You get like 5 - 10hp just by taking the smog pump off haha.

 

Everyone keeps talking about how the "Y" pipe is restrictive and no good. I recently went to a reputable exhaust shop and asked about installing duals with two cats and high performance mufflers. The installer, (been installing performance exhaust for 20 years) said the current set up I have on my 81, (2-1-2)-- 2 1/2 to a high flow cat (magnaflow) into a 2 1/2 "Y" pipe to two "straight flow" performance mufflers will be the same performance output as "duals" with two cats. I have yet to dyno, but it feels a "fairly good kick in the pants," for an 81. Oh, and its still all stock. Anybody have any further comments on this advice?

 

With an all stock L-81, you probably won't notice a huge difference with dual cats as a single high flow with a properly built exhaust system. The original cat was highly restrictive and really a killer on the flow anyways.

 

I agree with uk paul. keep the computer. install true dual exhaust with either a x pipe or h pipe. keep the o2 sensor in the exhaust. preferibly the pre heat 3 wire type instead of the 1 wire type. the other 2 wires go to +12v and ground. and work from there. the computer should function properly. it's not the computer that holding the power back. it's the breathing of these smog motors. however if you want an eariler 350 up displacement engine then find one in a junk yard and build it to what you want.

 

I personally dislike the idea of a computer controlling a CARBURETOR. Fuel injection, fine, that makes sense, but a carburetor? Electro-mechanical isn't exactly reliable.

Besides, remember the EMP thread? When we get struck by EMP, us without computers will still be rolling!

 

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I live in a state with no emission testing, so everything was taken off my 81. new distributer (HEI).. edelbrock preformer manifold and edelbrock carb. one thing if you disconnect the computer and you have an automatic tranny it won't lock up the coverter, unless you install a lock up kit from bowtie or b&m. you can also lock it by grounding the plug on the left side of the console near the lighter.


Can you explain more? I just put in a GM crate motor and I have an automatic. THANKS!

 

Do a search on TCC on the forums, you should find something about making it work. Or check out bowtie overdrives, they have a kit to make it work.

 

I agree. Working on carbs is a lost art in today's world. I work part time as a tech at a local repair shop and most guys I have worked with have no idea how to fiddle with a carb. Learning on carbs makes EFI troubleshooting and modification much less complicated.

But if he did want to do EFI..... there are some realy cheap ways to build efi systems.... mega squart computer $300, used manifold 200, and an old gm truck throtle body.... and you can still use a distributor.... but carbs are fun

 

 

TCC lockup: I don't know what wires/relays are left in your car but here's the basics of what you need to do.....
find the brake TCC switch on the brake pedal & follow the wire (ppl) from it (not the constant 12V, the switched 12v that's cut when the pedal is pressed). If all wires have been scrapped you'll still hopefully have a 12v fused supply connected to the switch. At a convenient point run this wire to a switch somewhere in the cabin (the wire originally terminated at a relay connector in front of the firewall directly in front of the driver). Take a wire from the other side of this switch & connect it to the harness that goes to the trans (if it's still there). You need to connect it to the wire marked "A" on the connector which originally had a pink/black wire on it. Careful if you cut the pink/black that you insulate it as it's a 12v supply. You've now got a 12v feed to the TCC which is cut when you brake & also when you throw the switch that you've fitted in the cabin. If you're missint the harness to the trans then you need to connect the 12v feed to pin A on it.
The next thing is a ground so connect a wire to pin "B" on the harness connector & run it to a good ground point. There are other ways of doing it, but this seems to be the easiest. The only "gotcha" is that the harness connector to the trans is labelled "B" at the top & "D" at the bottom (don't know why, it caused me a problem on mine for a while - not helped by not being able to see the trans connection at the time). If you've not got the stock harness in place then connect the ground wire to pin "D" on the trans connector. Somebody might jump in & point out that the original setup used a relay to switch power, so it's not a good idea to junk it. I measured the resistance of a new TCC solenoid & it worked out that the circuit will be pulling a max of 0.5A ie not enough to need a relay (mine's worked fine like this for 4 years).

2-1-2 exhaust pipes: As I said earlier, my Vette was bought with the stock exhaust system in place, but with the cat having been removed & replaced with a short length of pipe. The exhaust gas from both banks of cylinders have to share this pipe so it's not much different to a single pipe system ie the pipes from the manifolds join & then run to the muffler using one length of 2 1/2" pipe. You wouldn't fit an exhaust system like that & expect decent performance! The biggest seat of the pants improvement on mine that I ever felt was due to ripping out the 2-1-2 system & replacing it with true 2 1/2" duals (I am SO glad that I listened to forum members & not the Vette specialist who told me to fit a 2" system as it'd fall flat on its face with a 2 1/2" system. Cheers lads ). I still had the stock manifolds & mufflers in place. When I eventually swapped out the manifolds & mufflers it was hard to tell if there was a power increase (meaning that it can't have been that much if there was). The '81 owner that I sold my duals to (I later made a custom system) also said that there was a big improvement. If you go back 2-4 years in the archives (if possible?) you'll find plenty of posts from people saying the same thing.

[QUOTE}
Electro-mechanical isn't exactly reliable
[/QUOTE]
I work in electronics. Pure digital isn't exactly reliable either.... especially if it comes from a certain far eastern country Course, another thing about electro-mechanical design is that it was used for missile guidance when I worked in that area

Efi would be great on an '81 & there's no arguement that it would be more efficient than the stock computer/carb setup. But what's the point of Efi with the stock cam, exhaust & heads (with associated low CR) still in place? The engine is a slug in performance terms & injecting the slug is just going to work out a frustrating waste of time/money. Best thing to do (assuming it's for off road use ) is to address the smog control systems (including low CR) & then add Efi to get the full benefit of it. So far I've changed my cam, exhausts & intake (not sure if swapping the intake was really worth the money?) & need to change the heads to get the full effect of what I've done so far. Changing the heads may very well get me the performance that I want from it (judging by how much difference new heads made to a mates C3, it probably will work out that I'll be happy with just the heads). The difference between how mine now runs compared to when I bought it is night & day. My mate's (with basically the same engine) with decent heads leaves mine for dead. How far do you want to go? Will a motor from a wrecked C5 drop straight in?

 

I have a 1980 L82. Is it simply a matter of removing the smog pump? What else must be done once it is removed?

 

A previous owner had removed the smog pump from mine, but what it looked like was that he'd pulled off the pump & all the pipes that went with it, plugged any vac pipes left going nowhere, left electrical connectors unplugged & just stuffed down the front of the firewall & wound some bolts into the stubs on the ex manifolds (I later took the pipes out (drilled them out) & got the holes filled with weld). I'm not sure if you can just disconnect the pipe to the cat & plug the hole left as the cat was taken off as well.

 

LS1 won't drop straight in a C3, lots of work involved with that. Much easier to just make an SBC go faster.

As for removing the smog pump. Pull it off and plug off any vacuum hoses. There are other things associated with it, though, like the AIR tubes, but that requires changing the exhaust manifolds.

My suggestion is to go with technology no newer than 1975. Much easier to work with and make power with. Removal of emissions stuff, upgrade heads, cam, and exhaust and you're putting out good power.

 

Don't let them scare you off!! Ditch the computer and learn how to tune a carb!!

Ditch all the computer crap.
Ditch all the smog crap.
Cut out your Cat and go straight dual pipes.
Add headers.
Get a new MSD distrubutor. (*a must w/out 'puter)
Get a new carb. (*a must w/out 'puter)
Get a better flowing intake. (ie: Edelbrock performer).

I promise that's all worth an easy 50hp and probably more! But you won't be satisfied, I promise. So next......

Get a new cam.
Get some new heads.

Now ya talking......and most are happy doing this. Good thing about these steps are you can do a little at a time. Start out with simply unhooking the computer, capping off the smog, and replacing the distrib. and carb. I would also stronger recommend go true dual exhaust without the cat and adding a new intake manifold.

Down the road, add the headers, heads, and a new cam.

*Note: (before doing any of this, check your engine compression on each cyclinder. I failed to do this, and really just waisted my time and money trying to fix a dog.)

Good luck, and jump on in!!

 

Doesn't have to go MSD, though. He could get a Pro-Comp HEI with vacuum advance for $80 on ebay. Or the MSD version of it for probably about the same.

 

Sounds like someone's afraid of computer re-programming...carbs suck.

 

He's 17, not 27, carbs are easier and less expensive to get plenty of power with. Also a lot less complicated.

The car came with a carb and has all the stuff for a carb, let it stay with a carb and make lots of power with less work.

BTW, I've yet to see someone re-program an '81 vette's computer.

 

If it was a regular carbureted car, I might agree. This one has a big chunk of the needed wires and sensors for FI, though.

Any computer can be reprogrammed, if someone is willing to decode the programming on the chip. www.diy-efi.org/gmecm probably has the info needed for the '81 comp, if someone actually wanted to retune it.

 

He's 17 so is probably a bit tight on cash (especially if he's bought an old C3 ). Ditching the computer in itself is going to gain how many hp? Not a lot, I'll wager, maybe even lose some if it's not tuned properly afterwards. My advice (having done it) is to ditch all the emissions stuff if it's legal to do so (except for the charcoal cannister as it's not sapping any power, though if it's easier to pull it off then go ahead). Don't know if that will gain much in power but it'll certainly make for a more reliable car (less vac pipes, etc to fail). Then fit dual pipes. That gave me the biggest seat of the pants power increase I ever had - more than a new cam, more than headers, more than a Performer intake, etc. The only thing I expect to give a better kick in the bottom is new heads (I hope). While changing to dual pipes it would make sense to fit Headers at the same time as doing it later would involve a lot of mods to the dual pipes ie you'll end up doing the same job twice. How much will a new dist & carb cost compared to the cost of dual pipes? And which will give the best bag-for-the-buck?
Somewhere on here will be a link to Ganeys exhaust comparisson. That's well worth reading as it shows the type of gains possible with a simple exhaust swap.
If the computer is working OK then just leave it alone. If it's messing about then scrap it. If it's flagging up problems then don't scrap it & ignore the problems, but find & fix them (& if the problems are in the computer then scrap it). While I'm no great fan of computers (I've spent 27 years working with the buggers), junking a functioning system just doesn't make sense & the only time I'd do that is if I was to fit a cam that lowered the idle vacuum to a point where the computer couldn't handle it.
If you have a working computer then I'd suggest advancing the ign timing from the stock 6* BTDC to something up to a max of 13*BTDC (I went for 11). This won't alter the advance curve shape but will advance the entire curve (if you get pinging then back it off a couple of degrees). Advancing mine made the engine feel far more responsive than it used to be. This won't cost you a cent to do & probably won't give the ideal spark curve that you can get by setting up a normal distributer, but it will make it a heck of a lot better than it is at the stock setting.
Swap out the diabolical, power sapping exhaust system, advance the timing & see what you think of it. The time you should consider ripping out the computer is when it goes wrong or when you're ready to change the cam. Cam selection is an art in itself & if you choose one (or somebody here recommends one) that isn't computer friendly then it'd be insane to get a lesser cam because of the computer. In that case get the cam you want & junk the computer. If the choice of cam is computer friendly then just fit it & enjoy
Something nobody ever says about the computer system is that it can actually help you. After I got my Vette it used to flash errors up regularly at throttle openings just above idle. I was getting all the "Scrap the computer" advice but a couple of people here had far more tweaked L81s than mine now is & were still running the computer. They talked me through diagnosing the system (which is a lot easier than battling with PC Windows problems!!!) & I eventually found some small vacuum leaks that I'm positive I wouldn't have found had the computer not flagged them up. While it felt like it ran fine, fixing the leaks made it feel like a car straight off of the showroom floor, instead of a slightly tired one with 70 000miles on the clock. Without the computer I wouldn't have found the leaks as I wouldn't have been aware of them.

 

Unlike Paul, my computer system was making my engine work worse. I have a feeling it didn't like my cam much, and the carburetor was in need of some serious help. That alone was my incentive to scrap it. I feel that a normal electric choke q-jet and vacuum advance HEI have made my vette so much friendlier and reliable. The thing I hate about the '81 Vette is its system is basically unique from every other vette, and that makes it a pain to make power with. By changing to a tried and true system, which really didn't cost much, I can now do upgrades the same way everyone else does.

I also hate wires and vacuum hoses being all over my engine!!

Vacuum leaks don't happen if there's no vacuum hose to leak from.

Total props to Paul for getting the system to work for him. However, it's still my opinion that the system is a flaw in itself. The one thing I actually like that it did was the TCC lock-up. That was a great feature, but changing my carburetor's mixture is a feature I don't want.