I just got ahold of this rear exhaust K&B .40. I have no idea what model number this might be or when it was produced. It appears to be either brand new or run just a couple of times at the most. As can be seen here it's missing the carb, venturi and NVA, or whatever it had originally come with. I'd like to hear some suggestions on what to put back on it and what this engine would be happy with. Some venturi diameter suggestions would be great too. As a reference, can anyone tell me what diameter venturi it would have been supplied with?
 
 Thanks!

 Yeah, I don't really get the feeling it would be a first choice for a stunt engine. I only ended up with it because it was bolted on a plane that I purchased from a private party.

 I'd just like to put a venturi and NVA on it so that it would be complete and ready to run, who knows on what.

if theres a big diferance in the port hights at the top , Ex higher , its a pipe liner .

if its less than 3 mm might be for a boat , or anything .

They have BIG intakes std . 20.000 rpm .
throw any R C carb on , with a adapter sleeve .

My 7.5 DF runs good . 110 intake , 160 Ex. BUT its running a 6.5 head  which works better at 10.000 rpm .     

My guess is that it's an R/C version, and somebody took the throttle out. But I'd look at the exhaust timing to confirm that guess. If it has the "high timing", I'd love to have it for a "NW C Speed" model, if you want to get rid of it.  See if I can still get around the pylon and fly monoline...Yee-Haw!

Assuming that you're going to put a 5/32" (.156") spraybar through it, .312" is a LARGE venturi for a .40 on suction, but it will run alright. I ran a .312"/.156" combo on my K&B .40 (#4055), but it was still pretty weak compared to a .46LA with only a .285" venturi.  A .272"/.285" is about average for a .40 with that .156" spraybar through it, but some use only a .257".    Steve

 I just pulled the head off to check this thing out. I don't know what the "high timing" engine is supposed to measure but maybe someone can fill us in.

 Using a machinists ruler I took a few measurements from the top of the cylinder sleeve, here's what I came up with...

 -Top of sleeve to top of exhaust port opening = 9/16"

 -Top of sleeve to bottom of exhaust port opening = 27/32"

 -Top of sleeve to top of intake port opening = 11/16"

 Without tearing the engine down further I couldn't get the bottom intake dimension with any confidence because of the piston being in the way.

 There is also F. LEE MFC (or MFG?) stamped into the left engine mount. What's that telling us?

 As can be seen the engine has been mounted, but it appears and feels to only have been run a few times at most.

 

 Aha! That's very interesting, thanks for the info Juan.

O. K. . Humongous is probly more exact ! . 



Thats a 5 cc , though the same to look at .

 Nice.

 What do you have that one set up for Matt, Stunt, Speed, Free Flight,...

Just a picture flogged of ebay , of a ' 4.9 ' ( all the SRIIs are rated in c.c. rather than Cu. In. )

The intake appears to be standard across the range , 4.9 , 5.8 , 6.5 .  F.I. .

Ive a 7.5 DF with 160 Ex , 110 In, & 90 / boost , on the sleeve .

Look up the exhaust port under a strong light , turn crank till the piston tops the far 9 front / intake ports , and estimate m.m. Ex still open .
if its less than 2m.m. its NOT the tooned pipe set up . If its ' lots ' it IS for a pipe , or Mini Pipe . a lot came with a straight tube = mini pipe .

This looks like a Tuned Pipe sleeve :

ports are a mile differant in top edge hight .

 Thanks for all the info Matt, but at this point all I'm wanting to know is which version of this engine you guys think I have. Please review the dimensions I gave above.

 Some venturi diameter suggestions would be nice too, Steve has given some good info there.

 
 

    The venturi that came in the original engines was .375" I.D. with the two piece racing spraybar as in the pic above and was made to run on pressure only. The pylon racing versions that I saw had a carb that actually had no idle circuit and was made to run wide open then act as a shut-off.
    The engines were called SRII's when they first came out as they replaced the very limited production SRI.
 Very high performance engine in the day. They are still seen frquently in classes B(4.9cc) and C(5.8 & 6.5 CC) gas in freeflight. Limited numbers of .41's were made to compete in Class D gas.

I ran K&B 6.5s in Rat for all the  years after they appeared until I effectively gave up the event in the mid-80's. There never was, to my knowledge, any such thing as a "high timed" 6.5: they were all the same, timed for mini-pipe use. I cannot speak to changes that may have been made post about 1984.

That being said: the engine you have in front of you is an early 6.5. You can tell by the fact that there is essentially no radius between the cylinder casting and the casting for the bottom end. Early models had a tendency to break right there and K&B made a later version (very early 80's if memory serves) that had a significant radius there.

Since the engine is an early model, it will be mini-pipe timed, certainly suitable for many high performance applications, but totally unsuitable for stunt (if that's what you had in mind).

 Well folks, nothing against it, but I've decided that I have no use for this particular engine.

 FWIW, I've looked it over closely and I'm thinking it hasn't been run any more than a couple of times, if at all. It turns over smoothly and feels just like new. Other than having been mounted there are no marks on it. It should only need a venturi and NVA to be ready to go. I have no idea what it's worth but I do know it's not enough to retire on. If anyone has any interest in this engine, as is, I'm open to offers. The above photos show it in detail. It is not listed in the Classifieds, just PM me here or whatever works for you. If I don't hear anything soon it goes to Ebay, probably next week.

 Thanks!