Does exhaust affect low end torque?

Discussion in 'Small Block Tech' started by garybuick, Mar 24, 2016.

  1. garybuick

    garybuick Time Traveler

    I know for max HP, dual exhaust is better than single but what about for Torque? Does single exhaust allow for more low end torque? Does dual exhaust lower low end torque while adding higher rpm hp?
     
  2. alec296

    alec296 i need another buick

    Yes duals will trade off power or move it up rpm range alitte but I doubt you will lose any drivability on a stock engine and use of balance tube scavengeing and some tuning trick can help with the power change. But a cam for low end could give you plenty of power that you would not need to worry about torque issue. The crower level 2 cam would make great low end power. Also Howards cams has a lower rpm cam similar to the crower with around a 260ish duration that could be good also.
     
  3. 8ad-f85

    8ad-f85 Well-Known Member

    Yes it can.
    The question cannot be answered accurately as it's asked.
    Usually...going from a small single to a REASONABLE sized dual helps low end torque.
    If the single exh. is pretty good, a dual might not do anything.
    There are math formulas out there to guide you, but generally not used unless it's a max effort.

    Freeing up some restriction helps pull mix into the cylinder, which makes more torque.
    Too large diameter of a pipe (esp. really close to the engine) kills the exhaust velocity...which sort of halts the scavenge. (Think of drafting in Nascar)

    For some interesting Googling, try "no loss exhaust systems" with David Vizard.

    Ponder for a moment the size of exhaust pipes on semi trucks...
     
  4. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    Low RPM scavenging is conducive to increasing low-mid RPM torque, and can be achieved with a pipe diameter equal to the exit port size on the manifolds, along with a means to use the exhaust pulses from one side to help pull out the exhaust on the other side.

    This can be achieved (on manifolds, let's say) with either a scavenger series "Y" pipe or a good "X" pipe.

    Velocity recipes are as follows:

    1) Use a Flowmaster scavenger series "Y" pipe sized 2" in, 2.5" out and use MANDREL bent 2" pipes from manifolds to "Y" pipe, then 2.5" MANDREL single pipe on out to a good flowing muffler.

    2) Similar to example 1, but instead use the 2.25" in, 3" out "Y" pipe, using 2 1/8" (this is important, don't use 2 1/4" pipe) mandrel up to "Y" pipe, then 3" back to good flowing muffler.

    3) Same as examples above, only after the "Y" pipe, splice in a one in, two out so you can use duals (mandrel or not). This will act as a type of 'long' "X" pipe.

    4) Use 2 1/8" mandrel from manifolds up to a 2 1/4" "X" pipe, then 2 1/4" duals on back.

    It's important to understand that the most important part of your exhaust exists from the heads on back to the scavenger merger pipe (Y or X), and from there on back isn't quite as important (though still is, up to a point).

    Coating these 'head pipes' with ceramic or a very good extremely high temp coating will aid in scavenging and overall performance of your engine, by keeping the heat inside the pipe as best it can. Coating your headers/manifolds in such a manner is also desirable for the same reason.


    Gary
     
  5. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    To the text in bold, I'd like to point out that a good, scavenging single will outperform your typical 'no crossover' muffler shop bent dual system (when hooked to manifolds) any day of the week. lol

    Science bitches!

    I've seen people (personal testimonies, and I've driven them myself) who swapped out their factory single WITH a cat to a 2" dual with turbo mufflers and no crossover, and the car was noticeably slower at all RPMs...

    True story.

    But hey it sounded 'cooler' I guess. :rolleyes:

    I suppose it depends on how well the single is set up. The old factory systems that lead one pipe into another is a rather poorly thought out design, and a dual system would be an improvement over THIS (particularly if it was a larger CID engine), but when you have two smaller pipes side by side leading into a larger single pipe, it's tough to beat without using an "X" pipe dual system.

    As a note, Flowmaster's "Scavenger Series" Y pipe merge pipes use a patended "D" port design, where the two inlet pipes have flat areas (the 'line' on the "D") that sit inverted and lined up next to each other, then welded together. This creates more surface area for maximum scavenging from one side to the other, then has a gradual and gentle transition into the larger single pipe.

    Some examples extracted from the wonderful internet:

    102_0208.jpg 2611.jpg IMG_20120129_145334.jpg IMG_20120212_112553.jpg



    Gary
     
  6. garybuick

    garybuick Time Traveler

    very interesting
     
  7. wovenweb

    wovenweb Platinum Level Contributor

    Where does one find 2 1/8" mandrel bent pipe to connect to factory exhaust manifolds?
     
  8. sean Buick 76

    sean Buick 76 Buick Nut

    If you cant find 2 1/8 then have 2" expanded to work.
     
  9. alec296

    alec296 i need another buick

    If your going for duals TA performance has down pipes for 350. They are 2 in at manifold but flared right away to 2.5.
     
  10. garybuick

    garybuick Time Traveler

    this is wild! so all other things being equal, an optimized single exhaust system can be much better for low end torque than duals.
     
  11. alec296

    alec296 i need another buick

    Yes a long with a 2 barrel carb for tighter control of air/fuel but those flow master y scavengeing pipes are not cheap. So a combo of them and the labor to make fit can out cost as much as dual system if your not counting. But with the crower level 2 and 8.8-9 to 1 compression. Will be more then enough torque and duals won't affect it so much .howards cams as a low end cam that will work also. Even the level 3 should be good with about 9 to 1 and straight up it should have a good dynamic compression ( I think it was about 7 to 1) and a 2000 converter will work very well and be ok for regular to mid grade fuel .
     
  12. Gary Farmer

    Gary Farmer "The Paradigm Shifter"

    Summit Racing sells mandrel 2 1/8" pipes.

    They're not as common as 2" or 2 1/4", but there's still a decent selection there for them.

    Remember that 16 gauge steel is 1/16" thick, so that on a tube, you have 1/16" on both sides making total diameter thickness for 16 gauge steel 1/8" thick.

    Exhaust tubing is measured in what they call O.D., which is 'outer diameter', so a 2 1/8" tube has a true 2" inner diameter, matching the 2" exit port on an iron manifold.


    Gary
     
  13. Gary Farmer

    Gary Farmer "The Paradigm Shifter"


    The "Y" pipe scavenger series pipes are about 45-50 bucks (about half as much as a good muffler), and you only need one. Even if it comes out the same (or a little more) as a dual system, I'd choose the one that works better, wouldn't you?

    Why skimp out on an effective exhaust simply because another upgrade adds power? Why not have both for even more power?

    It's when you add in all the things done, that may be good individually, but even better when working in unison, that gives biggest results!

    I'd say the 2" in 2.5" out for a 2 barrel setup, and the larger 2.25" in 3" out for a 4 barrel setup, though for a mild setup the smaller one would work fine on a 4 barrel setup too. A factory single exhaust was 2" into a 2 1/4" single (not even mandrel bent), back to a muffler, then a 2" tailpipe, and they ran 'ok' this way even as ****ty as it was. The 2" in 2.5" out would flow WAY better than this ever thought about.

    A mandrel bent 2.5" single flows better than 2" press bent duals. I've shown the math on this elsewhere.

    A mandrel 3" single system flows better than 2 1/4" press bent duals.

    For ground clearance sake, I'd do option number 3 as listed above in a previous post.

    For later model cars that came with catalytic converters and the single hump transmission crossmember, this is a no-brainer. You can have your cake and eat it too on exhaust flow with a single back to a large, free-flowing cat (and be street legal!), with either a large single outlet for continued mandrel single exhaust, or a dual outlet for press bent duals.

    They made them from the factory this way on GN's and Olds 442's, so the hardware and space required for it already exists.

    There's even room behind the axle for a transverse muffler on G body regals, where the GN muffler was located from the factory, which is a 2 1/4" dual in, dual out muffler.

    Walker makes a Quietflow transverse muffler available in stainless steel for a little over 100 bucks for this car.

    Magnaflow and Catco both make single in, dual out catalytic converters, ranging from 100 or so bucks to 150ish bucks, rated at 6000-7000 lbs. gross vehicle weight. Don't worry, there's room. I've spent over a year and a half researching this stuff, poring over pictures, analyzing different cars (in pics and up close actual cars), calculating a myriad of possible exhaust system scenarios.

    Anyway, back on track.

    Edit: to the text in bold, when you understand dynamic compression and its relationship to building power, this same scenario with a stock cam would equate to about 10.25-10.5:1 compression, and so the Crower level 2 cam doesn't really add anything other than trading about 10 ft. lbs. for 10 hp and about 300-500 RPM (lower) vs the stock cam given this consideration. Easier to do, sure, when you don't change pistons or do a whole lot of machine work, and so is the more attractive option (at first glance). The Crower level 3 is actually a closer match powerband wise to the earlier stock cams. The level 2 is a grunt cam, and would add more when comparing it to the later stock cams, not the earlier ones.

    Understand that swapping cams with earlier valve closing timing adds more power by simply boosting dynamic compression than the camshaft itself actually gives. The Melling sbc-11 has a much earlier valve closing than even the Crower level 2, and would boost DCR to premium fuel range without doing much at all to the lower end. Powerband would be similar (around 3800-4200 RPM peak hp). Crower would give (a little) more power due to much more intense lobe profiles, for a tradeoff of probably 10x less lifespan.

    For a cam with a similar powerband as the stock cam to give more power, it has to increase the lobe profiles to such an intensity that castrates its life expectancy. Such is the trade-off for a few more numbers.

    To build real power, you have to open the engine up (better flow) and rev it, or force air in. Either way, you gotta move the air. This is why low RPM scavenging and exhaust velocity are so important for low-mid range torque. If all you want is noise, put on big tubes with no crossover.

    There's only so much that can be done at low-mid RPMs, and the things I've described in this thread and elsewhere is about as good as it gets without turning it into a race engine or making lobe intensities so dangerous you need to go roller.


    Gary
     
    Last edited: Mar 29, 2016
  14. Gary Farmer

    Gary Farmer "The Paradigm Shifter"


    I'm sorry, (and no offense to TA), but these are Scheie...

    They were specifically made to hook manifolds up to their mandrel exhaust systems. I mean, they'll work, but aren't exactly scavenger-friendly.


    That's all I'm gonna say about that. lol


    Gary
     
  15. 8ad-f85

    8ad-f85 Well-Known Member

    You don't need as radical of a cam lobe if you do a wee bit of work to the valve bowls (very mild porting).
    The same thing is accomplished, you are getting more into the cylinder via faster airflow and a better working port (or intake tract).
    It's a better route than simply adding a wilder cam.
     
  16. wovenweb

    wovenweb Platinum Level Contributor

    I cringe at the thought of a cobbled together exhaust system done by a local muffler shop. At least in this area.
     
  17. sean Buick 76

    sean Buick 76 Buick Nut

    Yes exhaust does effect the low end torque of an engine, and as people are saying each combo is different.

    I will make some comments and summations that other people may or not agree with but this is my first hand view on things:

    I had a stock 73 Century with the 350-4 barrel and it could barely spin the tires on wet pavement. I did a tune up and hacked the exhaust off right at the Y so it was a single 2.5" outlet about 2 feet from the engine. I call this my 5 hour tune up LOL! I drove the car after the tune up, both with the crappy single exhaust and the cut off version so there were no other changes other than the exhaust. I then added a 2 foot and then later a 4 foot 2.5 extension to the exhaust to check out the effects on how it drives.

    Here it is with the cutoff at the Y setup, stock 73 Century no mods at all:

    https://www.youtube.com/watch?v=Qy1cOuE4x4Q

    https://www.youtube.com/watch?v=GljRr5PauLI

    https://www.youtube.com/watch?v=nbiqdPVLpnE

    When the exhaust was just cut off at the Y there was good high RPM power but there was a lack in low RPM torque you could feel it.

    Adding the 2 foot extension and it picked up more torque in the low and mid RPM, and there was no effect when I added the 4 foot extension except it was far less noisy thats about it.

    Whether single or dual you need the right amount of flow in the system, or you will leave power on the table. Too much exhaust flow will not hurt the upper RPM power but it will give a loss in low RPM.

    On other vehicles I have also found less low RPM power with open headers, and a gain when adding more piping. Obviously too much piping or piping too small is going to cost power.
     
  18. 8ad-f85

    8ad-f85 Well-Known Member

    I'll back up the above.
    It's quite well known that collector/merge pipes' lengths plays a huge part in the torque curve.
    Even high rpm Nascar engines have long collectors and merges.
    Exhaust formulas date back to the early 1900's.
     
  19. Gary Farmer

    Gary Farmer "The Paradigm Shifter"


    If you don't have the skills or means yourself, accompany the muffler shop worker while he's working under your car. Ask him if this is ok before hand, and that you have specific areas you want the pipe(s) to go. Don't just trust them to do it right or they may take shortcuts.

    They tend to do a better job when they know someone's watching, especially someone who knows a lot about his car, welding, etc. Tell him exactly where you want this and that to be. Most won't mind, and as long as you are a decent conversationalist, he may actually enjoy your company there.

    You can get a series of mandrel pipes that can be welded together sequentially, as long as he doesn't want to bend any instead of cutting or proper fitment (the shortcuts).

    The exhaust past the Y or X pipe isn't quite as important, and doesn't have to be 'just so' unless you feel uncomfortable with this. When I say 'past the Y or X' I mean 'mandrel or press bent'. There needs to be pipe beyond this.

    It'll be more work if you do mandrel all the way back. From manifolds to merge pipe isn't quite as painful. This is important though, so don't skimp on it unless you just don't care about getting the most out of your system.

    There are also pre-made systems available for many cars, if you wish to go this route. They'll just need some modifications. You can use those for the majority of the exhaust behind the merger pipe.

    I forget that many do not have the same metal working skills I have when making my suggestions, and so I must take everything into consideration for ease of fabrication.

    Depending on what you're willing to accept as 'good enough', it doesn't have to be perfect, as long as there's some form of scavenging merger pipe and 2" or 2 1/8" head pipes, along with exhaust at least up to the rear end. The axle that is. Not the rear end of the car, though this is where I prefer exhaust to exit.

    Always remember the most important part of your exhaust is from the heads back to the merger pipe. Spend most of your time there. The scavenger series "Y" pipe has a nice collector already, and an "X" pipe needs some exhaust pipe behind it too of course. I do not recommend raw, open exhaust, because I'm an old man now. lol

    There's a lot of science behind all this, so I encourage anyone to do as much research on it as possible before making any final decisions for themselves and their application.


    Gary
     
  20. garybuick

    garybuick Time Traveler

    so a two barrel would be better for torque? what can a 2bbl do that a qjet cant?

    how many cfms are needed for a sbb 350 that maxes out at 4400 rpm?
     

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