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 14 hours ago 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 9 hours ago 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