I have a '99 GMC suburban (with 36k original miles) sitting out in my driveway that doesn't get used much and I'm wondering what, besides the L31 heads which would require a new intake manifold, I should swap onto my '87 LG4. I'd like to keep decent fuel economy (close to 20 city if that's possible), too. I also really like the e4me q-jet, but if FI is that much better then I'd be willing to switch..

...Lastly, should I just drop the vortec 5700 into the camaro with a new cam and scrap the 52k LG4? If that'd even work, sounds like it'd be a pain in the *** though.

 

the heads are probably the most sought pieces on that motor, not too much otherwise to speak of. However, if its got less miles and in better shape, I would just grab everything and dump it in the the F-body. If you stick with a carbed setup, all you'll need from the vortec is the long block (heads to pan), reuse your distributor, exhaust, carb, and get a a carb'd manifold (with egr).

you could use the fuel injection system as well, but that would be a lot more work (pump change, wiring, computer, etc).

 

If you swap the entire 350 in, but use the GMPP EGR Vortec carbureted intake, with your carb, and a 700R-4 and a 3.08:1 axle, and 235/60R15 tires, and a Painless Wiring lockup kit, then you can get 24 mpg at 65 mph. I've done that myself, it makes a great highway car that's still better than 99% of the other cars in traffic. If you're not concerned about HP, the Vortec EFI would give you an uncommon look under the hood. But you'll need to disable the VATS if it has that, you'll need to resolve the VSS, you'll need to disable the torque management, and you'll need to recalibrate the speedometer program in the computer. But if you keep your computer controlled QJ, you'll need the GMPP ZZ4 chip, the AH rods, and the G hangar to get you started. Either way could be made legal. With the QJ, you'll need to rig up an external EGR tube, but I found that wasn't too hard. Be aware that that intake manifold is close to $300 now.

 

With the Vortec spreadbore EGR intake on the L31, you can keep the E4ME, computer distributor, computer lock-up, etc.

To keep the EGR functional, you would need to plumb exhaust gases to the intake manifold as stated above.

I don't believe the ZZ4 chip is available anymore. At least, it wasn't last time I looked for it. It isn't really necessary, either.

 

I've tried running a mild 350 on an LG4 chip, it doesn't work.

 

I'm running mine on an LG4 chip. Of course, it was the '86 LG4 system, which may be better than the earlier LG4 computers.

And, you might consider mine less than "mild". . .

 

Well, I found out that all I can get out of it are the heads, so when I bolt those onto my 305, would the STOCK LT4 cam be a decent choice? I don't really want to get work done on the heads if I don't have to so I'm sticking with 1.5:1 rockers which would give me .45x lift, and I believe the vortecs are good for up to .470. Also, does anyone know the actual CR of an '87 LG4? My GM shop manual only puts it at 8.6:1, but I've heard that it went up to 9.3 or 9.5 after 86.. As far as the EGR goes, is it a necessity?

 

sorry, but it really is around 8.6:1, though that 9.5:1 claim keeps resurfacing. I've disassembled enough of them to know. You need to have the Vortec heads milled about 0.035", which will require removing the valves first. Otherwise you'll be around 8.0:1. You should be able to just keep using the valve seals that are on the heads, they really don't need to come off. But here's where you find out how competent the shop is. If they're competent, they'll respect your stated wishes to leave them on and take care to not damage them. The LTx cams are exactly as you say, go ahead with it. I suggest stainless valves with undercut stems, and have the shop put a small 30 degree back cut on each of them. Also polish the exhaust ports.

 

'87 LG4's had partial dish pistons, unlike the full dish pistons of the '82-'84 LG4's. '85 & '86 had flat tops with 4 valve reliefs. All had 58cc chambers.

I don't know what you've disassembled, Attilla, but that is what the data says, and it is consistent with what I've seen. The only '87 I've seen with full dish pistons was also 0.040 over, and had one 081 head and one swirlport head - heritage unknown, but sure looked like a botched dealer warranty rebuild to me.

 

I've been rebuilding engines, mostly SBCs, for a living for nearly 10 years now. I've disassembled dozens of virgin 305s of all years. If it doesn't have flat tops, it isn't 9.5:1. The last 305 assembled with flat tops was in the end of the '85 calendar year. The OP will see what's in there, and it could be a set of 30-over flat tops.

 

Are you going to scrap the truck since your picking parts off of it? If so, and it where me, I would swap the whole thing over (engine intake and fuel injecton). The late model FI systems are pretty good, and would be an improvement if your looking for increased fuel economy (my old vortec headed 350 got around 28 MPG on the highway). With tuning, you could even get more out of it.

How much money do you have to play with? There are some worthwhile upgrades to the setup that will help performance. One of them is swapping out th existing injector assembly for one with standard type fuel injectors.

I have the vortec setup on my camaro with an aftermarket victor-E intake, and I really like the way it runs. Even with a cam, the drivability is quite good.

If you dont have a lot of experience, just stealing the engine out of it and using your q-jet would be easier.

 

If nothing else keep the short block for a future engine build. Has roller cam and 50% chance of being 4 bolt mains.
Same bottom end as used in ZZ4 crate engine.

 

I thought the L31 has a cast crank and pistons, no? I know the rods are the same, but IIRC the ZZ4 has hypers and a forged crank.

 

How do the TFS-303100006s compare to L31 vortec heads? I'm looking at them and I figure the 56 cc combustion chamber will help me raise my CR a little bit, plus they allow for a higher lift cam. They seem better but they're also almost twice the price.

 

Buy the #30300001 for $1000 and put what ever springs you need in.You are paying $200 for higher lift springs
$40 worth of LT4 /ZZ4 springs will get you to .525 lift.

http://www.summitracing.com/parts/TFS-30300001/

 

Well, the only difference is aluminum vs cast iron, correct? I don't really feel like shelling out $400 more for that and keep in mind I'm still running a 305 so I think lift over .480" would be a bit excessive, anyway. Feel free to correct me if I'm wrong, I'm still a new guy. I'm liking the TFS more than the vortecs because they're ready to go with the 56cc chambers. Now to decide on a cam..

 

Exactly ,
as mentioned above you would have to pay to cut the Vortec's down to get the compression up and need a new intake to suit.
The Vortecs are a great budget head but the costs involved in fitting them to your particular setup makes the TFS look very good pricewise

 

Okay, from what I've read, .600" lift is typically the max for 350s, that can increase performance anyway. Is there some formula I could use to find the max lift for the 305 so I could find a cam to go with the TFS?

 

Why do you want to max out your lift? A better way to go would be to figure out what kind of power you want to make and whether you're willing to make the practicality sacrifices or the money sacrifices to get to that power level.

Picking a cam based on lift is like picking a motor based on the stroke. There's so much more to it.

 

I'm taking duration, timing (ivo, ivc,evo,evc), center and lobe centerlines into account as well, but I'd like to know at what point lift becomes useless in the 305 as compared to the .600" for the 350.