Irhal

I will lay my hands on a pair of 305 HO heads... where can I find casting numbers to see if they really are HO heads and what can I do to them to make them flow even better? or is that gonna kill my LG4? I'll stick a cam in there plus a 3 inches exhaust... not sure how much better it'll be but I'm sure it's better than nothing... any thought on that? advises?

tilstad

I thought the lg4 heads where the same, or nearly the same as L69 heads which I'm guessing you're reffering to. It was the rest that was different if I recall it right. airbox, cam, exhaust, manifold etc.

ljnowell

lg4 and l69 heads are the exact same casting number IIRC. The main difference between the engines were pistons (in the early lg4's they were dished), and cam.

Irhal

why would someone look for those heads real bad then? is it urban legend? I always thought HO engines flowed more air... I guess it is only because of the cam?

ljnowell

Those heads are desireable, every time I go to the pick your own yard I check for a pair. They are very good heads for porting and bigger valves. They perform well on a 350.

Irhal

alright I'm lost... you're telling me that there is no differences and yet you are looking for them in a scrap yard? I have to do some bodywork for a friend of mine and he offered to give me a pair instead of money, plus a cam... what can I do with those heads? what is different?

ljnowell

Yes there are no differences, and yes they are decent heads. They are not aluminum aftermarkets by any means, but with work they are good. The heads were not the problem with the LG4, it was everything else.

Irhal

ahh alright, thanks

ljnowell

As for what to do with them, sitting bull has a good thread on head porting, follow his instructions and they will flow nicely. Also, you need bigger valves.

tilstad

I think what he's trying to say is that lg4 and l69 heads are way better than say tbi heads. And on a 350 the small chambers would give a little higher compression. I don't think he means that lg4 heads are better than say a -86 350 tpi (L88), but better than late 70'ties 350 heads on the 140hp(?) versions which is the most common of them all.

screaminformula

the only difference between an L69 and an LG4 is a cam and compression ratio...at least that is what pretty much all literature states...

Josh

tilstad

And the dual snorkel aircleaner, which don't come cheap these days.

screaminformula

well yea, i knew that one (AND NO THEY DON'T COME CHEAP!!) but i was referring to internal engine differences...

Josh

Irhal

I gathered that the chambers are smaller and the valves are different in the 305 HO heads... now, if this is true my question was.. is it worth bolting them on my LG4?

five7kid

iTrader: (14)

Okay, one more time:

LG4 and L69, at least in 3rd gens, used the same head castings, 416 from 1982-1986, and 081 for 1987 LG4's. The chamber size (at least as far as the factory is concerned) is determined by the casting. Therefore, LG4 and L69 will have the same size chambers.

The '82-'84 3rd gen LG4's had lower compression because they had dished pistons in them, which, when combined with the 58cc chamber 416 heads, produced 8.5:1 compression ratio. The L69's and '85-'86 LG4's had flat top pistons with 4 valve reliefs that, when combined with the 58cc chamber 416 heads, produced 9.5:1 compression ratio. If you want to keep the compression ratio up in that range, use a steel shim head gasket like the factory did when you put it back together.

And, for the record, 3rd gen LG4's and L69's all used 1.84" intake and 1.50" exhaust valves.

If you want to improve the performance of an LG4, you do the following: Replace all of the exhaust with headers, y-pipe with 2-1/2" downpipes to 3" at the cat, 3" cat, and 3" cat back to 3" inlet muffler (single 3" outlet or 2 x 2-1/2" outlets is your choice). Replace the cam with something with a little duration and lift (I like mine a lot). Replace the valve springs with something that can handle the lift of the cam. Upgrade the ignition coil and module with aftermarket pieces. Replace the single-snorkel air cleaner with a dual snorkel unit, either a factory type or fabricated one (see the tech articles on the Board home page for the latter). If you want, further improvements can be had by having the heads reworked for 1.94" intake valves, and cleaning up the port bowl area (do a search for porting, you'll find out what is required). Pinning the rocker studs or having the heads machined for screw-in studs is a very good idea with an upgraded cam & springs. If you want, you can put an aftermarket performance intake on it such as the Weiand Action+ or GMPP q-jet intake manifold.

Irhal

your reply, five, should be made into a sticky or a tech article... that way no more urban legend about HO engines... thanks

tilstad

Yeah, that was what I was trying to say too 57kid, but you put it so much more accurate and precisely.

Now that the thread has been answered, how big a gain would you say that a dual snorkel airbox would be on a otherwise stock lg4?

Or, should one swap, cam, airbox or a manifold first? Exhaust is a bit down the line for me, no kat as of now.

What would be a cheap, and good bang for the buck cam on the lg4? A used one perhaps?

Irhal

as for the cam... is there a way to know the specs of one when you get it used? I guess a machine shop can measure it for you?

tilstad

I guess that could be done... but I was more in the thinking of getting a stock cam, like a lt1 cam or something. But I don't know which one will be best suited.

Irhal

oh and you speak about a dual snorkel airbox... wouldn't a rounded, chromed airbox like those sold by Edelbrock be better? or what makes the dual snorkel so special?

tilstad

The air in the engine bay is hot, you don't want that, you get expanded air, which translates to fewer oxygen molecules in the same air volume.

Cold air is the opposite, fresh cold air from the front of the car, or like the setup I have, from the cowl induction in the hood. I just thought I could benefit from a dual too, and if I mount the performer manifold I just got, it may not fit since most aftermarkt manifolds are a bit higher than stock.

That's why they use intercoolers by the way, make the air colder, so you get more molecules in there. N2O, or nitrous, is similar, liquid air (-190 degrees celcius or so)

Irhal

yes... that I figured out... was just wondering if the airbox would do anything good... since I can lay my hands on one I guess I should take it... thanks guys for your patience with my newbie questions

tilstad

THe single snorkel aircleaner is considered too restrictive, even for a lg4, And trying to cram out even the smallest amount of additional hp, it's going to be more and more of a bottleneck as you raise the bar.

Other than that, it looks stock, not jerry-rigged. That's about it.

By the way, my cowl induction netted me 2 tenths in the 1/4.

five7kid

iTrader: (14)

https://www.thirdgen.org/techbb2/sho...hreadid=261488

FAQ forum.

five7kid

iTrader: (14)

In 2000, I "raced" the Camaro with a pretty much stock '86 LG4 - L98 cat-back only real "improvement". Stock 3.08 open rear. It ran low 17's here (low 16's at sea level) after replacing a weak fuel pump (was an embarrassing 17.65 first time out, stuttering all the way when above 3500 RPMs).

Replacing the single snorkel air cleaner with an open element took off 2 tenths. Other tweaks & tricks (removed all AC equipment, emptied trunk, advanced timing, fatter/shorter rear tires, skinnier fronts, etc.) finally produced a best of 16.85. In 2001, I was back to racing the '57, but had an intake gasket coolant leak, so in the process of fixing that put on the ZZ4 intake - also now had 2.93 posi and different tires all around - I took it out just to see what it would do and it ran a 16.80. You can see from the sig what it runs now, lack of 2-3 shift at WOT notwithstanding (dual snorkel, AC back in, subframe connectors, etc.).

Now, open element vs. dual snorkel: I don't have any data with the Camaro, but on the '57 I did several back-to-back runs with open element and dual snorkel "cool air inlet" air cleaners. The latter was a consistent tenth faster, with the improvement already showing up in 60' times.