TT versus OS

[jelys]

I just wonder what makes the standard version of the TT inferior in performance to the OS? Looking at the specs in the adverts. Some says 1.6 hp and others 2.1 hp compared to OS 1.3 hp. I know one should not rely on advert but anyway. I am a newbie but my engineering background tells me you don't loose that much in a good gear system, and by having the opportunity to use a 1.19 gearing you could increase the efficiency and win the lost back by turning a bigger propeller at lower revs. (As you probably know, in Europa it is very popular to run geared engines in the 3.5 monohull class)

Are there any other differences between the engines apart from weight and wetted surface? How about timing and exhaust restriction?

I understand TT has made some changes to the engine over the years. Some of you probably knows the development history?

jelys

 

[Jerry Dunlap]

I just wonder what makes the standard version of the TT inferior in performance to the OS? Looking at the specs in the adverts. Some says 1.6 hp and others 2.1 hp compared to OS 1.3 hp. I know one should not rely on advert but anyway. I am a newbie but my engineering background tells me you don't loose that much in a good gear system, and by having the opportunity to use a 1.19 gearing you could increase the efficiency and win the lost back by turning a bigger propeller at lower revs. (As you probably know, in Europa it is very popular to run geared engines in the 3.5 monohull class)

Are there any other differences between the engines apart from weight and wetted surface? How about timing and exhaust restriction?

I understand TT has made some changes to the engine over the years. Some of you probably knows the development history?

jelys

I don't know any of the timing numbers, intake or exhaust for either the O.S. or TT. I have run both engines. The O.S. is much the faster engine. With extensive mods, some folks have made TTs run well. I will say the TT is a beautifully crafted engine. I runs well. But, "well" doesn't cut it in a racing situation.

JD

 

[Dyno]

The TT is an excellent setup if you run in a windy condition. The boat gets help getting on top of the water which in turn, allows the engine to rpm and the boat will perform.

Had the boat dialed in and showed up race day. Only thing changed, flat water (no chop or wind)and the boat was not able to perform as setup.

 

[camaroboy383]

jelys,,,,,hands down stock for stock the o.s will out perform the tt...the tt's are awfully heavy which is another thing that makes them slightly slower... a properly modded tt is nothing to sneeze at,,, they really do fly with proper setup and a decent hull.... the 1.04:1 ratio is what im familiar with and the only prop you will ever need on that gear set up is a octura x637 or a x640 reduced to 38mm or just under... no other prop will give you the results those two props will..

by the way the engine you asked about on (ebay) has the 1.04:1 gear ratio... B)

alden

 

[Tim_Duggan]

...my engineering background tells me you don't loose that much in a good gear system, and by having the opportunity to use a 1.19 gearing you could increase the efficiency and win the lost back by turning a bigger propeller at lower revs. (As you probably know, in Europa it is very popular to run geared engines in the 3.5 monohull class)

Are there any other differences between the engines apart from weight and wetted surface? How about timing and exhaust restriction?

I understand TT has made some changes to the engine over the years. Some of you probably knows the development history?

jelys

A modded TT with the gear reduction set and a short pipe is a beast. Problem is keeping a flex cable in it. Gear reduction = torque multiplication. It also causes some wierd handling effects on a tunnel.

 

[lohring]

The big advantage of the Thunder Tiger lower unit is the number of engines you can run on it. All the RC car and 3.5 marine engines have the proper rotation. Jerry Wyss in our area has run everything from inboard marine 3.5 engines to a 30 monster truck engine.

Lohring Miller

 

[Jerry Wyss]

I assume your talking about running outboards on monos, yeah?

Actually the XM and TT sleeve timing numbers are about the same,, and the TT timing

numbers haven't changed one bit over all those years of production, quite sad.

O.S. hasn't changed theirs either over a shorter time of production but can be set-up

to run much better than the TT in stock form,, on a tunnel!

The power margine on these two engines is rather small to have an O/B prop burried all the time behind a mono. I suppose it can be done, I just haven't seen it myself,, anything impressive that is.

My complaints with the TT are, "soft pistons", a crummy situation no matter what you do.

The "case bore" where the "crank induction port" opperates has "iffy" tolerance

most of the time. The only things that you can do are, "weed thru a supply of cases",

or run more castor in your fuel.

Some cases are so far out that they will never run right, just had that problem recently.

I have used the TT PRO-21BX-R(#9475)Long Stroke Buggy Engine adapted to the O/B lower but

those were all modified engines. These motors are the newer "EVO" models,, much harder

piston and a significantly better sleeve. The crank boring is much better too.

Trouble is, I doubt that very many TT engines will be available for very long. All I use

of the O/B mostly is the lower,PTO,the assembly that makes them steer and tilt adjust for

some of my Frankenstein motors.

 

[jelys]

I assume your talking about running outboards on monos, yeah?

Actually the XM and TT sleeve timing numbers are about the same,, and the TT timing

numbers haven't changed one bit over all those years of production, quite sad.

O.S. hasn't changed theirs either over a shorter time of production but can be set-up

to run much better than the TT in stock form,, on a tunnel!

The power margine on these two engines is rather small to have an O/B prop burried all the time behind a mono. I suppose it can be done, I just haven't seen it myself,, anything impressive that is.

My complaints with the TT are, "soft pistons", a crummy situation no matter what you do.

The "case bore" where the "crank induction port" opperates has "iffy" tolerance

most of the time. The only things that you can do are, "weed thru a supply of cases",

or run more castor in your fuel.

Some cases are so far out that they will never run right, just had that problem recently.

I have used the TT PRO-21BX-R(#9475)Long Stroke Buggy Engine adapted to the O/B lower but

those were all modified engines. These motors are the newer "EVO" models,, much harder

piston and a significantly better sleeve. The crank boring is much better too.

Trouble is, I doubt that very many TT engines will be available for very long. All I use

of the O/B mostly is the lower,PTO,the assembly that makes them steer and tilt adjust for

some of my Frankenstein motors.

Thanks for all the good info guys.

And Jerry, we are still talking about running outboards on tunnels.

I don't think they are any good on a mono, because of the high CG.

Just on the topic of gearing, I liked to mention the almost standard in Europe with 3.5 inboards on a gearbox in the mono class.

The boats are bigger though to cope with the increase in torque.

Tim mentioned problems with the flex cable running the 1.19 gear set. Do you experience the same

with your long stroke engines?

And are there any good aftermarket flex cables for the TT?

jelys

 

[Tim_Duggan]

My TT had the EVO motor on it like Jerry, and was very modified. Raised timing, different head button, skirted and lightened piston etc and I ran an aggressive pipe with short pipe length. It was on a HTB290 hull. I would break cables regularly. With the 1.04:1 gears too. In some cases in under 45 seconds, and in others I'd get 3 x 12 oz tanks to a shaft. Too unreliable and inconsistent to race with.

I did get some cables made by Kris Flynn, but sold the motor to Camaroboy before I got a chance to test them. He should be able to give some feedback on them hopefully.

If you want a motor that you can develop, don't get frustrated easily and love a challenge, then the tt fits the bill. If you want reliable, fast and easy, the OS is the way to go.

 

[Jerry Wyss]

I assume your talking about running outboards on monos, yeah?

Actually the XM and TT sleeve timing numbers are about the same,, and the TT timing

numbers haven't changed one bit over all those years of production, quite sad.

O.S. hasn't changed theirs either over a shorter time of production but can be set-up

to run much better than the TT in stock form,, on a tunnel!

The power margine on these two engines is rather small to have an O/B prop burried all the time behind a mono. I suppose it can be done, I just haven't seen it myself,, anything impressive that is.

My complaints with the TT are, "soft pistons", a crummy situation no matter what you do.

The "case bore" where the "crank induction port" opperates has "iffy" tolerance

most of the time. The only things that you can do are, "weed thru a supply of cases",

or run more castor in your fuel.

Some cases are so far out that they will never run right, just had that problem recently.

I have used the TT PRO-21BX-R(#9475)Long Stroke Buggy Engine adapted to the O/B lower but

those were all modified engines. These motors are the newer "EVO" models,, much harder

piston and a significantly better sleeve. The crank boring is much better too.

Trouble is, I doubt that very many TT engines will be available for very long. All I use

of the O/B mostly is the lower,PTO,the assembly that makes them steer and tilt adjust for

some of my Frankenstein motors.

Thanks for all the good info guys.

And Jerry, we are still talking about running outboards on tunnels.

I don't think they are any good on a mono, because of the high CG.

Just on the topic of gearing, I liked to mention the almost standard in Europe with 3.5 inboards on a gearbox in the mono class.

The boats are bigger though to cope with the increase in torque.

Tim mentioned problems with the flex cable running the 1.19 gear set. Do you experience the same

with your long stroke engines?

And are there any good aftermarket flex cables for the TT?

jelys

I had problems with a prop 38mm and up,, I generally run a Octura X640 cut down to the

37.5mm area without much problem. I run a O.S.21VZ-M adapted to the TT O/B PTO and lower

usually for racing. I keep 3 flex shafts in rotation so I can keep an eye on them for bulging next to the square end.

My TT 21BX-R's didn't have any more of a problem with breaking shafts and I run the same prop as above. It may be the boat difference between Tim and I,, I run the Lynx alot more than the HTB. Me thinks the Lynx may just run a little "dryer" than the HTB, it appears

that way to me.

I do have a flexshaft problem with the O.S.30VG(P)-X on the TT lower. The only shaft that

would hold up was one that Thunder Tiger supplied with their O/B's a few years back. The

shaft had a "single gold colored wire" wound with the rest of the darker wires. The windings were wound much tighter, giving a much stiffer flexshaft.

Granted, the latest TT flexshaft's are not very good and they will bulge, fairly often,,

matter of "days" for me than minutes.

 

[camaroboy383]

well,, the bxr engine i got from you tim rips,,, i have yet to break a shaft with that engine... i for sure keep an eye on it,, but no breakage yet... i had plenty of the tt shafts break and bulge like jerry said... switched to lawless shafts and never had an issue since... i have yet to try the shaft made by kris,, it really kind of scared me how tight the square went in the pto and prop shaft... if it were to break flush you would be beat for sure,,i highly doubt you would get it out... i do how ever snap every prop drive dog shear pins like its my job,, ive tried every paper clip known to man,, none ever make it past the 2nd tank of fuel..i pin them now with a hardened drill bit,, red loctite and press it in,, snap the bit off and file the sharp edge.. this has served me well on all my tt's all season... also a common thing people do on the tt is over tighten the prop and bend the shear pins,, creates a enormous amount of load on the shaft cause the dog is mushed into the nylon washer... mine is mounted on the htb 290 and really fly's.. the x637 pretty much garantees the appropriate load so reduces the chance of shaft breakage... beyond what jerry mentioned is pushing the stock shafts to the edge..

alden

 

[camaroboy383]

oh ya also to add to what i said about kris's shaft for the tt,,, i did bring this to his attention.. i have yet to send him a prop shaft so he could aquire a perfect fit... its as simple as squishin up the square a touch.. i was not at all implying the shafts are no good,,, as they look excellent and the length is spot on... keep up the good work kris..

alden