Not a Clone

 Here's the thing. When I bought my 65 K-code Mustang it had some Shelby GT-350-like modifications. First off, it's Wimbledon White and it has a blue rally stripe along the rocker panel. More subtle, it has Koni shocks, a Monte Carlo bar, and Shelby OTC underrider traction bars. Also, it is a special order DSO, like the Shelby cars. It has a Holley 1850-4 600 CFM carb (Shelby GIMD-9510-D) on a stock cast iron intake manifold. My 65 mustang's build date was Nov 1964 at the San Jose plant in California. This is the same plant that delivered all the K-code Mustangs to Shelby American to become GT-350s. The first three prototype GT-350s were built in San Jose in Oct 1964; the initial production run of K-code Mustangs were delivered to Shelby American in Jan 1965. That means my car was built between the three prototypes and the first production GT-350s. Since I have owned my 65 Mustang I've added a new SS Tubes fuel line that is bent for the GT-350 fuel feed. That means that it's set up for the LeMans bowl Holley 3259-1 carb on a hi rise manifold. 

On the 2026 Irrigation Festival week car show I was walking with my friends Scott, Chuck and Mike and we met someone they knew with a 64 1/2 Mustang convertible, Chris. He mentioned that he had a Shelby manifold that he didn't need and would anybody want it?  Well, yes, I said, and we agreed to meet the next day. So the next day we met and I made a new friend who gave me the manifold, a Shelby SFJD-9425-F,  just like that! Mustang people are the best! It was in very good shape, just surface scale but no corrosion damage. I had the manifold media blasted and powder coated by Matt at the Dog House. I like this manifold because it is an OTC speed part from the 1967-1969 Shelby Parts Catalog, not a reproduction, not a take-off from a GT-350 or Cobra or whatever. I want my car to display its speed parts like they were bought back in the day, after the new car warranty ran out. 

The other half of this story is with the Mopar people, specifically, my dear departed brother, Bob. He had been building carburetors for years out of his tiny house. And when he died I helped put his house in order, in a very big way. I loved him dearly and would have done anything to help but one of those things was coming into possession of his 1966 Plymouth Valient Signet Commando Formula S. Now this Valiant I have known since he bought it in 1967. He drag raced it with the original 273 V-8 Commando engine and 4 speed and then with a 340 with W2 heads and automatic. This car has seen it all, but amazingly, the whole time it wore all of its original trim and interior - all of it. So some time back in the early 90's he put the car back into the street and used a 360 crate motor that allowed him to run original LA series engine parts - to make it look like the original 273.  One of the things he did was to run a Holley carb with LeMans bowls to keep the height low so that he could run the original, Chrome, 10-inch air cleaner. Pure 273 Commando, just like factory original. Only now a 360. So this carb was from a Chevy big block dual-quad. A Holley List 4239-S which is a 4160 with no choke (like the back carb of a dual quad set-up) that was specially set-up for an Edelbrock manifold.  He had converted it to run a 5812 secondary metering block so that the LeMans bowls and transfer tube would fit. And it had 1 5/16 primary and 1 3/8 secondary (725-ish CFM) venturis and could be configured very much like a clone of the List 3259-1 that came from Shelby on the GT-350. On the Valiant it ran OK but had a big off-idle flat spot. I've rebuilt it, tinkered with its settings, and improved the flat spot but it's still there on the Mopar 360.

So, of course, I had to try it on the Mustang's 289 HiPo. And on the 289 it worked really well. The engine was very responsive off-idle and gave excellent power all the way up to where the secondaries open up and then it goes lean, surges and backfires. Its basically unrunnable on the secondaries. And again I tried resetting the float level and other tuning like replacing the secondary diaphram and spring without improvement. But I've had a taste of what it can do so I'm hooked and want that Shelby power. If I open up the 1968 Shelby Parts Catalog to page 17 I see that the carb I want is a GIMD-9510-B. But I'm getting ahead of myself.

I said that my brother's 1966 Valiant was a Signet Commando Formula S.  Look that up with your AI and it will say that the Signet was a trim level associated with the exclusive 2-door hardtop body. The Commando refers to the 273 CID engine with 4-barrel carb making 235 horsepower. In 1966 there were only 198 Valiants produced with the 273-4bbl “Commando” engine with the four speed manual transmission, this number includes Signet & 200 model versions with this power train combo. So a fairly rare performance option. But hold on a minute, the Formula S was a Barracuda only trim level, not offered in the Valiant line. Again, according to AI, "the 1966 Plymouth Barracuda Formula S was Plymouth’s dynamic response to the Ford Mustang. Featuring the high-output "Commando" 273 CID V8 engine, heavy-duty suspension, and Goodyear Blue Streak tires, it delivered authentic muscle car performance in a distinctive fastback package." Here's the actual product literature:

Bob knew that his Valiant had come with the optional HD suspension package and had the Goodyear Blue Streak tires on the wide rims and correct wheel covers. And the Barracuda was just a fastback version of the Valiant body and chassis. So really, all he was missing was the tachometer in a special dash. So, he figured that his Valiant was just the same so he went down to the dealership and picked up the Formula S badges and put them on. Done. Not a clone, a 1 of 1 vision of the Valiant that Plymouth never made.

According to the 1968 Shelby parts catalog, the GIMD-9510-B is equivalent to the 715 CFM Holley List 3259-1 with the LeMans bowls; the GIMD-9510-F is the 715 CFM with the cathedral bowls. Both are technically center-pivot bowls and the cathedral bowl superceeded the LeMans bowl. The 1969 Shelby catalog indicated that the GIMD-9510-F was the Holley List 4118. I have bought a Holley List 4118-S and I will clone the style of the List 3259-1 by replacing the cathedral bowls with the LeMans bowls I have from Bob's carb. Here's some inspiration for what I want to do with the 4118. AFS - Paul's List 4118 with added Lemans bowls By combining the Shelby manifold and Holley List 4118 carb I am making a representation of what could be bought directly from the 1967-1969 Shelby catalog of aftermarket parts. My goal is to recreate some of the power characteristics of the GT-350 (without the headers). Not to make my car into a GT-350 clone. It's a thin line of making the former without implying the latter.