Change to the smaller 2in exhaust manifolds in 66

[Clem Z.]

Re: Change to the smaller 2in exhaust manifolds in 66

i would guess all the smog testing was done with that manifold and to change it out all the tests would have to be run again if they change the manifold. the 375 HP 396 chevelles used the high rise manifold from the start

if i remember correctly when GM first sold the 454 with open chamber cast iron heads and 12.5:1 CR crate engine it did not come with a intake manifold.

[Norris W.]

Re: Change to the smaller 2in exhaust manifolds in 66

i would guess all the smog testing was done with that manifold and to change it out all the tests would have to be run again if they change the manifold. the 375 HP 396 chevelles used the high rise manifold from the start

Maybe, but if that's true then didn't they have to reverse the process for the low intake on the 396/375 in the 70 Nova, Camaro & Chevelle?

if i remember correctly when GM first sold the 454 with open chamber cast iron heads and 12.5:1 CR crate engine it did not come with a intake manifold.

I have an early 70's LS7 crate motor in a '69 Camaro and it came out of the box with NO intake manifold.

[Clem Z.]

Re: Change to the smaller 2in exhaust manifolds in 66

Maybe, but if that's true then didn't they have to reverse the process for the low intake on the 396/375 in the 70 Nova, Camaro & Chevelle?



I have an early 70's LS7 crate motor in a '69 Camaro and it came out of the box with NO intake manifold.

i would guess the engines were already tested and did not require retesting if the engines were not changed. i don't remember seeing the "low" aluminum manifold on anything but the 70 454/450 chevelle. i will have to check my NHRA spec sheets to see what manifold was on those cars in 70

[Norris W.]

Re: Change to the smaller 2in exhaust manifolds in 66

Clem, I'm not positive, but I THINK the 70 SHP Nova had it also and wasn't there a SHP Camaro in '70 also? Also, the SHP 402 was THE BIG motor early in the 70 model year for the Chevelle since the LS6 didn't come until later in the year. I've only seen one SHP 396 (402) at a Chevelle show, but it had the low intake. Obviously I wouldn't know it to be original to that car.

[Clem Z.]

Re: Change to the smaller 2in exhaust manifolds in 66

Clem, I'm not positive, but I THINK the 70 SHP Nova had it also and wasn't there a SHP Camaro in '70 also? Also, the SHP 402 was THE BIG motor early in the 70 model year for the Chevelle since the LS6 didn't come until later in the year. I've only seen one SHP 396 (402) at a Chevelle show, but it had the low intake. Obviously I wouldn't know it to be original to that car.

the NHRA specs shows you are correct the 3963569 was used on both the 402 and 454 SHP 1970 engines.

[Bill M.]

Re: Change to the smaller 2in exhaust manifolds in 66

i was told when i asked one of the GM engineers about the 70 454 chevelle that low manifold was used because that manifold was also to be used in a corvette with the SHP BBC engine that was listed but never was produced. that manifold would allow the carb and air cleaner to fit under a corvette hood. i changed out the manifold on my new chevelle as soon as i got the car home.

Was it used on the 1971 LS6 (454/425) in the Corvette?

[Clem Z.]

Re: Change to the smaller 2in exhaust manifolds in 66

Was it used on the 1971 LS6 (454/425) in the Corvette?

yes it was according to NHRA spec sheet

[Clem Z.]

Re: Change to the smaller 2in exhaust manifolds in 66

my guess GM was committed to buy so many of those sunken manifolds from the supplier and they knew on one would buy one over the counter so they put them on all the engine that it would fit.

[Joe L.]

Re: Change to the smaller 2in exhaust manifolds in 66

yes it was according to NHRA spec sheet

clem and Bill-----


It had to be! The 1971 LS-6 used rectangular port heads, a Holley carburetor, and a standard 68-72 Corvette big block hood. The manifold in question is the ONLY rectangular port, square bore (Holley flange) manifold which GM EVER had available that would fit under a standard 68-72 Corvette big block hood.

By the way, I've got to admit that the GM #3963569 is my favorite big block manifold of all time. I just absolutely LOVE the configuration of that manifold.

[Scott S.]

Re: Change to the smaller 2in exhaust manifolds in 66

There was an interesting thread about this subject over on the CF in 2008. One of the participants in the thread drag races his car regularly. He races "B" stock, a 1966 L79, and he tested the 2" vs. 2.5" manifolds on a dyno with all other variables being the same. He got 6hp and 8 foot-pounds more torque with the smaller 2" stock 1966 manifolds.

http://forums.corvetteforum.com/c1-a...revisited.html

[Norris W.]

Re: Change to the smaller 2in exhaust manifolds in 66

By the way, I've got to admit that the GM #3963569 is my favorite big block manifold of all time. I just absolutely LOVE the configuration of that manifold.

I've just got to ask............. WHY? I own two of 'em (2 70 LS6 cars with THE original motors) and I think they make the top of those motors look extremely boring.

Trivia question since you like 'em Joe.............. do you know how to tell the diff between the 70 & 71 version at a glance?

[Joe L.]

Re: Change to the smaller 2in exhaust manifolds in 66

I've just got to ask............. WHY? I own two of 'em (2 70 LS6 cars with THE original motors) and I think they make the top of those motors look extremely boring.

Trivia question since you like 'em Joe.............. do you know how to tell the diff between the 70 & 71 version at a glance?

Norris-----

Cylinder numbers on the ends of the runners.

[Norris W.]

Re: Change to the smaller 2in exhaust manifolds in 66

Norris-----

Cylinder numbers on the ends of the runners.

I guess that one was too easy Joe. Sooner or later I'm gonna' find something to trip you up on.

It's always amazed me how many LS6 intakes show up on E bay with the numbers showing. Given the low number of LS6 Corvettes produced in 71 evidently every one of them had the intake removed and offered for sale on the internet.