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More exhaust restriction=more power

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by Blazer_Boy, Aug 1, 2002.

  1. Blazer_Boy

    Blazer_Boy 1/2 ton status

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    I always hear on here that mufflers and the right size exhaust tubing will make more power than say gigantic open pipes. I never bought it and ran tubular manifolds/shorty headers with 2 1/4" pipe and cherry bombs that dumped down right after the cab. I replaced the cherry bombs with Dynomax Super Turbo Muffs and the mileage went up and hand more power. Today I had a complete professional setup bent that exit out behind the wheels, all with the same muffs. Now it has a heck of a lot more power in every part of the band and when the secondaries hit on the higway, it'll throw you back in the seat.

    What is the physics behind a system that has more restriction in it (mufflers) and more pipe to go through. Does it have to do with making more cylinder pressure, or what?
     
  2. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    I know that if you don't have enough backpressure, the motor has to work harder to blow the exhaust gas out of the cylinders. I'm far from a physics major(unless dirt is involved /forums/images/icons/smirk.gif), but I believe it has something to do with a vacuum differential between the exhaust system and the cylinders. Kinda like the increased backpressure almost sucks the exhaust out......

    Does that make sense? Am I on the right track, brothers?
     
  3. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    BTW, your setup is alomst identical to mine(I still have the factory exhaist manifolds), and when I installed the system as a whole I got 20% better fuel milage. I can't say how much power I gained but I definitely noticed a difference in how easy I could accelerate at highway speeds. The low end didn't seem that different, however.
     
  4. joker89blazer

    joker89blazer 1/2 ton status

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    I have the same mufflers [they flow better than flowmasters, make less noisy and cheaper!]. A theory is that better flow is made on timing the gas pulses so that one pulse flowing from one cylinder sucks out the next firing cylinder, this would not work if the pipe was to large are free flowing. Only problem is this works best at a given rpm. That is the reason behind diferant lenght runners on headers. Sounds like you got your setup just right.I got two more mpg's with duals and dynomax's, and with more power......gotta love it /forums/images/icons/smile.gif
     
  5. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    The correct term you are looking for is scavenging. Too large an exhaust system and the exhaust can't scavenge properly.
     
  6. Cliffy

    Cliffy Registered Member

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    It seems you are all talking about Dual exhaust. What about single exaust?

    I'm gonna be putting my 350 in my scout. I wanna run single exhaust after my headers. I'm thinking like 2" pipe right after the headers and when they come together making it 2.5"
    Anyone know if I will get the benefits that you all are talking about?

    When it was in my blazer I had dual exaust running turbo mufflers.
     
  7. HispanicPanic

    HispanicPanic 1/2 ton status

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    what would be considered too much i have a 350 stock and 2.5 inch pipes going to my 40 series flowmasters and dumps my pipes are true duals would that be too much for a stock 350 ?
     
  8. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Exhaust 101! Class is in!

    Yep you have tuned the exuast to the engine. Dual 3 inch exhaust on a mild V8 will hurt performance. 2 inch exhaust pipes is about right for a stock or mild built SBC. As one of the other posters pointed out, if the exhaust is properly matched that it creates a "scavaging effect".
    What happens, particulary with headers, is as you have cylinders expell their burned gasses they expand into the pipes. Well since they do this at different intervals it creates pulses. well as that pulse travels down the pipe it creates a little vacume on the pipes that are not currently expelling exhuast. So when that valves opens to expell it's exhaust it already has a little help to pull the exhaust out. This is known as Scavaging.
    Now if the exhuast pipes are to big this effect is lessend so the actual exhaust volocity slows. If it's slower its moving less volume even thoug hthe pipe is bigger. Several other things factor in. A long tube header is going to be great for High RPMs but at low RPM's it will hurt low end torque. For a truck your better off with a Short tube header (plus they are not hanging down wher your going to smack the collectors or have problems with collectors interfering with the drive shaft). The "TRI Y" style headers really take advantage of the Scavanging effect at lower RPMS but they sometimes pose a little more clearence issues.
    The less bends in the exhaust system the better. WHen the exhaust has to change direction of travel it starts to tumble and it slows down. A cossover pipe on a dual system also helps with the scavanging effect by ballancing the odd firing cylinder that the SBC has. Thats the little pop you hear on a true dual system without a cross over. Unfortunatly cross overs on a 4x4 are difficult to do. You typicaly want to do the cross over closer to the engine. The siamese cross over being the best. The tranfer case and Cats if you have to run them will cause you to put them well behind the transmission.
     
  9. reddog64

    reddog64 1/2 ton status

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    Re: Exhaust 101! Class is in!

    so your syaing dual 3 inch flowmasters is probably too much for a mild 406 sbc...

    I should have paid less for the 2.5 inch and it would of been better???
     
  10. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: Exhaust 101! Class is in!

    Proably is a little big. When your talking diameter of the pipe when you go from 2 to 3 inches your talking a lot more volume. That's fine on a drag racer where your running at redline.
    Doing some quick math. The cross sectional area of a peice of 2 inch pipe is 3.14. 2.5 is 3.95. 3 inches i 4.71 (all in Square inches). So a Jump from 2-3 inches diameter is almost 1.6 square inches more volume.
    Unforunatly it kills low end torque because you cant get any exhaust volocity at low RPM's. For street use and resonable HP I would say that 2.5 would have probably been a better diameter and split the difference between low end torque and high end HP. I know I don't drive even my Supra much at redline. I sure don't drive my truck like that. I want to be able to have some low ind to get that fat pig moving.
     
  11. morphed86k10

    morphed86k10 1/2 ton status

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    Re: Exhaust 101! Class is in!

    good stuff Grim, but 1.6 square inches of volume? /forums/images/icons/wink.gif
     
  12. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Re: Exhaust 101! Class is in!

    errr well 1.6 inches of cross section area /forums/images/icons/blush.gif Hahaha blew that didn't I?
     
  13. bryguy00b

    bryguy00b 3/4 ton status

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    Re: Exhaust 101! Class is in!

    wow im kinda lost hear haha..what kind of exhaust system would be good for a 305? i know its nothing speacial but im not going to be able to upgrade for a while, and im really not that concerned about it either..could i run like duals, with 2" pips going to 40-50 series flows..(not sure the difference there)..and 2" out the back or something? there is no cat on my exhuast..right now its just the stock manifolds, with the y pipe going to the muffler..no tailpipes..what kind of headers should i run?

    Bryan
     
  14. 70~K5

    70~K5 1/2 ton status

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    Re: Exhaust 101! Class is in!

    If you're going to run duals go 2.25" to 2.5" pipes. Or for a single Go 2.5" to the Y and a single 3" from there.
     
  15. bryguy00b

    bryguy00b 3/4 ton status

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    Re: Exhaust 101! Class is in!

    ok the Y pipe is the pipe that goes from the headers to the muffler right!!??..sorry for the dumb ?'s

    Bryan
     
  16. 70~K5

    70~K5 1/2 ton status

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    Re: Exhaust 101! Class is in!

    The Y pipe in a exhaust for any motor that has 2 exhaust manifolds is the pipe that conects the 2 outlets from the motor to the single exhaust pipe going into the muffler of a single exhaust. A H pipe would be the pipe that conects a true duals exhaust to smooth out the exhaust and increase it's capacity.
     
  17. 70~K5

    70~K5 1/2 ton status

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    Re: Exhaust 101! Class is in!

    Then "most" late model cars with a V something engine has a Y pipe going into a single cat and muffler. And if they have dual tips at the back they use another Y pipe behind the muffler or a muffler with a single inlet and dual outlets. That muffler would be like having a Y pipe interal to the muffler. /forums/images/icons/grin.gif
     
  18. bryguy00b

    bryguy00b 3/4 ton status

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    Re: Exhaust 101! Class is in!

    ok, so it goes..Y or H pipe..then from that to the pipe to the muffler..then tail pipe out the back..?

    Bryan
     
  19. bryguy00b

    bryguy00b 3/4 ton status

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    Re: Exhaust 101! Class is in!

    what exactly are cherry bombs too? are they a kind of muffler or just take the place of them?
     
  20. 70~K5

    70~K5 1/2 ton status

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    Re: Exhaust 101! Class is in!

    "Cherry Bombs" are a brand of flow thru glass pack mufflers.
     

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