Turbo

[MarkScott]

Ok, with Foolwitools bringing out how to mod the larger motors, thought I'd start on the smaller one first.. Reason is, I have an extra 13mm crank to play with..

As you may have seen on another thread, here's a pic of what got me started.

That is out of a 11cc motor..

Ok, here is what I started with (well not actually, but it is a stock 13mm )

Turned it into this:

Not bad for a first timer with a dremel... What can be used to smooth out the cuts made with the dremel???

Mark......

 

[izitbrokeyet?]

a sandpaper disk might be a good next step on the crank.

I've messed up enough cranks to say this:

make sure you protect that crankpin nowadays I use a piece of brass over the pin to protect it from a slip of the wrist.

also you might consider opening up the close side of the crank by a couple degrees and making better transitions B)

 

[TimD]

make sure you protect that crankpin nowadays I use a piece of brass over the pin to protect it from a slip of the wrist.

I'll second that! I've turned new cranks into scrap also. Brass tube is cheap insurance.

 

[MarkScott]

Great idea... Know the pin was touched a few times will using the dremel.. Why didn't I think of that :blink:

Oh yea, thought I was being watched while taking some pics.. Spooky... :lol:

Mark.

 

[Pist'n Broke]

This is great, anything you guys can teach me on how to hop up my 12mm is great.

I have built a pretty mean 3 litre Evinrude but I need some direction on the lil ones.

 

[MarkScott]

also you might consider opening up the close side of the crank by a couple degrees and making better transitions B)

KB,

just reread this, interesting.. Will have to do that.. Spent hour + w/ 320wet.. Looks better than before..

Mark..

 

[wswatzell]

Just make sure you don't mess up, it looks like Marvin has an attitude!! LOL!!! :lol:

 

[nitrotoys]

Turned out nice mark,

How many total hours doing it did it take?

I have a mod crank from a IB motor. Its really hogged out inside, Maybe i will post that pic if i can find it to take one of it.

Tom

 

[MarkScott]

Turned out nice mark,
How many total hours doing it did it take?

I have a mod crank from a IB motor. Its really hogged out inside, Maybe i will post that pic if i can find it to take one of it.

Tom

Tom,

I'd say about 1 hour for cutting and 1 1/2 hours of wet sanding.. I've started working on a 13cc crank... It is taking a longer to do... Don't know if it's just harder metal or a worn cutting tool. Time will tell..... Might have to put the 11cc motor together for the June Fun Run..

Mark..

 

[james irwin]

MY TID BIT . TURBOS WORK GREAT , BE REAL CAREFULL HOW MUCH YOU TAKE OUT ? YOU WILL INCREASE THE CRANKCASE VOLUME , AND THEN MAKE THE ENGINE GO THE OTHER WAY . NUFF SAID GOD BLESS. J. IRWIN

 

[GTR]

Hi Guys

Interesting post - my observations:

Don't go chopping away the crank counterweight unless you have a good idea of why you are doing it and what you expect to achieve from it. Issues - turbo cut on end of inlet it to over come shrouding of intake port by the rod as it crosses. Turbo cut is biased one way or the other (depending on crankshaft rotation) to encourage spin of mixture in line with crank rotation. Want more power try and reduce the mixture turning 90deg anywhere in your motor. Thinning the counterweight and angling the edges is an attempt to reduce the smashing effect of the crankweight in to the mixture causing drag on its flow. Other obvious point for trimming piston and crankshaft is to unshroud the intake ports as much as possible.

Point made by James is very valid - be very cautious of increasing crankcase volume as you will subtley effect your engines ability to act as a pump. We are only talking about small crankcase volumes and increases (particularly in the smaller sizes) happen a lot quicker than you would think.

All in all a small amount done well will be a whole lot better than a lot done porrly without sufficient understanding of WHY you're doing it.

IMHO as I don't profess to be any kind of expert - fit is the key, along with continual good maintenance practices. Some people can really hog a motor out and make it go hard but for most consistent power through good fit and tuning will pay much bigger rewards.

I have no doubt some of the more knowledgable will chime in here and I hope they do, at least if you wreck your motor and its a dog you know how it got that way. <_<

 

[Rules]

Well put GTR, "its a dog you know how it got that way"!!!! I like that.... Just as you mentioned the turbo cut in the induction bore must be biased, have it's leading edge sharp, with a 90 degree drop off into the bore with a flared trailing edge. The whole reason for the turbo cut is to create a vacuum behind the leading edge to pull the mixture from the bore, assisting the primary draw. If the leading edge is rounded then all you get is better gas flow with no work being realized. I still have the prints from where I built a tiny axial flow 2 bladed turbine that slid down curved grooves in the induction tunnel, and was silvered in place. Maybe I'll dig it out and scan it, to send you if you're curious!!! Lots of work, but it actually pumped air when I spun the front assembly with the starter. I am not convinced about minimizing the case volume though, I had super good results adding a little known flow director to the rear plate of a Rossi .21 inboard which increased the volume a good bit over stock. Maybe the smoothed flow had more effect than increased volume. Another trick I tried with very good results was a thin spacer between the rear plate and the case on a rotor valve Picco. The crank engaged the disk just enough to turn it. The other thing, is the use of boost bottles which seem to give good results but violate the principal of primary compression. I am beginning to believe that the increased primary volume acts like a shop air compressor reservoir at speed and allows the engine to move more mixture when the pipe is correct at off wave. I am no expert either, but have really tried tons of things besides what is in the Jennings engine bible. I would guess the most powerfull engine I ever built and wildest setup was an inboard K&B that had an aircraft front plate with carb, and an outboard rear plate with carb. The rear plate carb was linked progressive and the extra crank counterweight really smoothed the engine. The only problem was pressing in the new longer crankpin perfectly straight. The thing was awesome, tremendous RPM, good low end with huge crankcase volume that started easy. Figure that one out!!! Have a great year!! John in Huntsville