Thermostat Housing

[Todd L.]

According to my JG the thermostat housing I need for my 74 LS4 is part #336773. Are there other motors this part was on? None of the catalogs I have, even list the part. Can anyone help me locate it?
Thanks

Todd

[Joe L.]

Re: Thermostat Housing

According to my JG the thermostat housing I need for my 74 LS4 is part #336773. Are there other motors this part was on? None of the catalogs I have, even list the part. Can anyone help me locate it?
Thanks

Todd

Todd------


I don't see how a GM #336773 could have been used on a 1974 Corvette. The GM #336773 thermostat housing is similar to a 3877660. The differences are that it uses TWO SHORT mounting bolts instead of a short and a long like the 3877660 AND it has no "triangular" extension for a carb return spring anchor point. The 336773 may have been used in PRODUCTION for some or all 1973 Corvettes, but I don't think for 1974. Primarily, the 336773 was used for 73+ MD/HD truck applications and, although it may have been used in PRODUCTION for 1973 cars, including Corvette, it was never specified in SERVICE for any 1973 cars----just MD/HD trucks.

1974 Corvettes used an outlet with a boss and NPT tapping on the top for an emissions control system thermo switch. There was just a SINGLE such fitting, though. Some later SERVICE thermostat housings (which were also used in later PRODUCTION) had TWO fittings requiring that one be plugged when used for earlier applications like 1974. I believe the 1974 housing with the single fitting was GM #336790, but other housings may have been used.

Dr. Rebuild might still have some NOS examples of the single fitting housing. I know they used to, anyway.

[Todd L.]

Re: Thermostat Housing

Joe,

Thanks for the response, I am confused though. This is the paragraph from the JG:
Thermostat Housing
The thermostat housings are engine color like the intake manifold. A part number is visible. The L48/L82 housing part number is 336790. The part number is generally found on the flange of the housing although it occasionally appears on the neck and may be obscured by the upper radiator hose. The LS4 housing number is 336773. Original housings have recesses near the shorter bolt holes, replacements do not. The thermostat housing does not have a boss or port in either year.

Would you or anyone have a picture of an original? Looking through Dr. Rebuild's catalog, all I find is housings for the L48.

[Joe L.]

Re: Thermostat Housing

Joe,

Thanks for the response, I am confused though. This is the paragraph from the JG:
Thermostat Housing
The thermostat housings are engine color like the intake manifold. A part number is visible. The L48/L82 housing part number is 336790. The part number is generally found on the flange of the housing although it occasionally appears on the neck and may be obscured by the upper radiator hose. The LS4 housing number is 336773. Original housings have recesses near the shorter bolt holes, replacements do not. The thermostat housing does not have a boss or port in either year.

Would you or anyone have a picture of an original? Looking through Dr. Rebuild's catalog, all I find is housings for the L48.

Todd------

It is VERY confusing. Here's why as I did a little more research on this.

The GM #336773 was manufactured in TWO DIFFERENT CONFIGURATIONS. Apparently, the drawing for the part was revised. The original 1973 version had no boss or fitting and was configured just like I described in my previous post. The revised version, which may have happened in later 1973 or 1974 had a cast-in boss on the top and was drilled and tapped for an NPT fitting. Why GM made such a major revision to the part and didn't change the casting/part number is beyond me.

The 336790 dates from about the same time period. As far as I can tell, it was only made with the boss and fitting. However, it's possible that there was a no-boss- and-fitting version of this one, too. I have not seen one, though.

I find it odd that the JG says that no 1973 or 74 used a thermostat housing with a boss and fitting. That's definitely true for 1973 and I believe that all 1973's used the GM #3877660 (no boss or fitting on ANY of these) or the 336773 (no boss or fitting version). However, I believe that 1974 was different.

For 1974 there were 3 different engines and 2 different emissions systems used. That means, theoretically, 6 different emissions configurations. I believe that at least some of these configurations used the thermostat housing-mounted thermo switch which would necessitate a thermostat housing with the boss and fitting.

So, I guess it boils down to whether your car has (or once had) an emissions system requiring the thermostat-mounted thermo switch.

By the way, the 336773 or the 336790 are applicable to EITHER a 350 or 454 cid application. Neither one is engine application specific.

What thermostat housing is on the car now?

[Todd L.]

Re: Thermostat Housing

If memory serves me correct, it is a generic housing with no boss at all, the previous owner had an aftermarket upper radiator hose. From doing my research, the car was purchased in Colorado Springs, CO. taken to MD, then to CA, where I have areceipt for emmisions control work done to the car. It then made its way back to MD, where I purchased it. It is now sitting back in Denver, CO waiting for me to return from my deployment. It did have a AIR system on it, however, the pump and diverter valve is not original, the diverter valve was rigged to work. I removed all the AIR equipment and plugged the hole on the headers, until I am able to locate/afford the proper exhaust manifolds, and AIR equipment.
Didn't all 74's have emmissions equipment, how do I tell what mine should have originally came with.
When I am finally judged, the manual seems to be very obscure.

Thanks for the help.

Tod

[Joe L.]

Re: Thermostat Housing

If memory serves me correct, it is a generic housing with no boss at all, the previous owner had an aftermarket upper radiator hose. From doing my research, the car was purchased in Colorado Springs, CO. taken to MD, then to CA, where I have areceipt for emmisions control work done to the car. It then made its way back to MD, where I purchased it. It is now sitting back in Denver, CO waiting for me to return from my deployment. It did have a AIR system on it, however, the pump and diverter valve is not original, the diverter valve was rigged to work. I removed all the AIR equipment and plugged the hole on the headers, until I am able to locate/afford the proper exhaust manifolds, and AIR equipment.
Didn't all 74's have emmissions equipment, how do I tell what mine should have originally came with.
When I am finally judged, the manual seems to be very obscure.

Thanks for the help.

Tod

Todd------


I'm hoping that Lyle Chamberlain will weigh in on this one because he's a lot more familiar with 73-74 Corvettes than I am. It may be that he's currently at the NCRS meet in Florida. Lyle, are you out there?

In any event, there are a few things I can offer. First of all, all 1974 Corvettes except those with L-48, auto trans, and federral emissions certification were equipped with AIR. So, your LS-4 is supposed to be so-equipped.

Also, the engine should be equipped with an EGR valve. It's very easy to see. It's mounted on the front left (driver side) of the intake manifold. There should be one vacuum line going from the EGR valve to the thermostatically controlled vacuum switch. For your application, I believe this switch is mounted in the fitting on the top of the thermostat housing. However, it may also be mounted in the manifold. In any event, the switch should appear GENERALLY like the photo attached (the attached photo is not a photo of the exact, correct-in-every-detail switch). The other port on the switch should connect to a vacuum nipple on the base of the carburetor.

One of the problems you will likely be facing here is that a lot of the emissions control equipment may have been previously removed from the engine. This creates BIG problems, but it's very common, especially with 1974 Corvettes. 1974 was the last year before the use of catalytic converters on most cars, including Corvettes. Due to federal emissions regs for the 1974 model year, on-engine emissions controls were being "squeezed" to achieve the required emissions. This created driveability problems with 1974 model year cars. So, a lot of owners sought to strip the engines of their emissions equipment, often creating more problems than they solved.

Basically, your engine should have EGR (exhaust gas recirculation), AIR (air injection reactor system), EEC (evaporative emissions control), PCV (positive crankcase ventilation), TCS (transmission-controlled spark), and a closed element air cleaner. It should also have a specific carburetor and distributor calibrated to work with the overall emissions control system.

Re-constructing the AIR system on your car won't be too difficult EXCEPT for the diverter valve. The rest of the system is pretty much available in rebuilt, reproduction, or replacement markets. The diverter valve you need is GM #7040361. The proper exhaust manifolds, GM casting #3969869, left, and 3880828, right, with AIR fittings are available in reproduction, but they are expensive.

Restoring the original, as-built engine configuration will be a challenge. However, keep this in mind: the very last Corvette that Zora Arkus-Duntov owned and regularly drove was a 1974 with LS-4. He said that it was his favorite Corvette of all time.

[Todd L.]

Re: Thermostat Housing

My other search is for the correct carb, right now I have a holley with an adapter plate matching it to the original intake. I am unable to fit the original air-cleaner assembly because of the height of the carb and adapter.

I know the EGR is there, but the vacuum lines are routed different, like you have said since the thermostat housing is wrong.

I do not have any of my pictures, otherwise I could see/post what it looks like right now (no matter how embarrassing).

Any recommendations on where to buy the different EGR, AIR, EEC, PCV, and TCS components. As well as the diverter valve?

Thanks for the help.

[Joe L.]

Re: Thermostat Housing

My other search is for the correct carb, right now I have a holley with an adapter plate matching it to the original intake. I am unable to fit the original air-cleaner assembly because of the height of the carb and adapter.

I know the EGR is there, but the vacuum lines are routed different, like you have said since the thermostat housing is wrong.

I do not have any of my pictures, otherwise I could see/post what it looks like right now (no matter how embarrassing).

Any recommendations on where to buy the different EGR, AIR, EEC, PCV, and TCS components. As well as the diverter valve?

Thanks for the help.

Todd------


A lot depends upon whether your intention is to do a 100% correct restoration (or, as close to it as you can get) or you just want a functionally correct system.

The "100% correct" restoration will require obtaining a lot of NOS or original used parts. That an get very expensive. Even a functionally correct system will not be cheap, but it will be less than going all the way.

A correctly numbered and dated carb is going to be tough to find and expensive when you do. A replacement Q-Jet which is configurationally and functionally correct might be a lot less. "Numbers" can be expensive.

[Terry M.]

Re: Thermostat Housing

Todd------


A lot depends upon whether your intention is to do a 100% correct restoration (or, as close to it as you can get) or you just want a functionally correct system.

The "100% correct" restoration will require obtaining a lot of NOS or original used parts. That an get very expensive. Even a functionally correct system will not be cheap, but it will be less than going all the way.

A correctly numbered and dated carb is going to be tough to find and expensive when you do. A replacement Q-Jet which is configurationally and functionally correct might be a lot less. "Numbers" can be expensive.

Lyle Chamberlin and Mrs. Ghamberlin were at the next lunch table to me in "Krazy Kats" restaurant in Kissimmee this afternoon. I believe he is in Florida for the Winter, but he will likely check in from time to time.

[Todd L.]

Re: Thermostat Housing

Can I go functional until I acquire the proper components? I have access to a 77 or 79 Rochester carb, it has an electric choke vice mechanical. WOuld I be able to make it mechanical if it would work.
I would eventually like to make it correct. It sounds like the car wants all the emission equipment, to run well though.
Every now and then I see a 74 LS4 carb on ebay, unfortunately it is always for an automatic.
What hurts the most is I was able to track down the second owner, who went through a messy divorce. His ex through all the excess parts away.
Once I get home, I can look at the routing of the vacuum hoses and see what is required.
As always any help/suggestions are welcome.

Tod

[Joe L.]

Re: Thermostat Housing

Can I go functional until I acquire the proper components? I have access to a 77 or 79 Rochester carb, it has an electric choke vice mechanical. WOuld I be able to make it mechanical if it would work.
I would eventually like to make it correct. It sounds like the car wants all the emission equipment, to run well though.
Every now and then I see a 74 LS4 carb on ebay, unfortunately it is always for an automatic.
What hurts the most is I was able to track down the second owner, who went through a messy divorce. His ex through all the excess parts away.
Once I get home, I can look at the routing of the vacuum hoses and see what is required.
As always any help/suggestions are welcome.

Tod

Todd------


Yes, you can restore it functionally and, then, replace individual components with correct components as time goes on.

I don't think that the 77-79 carbs will be the right way to go, even for now. However, you should be able to obtain a commercially rebuilt carb for your application for not a lot of money. Likely, it will even be configurationally correct, or mostly correct, except for "numbers".

By the way, you can obtain a United Remanufactured carburetor for your application from Rock Auto under number 33414. This is for a standard transmission application. It's also a 1974 year model specific carb (although not Corvette-specific) and not a multi-year "generic". It costs about 230 bucks + 30 buck core charge. I'm not a big fan of rebuilt carburetors, and I have no experience, at all, with this brand. However, one way or another, about your only option is going to be a rebuilt unit no matter which way you go. I'd say the chances of finding an NOS carb will be extremely slim and just about "zilch" as far as a correctly dated NOS carb is concerned.

[Todd L.]

Re: Thermostat Housing

I take it the United re-manufactured carb is a good one, as far as re-manufactured goes?
One question leads to another.
on the back of the 74 carb, I have seen pictures where there is a metal tube connected to the center bottom of the carb and leads over to the master cylinder. The holley on the car does not have this tube, the rear right of the intake is a rubber hose leading to the master cylinder.
What is the part called, what does it do, and where is a good place to look for it?

Thanks

Todd

[Joe L.]

Re: Thermostat Housing

I take it the United re-manufactured carb is a good one, as far as re-manufactured goes?
One question leads to another.
on the back of the 74 carb, I have seen pictures where there is a metal tube connected to the center bottom of the carb and leads over to the master cylinder. The holley on the car does not have this tube, the rear right of the intake is a rubber hose leading to the master cylinder.
What is the part called, what does it do, and where is a good place to look for it?

Thanks

Todd

Todd-----

I don't know too much about the United Reman carb rebuilding company or their products. However, they do offer a 1974-specific carb for your application at what I consider to be a reasonable price. Rock Auto is a good and reliable parts retailer, too, and they usually sell high quality stuff. However, you might also try local auto supply stores to see what lines they have to offer. That way, you could also see the carb before you purchase it. However, if you do get one from Rock Auto, you could always return it unused if, for any reason, you don't like it (e.g. it's not configured as-original). And, of course, if it turns out to be functionally defective in some way after you install it, I'm sure they would make that right, too.

As far as the fitting on the lower, rear center of the carburetor, it's a vacuum take-off point that's used to supply vacuum for the power brake booster. There is a reducing fitting, steel tube and bracket assembly, and rubber hose that completes the vacuum supply set-up. What someone has, apparently, done is to just connect a hose to a manifold vacuum fitting to supply vacuum to the brake booster since the Holley carb has no vacuum port for this. Actually, many applications originally used a similar connection to a manifold fitting for the brake booster vacuum. However, as you've noted, this is not how 1974 Corvettes were originally connected.

The fitting was GM #145476 and the tube/bracket assembly was GM #342411. Most unfortunately, the 1974 tube/bracket assembly was a one-year-only piece and was discontinued without supercession by GM in August, 1980. While earlier and later tubes are available in reproduction from sources like Dr. Rebuild, the 1974-only tube is not. However, I think you could use the 71-73 reproduction until such time as you could find an original 1974 piece. The fitting is also long-since GM-discontinued but is available in reproduction. It has any applications. Dr. Rebuild can also sell you excellent reproductions of the rubber tube and clamps to complete the set-up.

[Harmon C.]

Re: Thermostat Housing

The 73-74 thermostat housing information is one of the items needing corrected in the manual. In Mars PA at a regional I lost points for a 3972128 housing. I checked the five 73's in my garage and one was a 454 and they all had the 128 housing. At that point I checked for years and found the 128 on all but a few 73's.
I think the 74 should have one tapped hole in the housing and the information in this section has issues. Very few 74 454's have ever been judged so we have very little chance to get information.

[Todd L.]

Re: Thermostat Housing

If the JG is messed up does anyone know if a thermostat housing from a 74 L48 is the same as a LS4 thermostat housing?

Todd