I'm putting together some plans for an LG4-equipped '86 Z28 i may be buying soon. Anyone wanna help fill in some holes in my plan? The car has 72,000 miles on it, with a T-5 tranny. It will be used as a sleeper. I want to see the looks on people's faces when they get beat by an LG4 Now, keep in mind, I have no experience whatsoever with the LG4. I've worked on late-model LT1's and LS1's mostly, so my carb experience is next to nothing. Thanks to anyone who helps out.

1. Heads - I'm not quite sure what to use, I've been searching on here and it seems that the stock 416 heads, when ported, give some decent gains. It's also cheaper than buying brand-new parts. Should i stick with this or buy something else?

2. Cam - Another thing i'm not sure about....I don't want anything too extreme, just a slightly aggressive idle. Would the ZZ4 cam be a good choice? and while I'm at it, should I upgrade the rocker arms, pushrods, and valves? I'll have the engine opened up anyway....

3. Intake manifold/Air cleaner - I'll be getting a dual snorkel air cleaner. I'm also thinking about the GMPP ZZ4 intake manifold.

4. Exhaust - the choices are endless. i know the LG4 exhaust is incredibly restrictive. I'm going on five7kid's recommendations : "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)." The car has dual outlets right now, which i always liked. I'm not quite sure which cat-back to go with, as long as it's not Flowmaster. I've never been a fan of them. Anyone know where I can find sound clips of various exhausts on the 305?

5. Gears - I'm thinking 3.73's. The car may have them already, for all I know.

6. Bore - I know the LG4 has a small bore, which shrouds the intake valves. boring it .030-over, to 310 ci, should correct the problem, no?

7. Weight - I'm a big disciple of "Less is more" when it comes to weight. Rest assured, this thing will be well under 3000 lbs. when I'm through with it.

8. Nitrous - I'm toying with the idea...it would be an "insurance policy" of sorts. I'm not sure how much the LG4 can handle though. I was reading through some posts, and it seems the engine can handle a 125 shot with no problems.

9. Carb - i have no friggin clue...I did a search, and it seems that 650 CFM seems to be optimal for the mods i'm going to have. Or should i go bigger?

10. Ignition - i've always been partial to MSD ignition systems...one of their 6A systems should work nicely.

11. Fuel - how good is the stock fuel pump? I'm assuming I'll need to upgrade to a higher-flowing unit. What pumps are out there for the LG4's?

feel free to add any info you may have. Again, thank you to anyone who can help.

 

5. my auto car came with 3.23's stock, which arent too awful but its not a posi rear which kind of sucks.

7. shipping weight on my 82 hardtop was 3296 i believe, so your goal is reasonable but 300 lbs is still alot. I removed the A/C and all of the emissons as well as most of my interior which was shot. Id like to see what she weighs now.

9. You might be able to get the stock Q-jet to support your needs, im sure 5-7 will jump in on this topic.

10. i was considering an msd ignition for a while but shop around other brands may offer the same thing for less..or slightly more for about the same price. right now im looking into the crane hi-6

11. any mechanical fuel pump(bolts on block) for a sbc should work with the lg4. Some higher flowing mechanical pumps require a regulator though.

 

"6. Bore - I know the LG4 has a small bore, which shrouds the intake valves. boring it .030-over, to 310 ci, should correct the problem, no?"

Your openin a huge can of worms there. It doesnt make any sense to do. Basically your talking about rebuilding the engine, which doesnt really make sense. Instead of rebuilding a 305 you could get a 350 block for like 50 bucks.. I'm not saying don't mod the 305, I'm just saying dont waste your money on boring it unless it needs it, no sense rebuilding a perfectly good engine, and if it does get a 350.

 

"Your openin a huge can of worms there. It doesnt make any sense to do. Basically your talking about rebuilding the engine, which doesnt really make sense. Instead of rebuilding a 305 you could get a 350 block for like 50 bucks.. I'm not saying don't mod the 305, I'm just saying dont waste your money on boring it unless it needs it, no sense rebuilding a perfectly good engine, and if it does get a 350."

He said he wants a sleeper 305, not a 350.

 

what makes a 305 a sleeper? looks the same as a 350 externally.

 

Don't bother boring the block in an attempt to unshroud the valves. An additional .015" won't unshroud the valves. An extra eighth of an inch (about 10 times that much) would - but you can't do that to a 305 block. More benefit is available by unshrouding the chambers.

The ZZ4 cam won't work in an '86 block. The ZZ4 is factory roller, and '86 was still flat tappet. Well, you can make it work, but it's a lot of work and not really worth it. A good flat tappet grind from Comp, Crane, Lunati, etc., would wake it up. Just avoid the generic grinds like the ones Summit & Edelbrock carry.

If emisisons and fuel economy aren't on the table, then a 600 double pumper carb is the way to go with a manual transmission and 305. Any bigger will hurt throttle response and won't help performance.

Personally, I still think the World heads are better overall than ported & larger valve 416's. You should also do something about the rocker studs (pin or convert to screw-in), you'll need to change valve springs, probably cut down the valve guide for spring retainer clearance - by the time you do all that, you'll have about as much money in them as buying the Worlds, and still have inferior castings. Of course, I just found out that my "305" heads had 64cc chambers, but the compression loss didn't seem to affect performance. However, with positive type valve stem seals, they're good to around .550" lift, without any cutting beyond as-received - a nice benefit. The castings are less prone to cracking as well.

As for keeping the 305 vs. getting a 350 block to build: With a T5, you're torque limited, anyway, so as long as you don't do any high-RPM clutch dumps, a peaky 305 is probably a better choice.

Having said all that, after 3+ years of driving around a souped-up 305, I've had somebody ask me if it was actually a 350 exactly twice. And even then, they weren't particularly impressed. Frankly, the only person who cares is the person with the 305.

 

how about vortec heads? do they offer anything over the World heads? and while we're on the subject, milling the heads to increase the compression ratio....what's the highest i can go on the LG4 and still run on pump gas?

 

i may also be able to get a Flowtech cat-back for cheap...I'm not a big fan of them, but it's gonna be a hell of a lot cheaper than buying a brand-new system.

 

There's a big fan base for Vortec heads. You'll need to do some work on them as they aren't really performance heads as the factory does them. The valve guides stick up so much that only around .450" lift at the valve is possible (that varies from head to head), the best thing to do is have the guides and valve spring pockets cut to allow more lift and better springs - oh, the factory Vortec springs are performance junk, so figure on replacing them. They also have press-in rocker studs, same thing required there as for the 416's.

You'll need a different intake manifold, as the "old style" don't fit or match the ports. Then shaving them to get the compression back up, you're looking at about the same or more money than the Worlds. As for compression, about 9.5:1 is about as high as you want to go, although you could probably live with 10.5:1 if you're willing to use nothing but premium gas.

 

ok, so i'd be better off going with the World heads...

a friend of mine is selling a 154,xxx mile LG4, cheap. I may pull the heads off that and port them myself, as an alternative until I can get the World heads.

 

dude awesome, 305's all the way yeah,
anyways, i know for certain that the stock LG4 comes with stock 240 bhp and i have an 87 z28 i have modded the hell out of it the best intake htat i'm using so far is a edelbrock performer, with edelbrock rpm carb( i may have those last 2 backwards), with edelbrock TES headers and to ignite this all i use MSD 6AL box, Blaster 2 Coil, and Pro Billet Distributer. and the stock rear end is a Limited Slip with 3.27:1 from 86-92. oh and i'd make sure u don't put 350 heads on there they will not work correctly.

 

the LG4's didn't come with 240 HP stock, especially in 1986. it had 160 HP/250 ft. lbs. of torque.

 

160 is a "net" HP figure put out by the factory (as required by the Federal government). With the "cheating" allowed with "gross" flywheel HP - headers, no accessories driven by the engine, velocity stack instead of air cleaner, etc., you could easily see over 200 HP. But, without a cam change, I doubt you'd get to 240, although an L69 might.

Coz_305, the Edelbrock Performer is basically a stock intake manifold with Edelbrock's name on it. A Performer RPM would be a waste without a cam change. The Performer carbs are no better than the typical q-jet, and won't provide any power gains over a tuned q-jet (including a simple AV mod required on some LG4 carbs). Aftermarket coil and module will make a CC ignition work as well as what you put in. Basically, nothing you did provided any power improvement over what you can do with the factory equipment.

 

thats not what its looking like on this end.

 

What would be the best cam to use w/ the Performer RPM Air Gap in a 350 5-7?


Thanks,

 

You're working at it backwards. Pick the cam to match the heads, pick the intake to match the cam.

 

To match them up would you just look at the RPM ranges? i noticed that they state that the Manifold is good for Idle to 5500 and same w/ cams etc.


i would have just pocket ported stock 350 heads and i would want a came that is 1500-6500.
would i just get a manfold that would match that?

 

Turning a relatively stock LG4 over at 6500 rpms is a little bit wishfull. Better to stick to no more than 5500 rpm so that little old 305 can catch its breath. And not disassemble itself ...

 

yeah i agree, i mean....Overall is that how you make a combo work ? is to get all the parts in the same RPM range.