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Old 04-09-2010, 07:06 PM
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Exhaust sizing question? 3" or 2 1/2"

Hey Guys, I bought my headers finally and they are the super comp long lube for hooker. 1.75".

I have stock bottom end and the edelbrock performer rpm top end with 750 edelbrock carb elec. choke. 373 rear gears.

My question is... I bought the new super 44's from flowmaster 3" inlet and 3" outlet. I was talking to my dads muffler guy today about pricing on installing it.

He said he would do whatever I wanted but he would recommend going 2 1/2" unless I had a lot of horse power (around 600+ hp) because the 3" would have the effect of holding back ( like pulling a trailer or something)

So my question is, What do you guys think I should do. Its true duels without cat. and with not x-pipe. Is he right or am i missing something. I thought the better the flow, better the performance. I hope this is in the right section, Didnt know where to thread it. Thanks and would like to here some of your experiences with exhaust sizing.

also, I am stuck between having my tips come out behind my tires facing outward at an angle, or just strait out the back. Does that change the sound while in the truck or is that just for looks.

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Last edited by wild_man84; 04-09-2010 at 07:30 PM.
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Old 04-09-2010, 07:15 PM
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It would seem obvious that the OP would know to post information about their vehicle? After all this is an automotive related forum. For some reason all we know is that he has a truck... (duh?)

That said... wild_man84, what vehicle do you have and what engine is in it?
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Old 04-09-2010, 07:16 PM
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I agree with the Shop

I'd stick with the 2 1/2" setup for the exhaust 3" is just overkill. as for the exit location that is still a personal preference. it doesnt change the performance. but I will admit that having them exit pointing at an angle towards the ground makes your truck less obnoxious to those around you

My .02
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Old 04-09-2010, 07:22 PM
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Personally I would go with 3" pipes and I would use an X pipe before the mufflers. If this is a crush bent system it will not be a true 3" id. the whole way through anyway. I am assuming this is on a truck since you mentioned towing. On my truck I run the exhaust out the side behind the tire. The exhaust noise reflecting off a trailer can be irritating.

If I am reading you correctly you are using an Edelbrock RPM top end kit as in heads cam and intake. If this is in a 350 it will not be a towing torque monster and a 1/2" smaller exhaust will not change this. What are you trying to do with this project ?
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Old 04-09-2010, 07:24 PM
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350...4-bolt mains...no a/c... power steering... orange in color..... 85' block .....automatic ....vacuum advance timing.... 68 cc heads.... hyd. lifters...


not everything is needed about an engine for a response.... obviously i dont have 600 hp.. around 400hp..

intended use.... weekend mostly but may drive to work a few times a week. if im running late. lol..
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Old 04-09-2010, 07:29 PM
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Quote:
Originally Posted by RustoRod
Personally I would go with 3" pipes and I would use an X pipe before the mufflers. If this is a crush bent system it will not be a true 3" id. the whole way through anyway. I am assuming this is on a truck since you mentioned towing. On my truck I run the exhaust out the side behind the tire. The exhaust noise reflecting off a trailer can be irritating.

If I am reading you correctly you are using an Edelbrock RPM top end kit as in heads cam and intake. If this is in a 350 it will not be a towing torque monster and a 1/2" smaller exhaust will not change this. What are you trying to do with this project ?
sorry for the confusion..... I was reffurring to towing as holding back due to the exhaust size being to large.. you know. like if its out of time and it kinda feels like its holding back... Im not towing a yard rake in my truck..lol.. sorry about the confusion. i was trying to give everyone an idea about how he (muffler shop guy) said it would feel without the horse power to go with 3" pipes..
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Old 04-09-2010, 07:30 PM
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Quote:
Originally Posted by wild_man84
350...4-bolt mains...no a/c... power steering... orange in color..... 85' block .....automatic ....vacuum advance timing.... 68 cc heads.... hyd. lifters...


not everything is needed about an engine for a response.... obviously i dont have 600 hp.. around 400hp..

intended use.... weekend mostly but may drive to work a few times a week. if im running late. lol..

If it is primarily a toy I would definitely use the three inch. I started a thread on here some time back asking for a real example of a vehicle slowing down with the addition of a larger exhaust pipe. I am still waiting for the example.
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Old 04-09-2010, 07:38 PM
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As with almost any mod to an engine the Bigger the part(in your case pipe)the more upper rpm HP you would make in exchange for lowend torque.
For street car with street gears and all I would go with 2 1/2" .With 3" I think you would feel a bit of doggyness in the throttle response in exchange for a very minor HP increase up top,I doubt you will ever feel the differance unless your at the dragstrip were you'd prolly only see a tenth of a second anyways.IMO
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Old 04-09-2010, 07:40 PM
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Quote:
Originally Posted by RustoRod
If it is primarily a toy I would definitely use the three inch. I started a thread on here some time back asking for a real example of a vehicle slowing down with the addition of a larger exhaust pipe. I am still waiting for the example.

SO, no one could answer the fact that the car/truck would run faster with a 2 1/2" pipe rather than a 3". Personaly, I dont see how.. but my muffler guy told me a story where he had 3" and was racing circle track and an old guy told him if he took those I QUOTE damn big pipes off he would win one.. he said he changed to a 2 1/2" and won the the next 3 races.... that was his story. he does have a really good rep. from ppl that get work from him. But without explanation its hard for me to accept smaller pipe/ better power..
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Old 04-09-2010, 09:30 PM
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The larger diameter exhaust diameter causes the exhaust gas to cool too fast and slow down. Lower velocity exhaust gas negatively affects scavenging at low rpm. And therefor torque. It's a balance. Generally bigger will be better, but only up to a point.

Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe.

Also note the difference in 2.5 and 3" is huge. The cross sectional area of 2.5" is about 4.9sqin. 3" is about 7.1sqin. That's 69% larger.

Of course the number of bends and type of bending has a big affect as well. For 400hp, dual 2.5" should be more than enough.
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Old 04-10-2010, 06:05 AM
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well that answers my question. Im going with the 2 1/2" to my mufflers and 3" from the mufflers to the tips. will this be good. or should i continue 2 1/2" to the tips as well. See, I have already bought the 3" in/out mufflers. muffler guy said he could just bend the pipe to the muffler. should i trade the mufflers to 2 1/2" and run 2 1/2" all the way to the tips or will 3" mufflers and 2 1/2" pipes with 3" tips still sound good and not take away from my torque.
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Old 04-25-2010, 05:53 AM
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well guys...

I got my truck into the muffler shop yesterday and back... I went from my headers reduced down to 2 1/2 and 2 1/2 all the way to the tips.. I got the tips behind the tires kinda 45ed out... looks nice..... sounds mean.... super 44's are great... rice burners quiver beside me... lol
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Old 04-25-2010, 06:35 AM
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Quote:
Originally Posted by Landshark928
The larger diameter exhaust diameter causes the exhaust gas to cool too fast and slow down. Lower velocity exhaust gas negatively affects scavenging at low rpm. And therefor torque. It's a balance. Generally bigger will be better, but only up to a point.

Overlarge piping will also allow our exhaust pulses to achieve a higher level of entropy, which will take all of our header tuning and throw it out the window, as pulses will not have the same tendency to line up as they would in a smaller pipe.

Also note the difference in 2.5 and 3" is huge. The cross sectional area of 2.5" is about 4.9sqin. 3" is about 7.1sqin. That's 69% larger.

Of course the number of bends and type of bending has a big affect as well. For 400hp, dual 2.5" should be more than enough.
i beleave your rite 2.5'' for a high 9 comp motor, id say if you are running a higher comp ratio motor like 12-13 yeah go 3'' because the more comp ratio the more exhaust you have!
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Old 04-26-2010, 06:15 PM
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you know guys.. I want to appreciate all the help and guidance. I dont have a camera. hint-----im a hot rodder... id rather buy stuff for my hot rod than something ill just end up breaking like my last camera at the NHRA Finals in Atlanta.. lol.. I just wanted to thank everyone for their input on all my post. Even if i dont take your advise it leads to me learning and knowing why i choose what i chose.. And another thing.. I didnt know how complex exhaust system was. Thanks guys.. and when my friend comes up this weekend ill get him to take a picture and let you all see where all your help has been going.

Thanks Hotrodders....
Darrell
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Old 04-27-2010, 09:19 AM
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3" pipe is 44% more area than a 2.5" pipe not 69%.
Clive W
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