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Discussion Starter #1
I've been given thoughts to going back to iron manifolds that would be ported by Brzezinski Porting Service. The Hookers that have been on for 20+ years need to come off for re-plating,but honestly are a PIA to work around. Engine specs: 9:1 467 781 ovals w/2.19/1.88s Lunati 238/248 540/540 114/110 M-20,3:73s, Would I REALLY be killing performance THAT bad? recently retired and trying to make working on the car easier. Also thinking of a cam-swap in the near future. Looking to go back to my 3:08's if the county ever opens up again.thanks
 

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Kill 'performance'? No. Not in my definition of 'performance' and 'kill'.

Impact 'performance'? Yes.

How much depends on your exhaust system down stream of the headers. The more 'restrictive' (stock) the exhaust seem is, the less 'performance' will be impacted.

Rpm is also a factor. There will be more impact to 'performance' in high rpm; less (negligible?) for low rpm.

In general, a cam producing 'more' low end torque (I did NOT look up your current cam specs/characteristics) should alleviate the 'performance' impact.

Going to the 3.08 will keep you in low rpms at higher mph and benefit from 'more' low end torque.

It's 'easy' with todays parts to get 450 lb ft of torque at about 3800 rpm and 400 hp at about 5200 rpm (measured at the flywheel). A sb 383 can do that. Mate that torque to 3.36 rear, and a m20 4speed and I have enough (I might opt for the 3.08 rear if I did more highway driving). Whatever I 'lost' between the flywheel and the rear wheels due to the 'stock' type' exhaust and drive train would be acceptable.

Because it sounds like you are more into low rpm 'driving' (than high rpm 'racing'), the swap makes sense to me.

Just my opinion.

Pete
 

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I recently took the headers off my 65 Impala with 355" SBC in favor of 2.5" rams horn manifolds ported by Brezinski. Seat-of-the-pants, car feels the same. On the drag strip, a couple of tenths slower ET and maybe 1-2mph loss at most.

That said, I have a smaller engine and a smaller cam than yours, so your losses might be bigger. In your shoes, I would look at the Lunati 218/228 hydraulic roller - you'll lose a fair bit of performance, but it will be SOOOO much more street-able.

I hate headers with a passion, for all the reasons you list - loud, poor fit, frequently leak, make the car a pain to work on, etc. I'll never again have headers on a car unless it's a car used mostly for racing.
 

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does the amount of overlap affect the performance of headers? the 3 daily drivers I installed headers on over the years improved from idle on up, it made a huge difference on my L78 with the solid cam
 

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Discussion Starter #9
I recently took the headers off my 65 Impala with 355" SBC in favor of 2.5" rams horn manifolds ported by Brezinski. Seat-of-the-pants, car feels the same. On the drag strip, a couple of tenths slower ET and maybe 1-2mph loss at most.

That said, I have a smaller engine and a smaller cam than yours, so your losses might be bigger. In your shoes, I would look at the Lunati 218/228 hydraulic roller - you'll lose a fair bit of performance, but it will be SOOOO much more street-able.

I hate headers with a passion, for all the reasons you list - loud, poor fit, frequently leak, make the car a pain to work on, etc. I'll never again have headers on a car unless it's a car used mostly for racing.
that cam and the GM 454HO roller is what i had in mind. In 50 years wrenching my go to cam was the L-78 solid but with my compression I would like to drop about 20*duration so it suit where i drive at
 

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Discussion Starter #10
Kill 'performance'? No. Not in my definition of 'performance' and 'kill'.

Impact 'performance'? Yes.

How much depends on your exhaust system down stream of the headers. The more 'restrictive' (stock) the exhaust seem is, the less 'performance' will be impacted.

Rpm is also a factor. There will be more impact to 'performance' in high rpm; less (negligible?) for low rpm.

In general, a cam producing 'more' low end torque (I did NOT look up your current cam specs/characteristics) should alleviate the 'performance' impact.

Going to the 3.08 will keep you in low rpms at higher mph and benefit from 'more' low end torque.

It's 'easy' with todays parts to get 450 lb ft of torque at about 3800 rpm and 400 hp at about 5200 rpm (measured at the flywheel). A sb 383 can do that. Mate that torque to 3.36 rear, and a m20 4speed and I have enough (I might opt for the 3.08 rear if I did more highway driving). Whatever I 'lost' between the flywheel and the rear wheels due to the 'stock' type' exhaust and drive train would be acceptable.

Because it sounds like you are more into low rpm 'driving' (than high rpm 'racing'), the swap makes sense to me.

Just my opinion.

Pete
current exhaust is crimp-pipes 2 1/2 to super-hemi turbos 2 1/4 tail pipes. would up-grade to full man-bent system with fresh mufflers
 

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90% of my exhaust customers that I talk to just want a nice sounding car to cruise around in, even if they've got 500hp. Pleasurable drivability without the maintenance/interference/clearance/leaking issues of headers is their focus. Manifolds for strictly street cars just make sense. For racing and competition you need headers..but not for street cruising. Just get a 2.5" mandrel bent system with manifold downpipes and mufflers that suit your taste, and be done with it.
A word of caution on muffler choice- with 3:73's your only concern is what dB level you're comfortable with. With 3:08's, you might have to worry about drone too. You'll be in the 1800-2400ish rpm range during cruising and that's when drone can be a problem. Chambered mufflers are the worst culprits (Flowmaster Super50 and 70 series are much better), followed by perforated pipe straight-thru mufflers (although MagnaFlow does an excellent job it seems) and then reverse-flow turbo-style mufflers, which do the best job at controlling drone. Give us a call with any questions-Classic muscle car exhaust
 

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2-1/2" dual exhaust. Mandrill bends, no X or H pipe, Dynomax Super Turbo mufflers #17749... They will start off very quiet but once the miles build up they will sound better and better..
 

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I have magna flow knok offs and the sound great and are a see through design.
AP exhaust Xlerator XS1229 , 3" mufffler. Come in 21/2 also.
Running the same mufflers in my car, but I am using the 18" 2.5" version with an X-pipe. Love them. I've had three different mufflers on my car, and these are my favorites.
 

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I'm with you oldguy. The Hedman headers leaked, had cracks where they were "massaged" , leaked at the collectors, cooked starter solenoids, burnt plug wires, etc. I put the stock manifolds back on (the 396). It's just a street car and I really don't notice much difference. It's 2 1/2" exhaust with Magnaflow straight thru mufflers. I like the look of the stock manifolds too.
702199
 

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I'm with you oldguy. The Hedman headers leaked, had cracks where they were "massaged" , leaked at the collectors, cooked starter solenoids, burnt plug wires, etc. I put the stock manifolds back on (the 396). It's just a street car and I really don't notice much difference. It's 2 1/2" exhaust with Magnaflow straight thru mufflers. I like the look of the stock manifolds too.
What did you use on the manifolds (paint / coating)? Looks great! You said you didn't notice much difference.... Any porting, or are those just stock manifolds?
 

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No porting. Just some repop manifolds. Bolted them up with no gaskets. No leaks. I only wind mine up to 5-6 grand anyway. Probably lost some juice on the dyno, but still sets me back in my seat. I did find you can watch the manifolds rust before your eyes if you don't coat them. Cleaned the surface rust off and brushed on the POR manifold paint . I just touch them up once a year as needed, but they stay looking nice.
 

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When i bought my 70 ls5 it had day 2 headers and h pipe ,offenhauser intake and 780 holley.I put the original manifolds and exhaust back on the car and putting my original intake and 7040204 carb back on this winter.If i want the hp blast ill modify my 2016 mustang,its 435 hp stock so easily moded to 500 hp with ac on in the hot weather.Im 50 plus so bragging rights doesnt mean anything to me now.Having a numbers matching ls5 is all i need.
 
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