Mickey Thompson's Challenger One. Still alive, Feb. 8

[Big John]

Thanks for the great info.  I expect Marine or aircraft quality epoxy may be more stable than the general craft quality counterpart. I will have to try the microballoon fill technique.  I found that the epoxy doesn't seem to 'wet' the glass cloth and allow the fibers to move as freely as with polyester needing more finesse to get it into tight spots.

[Ace-Garageguy]

1 hour ago, Big John said:

...I found that the epoxy doesn't seem to 'wet' the glass cloth and allow the fibers to move as freely as with polyester needing more finesse to get it into tight spots.

More than likely that has to do with the type of "sizing" that was applied to the f'glass cloth or mat.

Some materials that work with polyester resins don't wet out well with epoxy, which is why we have to be careful of that very thing when doing aircraft work.

The extremely fine-weave glass cloth I use on models now, primarily, is made by Hexel IIRC. It's not very expensive and works very well with the MGS epoxy.

I'll look up the numbers if you're interested, though how it will work with other epoxies, like the Bob Smith 30-minute stuff (which I need to experiment with), I don't know.

EDIT: Because of the high-strength nature of the MGS resin, I can make body parts that are only .030" thick but are stronger than styrene injection-molded parts that are much thicker. The downside, besides having to be mixed on a gram scale, is that the MGS takes 24 hours for a full cure at room temperature, and to reach full aviation strength it needs to be post-cured at much higher temps.

In general, the longer any epoxy takes to cure, the stronger it will be.

The longest-curing stuff from Bob Smith and other hobby-grade epoxies I'm currently familiar with is 30 minutes (though that may be the "working time"), so I suspect that parts made from it won't approach the strength I get from MGS...but only testing will tell for sure.

Edited Saturday at 08:20 PM by Ace-Garageguy

[Wickersham Humble]

Upon release, I bought this kit, and my bro bought the Ivo 'Showboat' dragster; they defeated us!  Wonderful kit, but so complex (as were the original subjects!!) and too fiddley for impatient teen-agers in the early 'sixties!  Anyone who builds the 'Challenger' is an artiste! Go, Bill!

I still have bits and pieces of both cars in my parts drawers; don't think at 80 I'm up for a rematch, tho!  Just swapped a generous forum member for a Mono 'Sizzler' kit, partially assembled but tasty, that is distracting me from my 1/1 duties now; doing the Bantam coupe body as a twin-SBC stormer, and putting the hemi in my old 'Green Hornet' chassis to revive it.  The blown Olds will be handed down to an old Lindberg duece roadster kit.  I bought a pretty decent 'Hornet' assembled kit at a 1/1 swap meet (a great place to find very modestly priced models cars stuff, I've found !) and am going to polish it up as a restoration to go with the other 1/24 diggers I have.  The 'trimmed' GMC 6/71 on the 'Hornet' is one of the few I've found to resin-cast from; most Jimmy blowers in kits have the full mounting-flange ribs.  Seems like ones with ribs/mounts trimmed were used mostly on street rod cars, for looks, back in the early days.  Bill is the olde speed equipment guru; what's his take? 

BTW, the valve covers on the Long John dragster just fit the Sizzler hemi heads, likewise the unique header. Easy to drill out the ends of the plug-wire looms and run wires from mag.   I'm filling their recesses on the 2-piece body, and cutting a hole up top to run a 1/24 Offy four, very period piece!  Wick

[Ace-Garageguy]

1 hour ago, Wickersham Humble said:

The 'trimmed' GMC 6/71 on the 'Hornet' is one of the few I've found to resin-cast from; most Jimmy blowers in kits have the full mounting-flange ribs.  Seems like ones with ribs/mounts trimmed were used mostly on street rod cars, for looks, back in the early days.  Bill is the olde speed equipment guru; what's his take? 

Well...a lot of guys call them "pruned", and I'm pretty sure there were some cases that were cast in that configuration, probably aftermarket as far as I've been able to find. "Sneaky Pete" Robinson comes to mind as one of the suppliers, cast in magnesium.

EDIT: Though I could have sworn there were OEM "oval case" GMC blower housings...because some that I've seen appear to be cast that way with no evidence of machine work or grinding marks, just areas that appeared to be as-cast...I haven't found any photos, and most people say "no, they all had the big lower mounting flange".

There ARE, however, non-GMC Roots style blowers that came looking much like "pruned" GMCs.

Anyway, "pruned" blowers were on everything from drag cars to rods, and were almost always used on the Potvin-style front-blown setups.

Most frequent reasons cited for using them on a top-blown setup were for ease of valve cover clearance, especially on SBC engines, and superior manifold-to-blower sealing. An engine used in competition with a solid-lifter cam will require frequent valve-lash adjustments, so anything that cuts the time down to do that is a plus. And keep in mind that the OEM GMC blower was designed to scavenge the block of a two-stroke diesel, not to provide many extra PSI of supercharging pressure, so the revised mounting required with a "pruned" case, that moved the mount bolts inboard to surround the gasket flange, could be a huge improvement.

I also seem to remember that some excessively weight-conscious drag racers who were looking for every ounce they could save would run "pruned" blower housings for that reason, so cast-that-way magnesium cases would be a natural.

EDIT 2: Below is a magnesium 6-71 case cast pre-"pruned" in magnesium, by George Montgomery and Pete Robinson, probably used a "pruned" aluminum OEM GMC as a pattern, reputed to be one of about 200 made.

More info here, including a copy of a contemporary Car Craft article that specifically states these things were indeed cast without the big OEM mounting flange.  https://www.jalopyjournal.com/forum/threads/how-is-a-pruned-blower-case-mounted.999144/page-3.

I KNEW I'd seen 'em cast that way somewhere...  

 

 

Edited yesterday at 01:16 AM by Ace-Garageguy

[Wickersham Humble]

My step-dad had trucks, and we had a lot of misc equipment around; one piece was a Borg-Warner built Roots blower that had a 'trimmed' case from the factory, as I believe after thirty or forty years past.  He'd seen such a supercharger used to 'blow' grain through a tube at an elevator such as he ran, and bought it to try and build a similar device.  Somewhere I have an ad from an old Mechanix Illustrated or similar mag advertising these as surplus equipment.  Never seem one on a hot rod, though.  It seems like the trimmed case era was mostly late fifties?  Thx for the insights.  Wick

[Ace-Garageguy]

9 hours ago, Wickersham Humble said:

... It seems like the trimmed case era was mostly late fifties? 

                                              Wick: You have a PM

In my mind, the most famous of all the trimmed-case cars was the 1966 iteration of Ohio George's Ford SOHC-powered '33 Willys. 

                            

Its engine is shown below with one of his (and Robinson's) magnesium 6-71 housings, cast in the "trimmed" or "pruned" configuration.

EDIT: Good color reference for Dow 7 too. It is NOT sparkly metallic as is often portrayed by modelers. 

 

 

Edited yesterday at 01:46 PM by Ace-Garageguy
punctiliousness

[Jack L]

1 hour ago, Ace-Garageguy said:

                                              Wick: You have a PM

In my mind, the most famous of all the trimmed-case cars was the 1966 iteration of Ohio George's Ford SOHC-powered '33 Willys. 

                            

Its engine is shown below with one of his (and Robinson's) magnesium 6-71 housings, cast in the "trimmed" or "pruned" configuration.

EDIT: Good color reference for Dow 7 too. It is NOT sparkly metallic as is often portrayed by modelers. 

 

 

 

[Wickersham Humble]

Great pic; custom blower case, etc. is really distinctive!  I used to like Never-Dull, but after spiffing up the cam cover and intakes on my 240Z, I find that getting the residue off takes too long (what you don't catch reappears when the metal heats up, like driving to our local concours yesterday -- embarrassing, kept hood shut!)  I may go back to 0000 steel-wool and some polish.  Oh well...   I tried to simulate Dow 7 on a belled-intake (through the radiator bulkhead on the Z, for 'ram' air...) with paint; luckily I kept it subtle -- and flat.  Bobbed the air filter horn and used a Spectre kit hose and adapter; looks and sounds pretty good.  Any suppliers of your knowledge sell a Dow 7 paint that looks okay?  Right; lots of builders use something that makes it look like Metalflake in scale.  Wick

 

[Wickersham Humble]

Not to belabor a topic, but it's an interesting one; viz the Car Craft article by Lang.  I wondered, though, if pruning the original down was a great idea as fuel loads and probably pressures increased in the slingshot era?  By the time the rear-engined diggers had taken over, weren't the race sanctioners requiring safety straps on blower/injector assemblies to prevent 'popping' the stuff when the bypass valve couldn't handle a backfire under full pressure?  Seems like the flanged GMC would be tethered to the manifold better... but maybe I'm all wet.  Bench racing... ahh!  Wick

[Big John]

And here I thought they were only 'Pruned' for Potvin use. Cool 427.

[Wickersham Humble]

On the other hand, there is a photo in an old hot rod book of an 'unpruned' 6-71 front mounted on a 90-deg. angle (so is the crank drive for it) with the intake facing forward, and the big rectangular 'blow' side aft into an awkward looking fabricated manifold, Enderle injectors, as I recall. Old hemi, as I recall -- and that's not easy!  I'll find it asap.  A one-off; too many right angles probably.  

The Potvin front drives were very popular, too; seems like everyone thought it was the future with blowers.  Even the nutty sports-racer Bocar used it with SBC.  Viz, the AMT 'Double-Dragster' kit.  The twin-engined rail was modeled on 'Double Trouble' I think, with Dragmaster frame, etc.

I don't know what the old man did with the Borg-Warner huffer; not too large.  Who remembers the GMC 5-73 (??)    Wick

[Ace-Garageguy]

9 hours ago, Wickersham Humble said:

Not to belabor a topic, but it's an interesting one; viz the Car Craft article by Lang.  I wondered, though, if pruning the original down was a great idea as fuel loads and probably pressures increased in the slingshot era?  By the time the rear-engined diggers had taken over, weren't the race sanctioners requiring safety straps on blower/injector assemblies to prevent 'popping' the stuff when the bypass valve couldn't handle a backfire under full pressure?  Seems like the flanged GMC would be tethered to the manifold better... but maybe I'm all wet.  Bench racing... ahh!  Wick

This is one of those niggly engineering buggers that works both ways.

On the one hand, the big fat mounting flange on the case as delivered by GMC, with big fat bolts holding it down, was undoubtedly 'stronger' than a bunch of smaller studs and nuts installed around the perimeter of the mating surface between case and manifold after the big ol' mounting flange and stiffening ribs were machined off.

On the other hand, as I mentioned above, sealing of the mating surfaces was said to be an issue on the OEM cases, as the mating surface on the case was essentially unsupported, so the perimeter fasteners, smaller but closer together and right on the face, installed out of necessity on the 'pruned' cases, would provide better clamping of the mating surfaces to each other.

When Ohio George and Sneaky Pete tooled up to cast their pre-'pruned' cases, they would have most likely heavily reinforced the mating area by using thicker material in both depth and width, so the flange itself would be stronger, and could accommodate larger fasteners as well.

The photo below illustrates the non-'pruned' configuration, with the big mounting flange made to take heavy hardware.

The photo below shows the underside of a case in the 'pruned' configuration, with studs installed around the perimeter of the mounting face (and also appears to be oriented upside-down compared to the one above...which you can do).

 

Edited 16 hours ago by Ace-Garageguy

[Wickersham Humble]

• Great photos!  Yep, I suspect when they re-engineered their cases, they took pains to make sure flanges were substantial.  Blowers, of so many types and designs, are a whole other story in rodding.  Never owned one, myself, but most could say that.  My wife's (late) cousin Jerry had a Graham or Frenzel centrifugal mounted to work on his 21-stud flat motor, but to my knowledge never got it going.  It was to be the secret weapon in his '34 coupe to knock off my PowerPak /55 Delray coupe, for the glory of Ford.  Lot's of Fords did that, but not his -- of course pitting a 265 against a 390FE (or Robert Hight's* 413) was not a way to top street honors in our tiny town (closer to OR and NV than CA, we always claimed!) but you're only 17 once!  Ah, the memories!
• I got to see Mick's Challenger at a car show, after his sad demise.  Interviewed him once, on the 421 Tempest SD racers of '63.
• Wick
• *Funny car driver Robert Hight's uncle, and name sake.  He had a '62 Sport Fury 361-B that could beat me too, after second gear.