Northwest Speed Scoop
May 2011

By Mike Hazel

An X-elent engine setup

The following piece was pulled off of the Delphi Speed forum, written by Glen Dye in how to set up a Super Tigre X-40 for Speed.  While specific to  that engine, some of the information is of a general nature and useful for other applications.

A...PROPERLY...SET-UP...X-40, especially with Nelson Sleeve & Piston ... will  be competitive with anything else, and slightly lighter and smaller than a Nelson, or an O.S, VRP.

The Original  HI-NITRO, Shadel F-1 test prop was a Top Flight Super Maple (TFSM) 10 x 6 cut to @ 7-1/4 ~7-3/8 diameter and balanced, with Square tips.   An "Average" engine would turn this @ 23,500 RPM on the ground.   The "better" engines were in the 24 K ~24,5 K range, and the best  'Team Samurai' engines were up around the 25+ K range.   Mike Hazel has  a mold for these test props.

Your X-40 with a properly installed Nelson, AAC Piston and Sleeve should  duplicate the very best of these engines.

If  you decide to put the Nelson AAC  liner in the S.T:

1) Bore crankcase, and face top of case to accept the 1.0"  O.D. Nelson liner. @ +.001"

2)  Thin the underside of the Nelson Sleeve to bring the timing to the desired height, as the Nelson sleeve is thicker than the S.T.   X-40 crankcase tops are all over the place, as to height, so measure carefully here....first!

This needs to be done in an accurate...1.0"  5-C  Collet so that the 'new' underside of the sleeve is perfectly square with the long axis of the sleeve 1.0 " diameter.  Put the piston in 'tight', near the top of the sleeve first!
     I would start with the transfers & boost @ 130 ~135 degrees, and the exhaust @ 165 ~170 degrees.   Deck height @ .155 ~.160". Nelson or NovaRossi "Turbo" plug head (1 pc).   Stock S.T. heads were modified to use only the short reach K&B-1S with a double-bubble chamber.  Start with .018 ~.012"  head clearance, and work down to the best RPM's for your setup.

Chamber dimensions are the same as the Nelson.  Ditto the dimensions on the rod, wristpin, and piston ... not a coincidence!

The rotor and backplate need work too ... Open @ 30 ~ 35 deg.  ABDC, and close @ 68 ~72 deg.  ATDC, and balance after re-timing. The rotors can be anything from 45 x 45 deg. (STUNT) timing to @ 40 x 65 deg.   Re-Relieve the running 'face' of the backplate if it isn't at least @ .010 ~.015" deep.
     You also need to make sure that the backplate rotor face is TRUE, and the shaft-hole centered within @ +/- .001".  Rotor clearance is @ .001 ~.002", and  Red Locktite   the shaft and set-screw.  The last red-box S.T's from the late 80's,  were very bad in the backplate machining dimensions.  Also the sleeves were bad for roundness... .001 ~.002" out-of-round was common!   They were probably just "Using-Up" some left-over parts, that were sub-standard...(?)
     Mini-Pipe and Exhaust Stub:  You should  be using either the K&B .875"  OD Mini-Pipe or a later 1.0"  OD mini-pipe and barstock adapter. Length of .875 Mini-Pipe starts  @ 3.6" overall length, and the 1.0"  @ .4" shorter.  Make several in this range, @ .100 or .125" different in length to see what works the best on your set-up.

Venturi and NVA:  Shadel used a "One-Sided" NVA that works better than the stock S.T. one, or one of my similar TWA ones.  You can also make up a Steel venturi, that will be slightly larger (@ .020 ~.030") ID, and last longer.  Use a Lock-Nut on the Venturi -Lock bar.

The crankshaft seal area ahead of the rear bearing needs to be @ .001"  bigger diameter and plastic-cage ball bearings with at least a loose clearance...(.0005 ~.0008" radial clearance).  Best would be some of Greg Settle’s custom ceramic ball bearings.

If you are going to run the Hi-Nitro Fuel, the engine willneed to be fitted much tighter, approaching TDC.  I would start with @ .156" below TDC, where the piston sticks  “clean and dry”.

It will then need to be carefully run-in.   Start with a TFSM  9 x 6, cut to @ 6.5 ~7" dia., and 10 ~15 % nitro fuel with  25 ~30 %, all-castor fuel.   Then the same prop on 40% nitro, still all-castor fuel followed by the cut-down 10 x6 TFSM, and then 65 ~75 % nitro fuel with synthetic oil.

One to three short (@ 1 ~2 minute) runs are all that is required for each setup.  Total 'run-in' time a 10 ~15 minute total.  Always start slightly rich!  Then bring up to peak RPM for  10 ~20 seconds, and then back down rich,  several times.

Shut off rich @ 20 ~30 seconds, and then pinch-off.    Check the plug.  One plug   should last until you get done with the last hi-nitro runs.

Note:  High nitro will use a plug a run!  The wire needs to go out the exhaust port, not, repeat, not be trapped in the combustion chamber area.  This will 'pepper' the top of the piston, and underside of the combustion chamber on the head, similar to glass beading, or 'mild' sand-blasting.  Use good after-run oil!  Keep good notes!

If... you're going to use 10 or 15% fuel, the above break-in procedure can be abbreviated to just @ 2 ~4 slightly rich short break-in runs, following the same run-pattern, on the  smaller TFSM  9 x 6 prop, trimmed to give  23,500  ~ 25 K, on the ground.

And now for some fun...... Ron Bennett provided this website link; go to it and see how you do.  Ron says, “Try it and test your timing reflexes - makes you think a bit about timing models”.

That’s it for now, see you at the speed circle!

-- Mike Hazel

This page was upated March 30, 2011

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