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I have a 434sbc ~650hp N/A with 3.5" collectors on my headers. Do I buy and install a 3.5" x pipe to mufflers or is it best to neck down and run a smaller diameter exhaust system?
 

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Discussion Starter #6
Do you need a X?

If so yea and spray 400 hp .
Not 100% convinced of my design. I just saw a 3.5 xpipe setup so started wondering. Found the correct reducer to get to 3". Sure its an old debate of x vs h but really up for any options that just ends with a pair of good mufflers.
 

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I have the same size and about the same HP motor I went from 1 3/4 header and 3'' exhaust to 1 3/4 stepped up to 1 7/8 header and 3.5'' exhaust same brand and style mufflers as old system and only gained a lighter wallet but no ET difference. 3400lb car ran bottom 10s to a high 9 sec passes on motor.
Both systems had an H pipe set up.
 

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There is no performance advantage to be gained through 3.5" or even 3.0" exhaust system. 2.5" pipe will work fine in this type of application, along with 'H' pipe.
 

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There is no performance advantage to be gained through 3.5" or even 3.0" exhaust system. 2.5" pipe will work fine in this type of application, along with 'H' pipe.
So are you saying from experience that dual 2.5" will not be a restriction on a 650hp Small block? If so, do you think it would be better if the headers were also made with 2.5" collectors?
 

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There is no performance advantage to be gained through 3.5" or even 3.0" exhaust system. 2.5" pipe will work fine in this type of application, along with 'H' pipe.
You have been saying this on every forum you belong to for years. I would love see the data that backs your claims up.
 

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I have been building turbo Buicks for many many years. One car I helped build the majority of the power train/fuel system/etc. Had a single turbo StageII with a 3.5" downpipe. He also had a three muffler 3"system on it and you could hear the Weldon fuel pump over the exhaust sound. Car owner HATED the dreaded Buick Turbo 2200rpm drone! Well, after a few years running 9.1's @148, myself and another local smart guy talked him into a Dyno session with a cut-out installed in the down pipe. Ran it first all capped up and running through three Dyno Max Ultra Flo's (the third muffler behind the rear end, was a custom made cross-flow muffler in 3"). Then we ran it with the cut-out open and that sum bitch picked up an amazing SIX FUCKIN HORSEPOWER!!!
What was amazing to us "smart" guys was that it would have ran NO faster. (Maybe .05 if he removed 50 lbs. of exhaust weight. Who knows.
His Street car (same guy) runs 9.9's @136 through a similar 3 muffler system but in 2.5". I can't hear him drive up my long driveway. Idles smooth as glass, too.
LOUD does not mean fast!
 
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