SS exchangers are hotter ????

Olivier 3.0 · 01-09-2002, 03:42 AM

Hi !

A friend of mine is rebuilding his engine, and wants to upgrade to SS exchangers (SSI or others), but he was told that stainless increases heat, and may be bad for cylinders

...

I can't agree with that, but he has to be convinced; I tried several searches on the PP board, with no success...

What is your opinion about that?

BTW, he owns a '81 SC, and SSI's are a bit expensive; will he get the same results if he puts "normal" pre-74 exchangers ?

patalive · 01-09-2002, 04:37 AM

When I put SSIs (with dual outlet Monty) on my SC, I noticed that the oil temps went up quicker (particularly in stop and go traffic) but ultimately to a lower temp than the stock headers. On the highway, temps were noticable cooler with SSIs.-

When I reverted to a 2-in/1-out Dansk muffler, I did notice a slight increase in temps, but still not higher than with old stock set up.

Chuck

Tony911Z · Tony911Z's Garage

Have you guys readjusted your settings after installing the new systems? I think the increased flow means that you'll run lean untill you do. A buddy installed a BB header setup on his '77 turbo and we were horified to see the whole exhaust system glowing red hot untill he made some adjustments.

patalive · 01-09-2002, 06:23 AM

I keep my SC on the rich side, so much so that we have to dial it back when it's time for the emissions test, every two years.

Chuck

RarlyL8 · RarlyL8's Garage

Thousands of satisfied customers (including myself) can't be wrong.

Your friend is mistaken when it comes to stainless and the SSI.
This system is nothing but a win-win. I cannot find a single fault after years of driving with the SSI system and many different mufflers.

island911 · 01-09-2002, 06:26 AM

Cat-converters are designed to hold heat, so they can create even more heat, by combusting any partially burned fuels.
The only ways I could imagine an increase in temp's in the SSI's is as Tony says, or by the fact that you know your foot will be in the gas that much more

'81 SC COUPE

Clark Griswald · Clark Griswald's Garage

Perhaps your friend heard that SSI "produce more heat".

This is true, they crank plenty of heat to the passenger compartment. More than most other heat exchanger options.

Your friend might have misinterprated this as engine heat.

john walker's workshop · 01-09-2002, 08:45 AM

one property of stainless is that it holds heat better than ferrous metal. when welding it, you use lower heat or it "holes". the heater works better because of this. never heard of any actual hot running complaints yet.

911nut · 911nut's Garage

To elaborate on John's statement, stainless steel is not as good of a thermal conductor as carbon steel (that's one reason why kitchen utensils are made from it). So where a stock, carbon steel heat exchanger will give up heat to the air under the car through radiation and conduction, the stainless heat exchanger has more thermal energy to impart to the cabin air blowing through it.

island911 · 01-09-2002, 11:02 AM

Silver: 241 Btu/h/ft/°F
SS: 9.4 Btu/h/ft/°F
one benifit of SS kitchen utensils.
Ti: 4.3 Btu/h/ft/°F great for camping utensils.

For the heat exchangers thermal cond;
SS: 9.4 Btu/h/ft/°F
1020 Steel: 27.0 Btu/h/ft/°F
=>heat moves about 1/3 as fast thru the SS walls . . assuming the same wall thickness.

However, Stainless specific heat (heat storing) is 20% higher than 1020 carbon steel

More than you wanted to know

Olivier 3.0 · 01-09-2002, 11:38 PM

Ok, that's pretty clear to me... and I promise I 'll buy a "little chimist" kit next X-mas, Island

!

but nobody has answered me about the Stock pre-74 exchangers efficiency vs SSI, for HP

???

Merci

911pcars · 01-09-2002, 11:58 PM

"....Stock pre-74 exchangers efficiency vs SSI, for HP"

The SSIs are replicas of the early heat exchangers thus they provide the same power, no more, no less. However, they should last a lot longer. Look elsewhere for add'l power if you're starting off with early heat exchangers - maybe the muffler for a little improvement. Even starting from a stock SC exhaust system in good shape, you're "only" looking at what, 15 hp max? This figure might be optimistic from the heat exchangers alone.

Significant horsepower gains on a 911 are not cheap to come by.... not like a 'merican engine.

Sherwood Lee
'69 911 w/orig. heat exchangers that don't leak. At least I don't think I have any long term affects from CO overdose.