I just got a 91' Z28 305TPI Auto, it's stock right now, as far as I can see. (Still a much better improvement than my 86'305 4 brl.) I was just curious about 3 things. First off I was wondering what are the 1/4 mile times some of you'll got with a car like this. I'm guessing low 15's. My friends say mid though.....(Damn negative import guys) Also what is the horse power rating on these stock. I keep on sites the the 5 speeds are rated 25hp more. How is that posible. My last question is just if you'll know anyone who's used a sneaky pete nitrous shot on one, and what'd it run with that. Thank for any help answering these questions!

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91'Z28 305 TPI

 

I've seen magazine tests that have it running 14.9(BS) to 16.1(BS). My best guess would be somewhere in the middle, between 15.3 and 15.6 (just a guess) based on some of the cars I've beaten in races. The car has 205 HP. I believe the 5 Speeds had 225 or 230, but they had different cams.

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1991 Firebird Formula
305 TPI
Auto
K&N Filter
Grant GT Steering Wheel
5% Rear tint
Pontiac Windshield Decal
No real mods yet!

Former owner of an 88 2.8 Firebird....RIP

 

really the cams were differnt!!! I looked through like 5 sites that said the were the same cam. (Damn unoffical internet info) Thx for the help man

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91'Z28 305 TPI

 

The cam is the same for all 90-92 LB9 cars. Don't believe anything else. The HP difference comes from the exhaust. The entire exhaust, from the manifolds to the exhaust pipes exiting the muffler, are smaller than that of the G92 (5 speed) 305 TPI. In fact, it's the same as what the 305 TBI cars have. 2 1/4 inch cat and cat back, 2" y-pipe, and dinky manifolds.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

 

Forgot to answer the original question. Mid 15s is what you'll run, most likely, at somewhere between 87-90MPH. That stock exhaust really kills performance. I installed a Flowmaster catback and dropped .3 and gained 2MPH. Free/cheap mods like a ported plenum and shimmed fuel pressure regulator were worth about another .3 and 2mph. Since the stock manifolds are so small, headers and a Y-pipe should be worth a similar amount.

 

Thanks for the info guys. I'm glad you confirmed that the 5 speeds and Auto's have the same cam, cause it was driving me crazy trying to find the difernce, after the guy told me they were differnt. So from what you'll said, I'm looking at mid 15's. I hope the sneaky pete will get me low 15's than.

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91'Z28 305 TPI *stock for now*

 

Sorry for the misinformation, but thats what Ive been told in the past. Mr. J is right about the exhaust though, ask any of the owners about exhaust swaps and you'll see gains like his!

 

no problem dudelovett. Thanks anyway man. My only question I still want answered if anyone knows is the benifit of a sneaky pete on one of these stock? Thanks again everyone

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91'Z28 305 TPI *stock for now*

 

Interesting... I have never heard this before. Although it may be true these cars got different exhausts, it is a fact that they did not receive the same cam. Before I get into the cam, I'd like to state that previous to 1990, all TPI Camaros did in fact get the larger exhaust. So it seems inconceivable to me that GM would install the "TBI" exhaust on TPI Camaros in 1990.

As for cam info, according to the Camaro Technical Database, the cam is different for 1990-92. Here's camshaft info directly from this source:

305 5-spd / 305 Auto
Tach yellow line--4500
Tach red line-----5000
GM Part No----10088155
Lift-----------350/384 (can you say "peanut"?)
Duration @ 50--179/194
Lobe Separation----109

G92 305 5-spd / 350 Auto
Tach yellow line--5000
Tach red line-----5500
GM Part No----10111773
Lift-----------413/428
Duration @ 50--202/207
Lobe Separation----116

I tend to believe this information simply because the "better" cam listed was used exclusively from 1990 - 1992. It was modified slightly from the "better" 1988 - 1989 cam.

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Willie

Supercharged 1987 305 IROC-Z, Daily-Driver, Emissions-Legal.
12.57 @ 111 mph.
12.04 @ 114 mph (50-hp nitrous).
http://members.optushome.com/au/downunder1/rides/willie/willie.html

1987 "20th Anniversary Commemorative Edition" Z28 Convertible -- Super Chevy Show Class Winner, 1998.

[This message has been edited by Willie (edited January 13, 2001).]

 

Wow man, thanks for all that info. But as far as I could see from what you wrote, it looks like the 305 5 speed and auto had the same cam. UNLESS you had the High Output 305 5 speed, which utilized the 350 L98 cam.

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91'Z28 305 TPI *stock for now*

 

jesus h christ, we are going to confuse the **** out of this guy. Willie, the GM Factory Service manual for 91 and 92 Camaros and Firebirds lists one LB9 cam. The horsepower difference between the G92 and non G92 305 TPI comes from the exhaust, not the camshaft. The Camaro Technical Database is in error. The existence of the TBI exhaust may seem inconcievable to you, but I've already seen the truth with my own eyes, and so have others.

Check out this thread.
https://www.thirdgen.org/messgboard/...ML/000717.html


The cam is the same. I've done mild mods to my supposed 'peanut cam' car and am running 94MPH in the 1/4. If I have the peanut cam, then so doesn't every other 305 TPI, G92 5 speed or not.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

[This message has been edited by MrJ (edited January 13, 2001).]

[This message has been edited by MrJ (edited January 13, 2001).]

 

Nah man I'm not confused. I'll take your word on the exhaust. I'm pretty positive now there is no cam deference

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91'Z28 305 TPI *stock for now*

 

In the TBI section (recent post) a guy bolted on a TPI intake and fuel pump to his old TBI LO3 engine.

The old TBI motor made same power a 305 TPI auto made.

Sound like the auto 305 TPI and 305 TBI got the same cam?

Maybe the exhaust was the same too?

Would this imply the only real difference in a 305TBI and 305TPI auto was the intake and fuel system?

 

No, it's a proven fact that the heads are different... the 305 TBIs have a weird 'swirl port' head design that is supposed to promote low RPM torque. It's also pretty much proven that the 90-92 305 TPIs have a different cam. The GM factory service manual specifies only one camshaft for LB9 cars, and it's the same one as the 350 TPIs. Also, a member of Thirdgen.Org, Madmax, pulled the cam out of his 91 LB9, measured the specs, and found it to be the 'good' cam.

The exhaust is so damn tiny (yes, it's the same as an LG4 or L03 exhaust) that it's severely choked from the factory. I'd be real surprised if swapping a set of 350 TPI exhaust manifolds and the Y-pipe wouldn't be worth a solid 25hp.

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91 Trans Am WS6
Bright White
5.0 TPI auto
Flowmaster 3" 2 chamber catback
Trans Go shiftkit
2000 stall converter

Built on Wednesday

 

When did MadMax get a 91 LB9? Last I heard he had an 86 Trans Am.

And does he know if that 91 engine is from a G92 car or not?

 

I figured you'd show up. His 305 TPI is out of a 91 Z28 NON-G92 car. He pulled the cam and showed me the specs:


202/207
.413/.428

how much more proof do you need?

 

Here are the complete specs I got, I borrowed the comp cams format:

ENGINE: CHEVY SM BLK 305-350
INTAKE EXHAUST
VALVE ADJUSTMENT HYD HYD
GROSS VALVE LIFT .413 .428
.006 TAPPET DUR 259 265

VALVE TIMING OPEN CLOSE
AT .006 INT 8 BTDC 71 ABDC
EXH 61 BBDC 24 ATDC
THESE SPECS ARE FOR CAM INSTALLED
AT 119 INTAKE CENTER LINE

INTAKE EXHAUST
DURATION AT .050 202 207
LOBE LIFT .2750 .2850
LOBE SEPARATION 115.5

The exhaust center line is 112. The only spec that was off was the lobe separation, which was off a degree, its supposed to be 114.5. I never found spec for valve timing events, so I assume they are correct since everything else checked out ok.