1991 GMC Sonoma Autocross Truck - A Tale of Independent Supension, V8 Power, and Scope Creep

Damn, missed the update from the departedMephitidae and only noticed because of todays posts.  There's a high likelihood of me heading down there in the next 2-3 months.  I will certainly PM if I do.

In reply to classicJackets :

I don’t own a truck but I’m down to ride along.  Booked solid this weekend, maybe next?

Mid-ohio next and out again the weekend after.. I'll shoot you a text, maybe I can get down there and just bring a bunch back up for the people on this thread.. so we can get more autocross Sonoma!

In reply to classicJackets :

Brilliant!  

Progress has been pretty slow, as I've been taking advantage of the good weather to work on non-automotive projects. . .

Getting very close to done on walling in the carport on the sides of my garage, I'll have all sorts of room for shenanigans then!

Also worked on accumulating some parts, and finally have enough to start doing something with. Starting with a transmission, a low mileage Aisin AR5 out of an 06 Colorado 2WD.

Then came the engine management, an ECUMasters EMU Black. Cheapest one I could find that could do drive-by-wire.

Then a Quarter Master twin disk. . .

With a custom drilled flywheel. . .

And a flex plate to engage a starter motor. . .

And finally, the piece de resistance, a 4.2 Liter Inline 6 from a recently wrecked GMC Envoy. I've been waiting for a good one to come up for months, and waiting for the engine to make this post. 

Now to put it all together!

Oh this is good! Very good.

This is a rad project. Nice score on that circle track car with all the parts it donated. Atlas inline six is a fun choice too. Have you seen the Plymouth Road Racer being built by Phil Greden (aka Murilee Martin) with the same engine?

Question about the front suspension setup though: is there any way to flip the wheels and mount them backward, to reduce the massive negative offset? It looks like your scrub radius is immense, from the photos. Maybe I'm misunderstanding but it looks like a go-kart setup with that much scrub. Would be nice to get the Dave Point inside the contact patch, at least.

Hey Dude, can you link to the Plymouth build you're mentioning?  I need something to read and that sounds interesting.

Google

murilee martin 1941 plymouth

Last I heard it still dosn't run, and is in wiring limbo.

In reply to pres589 (djronnebaum) :

Here it is... all of his posts in one place: https://autoweek.com/diy/1941-plymouth-road-racer

Phil is a super interesting dude. In addition to his numerous talents as a writer, he's one of the main 24 Hours of Lemons judges and the arbiter of all things BS-related and theme-related in that series. He has an awesome series of photo postings on Instagram too where he uses 100+ year old cheap film cameras to photograph junkyard cars.

I remember reading his write-up about how he got to about where he was at the time on TTAC.com.  His tech/photog/writing work seemed both really in-line with my own interests and also kind of not stable enough for me to want to try and make a leap into vs. what I think I'm doing now for work.  He's worked on some cool projects.

In reply to Duder :

I already have wheels with 4 inches more back spacing picked out to correct that issue, but good eye! There is a reason I made sure to get a power steering rack as well.

That's one way around the "no available domestic manual trans option." I like it.

In reply to gumby :

It's a shame the clutch setup was ungodly expensive. . .

whiskey_business said:

In reply to Duder :

I already have wheels with 4 inches more back spacing picked out to correct that issue, but good eye! There is a reason I made sure to get a power steering rack as well.

Sweet, good thinking. We don't want no scrubs...

Awesome dude! And also I wonder why the carport space wasn't closed in in the first place...

In reply to Robbie :

I actually do know, the previous owner of the house had a massive camper he parked on the side and a shed for a pool pump and filter in back! All that is long gone.

Also, the more I visit this thread the more I realize the title is completely wrong! Mods, could you please change the title to something more appropriate for something that has no V8 power, and no independent rear suspension?

Edit: Maybe something that references al the circle track bits?

In reply to whiskey_business :

Enclosing the full dimensions of the concrete pad is quite an upgrade.  I like where this is leading.

Good seeing you again last night Elliot!  Garage upgrade will be a great working space.  I’ll catch up with you on clutches when I drop the 3 speed out of the Cougar for the TKO600. 

In reply to wawazat :

Good to see you too Todd, hope the throwout bearing works for you!

I have had totally awesome luck with this thing in the past few days. 

It started off with a bit of a low point, I got a bit sloppy removing the exhaust manifold and broke off two bolts in the head. Drilling was almost pointless, as they were Grade 8.8 bolts, and my parts store EZ-Out acted softer than the bolt material. Not fun.

But, with a cold beer in one hand and a hot TIG torch in the other, I was able to build up the broken bolt pieces far enough to grab with vice grips. And voila!

Second bit of my streak was the aforementioned Quarter Master clutch, which will from now on be referred to only as the Hail Mary. For some reason, I thought that without having located and measured an engine, or even having seen one in person, I should order a custom drilled flywheel at huge cost. I blame my impatience and self-inflicted lack of progress on the truck.

Better yet, I had the flywheel patterned off a flex plate ordered from RockAuto, and sent directly to Quarter Master without even seeing it first. 

But, it appears to all have worked out fine, and I'm on my way to buy a lottery ticket right now. The bolt pattern and pilot diameter are perfect.

Which will make this the first ever twin-disk clutch attached to a GM Atlas 4200, and one of very few manual transmissions. Fingers crossed that the good fortune holds up!

Hold off on the lottery ticket...you used up your good luck for the moment ;)

Seriously...cool stuff happening for sure!

In reply to ClemSparks :

Small progress and some frustration. The stock intake would be a tight fit to the hood line, so action was taken.

Separated the stock plastick intake runners from the flange with a band saw, so that the flange could be used as a pattern on a piece of 4"x24"x.5" aluminum flat bar stock. Learned a valuable lesson about measuring before purchasing material.  . .

Well, I guess I can use that for something else. 

Measure once, cut twice!