2 inch or 2 1/2 inch exhaust manifold

[Duke W.]

Re: 2 inch or 2 1/2 inch exhaust manifold

I can't imagine why they went with 2 inch manifolds just increase the diameter of the pipe back to 2.5 . Why go to the trouble of redesigning a cast iron part? They had what they needed on hand already.

Neither can anyone else, but the 2" ram horn manifolds had been around since 283 days, so both parts were in production. It may have been a parts consolidation issue - save cost. Corvette had to absorb increased cost for the hokey 2 - 2.5" head pipe, but that was only a little over 20,000 units a year when Chevrolet was annually selling over one million cars and light trucks back then, most of which had small block V-8s.

Duke

[Peter J.]

Re: 2 inch or 2 1/2 inch exhaust manifold

Mike,
Since you don't care about your car's original configuration why not get a set of these larger diameter side pipes. I know nothing about the company but have always known about the restrictive nature of the stock system and wondered why nobody ever did this.

http://www.sweet-thunder.com/corvette_sidepipes_63_67.html

[Michael M.]

Re: 2 inch or 2 1/2 inch exhaust manifold

Mike,
Since you don't care about your car's original configuration why not get a set of these larger diameter side pipes. I know nothing about the company but have always known about the restrictive nature of the stock system and wondered why nobody ever did this.

http://www.sweet-thunder.com/corvett...pes_63_67.html

Peter
Actually, I do care about the original configuration. I was pretty much just putting off the extra work until sometime in the future.

I did speak to someone at sweet thunder earlier in the week. I was looking into their new quieter sidepipes. I figured they were even more restrictive so maybe changing the manifolds to 2.5 inch would help some. Now I might just go back to original configuration and lose the side pipes altogether. I'll have to figure out what to do with those brackets though.

[Peter J.]

Re: 2 inch or 2 1/2 inch exhaust manifold

Mike,
I know the bias we (the NCRS) has about adding side pipes but I never really cared about all the lectures I got when adding side pipes to my 66. I had a couple of older friends when growing up in the sixties that had mid-years with side pipes and almost fifteen years a go when I got mine it was one of the things that I had to do. I haven't regretted it once. I have had a few fellow judges tell me "you know that will never do in judging and I should change back". I don't see that happening in my case.
Pete

[John M.]

Re: 2 inch or 2 1/2 inch exhaust manifold

Not to change the subject, sort of, but what was GM thinking when they put 2" pipes on 69 BB Corvettes (or all Corvettes that year)??

[Michael M.]

Re: 2 inch or 2 1/2 inch exhaust manifold

Mike,
I know the bias we (the NCRS) has about adding side pipes but I never really cared about all the lectures I got when adding side pipes to my 66. I had a couple of older friends when growing up in the sixties that had mid-years with side pipes and almost fifteen years a go when I got mine it was one of the things that I had to do. I haven't regretted it once. I have had a few fellow judges tell me "you know that will never do in judging and I should change back". I don't see that happening in my case.
Pete

Hi Pete,

Oh I totally understand, after all, it is the corvette restorers society, not the corvette customizers society. That is the point of the whole organization, that's what the founders intended so it should come as no surprise. Why join if you're gonna argue about it. I bought my car knowing the pipes were added, but I liked them anyway. It's something you can reverse later. The rest is pretty original. I had one sagging spring in the front and some deteriorated bushings and ball joints or I would have left that alone as well. I can't wait to drive it with a tight front end. I would love to do a body off resto, but I only have one fun car, so it's gonna have to wait. The paint and body look good enough for now, no worry about paint chipping. The exhaust manifolds are really rusty, I don't think they'll be any detail left when cleaned up so I'm gonna swap them out for.....?

Mike

[Jim H.]

Re: 2 inch or 2 1/2 inch exhaust manifold

For me, participation in NCRS doesn't come with the requirement that my car Top Flight. A Top Flight would be nice some day, but it's not the focus of my enjoyment of my Corvettes or my participation in NCRS. My 66 L79 came with non-original side pipes and I opted for 2.5" '65 hipo manifolds. I like the look of the pipes and for the first hour or so on a trip, I enjoy the sound. I'm on my second set of pipes; first set were Trans Am deafening but Sweet Thunder's GM sound are fine for me, although any side pipe will be louder than an undercar exhaust. So I wear earplugs, leave the radio off, and find the relative silence and lack of radio distraction conducive to deeper thought. When I had the car flight judged, I was happy to Second Flight knowing that the side pipes, 5 speed overdrive, Nardi steering wheel, and aftermarket KOs gave me far greater daily pleasure than the Top Flight ribbon.

[Robert I.]

Re: 2 inch or 2 1/2 inch exhaust manifold

do the 2 1/2 inch manifolds use a longer bolt than the 2" manifolds?

[Joe L.]

Re: 2 inch or 2 1/2 inch exhaust manifold

do the 2 1/2 inch manifolds use a longer bolt than the 2" manifolds?

Bob-------


If you mean the bolts that retain the manifolds to the heads, the 2" and 2-1/2" use the same bolts.

[Gene M.]

Re: 2 inch or 2 1/2 inch exhaust manifold

For me, participation in NCRS doesn't come with the requirement that my car Top Flight. A Top Flight would be nice some day, but it's not the focus of my enjoyment of my Corvettes or my participation in NCRS. My 66 L79 came with non-original side pipes and I opted for 2.5" '65 hipo manifolds. I like the look of the pipes and for the first hour or so on a trip, I enjoy the sound. I'm on my second set of pipes; first set were Trans Am deafening but Sweet Thunder's GM sound are fine for me, although any side pipe will be louder than an undercar exhaust. So I wear earplugs, leave the radio off, and find the relative silence and lack of radio distraction conducive to deeper thought. When I had the car flight judged, I was happy to Second Flight knowing that the side pipes, 5 speed overdrive, Nardi steering wheel, and aftermarket KOs gave me far greater daily pleasure than the Top Flight ribbon.

Wonderful.....! You have second flight, absolutely nothing wrong with that. You have the car the way you want it and still is second flight with all your modifications. Good for you. Enjoy it and drive it.

[Robert I.]

Re: 2 inch or 2 1/2 inch exhaust manifold

"If you mean the bolts that retain the manifolds to the heads, the 2" and 2-1/2" use the same bolts"

Yes, that's what I mean.

I threaded one of the longer bolts into the head and covered the rest of the bolt with masking tape. About 3/4 inch goes into the head. Then I measured the amount of thread coming out of the manifold. Only about 7/16th inch exposed.

You wouldn't want 3/4 inch, but I think 1/2 or 5/8 inch would be better.

[Joe L.]

Re: 2 inch or 2 1/2 inch exhaust manifold

"If you mean the bolts that retain the manifolds to the heads, the 2" and 2-1/2" use the same bolts"

Yes, that's what I mean.

I threaded one of the longer bolts into the head and covered the rest of the bolt with masking tape. About 3/4 inch goes into the head. Then I measured the amount of thread coming out of the manifold. Only about 7/16th inch exposed.

You wouldn't want 3/4 inch, but I think 1/2 or 5/8 inch would be better.

Bob-------


Generally, acceptable thread engagement length is equal to the thread size of the fastener. So, in the case of these 3/8-16 bolts, 3/8" thread engagement would be acceptable.

[Russ S.]

Re: 2 inch or 2 1/2 inch exhaust manifold

As a former machinist, I was always told that the accepted thread length was 1-1/2 times the diameter of the bolt. 3/8 thread engagement on a 3/8 bolt is not enough.

Bob-------


Generally, acceptable thread engagement length is equal to the thread size of the fastener. So, in the case of these 3/8-16 bolts, 3/8" thread engagement would be acceptable.

[Joe L.]

Re: 2 inch or 2 1/2 inch exhaust manifold

As a former machinist, I was always told that the accepted thread length was 1-1/2 times the diameter of the bolt. 3/8 thread engagement on a 3/8 bolt is not enough.

Russ------


That's not what I've ever understood. And, for example, check out the thread length on a standard 3/8-16 nut.

[Russ S.]

Re: 2 inch or 2 1/2 inch exhaust manifold

I get your point Joe and maybe it would be ok in steel but certainly not in cast iron or aluminum.