It's been sitting in a box for well over 30 years, getting back into cl with a warm up project. Would like to swing a 10-5 or 6 at about 12K. 2-4 break is not real important. Out of the box it looks to turn some unholy rpms. RE with @5"minipipe and monstrous intake. Suggestions on venturi sizes, extra gaskets...?

Any old .35 would power the plane, was hoping the minipipe would muffle things down inside of the old Kostura Yak jet fighter.

Well, you'd certainly make a JET fighter out of the Yak. The KundBeast 4.9 is pretty much a honkin' motor for FF and maybe CL speed? It is a little brother to their .40 pylon motor I think. I suppose there is a chance that you could find/build a tuned pipe (not a 1/4 wave minipipe!) that would help tame the thing, but...why? If you want to fly the Yak, get something in the known universe that is proven to work good on a sport plane. If you want to do engine development, that's fine too but you will have a long way to go to tame it for a sport plane. For example, it would probably pull a B-TR on 60' lines into the 130 mph range???  I don't know anyone who has tried it, though....

Hello I tried the K&B 6.5 FI RE on stunt model when I was a young lad, not the best match up but it worked sort of. On a really light model not needing a big prop and the right tuned pipe it might work but a poor engine choice for stunt compared to many options.
Regards Gerald

You can de-tune it but it's going to be heavy and use alot of fuel. Venturi .275" with .156 spray bar and some kind of exhaust restrictor. You would run the engine flat rich. 12K is idle for that puppy. I'd see about selling it to a free flighter and get an OS LA 25.

MM

There's a review of the K&B 4.9 at https://sceptreflight.com/Model%20Engine%20Tests/K&B%204.9cc.html

Thanks for the info guys. Looks like a pass for this project, I'll find something ...slower.

The K&B 5.8, 6.5, and 7.5 were BIG case engines.
The 3.5 (.19) was small case enigne.
So what case was the 4.9 (29)?  If is a BIG case engine you would have a 29 with the weight & size of a 46.

Quote from: Paul Smith on March 20, 2026, 07:34:47 PMSo what case was the 4.9 (29)? 

It looks to be a big case. It's the one pictured in Mr. Hampton's link.

Quote from: Michael LeGate on March 20, 2026, 08:17:18 PMIt looks to be a big case. It's the one pictured in Mr. Hampton's link.

OK, maybe it's time to fess up but sceptreflight is my web page that I started back in about 2003 by going through all my old magazines and scanning any suitable engine tests then searching the internet using the wayback machine for any defunct tests. Later I relied on other people sending me scans from their magazines to help add to the lists but for some time now new tests have slowed to a crawl. Right now I'm relying on one modeller who has virtually the entire collection of Aeromodeller magazines (thanks Danny) with about another 16 or so tests still to be requested.

While I'm fessing up, huge thanks to my daughter for organising (not to mention also paying for!) the means to be able to upload and store all of the tests. I couldn't have done it without her .

Awesome work, Brian! Thanks!

Yes Thank you Brian!  It's a great source for info.  Hope you keep it up long into the future.

Dave

Theres actually ads around for tom Dixon reworked STUNT  SR II   6.5s ! .

Think he mighta had K&B do him some liners . In the 7.5 theres DF & outboard . The outboard might work ( liner ) .

Mine has insane 110 - 160 timing . Supplied with a .40 head . It will tow 72 ounces on a 11 x 7 running slow - ish .
Figure it pulls the charge trapped between head & liner about half stroke , keeping the chamber lit . Maybe .
as in running at the break , pretty much . Tho only FLOWN it a few times . ( the engine ).

old PAMPA or Slis Lina have Dixons comoishilles .

Quote from: M Spencer on March 24, 2026, 06:20:50 PMTheres actually ads around for tom Dixon reworked STUNT  SR II   6.5s ! .

Think he mighta had K&B do him some liners .

  Extremely unlikely bordering on impossible that K&B made special iiners for Tom D.  K&B was dead or on its last legs before Tom Dixon started "modifying" engines.  Tom Lay may have done some K&B 6.5 modifications, he asked me about them at a contest in the mid-90's, but with a million completely bulletproof and easy-to-deal-with 40 or 46VFs around, it didn't make a lot of sense to try to find other engines.
 
   Unlike some of the others, Tom L. did not attempt to grind away at a K&B 6.5 or similar to "fix the timing" or whatever else people do, it was intended to set up the engine to run well in stunt with a tuned pipe, which was and is the competitive IC configuration. Very shortly after, PA engines appeared, and aside from some of us die-hards sticking with VFs, they became the dominant engines, and then the PA61 just took over.

  My advice, as always, is *do not grind or "retime" any engine*, and only do it for experiment if you have unmodified original components, because you will need it once you decide that grinding things is not the right approach. As far as I know, there is exactly one "grinding" operation that is proven to "work" after a fashion (although it is arguable whether it is better or not - since there have been a bunch of arguments about it), but it is certainly not to the liner.

   Brett

   

Hello

Yes I saw it after searching Tom Dixon stunt modified 6.5! The post was on SLIS Nordic Control Line dated 14.8.25 where someone is using a 6.5 on the F2b model and Guy Bevan from Australia mentions he had a Tom Dixon modified engine "I had a k&b 6.5 in a Cavalier profile. Tuned by Tom Dixon years ago and ran very well!" An interesting and unexpected post.

Regards Gerald

Any old .35 would power the plane, was hoping the minipipe would muffle things down inside of the old Kostura Yak jet fighter.
[/quote]


Send me an address as I have something for you.  State .35 or 40.

i dont remember ever seeing a front intake 4.9

I don't know how many they made, Bob--but they definitely had 'em.

Send me an address as I have something for you.  State .35 or 40.
[/quote]

Thank you for the offer Sir but that engine really needs to go to an interested youngin' with a case of Hobbypox.

Like most of you I've got boxes of runners, boxes of junkers and boxes of oddball gems. Really need to find a box of gumption, clear out the shop and start building instead of dreaming.

In my opinion trying to get the K%B 4.9 would be more trouble than it is worth.  First off the displacement is small for the weight of the engine.  If your motor has the older lower timed liner, it might be able to work in a fashion by someone who knows what he is doing. The fits on the liners were quite variable, and no parts are currently available.  I used these motors back in the 80's in B speed.  I think my best speed was 175 back when fuel was unlimited. Once the fuel was changed I never could get past 145 or so.

Mike, you should see my K&B 4.9 with Nelson 36 combat AAC P/L. The bore in the 5.8 case was too big for the Nelson liner so I took a little off the OD of the liner so it dropped into the 4.9 case. I had fun port matching it. Still not quite as fast as the Nelson 36 but I won some slow rat races with it. I mostly did it to get the good Nelson piston fit.

Bob, the front intake shaft/case assembly is the same on the 5.8 and bolts right up on the 4.9 along with the standard back plate. Easy to make a front valve from parts as they all interchange.  Of course you need the Glen Dye billet rod and Boca bearings when you're loaded for bear. Also, the front case and back plate gaskets from a K&B 4011 will fit those engines.

MM  

Speaking of .30's, departing a touch off-topic but not too far off. For a .30, this seems to exude power. (Looks can be deceiving? ) A bit heavy at 12.8 ounces without muffler. Peter Chinn gave a review of its bigger brother, a .40:

Sceptre F./Feb. 1979 Radio Modeller - Irvine Sport 40

Received a week ago, an E-Bay win for only $19.50 (plus shipping and tax = $30.38) an almost NOS Irvine Sport .30 Mk-II with muffler. It is my first Irvine engine. Seems to be a rather free breathing Schneurle with some of the most generous Schneurle porting I have ever seen. A VR/CS member on RCG mentioned it would be a good engine for a 63-in. Keil Kraft Super 60, an early R/C cabin model of the 1960's.



Can it be used for stunt? Best size of plane?

Seeing we've moved into Irvines, here's my Irvine 40 RLS which, because it uses the crankshaft from an Irvine 46, shows the reason for the LS (long stroke). To the best of my knowledge this is the only one in Australia and, having used 40 VF's, IMO the Irvine is far superior. I've also got a NIB Irvine 61 RLS which, kind of like the 40 RLS, uses a crankshaft from an Irvine 72