AMT Sock-it-to-Me Corvette MSP: Gasser Suspension Dynamics 101, Jan. 29

[Ace-Garageguy]

NOTE: Though technically this is a drag-car and should possibly go in the "Drag Racing" section, I've posted it here because it addresses several of the many issues confronting builders of this particular kit (which can be built many different ways, but ALL of them will be affected by this kit's shortcomings).

NOTE 2: I strive for technical and historical accuracy with most of my work. Though this class of car was one of my favorites in the way-back-when, there weren't a lot of them running in my part of the world at the time. Information on the web about these things is sketchy at best, so if anyone sees me doing something wrong, PLEASE feel free to mention it. I appreciate input from people who know what they're talking about.  

The build that follows is based on the fairly recent release of this kit...      ...which I bought entirely because of the box-art.

I'd wanted to do an old early-to-mid-'60s modified-sports (MSP) drag car for some time, and this AMT kit looked like a likely starting point for something along these lines (below).

Look close and you'll see this thing has a gasser stance, but WAY more engine setback, and also appears to be a one-piece clone body (no door seams). This is in keeping with the MSP rules, which allowed 25% engine setback (defined as the distance from the front axle centerline to the first spark plug hole, as a percentage of wheelbase). True gassers could only run a 10% engine setback, and were built under more restrictive rules generally. The MSP class was never very big (though it was one of my favorites) and ended up getting lumped in with the "altered" class eventually, which was quite similar in specification...other than the bodies.

When I actually OPENED the box, to say I was disappointed is an understatement. Though there are some neat parts in it (and the decals look GREAT), the body is really kinda poor, and the chassis is the typical old AMT blobular style with molded-in everything. The "gasser" parts are not well done either (I was hoping for something much better), so I decided to hack it into what I wanted while using up some other 50-year-old parts in the bargain.

The first problem is the nose. The white body on the left is from the SITM kit, with ridiculously undersized headlights. The shape and profile of the front of the hood is also entirely wrong. Compare it to the red body, which is the old AMT '59 Corvette (Reggie Jackson version in this case). While the red '59 still isn't right, it's a lot closer than the SITM version.

Next big problem is the chassis. On the left is the SITM unit. Wrong frame-rail design, stuff molded in, etc. Far right is the blue chassis from the Revell Miss Deal Studebaker funny car kit. It's obviously C1 Corvette...which I hadn't realized until this point...but Tim Boyd had used this chassis under something similar some time back, so I opted to use a glooey earlier MPC C1 chassis, in the center.

I had an extra AMT '59 upper nose floating around from another project's leftovers, so it got loosely grafted to the front of the hacked-off SITM body, all on the old gluebomb chassis.

I used the SITM firewall and some strip stock to mock up and jig the chassis in position with the rails parallel to the rockers, at the right height relative to the body. I found a mystery Ford 9" with some slicks, decided to use the lift bars from the Miss Deal kit, and mocked up a straight axle in the front.

All mocked-up with the engine in about the right place, etc.

 

 

 

Edited January 29, 2019 by Ace-Garageguy

[DumpyDan]

Interesting build

[Pim]

looks good mate are you going to finish it? 

[vintagercr]

I will be watching

[James2]

oh boy...

[Rider]

Wow, some great detail/correction mods going on here, really great stuff.

[Rascal]

Ive been spending a lot of time in this section looking for some inspiration for my junk-yard/yard-sale chop-shop build. You guys do some really neat stuff! Well done on the body mods, can't wait to see how this polishes up

[Johnt671]

This looks like it will be a real challenge and a nice build. I do like the Corvettes up to the late 60's. Good luck.

[Snake45]

I just bought an AMT '59 last month with the idea of maybe trying something of this exact kind. So you KNOW I'll be watching!

[geewhiz]

You're doing a great job making the SITM Vette look like something resembling a Corvette...I love where you're going with this project and I look forward to seeing the updates!!!

[Jantrix]

Looking good. Give us some more.

[Ace-Garageguy]

My sincere thanks to everyone for their interest and responses, and as mentioned above...if anybody sees I'm going off track and doing something not technically or historically accurate for the old MSP class, PLEASE bring it to my attention.

Though this is a "what if" model, I would like it to be correctly representative of this type of old drag-racing car.

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I removed the tacked-on nose to begin careful final-fitting, made up some little mockup spacers for the rear end, removed the center X-member (it won't clear the lift-bars), and began filling the hooyahs where the original frame made detours around the font suspension. 

Here, I've adjusted the mocked-up front straight-axle (partially to determine whether I'll need to use a dropped axle or a straight one to get the stance I'm after, and partially to see if a transverse spring will work...which is easier to make...or whether I'll need to do semi-elliptics parallel to the frame rails), and mocked up the rear axle (to determine whether I can use coil springs or again, semi-elliptics). I've also put in some temporary stanchions to hold the body at the right height relative to the frame. The front of the frame rails has also been extended to pick up and support the front of the body.

Here, the body is sitting on the stanchions and the frame is sitting on the hard-mocked suspension. The major dimensions and stance shouldn't change after this. The nose has been trimmed and carefully fitted to the SITM body shell, checked for square and about the right droop in front. I've also made some 'lips' on the nose to later be filled, in an effort to get a 'face' that more closely resembles the real 4-eyed Corvettes.

The engine in the first mockup was a Buick nailhead I just happened to have lying on the bench (from another ongoing build).

The engine I'm actually using, in an effort to do most of this build with old-school parts available around 40-50 years ago, is based on the old AMT 409 from their first '57 Chevy. We're going to pretend it's the rare 427 Z-11 version of the W-block. The blower, injection and drive are based on old Revell Tony Nancy double-dragster parts, while the Vertex magneto and T-10 gearbox are from an AMT parts-pack.

Engine mocked up in the chassis. The W-block isn't the best possible engine to use here, as the location of the plug holes tends to make the engine need to sit farther forward in the chassis than some others would to comply with the 25% setback rule...but the 409-427 was the biggest Chebby available at the time this model is supposed to represent.

Once the engine was pretty well where it goes, Lefty was kind enough to help me fit the thing for a driver. The extreme amount of engine setback made it necessary to set the driver's seat rearward too, and the back of the cockpit had to be trimmed to allow for this. Lefty is a big guy, a 1/24 figure that would be a 6+ footer weighing at least 220 in 1/25, so if he fits the car, just about anybody would.

 

 

 

 

Edited December 18, 2016 by Ace-Garageguy

[Ace-Garageguy]

I put a crank-centerline stub on the front of the engine, and made up a front mount-plate, using the jigs I'd made earlier to hold the engine in place while measuring and fitting the plate. Lefty helped with test-fitting too, to keep me honest about foot-room so somebody could actually drive the thing if it was full-scale.

The first mount-plate I recall seeing in reality was at the bellhousing ends of the Pontiac engines in Mickey Thompson's Challenger I, built in 1959. Though I'm certain they were used prior to that, trying to ferret out the history of engineering features on race-cars on the internet can be frustrating. Often, sources don't agree with each other, and then also you get endless repetition of just flat wrong info. There's no reason front and mid plates couldn't have been used on a car like this built in the early 1960s...but I don't know for sure if they were. But since this is a what-if model intended to represent what could have been built at the time, it's OK with me if nothing actually was.

The bellhousing was removed from the engine with my new favorite tool, one of the the .007" thick photo-etched saws from MCG.

Before I finished that cut, I decided to remove the old trans to make way for the parts-pack version. Doing this now let me "machine" the rear face of the bellhousing to insure it would be square with the engine and perpendicular to the crank centerline.

Once the bellhousing was separated from the engine block, I filed a groove and installed a piece of styrene rod to simulate the crank and gearbox centerline.

Using the angle of the front plate established with the trans in place, as well as the extended crank centerline, I was able to mock-up the engine block at the right angle relative to the rear end. There is another temporary fixture under the oil pan, just visible here, that held the engine stationary so I could measure and make up a mid-plate to hold it there permanently. The fitting mockup shown is cardstock.

Taa daa. Dimensions and angles from the cardstock mockup transferred to styrene, which fits exactly.   

 

Edited January 1, 2017 by Ace-Garageguy

[Jonathan]

That's some nice work there!

[Ace-Garageguy]

That's some nice work there!

Thank you sir!

With the mount plates in place, the roll-cage is moving pretty quickly. Should have some more updates shortly.   

[DrKerry]

Love it!!!!!!!

[DumpyDan]

This is looking better and better, great stance.

[espo]

Outstanding engineering on this build. I like the old 409 engine idea.

[Ace-Garageguy]

Kerry, Dan & Dave...thanks for your interest and comments.

Far as the engineering goes, I build them as close to reality as possible...which is one big reason I often get bogged down. It's sometimes actually harder to do something and have it look good in 1/25 scale than it is in 1:1. You simply can't get in there to measure and fit and paint, etc., so 1:1 techniques and ideas don't always translate easily to model cars.

Still, I enjoy the additional challenge of working out as many of the major functional details as I can...and I'm really trying to keep this one going through to completion.  

[doggie427]

Love this build and all the little refinements that make it realistic. I especially like the tip of using a rod to establish  the crank centreline. 

 

 

 

 

Edited January 2, 2017 by doggie427

[geetee66]

Wow!

So many modifications!

this is going to look amazing when you finish it.

[D. Battista]

A lot of work so far....looks like you've got it steered in the right direction. I like where you are going with this... and I have learned some modeling tips by watching your work.

Good job so far....  any choice on body color yet ? 

[James2]

I always enjoy some scratch building and your doing some nice stuff here. I do have a question. 

The original car engine set back does not appear to be as drastic as your rendition.  And though the opening is larger than the blower, the block seems to end where the fire wall would be. Your model has the blower cut clear into the dash! 

Is this intentional or am I missing something?

I'll brace myself and wait for an answer...

[doggie427]

Modified Sports Cars were allowed a 25% engine setback ( like an altered) and unlike the gassers and street roadsters which were limited to 10%.

[Ace-Garageguy]

... I do have a question. 

The original car engine set back does not appear to be as drastic as your rendition.  And though the opening is larger than the blower, the block seems to end where the fire wall would be. Your model has the blower cut clear into the dash! 

Is this intentional or am I missing something?

 

doggie427: "Modified Sports Cars were allowed a 25% engine setback ( like an altered) and unlike the gassers and street roadsters which were limited to 10%."                                                --------------------------------------------------------------------------------------------------------------------------------------------------------------------------

Exactly.

I appreciate the interest in this thing and as I said at the beginning of the thread, if anyone sees me doing something that doesn't reflect technical or historical accuracy, please feel free to call me on it. Really.

Most of my models are intended to accurately represent period-correct cars, though usually not replicas of specific cars. I try to do enough research to get in the ballpark, but I've been known to make a mistake or two.

The "25% setback" dimension is arrived at by measuring the wheelbase of the car and dividing it by 4 (25%). This number is then used as the maximum allowable distance from the front axle centerline to the middle of the farthest-forward spark-plug hole.

The scale wheelbase of this little car is approximately 105". 25% of that is 26.25", so to be class-legal, the front spark-plug hole center needs to be a maximum of 26.25" back from the front axle centerline.

This dimension is marked roughly as the vertical line on the side of the body in the first mockup shots. In the first mockup shots, the engine is definitely too far back. You'll notice the front face of the blower housing is several scale inches behind the reference line.

As the build has progressed, I've taken more care to get the dimensions reasonably close to accurate. If you'll have a look at the most recent mockup shot, you'll notice the front face of the blower housing is now in line with the 25%-setback reference line on the body. The front face of the blower housing is roughly in line with the forward spark-plug hole, so we're really pretty close to class-legal.

HOWEVER...

I used a Buick nailhead for the early mockups, and I've since switched to a Chevy W-block.

I remarked earlier that the W-block wasn't really the best engine to use here, but I didn't fully elaborate.

The nailhead's (and many other engines) forward plug hole is somewhat farther forward in relation to the rest of the engine than the W-block's forward plug hole (see photos below).

This results in a class-legal installation of a W-block placing the engine slightly farther forward in the chassis. In the case of this particular model, the W-block is actually 1.25 scale inches too far back to be strictly class-legal. I decided to allow this 1.25 mm discrepancy to remain, rather than correcting it after I discovered it. The engine placement would be class-legal and correct for some other engine choices, and the look of the car would be identical...with the blower cutout appearing as it is.   

                                                             

 

 

Edited January 2, 2017 by Ace-Garageguy