Technical Switching Engines & Exhaust diameter

Long story short, I’ve experienced some pretty costly plumbing issues at my house which pretty much killed my budget for using my GMC inline for now due to The machining and parts costs. As I have a solid running 350 in the corner of my garage, new clutch etc I am going to forego an interesting powerlpant in the name of being pragmatic. I’ll save the Jimmy for something down the road. The SBC is mild with fresh camel himps a mild cam intake etc. it will breathe through 2.5” replica rams horns.

I have 2” exhaust tubing and 2” porter mufflers that were slated for the GMC. Will this suffice for a dual exhaust on the SBC? This is for a custom so not worried about high RPM but don’t want a slug or not getting the best out of my setup. The car will run 4 speed Saginaw with granny 1st, 3.08s and 28” tires in a Chevy styleline if that helps. Thanks and Merry Christmas!

 

Honestly I don’t think it would bother anything at all. The mufflers are not restricted and you have everything there paid for I would go ahead and use what you have.

 

If it is a custom, and you are gonna drive it like a custom, no prob.
OTOH
If you like mashing the go pedal and you are like me,,,
the brain will always want to know, what was possible.
That said, I'd want to use what I have and challenge my will to accept it

 

Yeah. I’m sure it would work but in the back of my mind I think it would bother me. I’ve read a bit of conflicting opinions on exhaust diameters etc. I’d rather not spend unnecessarily but would rather do
It right. Thanks guys

 

I doubt you'd gain anything by going larger. I've got a 69 Corvette with the 350 horse 350 and it used 2" pipes all the way. GM used 2" for all the 427's in 69 as well. Going to 2.5" tubing would have cost GM no more than 5 bucks additional at that time, so if it had been worth any significant additional power, they would've used the bigger pipe or offered it as a high profit option. You can add a crossover pipe for near no money and gain some performance, and a system with a crossover generally sounds better than the same system without.

 

It doesn't have to break the budget or the bank if you do it at home, but it does take some time and effort just the same.






It might be hard to tell, but I have a 2" slip ring fit into the ends, same tube with a slice cut out and they were squeezed and sprung free the tension holding them in place.

 

You'll be fine with the 2" pipes. And with 2" rams horns, if you have any and they're easier to connect to the pipes.

The pipes in my 327 powered Corvette are no bigger than that, and it is rather sporty when I push the go pedal.

 

2 inches will be fine. That is the typical diameter used back then and the bigger is better is more for the group that are thinking "well, I have to buy the whole thing and the next size up is only X% more".
See wheels, tires, brake rotors, condoms, etc.

 

55 Chevy's only used 1-7/8" exhaust. With gl***pacs they always had a nice rap. It was lost when everyone went to the large pipes everyone uses now. As others said you will be fine with 2".

 

I understand unexpected plumbing problems and the unexpected cash outlay. I'm kinda in the middle of that now as I'm halfway done paying for a $41K plumbing job to replace cast iron pipes under a slab foundation.

Nothing is permanent. If you have the pipe now, use it. If it's going to bother you that it's not what you wanted, change it later when the funds are there. OR, just wait a month or two until you can afford the 2.5" piping... If you rush it and it comes out not like you wanted, you'll hate it and want to redo it anyway.

3blap.

 

You'll notice no difference with the 2", 2.5" will generally be a little louder. If you gained some HP we're most likely talking single digits.

 

Might make a difference at 7500 rpm, but I doubt a custom will ever see that.

 

Thanks guys! I tend to overthink things to the point of ****ysis paralysis.

 

Well if it make you feel any better my plumbing issue was realized when I received a $1200 water bill. It took quite a while to
Locate the source of the leak as I have a complicated property. The end result was. A failed $2 elbo buried 6’ beneath the concrete slab outside the house. Ugggh.

 

I feel your pain. We had to spend $25K last year to replace all our cast iron sewer pipe. That cut into the hot rod budget!

 

Damn. It doesn't make me feel any better. I had another problem similar to that just before I got to replace the cast iron sewer pipes in the previously mentioned house... Bought a house in Trinidad, CO over labor day weekend. Replaced the water heater (new unit left behind by previous owner), which is in the ba*****t next to the 1yr old HVAC unit. Went out of town in December to get the rest of my junk from my old hometown, planning on being gone 1 month, it took 2.5. After I left, the battery in the thermostat died, froze the water pipe going to the washing machine.... flooded the ba*****t. I don't recall the water bill, but it wasn't anywhere near yours. I did get a call from the city saying that had a "high water flow alarm" at my residence... at which time they shut the water off to the house. when I got back to the house, I got to buy a new gas flow control valve for the water heater ($150-ish) and EVERYTHING on the HVAC that was under water... blower motor, motherboard, and a few other things. That was $700-ish... all because of a $2.00 battery though.

Digging 6' down under a slab does NOT sound fun. Did you get it fixed?

3blap.

 

my opinion 2 inch pipe is more then enough

 

FWIW. Common cheat sheets, but I have used 2.25” on 400 cu in pontiacs that weren’t going to get rev’d that much and it worked fine. So 2” on a mild 350 isn’t gonna hurt (IMHO).

 

On our 57 Chevy , I wanted "quiet" and a single exhaust [road racer's prefer single exhausts]
So I used a 2" exhaust system on the L/H side.
On the R/H side I purchased a bit of 2" tube and 1x 2" U bend which I cut into 2 x 90° bends.
The R/H side crosses over behind the transmission [main case] and I used a 90° bend to blend this into the L/H side.

Doing it this method gives the engine a nice quiet burble at idle,
And later [if I desire] I can simply "cut'n'weld" a twin exhaust [the cross over pipe can be used as an X pipe]

If you did this , You can add a flange to the front section.
Then later you could still use the majority of the exhaust for your GMC engine

 

Unless you’re chasing ET or dyno numbers you shouldn’t need to worry about it…

 

Honestly people worry about exhaust size way too much. Keep in mind that same SBC likely had a single 2-2.25" single exhaust stock. So your vastly increasing exhaust size simply by adding another pipe. And the HP difference between say 2" and 2.5" is so small you likely wouldn't notice. Only noticable change is tone

 

Ouch!!
Fixed the pipe. Now need to redo the concrete

 

Thanks everyone for saving money and the peace of mind!

 

Honestly the smaller pipe will actually likely help with throttle response if not actual torque. Im running 2" lakes pipes on the bone stock 200 HP 76 350 in my 53 Chevy and for being powered by a smog engine that thing gets up and moves

 

I think your SBC will have a nice sound with that set up. Just lately I struggled with what size exhaust pipe to run and ended up with 2.25.

Years ago I had a '58 Ford Wagon that had a 312 with 2 inch pipes. Man that car sounded nice.

 

I believe Cadillac ran 500+ cubic inch motors through a single 2 1/2" exhaust system. Your SBC will be just fine.

Last year I got to do the cast iron pipe inside replacement at our side by side duplex, then a couple months later (after it warmed up so they didn't have to deal with frozen ground) I got to replace the outside cast iron all the way to the street, it ran under our front patio and sidewalks, so cement work was also required. That will upset the household budget for the year. We did 26K worth of new windows, and then a surprise 25K roof, the year before the plumbing. The roof and plumbing were surprises, the windows were planned for, had I known the roof and plumbing were coming, the windows would have waited.

 

It’ll sound great with the Porters and 2” pipe and I’m sure it will perform just fine for a street cruiser.
A poorly placed (by me) cottonwood tree cost me a fortune a couple years ago. It killed the main line into the house. We didn’t find the real problem until after we had the well pump replaced for mucho dinero. New pump - same problem! Dang. My dog found the muddy spot out in the yard. Then my daughter and I dug about five feet down and found a root had broken the water main. Easy fix from there, if you like mud wrestling. Lol At least we won’t have to worry about the well pump for a while.
Good luck with the concrete.

 

I used to be the "2.5 inch pipe on everything guy" but now since building a few early Ford rods n kustoms I have really found the sound I like the best is 2" pipes and gl***packs on anything less than 10.0:1 compression, it has that great '50s cackle sound.

 

Hello,

It seems as if you want to have some power from your motor. But, the end result of using a 3.08 rear gear may be going backwards, using the quote: “don’t want a slug or not getting the best out of my setup” statement.

For tons of full power in the SBC motor utilized for acceleration the 3.08 is not going to feel as if you are using all of the SBC power available. We used 3.55, 3.73, and 4.11 gears for daily driving in our Chevy sedans with v8 power. Some had similar stock headers and one had Hedman Headers. But, they all had at least 3.55 or 3.73 gears. The high performance 57 Chevy with a built up 283 used 4.11 gears with Positraction from our extra unit. I had the 4.56 Positraction in my own 58 Impala to use when racing and doing late night acceleration runs.

The two times we used the 3.55 gears was to go from Long Beach to San Diego one time and from Long Beach to Santa Barbara on another cruise. If and when we knew a big race was coming or just to cruise locally, the 4.56 Positraction gears were in place for the best results. YRMV
1962
We still had some 348c.i. + 280/300 hp to use for power and that worked with the 3.55 and 3.73 gearing. But, definitely using a set of 3.08 gears would not have had such great results in any high performance encounter.


Jnaki

At the time, I had put on straight through, tubular Corvette Mufflers on our set up. I am ***uming the straight through had less restrictions than a wide vented stock muffler. It helped that we had at least 300 hp for power, regardless of what gearing was in the back. Stick shift or C&O stick hydro phase.

The whole exhaust system ran best when connected all the way past the rear axle and bumper. Quiet and powerful, with no crackling or pop pop when the accelerator is let off. Like the name brands like Porter or Magnaflow. (read the story on twin exhaust on the HAMB)

https://www.jalopyjournal.com/forum/threads/exhaust-drone-resonance.1345303/page-2#post-15776008

 

plumb the exhaust with the 2" and enjoy the ride....your **** dyno won't know the difference...