I just picked up a new Irvine 40 mkII side exhaust on Ebay the owners manual that came with it lists only Castor based fuels. What would people suggest for brake-in and for stunt use.

The Old OS H40S & FSR intakes fit . A 10 x 4 three blade works , but underproped .

Thank you everyone for the information. I've gotten some break-in runs on it with the irvine venturi with the goofy needle valve with Sig champion 15% nitro 20%50/50. With this setup I can't get the engine anywhere close to 4 cycling. I live at 6300 ft which is why I have 15%. I'm guessing the 15% was the problem getting it to slow down, I have methanol and sig castor that I think I'll mix 75/25 for the rest of break-in. Also have a 40H venturi  but can't find a needlevalve/spraybar for. Thanks again guys for the info.
Michael Millard

 Just an update on my Irvine.Ordered and installed OS 40H derilin  venturi and needle valve from Ebay control line store ie Shtterman  which seem to work well. the venturi has smallest throut. Finally getting close to being broke-in. Thanks again for the help. Michael Millard

Precision Aero / randy smith , is obviously the place to go for a pipe .

I think the timings 120 / 140 , so a notch lower than the OS VF .

My 40 dribbled so put a sealed front bearing in . But its thicker . Prop Driver 1/16 th Fwd .

I would run in on CASTOR , as the ring is DYKEs and ' well fitted ' . they go in a K&B 40 TIGHT .
Theyre a crry on in a sense from the K&B SR IIseries . Were T&L K&B stunts ( adds in old SLIS LINAS mag aroung 1980 / 1990 )

Acording to the sceptre flight tripe , the R E is pretty much a M II , but R E . I got a head insert ' HEMI 'd . just in case .

Unpiped , theyve got a ton of grunt , IF theyre REVED . a 10 x 4 three blade tornado & it took off like a cut cat . So Id think a pipe unecessary .
Unless you enjoy the complexity . the K&B and maybe OS rear Flange interchange , so it should be quite straightforward . a few guys in the U S have used them .

https://sceptreflight.com/Model%20Engine%20Tests/Irvine%2040R%20RC.html

The BLACK glass filled nylon are fine , IF you dont carry the plane , or half the plane , by grasping a prop blade . this dosnt help any prop .
Casting the plane to the ground ( in the pits ) can do it to . Even to a fibreglass prop . SPLIT the blade .

Grish Tornado , in the triangular 60s bubble packs , were STIFF . Some bagged with the yellow tag , were soft . Some very soft .
Later WHITE , Some were polypropolene .( or suchlike ) . on a hot day the 11 x 4 on the 21 / 40 had the blade ends pulling themselves forward , curved , to 90 degress . Tangental or something . Notta Lotta use .

If you deck the black ones , theyll de blade themselves . or you will . If you lookatit likethat . They WORK good though . IF YOU LOOK AFTER THEM . Not that theres any left , these days . F'glass copies available in the U. S.

a BOLLY 11 x 4 three blade'd likely suit the IRVINE , on a .30 or .32 intake . .275 up , likely suit it . the VF's PIPED they found you didnt need to reset the cabodle with the barometer , on the .275 . Mr Buck & Co .
tooned Pipe operation artical ,  it on here , somewhere .

AS you mentioned TUNED PIPES  , youd beta digit out , and havea READ . as they seemed to figurem out .

Sorry to reinstate an old thread, but I've just discovered an Irvine 40R in a box of engines left to me by my father
I was hoping to give it a try on a piped setup as I've never used one before.
I'm led to believe these Irvine would give an OS 40VF a run for its money

This may help or not but here goes. I have an Irvine 40RLS which is based on the same crankcase as your engine but internally is quite different as it's designed as a CL stunt engine but then again the VF's were designed for R/C .
I used an Eather tuned pipe set at around 17.25" and an Eather 3 blade 11.25x4 CF prop. Revs were around 10,500 and fuel was straight 80/20 all castor. Tank of course was a plastic uniflow. In my opinion, having used both the VF40 and 46 in the same model with the Irvine RLS, the Irvine beats the VF hands down.

mark  you best give me a call  on 02088441727  i can give you some pointers   at home between  4 to 5 most days    roy cherry