I own an '85 Trans Am with an '87 350 TPI. I've seen a lot of cars in your magazine that have a TPI, but instead of a Mass Airflow Sensor they use a direct bolt-on air filter. How is this possible? Everyone I talk to says that doing this will throw the computer into a limp mode. I would like to get rid of all that plastic junk up in the front of my car, but don't know what to do.
North Richland Hills, TX
They're right-simply remove the MAS (Mass Airflow Sensor) on a system requiring one and the engine goes into "limp" mode. There is an alternative but, as we'll see, it's no panacea. The '90-'92 production TPI engines use Speed Density air/fuel metering in place of the earlier MAS. While the MAS must be located in front of the throttle-body within the inlet tract to provide real-time measurement of the air mass inducted into the engine, Speed Density metering relies on Manifold Air Pressure (MAP) and Manifold Air Temperature (MAT) sensors that screw into the intake manifold. Whereas the MAS system directly measures airflow into the engine, Speed Density systems rely on a preprogrammed map of values that relate engine speed, vacuum, and air temperature to engine air flow.
Major performance changes to the engine require "remapping" the Speed Density computer's preprogrammed lookup table. The direct-measurement MAS is more forgiving of engine changes or modifications-at least up to the point that the MAS itself becomes a flow restriction (about 325 hp for the GM production TPI MAS unit). On the other hand, the somewhat bulky MAS is harder to package in a nonstock installation, which is why most custom TPI swaps use Speed Density; with the MAS deleted, they can bolt an air filter directly to the throttle-body. Unfortunately, for similar tight-clearance reasons, most of these swaps use those little horsepower-robbing, restrictive square air filters. And, the nonducted bolt-on air cleaner setup sucks in hot underhood air instead of cool ducted ram-air from the front grille area. That's not good because every 10-degree-F air temperature increase results in a 1-percent power decrease. For example, if the engine compartment temperature was 150 degrees F and the outside air temperature was 80 degrees F power would be down by 7 percent! Why shoot yourself in the foot?
Converting from MAS to Speed Density requires a new computer (remanufactured PN 16198262; may be labeled "1227730"), an appropriate PROM chip for your application, a different knock sensor (PN 10456549), a MAP sensor (PN 16137039; stamped "039," "460," or "466"), and a new TPI wiring harness (contact TPI Specialties or Howell Engine Developments). The existing MAT sensor works. Stock Speed Density TPI intake manifold plenums had an extra bung to mount the MAP sensor, but you can mount it with a "tee" arrangement off your existing manifold bungs. The new wiring harness won't have wires for the ninth cold-start fuel-injector, which is no longer required; just leave the extra injector in place to seal up the hole in the intake.
But why hassle with all this when there's a way, as suggested by TPI Specialties, to clean up the ugly Firebird right-angle induction tract while retaining the MAS sensor? Install the cleaner '85-'89 Corvette-style induction tract that gulped air from a large, flat air filter assembly located directly in front of the radiator. Remove the Firebird's existing top radiator plate and (if so equipped) A/C condenser support brackets to lean back the top of the radiator and condenser as far as you can without the electric fan hitting the belt drives. Make (or have a local sheetmetal shop fabricate) new top support brackets out of a 0.060-inch aluminum plate to support the repositioned radiator and condenser. The new angle provides clearance for the "over-the-top" Corvette induction tract routing. The Corvette induction tract is shown in the accompanying parts list; you may retain the Firebird MAS unit.
Howell Engine Developments
6201 Industrial Way
Marine City, MI 48039-1326
TPI Specialties Inc.
4255 County Rd. 10
Chaska, MN 55318-9226
What's The Diff?
I have a '72 Olds Cutlass fastback with a 350 Rocket backed up by a TH350. I am almost done with this project except for the rearend. I want to replace the open diff and 3.23 gears with a posi and 3.73s, but I am having a very hard time finding parts. If I use a rearend out of another GM A-body, will it be a basic bolt-on part except for the U-joint? If not, what modifications are needed? If it won't work, who has parts for the 10-bolt that's under it now?
Kansas City, MO
Any '68-'72 GM A-body rearend bolts in as a complete assembly, although a conversion U-joint may be required. However, there shouldn't be any problem finding parts for your car's existing rearend if it's the original factory-installed item: Unlike other A-bodies of the same vintage, the '71-'72 Buick Special (includes Skylark) and Olds F-85 (includes Cutlass) came with the 8.5-inch ring-gear "corporate" 10-bolt rearend. Ring-and-pinions and differential cases from many other trucks and passenger cars (including the '71-'81 Camaro/Firebird and '73-'77 A-bodies) fit, plus there's a huge selection of aftermarket parts available.
Performance With A Price
I drive a '79 Volvo 262 Bertone with a '90 Mustang H.O. 302, AOD trans, and all computer functions intact. I'm running cast-iron manifolds to 2-inch pipes to a single three-way cat. From there back, it's Volvo 1 7/8-inch pipe with a muffler from a six-cylinder Camaro. I drive the car a lot and really appreciate the quietness. What do you feel is the minimum-size exhaust that I should use, and will a freer-flowing exhaust really help my gas mileage?
Drexel Hill, PA
Up to a point, reducing exhaust restriction generally helps gas mileage. But going too large can overscavenge the engine and result in a mileage reduction. Proper exhaust size is a function of both engine output and displacement. Ford used a full 2 1/4-inch dual exhaust system on the Mustang, complete with dual cats and mufflers. Assuming the engine is stock, in theory, 2-inch dual pipes should be adequate, as indicated by the accompanying exhaust system recommendation chart courtesy of Flowmaster Mufflers. Specifically, it's the 1 7/8-inch single-pipe and weak, little, single six-cylinder muffler that's holding you back. If there's insufficient room for dual pipes and mufflers after the converter, use a single 2 1/2-inch pipe and corresponding low-restriction aftermarket muffler. The converter inlet and outlet should likewise correspond to the inlet pipe sizes.
2975 Dutton Ave.
Santa Rosa, CA 95407-7800
Ford Motorsport sells the Tremec heady-duty five-speed under PN M-7003-R58.
I have a '68 Ford Ranchero that I have been wanting to upgrade to an overdrive Tremec 3550 five-speed in place of my current four-speed Top Loader. Will it bolt to my bellhousing and allow me to use my stock clutch and linkage? I know I may have to modify the driveshaft and other things.
The Tremec five-speed uses the Top Loader trans-to-bellhousing mounting-bolt pattern, but its standard input shaft length is the same as an '83-'93 Ford V-8 T5-about 5/8-inch longer than the small-block V-8-type Top Loader. Spacer plates are available from Dark Horse Performance, McLeod Industries, and Total Performance that let you bolt a Tremec up to a stock-type Top Loader bellhousing or equivalent aftermarket scattershield. Alternatively, the correct-length (shorter) input shaft and required corresponding shorter bearing retainer is available from Tremec distributor Dark Horse Performance. Either way, the stock clutch and clutch linkage remain unaffected.
Overall, the Tremec trans case length is about the same as the Top Loader, but the mount is slightly further back. If installing the Tremec using a bellhousing spacer plate, slide the trans-support crossmember straight back from the forward C4/four-speed frame holes so it lines up with the rear C6 mounting holes, retaining the mount pad's normal forward orientation. If installing the Tremec using the optionally available short input shaft, use the rear C6 mounting holes, but flip the crossmember around backward (which actually puts the mount closer to the front).
The special "short" input shaft lets the existing driveshaft and 28-spline yoke bolt up to the standard Tremec 3550 with no mods required (with the spacer, you'll need to shorten the driveshaft 5/8-inch). Heavy-duty TKO Tremecs require a 31-spline C6-style yoke.
Dark Horse Performance
16617 SE 134th St.
Renton, WA 98059-6923
1600 Sierra Madre Cir.
Placentia, CA 92870-6626
44050 N. Groesbeck Hwy.
Clinton Twp., MI 48036-1108
A Flock Of 'Bird Questions
The '89-'97 Ford Thunderbirds came with an IRS; was there ever a limited-slip differential offered, perhaps with the Turbo Coupe? Are there aftermarket units available? What ring-gear size was used and are there performance gear sets available?
On another matter, was there ever a factory installation of a Borg-Warner T5 behind a 2.3L four-cylinder? I'm not sure which tranny was in either the SVO Mustang or the '84-'87 Turbo Coupe T-Bird. I need part numbers for the bellhousing if you could. Also, what type of clutch mechanism was used-cable/linkage or hydraulic?
T-bird IRS: Most '89-'97 T-bird (also '89-'96 Cougar, '93-'98 Lincoln Mark VIII, and '99 Cobra) IRS (independent rear suspension) rearends use essentially Ford 8.8-inch-type components. A few of the T-birds and Cougars came with the weak 7.5-inch diff; not suitable for performance use, it won't be covered in the following discussion.
Internally, the IRS units are similar to the corresponding Mustang/passenger-car solid rearends with much component interchange. Stock and aftermarket ring-and-pinions listed for the 8.8 differential fit the T-bird housing.
Ford Trac-Lok limited-slip differentials are a common factory option on both IRS and solid 8.8s, but differential interchange is a little tricky: Whether standard or limited-slip, Ford original-equipment production, Ford Motorsport, and aftermarket differentials designed for the 28-spline Mustang/passenger-car 8.8 rearend can't be swapped into the T-bird housing as complete assemblies due to differences in the axle retention method (31-spline "truck" 8.8 diffs don't fit because of dissimilar axle-spline counts). However, the current Ford original-equipment service-replacement 28-spline 8.8 Traction-Lok complete differential assembly (PN E9SZ-4026-B) is a universal unit that fits both the Mustang/passenger car solid rear and the IRS 8.8 housing.
A Ford 8.8 original-equipment Mustang/passenger car production Trac-Lok (as well as the Ford Motorsport diff, PN M-4204-F288) can be made to fit the T-bird by swapping in T-bird side gears (PN E9SZ-4236-C, two required). Auburn Gear recently introduced an 8.8 T-bird limited-slip diff (Auburn PN 542080) that's available through selected distributors like Tom's Differentials. Finally, Ford Motorsport also offers an 8.8-inch aluminum IRS carrier assembly (the entire housing) complete with Traction-Lok and 3.73:1 ring-and-pinion under PN M-4001-M373.
2.3L T5: The Borg-Warner T5 was available behind 2.3L engines starting in 1983. The input shaft was unique to the 2.3L engine, so V-8 versions won't interchange. Platforms include Mustang, Capri, Cougar, and T-bird. Ratios, shifter location, and shift linkage may vary per application. T5s from '85-and up are the stronger "World Class" version. The last year for the T-bird/2.3L engine (and corresponding trans) usage was 1988. Various bellhousings were available, depending on model year, clutch size, and type of clutch linkage. T-birds had cable clutch linkage through '86 (2.3L/T5 bellhousing PN F1ZZ-6392-A, replaces E3ZZ-6392-B, also fits Mustang through '86). T-birds used hydraulic linkage in '87-'88 (bellhousing PN E7SZ-6392-A, not replaced). If you have trouble finding a 2.3L-compatible T5, try Stick Only.
Auburn Gear Inc.
400 E. Auburn Dr.
Auburn, IN 46706-3499
Ford Motorsport Performance Equipment
44050 N. Groesbeck Hwy.
Clinton Twp., MI 48036-1108
9900 Glenoaks Blvd.
Sun Valley, CA 91352-1018
18150 Foothill Blvd.
Fontana, CA 92335-8510
15709 Paramount Blvd.
Paramount, CA 90723-4332
I have a '90 Camaro RS that I would like to mount some new wheels and tires on. The car right now has 15x7 wheels with P215/65R15 tires. I just bought a brand-new set of '97 Camaro Z28 16x8 rims, and P245/50ZR16 Comp T/As to go along with them. These new wheels have too much backspacing (6 3/4-inches), so can you tell me whether any company makes adapters or spacers to fit these rims on my car? If I use a spacer will this be safe for a daily driver?
Vette Brakes offers bulletproof wheel spacer-adapters. Made from heat-treated aircraft aluminum, they're available from 3/4- to 3-inch thicknesses in 1/4-inch increments. Strong enough even for racing (if legal per sanctioning-body rules), the adapters use separate fasteners to retain the spacer on the hub and the wheel on the spacer. You'll need to tell Vette Brakes the required spacer thickness and whether the spacers need to fit U.S. or metric fasteners.
Vette Brakes & Products
7490 30th Ave. N.
St. Petersburg, FL 33710-2301