OB tunnel engine question

[marktrish]

I'm looking to get back into 21 OB racing. Wondering who makes a good reliable OB engine. I see that K@B is still around along with OS. Also seen the Thunder Tiger Pro 21M. Rossi? Mac? Don't want to break the bank...not yet anyway. Also interested in a pipe as well. Thanks for your help guys. Mark

 

[Jerry Dunlap]

If you're looking to get back into mod 3.5 tunnel racing, the CMB RS OB with either a Silver Bullit or Cooper pipe is a really stong engine. However, it is pricy. For stock racing, the O.S. 21 is a very good choice.

JD

 

[piper_chuck]

Adding to what Jerry already said, if you're starting out, consider staying stock. You can get pretty good speeds with a stock OS engine and it's WAY easier to get the engine running reliably. Once you learn about tunnel setup, driving, etc, you can either add a pipe, or do what many do and buy a second boat and engine!

 

[topfuel443]

I agree with Piperchuck, its hard to beat a stock OS, reliability and speed are there...

~James

 

[Tim_Duggan]

Ditto!

Stock OS with an ABC 40x53 or a modified Octura 1440 rocks! Especially on a Lynx!

Tim.

 

[marktrish]

What would be a good pipe for the OS? And I assume that if a pipe is added you would run in the modified class.

 

[Jerry Wyss]

What would be a good pipe for the OS? And I assume that if a pipe is added you would run in the modified class.

Oddly enough, the O.S.XM is one engine that can run really strong in the stock configuration.

Takes a special cut 1440 or the ABC 40X53 prop like TimD mentioned, with at least 50% nitro

and pull it's head shim out. As Tim said, it helps to have the Lynx boat to get the full potential

from the stock config. A pipe is not essential to get power outa this motor.

Greg Roth, "topfuel443"and many others have used pipes on the XM with good success as I

think many of them have already stated throughout this site on how they did it.

Mr Redundant

 

[topfuel443]

yes to what Jerry said...

I have run an OS with a number of different pipes. The XM in stock configuration and stock muffler, compared to an equally stock OS with a tuned pipe on it (I dont care which one, ive tried em all and even made a few) is not much difference between the two. Sure, you can make a piped OS run a little better than a non piped OS, but not enough to warrant the 80+ bucks youll spend on a pipe and header with just that modifcation. Eric Betty has officially run 59.226 MPH with a stock configuration OS motor, and If I remember right he had a one way pass of around 61MPH. (if anyone has never seen a genuine {GENUINE} 59+ MPH .21 tunnel run (there are not many!)... that is HAULING ASS... what makes it even cooler is that it was with a sport boat, way to go Eric!)

Spend your time and effort in your boat set-up and finding/tweaking the right prop and you already have the motor package needed to go fast.

They are great right outta the box, just pull the headshim, get some good 60% nitro with good oil and enjoy!

~James

 

[piper_chuck]

Another great thing about not putting a pipe on the engine is you can race in two classes with one boat/engine. Once one goes down the pipe path, the boat can't run in sport tunnel any more. When one factors in spinouts, blow overs, collisions, dead engines, etc, it's remarkable how well a stock engine can do against the piped ones.

 

[marktrish]

Thanks guys for all the help. Mark