I have a completely stock 350 crate engine with quadrajet and dual exhaust. It has two cheap Thrush turbo mufflers, and I plan to replace them with two more of the same or an equivalent. The system that is on their now, from the previous owner, is all 2" pipe. The front half at the manifolds was chopped at angles and welded together instead of using bends. I definitely want to replace it. The back half, behind the mufflers, is in great shape, and very nicely bent, ***embled and hung. Would replacing the front half with more 2" pipe flow enough for the stock 350, or should I replace the whole thing with 2¼" or 2½"? If it makes any difference on a stock 350, it is on a pickup, so I value torque more than horsepower. Likewise, I value performance and gas mileage over sound if that makes a difference. I'm on a budget, so I want to keep the price down, but I don't want to put something on there that actually hinders performance. Thanks, Slonaker
The stock cast iron manifolds are usually no bigger than 2" at the outlets. There are a few that are 2-1/4 and only the Vette center dumps are 2-1/2". 2" or 2-1/4" shouldn't make much difference. Even if you go with 2-1/4 from the manifolds to the mufflers, 2" tailpipes are fine because the mufflers are a major restriction and the smaller tailpipes will not matter. Just getting rid of the mitered bends will be a big improvement in flow. Addition of a crossover pipe would be beneficial too.
I'm thinking 2" is pretty restrictive, for the headpipes anyways. I usually run 2 1/4". My Rivvy 425 runs 2 1/4" to the muffler (2 in and 2 out) then 2" for the tail pipes. Not a high revving HP motor but definitely torquey.
2" would be absolutly fine for a stock 350, you wouldnt gain or lose anything by going to 2 1/4", but 2" pipes will "rap" better if thats what your looking for.
I like running 2.25" pipe - it matches up well to most decent SBC exhaust manifolds. You didn't mention if you're running manifolds or headers? One thing I like to do is run a larger tailpipe to get a deeper/mellower tone - 2.25" to the muffler (expand to fit), 2.5" muffler and tailpipe. Another thing - as a general rule - the more bends or tighter the bends the larger starting diameter I like to use (as 99% of the exhaust shops crush bend the stuff and it'll reduce area a little bit....) And do yourself a favor and get some good mufflers - generic "turbo" mufflers don't belong on a real hot rod
the generally preferred way to run a performance exhaust, is to run larger, then smaller tube the same as what you described, but the theory behind it is that as the exhaust cools, the g***es contract, so running smaller pipe towards the rear keeps velocity up as the g***es contract. it has nothing to do with the restriction of the mufflers. it's faulty logic to say that one restriction upstream makes another restriction downstream okay.
Think of it this way - wasn't the typical pipe used from the factory of the 1 3/4" or 2" variety? And this was used to pump all 8 cylinders through a Y-pipe and through single exhaust. If you run a 2" pipe, and true dual pipes, you are only going to be running 4 cylinders of flow through each side anyway. 2" would be plenty enough for this type of application. However, if you were going to run a single pipe from the Y-pipe back, I'd jump up to 2 1/2" and run with it. I've got a bone stock 350 in my '89 Chevy pickup, and I run 3" pipe from the 3" collector on the Y-pipe all the way back through a 3"/3" flowtech muffler. It sounds great, rumbles nicely, and has no popping back through the exhaust on decel. The 3" was a ***** to bend though.
I'll be running manifolds. So, maybe a good compromise would be to go with 2¼" off the manifolds into 2¼" mufflers, then reduce it down to the existing 2" tailpipes? That saves me some money, and leaves me the option of replacing everything after the mufflers with 2¼" later on if I do performance mods. The tailpipes that I am considering keeping look mandrel bent, and the stuff the exhaust shop does is crush bent. They might end up about the same diameter at the bends anyway. Slonaker
Id fix the bend but the rest isnt worth the money for what youll gain out of a stock 350 in my opinion. My 302 68 Bronco had the duals done like that and I fixed it and it didnt do squat. Why do people do work like that any way?
I understand what you are saying, but I'm doing it because I'm getting some better manifolds, and the pipe coming off them has to be changed anyway due to different flange locations. Everything before the mufflers looks like it was put together out of rusty, straight pieces of s**** in someone's driveway. I have been chasing rust holes and bad welds around it for the last five years, and I'm tired of it. It will be worth the cost just to get to quit messing with it. Thanks for the information, everyone. Slonaker
You should be able to pump out plenty out of 2" pipe. It is the sound that makes a difference to perception. If you want a deeper tone, go up in diameter. I work in exhaust and the muffler generates about 2/3 of the back pressure in the system. A good flow through muffler will be a benefit, mandrel bends and few of them will help. The cross over pipe (H pipe) will add a smoother sound and aid in scavaging (pull through the exhaust ports) for both sides. It will make a difference in performance AND sound. A common trick is to run a wax pen down the pipes and where it stops 'burning off' the pipe is where to put the H pipe. Don't know WHY, just know it does OK. This is usually around the trans area so you may just **** it up and put it aft.
I'd go with at least 2-1/4 all the way back. IT will be plenty big for a stocker and you might want to add some HI PO stuff to it later and you can always us the extra breathing room.
The performance SBC of the late 60s had 2 1/4" head pipes with the front 6" necked down to fit the 2" manifolds and 2" tailpipes. I always use 2 1/4" all the way. It keeps the throttle response up at the lower RPMs (real world driving) but can still handle the higher RPMs when needed. It gives good sounds with a performance muffler even on a basic stocker. I can't believe no one has recommended 3" mandrel bends. It seemed most of my customers wanted 3" like they would ever need it on the street with a mild engine. They all were convinced that 2 1/2 would choke the engine off and keep it from reaching it's potential. poppy****!
That's why I asked here. I knew that anywhere else the answer would be "You absolutely have to have ceramic coated high dollar headers, 3" pipe with mandrel bends, an X pipe, and flowmasters." Slonaker
Couple things to consider With your manifold diameter, 2 1/4 would be preferable and won't generate as much drone as 2 1/2. If performance gain is what you're after, a crossover might do as much, or more, than increasing pipe diameter. Good Luck!
I like big singles. 2 1/4 off the manifolds to a 2.5 Y pipe and large volume muffler (or two with duals out), 2.5 out. Muffler as far downstream as possible. Depends on the body and undercarriage. The single promotes velocity and scavenging to make the most of available torque. It also costs less for one run of pipe.
Have a stock 350 4 bolt with long tube 3 inch headers would it benefit me to keep 3 inch exhaust with a good set of 3 inch flowmasters . got this shoved down in a 64 g 10 so my headers are already close to the back axle any suggestions trying to do it right the first time
Dang, you resurrected an 11 year old thread! At this point you might as well start a new one. Re your question, 3" is really over kill for a dead stock 350. Will it benefit you? I guess that depends on what you consider a benefit. I don't think you will realize any performance benefit over using 2.5" mufflers and tail pipes. But you may prefer the look and sound. Not very traditional though, that's going to sound rather modern. What's it going in?
1964 first generation g10 wasn't easy lot's of fab work for me mounts and transmission had to set it in with a chain pull through the sunroof. Lol 1964 first generation g10 van
Man, you're taking me back to my mid 70's high school era and the van craze that was going on then. I have a lot of memories of crazy times spent in a V8 powered van, not all of them involve driving! haha!
I use 2 1/4" tubing up to 2 1/2" mufflers at the back and short tail pipes. Engine is stock SBC with a nice exhaust tone. Sounds best at 60mph+
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