Got valves?

"FastIndy" (FastIndy)
09/23/2014 at 11:00 • Filed to: Cosworth, DOHC, Fiero

Sure, you may know about GM's lone foray into greatness with Cosworth in the mid-1970's. The product of that unholy union was the Cosworth Vega. That car gained its share of mixed fame and notoriety. But what if I told you that wasn't the only time that GM mixed some British in with their 4-banger?

Pictured above is the Cosworth DOHC conversion cylinder head for the Pontiac Super Duty 4-cylinder engine. The head (and extensive accompanying kit) converted the 2-valve, cam-in-block Pontiac SD4 into a high-revving DOHC powerhouse. With the SD-4 available in displacements up to 3.0 liters, the potential existed for this combination to make some serious power, and it did. This Cosworth SD-4 powered Pontiac Fiero drag car ran into the high 9's, naturally aspirated:

But the Cosworth-Pontiac hybrid's true purpose was a little more noble: IMSA GTP class racing. Spice Engineering fielded the DOHC engines in the Pontiac Fiero GTP race cars in the Camel Lights series.

The Fiero GTP met some success in the Camel Lights series until it folded. The Spice SE86 chassis lived on with Ford Cosworth V8 power, even !!!error: Indecipherable SUB-paragraph formatting!!! in 1987.

Cosworth made the cylinder head kits in limited numbers. While the Cosworth Vega remains memorable, one of the most powerful GM 4-cylinder engines in history lives on in obscurity. To this day, its existence remains little more than a rumor. Indeed, the heads were made in very small quantities and are exceedingly rare.

(Photo Credit: !!!error: Indecipherable SUB-paragraph formatting!!! )

So how does a person combat this undeserved lack of fame and return to the platform some of its former pride and glory? Turbocharge it, of course! I found one of the kits several years ago while in the process of building an 8-valve Pontiac SD-4 for a 1984 Indy Fiero. I'm shooting for 800 horsepower out of a 2.6L build.

8V:

16V:

(Reposted for the morning crew)

DISCUSSION (4)

Jedidiah > FastIndy
09/23/2014 at 00:12

Was just reading about interesting 4 cylinders earlier today.

I learned many things about the Offenhauser, Quad 4, Cosworth Vega and now a Pontiac.

Good day.

Kanaric > FastIndy
09/23/2014 at 01:07

Shows how dumb GM was. They should of had this as a high performance trim on the Fiero. Pontiac Fiero Cosworth? Why not.

Birddog > FastIndy
09/23/2014 at 01:55

The SD4 was never offered in a production car. That's why it's overlooked. The production Duke was developed alongside the 301 using similar techniques and sharing some parts. (The Iron Duke was Pontiac's second 4 banger built from a cut in half V8.) Neither are recognized as great engines. In stock form at least.

I remember seeing the SD4 stuff in the depths of the GMPP catalogs back in the 80s through the early 90s. I think it'd be a blast to see one built and on the road.

Sweet Trav > FastIndy
09/23/2014 at 11:36

Great Write Up!

know anything about the OHC Pontiac Firebird Sprint Motors?