AMC Gremlin vintage road racer

[mike343sharpstick]

OK here goes, IMSA Gremlin build
A buddy and I road-tripped to Virginia from Wisconsin last spring to get this thing. Long story short I LOVE race cars and AMC’s, and this came up for sale and the price was right. No log book and I have no historical photos as of yet.



What I do know is that the car was driven by two racers between ’75 and 80-something. From what I can tell the body is a 1974/75 model.
- Don Knowles: Raced in IMSA RS
- George Beasley: Raced IMSA RS and a few SCCA events at Summit Point about '79 or so, sponsored by Pegasus motorsports.

It’s been stored off-site until a few weeks ago when I brought it home. Initial inspection shows the first thing it needs a new cage. What I want to do with the car is first hit some SCCA AutoX events to learn how to drive, and then participate in some Vintage road racing events when I’m relatively sure I won’t embarrass myself.

What’s really cool is that the wife and kids are on board with the project! When I sheepishly asked my wife if this is something that could happen, her response was, “Sure, but it has to be Purple”. That was that, and now it’s in the garage!

What I need to do first is build a cage to meet current SCCA specs, haven’t done that before. A good friend is a professional welder so for the finish welds I’ll be able to have him lay the final welds, I can do the fitment work and tack it together on my own.

From what I have seen it all starts with the placement of the driver seat, I bought a Kirkey aluminium seat and some metal to get it properly fastened to the floor. From there the main hoop, and so on.
The overall goal is getting the car from here:

To something like this, but not the R/W/B paint scheme:


First major question is this, What Tube diameter to I need to build the cage with? I have the SCCA General Competition Rules & Specifications document. Section 9.4 spells it out the regulations pretty clearly, however I do not know the weight of the finished product, so what tube dia. Do I need to use.
Here is the chart:

GCR Vehicle Weight Tubing Size (inches)/(outer diameter x wall thickness)
Up to 1700 lbs 1.375 x .080

1701 - 2699 lbs 1.500 x .095
1.625 x .080

2700 lbs and up 1.50 x .120
1.750 x .095
2.00 x .080

Do I just go with 2.00 x .080 tube dia and be good no matter what or is that foolish. Do I go for 1.625 x .080?
Is there a chance a gremlin could weight more than 2,700 pounds?
Probably not but I have no basis to make an educated guess, a stock Gremlin weighs 2,633 pounds per Wikipedia.

Here we go!!!

[hauen]

Cool project! If it were me I'd just go with 1 3/4" tube and be done with it. You'd be surprised how heavy even a small American car of that vintage is. My '78 Fairmont in race trim was 2477# without me in it and it was about as chopped and gutted as you could get and still be considered a "stock" car.

[racingsnake440]

This is going to be cool! Looking forward to the updates. What running gear plans? I think there's a fair chance of it weighing around 2700# so I'd probably just use the 1.75 too. Our Lemons 3rd gen Camaro is right around 3000# and it's pretty well stripped.

[Bamfster]

I tend to over build stuff so I say 1 3/4" too.

That thing is cool .... I've wanted a gremmie for years.

[stangbanger]

sweet project! Are you keeping/ hopping up the straight six?

[mike343sharpstick]

I-6 is required for Vintage Group 8 participation. It's already equipped with a header, offy intake and a holley 2bbl. I have no idea what's under the valve cover yet? When/If I need to change the I-6, I was thinking a high compression E85 motor would be a low buck, good performing race motor.
All just ideas at this point, focusing on the cage and main body structure now. Hard to do with this ADD always blind-siding me, LOL... look! a shiny penny!

Ughhh, focus!

Obviously a V8 will fit easily in the engine bay, and I currently have 2, the stock 343 that's currently in my Javelin, and a 401 that I'm building for said Javelin. Do you suppose the 401 will someday find its way into a caged road race gremlin ;)

It has running gear that should handle such a power-plant, it also already has a T-10 and a Heavy Duty AMC 20 rear axle with a spool (or a very tight Limited slip), panhard bar, rear anti-sway bar, etc. etc. all good stuff but in dire need of a rebuild.

[Huskinhano]

I'm lovin this! I'm digging the six. AMC built some pretty tough sixes. They used 1/2" bolts on the main bearings. Man, if that was in my driveway I would be sooo tempted to fire it up and go around the block as is. Still have the keyed axles?

[mike343sharpstick]

I have the name of some local fab-shops, S&W sells a cage kit for the gremlin, but it's only available in 1.75 Dia. by .120 wall. I'm just not good with using that much wall thickness (2.17 pounds per ft.) when I only need .095 wall with 1.75 dia. tubes.
It's not the design I want to use so it would need some customization anyway.

I've narrowed the prefered tube dimensions down to two possible options for the 2,700lb and up requirement.
Dia (in) Thick(in) Weight (lb/ft)
1.75 0.095 1.596 lb
1.5 0.12 1.769 lb

I find it interesting that the 1.75 thin-wall tube is lighter that the smaller 1.5 dia thicker tube, so that seems to be the best option.

[SuperBuickGuy]

.... and now you have a great excuse to buy a tube bender. I bought the Eastwood version of the bottle jack and pendulum design - it works okay, but it needs a higher capacity jack for .120 wall 1 5/8.... (in case you were thinking about purchasing it).

[milner351]

I have the HF bottle jack bender, a gift from a friend for making his ranger pre runner style tire gate. He used .120 wall tubing and it required filling the tube with sand before bending to prevent crushing / wrinkling the tube. Not exactly convenient. If you were closer you'd be more than welcome to borrow it - but it's a heavy sob - shipping would make it cheaper to buy your own.

Go with the 1.75" .095" wall - that makes more sense IMHO.

[mike343sharpstick]

I am going to work with one of the local shops and see how that goes before I consier my own bender.
I "try" not to buy tools I can only use once, LOL. Plus with 4 cars and two motorcycles in my 3 1/2 car garage I'm kinda out of room for a tube bender.
Hoping if I buy the tube from the local race shop I can get it ben't for a reasonable cost. Then I can cut it, notch it and tack it together at home.

[t russell]

cool car

[Bob Holmes]

Make sure you only use DOM tubing, not ERW. ERW is not allowed by the SCCA.

Also realize that the large tubing is required for specific required items, you can use smaller tubing for other areas.

Best cage building thread I know of is at Corner-Carvers:

http://www.corner-carvers.com/forums/showthread.php?t=27556&highlight=roll+cage

While safety is the primary purpose of a cage, a very close second is to use it to stiffen the chassis for better performance. However, you need to carefully review the class you intend to enter, as it may be very restrictive on the number and type of attachment points allowed.

Bob

[milner351]

Bob - are there manufacturing markings on tubing that calls out the alloy and construction? DOM has no weld seam correct?

[mike343sharpstick]

Thanks Bob, I have been reading the SCCA General Competition Rules & Specifications document, exciting stuff, lol.
I also spent a bunch of time looking and photographing lots and lots of cages this summer at several vintage events. I also contacted some folks in the VSCDA and a co-worker that races in local SCCA events.
Lots of info out there and my head is swimmin'!
Now I need to read the 35 pages of that thread closely, I bounced through it quickly, Awesome.
Stuff like this shows the seriousness of cage construction.


In my previous racing career when things went bad you would just hope the bounce didn’t hurt ‘too’ much. Also a good idea to let go of the bars, but there were occasions when you thought you could save it until the bitter end and get your hands squished a little. Oh, and this is important... don’t try and stand until your totally stopped. LOL.
Oddly I can joke about that but bouncing around in a cage freaks me out a little.