Tail pipes--2.5 vs 3 inch

Exhaust exits just under the middle of the rear bumper, I don't have a good picture showing the tail pipe tips but you could clearly see it in the first picture and also kind of see it in the picture below. My car is back half and I'm running a fuel cell in the trunk.

 

BIGGER is always better!!!!! lol
I thought the 3" full exhaust would "hide" some of my cam/compression.......uh NO!!!!! any 3rd grader would know my chit was hitting...and hitting hard!!! that was 27 yrs ago. Eventually I will get back to it but I have come to realize you can NOT hide a 11:1 cammed up motor from SOUND!! It is going to thump, rump, and rumble regardless of what you use for exhaust. The only thing you CAN manage is how loud and at what speed the drone makes you go deaf!

FWIW ....on exhaust I would NEVER buy some "kit" unless it was 100% stock stuff as I have NEVER seen one that actually FIT 100%. If I have to cut and weld chit....I might as well bend what I need exactly how I need it!!....GO LOCAL SHOP then regardless of what "special" stuff you have...the system will be 100% exactly what YOU need!

 

psst Jodi...is that Comp engineering diagonal link clevis's on those ladder bars?......don't see those anymore

 

I run a full 3" mandrel bent exhaust, with 3" mandrel bent tail pipes, I also use a termination box, just a different take on the X pipe. I'm only making 540hp FW with my 350 SBC, but I would be confident that this exhaust setup could support your 630hp/BBC.

I build and test my own mufflers/pipes, a good rule to follow is you need 2.2 cfm per hp to have a "zero" loss system. So taking the fact of a 3" open pipe has 7.071 Sq in., this can move 813 cfm, with a dual exhaust, that's 1,626 total cfm, so 1,626/2.2 = 739HP.

Now, if you get a muffler shop to "bend" a 3" system for you, and it's compression bends, then you would have to see how much Sq in area you lost and go from that, (dual 2.750" can support 621hp) word of caution, getting 3" compression tail pipes made will be a little difficult. Using mandrel bends, with some patience and fab skill, can be done, and tucked well and trimmed just like you want, I wanted the same, as you can see, no tail pipe shows.

The next issue is mufflers, not to many sell them on CFM, it's all in/out sizes and offsets with "sound" ....so your 630hp would need a total of 1,386 cfm, divide by 2, so each muffler needs to flow 693 cfm. Flow bench tells the story, but pressure taps are even better.

Here's a few pics to give you an idea. Hope this helps. Cheers.

 

I ran a Torque Tech 3" system on my '80 for years , 496 BBC . I believe the company is out of business which is a shame as it was literally a bolt on system , no cutting , trimming or modifying anywhere (Other than welding V bands on the connection at the headers and the outlet of the mufflers) .

I also made 3" turndown's that had V bands also so I could run those when I wanted to and remove the tailpipes .



Most local shops use a compression bender , you'll have to search for a true mandrel bent system if you are going local.

G72ZED is very accurate with his formulas , 3" is/was right at the limit for me , if/when I rebuild the car I will use a 3-1/2" system .

Hope this helps

TOM