Lleksam

Hi all
I have a RCMK Special tournament rear exhaust, But when I install in my DaVette sprint the exhaust hangs so far over back it looks stupid, what do I need to change-do to change to side exhaust?
I have a Zen 260 pum that im building boat with at moment, perhaps I can put the Special tournament head on that??
Thanks Guys

Steve Seebold 100

Build a rigger for your RCMK. I have a rear exhaust Quickdraw High Rev 25 that's going in one of Marc Grim's riggers.

HendricX

Buy a short and silent exhaust for rear-exhaust at http://wd200-modellbau.de.

Not on his website , ask Werner for picture and measurements.

It's the tiny/short one he showed me this weekend at the Eersel-meeting.

Another option is the short exhaust (345mm) from Frank Langwald > http://edelstahl-reso.de.tl/

Lleksam

Thanks HendricX, will look into that, engine is supposed to be something special, relocated flywheel I bought it sometime back from a guy who used to sell - modify them in UK its supposed to be a "works" engine, I have never even started it yet,


Steve, will also look into a hydro maybe

Thanks guys

Steve

The Ghost

I made my own headers up out of deep V headers to fit my jet boats.

Cheers

Lleksam

Nice a pair of Swash hulls with Jettec jets, I bet Adam loves you,;-) and good your headers are too

but both of your engines are side exhaust, take exhaust out of rear of engine and on a DaVette thats 2" shorter than a swash, put 8" of header and 17" of pipe, remember CoG on Davette is some where near 10" from transom to spark plug you will see what i mean, having pipe hang 18" over back of boat is Ugly to say least, but with exhaust coming out of side I can 80 deg forward and 180 deg back over top of outlet, same as on Zen thats in Davette now

Steve

danielplace

No doubt you have to wrap some header around to make it short enough to look right. Your system looks great.
Sometimes the header gets longer than you can tune the pipe with. It is probably good though for the pump with the low end power instead of peak RPM.
These K30's really deliver some serious power. A Quickdraw Deep Vee pipe welded to suit your application would be a nice exhaust that would be tuned well to suit the K30.

Are the pumps dependable with the K30 engines? I think a jet pump would be some fun. What kind of speeds do these do? Neat boats.

The Ghost

Have you looked at any outboard pipe setups, you may be able to modify one to suite.

Cheers

Lleksam

Hi Thanks
Daniel, I have no idea about the K30 engine at all, This one is a R254 Special, but speed wise there not as quick as some propped boats but they dont need so much room to turn and acceleration is blistering

Ghost, No I hadn't thought of that way out, my idea was just to turn head a quarter to make side exhaust same as the one on Zenoah


Steve

The Ghost

Steve,
You would need a new piston as the ring end gap would be in the wrong position with the rear exhaust piston.

Cheers

phillio35

i would leave the zen in it as the power is wasted in these boats its a fun boat not a racer .i had one with a j and g and was to much for it

Ron Olson

My Feedback: (1)

You can't just turn the head 90 degrees as it's rectangular. The rear exhaust engines are better suited to low-profile mono's, sport hydro's or 'riggers. I had an RCMK R-254 in my JAE 'rigger and have another that I don't know what I'm going to do with, either find something to drop it in or sell.

Lleksam

Thanks all,

Ron, think im going to get Dana's new cat when it comes up for sale through Mountain and put RCMK in that


Phil I read your build, could be same boat as one i have, have a look at picture specifically exhaust and cut down 5" rails to fit radio box in, It seems Like this DaVette has been a few colours in its short life


Ghost, Thanks That was what I thought


Steve

F1madness

To change to side exhaust you need to change the crankcase,flywheel and piston as iv looked at doing it myself 

Lleksam

Thank you, half expected crankcase, but flywheel came as a surprise.

Steve

F1madness

Hi bud
you have to change the flywheel as the coils mount differently and the pick up on the flywheel for the main coil on the RZ is different throwing the timing out for the spark
so if you use a RZ flywheel on SE setup it wont fire up due to this

Lleksam

Logical really didnt know why i didn't think of that DOH

Steve

phillio35

hi mate was it orange then before and did you buy it from billy also did you get the pump with it thought it looked familiar

Lleksam

Hey Yes I did, but was blue when i got it, I already had a Davette this was a second one, other one is electric with the motor - jet unit below in it, when i get it back from painter, and a ally one too, that i made a year or so ago thats another electric, Just waiting on few parts for Jettec unit

Lleksam

Hi Dave Marles of Prestwich Model boats came up with ideal solution to my original problem

turn Cylinder and piston 180 degrees, match lower end of transfer ports, and make a 180 degree header....... simples!!

Thanks Dave, "You the Man!!"

Steve

danielplace

Flipping the cylinder/piston without changing direction of rotation also changes the ignition timing 2-3 degrees because you have effectively changed when the piston is at TDC by flipping the piston pin offset to the opposite side so where the piston used to go to TDC first then the rod now you have the rod arrive first then the piston. Since the crank orientation at TDC is also your ignition timing.
Put a 11" degree wheel on the engine and find TDC and flip the piston around and watch TDC you found before on the crank change.

It may not make a ton of difference just a note that it does affect the ignition timing.

What you want to do is get a K30 cylinder with the closed up transfers that support the piston for a rear exhaust to have long life.

DaveMarles

Daniel. It does not effectively or actually change the TDC position. There will be a very small change to the ignition timing which is unlikely to change the performance at all, but considering the changes made already on this engine regarding the ignition, I think it's a moot point anyway.

danielplace

TDC is always TDC. The highest point the piston travels with the crank centered on that point always has been and always will be TDC. I think we know what TDC is and that is never going to change. The cranks position in relation to the TDC you have now is what has changed.

What was your TDC on the degree wheel attached to the crank is no longer correct and piston won't be at TDC if you are on the same mark you had the piston at TDC before. A offset key could get the ignition back to the same advance it was previously at. Or just bolt the flywheel on where it is supposed to be without any key since the key is only for assembly purposes anyhow. If your key is what is keeping your flywheel where it belongs then your flywheel is not properly seated.

It does change the position the crank was in while being centered on the piston being at TDC to a new flipped around location.

Normally the piston pin offset is favouring the exhaust and they are always offset in that direction. Flipping it around without counter rotating it changes not only the ignition timing but the rod angularity on the power stroke among other things.

Not trying to say that any of this will make or break a engine from performing at it's best. Only extensive testing would show the advantages and/or disadvantages to doing this. Simply noting that this does change numerous things about the assembly is all.

When you do this to a side exhaust engine the effect of flipping the cylinder without counter rotating has all the above changes but also puts the working side of the piston on the exhaust side of the engine. This might not matter on lower RPM engines that aren't being pushed to their limits but for a high rpm fully modified marine engine it can certainly cause premature failure. You want the piston running on the cool, wet lubricated intake side that isn't exposing the working side to exhaust heated dry side of the cylinder.

A rear exhaust engine with open transfers is always going to be less than perfect.

The Ghost

Seen this while looking for something else, This may be usable for the rear exhaust engine.
[link=http://www.ebay.com.au/itm/Dual-Stinger-Twin-Tuned-Exhaust-Pipe-fit-HPI-KM-ROVAN-Baja-Buggy-5B-5T-5SC-Truck-/271200200206?pt=UK_ToysGames_RadioControlled_JN&hash=item3f24caa60e]Exhaust System[/link]

Cheers