Getting to the Tip of TPI

Everyone might not be ready to ditch their carb for fuel injection, but we doubt that too many would argue that, in most situations, an electronic fuel-injected engine will run better across the operating range. Retro-fitting OEM units onto earlier trucks has been popular for several years now, and the unit that really got the trend rolling was the '85-up GM Tuned-Port Injection (TPI). They not only looked trick but worked well. No longer the belle-of-the-ball, TPI-equipped engines are dirt-cheap these days. So we decided to take another look at a few of the differences that you should be aware of and what to look for when scouting the junkyards for one.

All '85-92 TPI units are basically the same. A few things changed over the years, but the TPIs on 305s are basically the same as the units on 350s, except for the injectors. The Corvette units are the same as the F-body units except that the fuel-rail fuel inlets are on the passenger side, and all Camaro fuel-rail inlets are on the driver side.

The '87-92 F-bodies were produced with both the 305 and the 350, but the Corvettes all had the 350. The '85 F-bodies and Corvettes all used a mass air flow (MAF) with a 1227870 computer. The '86-89 F-bodies and Corvettes used a 1227165 computer with mass air flow. All '85-88 models used a ninth injector for cold start, but the '89 models were the only ones where GM used the mass air flow computer and fired all eight injectors for cold start. The '90-92 F-bodies used the 1227730 computer and fired all eight injectors for cold start. The '90-91 Corvette used all eight injectors for cold start and used the heat resistant and water-proof 1227727 computer (designed to be used under the hood). All '90-92 F-bodies and '90-91 Corvettes had speed density and used a manifold absolute-pressure (MAP) sensor and not mass air flow. The older units can be converted to the more desirable speed density by changing the harness and computer for classic truck retrofitting applications.

Most people have heard that a mass air flow sensor is more desirable when changing the cam or making engine modifications. But, now that tuners have gained the ability to reprogram the computer chips, it's possible to get a better calibration and cleaner-running engine with the speed density.

If everything goes as planned, we hope to be installing one of these units in a truck and provide you with a few installation and tuning tips to help you get your classic truck into the fuel-injected age.

Here's an '87-91 Corvette intake designed for aluminum heads, but it can also be used on early cast-iron heads. When used with the aluminum heads and emission controls, the heat riser tube port (A) brings exhaust from the header to the intake for the EGR. The EGR valve port is shown here (B). Street & Performance supplies plates with gaskets to block off these two ports when used in non-emission controlled vehicles. These intake gaskets have a metal insert with a small coolant hole to allow a measured amount of coolant to exit the rear of the heads through to the intake.	This gasket is used on all other TPI intakes except Corvettes.	Here's a look at the top side of the fuel rails with the injectors. The '85-88 Camaro unit on the left shows the ninth injector and fuel line coming out of the front of the fuel rail. The '89-92 unit without the ninth injector is on the right.
The fitting on the left is used when converting '85-88 fuel rails to driver-side rear exit. The one on the right is used when plugging the '85-88 driver-side fuel rail to eliminate the ninth injector when using the newer-style computer that fires all eight injectors during cold starts.	The fuel inlets and returns differ between the different years. The '89-91 Corvette fuel rail (left) has a female 16mm passenger-side inlet and a female 16mm return. The '85-88 Corvette (middle) has a female 16mm passenger-side inlet and a female 14mm return. The '85-92 F-body (right) has a female 16mm driver-side inlet and a female 14mm return.	In order to convert from the metric fittings to a standard AN fitting, S&P offers these two new fittings--16mm O-ring to AN6 and 14mm O-ring to AN6.
Street & Performance can clean and match your injectors and provide O-ring, tips, and performance screens. The ones that you are most likely to be dealing with are the '85-86 F-body and Corvette Bosch Pintle injector with a plastic tip (left), the '87-88 F-body and Corvette Bosch Pintle injector with an aluminum tip (middle), and the '89-92 F-body and '89-91 Corvette multi-tech (Rochester) injector (right).	All the passenger-side TPI tubes (top) for all '85-92 models are the same. There are two different driver-side tubes. The '85-88 units (left) had the ninth injector port (arrow), while the '89-92 F-body and '89-91 Corvette tubes (right) didn't.	This cold start plug from S&P is used on a '85-88 driver-side tube to plug the ninth injector port.
The plenums break down into three groups--'85-88 (left), '89 only (middle), and '90-up (right).	The stock TPI fuel-pressure regulator used on '85 models was 30 pounds at idle; '86 and later models all used a 38-pound regulator.	Street & Performance offers an adjustable fuel-pressure regulator kit that includes upper gaskets, a tamper-proof tool for installation, and an adjustable regulator. The adjustable fuel-pressure regulator can be used to put 305 (19.9 pounds) injectors on a 327 to 350 engine or used with 350 (21.9 pounds) injectors on a higher horsepower 350 engine. A 300-horsepower plus 350 engine or 383/406 should use at least a 24.9-pound injector.
A large HEI distributor (left) with a self-contained coil in the top of the cap was used in the '85-86 F-bodies and '85-91 Corvettes. The '85-86 units were non-roller cam distributors. If an early-type distributor is used on a roller cam engine, you will need the GM 104560413 distributor gear. Early distributors have a twist-lock cap while the '85-up TPI HEI distributors had the screw-down-type cap. The small electronic distributor (right) was used on '87-95 small- and big-block injected engines. NOTE: truck distributors have a built-in rev limiter that can be change by using a Camaro module.