When to replace heat exchangers?

[tirwin]

I was doing some other work on the car and I was noticing how much rust there is on is the heat exchangers. The exhaust flange nuts are really extra crispy. I'm just wondering when I should think about replacing them. They are not causing any problems yet.

[RedCoupe]

There's quite a bit of rust showing. Makes me wonder what might be lurking on the inside of the heat exchanger "muff". I suspect that your car saw some road salt during its lifetime, so I think I would run a boroscope in the air inlets and outlets just to be sure that all is well. If okay, I would do a thorough inspection on a routine basis after that. Also, because you can hear exhaust leakages,on a regular basis I would put the car on a lift, start the engine, and have an assistant briefly hold a rag over the exhaust outlet while you listen closely to each HE for leaks. The bottom line is that carbon monoxide is odorless, so you want to check everything pretty frequently.

[porwolf]

Seems as long as you don't smell exhaust when you turn on the heaters you are OK. The exhaust manifolds have a lot thicker material than the heater boxes around them and should last a lot longer, of course.

[Gogar]

I'm with porwolf, as long as you don't smell it you're fine.

You could roll the dice and try to get them coated for a few hundred bucks, but it's possible the sandblasting prep will munch that rust and make the problem worse.

There's LOTS of stock SC exchangers available out there though, so you've got that going for ya.

[tirwin]

Thanks for the feedback. I had thought about SSIs at one point but one of the local guys with an '82 did a before/after dyno run and the results were not worth the cost in my opinion. In the meantime I'll keep an eye out for a set of stock exchangers in the classifieds.

[porwolf]

Originally Posted by tirwin

Thanks for the feedback. I had thought about SSIs at one point but one of the local guys with an '82 did a before/after dyno run and the results were not worth the cost in my opinion. In the meantime I'll keep an eye out for a set of stock exchangers in the classifieds.

I think before you smell exhaust in the cabin you only lose some hot air and the heater my not work like new.

[RDM]

Originally Posted by porwolf

Seems as long as you don't smell exhaust when you turn on the heaters you are OK. The exhaust manifolds have a lot thicker material than the heater boxes around them and should last a lot longer, of course.

Carbon monoxide is colorless and odorless. If you suspect a problem, get a detector to be sure. My friend thought he had a problem and got one of these: Amazon.com: Quantum Eye Carbon Monoxide Detector: Everything Else

At $8 it's a no-brainer.

[boyt911sc]

Tim,

The rust you see on your HE are not really that bad to make you worry about exhaust fumes. I have dissected several HE a lot worse condition than yours and the exhaust pipe inside the the heater box is very thick to worry about it. The deterioration at the weld points is normal for 35 years old HE's. By the time you are able to create a hole on the headers' exhaust pipes due corrosion, the tin sheet heater box would be almost disintegrated by rust. The wall thickness of the exhaust pipes is substantial to resist rust. This is not a problem right now.

Tony

[tirwin]

Thanks, Tony. I didn't post a picture of them but the flanges are in the worst shape -- they are entirely rusted. I don't think they're causing a problem but they are going to be a bugger to get off when the time comes. The nuts on the cat pipe were not as bad and the rust had made the metal so soft that it was really hard to not round the nuts so I don't want to think about trying to get those flange nuts off. That's probably the best reason to do something because that is just going to continue to get worse.

Given these appear to be the original HEs I don't think there is any urgency to replace them but it would probably be wise to put them on the "while I'm in there list" when time and opportunity allows.

[jchris]

I thought I read somewhere that the material of which the pipes are made is more resilent than the heater box sheet metal, fwiw. Anyway, mine looked terrible, and like Tony, when I replaced mine I looked and the pipes were fine.

Incedentally, I went from old rusty originals to oem w/gutted cat, to ssi/m&k 1 out. Both steps were incrementally better in both heat and engine response, and I could barely be happier with my drivetrain now. Though admittedly the $/HP ratio is out of whack with the ssi. At least now I can stop obsessing about the exhaust and move on to the next thing, what ever that may be!

[boyt911sc]

Tim,

Even with the HE removed from the engine, it is a very tedious job to get the rusted nuts and bolts off. The next time you plan to drop your engine would the best time to work on your exhaust system replacement. I prefer the one-day drop and one-day install procedure. In 2 days you'll be able to replace and work on your exhaust project with less back pain and don't forget the broken exhaust stud (if any). I doubt if you could remove and replace the HE by yourself in a day's work. Probably yes and at end of the day too exhausted to even enjoy some beer. Time to save for a set of SSI. How much they cost now? Last year, I bought a set of SSI for a PP member for $1,100 delivered to my house. That's probably the last USA-made SSI PP had in stock before moving the production facility to Europe.

Tony

[tirwin]

Chris,

I pulled the cat and found it had been cored out by some PO so I already had a test pipe of sorts. Makes the actual test pipe I was planning to put on a moot point.

I was very much on the SSI bandwagon until I saw the dyno results from sbmackie. He keeps threatening to do a write-up on his before/after results so I won't steal his thunder, but it definitely made me rethink the $/HP gains. The cost of the SSIs is double OEM heat exchangers and then you have to factor in the cost of the oil lines, heat backdate and 2-in muffler. I know that flies in the face of conventional wisdom around here but it is what it is I guess.

[Bear911]

Yes CO is odorless and colourless, but it won't be present in the cabin without one smelling the other exhaust fumes as well. I've always felt that the 'odorless' chemistry class factoid creates unnecessary paranoia.

But yes, don't use the heater if it smells like your exhaust. CO has a 200-250 times greater affinity for haemoglobin compared to oxygen.

I think the danger was greater (as was the usefulness of CO leak detectors) when generally more people smoked in their cars and wouldn't smell anything out of the ordinary. If you smoke in a 911 you deserve to be poisoned anyway.

[fintstone]

Those look to be in good, usable condition. In GA, those will likely outlast you unless you want to replace for purely cosmetic reasons.

[ParkerFE]

Originally Posted by porwolf

Seems as long as you don't smell exhaust when you turn on the heaters you are OK. The exhaust manifolds have a lot thicker material than the heater boxes around them and should last a lot longer, of course.

I would replace with new heat exchangers or headers w/heat.. I have ones made by Rarlyl8 and am pleased. FYI, carbon monoxide has no smell and is deadly.

[Fabspeed Motorsport]

Fabspeed Motorsport offers a lifetime warrantied header muffler kit with heater boxes. Not only does it drop about 40lbs of the car but it also is good for another 24hp!!!!!!!!!!!!!!

[tirwin]

Tim,



Even with the HE removed from the engine, it is a very tedious job to get the rusted nuts and bolts off. The next time you plan to drop your engine would the best time to work on your exhaust system replacement. I prefer the one-day drop and one-day install procedure. In 2 days you'll be able to replace and work on your exhaust project with less back pain and don't forget the broken exhaust stud (if any). I doubt if you could remove and replace the HE by yourself in a day's work. Probably yes and at end of the day too exhausted to even enjoy some beer. Time to save for a set of SSI. How much they cost now? Last year, I bought a set of SSI for a PP member for $1,100 delivered to my house. That's probably the last USA-made SSI PP had in stock before moving the production facility to Europe.



Tony

Tony a new set of SSIs goes for $1900+. The used ones were being snapped up last year because people were worried about the quality going down after being sold to Dansk. I haven't looked to see if the prices have come down lately, but I suspect there will continue to be a premium for "original" SSIs, if for nothing other than perception.

Personally, I love the SSI setup, don't get me wrong. Not sure I can justify the cost based on HP/torque return on investment.

I got a sweet deal on a used test pipe and muffler from a fellow Pelican. The muffler was a custom build from another Pelican. Very light. It's pretty loud and blatty compared to the stock muffler. Kinda makes the car sound like an old school muscle car at idle and then it really opens up at speed. A few minutes with the angle grinder and a coat of VHT paint and it looks brand new. That's hard to beat.

[Josh D]

Originally Posted by tirwin

I was very much on the SSI bandwagon until I saw the dyno results from sbmackie. He keeps threatening to do a write-up on his before/after results so I won't steal his thunder, but it definitely made me rethink the $/HP gains.

I can only speculate that your friends car has not been tuned to the SSI's, and therefore hasn't seen any gains?

I added early heat exchangers on my big port, K-basic SC and, along with some A/F and timing adjustments, really, really woke up the car. No before and after dyno proof, but the change was unmistakeable.

BTW, I bought used early factory heat exchangers, new oil lines, and a NIB used Bursch 2 in/1 out muffler for under $1K. I don't live in a wet climate, so I'm ok with stock steel HE. Just something to think about.

[tirwin]

Quote de tirwin

I was very much on the SSI bandwagon until I saw the dyno results from sbmackie. He keeps threatening to do a write-up on his before/after results so I won't steal his thunder, but it definitely made me rethink the $/HP gains.

I can only speculate that your friends car has not been tuned to the SSI's, and therefore hasn't seen any gains?



I added early heat exchangers on my big port, K-basic SC and, along with some A/F and timing adjustments, really, really woke up the car. No before and after dyno proof, but the change was unmistakeable.



BTW, I bought used early factory heat exchangers, new oil lines, and a NIB used Bursch 2 in/1 out muffler for under $1K. I don't live in a wet climate, so I'm ok with stock steel HE. Just something to think about.

That's good to know.

I can't speak to how tuned Scott's car was before and after. He was already running a test pipe and a more free-flowing muffler so maybe the difference over a completely stock setup is greater.

[tirwin]

Originally Posted by AJ@Fabspeed

Fabspeed Motorsport offers a lifetime warrantied header muffler kit with heater boxes. Not only does it drop about 40lbs of the car but it also is good for another 24hp!!!!!!!!!!!!!!

AJ,

That setup looks great. 24hp? That's like a 13% HP gain from a stock engine. Don't take this the wrong way, but do you have dyno data that backs that up? I'd love to see what the HP and torque curves look like on the same car before and after. Is that something you're willing or able to share?

I'm assuming they are, but I'll ask anyway... are those equal length primaries?