Heats on-Which scooter  
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All Forums >> Glow Engines, Gas Engines, Fuel & Mfg Support Forums >> Engine Manufacturers Direct Support Forum >> Jett Engineering Support >> Heats on-Which scooter
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Heats on-Which scooter - 2/5/2006 7:28:10 PM   
rmenke


 

Posts: 1773
Joined: 6/25/2004
From: Merced, Ca., CA, USA
Status: offline 		Bob:
Recent e-bay purchase of OS vrdf destined for Alley Cat turned out bad. So, back to decisions. Need a motor that will give me 19-20K in standard 60 frame. I know the OS will give 20 with ease, but love Jetts, hate OS, but will tollerate them if I get my speed.
Looking at the Jett Fire rear exhaust 60 and wondering if this puppy will put out something close to the vrdf. Now, throw the BSE 90L into the mix (sitting on the bench) and give me your best shot for speed and reasonable life. I know this sort of puts you on the spot, however you and Dub don't seem to mind dealing with reality. I have the BSE 35, 50 and 90, 35 just great, 50 and 90 need more rpm for my needs. My 90 is the older L, not LX, but has 6 runs on it, so its gotta give service.
       Post #: 1

RE: Heats on-Which scooter - 2/6/2006 3:24:14 PM   
bob27s



Posts: 4819
Joined: 4/9/2002
From: Cleveland, OH, USA
Status: offline
quote:

ORIGINAL: rmenke

Bob:
Recent e-bay purchase of OS vrdf destined for Alley Cat turned out bad. So, back to decisions. Need a motor that will give me 19-20K in standard 60 frame. I know the OS will give 20 with ease, but love Jetts, hate OS, but will tollerate them if I get my speed.
Looking at the Jett Fire rear exhaust 60 and wondering if this puppy will put out something close to the vrdf. Now, throw the BSE 90L into the mix (sitting on the bench) and give me your best shot for speed and reasonable life. I know this sort of puts you on the spot, however you and Dub don't seem to mind dealing with reality. I have the BSE 35, 50 and 90, 35 just great, 50 and 90 need more rpm for my needs. My 90 is the older L, not LX, but has 6 runs on it, so its gotta give service.


Remember, the FIRE 60L is a "40" size engine. Tweeked with 60LX updates, and a short pipe, it will happily turn 20K rpm, but with a 8.8x8.5 or maybe a 8.8x9 prop. Im pretty sure those are not going to cut it on the Alley Cat.

And it is nowhere near the performance of a VF fan 90 engine. The fan engine has a huge rear intake rotor, huge carb, lots of air/fuel with every stroke. A front intake engine is limited by the passageway of the crankshaft. There is only so-much crankshaft you can cut away, and expect it to remain intact

You can have the existing SJ-90L updated. Im not entirely sure of the cost of making it an LX setup - somewhere around $50 id guess.

The highest practicle output I have seen from any of the Jett 90 size engines, has been a FIRE-95 engine with the actual Fan-Jett 95 sleeve and piston in it. Was basically a front-intake fan engine. That was turning a 10" diameter prop up around 18K rpm - then the prop let go (what a mess.... trashed the engine too).

Can a 90LX turn up to 18-19K rpm? Most likely. Put a 10x6 on it and stand back. And through my own experiments, Ive installed a 90L in a dynamax fan and let it scream on a 5" rotor (which was impressive) but Im not sure Id recommend that.

Getting 20K rpm while turning a practicle and usable prop - from a 15cc engine is asking a lot. Keeping in mind that a few FIRE 90L engines have been set up for turning 16K+ rpm with 10x10 or 11x7 props - that should give you a bit of a baseline of what is possible. You might squeeze another 1000 rpm or so more with a different carb, timing, head button .... but Id imagine that would be it (especially from a prop-tip-speed point of view).

The only other thing that has been considered in the past was something we have called the "BSE-100LX". Has not been tried yet. On paper, it should get you the same 16K rpm as the 90LX, but with power and thus more prop out front. The key here would be to keep the rpm down to 16K or closer to 15K rpm - the phyical properties of the engine would be pushed to the limit. But consider a 11x10 prop turning like that Again, its just on paper... been a back shelf project.

Dub is frequently willing to try new things. You pay for them of course. And as is policy, special configuration engines are not under any warranty. email to jettengr@sbcglobal.net and tell him your request.... you basically want an all-out 90 size F-1 engine.


_____________________________

Bob Brassell
Jett Engineering - Engine Mfg Support Forum Host

(in reply to rmenke)
       Post #: 2

RE: Heats on-Which scooter - 2/6/2006 6:38:54 PM   
rmenke


 

Posts: 1773
Joined: 6/25/2004
From: Merced, Ca., CA, USA
Status: offline 		Bob:

Thanks, your info gives me a logical direction. Gonna stick the 90L into the AC and give it some time in the air and additional breakin which it needs. Will go for the LX muffler and pick up a few R's. My 50L in the Matney Animal Zoomer should keep the crowd in the rear view mirror for this year if it ever gets here. Hopefully the AC will be up to the job as I need the larger aircraft for these old eyes. Don't think the AC would stay togeather with the VF engine at full song. Going to keep an eye out for a thin wing 40 pattern ship, build it strong and try one of those VF monsters. Again thanks for your direction.

(in reply to bob27s)
       Post #: 3

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