Exhaut manifold question for 69 350
02-18-2024, 12:03 AM
#1
Instructor
Thread Starter
Exhaut manifold question for 69 350
Probably discussed many times, but I could not find the info I was looking for in the forum.
I have a '69 350/350 4-speed with side pipes. Engine is completely stock and original. Im thinking of switching out my 2" exhaust manifolds for a new hi-temp ceramic coated pair of ram horns as they look stock, always look new, no rust spots, etc. My concern is that the new manifolds are 2.5" at the outlet. A couple of questions;
1) Will the size difference have any negative effect on performance as these engines were designed with the 2" outlet.
2) Would I need to modify timing with the change to a 2.5" manifold?
Lastly, I'm assuming the change would require modification to a larger connector that then goes into the side pipes, correct?
Thanks very much in advance for your advice!
I have a '69 350/350 4-speed with side pipes. Engine is completely stock and original. Im thinking of switching out my 2" exhaust manifolds for a new hi-temp ceramic coated pair of ram horns as they look stock, always look new, no rust spots, etc. My concern is that the new manifolds are 2.5" at the outlet. A couple of questions;
1) Will the size difference have any negative effect on performance as these engines were designed with the 2" outlet.
2) Would I need to modify timing with the change to a 2.5" manifold?
Lastly, I'm assuming the change would require modification to a larger connector that then goes into the side pipes, correct?
Thanks very much in advance for your advice!
02-18-2024, 01:11 AM
#2
1967 Pedal Car Champion
I don't see any negative on performance. A lot of folks up-size the 2" to 2.5" for better performance. That said, unless you are also changing the entire system to 2.5" then any performance gain will be minimal to nothing. Additionally, it's frequently said that the side exhaust actually hurts performance due to design restrictions that the under-car system doesn't have.
02-18-2024, 01:31 AM
#3
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As one who has installed the ceramic coated 2 1/2 inch aftermarket exhaust manifolds I think I can field your questions.
1. Performance is not affected in a negative way whatsoever. In a positive way, yes.
2. Ign timing is unaffected.
Now, on to the things you didn't ask.
The pipe that connects to the 2 inch manifold uses a donut packing. The 2 1/2 inch manifolds use a flat gasket. The flanges that come with the aftermarket manifolds are garbage at best. Your local exhaust shop will be able to remove the 2 inch section of pipe from your current exhaust and make up 2 1/2 inch replacements, and they likely will have much better quality flanges on hand.
you WILL need to change out the pipe below the manifolds to the correct size and the different type of flange.
All well worth the effort. These ceramic coated manifolds not only stay looking great for years. But really do help your engine breathe better.
Perhaps not long tube headers. but much better than the stock manifolds.
Well worth the effort. But do consider you will need to have a good exhaust shop modify your pipes.
Also consider if your running a carburetor, although timing will be unaffected, jetting is likely to be affected.
1. Performance is not affected in a negative way whatsoever. In a positive way, yes.
2. Ign timing is unaffected.
Now, on to the things you didn't ask.
The pipe that connects to the 2 inch manifold uses a donut packing. The 2 1/2 inch manifolds use a flat gasket. The flanges that come with the aftermarket manifolds are garbage at best. Your local exhaust shop will be able to remove the 2 inch section of pipe from your current exhaust and make up 2 1/2 inch replacements, and they likely will have much better quality flanges on hand.
you WILL need to change out the pipe below the manifolds to the correct size and the different type of flange.
All well worth the effort. These ceramic coated manifolds not only stay looking great for years. But really do help your engine breathe better.
Perhaps not long tube headers. but much better than the stock manifolds.
Well worth the effort. But do consider you will need to have a good exhaust shop modify your pipes.
Also consider if your running a carburetor, although timing will be unaffected, jetting is likely to be affected.
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brookiez28 (03-12-2024)
02-18-2024, 03:14 AM
#4
I just bought the Corvette Central 1964-1965 2.5" downpipes part number 322414 to bolt onto my 68: Clumsy bigger things so pay attention to shipping charges. I got mine from RPI because they had better shipping choices but doesn't seem to anymore.
https://www.corvettecentral.com/c2-6...ipes%2f1964%2f
https://www.rpidesigns.com/shop/item...i-performance/
https://www.corvettecentral.com/c2-6...ipes%2f1964%2f
https://www.rpidesigns.com/shop/item...i-performance/
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brookiez28 (02-18-2024)
02-18-2024, 05:57 AM
#5
Platinum Supporting Vendor
Please use Feb24 code for best savings
02-18-2024, 11:49 AM
#6
Instructor
Thread Starter
I don't see any negative on performance. A lot of folks up-size the 2" to 2.5" for better performance. That said, unless you are also changing the entire system to 2.5" then any performance gain will be minimal to nothing. Additionally, it's frequently said that the side exhaust actually hurts performance due to design restrictions that the under-car system doesn't have.
Appreciate your feedback!
02-18-2024, 11:52 AM
#7
Instructor
Thread Starter
As one who has installed the ceramic coated 2 1/2 inch aftermarket exhaust manifolds I think I can field your questions.
1. Performance is not affected in a negative way whatsoever. In a positive way, yes.
2. Ign timing is unaffected.
Now, on to the things you didn't ask.
The pipe that connects to the 2 inch manifold uses a donut packing. The 2 1/2 inch manifolds use a flat gasket. The flanges that come with the aftermarket manifolds are garbage at best. Your local exhaust shop will be able to remove the 2 inch section of pipe from your current exhaust and make up 2 1/2 inch replacements, and they likely will have much better quality flanges on hand.
you WILL need to change out the pipe below the manifolds to the correct size and the different type of flange.
All well worth the effort. These ceramic coated manifolds not only stay looking great for years. But really do help your engine breathe better.
Perhaps not long tube headers. but much better than the stock manifolds.
Well worth the effort. But do consider you will need to have a good exhaust shop modify your pipes.
Also consider if your running a carburetor, although timing will be unaffected, jetting is likely to be affected.
1. Performance is not affected in a negative way whatsoever. In a positive way, yes.
2. Ign timing is unaffected.
Now, on to the things you didn't ask.
The pipe that connects to the 2 inch manifold uses a donut packing. The 2 1/2 inch manifolds use a flat gasket. The flanges that come with the aftermarket manifolds are garbage at best. Your local exhaust shop will be able to remove the 2 inch section of pipe from your current exhaust and make up 2 1/2 inch replacements, and they likely will have much better quality flanges on hand.
you WILL need to change out the pipe below the manifolds to the correct size and the different type of flange.
All well worth the effort. These ceramic coated manifolds not only stay looking great for years. But really do help your engine breathe better.
Perhaps not long tube headers. but much better than the stock manifolds.
Well worth the effort. But do consider you will need to have a good exhaust shop modify your pipes.
Also consider if your running a carburetor, although timing will be unaffected, jetting is likely to be affected.