2" into 5" stacks
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2" into 5" stacks
Bought the 94 F350 7.3 turbo dually last august , done all the 'usual' mods like turning fuel up , tweeking injector pump timing , increasing boost pressure , installing pyro/boost gauge , got rid of throttled intake scoop , K&N filter...................last on the list is to replace the restricted down pipe off the turbo , problem being the down pipe goes into a 2" 'Y' branch , both exhausts run off the 2" Y branch & connect into the two 5" stacks which go through the bed ....just wondering if the 3" down pipe is worth the aggro? , the other problem being if i replace the crushed down pipe with 3" is it ok to still use the 2" exhusts into 5" stacks? , what i was thinking is to use a 3" X 2" X 2" Y branch , any ideas?............i realise EGTs will drop when getting rid of the existing down pipe but wondering if the 2" exhausts will still be restricted , stacks are coming through bed directly behind double cab.
Thanks.
Thanks.
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Problem i got is the base of stacks are real close to chassis rail where they come through the bed , the 2" coming off the stack is real tight to get in there...
Elder User
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So either redo your stacks, or don't run stacks at all.
If I had to pick between letting my truck breath better, getting more power, and lowering my EGT's, or having stacks?
It's a no brainer for me.
But do what you want man, at the end of the day it's your truck.
Postmaster
Joined: Apr 2009
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From: Malahat/Cowichan Valley
hooah!! well said dave! pulling numbers from places no one wants to think about, a dave specialty! hahaha
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Post Fiend
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I am teachng myself surveying and survey math right now.
So many blueprints we get have bad information on them, I will be able to check their numbers before summer gets here.
And when I draw an "as built" print, it will be exact.
56 and still learning new stuff.
So many blueprints we get have bad information on them, I will be able to check their numbers before summer gets here.
And when I draw an "as built" print, it will be exact.
56 and still learning new stuff.
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Well , got down pipe out without cutting , just disconnected trans cooler line off tranny & out she came , took around 15 minutes , most time was spent getting to the clamp between turbo/downpipe...............the downpipe measures around 1" where it's flattened 
, cut the floor seam with a recipro saw so the 3" should clear nicely , will take the truck out later & see how it goes , the engine is no louder without a downpipe , only difference is you can hear the turbo spooling.
Thanks.
, cut the floor seam with a recipro saw so the 3" should clear nicely , will take the truck out later & see how it goes , the engine is no louder without a downpipe , only difference is you can hear the turbo spooling.Thanks.
Posting Guru
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From: Peterborough, Ontario
One distinct advantage I have with my toolmaking background when it comes to dirt playing, drawings and math are strong points in my experience. I do have to work more on figuring volumes and the like with some of this stuff, but so much of my work is small stuff, it's guesstimate and go anyway.
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Took the truck out without a down pipe fitted , seems to of lost some power
, can't see why this would be as the turbo has to be spooling quicker...........drove the truck up an incline & found boost to be the same (15psi) , also EGTs remained the same as they were before , should be making more power as this truck belches black smoke out the stacks when initially floored , can't comment on the smoke with the down pipe off as i can't see the turbo outlet............maybe it has picked up but i just can't feel it due to it running slightly louder.
, can't see why this would be as the turbo has to be spooling quicker...........drove the truck up an incline & found boost to be the same (15psi) , also EGTs remained the same as they were before , should be making more power as this truck belches black smoke out the stacks when initially floored , can't comment on the smoke with the down pipe off as i can't see the turbo outlet............maybe it has picked up but i just can't feel it due to it running slightly louder.
Logistics Pro
Joined: Sep 2007
Posts: 3,737
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From: Western Mass
The 3" downpipe is already a lot better than the crushed stock one, you might not be loosing that much running the dual 2" pipes, look at the amount of work/cost to redo how the stacks are versus the 0.781 square inches of flow. Is it worth it to you?
thats your decision.More math to help (or confuse) you, can you fit 2 1/4 pipe between the chassis to the stacks? two 2 1/4" pipes will be 7.952 square inches, better than a single 3".
two 2 1/8" pipes would be 7.093 square inches, about the same as a single 3".
Cargo Master
Joined: Feb 2010
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From: NY
Dude, I think you are confused. Cross sectional area of a circle is pi r squared. The radius of a 2 inch pipe is 1 inch, square 1 inch and you get 1 inch, then x it by pi and get 3.14. I agree with Dave
Logistics Pro
Joined: Sep 2007
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From: Western Mass
Remember that we are talking about taking a 3" pipe, then splitting it into two smaller pipes. Currently the OP has two 2" pipes EACH is 3.1415926... square inches, COMBINED they are ~6.283 square inches.
I'm not saying Dave is wrong, I'm just throwing some more facts for the OP to consider since he would need more modifications to change the 2" pipes going into the stacks.