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You sold your 81, then turned around and bought a 78, took all of the paperwork from the sale, and locked it in the car at an offsite storage location. And you have no pictures on your phone, or from a nearby family member or friend, or from the original listing on Craigslist, FM, Bring a Trailer, or wherever you found the 78 to buy. And you didn't even check to see if it was an L48 or L82 when you bought it. What color is it? What transmission does it have?
I'm not going to say that sounds like the far-fetched tale an AI would tell us, but FFS...
On the off chance you are a real human, do you remember if the underhood system had one or two snorkels? In 1978, dual snorkel CAI was used on L82s., single snorkel on L48.
Here's a dual snorkel system from a 78 L82 installed on my 79 L48. Did it look like this? I HATE chrome, and only chrome aftermarket lids are available right now, but this system should perform better than just about anything else you can put on that car, at least up to 400 hp or so.
You sold your 81, then turned around and bought a 78, took all of the paperwork from the sale, and locked it in the car at an offsite storage location. And you have no pictures on your phone, or from a nearby family member or friend, or from the original listing on Craigslist, FM, Bring a Trailer, or wherever you found the 78 to buy. And you didn't even check to see if it was an L48 or L82 when you bought it. What color is it? What transmission does it have?
I'm not going to say that sounds like the far-fetched tale an AI would tell us, but FFS...
On the off chance you are a real human, do you remember if the underhood system had one or two snorkels? In 1978, dual snorkel CAI was used on L82s., single snorkel on L48.
Here's a dual snorkel system from a 78 L82 installed on my 79 L48. Did it look like this? I HATE chrome, and only chrome aftermarket lids are available right now, but this system should perform better than just about anything else you can put on that car, at least up to 400 hp or so.
LMAO i am not an AI but it damn well seems like it the 81 was a pain in the *** guy pulled out on me i just wanted to do some preliminary research on what would need to be done. kinda similar with this one im getting more info on it now and im trying to see what would need to be done so i can get funds in order to start working on it ASAP to have it ready for the summer. im getting more pictures tomorow and facetiming the man with it to get a full rundown. unfortunatley the guy doesnt have any pictures of the engine posted. from what i can tell its an l48 the tach doesnt say l82 nor is it badged as such. i will have more info soon its an anniversary edition with the 4 speed manual yeah i dont love the look of the snorkel but i might have to keep it lmao. i hopefully should get teh car next week im talking to the man im buying it from tomorow on a facetime to get a very detailed description of the car. its been my dream to own a C3 ever since i saw em but as you can tell i have much to learn. so im as of right now im gonna go with i have an L48 im putting dougs sidepipes and headers on it but what else should i do to wake it up? people were saying for the L82 get Lars papers and do the dist and carb is it the same thing for the L48? im really sorry for all the confusion guys you have been so helpful im really tryna learn here im new to this **** but have a passion for cars my father instilled in me.
Re curving the distrib and re-jetting the carb gets rid of a lot of the emissions tune. EGR delete plate. Biggest bang for the buck. Maybe $40 if you can do it yourself. But note QJets are nortoriously hard to re-jet and parts are hard-to-almost-impossible to get. These years are set very lean, but little gain in carb tuning at this level. Big change in distrib tuning.
Cat delete, true dual exhaust, with headers and free flowing mufflers is next. Costs more $ sure. But really uncorks these late 70s L48s to near 71 levels. Your 175HP should climb to 270 gross HP, 220 net. You will need to re-jet the carb now or it will run so lean you could hurt it. If you already have an L82 you will be a step ahead in power with a better cam.
Then the stage is set for heads & cam. Intake too. Might as well do them all at once. More $, but big HP return. Edelbrock heads and a 268H cam or similar parts, will have you over 360 HP gross/290HP net. Could be more. Stronger than an L46 or an LT-1 thanks to the heads. Re-jet the carb yet again, or do it all at once, and then re-jet. By far the best option is to send the carb to Lars and have it tuned right the first time.
Only after all that do you need to think about gears. You may have 336 already.
Last edited by leigh1322; Jan 20, 2024 at 10:34 AM.
Re curving the distrib and re-jetting the carb gets rid of a lot of the emissions tune. EGR delete plate. Biggest bang for the buck. Maybe $40 if you can do it yourself. But note QJets are nortoriously hard to re-jet and parts are hard-to-almost-impossible to get. These years are set very lean, but little gain in carb tuning at this level. Big change in distrib tuning.
Cat delete, true dual exhaust, with headers and free flowing mufflers is next. Costs more $ sure. But really uncorks these late 70s L48s to near 71 levels. Your 175HP should climb to 270 gross HP, 220 net. You will need to re-jet the carb now or it will run so lean you could hurt it. If you already have an L82 you will be a step ahead in power with a better cam.
Then the stage is set for heads & cam. Intake too. Might as well do them all at once. More $, but big HP return. Edelbrock heads and a 268H cam or similar parts, will have you over 360 HP gross/290HP net. Could be more. Stronger than an L46 or an LT-1 thanks to the heads. Re-jet the carb yet again, or do it all at once, and then re-jet. By far the best option is to send the carb to Lars and have it tuned right the first time.
Only after all that do you need to think about gears. You may have 336 already.
i mean would it just be worth it to get a new intake and carb? instead of re jetting if its really a pain in the ***? or even just a new carb. and then how do i go about re curving? is that what i should email lars about? ive got the cash to do some stuff im gonna do a full side exit and then i would rather just tune the carb and dist instead of getting a new carb. but if its easier and can yeild better results i can buy a new carb
i mean would it just be worth it to get a new intake and carb? instead of re jetting if its really a pain in the ***? or even just a new carb. and then how do i go about re curving? is that what i should email lars about? ive got the cash to do some stuff im gonna do a full side exit and then i would rather just tune the carb and dist instead of getting a new carb. but if its easier and can yeild better results i can buy a new carb
Curving the distributor isn’t that hard. I would recommend doing some research on the GM HEI distributor and how it works. From the factory these had very strong springs in the mechanical advance that would prevent you from getting full advance until nearly redline, this was done to increase the exhaust gas temperature and burn off more hydrocarbons. Removing these springs and replacing them with lighter ones that allow you to get your full mechanical advance at about 2,800 to 3,000 RPMs will make the engine run much happier, and make more power. I would email Lars about it though, the timing papers are worth their weight in gold.
Rejetting a quadrajet is not that hard. Only a matter of removing the airhorn/top and removing them with a flat blade screwdriver. Of course if you’re in the carb you’ll probably want to check a few other things, float level, choke pulloff operation, etc. Again, learning as much as you can about them before tearing into it will help you immensely. There’s plenty of websites and videos that are great resources.
The L82 intake is already pretty good, and shouldn’t be a restriction from making power with the stock heads and camshaft. If you ever need to replace the gaskets I would get one that blocks off the heat riser, but with how much power the engine makes I would imagine the difference of intake air temperature would only be in the single digits of horsepower, not nearly enough to feel in the seat of your pants.
If you get any pictures of the car/engine before you buy it post them on here! There’s plenty of people that would be happy to identify any problems with the car, and tell you if you’re getting a good deal.
Last edited by Piersonpie; Jan 20, 2024 at 08:39 PM.
Curving the distributor isn’t that hard. I would recommend doing some research on the GM HEI distributor and how it works. From the factory these had very strong springs in the mechanical advance that would prevent you from getting full advance until nearly redline, this was done to increase the exhaust gas temperature and burn off more hydrocarbons. Removing these springs and replacing them with lighter ones that allow you to get your full mechanical advance at about 2,800 to 3,000 RPMs will make the engine run much happier, and make more power. I would email Lars about it though, the timing papers are worth their weight in gold.
Rejetting a quadrajet is not that hard. Only a matter of removing the airhorn/top and removing them with a flat blade screwdriver. Of course if you’re in the carb you’ll probably want to check a few other things, float level, choke pulloff operation, etc. Again, learning as much as you can about them before tearing into it will help you immensely. There’s plenty of websites and videos that are great resources.
The L82 intake is already pretty good, and shouldn’t be a restriction from making power with the stock heads and camshaft. If you ever need to replace the gaskets I would get one that blocks off the heat riser, but with how much power the engine makes I would imagine the difference of intake air temperature would only be in the single digits of horsepower, not nearly enough to feel in the seat of your pants.
If you get any pictures of the car/engine before you buy it post them on here! There’s plenty of people that would be happy to identify any problems with the car, and tell you if you’re getting a good deal.
alright sounds great man thank you so much for all of the info. I’ll be sure to send an email to Lars to get some of that stuff, but do you have a link to a website or a YouTube video just so I can get a brief basic overview to start looking then go from there just so I know I’m looking at the right stuff. And yes I’ll throw some pics down but none of the engine bay I don’t have any yet.
Curving the distributor isn’t that hard. I would recommend doing some research on the GM HEI distributor and how it works. From the factory these had very strong springs in the mechanical advance that would prevent you from getting full advance until nearly redline, this was done to increase the exhaust gas temperature and burn off more hydrocarbons. Removing these springs and replacing them with lighter ones that allow you to get your full mechanical advance at about 2,800 to 3,000 RPMs will make the engine run much happier, and make more power. I would email Lars about it though, the timing papers are worth their weight in gold.
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Recurving a distributor is more than just throwing a set of lighter springs in there. It also involves reworking the centrifugal advance mechanism to limit the amount of centrifugal advance for more initial advance for better off the line performance.
I bought this book and studied it cover to cover. Then I called Cliff, explained my goals and which model Q-jet I had. He put together a rebuild kit for my needs. I'm very satisfied with the results. It was a fun and fairly easy project.
Alright guys i got a little update here. I have confirmed it is an l48 i know that for sure. So just to confirm retune the carb and recurve the dist is what i should do to wake the car up? The same as an l82? And then i saw that someone said on the forum when i put the side pipes on i have to rejet my carb how do i do that? And is it totally nessisary?
Changing the exhaust is a huge change on this era of 350. I dropped the convertor and put headers and real duals on my 75 L48 when it was only 3 years old. It leaned it out so much the plugs ran snow white and it stuttered in the winter in cold weather at cruise. So yes it needs re-jetted after that, as I did not want to burn a valve. But that was 1978, before EFI. Now days, for that, you will likely have to send it to Lars. Very few other people have jets & rods for these anymore, and also actually test them. You might be able to call Cliff Ruggles, or The Carb Shop, for jets & rods, but which ones to choose would be up to you to figure out. You could always just try it and see just how bad it is. It is the part throttle cruise zone where it goes really lean, and that is hard to change without new rods. But please don't burn a valve. It is this exact fine-tuneability, to lean it out at cruise, that gives it the MPG. 95% of local carb shops these days do not any longer have the parts or expertise to successfully re-jet a Q-Jet, or an AVS either, or anything more complicated than a simple Holley. Almost anyone can re-jet a Holley, but not the other two.
If you want to just change the carb and go, there is one particular Holley that Jebby has used a lot that he has found, that you can just bolt on and it works well on most street performance builds, IIIRC it was the Truck Avenger, not the normal car version. It has the good medium street performance transition circuit jetting, that you need. The car version is too lean.
If you insist on going with the less expensive Edelbrock AVS, be prepared to dig into it for re-jetting, but at least jet-kits are available. It may or may not work on a very mild stock-cam'd engine out-of-the-box, but that's it. You may want to download the instructions on that one first, to see how complicated that process is, before you decide to go down that road, If you tune it with a wide-band you can get it right, but it takes effort on your part.
The Q-Jet is still the better carb of the three, and worth the effort, but it kind of tops out around 400ish HP specifically a low idle vac around 11-12". I suppose the AVS is almost as good, but it is just as hard to tune, because both of those have jets & tapered metering rods, and you need to change both at the same time, to re-jet it. The Holley design is much simpler, you tune it by only changing jets, but it does not have metering rods, the transition circuit fuel is fixed, so you have to buy the right one in the first place. But because of those tapered rods, the first two can get very good gas mileage, but the same rods make them sensitive to mechanical component changes.
If you want to ever go with a "big" street cam, just go with the Holley. It is much more easily tuned, and basically the only one of the three that can be tuned well with an idle vac below 12". But it is almost impossible to get the last 2-3-4 mpg back without virtually re-engineering the carb, and having adjustable air bleeds and swappable idle/transition jetting.
Attached is the tuning papers for the AVS. Three stage AFR chart is on page 3. Rod/jet selection chart(s) begin on page 19. For some "Light" reading! LOL An AVS and a QJet can switch AFR between part throttle cruise and mild part throttle acceleration, due to the tapered rods, as seen on page 3, a Holley can not.
Last edited by leigh1322; Jan 22, 2024 at 10:27 AM.
Changing the exhaust is a huge change on this era of 350. I dropped the convertor and put headers and real duals on my 75 L48 when it was only 3 years old. It leaned it out so much the plugs ran snow white and it stuttered in the winter in cold weather at cruise. So yes it needs re-jetted after that, as I did not want to burn a valve. But that was 1978, before EFI. Now days, for that, you will likely have to send it to Lars. Very few other people have jets & rods for these anymore, and also actually test them. You might be able to call Cliff Ruggles, or The Carb Shop, for jets & rods, but which ones to choose would be up to you to figure out. You could always just try it and see just how bad it is. It is the part throttle cruise zone where it goes really lean, and that is hard to change without new rods. But please don't burn a valve. It is this exact fine-tuneability, to lean it out at cruise, that gives it the MPG. 95% of local carb shops these days do not any longer have the parts or expertise to successfully re-jet a Q-Jet, or an AVS either, or anything more complicated than a simple Holley. Almost anyone can re-jet a Holley, but not the other two.
If you want to just change the carb and go, there is one particular Holley that Jebby has used a lot that he has found, that you can just bolt on and it works well on most street performance builds, IIIRC it was the Truck Avenger, not the normal car version. It has the good medium street performance transition circuit jetting, that you need. The car version is too lean.
If you insist on going with the less expensive Edelbrock AVS, be prepared to dig into it for re-jetting, but at least jet-kits are available. It may or may not work on a very mild stock-cam'd engine out-of-the-box, but that's it. You may want to download the instructions on that one first, to see how complicated that process is, before you decide to go down that road, If you tune it with a wide-band you can get it right, but it takes effort on your part.
The Q-Jet is still the better carb of the three, and worth the effort, but it kind of tops out around 400ish HP specifically a low idle vac around 11-12". I suppose the AVS is almost as good, but it is just as hard to tune, because both of those have jets & tapered metering rods, and you need to change both at the same time, to re-jet it. The Holley design is much simpler, you tune it by only changing jets, but it does not have metering rods, the transition circuit fuel is fixed, so you have to buy the right one in the first place. But because of those tapered rods, the first two can get very good gas mileage, but the same rods make them sensitive to mechanical component changes.
If you want to ever go with a "big" street cam, just go with the Holley. It is much more easily tuned, and basically the only one of the three that can be tuned well with an idle vac below 12". But it is almost impossible to get the last 2-3-4 mpg back without virtually re-engineering the carb, and having adjustable air bleeds and swappable idle/transition jetting.
Thanks for all the info man. Yeah i remember seeing jebby by post that somewhere and to be honest i have been thinking maybe doing a new carb would be the way to go. In the future i would want to use a pretty good sized street cam and do heads on it to really open her up. But thats down the road a ways. And i could send it to Lars and have him do it but id rather maybe buy the Holley and do it myself. My question is i know some Holley carbs dont fit on the stock intake would the Holley truck one fit? Or would i have to get a Holley intake too? And if i decide to reject the carb really how hard is it? Like for me with as of right now pretty damn minimal carb knowledge would it probably just be better to buy the truck avenger learn how to tune it instead of tearing open a whole carb.
A Holley is probably the easiest way out.
Although you could rebuild the QJet for less, and have a better carb.
The Holley is a square bore, so you need a square bore intake, not a Q-Jet one, and not an adapter.
There is one Jebby likes best, I forget the #. 2101?? But there is also a 2701!
The QJet is a spread bore and needs a spreadbore manifold.
I think the 2101 work either way.
You have to be very careful with intake manifold selection on a C3, many of them are too tall.
Only a few fit under the low hood.
Last edited by leigh1322; Jan 22, 2024 at 10:47 AM.
A Holley is probably the easiest way out.
Although you could rebuild the QJet for less, and have a better carb.
The Holley is a square bore, so you need a square bore intake, not a Q-Jet one, and not an adapter.
There is one Jebby likes best, I forget the #. 2101?? But there is also a 2701!
The QJet is a spread bore and needs a spreadbore manifold.
I think the 2101 work either way.
You have to be very careful with intake manifold selection on a C3, many of them are too tall.
Only a few fit under the low hood.
ah okay well that definitely aint cheap LOL. Any clue on where i could find the parts to rebuild my qjet?
A Holley is probably the easiest way out.
Although you could rebuild the QJet for less, and have a better carb.
The Holley is a square bore, so you need a square bore intake, not a Q-Jet one, and not an adapter.
There is one Jebby likes best, I forget the #. 2101?? But there is also a 2701!
The QJet is a spread bore and needs a spreadbore manifold.
I think the 2101 work either way.
You have to be very careful with intake manifold selection on a C3, many of them are too tall.
Only a few fit under the low hood.
Edelbrock is a smart company. At their web site several Intakes have an *asterisk next to the part number.
Why is that? It's called CYA (cover your ***). They had so many Intakes being returned, not because of quality issues but rather hood clearance issues.
Customers said: Why didn't you tell me it won't fit? The asterisk claims: * Will Not Fit Under Corvette Hood.
Edelbrock has no way of knowing what hood or what air cleaner or filter cartridge height the customer has. That's the reason for the disclaimer.
What they are assuming you have and not telling you otherwise is, that is with the stock air cleaner. Then NO, some will not fit.
Here is where a "drop-base" air cleaner shines. Yes, it does fit now.
I have the Eddy 7501 Air Gap, which is the taller of some. Low hood profile. Drop-Base air cleaner. Even enough room for a carb spacer too.
I also run a 2.75 tall filter and not the traditional 3".
Nobody with any intelligence claims side pipes rob power. Too many variables involved.
when my L-82 was stock I replaced the quadrajet with holleys quadrajet replacement in the double pumper configuration and the car was noticably quicker.
DUI will make you an hei curved for your specific application if you don't feel like playing with springs and weights.lars is the guy if you want to keep your quadrajet.
