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Project Sten TPI Engine Buildup

A V8 for the Sten

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Back in the Mar. ’11 issue, we introduced Project Sten, our low-buck, lightweight, V8-engine-swap S-10 pickup. The idea was to find the most affordable, lightest, shortest-wheelbase vehicle we could stuff a small-block into and have some autocross fun. We found the ’90 S-10 on Craigslist for $1,100, and after quite a bit of research, it was time to start assembling our small-block.

We initially considered stuffing in a 5.3L LS truck engine (or an aluminum block 5.3L, such as the one Jeff Schwartz used in his little brown Vega), but we decided car crafters would probably be attracted to a more affordable small-block. This seemed like a more cost-effective solution that still offered the potential to make power. The one issue that makes a California project like ours complicated is that this engine must be emissions-legal. California has rules about engine swapping on emissions-controlled vehicles, and Rule No. 1 is that you must install an engine from the same year car or from a newer vehicle. So we couldn’t put an 11:1 compression ’70 LT1 in our S-10.

With a ’90 truck, this limited our choices. We chose to simulate a ’90 Camaro 350 TPI engine using a one-piece rear/main seal block. We say simulate because we already had half the needed parts lying around the shop, so it seemed like a good idea.

Our very first step (after purchasing the Sten) was to buy a book about swapping a V8 into an S-10 by Mike Knell of Jaguars That Run (JTR). We quickly discovered that we’d be forced to use the ultrarestrictive F-car iron exhaust manifolds. That is because no one makes a legal S-10 swap header. Several companies offer headers including Sanderson, Hooker, Hedman, and others, but none carry a California Executive Order (E.O.) that would make them legal as direct replacement headers. If you don’t live in California, do whatever you like. We’d suggest shorty headers. They fit better and offer more ground clearance. The worst part about the factory manifolds is that the passenger-side manifold necks down to a ridiculously tight inside diameter of 1.55 inches. That’s just stupid. No wonder the TPI Camaros were pigs.

We bring this up not to whine but to offer the reason we did not build a really powerful engine—the exhaust manifolds are equivalent to stuffing an Idaho spud in the tailpipe. The stock horsepower rating for a ’90 TPI engine was only 245, so there’s certainly room for improvement, but we estimate that around 275 hp is all we can expect out of this engine. It might sound lame (let’s face it—it is lame!), but when we plugged 275 hp into the Quarter Jr. dragstrip simulator, it spit out a 13.50/102-mph estimate, even with a pedestrian 2.20-second 60-foot time. This is achievable mainly because we expect the truck to weigh in at 3,000 pounds with driver and fuel.

So we’ve only hit the wave tops on building this engine after doing this story way too many times before. This is actually the engine we originally assembled for the Feb. ’09 issue (“A Boat Anchor into a 611HP Screamer”). If you remember, we stopped after breaking a piston. A postmortem inspection also revealed a cracked cylinder wall. So it was back to Jim Grubbs Motorsports again for a sleeve. That’s when Grubbs asked, “Did you know this cylinder has been sleeved before?” Apparently, the previous shop did a good job and a new sleeve would not be a problem, but it was feeling like someone just poured boric acid into an open wound.

Our prospects improved mightily after JGM completed the block machining and we finished assembling the long-block. Our intention was to follow the spirit of the emissions laws (assuming the California Air Resources Board doesn’t read Car Craft), because neither the TPIS cam nor the Dart heads have E.O numbers. However, the cam is mild enough to pass a smog check with no problem. The final piece in the puzzle was engine control. We’ll deal more with this issue in a later story, but the current plan is to start with the stock TPI speed density computer connected to a new Painless wiring harness. We’ll have to make some changes to the chip to compensate for the camshaft and bigger fuel injectors, but it’s possible the engine will run decently with a stock PROM. We’ll get some chip help from our friends at TPI Specialties, as this OBD-I computer requires a chip to be burned rather than the now more refined method of merely digitally reflashing an EEPROM. Eventually, we may try an aftermarket computer just to make life simpler. It won’t be emissions-legal, but we figured other readers who are not encumbered with California-style emissions rules might want to see more flexible alternatives. With that said, let’s dive into our Project Sten TPI motor.

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