Headers VS Exhaust Manifold - Impala Tech
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post #1 of 20 (permalink) Old 05-12-2016, 03:21 PM Thread Starter
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Headers VS Exhaust Manifold

Hi all,

I currently have a 67 Impala, 350 small block engine - I installed headers 5 years ago (about 60K miles on them) - most of the driving was done in the last 3 - 4 years. About 3 - 4 months ago the driver's side header had a rusted out brittle area, which created a hole. I welded a piece of metal onto it, and since them I've had a few other holes around that area, which I just patched up with Quick Steel (high temp). I can tell it's starting to wear in that particular area.

This is an every day driver in California - been cross country a few times, drives through rush hour LA traffic (even in the 100 degree summer), so maybe the headers just took a beating??? I don't know the brand as I was still learning when I purchased them so maybe that had something to do with it???

I'm getting ready to replace the headers because the patch work isn't cutting it anymore. I'm wondering if I should install an exhaust manifold instead? I don't care about power and sound, I just want the most reliable option that I won't have to worry about in another 60K miles regardless of where I drive (I know nothing is 100%, but any advice/opinion/experiences you can share would be great!).

Thanks!
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post #2 of 20 (permalink) Old 05-12-2016, 10:32 PM
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Takes a long time to rust through a quarter inch of cast iron. There has been a number of threads posted on the advantages of a free breathing 2-1/2 inch (Corvette) ram's Horn exhaust manifold compared to most tube type headers. You have to spin past 4,200 to 4,800 RPM to exceed the flow rate of the cast iron factory exhaust system (the lines on the dyno sheet crossed back and forth a few times within this range due to valve train issues most likely due to valve spring harmonics).


Just type 2-1/2 inch ram's horn into the search button above to find a few.


Big Dave
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post #3 of 20 (permalink) Old 05-13-2016, 10:33 AM
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I you don't care about performance or sound like you said then there is nothing more reliable and maintenance free than the factory cast iron exhaust manifold.

66 impala,283 power glide, Aztec bronze
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post #4 of 20 (permalink) Old 05-13-2016, 01:00 PM Thread Starter
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Thanks guys... Appreciate both of your responses - I'm going with exhaust manifolds .
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post #5 of 20 (permalink) Old 09-04-2016, 01:22 AM
 
 
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Greetings,
I recently installed a crate 350/290hp motor in my 64 Impala. I am using the original cast iron manifolds, but would like to go with headers. First question is, what brackets do I need for the factory AC compressor and driver's side alternator when installing headers? Second, who makes a 2 1/2 cast iron Rams horn manifold which will accommodate factory AC and alternator bracket?
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post #6 of 20 (permalink) Old 09-04-2016, 11:01 AM
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You can buy two and a half inch reproduction cast iron manifolds from Corvette reproduction houses or from Speedway dot com a speed shop that caters mostly to roundy round racers.

There are no A/C brackets for tubular headers that I know of. If you read the foot notes associated with the part number that matches your car you will see that Ac and frequently P/S is excluded from the application chart.

You can also buy the same factory casting that was installed on your car in a two and a half inch size instead of the two and a eighth inch size the factory used that have been "sand ported" to flow more than a tubular header. This is a Smokey Yunik trick that he used before it was banded by NASCAR where he bolts a set of cast iron manifolds up to a mud pump and forces a slurry of sand and sea water through the manifold for days at a time (He lived in Dayton Beach and had a canal behind his shop that opened onto the ocean so sand and sea water were free). When he was done with them there was not only no casting flash inside but the sand had opened and straightened out the passages to flow better.

Unfortunately this is a labor intensive operation, and it wears wears out the pump and the fixture you welded up to do this. As a result, these manifolds are not only illegal (not that any one who chases their tail on a circle track would cheat) they are expensive.

Big Dave
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post #7 of 20 (permalink) Old 09-04-2016, 11:59 AM
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Just some additional data:

The 2 1/2" ram horn manifold were not exclusively Corvette parts. They were standard on all 300 hp (and greater) sbc engines 1962-1964 (and maybe other years; I don't know). Standard exhaust system for those engines consisted of 2 1/2" down pipes to the mufflers, 2" tail pipes from muffler to behind rear wheels (mufflers had 2 1/2" inlets; 2" outlets). Sbc engines less than 300hp had 2" ram horns and 2" pipes thru-out.

Dorman makes very nice replacements:

left side: https://www.summitracing.com/parts/r...-504/overview/

right side: https://www.summitracing.com/parts/r...-503/overview/

The '64's are slightly different when it comes to the alternator bracket. Here's a link to some hopefully helpful info:

2.5" Exhaust ? - ChevyTalk - FREE Restoration and Repair Help for your Chevrolet

hope you find this info helpful.

Pete
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post #8 of 20 (permalink) Old 09-04-2016, 01:14 PM
 
 
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Thanks Pete, I may purchase two left side manifolds and hope the passenger side clears the additional piece. I have not found a smooth 2 1/2 cast manifold to use on the right side, they are sold in sets.
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post #9 of 20 (permalink) Old 09-04-2016, 04:01 PM
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Quote:
Originally Posted by Chubbz View Post
Thanks Pete, I may purchase two left side manifolds and hope the passenger side clears the additional piece. I have not found a smooth 2 1/2 cast manifold to use on the right side, they are sold in sets.
That's what I did. I 'removed' the alternator bracket from one of them, put in on the right side. Because the 'worked' section of the manifold is back by the #8 plug, one has to look real hard to notice it wasn't made for that side.

Here's a pic.
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post #10 of 20 (permalink) Old 09-04-2016, 05:49 PM
 
 
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That's great, know I know it works. Is there room between the head and firewall to just leav it as is? Any other modifications made?
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post #11 of 20 (permalink) Old 09-04-2016, 10:22 PM
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Didn't try, don't know if it would have 'fit'. I bought them intending to remove the bracket. If I had to guess I would say no for my car. I could not fit the larger HEI distributor due to firewall interference (I used a small cap w/external coil, it looks very original). I read where others have not had that problem.

Other mods? No, bolted right on. My car is a '63 so I had no problems with the alternator mounting bracket. Don't know what you have, it looks custom from the pic.

I do not know what your A/C will do to the installation.

My car had 2" ram horns and 2" dual exhaust prior to the change. I had to change the down pipes, the heat exchanger valve (I used a spacer), and mufflers. I chose to replace the tail pipes, but the new ones are still 2".

They manifolds came with gaskets. They would have 'fit', but the exhaust ports in my heads are larger than OEM and I used different gaskets.

I have an electric choke. If you have the standard OEM type choke, you will need to drill a hole for the heat tube (there is a place for it, it's just not drilled).

If you have Vortec heads, I've read the ram horns will not work with those, but I do not know from experience; just read it.
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post #12 of 20 (permalink) Old 09-04-2016, 10:56 PM
 
 
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I don't have a Vortec motor so I believe the standard gasket will work, but I will have increase the exhaust pipe from there down.

I'll pick up a set and grind off the ear before I have them ceramic coated.
I should be able to reuse the existing brackets and bolts with the aftermarket ram horns.

I have an Edlebrock carburetor with electronic chocke and RPM intake. The K&N air cleaner is the other upgrade. The cruise control is factory.
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post #13 of 20 (permalink) Old 09-04-2016, 11:21 PM
 
 
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Let me ask you this, will I hear or feel a difference when upgrading from 2" to 2.5" aftermarket ram horns? My stock 2" horns are solid with all new gaskets when we dropped in the crate engine. It may not be worth it, what are you thoughts? Any other members?
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post #14 of 20 (permalink) Old 09-05-2016, 08:31 AM
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I would doubt it. You have a heavy car compared to a '64 Chevy II with the same motor in it. Headers or a free flowing exhaust in general can add about twenty five horsepower to your motor's power level, but you have a lower ratio of horsepower to weight than a lighter car does so your butt dyno probably will not be sensitive enough to notice the difference.

Big Dave
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post #15 of 20 (permalink) Old 09-05-2016, 10:34 AM
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You will feel it the most (how much is hard to tell and I would only be speculating if I were to say more) as the RPMs elevate (somewhere near 4k and greater).

I noticed you appear to have a single bowl brake master cylinder. I would give upgrading to a dual master cylinder priority over the exhaust upgrade, but that's just my opinion.
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post #16 of 20 (permalink) Old 09-05-2016, 11:32 AM
 
 
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Thank you, do you know where I can find exhaust manifold decoders? 3749965 LH and 3747038 RH.

Yes, I am looking into upgrading the entire brake system to disc brakes. The rub is I would like to keep my 14 inch rims with original hubcaps. I don't know if they make a 10 inch rotor to squeeze inside a 14 inch rim, I'll keep looking. ?
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post #17 of 20 (permalink) Old 09-05-2016, 12:14 PM
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Those are two inch manifolds that fit a 1958-'63 283 and the 1963 327 and are for a motor without A/C. The LH casting to use A/C is 3750556 in a two inch exhaust. They are for a base motor up to 300 horse with the 327 (the 300 horse 327 is still considered a base motor as it is the same motor as the previously rated at 275 horse without any other change in parts except the decal, you had to jump to a 330 or a 350 horse 327 to hit the high performance rating).

This information can be found in Alan Colvin's Chevrolet by the Number 1960-'64, and without mentioning the size in Mark S. Allen's Chevy Impala 1958-'70 pocket book. The pocket book doesn't have as much information or any of the cool GM engineering blue print drawings of the parts (great if you are looking for dimensions) but it is small enough to fit in your shirt pocket and go out in the field.

Big Dave
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post #18 of 20 (permalink) Old 09-05-2016, 12:20 PM
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Are those original 2"? eBay perhaps? I never looked for them.

You may find some interesting opinions (including mine) on disc brakes in the 'Brake & Suspension' section.
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post #19 of 20 (permalink) Old 09-05-2016, 12:56 PM
 
 
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Thanks Big Dave, that's great info. The manifolds were on the 327 /250HP that came with the cat. It's drained and tucked away in the garage.

As for brakes, I found a company out here in California.
http://www.abspowerbrake.com
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post #20 of 20 (permalink) Old 09-05-2016, 04:02 PM
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Chevrolet introduced disc brakes to the rest of the fleet in 1969. If you wanted disc brakes before that you had to buy an expensive option that repurposed the front rotor off of a Corvette from 1965 to '82 with the matching Girling calipers and brackets on the Impala and the Camaro (don't know it they were offered back then on a Chevelle because I considered a mid-size Chevelle to be a big barge compared to my preferred Camaro or Chevy II.

I know the Impala had them in 1968 because the Chevrolet Caprice my mom drove was a ordered as a luxury police car for the Clearwater Police chief. It had a 350 horse 327 and disc brakes with 15 inch rally wheels and a TH400 tranny. Even had the cool 160 mph speedo that said "Certified". I maintained that car for my mom in my garage.

The 1969 brakes were not of a fixed bridge design like those used by Girlings, or Brembo or PBR. Instead they cheaped out with a single piston full floating design that could be easily installed on the production line (no shimming required or trying to bleed multiple piston calipers). The Camaro used a "special" 14 inch steel wheel that had no drop down to allow mounting the tire bead easily as the interior of the wheel was totally flat. That wheel was available as a Rally or a plane steel wheel for a full wheel cover or dog dish hub cap. Those wheels are still made today new by Kelsey-Hayes and sold in Camaro reproduction web sites and catalogs.

Big Dave
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