Exhaust throttle & Venturi ?

[Don Templeton]

I ran this set up on Ackerman OPS 67s thru the 70s and early 80s with Crapshooters and really had good success, "other than my driving". :blink:

I'd just like to hear some thoughts on this set up with todays engines from you "so called newbies".

Thanks,

Don

 

[Don Ferrette]

Well let's see, I'll do it like this-

Likes-

Instantaneous throttle response.

Dislikes-

Very tough to mill slow for extended periods without loading up & quitting.

Much shorter coupler life due to higher heat.

Makes one hell of a mess inside your boat blowing excess fuel out the venturi at anything less than wide open.

Advancements in todays engines have, in my opinion, made exhaust throttles sort of obsolete.

 

[AndyBrown]

With the correct venturi design they really can mill very well. Most of these systems used a small bore venturi to achieve this. Only draw back here was limited horse power.

To me the worst problem was the mess they made in the Boat.

There is the possibilty these days to build better sealing units and the ability to use larger bore venturis. I've done this with very good results.

I have spent enough time on this subject to have actually had thoughs of building MACs with the exhuast throttle unit built right into the Crankcase.

Could be in the Future.

 

[Spraguepsycho1]

Andy,

have you tried making an engine with a variable exhaust valve like the dirt bike 2 strokes use, with a normal carb? the variable port timing might work pretty good for flattening out the powerband. I don't know if it would be practical on a glow engine, but on bigger 2 strokes they really work.

 

[Don Templeton]

That sounds about right Don. I was running what we called a sprint boat (60 in a 40 hull). With the turn fin technoligy at that time, the boat had to be settled a little before you threw it into the turn and hit the throttle. The instant response was amazing. Also, I always liked to launch at the last possible moment. Hated milling!

Thank's for the input,

Don

 

[Don Ferrette]

Now I will say this, they were excellent on my o/b tunnels when I ran them & there was no mess 'cause the motor hung off the back of the boat. The bad thing back then was the exhaust throttles for the outboards was cheap & rather cheesy. Hey Andy- food for thought on your MAC 21 o/b powerheads & the MAC 45 powerhead if you go thru with building them.....

 

[Don Templeton]

Just testing to see if I can get a photo to come up.

"WOW, it worked"

 

[AndyBrown]

WOW....... does that bring back Memories! ....Old Crapshooter, OPS, Exhaust Throttle.

My fisrt rigger had an Exhaust Throttle. Was back in the mid 70's.

Andy

 

[[email protected]]

[SIZE=14pt]Man, I don't miss cleaning up the mess from those things. They had some great power but a drag if you had to sloooow down quickly. Stall city. On the O/B they were good but man could it empty out a fuel tank quickly, not to mention the ruined paint jobs on any boat in the surrounding area. LOL [/SIZE]

 

That's a wild header on that engine.

 

 

 

[TimD]

A well designed venturi will outperform a carb, but a carb is a lot more forgiving for throttle settings other than Wide open. I'm considering going to 1 if I can find one - Don Gardner doesn't make 'em anymore.

 

[Scott Schneider]

:blink: Yuck I have been slimed !! WOW that brings back memories of the yuck yuck of model boating, I am not talking laughter either. But they sure did work well when you had a tight barrel on the Ex throttle and had venturi and tank height set just right.

Those L.A.W. ones and the C.B. ones were super and when O ringed made no mess !!

If I had my choice of a carb or EX throttle I would take the latter if the seal on barrel could be maintained and the mess was not there, A super system with super throttle response but mostly a major P.I.T.A. because of the mess and set up hassles. Scott

 

[Al Waters]

For years I had always run throttle exhausts on my Piccos in my Scale boats ( I have never owned an EXR). When I first started running the K motors in my Scale, I was having a hard time adjusting to the change of running a no low end carb. I have since learned how to run box stock K motors successfully.

While trying to find the right prop and pipe combination with the K motor I did test with the throttle exhaust. I really liked the way it ran. The throttle response was instant. I used a Rum Racing Products header adapter which is the same as what comes with all carbed motors today except that it will accept the throttle exhaust. I wired open the barrel on the carb on the motor. Any mess I had, if any, was created by the barrel on the throttle exhaust.

I liked the setup up because it was something that I was used to.

Al Waters

Southern California Scale Thunderboat Association

NAMBA Scale Unlimited Chairman

 

[MarkScott]

I've got three Gardner XXL units for my K&B OB's.. Well, really I have two, one is currently on "loan" status to a certain Jockey we all know.. It's been years, but I believe the fastest this motor ran was when I didn't use a venturi at all. The needle was set in place where the carb set screws were...

Mark..