Im wondering specifically what makes the horsepower ratings different for all the 305's. Before someone mentions the Tech link, yes I have checked it, its nice to look at but doesnt explain anything .

Im wondering, what makes the differences for power in the LB9 vs. the LG4 specifically. I am using a complete TPI setup from a 87' LB9(auto.) Trans Am on my 87' Monte Carlo LS's LG4. The LG4 on the Monte is rated at 150hp and the LB9 car was 190hp. From what I have read the heads are the same, as well as the block itself. All that differs is the roller cam vs. flat tappet cam and TPI vs. carb. Right? Or am I wrong.

Im making my LG4 a roller motor with the LB9's parts, but will be using a 88' 5 speed TPI roller cam, so no peanut for me .

Is the only difference in the 87' auto vs a 88' 5 speed the cam and exhaust?

I will be using Hooker smog legal headers with a gutted out cat/Hooker dual exhaust(2 mufflers/MCSS style) which I think will add a combined 30-40 hp(stock the LS has a single wimpy exhaust and restrictive cat.) and the roller cam Im thinking will add 10 hp too. Only other mods will be a K&N with a 88-89 air intake extended farther from the engine, maybe porting the plenum.

What do you think the hp/ft lbs will be about with those mods on a LG4(along with the TPI)?

TIA

 

The LG4 used in the 1987 Camaro was rated at 165 hp (Sport Coupe) and 170 hp (Z28). I have no idea why the difference. I don't know why the 1987 Monte Carlo LG4 was rated at a lower 150 hp.

1987 190 hp 305 TPI (Auto)
The short blocks for the 1987 LG4 and 305 TPI are identical, including heads and "peanut" cam. The differences are the induction system (carb vs. TPI) and exhaust. The LG4 used exhaust manifolds with 1-7/8" outlets and a 2-1/4" system with corrugated bends. The TPI used exhaust manifolds with 2-1/4" outlets and a 2-3/4" mandrel bent system. This would explain the 20 hp delta (170 vs. 190).

1987 215 hp 305 TPI (5-speed)
The only difference between this engine used with the manual transmission and its sister used with the automatic (190 hp) is the cam.

Speaking of cams, both engines above use the roller cam. The flat hydraulic cam was last used in a Camaro in 1986.

1987 auto vs. 1988 5-speed
I've outlined the difference between the 1987 auto and 1987 5-speed above. The difference between the 1987 5-speed (215 hp) and 1988 5-speed (220 hp) is only the cam. Both were rollers, but had slightly different specs:

1987
#14093643
Lift: 404/415
Dur @ 50: 202/207
LSA: 114.5

1988 - 1989
#10088155
Lift: 415/430
Dur @ 50: 207/213
LSA: 117.0

Both cams were also used in the 350. The 1990-92 version was slightly milder, making the 1988-89 variant the best stock cam used in a third gen Camaro. Hope this helps.

 

Thanks alot for the reply, it helped shed some light, for me anyways.

Did the 87' 5 speeds have dual cats too? I just always wondered if the cam alone gave it the 25 more hp.

If I use the 88-89 5 speed cam with my 87 LG4 motor and the TPI(using stock wiring/everything else) I guess it should run at least 215 hp then with the Hooker headers/catback. That is all in speculation of course.

 

Did the 87' 5 speeds have dual cats too? I just always wondered if the cam alone gave it the 25 more hp.

Cam only. The dual cat system was first used in 1989.

If I use the 88-89 5 speed cam with my 87 LG4 motor and the TPI(using stock wiring/everything else) I guess it should run at least 215 hp then with the Hooker headers/catback. That is all in speculation of course.

Sounds reasonable to me.

Willie

 

It was 165hp for the 87 LG4 in all g bodies. Not 150hp. haha, it seems like everytime someone talks about a 305 they're always badmouthing it and they always state the hp rating at least 10-15hp lower than what it really is. They usually get called 145hp. Now the late 70's 2 barrel 305's they were low hp!

Sounds like its gonna be a good motor in your monte. With under 100K on it, it should last quite a while too, I'd say its worth doing the mods your doing. I like the fact that my 305 Cutlass is an 87 so I can put a roller cam in it easily.

 

I believe its 150...Im sure I could be wrong but I think its close to being accurate. The Grand Prix LG4 is rated at like 160 or so, but I think thats for marketing reasons since they had no high output version of the GP. The LG4's in the f-bodies were rated at 165-170 and they had more free flowing exhaust than the LG4 g-bodies for sure.

The 350's in the late 70's had 150hp hehe .

Im also glad I have a 87' motor so I can swap it to a roller cam so easily...

 

77-79 LM1 350 is 170hp at 3800 rpm and 270 lbs torque.
LG3 305 2 bbl is 130hp :-)

I really thought all 87+ LG4's in g bodies were 165hp. Maybe I'm wrong.

 

Well Willie, I can tell you the Z28 had an electric fan, but the MC SS had a clutch fan. There's a handful of horsepower right there. Other than that, I can't imagine what the differences might be. Why did you settle for a LG4 one when there's so many L69 ones around?

Yeah those late 70s 350s were a real terror werren't they??? I had a bunch of late 70s Z28s, I could not believe how much faster the L69 was when it came out.... I got one as soon as I could afford one. It was so much faster than the 350 I traded in for it (79 Z28 350 with a Comp HE 268 cam and Holley 650 carb) it wasn't funny. It would totally rip a new one out of those joke Vettes with the CFI 350, probably a good half-second faster in teh 1320 at least. But people still to this very day want to hear about what a 350 with their 882 or 624 heads that they have laying around will run like. Too bad I don't have time slips; I bet that 4-speed car was low-16s, and the 78 auto car I had at the same time was high 16s or low 17s.

Just goes to show, cubic inches may be real important, but you can still screw up a motor no matter how many of those you put in it.