Looney

I just recently got an 87 tran am GTA and was wondering how to tell if its a 305 tpi or 350 tpi, no idea and if theres anyway I can improve mileage. I'm getting around 11 mpg being nice to it, any ideas??

Atilla the Fun

Start by replacing the exhaust oxygen sensor.

Wadebryant

The eighth number in the vin code is the key to the 305 vs 350 question. If it is a number 8, the car was orginally equipped with a 350. If it's an F, then it's a 305tpi.

87WS6

iTrader: (1)

The VIN code or RPO codes will tell you if it came with a 305 or not. Unfortunately the only way to know what engine is actually in the car now is to check the block casting numbers. Even that isn't 100% full proof as you could be dealing with a stroker motor and not know it. That aside it is a fairly reliable way to know.

The eighth number of the VIN will tell you if you have a 305 or a 350. You are looking for an "8" to indicate a 350 engine.

S = 173 ci V6 LB8 (1987-1989)
T = 191 ci V6 LH0 (1990-1992)
F = 305 ci V8 LB9 (1987-1992)
H = 305 ci V8 LG4 (1987)
E = 305 ci V8 L03 (1988-1992)
8 = 350 ci V8 B2L/L98 (1987-1992)
7 = 231 ci V6 SFI Turbo (1989)

There were no 350CID engines offered in the third generation F-bodies before 1987. Let no one tell you different because no one has EVER been able to prove there was. There is a persistent rumor about 50 some odd test cars yet no one has ever seen one. Even if they did exist at one time they probably all went to the crusher and never made it into the hands of the public. No 350CID engine was ever offered with the 5 speed manual transmission. So if your car came with a manual transmission it was not originally equipped with a 350. Some claim this was the case however Pontiac Historical Services documentation refutes this and again no one has ever proven otherwise.

If you have the RPO code sheet affixed to either your center console or in the rear cargo compartment lock box you can check the RPO codes. RPO code "L98" or "B2L" indicate a 350CID TPI engine. There is no difference between L98 or B2L but either would indicate it came with a 350. The other RPO codes for engines are L03, LB9, LB8, LC2, LU5, LG4, L69, and LHO.

LB8, 2.8L V6 Multiport Fuel Injection
LHO 3.1L V6 Multiport Fuel Injection
LG4 305, Carb
LU5 305, Crossfire Fuel Injection
L69 305, Carb, High Output
L03 305, Throttle Body Injection
LB9 305, Tuned Port Injection
L98 350, Tuned Port Injection
LC2, 3.8L V6, Turbocharged, 20th Anniversary Turbo Trans Am (1989 only)

Again the above information will only tell you what the car came with originally. You need to check the block casting information if you want to know what is in the car now. This information can be found on the "deck" behind the driver side cylinder head. You'll need a light and a mirror to read this information. Or you can crawl under the car and look at the last 3 digits of the block casting numbers which are shown on both the passenger side and driver side of the block. I can read this information on both sides of my block without too much trouble. Its easier if you have the whole casting number but the last 3 digits will suffice in a pinch. You'll need a flashlight and just the right angle to read these numbers. Again this isn't 100% either as it doesn't account for stroker engines. 327, 335, 383, etc.

Good luck.

As for your gas mileage, you should start with the O2 sensor but more than that you may have PROM issues, general tune issues or any number of other things going on. How does the car run? does it idle high, or have a surging idle? Do you get a SES light?

Looney

The eighth number is , so its a 350 umm, where is the O2 sensor located? and how much does one usualy cost? anyway to tell if its bad?, I don't know what an SES light is either, sorry Im very new to alot of this stuff. The car idles around 750-850 in park and runs steady.

87WS6

iTrader: (1)

The O2 sensor is located on the driver side exhaust manifold. The "SES" light is "Service Engine Soon." It appears on your instrument cluster when a problem is detected. As far as the idle, it should idle around 500-550rpm when in park or neutral once it reaches operating temperatures. (About 160 degrees or so.)

Looney

When I flushed the radiator in the car and was putting cold water in the car the idle dropped down to 500 and it idled that way until I stopped flushing it