I have a 1978 C3, manual 4 speed trans, 350 ci 300 hp with mild street cam. with a standard exhaust set up: come off headers, down to where they join, single pipe to Catalectic converter, then to a Y-pipe split to mufflers on right and left. At least that is the way it has been since I got the car.

I do not have smog regulations where I live. Smog/air pump is bad and needs replacing, So I have removed all the smog system components. Except the Cat. Converter. Which I read will plug up in time. Which is not good???

I am thinking of installing dual exhaust from headers to existing mufflers (new; well 3k miles ago)

Besides allowing the car to breathing better and reduced back flow, Is there a negative side to this change I have not thought of??? ​​​​​​

I am working my way to an EFI system.

Any experience with this out there???? good or bad...

dntb1523@hotmail.com

 

Long tube headers and true duals are one of the best mods you can do to 75-82 Vette's.....

Jebby

 

Thanks for the info.....good news is always welcome.

 

My stone stock 3 year old 75 4 spd L48 really woke up with true headers, dual exhaust and a good distributor & carb tune. Felt like a completely different engine!

Maybe 50+ HP? 165 to 210?

 

Since you are opening up the exhaust, make sure you also allow more air into the intake as well and check your air fuel mixture.

 

Thanks, Leigh1322

I will look into that more. Sounds good,

DB

 

Good advice, Thanks.

 

I have been running "true duals" as people here call them on my 1968 C3 for 29 years. Would there be any benefit to having a cross over tube connecting both sides together? How about on a High Compression engine?

Your thinking of going to an EFI system? Call the guys at EFISYSTEMPRO.COM. They sold me a Holley Sniper Stealth 4150 and a Holley Fuel Tank Module that came with the Walbro 255 liter per hour pump already mounted on my Fuel Level sender plate. On my C3 it is on the bottom of the tank so it was a 20 minute job to set up my fuel system. Oh, by the way the fuel regulator is also inside the fuel tank so you don't need a return line. I have my car running and it is great to see it running properly not burning the eyes or anything. Holley makes some nice EFI systems and they have good support if you don't mind waiting on the phone.

When I bought my system from EFISYSTEMPRO you get a Holley Tier Three technician to help you in your install. He gave me his personal cell number and I am allowed to get help when ever I need it. This is why I bought the Holley EFI system at the EFISYSTEMPRO.com. The service they provide will keep you off the phone with Holley when you have a question. I would strongly recommend them to anyone thinking about the switch. My 427 sounds great and runs like it always has. When people look under my hood they don't see a EFI as the Stealth model looks like a Holley Double Pumper from the outside.

The very best part is I came in under budget thanks to their help! I wanted a new fuel tank but had no need to replace the old one so they suggested the $300 module over a $700 EFI tank. Not having a Return line is sweet too! Now I have a Big Block running around with a EFI system. I installed one Coolant temperature sensor and an O2 sensor and connected the wires and it was running. I will be adding control of the timing and ignition system to the Sniper once I have the fueling issues sorted out. It works the very best when it has control of the fuel and ignition systems.

 

On your advice I looked up the Holly 4150, I'll need to look further as I have questions....and I am not ready to make that switch as yet.

However, I did make an appointment with an exhaust shop to ck out what I have and what we need to do for an est. Basically remove what it there and replace with a new dual system, keeping the mufflers I have. They have more time down than running so still new ???.
A question came up about the heat riser valve, to keep or not...Do dual exhaust systems use two riser valves??? or just the one one? Do new cars today use riser valves??? or is it all computer driven. ???with sensors???
Once the EFI is installed do you still need the riser valve???

Climate is probably a concern, I live in Northern Nevada, 20 miles east of Carson City. We get temps into the 107 this year, the heat is a big concern in traffic so I try not to drive in that heat in town. The car runs hot as it is, about 200. Winter as low as 28, neither stay around long but we do get there. I do not drive in the snow or when it is that cold out side.....We do not get that much rain so far 1.12 " this year here at the house, some yr's more Reno and Carso City, that is a different story.

 

I have an 81 vette i removed the cat and put a straight pipe in there temp. now i have a set of hooker headers in the garage and will be running all new pipes into the mufflers i have already. wont be doing this untill after sept 1st

 

First thing before exhaust. Oh I live in Reno. You need to buy a exhaust pass under cross member. It simplifies the exhaust system. You install full long tube headers. Then install dual exhaust straight back from the headers. Use a cross over pipe like an H pipe or buy a X pipe to install

I went with 3 inch pipes because the future might include more power

 

You save labor money for a pass under exhaust and keep heat away from the transmission. Easy to unbolt the exhaust to work on anything. Just in my house garage I unbolted the exhaust system to put in my spare different gearing differential. I am done racing so I went back to 4.11.





I made these back in the 80's and they are still working fine 15 engines and 10 transmission R&R later

 

Good luck on the project. Edward.

 

A lot of work there, a labor of love, I'd say.
I'll take under advisement.
Thanks. Kull

 

You can buy a cross members for pass under exhaust. Like Bowtie Over Drives or G-force. I installed my headers at home and just drove it with uncapped headers to the muffler shop. They welded up the 3 inch system.

 

I purchased my crossmember from G Force so I can run 3” duals off my headers.
Its a bolt in crossmember and the quality is awesome.
Well worth the investment even if you just want a 2 1/2” system.

 

Allens. Bolt in, ditch the heat riser, chambered exhaust. Sounds awesome, but not obnoxious. Did mine on ‘79 on jacks and stands in a 1 car garage in about 2 hours, taking my time.

Still using stock exhaust manifolds, might do headers one day, might just get some summit coated ram horns — but for now, still smiling.

https://www.corvettecentral.com/c3-6...f%3fcount%3d72 - bracket

https://www.southerncarparts.com/c3-...IaAh5VEALw_wcB — exhaust

 

Good Morning all: I found a place called "JigSaw Automotive" in Carson City, he's been around awhile, Owner is Mike. They work on older and custom cars, trucks ect. Mufflers, exhaust systems, and just about every thing else. During his inspection and repair of the car he found a broken Exhaust flange and cracked manifold, all of which I did not know about. After a few calls I found one at summit in Reno/Sparks, NV. I made the 104 mile round trip drive ( from Dayton > Reno & back) so as not to slow him down on the repair. Sounds good, runs good, I happy....

 

Would have been the perfect time for real long tube headers