Hyper .21 minus the turbofan

[XXChAoTiCXX]

Hey all,

Just wondering if changing from a pullstart backplate to a bumpstart backplate reduces my Hyper .21 8-port's performance, because in doing so, I had to remove the con-rod driven turbofan. Did this thing really provide any "boost" and if so was it nominal, or will I notice a decrease in performance?

[evan811]

I dont know about this "boost fan", but, my removing the pull start and only having a backplate for a starter box, you gain more power because there is less drag on the engine....

[AC48]

Never heard of having a turbo fan??

Usually when switching to a bumpstart you gain a little power, less drag on it like evan said.

You man be thinking of the starter shaft of the engine, its not a turbo fan it just connects the conrod to the pullstarter.

[olds97_lss]

No, I think some engines have what looks like a turbine on the internal one way bearing... not really sure what it's for, but I've seen it in parts explosions.

It might be something like what Orion is trying with their new crank/backplate design to help the fuel/air mixture accelerate through the engine.

http://www.teamorion.com/faq/wasp_rev.asp

It isn't the "same" thing, but may be based on the same principle.

[XXChAoTiCXX]

This really was a turbo. It wasn't in the conventional location of a turbocharger, but it had a pin that fit into a hole that was off-center in the con-rod. As the con rod went up and down, it spun this turbine in the back of the crankcase. The only thing I can think of that it may have doen is creat more low pressure inside the case so the carb pulled in more air. I am still getting familiar with the nitro engine theory, so I may be all wrong. The engine is also reffered to as a Hyper .21 Turbo, and when it had a pullstart, it said "Turbo" on the back of the pullstart casing. I realize that the removal of the pullstart causes less strain on the engine, but without this turbo thing I wonder if my performance will change.

[HeartBreak]

It shouldn't. Some pullstarts have their one-way bearing inside the case (like Megatech/SH does). Others have it outside, like Traxxas, with a shaft that goes thru the backplate. The inside-end of the shaft has a circular piece on it (like a washer without the hole in the middle), with a slot or two. One of those slots engages a little nub on the end of the crankshaft, usually where the connecting rod connects. If you have that little nub, you'll have to grind it off. Doing that requires removing the crankshaft and taking a grinder to it.

[Plaidfish]

The Turbo part is actually the head button style.....a turbo plug has a threaded part of the plug and a tapered end over the element like this \ / and a standard plug is like this | |.....the turbo end is supposed to make a better seal and recess the element out of the lil dome on the head button, that makes the combustion chamber smoother as well.....more efficient combustion distribution....

[niggle]

Originally Posted by Plaidfish

The Turbo part is actually the head button style.....a turbo plug has a threaded part of the plug and a tapered end over the element like this \ / and a standard plug is like this | |.....the turbo end is supposed to make a better seal and recess the element out of the lil dome on the head button, that makes the combustion chamber smoother as well.....more efficient combustion distribution....

The one-way bearing on the pull-start version of the Hyper 21 has turbine blades cast into it. The HoBao parts list refers to the one way bearing as "21021 Turbofan"

IIRC this engine has never been available with a turbo head button, even the "Pro" versions with the silly boost port.

With the bump start backplate in place you should see a performance increase, firstly because there is no drag caused by the one-way bearing and secondly because the crankcase volume is decreased and the transer ports will work more efficiently. When the piston decends it pressurises the crankcase and forces the fuel/air mixture into the cylinder through the transfer ports. If the crankcase volume is reduced the pressure will be increased.

You won't need to hack the crankshaft journal as the drive pin for the one-way is in the one-way itself.

[dxm2]

I just recently removed the oneway-turbofan from my Hyper 8 Port and saw a substantial increase in performance. No more pull starts, or anything else back there for me. (I have the rattiest starterbox ever sold on Ebay, but it works great.)

Also, I did not have a new back plate, so I just used the existing plate and sealed up the hole with a nut and bolt and high temp sealant.