 at least OEM from Mercury.

Wayne had a 1.60 option for the Yamaha case but I believe he went back to 1.62 due to some manufacturing issues?

1.6 is a lot of gear for the fourstroke and IMo/testing only the 450R can spin it properly.

[MrMobley]

nice! The V8 sporty will hold a 1.60 or 1.75 and the 3.0L will do 1.62 and 1.75 at least OEM from Mercury.

Wayne had a 1.60 option for the Yamaha case but I believe he went back to 1.62 due to some manufacturing issues?

1.6 is a lot of gear for the fourstroke and IMo/testing only the 450R can spin it properly.

Tim, I've seen you saying this a few different places. You've done the testing, so I whole heartedly believe you. Maybe I'm thinking of it too simply, but I've been under the impression the torquier 4 strokes would handle the 1.6x gears as well or better than the 2 strokes. Does the torque curve just fall off at higher rpms? I'm glad I've seen you speaking about it as much as you have, we're going to put a sho on one of the Strokers soon and we were bound and convinced the 1.62 gear was damn near necessary for us to get it running how we want when its all buttoned up. I'm not sure what gear Ricky is running, but it seems like him and Chris have had good results with that current setup.

[Tim Powell]

Tim, I've seen you saying this a few different places. You've done the testing, so I whole heartedly believe you. Maybe I'm thinking of it too simply, but I've been under the impression the torquier 4 strokes would handle the 1.6x gears as well or better than the 2 strokes. Does the torque curve just fall off at higher rpms? I'm glad I've seen you speaking about it as much as you have, we're going to put a sho on one of the Strokers soon and we were bound and convinced the 1.62 gear was damn near necessary for us to get it running how we want when its all buttoned up. I'm not sure what gear Ricky is running, but it seems like him and Chris have had good results with that current setup.

I can only speak for the 250/300/450R as I have ran all 3 of them with 1.60 and 1.75 gears on the Allison XB-21. In our testing we find that by the time you pitch the 250/300R down to get the RPM back up, you dont have enough prop to get the speed back up to where the 1.75 will run with a bigger pitch. Now the 450 is a totally different animal and while it makes 1.75 a blast to drive, it really needs 1.60 gears. I was beating the doors off the limiter with a 34

The only Stroker we have got to play with was a new tall pad boat and it left here running 105 @ 6400 with a 34 CNC and a ghost on the nose. It was running 3+" above the pad. A good short pad boat like what Chris was recently testing could benefit from 1.60 gear because he was on the limiter at 109 with the same 34 CNC. I would like to get my hands on a good short pad and throw a 300R on it. I would take CB's recommendations, I believe RR has 1.62 gears.

[tritontr21]

I will pull them at some point, just need to max out what I currently have before I start making changes so I can document it. Some claim they have seen as much as 2 mph, I know when my 300xs was stuck at 99.8 about 6-7 years ago now pulling the windshields made no difference for me.

I suspect at some point I will also pull some of the tackle out.

I like to run record passes loaded too. Although you might carry an extra package or two of plastics and a extra battery too.

[Bigmagnum]

what modifications did you make to the sportmaster gear case?

[Tim Powell]

what modifications did you make to the sportmaster gear case?

None.