Radiator Shroud Extension

[Sheldon S.]

My car is a 1971 454 with automatic, no A/C. According to the AIM there should be a extension to the rad shroud. I purchased a repo from paragon but it is not correct nor does it fit. Does anyone know where to purchase one that is correct. I have never seen any original ones advertised on any forums or ebay.
Thanks
Sheldon

[Joe L.]

Re: Radiator Shroud Extension

My car is a 1971 454 with automatic, no A/C. According to the AIM there should be a extension to the rad shroud. I purchased a repo from paragon but it is not correct nor does it fit. Does anyone know where to purchase one that is correct. I have never seen any original ones advertised on any forums or ebay.
Thanks
Sheldon

Sheldon------


If the reproduction shroud extensions don't fit I think it must be because they're made too much like the originals----they didn't fit too well, either. In fact, I think that these may have been left off many cars at the factory because the folks on the assembly line had the exact same problem as you're having.

[Jeffrey A.]

Re: Radiator Shroud Extension

Sheldon and Joe

I have an original Shroud on my 68 BB that does have A/C and did exactly what Sheldon has explained. I purchased a repop extension from Paragon as well for my car and I do not know how to get on it without possibly damaging the original one. Being a BB A/C car there is not enough room for a finger to fit anywhere. Plus the repops are total different in color. The repops are much darker color then the original and stand out big time. I may just leave it off and take the point deduction when I have the car judge next month. If anyones know a a trick to get it without taking everything apart. I am all ears.

[Mark D.]

Re: Radiator Shroud Extension

eBay item number 110551700950 might work better for you although as others have stated, they never did fit very well.

I bought one from Cranes for my 69 and am very happy with it.

Regards,

Mark

[Ronald L.]

Re: Radiator Shroud Extension

Sheldon PM sent, got a good handle on shrouds for BB where there are a couple originals that have been in a barn for 30 years.

[Jack H.]

Re: Radiator Shroud Extension

I had similar problems with my '71 SB A/C car. The repro shroud extension did not exactly fit the factory original shroud. A little work shaving here/there and it DID install...

[Sheldon S.]

Re: Radiator Shroud Extension

What is the correct part number for the extension. I looked it up in a GM parts manual and I get 3974013, the one crane is selling has 3974014 on it and in the AIM it is different again.
Sheldon

[Joe L.]

Re: Radiator Shroud Extension

What is the correct part number for the extension. I looked it up in a GM parts manual and I get 3974013, the one crane is selling has 3974014 on it and in the AIM it is different again.
Sheldon

Sheldon------


As far as I can tell, the original shroud extension for your application was GM #3956089. This is the extension shown in the AIM and also the one specified in SERVICE. It was discontinued from SERVICE without supercession in July, 1983.

The GM #3974014 is the shroud extension used for 70-72 Corvettes with 454 and C-60. However, I would not rule out the possibility that it was also used for some 454 without C-60. It was discontinued from SERVICE in August, 1973 and replaced by the L73 454 extension GM #336152. The latter was discontinued without supercesion in August, 1990.

Just how the 3956089 and 3974014 differ I do not know. I also do not know how the 3974014 and 336152 differ. However, I believe these two are extremely similar.

The GM #3974013 is NOT a SHROUD extension. It is the lower extension also known as an "air dam" or "spoiler". It was used in PRODUCTION and available in SERVICE for 1970-72 Corvettes and also became SERVICE for 1968-69 Corvettes.

[Tom L.]

Re: Radiator Shroud Extension

Aside from judging, does the presence of the extension aid significantly in cooling these BB cars? Mine doesn't have the extgension and after reading this post was wondering if the effort is worth it in terms of engine cooling. Sitting in traffic on the way home from Carlisle with engine temps of 220-230 was a bit stressful! As far as judging goes I'm a long way off for that. Thanks!!

[Bill C.]

Re: Radiator Shroud Extension

Lynn,

That temp is way to high..... I live in FL and in decent stop/go taffic never see temps over 210 in the dead of the summer.

Now - use the AC and whole different story

Maybe time for a new Dewitt core etc.....

[Tom L.]

Re: Radiator Shroud Extension

I am aware that the heat I experienced was too high, the mrs. was particularly stressed sitting in traffic and watching the guage. There is a 5 year old aluminum radiator in the car that the previous owner installed. In addition, the pointed fan is not there. I'm using a functional 7 blade replacement fan. Apparrently I missed out on one in carlisle for a good price, a friend called me but I was too late. Aside from 90+ heat and traffic there is no issue. I was just wondering if the extension is a significant part of the cooling system. Any comments on the fan? Is it also a huge deal? Thanks!

[Jack H.]

Re: Radiator Shroud Extension

I disagree (220-230F temp too high). These Shark cars had a temp switch in the RH cylinder head to monitor coolant temperature. When temperature crept above a threshold, the temp switch closed and engaged the TCS/CEC system to feed vac to the distributor, and modestly raise engine RPM to pull more air through the radiator.

As coolant temp dropped, the temp switch would open and turn the TCS/CEC system OFF. The feature was rifle shot to prevent coolant system boil over during sustained idle periods in stop/go traffic...

I had the opportunity to 'test' the system on my A/C equipped '71 SB. It was a local 4th of July parade several years ago.

I watched the temp gauge climb (normally sits DEAD FLAT at 180F) in the 90F ambient and enter the red zone. CLICK! The CEC system kicked in.

Instead of panicking, I sat and watched. Engine speed climbed about 150 RPM with the CEC feeding vac to the distributor and with my foot OFF the gas, the temp gauge SLOWLY started to fall by itself.

Around 195F another CLICK, and engine RPM fell as the CEC system denied vac to the distributor. Not too long thereafter, the temp gauge began to climb again...

I watched the process cycle 3-4 times during the parade and the car did NOT overheat. Other, older/earlier Corvettes in the parade DID bite the bullet, spewing coolant merrily from their rad caps. Owners were forced to shut the engine down and push them to the side of the parade route!

This, of course, is a 'feature' of these cars that we do NOT test/verify during a PV test...

[Terry M.]

Re: Radiator Shroud Extension

I disagree (220-230F temp too high). These Shark cars had a temp switch in the RH cylinder head to monitor coolant temperature. When temperature crept above a threshold, the temp switch closed and engaged the TCS/CEC system to feed vac to the distributor, and modestly raise engine RPM to pull more air through the radiator.

As coolant temp dropped, the temp switch would open and turn the TCS/CEC system OFF. The feature was rifle shot to prevent coolant system boil over during sustained idle periods in stop/go traffic...

I had the opportunity to 'test' the system on my A/C equipped '71 SB. It was a local 4th of July parade several years ago.

I watched the temp gauge climb (normally sits DEAD FLAT at 180F) in the 90F ambient and enter the red zone. CLICK! The CEC system kicked in.

Instead of panicking, I sat and watched. Engine speed climbed about 150 RPM with the CEC feeding vac to the distributor and with my foot OFF the gas, the temp gauge SLOWLY started to fall by itself.

Around 195F another CLICK, and engine RPM fell as the CEC system denied vac to the distributor. Not too long thereafter, the temp gauge began to climb again...

I watched the process cycle 3-4 times during the parade and the car did NOT overheat. Other, older/earlier Corvettes in the parade DID bite the bullet, spewing coolant merrily from their rad caps. Owners were forced to shut the engine down and push them to the side of the parade route!

This, of course, is a 'feature' of these cars that we do NOT test/verify during a PV test...

It is also a "feature" of these cars that many by-pass or defeat -- and some on this board advise doing so.

[Tom L.]

Re: Radiator Shroud Extension

Yes, in fact I have taken that advice for 2 reasons; most here have a much greater knowlege of these cars and most of the TCS components are long gone.

Interesting to hear that 220-230 isn't an over the top temp. In fact the red zone on my temp guage is very close to 250, perhaps exactly at 245.

Any thoughts on the fan blade? Thanks!

[Jack H.]

Re: Radiator Shroud Extension

Yes, I've noticed the omnibus advice to convert to full time vac advance vs. ported & switched...

But, that might just obviate the 'problem' from the git go. I know I don't know the impact to the TCS/CEC system with a full time vac advance given extended periods of time under 'grid lock' conditions on very hot days. It might be the 'feature' was added to compensate for the effects of ported + switched vac advance vs. the performance profile of the earlier cars with full time advance...