True Duals - 2.5" or 3"? Did Search
05-18-2003, 08:08 AM
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True Duals - 2.5" or 3"? Did Search I'm thinking of going true duals (Dr. Gas X-pipe kit, Dynomax Magnum Race Bullet Mufflers 12"long), but I don't know if I should go 2.5" or 3". Mods are in sig, but I will also be doing a head/cam install here in two weeks. Cam is Comp Cam 224/224 .581/.581 LSA:114 and the heads are Absolute Speed Stage 2 heads. I have always heard that with stock bottom, stay 2.5" or you may lose power. But I have also heard some say if you have/do a heads/cam setup, the 3" would be better off. So which would be better for my setup? I did a search and never got a clear answer. It would help if someone had some proof which would be better. Thanks! 
05-18-2003, 10:16 AM
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Re: True Duals - 2.5 You could probably get away with dual 2.75", but I would go with 3".
With the heads and cam, you'll be expecting rwhp #s in the low to mid 400 range, right? So thats nearly 500 flywheel hp. With that kinda hp you're going to want your exhaust capable of flowing around 1100 cfm with no loss. Now a a single 3.5" will flow over 1100 cfm, dual 2.75s will flow 1366 no loss cfm, while dual 3" will flow around 1624.
But...
That is just the flow of a straight section of pipe, and most street cars dont run just a straight piece of pipe hanging off the collector. I guess a lot of it depends on if you want to do shortie duals or true duals all the way to the back bumper, but the longer the pipes are the more frictional losses there will be. Additionally, the longer the pipes are the more bends there will be, and if they aren't mandrel bent then you run into smaller cross sections at each bend. It sounds like you're doing shortie duals though. With this is in mind, I would do with the dual 3" pipes. Plus, if you ever want to spray some nitrous your exhaust wont be holding you back as much as if you went with 2.5 or 2.75
But, IMO, dual 2.5" is too small for a ~425 rwhp car.
J.
With the heads and cam, you'll be expecting rwhp #s in the low to mid 400 range, right? So thats nearly 500 flywheel hp. With that kinda hp you're going to want your exhaust capable of flowing around 1100 cfm with no loss. Now a a single 3.5" will flow over 1100 cfm, dual 2.75s will flow 1366 no loss cfm, while dual 3" will flow around 1624.
But...
That is just the flow of a straight section of pipe, and most street cars dont run just a straight piece of pipe hanging off the collector. I guess a lot of it depends on if you want to do shortie duals or true duals all the way to the back bumper, but the longer the pipes are the more frictional losses there will be. Additionally, the longer the pipes are the more bends there will be, and if they aren't mandrel bent then you run into smaller cross sections at each bend. It sounds like you're doing shortie duals though. With this is in mind, I would do with the dual 3" pipes. Plus, if you ever want to spray some nitrous your exhaust wont be holding you back as much as if you went with 2.5 or 2.75
But, IMO, dual 2.5" is too small for a ~425 rwhp car.
J.
05-18-2003, 03:18 PM
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Re: True Duals - 2.5 Is that a custom fabbed X-pipe or did you buy it from somewhere?
05-18-2003, 04:40 PM
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Re: True Duals - 2.5 Well, looks like 3" duals it is. 
Thanks for the info Crazyquik. I was worried that the 3" might have been too much. Nice setup BradWS6. Bet it sounds good.
Thanks for the info Crazyquik. I was worried that the 3" might have been too much. Nice setup BradWS6. Bet it sounds good.
05-18-2003, 04:52 PM
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Re: True Duals - 2.5 I bought the kit from Justin Sutton.I had to do some Fabing.The Headers are from Thunder Racing 1 7/8.Mufflers are Eldebrock RPM series.Yes it does sound good.
05-18-2003, 10:07 PM
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Re: True Duals - 2.5 I did 2.5" on my setup
two, 2.5" pipes is more flow capsity than even most big blocks need
by going with the 2.5, you have more ground clearance (lowered cars need this) and it also lets you run the pipes under (yes...UNDER) the rear axle so you can take the enxhaust all the way out to the rear bumper (don't have to dump under the car).
two, 2.5" pipes is more flow capsity than even most big blocks need
by going with the 2.5, you have more ground clearance (lowered cars need this) and it also lets you run the pipes under (yes...UNDER) the rear axle so you can take the enxhaust all the way out to the rear bumper (don't have to dump under the car).