I currently own a 1987 LT with the original lg4 still intact, in that neverending quest for more fun and power, i've settled on doing an engine swap. My goal for the car is a primarily for street use, while seeing some strip use, most likely eigth mile, and i know that all sbc's are the same size just different bore and stroke, so if possible i'll be utilizing any pieces of my current setup that carry over, and use what i have left over for some intake and exhaust mods, maybe even a nice cam. I'm currently looking at a stock replacement 350 shortblock from cmengines as my starting point, these are my questions,

1. I hear that lg4 heads with a little porting can be good performance heads and can also provide a nice bump in compression as well, how true is this.

2. Keeping im mind the best bang for my buck mentality, i'm looking for my power to come from my cam, intake exhaust combo, so what might be some of the best options for my cam, intake and exhaust. Any help here would be greatly appreciated.

3. I wanna end up somewhere around a streetable 300 - 325 hp at the crank...... Maybe more

i also plan on upgrading my rear end , gears and all, as well as tranny, but realistically, how long can i expect the stock setup to hold behind a stronger 350 before they go kablooey

 

1. True. 1.94" intake valves also help.

2. Comp XE268 cam, Edelbrock Performer RPM Spreadbore, Hooker 2055 headers and 3" parts on back.

3. Easily 300+ crank HP with the stock carb and distributor with improved air cleaner.

The stock tranny could stand a shift improver kit, larger bypass valve, etc., and a higher stall converter. Rear probably won't have a problem with that power level, but aftermarket posi, gears, axles, and a support cover would help it last a lot longer.

 

Your LT probably has economy gearing in the rear axle. And no posi. With the XE268 cam, don't expect to use overdrive until you change the axle ratio, and don't expect any acceleration until you install a posi, because instead of accelerating, you'll just be spinning the right rear tire. If you have an automatic transmission, be aware that the XE268 won't drive well with your stock torque converter. The best bang for the buck is a b&M TorkMaster 2400. It's also a good match for the XE268. Plan on a 3.73:1 axle ratio. If it's an automatic, a 3.42:1 is a tolerable second choice.

 

i found some affordable 3.73 gears, and i'm shopping around for a posi, but being that this car has about 140k on the clock, how should i go about upgrading my rear and what kind of $ are we talking

 

Rear axle assembly: realistically, it is fundamentally strong enough, so figure around $350-$550 for the posi, depending on what you choose. Figure about $130 for a "mega" gear install kit with wheel bearings, plus figure about $15 for the lube. Labor, if you're not going to do it yourself, should be $150-300, but you'll spend that if you do do it yourself, to get a tool to set the pinion depth.
If you have a manual trans, and you plan on running drag radials, plan on getting one of those aluminum girdles that have preload screws with jam nuts. And plan on switching to 28-spline axles.
So, there goes another $300-550.
If you do all of that, then the weak link is the ring gear. Be sure it's either genuine GM, or Richmond Gear. Nothing else is trustworthy if you're running a manual trans and drag radials.

 

I basically did all that to my rear (Eaton posi, Sierra gears and 28-spline axles, all new bearings & seals), with labor was around $1100. And I installed a support cover/girdle, another $140.

 

i was shopping around in my local trader and i found a guy selling a 350 block for $100, i met with him today to look at the engine, the only part of the casting code i could make out was 880, on the back driver side i saw GM 5.7 LG and under that it said 5gi or sgi, cant really tell, also the intake only has 4 bolts , could this be a vortec? also i found an h30 on the back of the engine, im thinking casting date info, if so that means august 2000 right?

 

Could be, what kind of marks are cast onto the outer ends of the heads? the good Vortec heads have casting numbers ending in 906 or 062. But they're often cracked, on the deck surface, between the center 2 chambers. This comes from a coolant leak at the rear of the intake, which leads to overheating, which causes cracking. But even so, the block alone is worth $100.

 

is there any difference in the vortec block and a standard 350 or is it just the intake and heads, also my trans is a standard 700r4, and while the cam and torque converter, and gears are both within my range as far as spending, the headers and posi at the moment aren't, i may be able to find a used posi at my local yard, but what about some alternative headers

 

The '96-'99 Vortec blocks are basically the same as earlier blocks, just have different things bolted to/put in them.

Headers is not a place to try to save money. You can find lower priced headers, but by the time you have them in your system and working as well as 2055's, you'll have spent more money.

Don't do the gears until you do the posi. One, you will be traction-challenged with higher numerical gears anyway, and two, you'll have to pay twice for the install. You won't be breaking things with highway gears and an open diff, so do the entire rear end at one time when you have the funds available to do the whole thing.

 

i have to wait till tomorrow to pull those numbers , i had to leave the engine at my granddads house,

atila, you said i wouldnt be able to use overdrive until i upgrade the rear if i used that cam, why iss that?

 

You can try it, but it'll surge badly. And that surging can kill the bearings in the engine. The XE268 has more duration, much more overlap, and a later intake closing than a stock cam, and these features help build more power, mostly by helping the engine breathe at higher rpm. But down around 1500 rpm, you'll actually have much less torque than stock. The XE268 builds torque quickly, but not quickly enough to do well turning 1600 rpm at 65 mph.
With a 3.73:1 and a 700R-4, you'll be around 2200 rpm at 65 mph. It might sound like a lot to you right now, but it's not bad when you do it, unless you got a bad muffler that is causing a droning noise.

 

makes much more sense now, thanks for the heads up

 

i finally got a chance to look at the numbers on my block today as well as the heads, the block came up as a vortec 5700 l31 4 bolts mains and the heads were the 906 heads, with no cracks which is even more awesome, all for 100 bucks, problem is, engine has some surface rust on it, removed one of the heads and the engine looks good but we'll find out tomorrow all the real details when we start to tear it down. one thing i think is funny, guy never fully drained oil from engine, kinda strange but oh well. on we go.

 

Good deal!

 

Not sure by what you've said so far if you plan on this, but I highly recommend pulling the oil pan and checking all of the crank bearings. I've known a few of these engine to lose bearings, might be why this one was only $100.

 

my main interest at this moment is the block assembly, the heads will be great later on down the road, i"ll be starting to disassemble my block today,after getting a little pricing done around town, ii found that my local napa will clean and bore my block, also install freeze plugs and bearings for around $260 plus parts, $40 for magna flux check, is this a good price for the above services?

 

Maybe I missed it glancing through, but what are you doing for intake? I'm guessing a 4bbl, junking the cc'd carb. I'd be interested in what you decide to run, I have a 350 in my car replacing my LG4, but it has all the LG4 top end, heads, cc'd carb, etc, and cold make a lot more power I'm sure with a cam and new intake setup. If you dyno your car, I'd love to see what you have for intake and cam if you're getting 300+ hp.

 

That's close to what my shop charges.

 

i planned on using the qjet cuz it breaths up to 750cfm just gonna need some help adjusting it, i'll probably be picking up an edelbrock performer manifold fitted to take vortec heads for later when i redo those,

 

Nobody makes a spreadbore RPM-type Vortec manifold of which I'm aware. Unless your cam powerband is above 5500 RPMs, a Performer Vortec spreadbore would be a very good match with a CC q-jet.

Junking a cc q-jet is an exercise in irresponsibility.

 

sorry about that thats what i meant.

And about qjets"s, they're great carbs when tuned properly.... problem is i'm not very good with tuning carbs.

 

subscribing i wanna know your final price count the machine shops around here charge like 500$ for that machine work thats why i havent got a 383 yet
btw for help with the Qjet try SMI induction theyre awesome and they can help you get in the ballpark with your combo for around 37$ parts shipped you can even just call them with Qs, i do lol

 

Probably no easier carb out there to tune than a CC q-jet.

 

im still running the stock tune lol just got some rods and hanger from a older 350 truck engine, good enough for now, im gonna do it right this summer though and get SMI to send me some