further thoughts & observations cetra .
NOW the other day I saw a 60 inch or was it 58 thing waffling along nicely , a bit like a big soft woffly rather than snarling ST 60 ,
and said to the bloke " that runs well , WHATS init ." Whereapon he said a S T G 51 . So I glared at it . AND the big 12 1/2 x 5 1/2 ( or some pitch ) three blade Eather prop. Astounding ! .
He further informed us , it was ' done ' by ( i missed the name ) possably Dixon . So might be bunged bypass & Hemi Head ? ANYWAY , was a soft quite torqey reponsive run . Last thing Id expect from a G 51
in a big plane .
Being as I runnem Hard .
Just dropped a 22 thou. old V 51 gasket in the shaved head oldGit 51 ( stripped and cleaned used ) , to give it a try , maybe on a 12 x 4 Bolly , for a soft snarl , we hope .
The 40 & 45 head match the BOLT PATTERN . Theres a ' plug to piston ' Max. according to Lew wollard ( on schneule Foxe 40 ) He carves the lower sleeve flange to drop liners . to 130 / 110 .
which is what they set the HP 40 to . Also other work good there . so the old ' Hemi , 1/16 th squish . shallow angle ( 3 or 4 deg. ) remove all sharp edges trick , if youve spare heads , could help .
Crank Timing , the REAR intake HP is 60 closeing . and works extremely well , balancing gusts & switch off down hill .
Randy Smith states the R C G 51 works well . I dont know the sleeve timing there . Bt the ducks guts is the Ro Jet 50 , on those big tapered 3 blade 12 1/2 Eathers everyone ( here ) runs . On many engines .
The Ro Jett Timing is io 40 ic 55 Ex ( 68 ) 136 trans & Boost 126 pistons 23 . 5 bore heads 1/8 squish 4.2 deep chamber .
G 51s ive got THREE differant Crank timings . Measured . theyre about 114n / 116 on the boost . 126 or 128 on the trans & 136 / 140 on the exhaust . Theyre were built for years . Ones a China 4 number stamp still
ITALY on case . Just grabbed my notes . wasnt expecting the varyation . Tho ive carefully measured them a few times . A flashlight into the lower case help exactitude with the angled port upper faces .
Lew left the Fox 40 boost center intact - only liftedouter 25 or 30 % for turbulance - said to be a neccesity . on that . ( Similar port layout . so we mention it .
a China G 40 is 124 T 110 b 155 Ex . 44 - 47 crank. ( ive got 44 - 47 for a old G 51 crank. stamped 3154 ) . slotted screw driver head screws . Late Italian ones were allen head / cap screw .
NOW !
ive got written , 43 - 50 . 57 , 57 , 64 ( which is 114 & 128 ) written for G 51 from a few decades back /
ALSO 51 - 41 63 58 68 . which is 126 T 116 B & 136 Ex . So are irritaed and annoyed . as were C L G 51 . But maybe NOT . AND ive not brung the G ( GS ? ) 45 ABC figures .
Could be any explanation includeing ' test ' figures with say a 1 mm feeler guage ( or stick ) on piston to try result from dropping sleeve ? perhaps . ( Im sure all the hights in the Ex Stack match )
NOW I will have to take another look .
the decompressed head with the upper fins knocked off , is ready now for test this weekend . Along with ( next ) a Rabe rudder , im hoping itll get theb 63 span 63? ounce Spitfire ' on track ' consistantly . the heads now low enough for the cylinder opening in the deeper ( of 2 ) cowl to be closed over . but'd be tight . will clean up the airfolw over it anyway .
the GARDNER G 51 was plain ringed from a old plane of his , from aniother bloke . and had had the BY PASS ( boost ) bunged . a piece of balsa , maybe tack glued - would TEST that theory . but was common.
( I debunged it in outrage
)
Id think differant squish band width Hemi'd heads would be worth a try ( alledgedly Big jim G - 51's ( or some ) were hemi'd . ive not seen ( or seen in ) one . Squish CLEARANCE . Close for effectiveness - is the trick .
at 22 thou. alledgedly ive lost the sudden B M E P jump that gives swirl & maintains ' pink free ' non Pre Ignition - runnig ( previously at high rpm on the 10 x 4 3 blade the resonance was distincnt & resonant !
cut the fins off a S T 46 muffler & the ring like blazes . THIS sounded like the sides / upper case R E S O N A T E I N G . Loudly . Id said that to Brian Eather on the phone . that'd be DETONATION he said .
Yes. indeed .
ahem . was the thought . detonateing the upper half into orbit it sounded like . The C L Horsepower is rated at 11.000 ( factory Figure ) the R C at 16.000 . therefore , the C L set to run up to 15 or 1600 . the two differant G 51 LINERS . same Crankshaft .
holding its own when it blowing viciously gusty , is in theory at least , not impossable . the H P 40 rear intake . with 130 100 timing at 40 open 60 close , on the crank ( a unrestricted passage one might say )
gets a 4 - 2 - yowl - 4 - off , run , in a wingover into a big gust up top . the old Scott motorcycle was said to Y O W L .
It coulda been called 8 - 4 - 2 run . but it was a normal 4 - 2 with another yowling faster two , under duress . And could drop straight back to braking . ' Throttle Shut ' !
Set the carbs closed , so the idles ' on the throttle ' for max engine braking . AND YOULL KNOW WHAT i MEAN . FASTEN SEATBELTS . The old back roads were pretty rough .
After the world rally Champs stage there , the local trick was time the bounce from the drop onto the leap to the bridge right, pull off 30 mph maybe ( they went from 90 )
for Max. braking . as the hard left of it was a wall / hill cuttaway , on the right . There was no room for error .
Another trick there was to have them all stand in the long grass roadside AFTER the corner . And have someone on the gate , to wave as they went into the paddock . as they were using the spectators BEFORE the corner , for dialing in the braking points . Haa GAUGHT YA . Told it worked on most of them . Mostly just a few front runners wernt fooled . 1980s world rally champs . ford Escorts , Vauxhauls & real rear wheel drive stuff .The banks outside the bends bend or break many an axle . Then theres the pot holes . but a FORD is under control as long as your not looking at the road in front out of the rear window , as they said then .
Id think the big chamber close squish HEMI might be the trick , for Engine Breaking . the HP head matched a std. ST 46 & K&B 40 chamber . Wide Squish , deep cup - POLISHED .
NOT the as cast lower face of a G51 Head . That may improove the economy , but a CLEAN FACE likely gets a sharper more distinct shock wave as the squish closes .
The ignition ' coming off ' / Going LATE , maybe the thing -m off load - for the down hill sections . ( a weber gave modulation on closing variation , for dirt rooads - UNLIKE most Carbs )
getting ' modulation ' on Engine Breaking - Off Load : might be the trick . But theres off load and right off load . As in it VARIES .
So the decompression ( Bigger Chamber ) for the ' soft break ' with the close squish may get THAT happening, we can always hope .
SO ; Old 40 & 45 heads are suitable for butchery for tests . Also for highest standard craftsmanship . ( think of caught most misprint / miss key )