I have a LG4 305 engine and I would like improve it.
What can I do? What can I change? Did anybody do the same work?
Any suggestions?
One more question: which is the difference between 305 and 350?
I need more power for my LG4, please help me!!!!!








'87 Z 28 completely stock no modifications
LG4 160k miles
soon to be destroyed if I can't find more power on it

 

The difference between the 305 and the 350 is the number of cubic inches.

Now that I've gotten the blinding flash of the obvious out of the way, their stroke is the same (3.48") but their bore is different (3.736" vs. 4.000"). Externally they are virtually indistinguishable, except by the casting number of the block. Most 350s come with heads that flow better than most 305 heads.

Many, many people on this BBS have the LG4, and the majority are (ahem) disappointed. Here are a few posts found by a quick search, where people have asked this question:

https://www.thirdgen.org/techbb2/sho...threadid=30659

https://www.thirdgen.org/techbb2/sho...hreadid=113431

https://www.thirdgen.org/techbb2/sho...threadid=33237

https://www.thirdgen.org/techbb2/sho...threadid=32896

 

That's a pretty good representation of 305-specific modifications. Putting in a 350 is fairly simple, though, but the "supporting cast" - exhaust, cam, air cleaner, etc., MUST be addressed whether going with a 350 or staying with the 305.

Chevy High Peformance magazine did a series of articles called "My Generation Camaro", which started with an '87 LG4, of all things. They really restricted themselves with their cam selection, never replaced the torque converter with a higher stall unit, and resorted to nitrous to meet their goals, but otherwise it was a good series. Had they done with I did, with their 3.73 gears and drag radials, they probably would have been very close to their 13-sec 1/4 mile goal without nitrous.

With a similarly modified 350: very fast, no problem...

 

thanks for your advices.
what about gears? 3.73 or higher?
Should I replace my stock distributor for a HEI?
What type of headers? for 305 or 350?
Pistons? stock or another?

thanks again

 

Gears depends upon your overall intended use. If you drive it daily and ocassionally race it, then 3.42's are probably the highest you want to go. If you only drive it occasionally and race it a lot, then 3.73's would be fine. With those gears, you're going to need traction help at the track.

Get headers and exhaust intended for '86-'91 TPI, single cat.

Your stock distributor is fine (it is called "HEI"), but a better coil, and perhaps an MSD/Crane/Holley add-on ignition system, would be helpful.

You don't need to change pistons. In fact, if the lower end of the engine needs rebuilding, including pistons, forget the 305 and go find a builder 350 block.

 

I'm told that people tend to put 305 heads on thier 350 because they give a higher compression?

 

I've been told lots of things I don't believe. Flow is not a matter of belief, however; physics takes over.

People in general don't "tend" to put 305 heads on 350s: rather, people "tend" to cheap out and use the garbage they have instead of getting the right thing, which costs money, and then try to rationalize what they did with flights of fancy. "Those grapes were sour anyway."

Typical 305 heads flow around 20-25% less than a set of typical 350 heads. The difference in compression might give you back 6% of that difference. The only time it makes sense to go that route is when you have something else that limits your total flow, that you can't get rid of; for example, if you're in a circle-track class with a 2-barrel carb rule. Otherwise, it's 3 steps backward in exchange for one step forward.

 

NO,NO,NO,NO,NO!
Just check this out.

 

I don't see where that article says anything different from what he's been told...

Notice that the FIRST THING THEY DID was to change the exhaust and add cold air induction. The motor had manifolds when in the car, but had headers & 3" exhaust on the dyno; and if you've ever been to an engine dyno cell, you'd know that its intake air temp is pretty much ambient, not underhood temp like a stock LG4 breather provides.. just like the advice he has been given.

Now notice that the next thing they did was to change the intake. Typical back-yard "unbolt the easy stuff you can see" type of mod. It did very little; mostly it bumped the peaks up a few RPM.

Then they put a decent cam, in fact the very one recommended by many on this board. The cam swap gave them a massive increase in power, 52 HP, which would not have been possible without the exhaust.

Then they upgraded the heads, and got 30 more HP.

There you have it: 42 HP from headers & cold air; 52 HP from a cam swap; 30 HP from heads; and 20 HP from an intake.

So which mods did the most, and which ones didn't have much effect?

 

What article?

 

http://www.goingfaster.com/spo/325_h...chevrolet.html
ya well maybe some people need some direction and thos enumbers are obviously not all that accurate but they are solid.

 

OK if ya still read, do what i did in my sig, it'll pick it up a bit, but add 3.42 or 3.73s like the other guy said. AlthoughI always got sick of the old," just put in a 350" speach, i have never heard the end of that one every time i say anything about my 305, but if your just out for spending less money for more power, just put in a 350 (I cant believe I actually said that) and add to that, they're a dime a dozen at any junkyard, a couple hundred for a rebuild kit, and another couple hundred for hipo parts, and your good to go. I just stick with my 305 because i love it, but yea, you can only do so much with a 305, and can get a lot more from a 350.

--Stormr

 

ya well those parts listed in the article I posted are all interchangable with a 350.
What would he do if he doesn't feel like doing a swap.

 

HEHEHE!
Even though it makes more sense.

 

http://www.angelfire.com/nb/thirdgen/343hp305.html

 

First thing I'd do is buy Vortec heads and manifold. Then a cam. Then a good carb instead of that smog era peice of crap. If you have to pass smog keep the egr otherwise ditch it. What year is your car? It makes a big difference.

Heads $800 fully assembled

Intake $200

Cam $150

Carb $450

That's a pretty good combo for $1600. That should keep you satisfied for a while. Then start saving for a good block, crank, pistons, rods, better cam and valvetrain parts, lots of machining and you'll have one hell of a tranny wrecking firebreather. That'll keep you happy for a little while, then you'll want more and start looking at nitrous and blowers. Then you'll deceide you need a 6-72 blown nitrous spewing big block. It just gets really ugly after that. Bottom line is you will never have enough HP.

 

How far do you want to take it? All it takes is money and time.
Is your 305 runnng good now? Are you willing to replace it? How much are you intending on spending?
It can cost a LOT of money.
Be prepared.

 

Ibought a 84 z28 5.0 h.o. with right at 50,000 miles, really mint car from an old couple, did some research. Beings it was carburated and had all the smog stuff on it, it put out only 190 horse from the factory. The h.o. heads are ported alittle bit more than the stock 305 heads. With edelbrocks cam/lifter kit, 600cfm carb and performer intake also from edelbrock, accel performance ignition system, hedman shorty headers, three inch exhaust, better cooling system, plus a few minor items that will help should push the little motor close but maybe not quit 300 horse, hey! its low miled, original and all bolt on items, alittle over a grand, including three core radiator plus retaining factory air! Later in time, and more money we'll go with the bigger horse motor, this is enough to have alittle fun and still be somewhat intimdating.