C2 GM #3969835 Carb/Intake Heat Shield

[Paul L.]

In what years was it used for the Holley fuel percolation problems?

[Joe L.]

Re: C2 GM #3969835 Carb/Intake Heat Shield

Paul------

GM #3969835 was a carb insulation which was NEVER used in PRODUCTION. This was a part that was scheduled to be used on 1970 Corvettes with LS-7 and NA-9 (California emissions). Unfortunately, the LS-7 was cancelled before PRODUCTION and was, consequently, never installed in a PRODUCTION Corvette.

Some GM parts references show the GM #3969835 as being once-available. I'm not sure that this piece was ever available through GM parts channels, though. Nevertheless, I AM SURE that the pieces were actually manufactured and there are some "out there". In fact, I have an NOS example [not for sale]. I think that these pieces may have been "surplused out" by GMSPO in the very early 70's since there were no applications ever actually built that would have required them, Corvettes or otherwise. Thus, some quantity of these "orphaned" pieces got out into the "parts world" and, ever since, have been valiantly, but unsuccessfully, seeking to SERVICE an application that never existed. Try as they may, they can never be "fulfilled".

1970 LT-1 applications used a different insulator, GM #3972156, which was later replaced by GM #3999198.

[Joe L.]

Addendum

By the way, NO carb insulators of the type exemplified by GM #3968835 (gasket with expansive and attached aluminum plate) were EVER ORIGINALLY used on a C2. The very first use of this type of carb insulator was for the 1970 model year for cars equipped with the NA-9 California emissions system (EEC).

[John H.]

Re: Addendum

Joe -

The August '03 Dealer Price Schedule shows it as discontinued in May, 2003, with a dealer price at the time of $9.88; I know it was at one time a field TSB part for correction of vapor lock on early-80's carbureted IROC Z/28's (I had the TSB done on my IROC company car back in those days).

[Joe L.]

Re: Addendum

John-----

Yes, you're correct. I did some further checking and although the part dropped out of the Corvette P&A Catalog after the last 1970 edition, this part did have another application besides the 1970 Corvette with LS-7. It was used for 1970 Chevelles with LS-6 and L-78. It did remain in the GM parts system until 2003 as you stated.

I'm surprised, though, that this part would have been used for retrofit for the carbureted IROC application. This piece has a Holley carb flange. I would think that the IROC would have used the corollary spread-bore piece, GM #3969837 or its later iteration, GM #10147945.

[Paul L.]

Re: C2 GM #3969835 Carb/Intake Heat Shield

Thanks Joe,
So they basically serve no purpose on a Corvette 327 engine?

[Joe L.]

Re: C2 GM #3969835 Carb/Intake Heat Shield

Paul------

Oh, I didn't say that and I certainly didn't mean to imply that, either. They are not CORRECT for any 327 Corvette, but they may very well be a VERY worthwhile addition to a 327 Corvette. I think that one of these may be very helpful in reducing or eliminating fuel percolation problems and other fuel problems.

As a matter of fact, I may use one on my "ZL-1" project. As I have mentioned before, my project engine installation is not going to be a 100% correct 1969 ZL-1, anyway. I'm going to be using all GM components (or, reproductions thereof) from the 68-72 period in a combination that GM never used in Corvettes(but, could have used). Most of the GM HP/SHP engines of the 65-72 period used different combinations of a rather limited basic array of components. Given all of the possible combinations of even a very limited number of basic components, they didn't produce all of the combinations (some would have been impractical, anyway). I'm going to make one of the ones they didn't.

Anyway, the GM #3969835 qualifies as one of the components from the 68-72 "parts bin". So, it might just end up on my project if it turns out that it proves useful.

For those so-inclined, one must always balance CORRECTNESS with FUNCTIONALITY. Sometimes, the functionality of a Corvette can be improved by retrofitting of components used on later model Corvettes to earlier models. Obviously, it can't be done with the majority of components, but there are select cases in which it can be done to advantage. After all, GM DID improve the cars and, sometimes, the improvements are easily retrofitable. GM even encourages and facilitiates this process when they supercede certain earlier components with later ones for SERVICE.

Of course, many times the retrofit of later components is at odds with the goals of an exactly correct restoration. So, if exactly correct restoration and exactly correct configuration are of paramount importance to one, then one has to forego taking advantage of later-issue components.

Keep in mind, though, that when changes are made to a Corvette, they must be done JUDICIOUSLY. There are some things which do change for the worse. There are some things which are inappropriate. There are some things that just won't work or work to advantage unless other changes are made, too. So, it's a process that has to be well thought out.

[Joe R.]

Re: Availability of #3969835

Joe,

Yes, the 3969835 was available from your local GM parts counter. I have a couple on the shelf for a Holley. Also have 3969837 which was for the spread bore carb.

As you say (not for sale).

JR

[Jack W.]

Re: Availability of #3969835

I have this vague recollection about hearing that the carb heat shield (3969835) was also used in SERVICE to address customer complaints of a fuel perc problem in their C2 holley-equipped SHPs? (Hard to restart after a hot shut down, I believe). Although, after just looking, I can find no TSB in my 65 M.Y. collection of same that mentions this. Nor any reference to it in a list of 66 M.Y. TSBs. If, as John advises, they just recently left production, shouldn't some still remain in inventory in places?

I have promised Paul that I would trace out a template of the 3969835 part, to enable him to carve up the still produced by Holley version in similar fashion, as the Holley-produced version presents interference issues, he advises. I'll get to it Paul, promise.

[Paul L.]

Re: Availability of #3969835

Jack,
I really appreciate your kind offer! But I found an NOS GM ...835 heat shield in the Southern USA. I should have it in about one week. Again thanks for your help!

[Paul L.]

Re: C2 GM #3969835 Carb/Intake Heat Shield

Joe,
Excellent reply! The correctness vrs. functionality concept is really what is driving this heat shield matter. I do have a minor fuel percolation problem with my 1967 and saw the shield as a possible solution. I read that the ...835 GM shield "might" have been a retrofit for the C2s in the late 1960s. While my car is far from correct it is basically stock in appearance. As Jack mentioned I did purchase a Holley shield but after twisting it about and nipping bits off here and there I didn't have the heart to put it on my car. So I fell back on the functional GM version. As noted with Jack I have located one (NOS) in the Southern USA. From the pic of it sent to me I can see possible clearance problems with the rear intake vacuum fitting and crankcase vent tube. So the 1970 service date (for the 350) sounds accurate as the intake would have changed by then and the vent tube was gone. But I will sort these things out. I would hate to cut the unit so other options may have to be pursued.

[Paul L.]

Re: Availability of #3969835

If anyone is interested there is a ...837 heat shield on EBay at the moment.

http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&category=34198&item=2454451711

[Joe L.]

Re: Availability of #3969835

Paul-----

This item is a GM #3969837 which is the Q-Jet-configured shield.

[Joe L.]

Re: C2 GM #3969835 Carb/Intake Heat Shield

Paul, et al------

Also, Dr. Rebuild can supply reproductions of both the GM #3969837 (Q-Jet flange) and the GM #3972156 (Holley flange) (later, GM #3999198). Except for the stamped-on part numbers, which are completely a non-issue for your application) I think that his reproductions will be "functionally exquisite".

Keep in mind that the GM #3969835 is designed for BIG BLOCK manifold configurations. The GM #3972156 or 3999198 are designed for small block manifold configuration. The latter is what you need.

[Paul L.]

Re: Availability of #3969835

I thought someone might be interested in that unit for a Q-Jet application.