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Exhaust manifolds and sound
#1
Hi there

Have been here a while but haven't posted much as there is plenty of information here and don't want to repeat questions. This particular question I can't seem to find and answer on though. I have a 1973 convertible, 351C 2V engine, C6.

The original cast iron exhaust manifolds for a 351C 2V engine, how much do they dampen the sound inside the cabin of the car versus headers while driving on the highway? Or is the difference not worth worrying about? Maybe the fact I've got a convertible means I'm thinking about the wrong things here because I've just got a fabric roof??

Would consider going the FPA header route if I stick with the header direction as hookers I had in the past (6921HKR) hung too low, got caught on something and broke an engine mount, need something with good ground clearance. Currently using a set of Sanderson 4V blockhugger shorty headers with the copper adapters to suit 2V heads but put them on at a time when I hadn't learnt about scavenging effects, the power I'm putting out doesn't warrant such large primary tubes. But then again perhaps I'm being finicky and maybe it wouldn't matter. The FPA's have a slightly smaller primary tube size which is more desirable for what I want, ideally something a tad smaller yet again would be better still but ground clearance issues mean nothing is available like that that I can see, needs to suit a 4R70W also which will be installed in future and FPA's fit the bill there.

Have been tinkering for a while with my car and got the fuel consumption to go from 13.8 US mpg (tired engine when purchased, jetted much too large etc etc), now revamped and much time spent on it it's getting about 18.8 US mpg now at 60 to 65mph. And I haven't put in the 4R70W / gone EFI yet so that will be interesting, aiming to max out at around 25 US mpg which I think would be pretty phenomenal. And before someone says why would you spend that much time getting a little more milage, well because I can.... lol Big Grin Fuel is more expensive here in NZ too. Would love to share my thoughts on how to get maximum economy if anyone wants to know although that may require a separate post.

Many thanks for your time.

Aaron

Aaron
  Reply
#2
(01-03-2019, 07:41 AM)Aaron_1973 Wrote: Hi there

Have been here a while but haven't posted much as there is plenty of information here and don't want to repeat questions. This particular question I can't seem to find and answer on though. I have a 1973 convertible, 351C 2V engine, C6.

The original cast iron exhaust manifolds for a 351C 2V engine, how much do they dampen the sound inside the cabin of the car versus headers while driving on the highway? Or is the difference not worth worrying about? Maybe the fact I've got a convertible means I'm thinking about the wrong things here because I've just got a fabric roof??

Would consider going the FPA header route if I stick with the header direction as hookers I had in the past (6921HKR) hung too low, got caught on something and broke an engine mount, need something with good ground clearance. Currently using a set of Sanderson 4V blockhugger shorty headers with the copper adapters to suit 2V heads but put them on at a time when I hadn't learnt about scavenging effects, the power I'm putting out doesn't warrant such large primary tubes. But then again perhaps I'm being finicky and maybe it wouldn't matter. The FPA's have a slightly smaller primary tube size which is more desirable for what I want, ideally something a tad smaller yet again would be better still but ground clearance issues mean nothing is available like that that I can see, needs to suit a 4R70W also which will be installed in future and FPA's fit the bill there.

Have been tinkering for a while with my car and got the fuel consumption to go from 13.8 US mpg (tired engine when purchased, jetted much too large etc etc), now revamped and much time spent on it it's getting about 18.8 US mpg now at 60 to 65mph. And I haven't put in the 4R70W / gone EFI yet so that will be interesting, aiming to max out at around 25 US mpg which I think would be pretty phenomenal. And before someone says why would you spend that much time getting a little more milage, well because I can.... lol Big Grin Fuel is more expensive here in NZ too. Would love to share my thoughts on how to get maximum economy if anyone wants to know although that may require a separate post.

Many thanks for your time.

Aaron

I understand you desire for excellent fuel economy. I had a 1979 Mustang, 302 2V and SROD transmission. I took it from 19 MPG at 55 MPH to 30 MPG. I used a Holley street intake, Holley 600 VS carb with a two stage power valve and revised jetting, long tube headers with 1.5 diameter primaries with 2.5 inch collectors, and a revise distributor curve. A lot more power came with the MPG improvements. Are you still using the stock cam? Chuck
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#3
Hi Chuck

The cam is just a standard stock cam basically, this one "Comp Cam High Energy, 252H". My engine builder through a cam grinder got a a slightly different profile put onto the cam to get a faster lift rate, I've got some figures here from a build sheet but it's all in mm and I'm a little confused I won't lie as to what is written down, his writing is not the flashiest lol.

The car has some power, what I'm not exactly sure yet and will only come to fruition on a dyno, I suspect it's around 270 to 300hp going by a computer modelled dyno but that may or may not be out a bit?? The wheels certainly spin if I hoof it off the mark so have to take a measured approach when launching. Usually sticking 3 extra people in the car helps to weigh it down and stick it to the road more.

Great results on your economy figures! That's quite amazing to go from what you had to what you got.

Cheers
Aaron

Aaron
  Reply
#4
The focus in 1973 and a few years after was meeting the new emissions standards, not mileage or performance. Chuck definitely got his dialed in, with complementary components.

As far as sound, yes, you will probably notice an increase with headers. Ceramic coating helps, and wrapping them helps even more.



“If you can't explain it simply, you don't understand it well enough.”
--Albert Einstein
  Reply
#5
(01-03-2019, 07:12 PM)Don C Wrote: The focus in 1973 and a few years after was meeting the new emissions standards, not mileage or performance. Chuck definitely got his dialed in, with complementary components.

As far as sound, yes, you will probably notice an increase with headers. Ceramic coating helps, and wrapping them helps even more.

Thanks for that Don, may consider going with the FPA's, think they will do well.

I've spent a fair amount on this engine and put new pistons in to make it more like a 351C was in 1971 or better. Yes my one was a dumbed down 8:1 compression engine when I got it. Now 9.6:1 with DSS pistons, dished to make sure compression is in check but has quench pads either side to make use of the aussie closed chamber heads I have on there now, quench is set very nicely. Electronic ignition, run a 195F thermostat (Robert Shaw with the copper hat added by a Pantera fella from ebay). MSD spark plug leads, autolite spark plugs XP25 with .048 gap. Am just running on a rebuilt motorcraft 2100 carb at the moment and she runs quite well, dual exhaust. Will hopefully get better as we move along Smile

Thankyou for your input guys!

Cheers
Aaron

Aaron
  Reply
#6
Here are couple pictures of headers that were on an H code 2-V cleveland I bought. He had just put the headers on and crashed the car. They are ceramic coated. The coating will make no difference in sound only head transfer levels.
The picture under my 73 vert which is also and H code with 4-V to 2-V heads. The clear great and do not hang down. I cannot tell you the brand I did not install them. The exhaust is very loud for sure on this car has cam also and drinks the gas, lol. I only drive to shows so I do not worry about mileage.

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[Image: 100-3353.jpg]

[Image: 100-3354.jpg]

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When a man is in the woods and talks and no women are there is he still wrong??
Tongue
David
  Reply
#7
Those rusty ones look good, will do some more investigating Smile Thanks for those pictures!

Aaron
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