After reading for 3 days on headers and exhaust pipe size, I think my head is going to explode. Is there a frame / mounting difference for headers or exhaust manifolds between a C2 and C3? I am looking at under car exhaust and there are very few headers available going that route. Plenty out there for side exhaust if anyone is looking. This will be going on a ZZ427 which GM rates at 490 hp/480 torque. The guy where I bought it from said it will probably dyno a little more. I won't know that for a couple weeks as their shop has had a covid outbreak. This is from the GM papers that come with the engine:

Exhaust Header Information: The engines were developed using 2-1/8" diameter x 34" long primary tube headers with 3.00" diameter collectors.

Here is more info on the engine:

Cylinder Heads:...Aluminum oval port with stainless steel valves (Intake/Exhaust). 2.19ʺ/1.88ʺ
Chamber Volume: .. 110cc
Ovate (Beehive) Valve Springs ........ 155 lbs. seat pressure at 1.880ʺ installed height
Camshaft: ...... Hydraulic roller tappet .. .527ʺ intake and .544ʺ exhaust
Duration:.... 224° intake, 234° exhaust @ .050ʺ lift
Centerline:... 110° LSA

To make thing more fun, I am using a Borgeson steering box. From what I have found on older threads in both the C2 and C3 sections, McJacks big block replacements, Hedmon Street Headers and Hooker Super Competition headers may clear everything. Sanderson block huggers were also listed. The Hedmans and Hookers may need to be dented for the steering box depending on the thread you read. The ZZ427 uses angle plug heads and has raised .300 exhaust ports.

I called McJacks and he stated his would work on the engine and clear the box. They are a 2" tube with a 2.5" collector. Here is a link to his: 65 - 69 Corvette Big Block 2" Primaries, Factory Cast Iron Replacements - McJacks Corvettes (vetteheaders.com)

The Hedmons have 2" primary and 3" collector and they are long tube.
The Hookers have 1-7/8" primary and 3" collector also long tube. Compare (summitracing.com)

The Sandersons have 1-7/8: primary and a 3" collector. Here is the link. Sanderson BB5 Corvette Header (sandersonheaders.com)

I stumbled across these but say C3 and don't know anything else about them except they are expensive. C3 Corvette Big Block Headers - American Racing Headers

Based on further reading both on and off the forum, it seems that the 500 hp range is the bubble between 2.5" and 3" exhaust and going 1-3/4 to 2" on the primary header tubes.

I'm leaning to the McJack shorty headers as I believe they will clear everything, but I do like long tubes. Of course, this is not a race car so I may never see the benefits of one vs the other. Keep in mind that I have no clue what the numbers on the heads and cam mean in relation to changing sizes of pipes both on the header and exhaust. I would look at comparisons and the head or cam number didn't change much to me, but it changed the recommendations on pipe size.

Don't get me started on the H Pipe vs X Pipe threads............ Thank God for whiskey.

 

C2/C3 frames are essentially identical, I don't think there is any diff in the area around the motor where headers go.
Doug

 

Thanks Doug. I see some for sale that say C3 but will fit C2 and wasn’t sure what the deal was.

 

there is no difference Chris, not in the area of frame to engine compartment. A friend of mine just went to side exhaust and removed his long tube headers, he had a full under car exhaust, and a 454 with angle plug heads, no issue with figment however he is running a stock steering box, these are headman headers jet hot coated . His is a 71. I’m going with factory side pipes and side pipe headers.

 

I have the McJacks headers you referenced in your email. Very nice and fit very well on my 496 with standard exhaust port location GM990 heads. There is a good amount of room around the tubes to the steering box I don't think you will have an issue with the raised .300 exhaust.

 

For street use, I would keep the primary header tubes at 1-3/4 inch................with 2-1/2 for tailpipes.

Too big of header tube diameter will affect low RPM response and torque.

Larry

 

Hooker 2134 headers fit your car . They are 1 3/4" x 3" long tube

 

Hooker 2134's are small block headers.

 

Sorry, my bad. RIF

 

Elwood—- I have a set of C2/C3 Big Block Hooker Super Competition undercar headers I bought 30 years ago and never used. They are new headers, silver jet coated, and you can have them pretty cheap if you want them. Pat Boyd 703-919-4294.

 

One other thing to think about is ground clearance with long tubes, depending on wheel and tire size along with suspension ( stance ) . You may want to go with McJacks.

 

I use McJack's because of the ground clearence issue.
A very nice header and performs well.
Good luck

 

Thanks all.

 

There may be another point of interference others haven't mentioned. It's where the long-tube header pipe meets the exhaust pipe at the fiberglass floor board (bottom of the "firewall"). I know that on the Thorley headers on my '64, the flange on the driver's side is right at the fiberglass and I covered that area of glass with a bit of heat shielding material.

I don't know what differences there may be in the fiberglass at the front of the floorboards between a C2 and C3, but I would imagine that they are not identical so this may be a consideration. The location of the steering box or even A-arms could also be a bit different relative to the engines position.

 

I bought the Hedmans for my car and the Borgeson box as well. The Edelbrock heads are on order but have been since August…I also bought the Pypes C3 stainless X-pipe exhaust. Hopefully it will fit as it is VERY nicely made. After watching Engine Masters, unless you are making over 600 whp, the 2 1/2” exhaust should be plenty. I have a couple of different mufflers to try but am going to try the inexpensive Dynomax turbos to reduce noise but hopefully not power. Wish it was in the car running so I could offer more/better info.