Carystone92

Hey guys, I have the 1992 Z28 LB9 305 TPI, it also has the five speed, out of the factory the LB9 in 92 with the 5 speed made 230 to the wheels, my engine was rebuilt by the previous owner and it runs well, but I would like to turn that 230hp into 300hp atleast.

Here is what I was thinking.

1: Port and polish heads, intake, runners and plennum.
2: Headers.
3: 3-31/2 inch catback with Flowmaster 80 series.
4: 22# injectors.
5: Comp cams XR258HR12.
6: 9th injector delete.
7: Throttle body coolant bypass.
8: Throttle body spacer?
9: A tune up.
10: High output spark coil.
11: MSD distributor?
12: Finally a tune with a new chip.

Let me know what you guys think.

Thanks.

Ty92Z

iTrader: (11)

Unless you have the G92, the hp rating on an LB9 M5 is 205. That is at the flywheel, not at the wheels. To get to 300 at the wheels, many here are going to recommend a 4 inch bore kit be installed in your 305. There is not a 9th injector on the 92.

sofakingdom

iTrader: (1)

No it didn't. It made 230 at the crank by the factory's "rating" system of the time, for whatever that's worth. Those cars were usually around 175 - 180 at the wheels, at the time.

Of all the things on your list, the only one with big payoff is the headers & exhaust. (in general... not sure about the Slowmaster 80, never had one that I know of, I had some Blowmaster shortly after they came out and I. HATED. IT. It was like dragging a 55-gallon drum tied to my bumper 100% of the time. I cut it off and gave it to one of my littlest bro's friends and I don't think he kept it long either) Cam and head porting are good ideas too. The rest (other than "tune-up"... basic maintenance, restores to "original" a part of what has been lost over time, is not a "mod") is either of no consequence or is detrimental. In particular, the larger injectors aren't a good idea. The ignition stuff is a waste of money and only decreases reliability below stock without returning any detectable benefit.

Conspicuously missing from your list is, adjustable fuel pressure regulator.

"New chip" is the wrong way to think about it. Tuning, yes; "buy a chip", not so much. Spend some time on the DIY PROM forum on this site instead.

truckerz

iTrader: (2)

Everything sofa said.

Another option, vortec heads and intake base, along with that cam, or a hotcam, headers, and a tune. A real tune diy or at a professional tuning shop with experience in OBD1 systems.

bjankuski

I had a 305 TPI 5-Speed and ended up with about 315 HP at the engine (260 HP at the tires) with these mods:
-350 Vortec heads
-Felpro 1095 head gasket .015 compressed thickness
-ZZ-4 cam, your cam choice is OK
-SDPC vortec base hand ported to fit the heads and open up the runners
-Arizona speed and marine large tube runners
-Custom chip by myself

Car ran 13.51 in the 1/4 at 101 MPH with street tires