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Crazy idea for DIY exhaust on the cheap

Discussion in 'The Garage' started by SkysTheLimit, Jan 22, 2007.

  1. SkysTheLimit

    SkysTheLimit 1/2 ton status

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    Maybe because it's quarter to 3 and I can't sleep that I dreamt this up but tell me if this would work.

    The topic is bending exhaust pipe yourself on the cheap. to bend it by hand and not have the pipe collapse, you need something inside to support.

    check this link out. http://favoriteprojects.com/how_to_build_a_tube_bender.htm

    I can order a garage door spring custom for about 12 bucks. with a wire size of .135 and an ID of 2.5" would yeild an outer diameter of about 2.77". That should slip just nicely into a 3" 16 guage exhaust pipe assuming a wall thickness of ~.065. the ID of 3" exhaust should be about 2.87".

    Idea being, insert spring which should bend freely. (how stiff are garage door springs? never messed with them). this would, in theory, allow you to bend pipe without collapse. then, remove spring and viola, custom bent exhaust pipe.

    Granted, you couldn't do crazy tight u bends but i think it'd be enough to run a custom exhaust on a lifted chevy and be cheaper than buying all the pre bent peices and welding them together. this way, you could buy the straight 4' sections from summit or a local shop and be done with it. use a peice of flex exhaust to do your mock ups then use it as a template to bend the other peices.

    someone tell me why this wouldn't work. genius or flotsom from a sleep deprived mind trying to be cheap as hell?
     
  2. beater_k20

    beater_k20 Banned

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  3. BUDDY

    BUDDY 1/2 ton status

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    I've also heard that if you fill the inside of the tubing with sand you'll get a mandrel bend, (one that doesn't decrease in diameter in the bend area), but you have to figure out how to keep the sand inside of the tube whilst bending it & you have to have a pretty nice bender at the same time. You couldn't use the harbor freight pipe bender, it's not strong enough.

    You're thinking outside the box though. I like it!!

    However, when I had my dual exhaust done it was only like $150.00. Of course that was about 8 years ago, so prices have probably gone up since then, but even if it's $250.00 now, I'd say that it's money well spent just because of the savings in my aggravation. I'm becoming a grumpy old bastard already & I'm just 31!!

    Later,
    Buddy
     
  4. SkysTheLimit

    SkysTheLimit 1/2 ton status

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  5. SkysTheLimit

    SkysTheLimit 1/2 ton status

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    16 tons not strong enough?? If a 16 ton jack can't bend it, theres no point in me trying to do it by hand....
     
  6. sandawgk5

    sandawgk5 3/4 ton status

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    Oh it will bend it but it will kink the **** out of it no matter how much sand or spring you put in it. That bender is ****. As for dual 3" that is ****ing huge. You talking enough exhaust for a built big block. Your bottom end would suffer dramatically going that large on a dual exhaust with the 350 in your sig.

    Ira
     
  7. BUDDY

    BUDDY 1/2 ton status

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    Ira, look at the bottom of his sig. 496 would most likely need the 3" dual.

    I say however, if you've got that kinda money in the motor though, you should definitely not skimp on the exhaust. Do it once, do it right.

    Later,
    Buddy
     
  8. 55Willy

    55Willy 3/4 ton status

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    whats wrong with $18 3" mandrel tailpipes? I'v done 3 rigs with the same parts. it's in the parts computer as a 88 to 98 chevy but they offer one that matches for the other side. 3 sticks of 3" straight and mufflers anywhere from $20 to 75 each depending on what sound you want.
     
  9. sandawgk5

    sandawgk5 3/4 ton status

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    Oops I only saw the 88 tbi 350:doah:.

    Ya a 496 should prolly go 3". I would just buy the universal 3" kit from summit. It is all mandrel bent, is actually made by flowmaster and is $65 per side. That is what I am using for my single exhaust I will use it for the bends and cut and weld it to route it the way I want.

    Ira
     
  10. SkysTheLimit

    SkysTheLimit 1/2 ton status

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    Ya, built 496 on spray needs to breath. I didn't realize they had kits available in 3" that were cheap and still flowmaster made. I'll have to look some more. 65 a side ain't too shabby. As for $$ in the motor, I don't have but about 2 grand into it. :D:D:D thanks to some horse tradin'. original build cost was about 12 large.

    I guess i need to edit my sig since technically the motor is installed and the TBI is out.

    thanks guys
     
  11. sandawgk5

    sandawgk5 3/4 ton status

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    Here is the part number at summit so you can look it up.

    FLO-15902

    Ira
     
  12. SkysTheLimit

    SkysTheLimit 1/2 ton status

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    Cool. Thanks Ira.
     
  13. sandawgk5

    sandawgk5 3/4 ton status

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  14. 1977k5

    1977k5 3/4 ton status Vendor

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    That is probably very wrong. The only way you could ever lose power by using smaller exhaust pipe is if you have headers that have equal length primaries. If you don't have these headers (which VERY few of us do because they are expensive and difficult to fit on a 4WD) then the bigger the better. Period.

    Rather than explain it any more, here's a quote from dyeager535 from another thread:





    "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/eng...re/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.

    "
     
  15. sandawgk5

    sandawgk5 3/4 ton status

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    I did not say it would not work on the top end I am saying if the exhaust is too big the bottom end will suffer. Nothing in what you posted refutes that statement. Not the topic of this thread though. He is running a 496 so it doesn't matter much.

    Ira
     
  16. 1977k5

    1977k5 3/4 ton status Vendor

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    I am going to take a little tangent from this thread to prove this.

    Headers that all have the same length primaries actually scavenge the exhaust from the pipes. As the engine runs, it makes pulses through each primary. If all of the primaries are the same length, they move through the collector one after the other. This creates an effect (I believe called the venturi effect) that actually creates negative pressure behind the pulse. This "sucks" exhaust out of the other 3 primaries and hence makes more power.

    This only happens if the primaries are all the same size. Practically no one with our trucks runs them because they are expensive and can be difficult to fit with front driveshafts etc. If you have these headers, then it is important to fit the primary/collector/exhaust pipe size to the size of the motor and the intended RPM.

    If you are not running headers that have equal length primaries, the bigger exhaust the better. Period. Less backpressure means less work to push the exhaust out, less exhaust left in the combustion chamber and hence more air/fuel that gets drawn back in.
     
  17. sandawgk5

    sandawgk5 3/4 ton status

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    And my statement is that at low RPMs your torque will suffer with a huge exhaust. What you are saying is true for high RPMs but down low you need some packpressure to aid in the scavenging "effect".

    I think we are talking apples to oranges.

    Ira
     
  18. 1977k5

    1977k5 3/4 ton status Vendor

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    I still disagree. I think my last post may not have been quite complete enough.

    At high RPM's and with big CID, you need bigger primaries to flow enough to not lose power. With less flow (lower RPM's and with smaller CID), if you run big primaries, the pulse that creates the "suction" (scavenging) kinda gets lost in the big tubes. It isn't as effective, and this is the only time having bigger primaries/exhaust tubes will actually cost you some power.

    Again, IF YOU DON'T HAVE HEADERS WITH EQUAL LENGTH PRIMARIES YOUR EXHAUST WILL NOT SCAVENGE AT ALL. Period.

    If you are not running headers with equal length primaries you will make more power at EVERY RPM with bigger primaries and exhaust pipe. This has got to be one of the biggest misconceptions in exhaust.
     
  19. sandawgk5

    sandawgk5 3/4 ton status

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    I guess we agree to disagree:D.

    Ira
     
  20. 1977k5

    1977k5 3/4 ton status Vendor

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    Ira, I'm not trying to start any crap with you, but back it up if you disagree with me :D
     

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