I did a quick search and didnt find any tach readings on this engine so I'll post my findings.

This engine has about 2-2.5 gallons through it on the stock piston ring. I'm not real happy about the longevity of the stock ring as the compression has gotten a little softer than it was right after the initial break-in. However, the engine does run well and idles nicely. The engine is very well mannered, even with the way I've been running it.

This engine came with a very small muffler, probably better suited for a .15 sized engine so I didnt use it. Instead I used the Macs Products full pipe right from the get-go.


Open faced exhaust
APC props
5% nitro 20% castor
McCoy MC59 glow plug
73°F air temp, breezy

9x4 - 16,890rpm
9x5 - 15,390rpm
9x6 - 13,890rpm
9x7 - 12,960rpm

Un-cut full pipe and header
Same fuel and plug

9x4 - 16,740rpm
9x5 - 16,060rpm
9x6 - 15,270rpm
9x7 - 13,830rpm
10x5 - 12,150rpm
10x6 - 11,520rpm

1/4" total cut from header down to 6" length

9x5 - 16,200rpm
9x6 - 15,270rpm

1/2" total cut from header down to 5.75" length

9x5 - 16,200rpm
9x6 - 15,000rpm

3/4" total cut from header down to 5.5" length The engine starts to get on the pipe at about 12,500-13,000rpm and jumps to 15,000rpm quickly.

9x4 - 17,370rpm - lowest idle 2,200rpm - reliable idle at 2,500rpm
9x5 - 16,400rpm - reliable idle at 2600

Initially I was tuning to the 9x6, but it doesnt seem to like the 9x6 so I decided to go down to the 9x5. Right now the pipe is peaked to the 9x5, with room to grow on the 9x4. This engine is on an airboat and being a bit draggy, the lower pitch higher torque props seem to work better. I've gotten the fastest speeds with the 9x5 prop.

This is the boat I am using the engine on:

APC makes a 10.5x4.5 that is a narrow blade that might work very well for you on the boat.

That isn't going to give me the rpm I need to get this pig moving. It's a very draggy 5lbs. The tuning window of the needle on a 10" prop is 1/8th turn from rich to lean. Too much prop/not enough engine.

Moreover, I can't run 10" props on the boat anyway - the CG would be too high. Besides, it's only a .29, not a .40.

http://www3.towerhobbies.com/cgi-bin...?&I=LX1552&P=0

That prop isnt the normal blade shape it is more of a normal blade. clip it down to a 9" and get great thrust and rpm.

I'll see if my LHS has one. I try to support my LHS where possible.

What is the best thing to do with the prop tips after cutting it down? Round it off a little and balance it?

yes sorry my last post here didnt go thru yesterday. Just round them off a little and then balance.

qwick .... you have seen this supertiger engine thats set up for air boats and has a muffler set up for air boats also.


http://www3.towerhobbies.com/cgi-bin...?&I=LXZUH4&P=0

http://www3.towerhobbies.com/cgi-bin...?&I=LXZUG8&P=V

Yeah, I've seen that one. Its basically a car engine with an air prop. It's intended to be a pusher, not a tractor prop. The exhaust system is a power robber also. I'm going to stick with my 29 on the macs tuned pipe. I can't afford another engine right now anyway.

well i think it could be used a tractor engine. most of our engines can be used either way. most of the trust load is on the rear bearing.

The head is too big I think. Besides, I will only collect Italian Tigres.

I run my TT .46 on this boat too when i want more power.

Since I posted my tach readings above, the compression has gotten a bit softer. I think this engine got a marginal ring from the factory as it loses it's seal quickly as the prop is rotated slowly. My s90 does not exhibit this behavior and it has a factory ST ring. I am going to re-ring the engine and after breaking the new (Bowman) ring in, I will retest the engine and post readings. I have another muffler or two ill test as well. The engine still runs good, but I think a better sealing ring will up the power a bit. In previous tests, I got a lower rpm reading after the engine was up to operating temp

I like the fact that Bowman rings cover the locating pin for the ring where others do not. Results to come.