'76 "Maintenance"

[plwindish]

I've been trying to get my '76 (acquired Jan '11) road worthy for trips to Springfield MO and Gettysburg this summer. After an 80 mile trip ending with 2 burned plug wires and a blown muffler, I've been making trips to the mechanic (new plug wires & tune up), muffler shop(still waiting on 2 mufflers) radiator shop today(some soldering starting to let go and getting freon checked). The 400 has been chugging and cold blooded until warmed up. Should I now be looking at rebuilding the Rochester 4 bbl also? Would that help the chugging and rough idle also? Also gas mileage is around 13, is that par for the 400 equipped Avantis? I'm wanting to keep the car original, has anybody just swapped out the 3 speed turbo hydra-matic for a 700 R behind the 400 and gotten better mileage and better driveability? Is this an easy swap, or does the drive shaft need to be altered? According to the tach, at 70, tach is right around 3000, give or take a 100. Engine noise and blown muffler is making me think about ear plugs when driving. One thing I noticed about exhaust system when under the car was no H pipe connecting both sides in front of the mufflers. I'd appreciate any advice that would make the beast more economical and travel friendly. Thanks.

plwindish

[p schmidt]

hey I'm in aurora (now offically 2nd biggest city in IL) I have a great mechanic that could help you get your car going if you need ...motors are one of his specialty's he can get you going with some 'punch' if you need it.... let me know if you want his number

[p schmidt]

there's no 'h' pipe because it's dual exhaust , one pipe each side straight back

Edited March 23, 2011 by p schmidt

[Gunslinger]

The Quadrajet, though much maligned, is one of the best street carburetors ever designed...and also one of the most misunderstood. A Quadrajet will give you great performance and will wring every bit of mileage out of your fuel if it's adjusted right by someone who knows and understands them. That's a tough thing these days as carburetors are so old school and most modern techs have little experience with carbs of any make much less a Q-jet. Find a rebuilder that knows and understands them. It could have any of a multitude of issues after all these years. It sounds at least like your choke needs attention. Once properly rebuilt you can amazed by the difference in performance.

At the same time as rebuilding the carb, I would clean out the intake passages and combustion chambers with a can of Sea Foam. It's available at Pep Boys, Wal Mart, etc. While the engine is running, pull the large vacuum hose off the power brake booster and slowly pour it into the hose...the vacuum will draw it in. That does a great job of cleaning out the intake and combustion chambers and will also smoke up your neighborhood. After that you should replace the spark plugs as all kinds of debris will be on them. Then a rebuilt carb should make a big difference.

Since you have true dual exhaust, you can have a muffler shop fabricate a set of front pipes with a crossover...you may not experience a "seat of the pants" difference in performance, but it might run slightly smoother...maybe. Engines of that era were down on power output anyway so any changes may not be that noticeable.

Transmission...I had a 700R4 installed in my '70, but my car came with the Borg Warner automatic, not a Hydramatic. It did require a new driveshaft, so I had an aluminum unit installed to save weight and reduce rotating mass. I'm not sure, but whether you need a new driveshaft may depend on whether you have a TH400 or TH350 behind your 400 engine. I think...not sure, but I think a 700R4 will use the same driveshaft as a TH400 but not the TH350. Hopefully someone else will know for sure. Also...if you do the swap, you should also replace the shifter...the shift lever will not line up accurately with the indicator otherwise...plus you also need the indicator and housing for it as the curved PRND321 for a 700R4 will not fit the housing for your original PRND21. Not a big deal to change but you need to know ahead of time to have the parts available when doing the swap or the car will be sitting for longer once you find out the hard way (ask me how I know!). Nostalgic Motors has all those shifter parts you need.

Get the Q-jet rebuilt and you'll see an improvement in drivability and performance even if you don't see a huge improvement in fuel economy. Make the swap to a 700R4 on top of that and you'll probably see fuel economy around 20 mpg or better depending on your driving style. That's about what I get and I have a heavy foot.

[plwindish]

hey I'm in aurora (now offically 2nd biggest city in IL) I have a great mechanic that could help you get your car going if you need ...motors are one of his specialty's he can get you going with some 'punch' if you need it.... let me know if you want his number

Is that #2 status for Naper-Aurora area or just Aurora? The area is getting some big towns with Naperville, Plainfield, and Aurora all still continuing to grow. Thanks, I'd appreciate a number and address of the shop as I have a son living in Naperville available for taxi service when dropping off a vehicle up there. On your other reply, I've seen several exhaust set ups with an H pipe connecting the pipes between the exhaust manifolds and before the mufflers. I think I heard somewhere it helps equalize pressures. I'm not entirely sure, but my '64 R 1 might have had an H pipe when I had it back in the 60's.

plwindish

[plwindish]

The Quadrajet, though much maligned, is one of the best street carburetors ever designed...and also one of the most misunderstood. A Quadrajet will give you great performance and will wring every bit of mileage out of your fuel if it's adjusted right by someone who knows and understands them. That's a tough thing these days as carburetors are so old school and most modern techs have little experience with carbs of any make much less a Q-jet. Find a rebuilder that knows and understands them. It could have any of a multitude of issues after all these years. It sounds at least like your choke needs attention. Once properly rebuilt you can amazed by the difference in performance.

At the same time as rebuilding the carb, I would clean out the intake passages and combustion chambers with a can of Sea Foam. It's available at Pep Boys, Wal Mart, etc. While the engine is running, pull the large vacuum hose off the power brake booster and slowly pour it into the hose...the vacuum will draw it in. That does a great job of cleaning out the intake and combustion chambers and will also smoke up your neighborhood. After that you should replace the spark plugs as all kinds of debris will be on them. Then a rebuilt carb should make a big difference.

Since you have true dual exhaust, you can have a muffler shop fabricate a set of front pipes with a crossover...you may not experience a "seat of the pants" difference in performance, but it might run slightly smoother...maybe. Engines of that era were down on power output anyway so any changes may not be that noticeable.

Transmission...I had a 700R4 installed in my '70, but my car came with the Borg Warner automatic, not a Hydramatic. It did require a new driveshaft, so I had an aluminum unit installed to save weight and reduce rotating mass. I'm not sure, but whether you need a new driveshaft may depend on whether you have a TH400 or TH350 behind your 400 engine. I think...not sure, but I think a 700R4 will use the same driveshaft as a TH400 but not the TH350. Hopefully someone else will know for sure. Also...if you do the swap, you should also replace the shifter...the shift lever will not line up accurately with the indicator otherwise...plus you also need the indicator and housing for it as the curved PRND321 for a 700R4 will not fit the housing for your original PRND21. Not a big deal to change but you need to know ahead of time to have the parts available when doing the swap or the car will be sitting for longer once you find out the hard way (ask me how I know!). Nostalgic Motors has all those shifter parts you need.

Get the Q-jet rebuilt and you'll see an improvement in drivability and performance even if you don't see a huge improvement in fuel economy. Make the swap to a 700R4 on top of that and you'll probably see fuel economy around 20 mpg or better depending on your driving style. That's about what I get and I have a heavy foot.

Thanks for the information Gunslinger. The radiator shop owner I dropped the car at today is old school and remembers the Avanti's on the road as daily drivers back when he was a delivery kid for the radiator shop he started working at. He told me he has a good "carb" guy up the road from him. That'll probably be the next stop on the "mechanical tour" for the '76, possibly before my mufflers get in to be installed. I also am going to be talking with a tranny shop to start inquiring about a 700 R. Nostalgic Motors will also get a call about the shifter indicator parts. Does the new plate fit exactly in the place of the current plate, or are mods required?

I'll see what the carb rebuild does before I go the Sea Foam route and have to change out my new plugs. I don't think I'll do anything with the H pipe in the exhaust pipes as the present pipes are in really good shape. I had heard there was an advantage to having both sides joined for pressure equalization, but that's not confirmed.

One question I had about the new plug wires going through the shielding on the 400 was where they come out at the bottom of the shielding, the mechanic zip tied the 4 wires together, then ran under the exhaust manifolds to the cylinders. I didn't take off the shielding on top to see if the 4 wires were all held together as they passed down from the top. I believe the shielding on the original Avanti's separated each wire in its own channel between the distributor and where they came out at the bottom. Wires should be insulated, but is there any grounding between each other when they are all touching? I haven't done it on this car, but I have come in contact with a spark plug wire with the motor running before and got a jolt. Bad wire or just me making a better ground than the plug? Thanks again for all the information.

[Gunslinger]

I think you should have the exhaust work done before having the carburetor tuned...it should be adjusted in the condition it will be running. There will be a difference in back pressure between now and with new mufflers. That may or may not make for a significant difference in carb adjustments. It may make little or no difference...hard to say, but I would still have new mufflers on before the carb gets adjusted.

There is a measurable difference between an exhaust system with a crossover and without....on a dyno. While measurable, it may not be of any practical difference. Every car and engine is different on that. Having a crossover will balance out the power impulses of each cylinder head and make for somewhat better idle and generally makes for a slight horsepower improvement, but generally at higher rpm's, which may or may not be where you drive your car at. I've seen tests that show where an "X" crossover performs better in this regard than an "H" crossover, but every type of car might not have clearance for one over the other, or either.

The shifter quadrant will fit exactly in place of the original...no problem. Unless you look closely, you can't tell them apart. The only difference is how the indicator lens attaches...with your original it attached with two screws...with the replacement made for the 4-spd automatic, the lens attaches with one screw and the other end is a tongue and groove type of arrangement.

Something else on the 700R4 swap...some have said they required trans tunnels mods for the swap, but since your car has a TH400 or 350, that shouldn't be a problem. I had no problem in my '70. What we did find out for my car was there was an issue with the backup light and neutral safety switches, so the shop doing the work fabricated a new switch setup. They said the issue was lack of clearance between the original switches and the exhaust pipe. I had 2 1/2" pipes installed rather than the original design 2" pipe, so that may have caused the trouble..not the transmission itself. Just something else for you to be aware of, but if you have a TH400 already, it may not be of concern to you.

Spark plug wires shouldn't be bundled together the way you say they are. They can suffer inductive crossfire. They should be kept separate and crossed over each other once. The wires shouldn't be grounded or the spark will go to where you don't want it...like your fingers as you found out! I experienced that once on my '69 Corvette...the coil wire had a pinhole and the spark was escaping and grounding out on the lid of the distributor shield, keeping the car from starting. When checking the car to find the problem, it shocked me to where I wanted to go into a dark room to see if my nuts had turned into night lights!

I don't know if Avanti II's came with spark plug wire shielding like the original Stude Avanti's did. They may have come with distributor covers only. You can buy wire separators (called wire looms) from a speed shop or suppliers like Summit Racing or Jegs. They attach to the valve cover bolts and keep the wires separated plus add some bling to the engine. You can run the wires over the top of the valve covers or the side or from underneath. A lot depends on what design exhaust manifolds the car has. If you have the "ram's horn" design manifolds, you won't be able to run the wires across the valve covers.

[Paul K.]

A coupe of things to add to the already accurate info from everyone.

The '76 had a crossover "Y" pipe off the motor next a Catalytic converter and then split into two mufflers and tailpipes. This is called a cat back system. Sounds like someone converted it to a 74 and earlier style exhaust. I would keep that unless you have emission laws to comply with.

Who knows what the motor is today unless you have ALL THE RECORDS. My 76 was ALL original and had the emission de-tuned SBC 400. I installed a 1970 Corvette grind cam for the 350/350 hp motor and flat to pistons to replaced the low compression dished ones.

My 76 had Corvette style ignition shielding complete from the distributor cover, tower style wire separators, and flat covers that hugged the side of the engine block and housed the wires before they met the plugs. If you google "Corvette Ignition Shielding" you will find many sources of repro sets.

I would also do the seafoam BEFORE the carb work.

[p schmidt]

give me your # and we can call you ....probably would be able to help you out even with the tranny....(just converted my dana 44 rear end to a posi unit)

*****I think it's just aurora only for the 2nd biggest city in Il.****

[plwindish]

I think you should have the exhaust work done before having the carburetor tuned...it should be adjusted in the condition it will be running. There will be a difference in back pressure between now and with new mufflers. That may or may not make for a significant difference in carb adjustments. It may make little or no difference...hard to say, but I would still have new mufflers on before the carb gets adjusted.

There is a measurable difference between an exhaust system with a crossover and without....on a dyno. While measurable, it may not be of any practical difference. Every car and engine is different on that. Having a crossover will balance out the power impulses of each cylinder head and make for somewhat better idle and generally makes for a slight horsepower improvement, but generally at higher rpm's, which may or may not be where you drive your car at. I've seen tests that show where an "X" crossover performs better in this regard than an "H" crossover, but every type of car might not have clearance for one over the other, or either.

The shifter quadrant will fit exactly in place of the original...no problem. Unless you look closely, you can't tell them apart. The only difference is how the indicator lens attaches...with your original it attached with two screws...with the replacement made for the 4-spd automatic, the lens attaches with one screw and the other end is a tongue and groove type of arrangement.

Something else on the 700R4 swap...some have said they required trans tunnels mods for the swap, but since your car has a TH400 or 350, that shouldn't be a problem. I had no problem in my '70. What we did find out for my car was there was an issue with the backup light and neutral safety switches, so the shop doing the work fabricated a new switch setup. They said the issue was lack of clearance between the original switches and the exhaust pipe. I had 2 1/2" pipes installed rather than the original design 2" pipe, so that may have caused the trouble..not the transmission itself. Just something else for you to be aware of, but if you have a TH400 already, it may not be of concern to you.

Spark plug wires shouldn't be bundled together the way you say they are. They can suffer inductive crossfire. They should be kept separate and crossed over each other once. The wires shouldn't be grounded or the spark will go to where you don't want it...like your fingers as you found out! I experienced that once on my '69 Corvette...the coil wire had a pinhole and the spark was escaping and grounding out on the lid of the distributor shield, keeping the car from starting. When checking the car to find the problem, it shocked me to where I wanted to go into a dark room to see if my nuts had turned into night lights!

I don't know if Avanti II's came with spark plug wire shielding like the original Stude Avanti's did. They may have come with distributor covers only. You can buy wire separators (called wire looms) from a speed shop or suppliers like Summit Racing or Jegs. They attach to the valve cover bolts and keep the wires separated plus add some bling to the engine. You can run the wires over the top of the valve covers or the side or from underneath. A lot depends on what design exhaust manifolds the car has. If you have the "ram's horn" design manifolds, you won't be able to run the wires across the valve covers.

The car's not finished at radiator shop yet(radiator repair,new overflow hose & coolant bottle, flush & AC check), so I will hopefully be getting the mufflers put on before messing with the quadra-jet. I talked with the fine folks at Nostalgic & George D from Chicago today and got the information on what is needed from them to go along with the 700 R. I also talked with my tranny guy about the swap. I'm now thinking I got the wrong license plates from the sec of state's office. I need to change them from AVNTI 11 to MONEY PIT. In IL there's probably many versions on MONEY PIT on collector cars though. I could change the VIN to a 9 digit SSN and call it "dependent" also.

The ignition shielding only covers the distributor and goes down each side and stops at the back of the exhaust manifold on each side. According to another reply on this topic, his had come all the way across the manifolds also. I don't know if different versions were put out in the same year or what was the case, but mine doesn't come that far. I remember a 390 hp '66 Vette coupe my brother had, just had shielding over the distributor and possibly down to the back of the exhaust manifolds similar to to what I have on the '76 Avanti, then it looked like a braided wire covering over the spark plug wires. When I've got the car back, I'll have to see where I can put separators in to keep them apart and not hitting anything. My list of things to do seems to be growing. It looks like the road trips to Springfield MO and Gettysburg are only 3-4 months,hundreds of miles and many $$ down the road.

[plwindish]

A coupe of things to add to the already accurate info from everyone.

The '76 had a crossover "Y" pipe off the motor next a Catalytic converter and then split into two mufflers and tailpipes. This is called a cat back system. Sounds like someone converted it to a 74 and earlier style exhaust. I would keep that unless you have emission laws to comply with.

Who knows what the motor is today unless you have ALL THE RECORDS. My 76 was ALL original and had the emission de-tuned SBC 400. I installed a 1970 Corvette grind cam for the 350/350 hp motor and flat to pistons to replaced the low compression dished ones.

My 76 had Corvette style ignition shielding complete from the distributor cover, tower style wire separators, and flat covers that hugged the side of the engine block and housed the wires before they met the plugs. If you google "Corvette Ignition Shielding" you will find many sources of repro sets.

I would also do the seafoam BEFORE the carb work.

My '76 is RQB 2392 with the SBC 400 & quadrajet. Shielding is only a box over the distributor and arms coming down on both sides to the back of the exhaust manifolds. Nothing is along side the manifolds, wires are tucked between inside of manifolds and heads. It doesn't look like there are any brackets or connection where side covers would go down along the manifolds. Over the years, who knows. The gentleman I got the car from had it from 10/84 to 1/11 and kept many many receipts so I'm pretty certain the engine is original and miles 60 k are the first time around. I did look up some of the shielding and saw the price ranges. I guess that's one reason why the Vettes bring the money the do in auctions, or its an example of everyone living on the Vette food chain.

My exhaust probably was changed to a '74 dual system w/o cat. The car's previous owner also included all his correspondence with the Illinois Emissions Testing to where they finally exempted the car because he had not even put 20000 miles on the car since '84. How's the 400 run with the cam and pistons you had put in? Did you do any head work also? Do you still have the TH 400 in it? What rear end did you have in it?

Thanks for the information.

[plwindish]

give me your # and we can call you ....probably would be able to help you out even with the tranny....(just converted my dana 44 rear end to a posi unit)

*****I think it's just aurora only for the 2nd biggest city in Il.****

708 508-4240 or plwindish@hotmail.com Are you a member of Chicago-land Avanti Owners? I went to my first meeting 3/2 in Elmhurst.

[Ray K.]

I agree. If you don't do the work yourself, getting an Avanti fixed can quickly turn into a money pit!! One suggestion, though - if you are going to replace your ignition wires, upgrade to 8mm silicone or better. My '82 has a GM 350 crate motor. The parts store originally gave me the wrong wires. How was I to know GM had 2 different styles of exhaust manifolds? I had to cut the rubber boots off the distributor end, get under the car, and feed the wires through the heat shields from the spark-plug end. What a hassle!

[p schmidt]

I think I'm a member but I never get a chance to go to the meetings..... your more then welcome to come to the shop in aurora and take a look at my car...right now the frame is leaning up against the wall, the motor/trans is sitting in a corner, the body is up in the air while waiting for the s/s rivets to come in (troughs are bolted up for now), exposed area open for access to rolbar screws, rear end posi-ed and powder coated, interior out, installed a electric fan for the motor, new rack and pinion front end, so it's a good time to 'see' what your car looks like when torn apart...should be together by end of april except paint and interior...maybe we could have a meeting over there with the club!...I'd post some pics but seems my files are always too large I even shrink them in infran view and still too big!

*** my guy can rebuild your quad, work on your motor, body, paint, trans., rear end or whatever he specializes in high performance, and power...

Edited March 25, 2011 by p schmidt