Dismiss Notice

Welcome To CK5!

Registering is free and easy! Hope to see you on the forums soon.

Score a FREE t-shirt and membership sticker when you sign up for a Premium Membership and choose the recurring plan.

Single 3" or dual 2 1/4"?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by BLUESMAN, Oct 28, 2001.

  1. BLUESMAN

    BLUESMAN 1/2 ton status

    Joined:
    Oct 3, 2001
    Posts:
    951
    Likes Received:
    1
    Location:
    Phoenix(but it\'s a dry heat...like an oven!)AZ.
    Single 3\" or dual 2 1/4\"?

    What does everyone think would produce more torque:A single 3" muffler and tailpipe or dual 2 1/4" mufflers and dual tailpipes?This will go on a non-cat truck.Oh and running Hooker headers.
     
  2. wakedog

    wakedog 1/2 ton status

    Joined:
    Mar 7, 2001
    Posts:
    233
    Likes Received:
    0
    Location:
    Minnesota
    Re: Single 3\" or dual 2 1/4\"?

    If its a 350 i would say 2 1/4 in duals, if its a 454 i would go with 3 in duals, just my opinion, i happen to have headers, no cats, and 2 1/2 in on my 350, i definetly like the torque it makes.

    <a target="_blank" href=http://www.bigredjimmy.iwarp.com>http://www.bigredjimmy.iwarp.com</a>
     
  3. Hossbaby50

    Hossbaby50 3/4 ton status

    Joined:
    Sep 1, 2001
    Posts:
    8,972
    Likes Received:
    0
    Location:
    Peoria, AZ
    Re: Single 3\" or dual 2 1/4\"?

    I got 21/4" duals on my Jimmy, and I like them alot. If your truck doesn't need cats, then I assume duals isn't a legal issue. I would go duals. They only reason I would run a 3" is if it was illegal to run duals. (oh wait, they're illegal on my truck. oops).

    My Chevy isn't broken, its just out of gas.
     
  4. Can Can

    Can Can Pusher Man Staff Member Super Moderator

    Joined:
    Feb 17, 2000
    Posts:
    15,552
    Likes Received:
    136
    Location:
    Cochrane, Alberta, Canada
    Re: Single 3\" or dual 2 1/4\"?

    I reecently installed 2 1/4" duals with Super Turbo mufflers(stock exhaust manifold and no cats), and can honestly say that I noticed a pretty good improvement in power and gas mileage.



    <font color=blue> NEVER FORGET, NEVER FORGIVE, NEVER SURRENDER<font color=blue>
     
  5. Brian 89KBlazer

    Brian 89KBlazer 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    779
    Likes Received:
    0
    Location:
    Ontario, Canada
    Re: Single 3\" or dual 2 1/4\"?

    Ok, I've got a question for your question! [​IMG]

    What HP are you making (even a guesstimate)?? The reason I ask is that I'm having my 350 rebuilt and will be adding a new Crane Cam; Flowtech Afterburners; etc and also running a full dueal exhaust. I contacted Flowmaster's tech line &amp; they told me that if the engine wouldn't make over 250Hp then 2 1/4 is fine BUT if my engine would be making in excess of 250HP (which I'm pretty sure it will); I should go to the 2 1/2" duals cause 2.25" would not allow the engine to breathe freely over the 250 HP mark!

    Just something to consider

    Good Luck

    Brian
    89KBlazer

    Build it Right or Don't build it at all!!
     
  6. Can Can

    Can Can Pusher Man Staff Member Super Moderator

    Joined:
    Feb 17, 2000
    Posts:
    15,552
    Likes Received:
    136
    Location:
    Cochrane, Alberta, Canada
    Re: Single 3\" or dual 2 1/4\"?

    Good info, Brian........Would it make a difference if you weren't running cats? I'd hate to think that I'd have to shell out for new exhaust when I eventually upgrade my motor.



    <font color=blue> NEVER FORGET, NEVER FORGIVE, NEVER SURRENDER<font color=blue>
     
  7. pcorssmit

    pcorssmit 1/2 ton status

    Joined:
    Jan 2, 2001
    Posts:
    1,346
    Likes Received:
    0
    Location:
    Denver, CO
    Re: Single 3\" or dual 2 1/4\"?

    I run full length headers into 2 1/2 pipes, into a Flowmaster Y, into a 3" big block Flowmaster (not sure of the "series" #, but the case is around 22" long), then finally a single 3" tailpipe in the stock location on the passenger side. I'm real happy with it, nice tone but quiet too. A single exhaust is generally better for low end torque. It is legal for me to run a true dual on this truck, and I actually bought the parts to do it, but changed my mind and went this route, and sold off the other stuff. Glad I did.

    Pete

    '83 K5, 350 TBI (ex 6.2), 700R4, NP208, Dana 60/14 bolt, 4.56s, Detroits, 3" lift, 15-39.5x15 TSLs
    '97 Dodge 2500 4x4 CC LB Sport, Cummins 5 spd
     
  8. Brian 89KBlazer

    Brian 89KBlazer 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    779
    Likes Received:
    0
    Location:
    Ontario, Canada
    Re: Single 3\" or dual 2 1/4\"?

    Hey CanmoreK5

    I told the tech that I planned to run dual cats but he seemd to ignore that info. He was more focused on the HP numbers. When he said dual 2.5"; I questioned him on the exact point Pete made; low end torque. I asked about the dual 2.5" providing sufficient backpressure for good low end torque &amp; he still maintained that the 2.5" was the size to go with. Like you; until I made the call; I was planning on 2.25" but now I think I'll go with the 2.5".

    I got a price for Cats on Friday &amp; for a couple of free-flow cats; it'll cost me about $148 (Canadian) each! That'll put me at $576 for 2 cats &amp; 2 Flowmaster 50 Series Deltaflow mufflers! I'm considering skipping the cats for now &amp; if I get busted; I'll get the cats then. I've talked to a number of locals &amp; no one has heard of anyone being busted for no cats yet!!

    Oh the money!!!



    Brian
    89KBlazer

    Build it Right or Don't build it at all!!
     
  9. Hossbaby50

    Hossbaby50 3/4 ton status

    Joined:
    Sep 1, 2001
    Posts:
    8,972
    Likes Received:
    0
    Location:
    Peoria, AZ
    Re: Single 3\" or dual 2 1/4\"?

    I got a 300HP GM crate 350 with 2.25" duals and it runs fine. The exhaust doesn't seem restrictive at all. I know it sure flows better then the factory exhaust did on this motor.

    My Chevy isn't broken, its just out of gas.
     
  10. Leadfoot

    Leadfoot 1/2 ton status Premium Member

    Joined:
    Nov 28, 2000
    Posts:
    3,112
    Likes Received:
    1
    Location:
    Western Massachusetts
    Re: Single 3\" or dual 2 1/4\"?

    Single exhaust is generally better for low torque, and one of the reasons is the exhaust pulses are evenly spaced helping to "pull" exhaust gases out of the chamber (not needed at high RPM). If you install dual exhaust, try to put in a crossover (a.k.a. "H" pipe). In a 4wd it is kinda tricky, I had to put mine rearward of the t-case and it is a upside down arch shape to clear the driveshaft. I had 2.25 without the H-pipe and now have 2.5 with the pipe and I think the 2.5 with pipe "seems" to have a little more low end. A good single exhaust without restrictive reducers, coupled with a good performance muffler can be a great setup too. Alot depends on emission requirements where you are from and how deep your pockets are. Hope this helps.

    See my rig at <a target="_blank" href=http://coloradok5.com/gallery/Leadfoot>http://coloradok5.com/gallery/Leadfoot</a>
     
  11. tlarsw

    tlarsw 1/2 ton status

    Joined:
    Jan 12, 2001
    Posts:
    270
    Likes Received:
    0
    Location:
    Cameron, NC
    Re: Single 3\" or dual 2 1/4\"?

    You will not see much difference between them, if any. I'd go with the cheaper of the two. I did a single 3" and dumped it down just prior to the rear axle. I had a dual 2.5" prior to that, that I bent up. Didn't really notice any differences in power. The big thing to be concerned with is the restriction of the muffler, the less the better!

    Also if you plan on using it offroad, you'll for sure beat it up, so use a setup that is protected as much as possible and works for your application. Also, if/when you end up replacing it, one tube is usually cheaper to replace.

    1986 K10 TPI350/NV4500/Gen2 Doubler/D60(ARB)/14FF(Detroit)/4.56 gears
     
  12. Thunder

    Thunder 3/4 ton status

    Joined:
    Jul 20, 2000
    Posts:
    8,946
    Likes Received:
    1
    Location:
    Northeast Nevada
    Re: Single 3\" or dual 2 1/4\"?

    Unless you are planing on installing a crossover or H pipe on the dual exhaust. I think the single 3" will do better on torque at low RPM
    A single 3" mandrel bent system also only flows just a little bit less than a dual 2 1/4 pipe. It is not really not enough to make that big of a difference on a truck.
    After doing a little reaserch for my truck I decided to stick with the single 3", headers, and big block flowmaster. It builds torque real well at low RPM.
    If you are looking for more power at wide open throttle then dual exahust is proababally what you want


    <font color=blue>NEVADA: Where the pavement ends, and the West begins.</font color=blue><P ID="edit"><FONT class="small">Edited by Thunder on 10/29/01 02:00 PM.</FONT></P>
     
  13. BLUESMAN

    BLUESMAN 1/2 ton status

    Joined:
    Oct 3, 2001
    Posts:
    951
    Likes Received:
    1
    Location:
    Phoenix(but it\'s a dry heat...like an oven!)AZ.
    Re: Single 3\" or dual 2 1/4\"?

    The K/5 is a 1978 model,with no cat. converter.I'm thinking it will make about 300HP with the cam,headers,intake and Q-Jet.I want to install a TH700 trans with a 241 T-case and 4.11:1 gears,35" tires.The K/5 is on a diet(no hardtop/tailgate and anything else I can pull!).I'm leaning towards the 3" single exuast with a Flowmaster muffler and tailpie.Thanks for all the input!
     
  14. hammer

    hammer 1/2 ton status

    Joined:
    Aug 29, 2001
    Posts:
    449
    Likes Received:
    0
    Location:
    Binghamton N.Y.
    Re: Single 3\" or dual 2 1/4\"?

    I would go with a dual exaust cuz that stupid y pipe or any other made up single exaust at some time has to connect together and either the front d-shaft or something else will be in the way
     
  15. Brian 89KBlazer

    Brian 89KBlazer 1/2 ton status

    Joined:
    Feb 17, 2000
    Posts:
    779
    Likes Received:
    0
    Location:
    Ontario, Canada
    Re: Single 3

    That was my main reason for going duals, Hammer. I'm building a new boxed chassis &amp; like I said earlier; switching to Flowtech Headers so why mess with the y-pipe when it's much cleaner/easier to run two pipes straight to the rear of the tires with a couple mufflers cut in line?

    I will try to find somewhere to run an H-pipe though; just not in the way for the front driveshaft

    Brian
    89KBlazer

    Build it Right or Don't build it at all!!
     
  16. 84_Chevy_K10

    84_Chevy_K10 Banned

    Joined:
    May 30, 2001
    Posts:
    17,669
    Likes Received:
    0
    Location:
    IL, USA
    Re: Single 3\" or dual 2 1/4\"?

    I meant to post this yesterday but it ended up in another thread....

    Get a set of headers and true dual 2 1/4" exhaust (bolt on Dynomax kit) and I'd bet that'd help immensely. Ditch the cat. Cheaper without it.

    As long as you don't have a visual inspection you can pass a sniffer test anyway. I helped my buddy's car pass over the weekend. No cats, no EGR, no smog pump, none of that nonsense, just an Edelbrock carb and intake and 1 5/8" headers and 2 1/4" duals with Flowmasters. It CAN be done.

    Bluesman,

    Your setup sounds great, but I suggest 4.56 gears. You'll be kicking yourself if you put 4.10s in it. I have that setup right now--and if I had the choice I'd have 4.56s. I am swapping my 700R4 out for an SM 465, so I'm glad I've got the 4.10s. But if I was keeping it, I'd go with 4.56 or 4.88 gears.

    And if I was in your shoes I'd save the money you'll spend on the 3" exhaust and buy the kit I did that I mentioned above.

    Tim
    '84 Chevy K10, lifted, loud, fast, and 3/4 ton axles
     

Share This Page