DP: to Flex or not to Flex?
Vibrations from the motor push the exhaust front and back.
Unless you have a flex pipe, the stress of this movement is put on the gaskets, and quite a bit on the manifold.
For those with aftermarket tubular manifolds, I'd think you'd want a flex pipe in there just in case. You wouldn't want to crack it would you?
In my other car I have a flex pipe in the downpipe and in the wastegate recirc...and it's an inline 6 mounted parallel to the frame runners.
This is what helix has to say about it:
"FYI: The factory downpipe does not have a flex section. The spring loaded bolts (between the upper flange and the outlet housing) provide ample vibrational dampening. A flex sectioned downpipe is not necessary. But many aftermarket downpipes incorporate a flex section either to: provide proper dampening because their universal flange cannot support the spring loaded bolts and/or the piping is inaccurately hand bent so it requires a flex section to fit properly."
Take that as you will, obviously theyre trying to sell theyre product and not others, but there you go.
"FYI: The factory downpipe does not have a flex section. The spring loaded bolts (between the upper flange and the outlet housing) provide ample vibrational dampening. A flex sectioned downpipe is not necessary. But many aftermarket downpipes incorporate a flex section either to: provide proper dampening because their universal flange cannot support the spring loaded bolts and/or the piping is inaccurately hand bent so it requires a flex section to fit properly."
Take that as you will, obviously theyre trying to sell theyre product and not others, but there you go.
Thread Starter
Newbie
Joined: Jul 2007
Posts: 29
Likes: 0
From: SoCal
wow, thanks for all the informative posts. I am considering these issues while at the same time looking over past postings regarding th 76 vs 70 mm DP's and any HP increase or TQ loss between the two. Also, if anyone knows off the top of their head a good listing of DP's makes that offer pieces with or without flex pipes I would be appreciative. Otherwise its just a matter of calling stores and looking for pics online.
cheers!
cheers!
Last edited by liquidh; Jul 18, 2007 at 10:57 AM.
Flex pipes should be used somewhere in the exhaust when the motor is mounted as it is in the EVO.
Vibrations from the motor push the exhaust front and back.
Unless you have a flex pipe, the stress of this movement is put on the gaskets, and quite a bit on the manifold.
For those with aftermarket tubular manifolds, I'd think you'd want a flex pipe in there just in case. You wouldn't want to crack it would you?
In my other car I have a flex pipe in the downpipe and in the wastegate recirc...and it's an inline 6 mounted parallel to the frame runners.
Vibrations from the motor push the exhaust front and back.
Unless you have a flex pipe, the stress of this movement is put on the gaskets, and quite a bit on the manifold.
For those with aftermarket tubular manifolds, I'd think you'd want a flex pipe in there just in case. You wouldn't want to crack it would you?
In my other car I have a flex pipe in the downpipe and in the wastegate recirc...and it's an inline 6 mounted parallel to the frame runners.
Simply put, a fully mandrel bent solid metal tube will make more power than a pipe equipped with some squirrely flex section in the middle of it. You wouldn't want lag your turbo would you?
Last edited by sonicnofadz; Jul 18, 2007 at 09:30 AM.
Yeah I guess thats why mitsubishi engineers put in a flex section from the factory. Oh wait a second, they didn't. But hey maybe you are a better engineer than the Mitsubishi engineers? Maybe not... Vibrational damping hmmm...maybe thats what the rubber hangers are for!? Simply put, a fully mandrel bent solid metal tube will make more power than a pipe equipped with some squirrely flex section in the middle of it. You wouldn't want lag your turbo would you?
Simply put, a fully mandrel bent solid metal tube will make more power than a pipe equipped with some squirrely flex section in the middle of it. You wouldn't want lag your turbo would you?I don't disagree that a fully mandrel bent exhaust is best for exhaust flow. Who wouldn't think that?
However, I have worked on and seen many cars with custom exhausts, no flex who crack manifolds left and right.
Personally, I have cracked 3 manifolds on my other car due to movement whereas the same manifold used on other cars with flex pipes have had no cracking issues.
The exhaust I am currently welding has a flex pipe on the downpipe and one for the wastegate recirc.
Am I gonna lose some power? Sure. But I won't have to remove all that crap again to reweld my manifold.
The factory exhaust has spring bolts which take up some of the movement with the gigantic donut gasket.
I don't disagree that a fully mandrel bent exhaust is best for exhaust flow. Who wouldn't think that?
However, I have worked on and seen many cars with custom exhausts, no flex who crack manifolds left and right.
Personally, I have cracked 3 manifolds on my other car due to movement whereas the same manifold used on other cars with flex pipes have had no cracking issues.
The exhaust I am currently welding has a flex pipe on the downpipe and one for the wastegate recirc.
Am I gonna lose some power? Sure. But I won't have to remove all that crap again to reweld my manifold.
I don't disagree that a fully mandrel bent exhaust is best for exhaust flow. Who wouldn't think that?
However, I have worked on and seen many cars with custom exhausts, no flex who crack manifolds left and right.
Personally, I have cracked 3 manifolds on my other car due to movement whereas the same manifold used on other cars with flex pipes have had no cracking issues.
The exhaust I am currently welding has a flex pipe on the downpipe and one for the wastegate recirc.
Am I gonna lose some power? Sure. But I won't have to remove all that crap again to reweld my manifold.
Cast manifolds are ridiculously strong, and no one should worry about them cracking. A tubular manifold is structurally much weaker, and cannot support as much weight, unless extra supports are welded in (as seen in many of Full race's tubular manifolds). But there are also different tricks you can do to prevent stress on the manifold. You can weld in a brace on the o2 housing that connects it to the engine block (like the way it came from the factory). You can use stiffer engine/tranny mounts as well.
To me, sacrificing performance so that my manifold might live a little longer is not a good choice.
Last edited by sonicnofadz; Jul 18, 2007 at 04:08 PM.
Flex pipes should be used somewhere in the exhaust when the motor is mounted as it is in the EVO.
Vibrations from the motor push the exhaust front and back.
Unless you have a flex pipe, the stress of this movement is put on the gaskets, and quite a bit on the manifold.
For those with aftermarket tubular manifolds, I'd think you'd want a flex pipe in there just in case. You wouldn't want to crack it would you?
In my other car I have a flex pipe in the downpipe and in the wastegate recirc...and it's an inline 6 mounted parallel to the frame runners.
Vibrations from the motor push the exhaust front and back.
Unless you have a flex pipe, the stress of this movement is put on the gaskets, and quite a bit on the manifold.
For those with aftermarket tubular manifolds, I'd think you'd want a flex pipe in there just in case. You wouldn't want to crack it would you?
In my other car I have a flex pipe in the downpipe and in the wastegate recirc...and it's an inline 6 mounted parallel to the frame runners.
I agree, ive had to replace 2 dp in my old car bc they had no flex section in them...obviously the interior lining of the flex piece isnt going to be as smooth as a mandrel bent piece of straight pipe and therefor you will lose a little flow, but I dont think it would overly noticeable or significant to the every day evo driver
I agree that not having a flex section puts more stress on the manifold, but I've been doing this for a long time now and have not had a manifold crack on me. Fortunately I am just using crappy $80 ebay manifolds right now, and I don't mind re-welding or replacing them. If I had a $1200 full race manifold...maybe not...
Cast manifolds are ridiculously strong, and no one should worry about them cracking. A tubular manifold is structurally much weaker, and cannot support as much weight, unless extra supports are welded in (as seen in many of Full race's tubular manifolds). But there are also different tricks you can do to prevent stress on the manifold. You can weld in a brace on the o2 housing that connects it to the engine block (like the way it came from the factory). You can use stiffer engine/tranny mounts as well.
To me, sacrificing performance so that my manifold might live a little longer is not a good choice.
Cast manifolds are ridiculously strong, and no one should worry about them cracking. A tubular manifold is structurally much weaker, and cannot support as much weight, unless extra supports are welded in (as seen in many of Full race's tubular manifolds). But there are also different tricks you can do to prevent stress on the manifold. You can weld in a brace on the o2 housing that connects it to the engine block (like the way it came from the factory). You can use stiffer engine/tranny mounts as well.
To me, sacrificing performance so that my manifold might live a little longer is not a good choice.
Cast mani's are awesome because they are reliable.
I wouldn't be as worried as much on a cast mani.
All the cracked manifolds that I have worked with or seen have been welded tubular.
But if you ever end up switching out to a tubular, it'd be nice to have a DP with a flex section already. That's just personal preference.
I don't believe the flex section will rob you of a ton of power.
Hell, I made 306awhp and 312 tq with a stock DP and no aftermarket catback. Just a test pipe and tune.
The ID of flex pipes are the same as the ID of your mandrel bent tubing so it's really just turbulence, not a change in diameter that you are dealing with.
nope, i never look into those. i just got the TurboXS downpipe since i'm running with the factory manifold.
I still think its a best manifold out there ,if its ported for the stock turbo.
sorry
I still think its a best manifold out there ,if its ported for the stock turbo.
sorry
Thread
Thread Starter
Forum
Replies
Last Post
