What size are Stock GM exhaust pipes for big blocks, small blocks?

[Jacob A.]

I have already ordered pipes, I was told the stock pipe was 1 3/4 inch, I am afraid that is going to rob too much h.p. so I went with the 2 1/4 inch pipe that is basically the same pipe but bigger. I am not sure where they are coming from, except they will be drop shipped.

What was stock on an L-71 side pipe car?

ANY ADVICE WOULD BE APPRECIATED!!!!

Thanks
Jacob

[Wayne M.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

I have already ordered pipes, I was told the stock pipe was 1 3/4 inch, I am afraid that is going to rob too much h.p. so I went with the 2 1/4 inch pipe that is basically the same pipe but bigger. I am not sure where they are coming from, except they will be drop shipped. What was stock on an L-71 side pipe car? Thanks
Jacob

Jacob -- Just measured a set of BB NOS GM pipes in my basement and they are 2.75" OD on the largest part of the straight, down to 2.4 - 2.5" on the bends to the manifold. Narrower of course where it necks down for each chambered section.

[Jacob A.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

Thanks Wayne,

I guess a better question would be if both the bigger and smaller pipes have the same diameter on the outside, but one has a smaller diameter on the inside with more baffling.

UGGH, this has been a hard decision to make.

Thanks,
Jacob

[Duke W.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

Assuming we limit the discussion to C2 under-the-car exhaust systems the nominal exhaust pipe diameter is:

All 250 HP and 300 HP w/PG, 2"

All other engine/trans combinations, 2.5"

All tailpipes were 2", and the SB manifold outlet size is a different story.

Duke

[Jacob A.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

Thanks Duke,

We are talking about BIG BLOCK and SIDE PIPE Corvettes to be specific.

Thanks,
Jacob

[Duke W.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

All C2 sidepipes - big block and small block - were the same core diameter, and I believe John Hinckley has reported that core diameter to be 1 7/8".

No matter how you slice it, the OE sidepipes are restrictive compared to the 2.5" under-the-car exhaust.

The aftermarket offers larger core replacement pipes that fit under the OE covers, but they are usually louder than OE.

Duke

[William C.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

When I was attending GMI in the 60's I lived with a couple of guys from Chevy Engineering. Their only comment about sidepipes was "It's like putting a cork on the exhaust system" with regards to flow efficiency.

[John H.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

Thanks Duke,

We are talking about BIG BLOCK and SIDE PIPE Corvettes to be specific.

Thanks,
Jacob

Jacob -

The only difference between SB and BB sidepipes was the shape/size of the inlet pipe from the exhaust manifold to the front of the muffler section; the muffler section was the same for both - 1-7/8" core pipe diameter.

Sidepipes were championed by Sales and Styling - not Engineering.

[Kenneth B.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

Jacob -

The only difference between SB and BB sidepipes was the shape/size of the inlet pipe from the exhaust manifold to the front of the muffler section; the muffler section was the same for both - 1-7/8" core pipe diameter.

Sidepipes were championed by Sales and Styling - not Engineering.

JOHN
Then what was the reason that 70 LT-1'S had 2.00 exhaust exit manifolds but then the pipes went to 2.5 & then back to 2.00?
KEN

[Jacob A.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

Thanks everyone for your input. I just got off the phone with Allan's, where the exhaust pipes are coming from. I am going with the 2 1/4 pipes. With over 460 horses on tap, I want to use the power as efficiently as I can.

Thanks for all of your help as usual!
Very Best,
Jacob

[Rick S.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

Thanks everyone for your input. I just got off the phone with Allan's, where the exhaust pipes are coming from. I am going with the 2 1/4 pipes. With over 460 horses on tap, I want to use the power as efficiently as I can.

Thanks for all of your help as usual!
Very Best,
Jacob

Why, are you going racing? Prepare yourself for a lose of hearing unless you are wearing ear protection. My buddy had a 65 396 car and he replaced his side exhaust with a set of Allan's and we told him to put his old original worn out sidepipes back on. You would have thought he had a NASCAR car, we heard him before we saw him.
Rick

[Jacob A.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

Why, are you going racing? Prepare yourself for a lose of hearing unless you are wearing ear protection. My buddy had a 65 396 car and he replaced his side exhaust with a set of Allan's and we told him to put his old original worn out sidepipes back on. You would have thought he had a NASCAR car, we heard him before we saw him.
Rick

NASCAR.... Sweet, I am stoked!!!! HAVE you looked at the car in my avatar, which is the original 435 car we are speaking about. I have completed #'s matching, but Look at those flares... she needs nascar like sound and performance!!!!

Ear protection, mmmm I will make sure I have my I-POD on with ear speakers.

Seriously though, thanks for your input. I spoke with Allens in great detail today. I was told that the stock, smaller sized pipes would restrict the engine with the amount of h.p. and torque I have on tap. I was told that the smaller pipes combined with the extra h.p. would create a lot of back pressure and heat. The heat could be a problem. He said that they sell a lot of the smaller pipes and end up exchanging them for the larger pipes.

I am not really afraid of excess noise... if I was, I wouldn't own a side-piped car. It is the nature of the beast.

thanks again,
Jacob

[John H.]

Re: What size are Stock GM exhaust pipes for big blocks, small blocks?

JOHN
Then what was the reason that 70 LT-1'S had 2.00 exhaust exit manifolds but then the pipes went to 2.5 & then back to 2.00?
KEN

Ken -

I don't know - I'm not familiar with the C3 exhaust systems.