Thermal reactors or not?

Lee Allen · 04-14-2009, 07:47 AM

I have just purchased a 1975 Carrera that shows a build date of 10/74 on the door sticker. Is this car going to have the Thermal reactors or not?

Does anyone have definitive photos of what the exhaust looks like from underneath with and w/o the reactors?

It does not have a smog pump and the pulley does not have an extra groove for one (though that could have been changed I know). It was sold In california originally.

thanks,

Lee

ljowdy · 07:57 AM

look under the car, if you see a cylindrical can under each bank of cylinders than you have Thermal's

I too had a 1975 that I purchased in 1977. The Thermal reactors were a chamber within a chamber. If I remember correctly, you could drill a bunch of holes in the outer chamber and that would allow heat to escape to the atmosphere and thus not cause the reactors to get so hot that they melted the engine.

Ricks911s · 04-14-2009, 08:22 AM

When I first bought a 1976 I didn't know what to look for either. I think the easiest way I figured out the difference was to look at what "heat exchangers" were and then "thermal reactors".

Thermal reactors hang right below the center of the engine and look like this: http://forums.pelicanparts.com/uploads13/heat+exchangers+0011220304496.jpg

Heat exchangers sit a little wider under the engine (these are the nice stainless steel kind): http://www.**********.com/UserData/Images/Large/253510.jpg

ossiblue · 04-14-2009, 08:26 AM

Only California delivered cars in 1975 required the thermal reactors so there is a good possibility that your car had them. Follow ljowdy's advice and look under the car--the reactors will be obvious. From what you describe, however, if all the other elements of the emissions system have been removed, it's likely a PO got rid of the engine killer thermos as well.

Lee Allen · 04-14-2009, 11:22 AM

Well I took a good look and the big Tubes (TR's) that Rick showed in his photos aren't there. that's the good news.

However, the heat exchangers look as if they were designed to bolt up to TR's, as there is a three-into-one fabricated "header" that then goes into the HE's from the engine exhaust ports and then bolts to the 3-bolt flanges that are in the middle of the Heat Exchangers. Obviously, this means that the HE's don't look like the ones in the photo Rick linked to. My best guess is that either (1) the TR's were removed by a PO or (2) Porsche built some of the early 75 cars w/o the TR's, or (3) I have a car that was built for a state other than Calif., so it didn't get the TR's.

Does anyone have any serial # that document when a change to TR's could have occured?

So, my next question: is this system still pretty efficient HP-wise?

I will post some photos later today.

Thanks,

Lee

Ricks911s · 04-14-2009, 11:30 AM

the "backdated" heat exchangers (I say backdated because your setup doesn't have the thermal reactors) I believe produces more horsepower than if you had the thermals there.

I wouldn't worry about those TR if they're not there. They suck.

Lee Allen · 04-14-2009, 11:35 AM

Indeed they do! I am glad they are not there! I just wasn't sure what I had, but it is much clearer now.

I think (hope) that this car was just built that way, not changed after delivery, as that means that the engine was never subjected to the heat issue produced w/the TR's.

Thanks,

Lee

ossiblue · 11:45 AM

Sounds like you have an aftermarket set of TR substitute "W" 's for lack of a proper name. They bolt to the heat exchanger in place of the TR's and have a, basically, "W" shape. There were some posts a while back that showed some pictures of them so hopefully someone who is familiar with the name and pictures will post.

From what you've posted, it sounds like you have a California car that came with TR's and California emissions equipment but it all has been removed. You can replace the adapted exchangers with proper 49 state ones if you want a cleaner look. Porsche did build 75's without TR's--for ROW and 49 other states, but I don't think you have one. My 75 was built for other states and never had TR's and the exchangers do not have the appendage you describe. The heavy evidence comes from your first post--"It was sold in California originally." That means it had to have TR's, if sold and registered legally.

Lee Allen · 04-14-2009, 11:59 AM

to actually make the calif emission numbers?

This car only has 64,000 original miles on it so it must have had the TR's removed pretty early in its' life.

Lee

ossiblue · 12:57 PM

Quote:

Originally Posted by Lee Allen

to actually make the calif emission numbers?

This car only has 64,000 original miles on it so it must have had the TR's removed pretty early in its' life.

Lee

Probably so, but I've heard of cars meeting the numbers with devices removed but they fail soley because the devices are missing. The car wouldn't be allowed in CA if the TR's were missing, regardless if the emission numbers were good. How certain are you of the 64K miles? Do you have docs? I only ask because that old of a car may have turned over the odo. That being said, I bought my 75 with 68K documented miles so it is possible that it is a low mileage car. If it is truly low mileage, probably the PO removed the TR's and other items before much damage (if any) was done.

BTW, you shouldn't fret too much over this if the engine checks out on a PPI (compression, leakdown, head studs, e.g.) It may even have some upgrades such as carrera tensioners. Is there any paper work on the engine? If it is solid now, with low mileage, you shouldn't worry. Just continue to keep it cool.

Also, the carrera engine may be built a bit differently than the regular 911 or 911S engine in 75--I don't know. Someone who knows will respond, hopefully.