What exactly are the differences between these two engines? I know that the L69 is the high output, and the LG4 isnt. But they're the same displacement, ect..

My dad, who has owned several 3rd gen Z28's said that the only difference was the Cam.

The reason I'm asking is that I was pretty certain that my 305 was a HO, but doing some research, i sadly found out it wasnt.

So anyway, would adding a double roller timing chain, some roller rocker arms, and headers bring the HP up to par with a stock L69, or am I fighting for a lost cause?

The L69 has a different cam and higher compression. It might also have different heads and intake?

the whole exhaust system is slightly larger and contains a less restrictive catalytic converter. It does have a different camshaft grind and a higher compression ration, i think around 9.6:1?? It's been awhile since I've looked up the specs on it, I think there's a link somewhere on the main site to thirdgen.org with more info.

Heads are the same.

You might try a search. The topic has been covered fairly extensively.

JamesC

The main difference is that the pistons are different. They are set up to give a higher comp. ratio than the LG4. The heads are the same as LG4's. The cam is different as is the exhaust. They came with either the 5 speed or auto. You could also get rear gears in the 3.42-3.73 range.

So the blocks are the same? I could just put in new pistons, a different cam, and a new exhaust system and it'd be technically a 305 H.O.?

Seems like I remember the intake valves were larger on L69's too, 1.84 vs 1.71 but I don't remember for sure.

Pete Cento, 84Z28 L69, T5, 3.42 posi disk

Okay, one more time...

Heads are the same. No differences in valve, port, or chamber sizes. Same casting in fact.

Pistons were only different through 1984. '85-up, LG4 got the 9.5:1 compression, and at the same time got the knock sensor and electric fan (L69 had KS and EF up to that point).

L69 got better exhaust manifolds, y-pipe, cat, and cat-back. L69 got a better cam. L69 got the dual-snorkel air cleaner. The PROMS were slightly different. L69 typically came with better rear gears.

In some LG4's, the secondaries were limited in how far the AV would open (that's easy to fix - see tech article).

If you have an '85-up LG4, an aftermarket cam, complete exhaust from headers to rear bumper, and dual-snorkel air cleaner will make you equal to or better than an L69.

Allright, thats all I wanted to know. Thanks guys, this board is the greatest!

So an 85 and up LG4 has 9.5 CR right? If so that clears up some confusion since some places say 8.5CR.

I found this on the Monte Carlo site. Seems like they remember the same as I did, valves in L69 were bigger. L69's also had the electric fuel pump before LG4's did as well.

Pete

**************************************************

http://www.darklair.com/monte/l69.html

Starting with a standard issue Chevy 305 small block, here are some interesting notes:

both use aluminum intake
early LG4 models had a cast iron intake however
both use the same heads
casting: 601
58cc chambers (60cc ?), 178cc runners (158cc ?)
valve size in L69 heads were larger
L69 : 1.84/1.50
LG4 : 1.76/1.46
L69 has 9.5:1 CR (flat tops) [these numbers changed]
LG4 has 8.6:1 CR (dished pistons) [these numbers changed]
L69 has a special cam, from the L-81 Corvette (hydraulic)
This is NOT a roller cam
L69 uses a performance calibrated PROM
L69 takes advantage of special exhaust/catalytic converter
L69 takes advantage of a higher stall torque converter
L69 : approximately 1900 RPM stall
LG4 : approximately 1200-1500 RPM stall
L69 uses a better fuel pump (from the Z/28)
the changes in the L69 setup yielded *roughly* 30 more horse power
the same changes actually yielded slightly less peak torque for the L69, but had the advantage of a flatter torque curve overall

Back to the main Monte page.

Pete,

I have 601 castings and before I worked them over they had 1.84" intake valves. I also had an iron intake manifold.

I think some 305s just collected all the leftovers that GM had laying in the parts bin

That's got a bunch of wrong stuff.

The head castings were 416 on both engines. I still have one of them from my L69.

The L69 cam is not the same as the L81 cam (thank goodness). That was the old useless 929 cam. The L69 has what was a new cam at the time, a good bit more cam than the old gutless 350s had.

The L69 and LG4 valves were the same size, 1.84" intakes.

The torque converter was no different.

The fuel pump was the same.

The torque was about the same from year to year, but the LG4's torque peak was at 2000 RPM (!!!!) while the L69's was at 3200.

The differences were: pistons, the LG4 had dished in earlier years, but L69 had flat-tops; cam, the LG4 had the "peanut cam" which is even weenier than the 929, the L69 had its own; electric fan vs. clutch fan; exhaust manifolds with 2¼" outlets instead of 2", large oval Y-pipe and catalytic converter with large 4-bolt flanges at each end, instead of the old pellet-bed cat; 2¾" I-pipe and 2¼" tailpipes, instead of 2¼" I-pipe and 2" tailpipes; 3.73 gears instead of 2.73, 3.08, or if you were real lucky 3.23.

Here's some facts.

https://www.thirdgen.org/newdesign/tech/techdb.shtml

Canadian-only ballast...

Your 305 probably came out of a truck too.

What we're more than likely going to do, is put a set of high compression pistons, and a crane cam in there. I've had my heads polished and ported, so they're good.

The hard part is going to be convincing my dad not to use those crappy LG4 manifolds, headers are too expensive, $300+ for headers that are emission legal.

Can anyone recommend a good, inexpensive set of manafold exausts?

Good and manifolds don't belong in the same sentence. The only reason I would go with manifolds is if you're racing and there's a rule against headers. I'm sure there are emission legal headers out there for less than $300. I think the hedman's are smog friendly and they are $100, and $100 for the y-pipe. Besides, you'll gain 30hp from headers, but if you're dead set on manifolds the 89-up tpi manifolds are best other than the ram horn manifolds, but they don't fit on thirdgens.

Could be that early LG4's had the smaller valves or it could be that other earlier non f-body 305's had the smaller valves. My SBC interchange manual is showing some 305's with 1.71 intakes. I have the original service manual for 84's but they don't have that kind of info in there. BTW I have a set of the good exhaust manifolds from a TPI350 (as far as I know) as well as the L69 manifolds which will be replaced by headers if your interested. They both have the same outlet size.

Later and Merry Christmas
Pete

Hah! What makes you say that?

Oh thanks!

For 3rd gen's, what RB said is correct. Although where the myth comes from that LG4s had smaller valves than L69s is way back when (in '76) when the LG4 was introduced. It did have smaller valves and an iron intake manifold, but sometime in very early '80s, GM up'ed the valves sizes and switched to aluminum intakes (just prior to the L69, and 3rd gen intro). Also the carb's secondaries were jetted differently (as was the "tuning").

All third gen F-body 305's came with 1.84" valves. THe ****ty 1.72" valves came on truck motors and other low perfomance motors.

Guess again, emissions legal hedmans for an 85 5.0L are 360 bucks Whereas the non-emission legal ones are 160. It doesn't make much sense, its just a little tube for an oxygen sensor, dont know why they'd mark em up so much.

The emissions-legal, $360 set includes A.I.R. tubes, O2 sensor fitting, and the y-pipe.

Sorry, that post was incomplete.

Here's what I intended to say:

Canadian-only ballast...