Newbie needs advice on 70 351C exhaust

helicopter

New Member
Mar 20, 2009
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Greetings everyone!

This is my first post and I look forward to supporting this forum.

Six years – I’ve been restoring a 70 Fastback for that long. I’m getting close to driving it. It’s painted, the interior is redone and most important I installed a 351C 4V mated to a Tremec TKO 5 speed. I’m running Hooker long tube headers and have a lot of cam in the car.

I’m ready to install an exhaust and I need some advice.

I wanted to do something different: Install catalytic converters! To reduce emissions. I was informed that my good motives for the environment were not a good idea – converters won’t work on that installation. So my first question, is that true? I would bolt the converters directly to the headers and run 3 inch pipe to compensate for their restrictiveness.

The other question is what muffler to use. I do not want the loud boomy sound. I’ve installed a lot of Dynamat to keep the interior quiet, and wanted a muffler that would avoid the booming low frequency rumble. What would you recommend?

If I ran a larger diameter exhaust, would it be worth it to install a crossover X, H or otherwise)?

Last, I installed a fuel cell. The fuel cell required a “bathtub” to be welded in and there may not be much clearance between the bathtub and the leaf springs to run the exhaust to the bumper. Would dumping the exhaust just forward of the axle result in more noise production?

Heli

:shrug:
 
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woodsnake

10 Year Member
Jan 16, 2007
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Hicksville, NY
The thing about the catalytic converters is that they are used to determine a
rich/lean for fuel injected engines. Usually a two or three wire sensor determines whether or not th engine needs more or less fuel.

If you are concerned about your cammed up muscle car emissions, just don't use it as a daily driver with your foot to the floor.
 

RacerX

Founding Member
Feb 2, 2000
822
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18
Dayton, Ohio
The thing about the catalytic converters is that they are used to determine a
rich/lean for fuel injected engines. Usually a two or three wire sensor determines whether or not th engine needs more or less fuel.
I think you might be confused with oxygen sensors which are upstream of catalytic converters and primarily read oxygen content in the exhaust gases and sends a signal in the form of a voltage variation to the control module to adjust fuel mixture. Catalytic converters were used long before fuel injected engines became the norm. They trap unburnt gas in the exhaust so it doesn't leave the tail pipe and burns it off.

I wanted to do something different: Install catalytic converters! To reduce emissions. I was informed that my good motives for the environment were not a good idea – converters won’t work on that installation. So my first question, is that true? I would bolt the converters directly to the headers and run 3 inch pipe to compensate for their restrictiveness.
I don't see the point but its your car. I think you'll burn them out mounting them to the headers though.

Last, I installed a fuel cell. The fuel cell required a “bathtub” to be welded in and there may not be much clearance between the bathtub and the leaf springs to run the exhaust to the bumper. Would dumping the exhaust just forward of the axle result in more noise production?
Noise will depend on the rest of the system but a shorter version will typically be louder than a longer version of the same system. You did know fuel safe makes a direct drop-in fuel cell for early mustangs didn't you?
 

65ShelbyClone

Founding Member
Sep 9, 2000
4,601
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109
Antelope Valley, SoCal
1.) I wanted to do something different: Install catalytic converters! To reduce emissions. I was informed that my good motives for the environment were not a good idea – converters won’t work on that installation. So my first question, is that true?

2.) The other question is what muffler to use. I do not want the loud boomy sound. I’ve installed a lot of Dynamat to keep the interior quiet, and wanted a muffler that would avoid the booming low frequency rumble. What would you recommend?

3.) If I ran a larger diameter exhaust, would it be worth it to install a crossover X, H or otherwise)?

4.) Would dumping the exhaust just forward of the axle result in more noise production?
1.) It depends on the setup before the converters. Lots of modern cars use cats without a smog pump, but they typically have rather lean cruise air:fuel mixtures for the converter to work properly.

2.) A regular 2.5 or 3.0" turbo muffler probably won't be too loud.

3.) It is usually worthwhile indtalling a crossover regardless of exhaust size. In addition to increasing power, they usually improve exhaust note, too.
 

helicopter

New Member
Mar 20, 2009
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:D
Noise will depend on the rest of the system but a shorter version will typically be louder than a longer version of the same system. You did know fuel safe makes a direct drop-in fuel cell for early mustangs didn't you?
Thanks everyone for the replies. I spent a lot of time reading other threads on the topic also. There was one thread where a really helpful poster pointed the forum to a website where exhaust sounds were recorded. Unfortunately there were not enough entries, but I respect the fact that in a very real sense, our work in building these cars is a thing that forums like this help make possible.

I'm working under time pressure.

I'm taking delivery of the car from a local upholstery shop. The entire interior has been redone with Recaro upholstery and I need to tow it to a shop that will install an exhuast system and my Magnum 500 wheels that have been SITTING IN MY GARAGE since being gifted to me for Christmas 3 years ago.

:mad:

The car is going to be an example to you all. Example: The fuel cell. I spoke with Fual Safe. Great people. Great product. My approach was to weld a bathtub in the trunk area so that I can install any fuel cell. They need to be replaced every 5 years or so. The bathtub also adds another layer of reinforcement. In fact, I'm toying around with the idea of fabricating a removable steel bulkhead to seperate the passenger and trunk compartments. It's like this:

I read enough crap on the Net about getting rear ended that I'm arguably paranoid. I don't know. This is another mod that I'm considering. I'll be posting pics of the restoration and my many lessons learned in the future.

Am I rambling?

I earned the right to ramble. :D

I'm a newbie to this forum but I've restored this 70 Fastback -- purchased for $800, which should explain its original condition -- to the point where getting it adequately insured is my biggest challenge. Everyone tells me not to dare use it as a daily driver. I've been breathing Stangs for years.

My Stang -- her name is Geena -- will be a working girl, a daily driver.

Respect to all of you'se who DO the art of making a paragon of American manufacturing a LIVING history.

AGGGGHHHHH!

I have no idea what exhaust to install. I'll check out the Turbo mufflers. I can't keep towing the car around town. Listen:

H pipes, X pipes: Their value is questionable. They reduce backpressure by effectively increasing the diameter of the pipe. To an exiting exhast charge, the second pipe appears effectively as a single pipe of larger diemeter and therefore lower couette flow resistance. Second, there is scavenging. An exhaust charge trailing edge has a lower pressure that "pulls" a suceeding exhaust charge.

Those two behaviors contribute to lower restriction and higher exhaust flow rate.

Here's the thing: lower restriction is accomplished by a fatter pipe. And scavenging is accomplished only on a carefully designed system. I see guys knee jerk spending on X pipes, but there is no data that I've seen that proves that a given X pipe setup is optimized for that car! You get under the lift and gawk that it looks like an X, but where's the beef in terms of real performance improvement? Problem is this:

Guys like me who are NOT wealthy can't afford to pay for testing to prove the stuff works.

I'm inclined to run with no converters, no crossovers, and 2.5 inch pipe going as far aft as my fuel cell bathtub will allow.

I'll check out the Turbos.

I got more problems then a fruitcake has nuts.

Magnum 500 wheels: 15X7 for the front; 15X8 for rear, still in the 2005 Christamas present boxes -- my idea:

225/60s for the front; 255/60's for the rear.

Is that crazy?

:lol:

Heli
 

RacerX

Founding Member
Feb 2, 2000
822
1
18
Dayton, Ohio
I'm a newbie to this forum but I've restored this 70 Fastback -- purchased for $800, which should explain its original condition -- to the point where getting it adequately insured is my biggest challenge. Everyone tells me not to dare use it as a daily driver. I've been breathing Stangs for years.

My Stang -- her name is Geena -- will be a working girl, a daily driver.
:nice: I have never understood the point of building a nice car and not driving it. I intend to drive mine as much as possible when its done.

Do a search on this forum, there was a thread posted a few years ago about a 351C build. There was a lot of discussion, a lot of it on exhaust and IIRC some dyno results.