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Discussion Starter #1
Im going to be having my exhaust done here soon. I dont know what size pipe to run with the 347. The car is going to be on an edelbrock spray kit adjustable from 50-100hp. I've been told nitrous likes big exhaust. So I was going to run 3" duals with an x-pipe through either flowmaster 40s or Magnaflos.

BUT Fords also from my knowledge like a little back pressure. So should I make it 2.5" instead of 3"? I'm really not sure what to do here....what do you sughgest?
 

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It depends on several things but I would guess that 3 inch would be too large. I would think your debate should be more between 2.25 an 2.5 inch. The short list is if you are over 350 hp x/or spend lots of track time above 6K PRM, x/or force induction then 2.5 might be better else you should have better response and overall performance from 2.25. If you plan to use the NOS a lot then go with 2.5 and a budget to replace lots of broken parts! The x-pipe will help. A very free flowing exhaust with low gas velocity will hurt torque. Also, 3 inch pipes will be very challenging to install plus a lot of extra weight. From a more technical perspective, calculate the realistic CFM flowing through the system and build your exhaust system for the requirements.

Note: I’m an active road course racer with SCCA and NASA, maybe drag racing with NOS has different requirements.
 

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I just happen to be thumbing through a old Car Craft (I think) that had a chart with exhaust size vs HP. It was interesting to note that a single 3" exhaust system could support 500 hp! Chech Dodgestang's home page, I think he has the same chart.
 

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As I was saying else where in this thread, I've read that a single 3" pipe can support up to 500 hp. Even if we say 400 hp, this is still a lot of power or even 350. With that being said and all the talk of "X" pipe vs "H" pipe for improved scavanging, I wonder has anyone ever thought about making a single 3" system? I wonder just how a "Y" pipe would work. Off hand I think it would work pretty well. Yeah, I realize a packaging may be an issue but aside from that. I've given thought on looking into doing this on my car. Anyone have any thoughts about this?
 

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On the topic of a single 3 inch system. It has a lot of merit as long as it is well designed. You should have the same savaging effects with less weight. I’m surprised more racers have not gone this route other then traditional wisdom. If I was designing a new system for my ’66 then I would use a single high flow system but I already have a full mandrel bend x-pipe duel system that works for me.
 

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I would be more concerned with your tri y's. Or are you swapping those out for something else.
2.5" would probably be just fine
 

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well, on my car i have long tubes with 2.5" exhaust, true x-pipe and flowmaster 40 series mufflers. i love it, but i do wish i went with 3" and electric cut outs, but i like loud. at the time i didnt have the extra money, bu now that i do i wish i went that way in the first place.
 

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Discussion Starter #9
yes the Try-Ys are getting the boot they won't fit my McCleod Scattershield so Ive got some brand new Hooker Comps with the ceramic coating ;)

So we're leaning more towards dual 2.5" pipes here? The Nitrous isnt going to factor in that often. Only at the local track once in a while.
 

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Discussion Starter #12
what sizes do you guys actually have on your cars??
 

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I have 3 inch from the collectors, into an 'x', into 3 inch mufflers, then 2.5 after the mufflers bent up and over the axle and out the back GT valance with my 408 cube, 400 RWHP 65.
 

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I'm running a stock 2" dual system with Dynomax mufflers. I only bought the Dynomax because they were the only cheap muffler I could fine that would fit. I like them very much, reserved enough not to piss off the neighbors but have a nice growl when you step on it.
 

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My GT(see sig pic) recently went 12.14 , 109.5 MPH with two inch mufflers and tailpipes...308,C4,3.89's,pump gas...
 
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