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Let's talk about headers, dual exhaust and TBI.

Discussion in 'The Garage' started by Can Can, Sep 13, 2006.

  1. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    The truck in question is an 89 V3500 w/ 454 TBI.

    Right now the truck has the factory manifolds with a custom 3" crossover pipe and 3" single exhaust. I've been contemplating upgrading to headers and dual 3" pipes. I'm in a non-smogged area so I'm not concerned with the usual emission laws.

    Other than having to install a bung somewhere in the system to accomodate the O2 sensor(which is a 3 wire heated unit), what other things do I have to consider before undertaking said upgrade?
     
  2. Cricket

    Cricket 3/4 ton status

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    All I did was add the O2 bung. Make sure to get a good set of gaskets, aluminized if possible.
     
  3. beater_k20

    beater_k20 Banned

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    i would seriously look into an X pipe too.
     
  4. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    I've said it once, here's #1000...

    You get what you pay for with headers... One of those parts imo that you can never spend enough on... $500 to $600 will get a sweet header, thick flanges, thick wall, ceramic, but get into a nice stainless :eek1:

    I'd say some Thorleys, ceramic, Tow rig? smallish primaries...

    Doubt you'd need to go 3', 2 1/2 or 2 3/4 would probably do ya fine.. Especially with a more bottom end orientated small primary..

    maybe toss a crossover in...

    pair of Flow 50's...
     
  5. yellowK20

    yellowK20 Well Lubricated Premium Member GMOTM Winner

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    Ditto , except for make it 40 series flows:laugh: if its a stockish small block go 2.5 if it's a Bigbbbblock or a bad ass mouse go 3"
     
  6. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    If I was recommending the bigger primaries (2" and up) or some long tubes I might go 3", but I think the 2.5 would flow fine on a low rpm, TBI towrig.. Free up a little space there too...

    I figured 50's, with the family and all... :wink1: 40's might be a tad aggressive..... :eek1: Tho smaller mufflers are always a good thing... :bow:
     
  7. beater_k20

    beater_k20 Banned

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    40s sound fine with a full tailpipe out the sides.

    i'm going to assume that with the boat, that's what he's gonna want.
     
  8. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    Okay, let me get this straight:

    Because I'm looking for power at lower RPMS for my towrig, I want a SMALLER exhaust pipe? Keep in mind that with a crewcab longbox the exhaust has to travel about 15' before it hits the tailpipe. I've heard about running a crossover between the two duals to "even out" the exhaust pressure, but I don't understand the physics behind it.

    As far as mufflers go, forget the 40s. I'm getting too old for barky exhaust. There is plenty of resonance inside the cab with the single Magnaflow, and if anything I would prefer to go quieter than louder. I have a pair of Dynomax Super Turbos on the K5 and I'm really happy with the way they sound.

    Ryoken, please school me on this smaller or bigger primaries thing....
     
  9. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    The smaller the primary, the lower in the rpm range you'll see peak torque...

    High rpm, high horsepower, motors like huge primary, long tube, tuned headers..

    iirc the Thorley's only come in 1" 3/4 for BB's...

    I'd still go with a 50 style muffler to keep size down...
     
  10. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    For a tow rig and keeping low end torque i would forget about a dual exhaust and stay with a single 3" exhaust. Now if you don't mind giving up low end torque for some mid to top end HP then go with a dual 2.5" exhaust. I used to run flow masters back in my race car days but i'm getting older and those things are noisy. I currently run a gibson muffler and couldn't be happier. I also would recommend a pair of ceramic coated stainless headers from Gibson, like someone already said a good pair of headers aren't cheap. I would also go with a set of shorty headers to keep the low end torque.
     
  11. Can Can

    Can Can Pusher Man Staff Member Super Moderator

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    And other than the relocation of the O2 sensor bung there are no issues related to the TBI that I have to be worried about?

    *edit* So basically I should stay with the existing exhaust setup and upgrade from the factory manifolds to some high quality headers. Geez, that sounds too easy....:crazy:
     
  12. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Nothing to worry about. If you run shorty headers you should be able to run the factory 02 sensor and be done with it.
     
  13. Citizen Rider

    Citizen Rider 1/2 ton status

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    imo a freeflowing muffler is a great thing. I have dynomax bullets on both my blazer and 95 silverado. Freeflow exhaust, not loud and obnoxious...Ill never go back to a regular type muffler.
     
  14. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Gibson mufflers are a free flowing muffler in case you or anyone else did not know.
     
  15. Cajun4x4

    Cajun4x4 1/2 ton status

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    x2...
     
  16. ryoken

    ryoken Puppy Fabricator Premium Member GMOTM Winner

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    I'd rather have the Tri-Y performance over a Shorty.....

    The Thorleys also do the matching coated Y-pipe for a single... Single 3" would be better, just assumed he "wanted" duels..

    Thats what I plan on, Thorleys, 3", highflow cat, maybe a magnaflow if I get it for my exhaust guy..
     
  17. blazinzuk

    blazinzuk Buzzbox voodoo Premium Member GMOTM Winner

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    My opinion may be different than some but will the system be mandrel bend or not. If not than go a half inch bigger in your system and try to minimize the bends in them. Non mandrel bent systems do not scavange as well as mandrel bend systems. I think Thorleys tri ys would work really well on your rig. Also whats your cruise rpm, below 2500 and stay smaller above 2500 rpm and go bigger and if you do run duals a xover is a must an x if possible but at the very least a crossover pipe. Remember depending on your muffler choice, that will be your restriction. No point in putting a 3" exhaust on if the pipe inside your muffler is 2". That is why I would recomend some type of baffled muffler or one that has the same size diameter tube inside the muffler as the rest of the exhaust
     
  18. 1977k5

    1977k5 3/4 ton status Vendor

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    I may just be a stupid engineering student here, but catch me if I'm wrong here:

    I understand completely how a cam can change how an engine can make power at different RPM's and bleed off power at its non-ideal RPM range (the velocity of the air flow changes with duration of the cam, etc.).

    The thing I don't understand is how smaller primaries on headers/smaller exhaust can cause an engine to make more low end torque. It seems to me that the more exhaust the engine can force out of itself the more fuel/air it can consume and hence more power. It seems that this would be the case no matter what.

    Honestly, I had a counter argument to myself for this at one time but I have consumed too much [​IMG] for tonight :D
     
  19. dyeager535

    dyeager535 1 ton status Premium Member

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    Primaries *sized* right (in other words, not too large, or too small) actually act to "suck" the incoming air/fuel charge into the cylinder during overlap. This is a big deal at all engine speeds, but as engine RPM increases, obviously the size of the primary that works best will change...you don't want backpressure, (which comes from increased intake velocity) but you don't want inefficient scavenging either.

    If the primaries are too large, the exhaust pulse is affected, and instead of traveling down the pipe effectively, the pressure waves lose their direction, if you will.

    Not to mention, as exhaust cools down it takes up less volume, again you start dealing with issues where the exhaust is not effectively traveling through the pipe, instead each exhaust event is "pushing" against the last one, instead of being pulled.

    It's a complex subject, and very hard to get just right in application, but this is essentially how the whole "backpressure is good" argument got into peoples heads...put 2.5" primary tube headers and 4" exhaust pipes on a stock small block, compared to 1.75", and single 2.25" pipe and of course, since the exhaust isn't effective in scavenging, the smaller size does better. Some people then just assumed it was backpressure that made the smaller tubes produce more power, which is not the case.

    Here is some GREAT reading, failing to read it only makes you less educated. :)

    http://www.popularhotrodding.com/enginemasters/articles/hardcore/0505em_exh/

    I just wish I had the time to try/test some of the things he mentions, like smaller exhaust in certain sections for less noise with no power penalty.

    And going back to one aspect of headers and an injected engine, of course changes can be made to take advantage of the headers, more exhaust out means more air/fuel in, right? In most cases the difference between manifolds and headers can probably be compensated for by the system, but obviously changes to fueling should be made in the PROM to take FULL advantage of any modification. Anything that changes airflow, fueling, or spark requirements should be compensated for in the PROM. Doesn't have to be, but the chances that performance (dictated by the stock PROM calibration) is less than it could be are probably 99%, even on a bone stock engine.
     
    Last edited: Sep 14, 2006

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