Hi, im in the process of making a 3" DP on my B series CRX. I have a chop saw, band saw, and belt sander, torch. to make this.. And a mig welder with some stainless wire to tack it up.

Now.. I needed it to be tighter off the turbo, so i took and made a cheater bend.. Like a pie cut type deal. This isnt going on a 500hp monster.. Just a stock block b18c.

I notice when i go to put it up to the 4 bolt flange.. It will be impossible to put the nuts on the studs.. So i came up with 2 ideas.

1. Use a 2.5-3.0" reducer.. ive seen them before, but shipping is very pricy to canada, and since its just a street car i came up with option 2.

2. Do what was done with this fullrace downpipe.. Just dent it in (evenly) After i heat it up a bit with the torch.



Ok.. Ill get some pics up of my cheater bend.. Let me know if its too agressive, before i tack it, or if i should spend some time and add another pie cut, and take a bit out of the angles to make it a bit more smoother.

Keep in mind, the car also has full 3" exhaust, a cat, and a canister style muffler.


Modified by HamiltonRex at 7:06 PM 1/12/2006

 

i would dent it, or try to figure a way to make it vband

 

cheater cuts are a no no...because not only does it look shitty...flow shitty...but it makes welding it shitty.

IF YOU CAN...take a hammer and caress that hummer to where you want it. I did this on my car...no problem.

 

Depending on the cost of your turbo.... weld a vband right to the housing

Just recently did that on my t3 and so far its great. Made things alot simpler than dealing with flanges/bolts etc.... 1 bolt and on/off.

My 60/63 did only cost me 50bucks though.... so it couldnt hurt to do what we did

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by splitime &raquo;</TD></TR><TR><TD CLASS="quote">Depending on the cost of your turbo.... weld a vband right to the housing

Just recently did that on my t3 and so far its great. Made things alot simpler than dealing with flanges/bolts etc.... 1 bolt and on/off.

My 60/63 did only cost me 50bucks though.... so it couldnt hurt to do what we did </TD></TR></TABLE>

I just had the same thing done. So much easier, plus you have some adjustment for fitment if needed. No need to dent or flare, just straight up true 3 inch DP.

 

use one of those donut pipes...

 

yeah.. My 1 pie cut is so small. maybe a 20 deg angle? And its made from the sharpest part of the pipe where it bend.. So i doubt its going to cause any significant loss of power.

And im not going to Vband it, Ive got a t3/t04e. And im just going to use the 4bolt flange, and dent it nicely.

 

anyways.. downpipe is done

Fits better then i expected

Only thing that sucks is that i have to use studs.. and on the bottom i have to start the back nut as i put the mani on, other then that it fits very well and should work very well.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ~RTErnie~ &raquo;</TD></TR><TR><TD CLASS="quote">cheater cuts are a no no...because not only does it look shitty...flow shitty...but it makes welding it shitty.

IF YOU CAN...take a hammer and caress that hummer to where you want it. I did this on my car...no problem. </TD></TR></TABLE>

Please post proof that it flows shitty. I know this is the internet but I'd like to see what proof you have that bends like this decrease HP:

 

Hey mine looks like that!

But i only used 1, just to get it tight so it would line up with my exhaust..

But yeah i think it should flow just side, i smoothed out the inside real nice after welding..

Pics tommorow

Mine isnt tig welded.. just did 2 passes with a mig and grinded down the weld but left a bit for strenght. Not as bling But should hold up fine for my needs. Plus i making my own stuff is always a good learing experience.

 

i know your finished now, but if u go to make another one, look into using doughnuts from the chassis shop.

heres mine, full 3". i ended up denting in the pipe where the bolts need to sit before welding the flange.

 

laws of physics. Air, in a fluid like state, will flow in a laminar pattern. And from Poiseullies(sp?) law in relating radius of a pipe to amount of volume it flows...you will significant reduce your overall flow by decreasing the radius of your laminar flow. Radius^4 ~ volume &lt;-- correlation between the two.

So yeah..pie cuts wont flow as well.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ~RTErnie~ &raquo;</TD></TR><TR><TD CLASS="quote">laws of physics. Air, in a fluid like state, will flow in a laminar pattern. And from Poiseullies(sp?) law in relating radius of a pipe to amount of volume it flows...you will significant reduce your overall flow by decreasing the radius of your laminar flow. Radius^4 ~ volume &lt;-- correlation between the two.

So yeah..pie cuts wont flow as well. </TD></TR></TABLE>

You need to retake geometry. You would be correct that you lose velocities if you change the radius but pie cuts do not change the radius of the pipe. the radius of the pipe always remains the same.


KNOW WHAT YOUR TALKING ABOUT BEFORE YOU SPREAD MISINFORMATION ON THE INTERNET!!!!!!


Modified by The Original Whitey at 3:38 PM 1/27/2006

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by The Original Whitey &raquo;</TD></TR><TR><TD CLASS="quote">

You need to retake geometry. You would be correct that you lose velocities if you change the radius but pie cuts do not change the radius of the pipe. the radius of the pipe always remains the same.


KNOW WHAT YOUR TALKING ABOUT BEFORE YOU SPREAD MISINFORMATION ON THE INTERNET!!!!!!


Modified by The Original Whitey at 3:38 PM 1/27/2006</TD></TR></TABLE>

Actually the radius of the pipe wont change...but the cross sectional area inside the pipe will. When the bead protrudes into the pipe it causes the air to swirl off of the wall...not alot, but like 1mm. This swirl holds the air off of the wall...effectively reducing the cross sectional area by 2mm.

BTW-I dont know it it really holds the air 1mm off the wall...i was just using that as an example.

 

excuse me sir but I do know what im talking about. I'm 10 credits from my BS in Mathematics and Applied Physics(double major). You WILL change the ID of the pipe by making pie cuts and you WILL loose flow. IF you actually listened to what I said you would understand it. the pipe will only flow as much as its smallest diameter at a given pressure. if you make the ID of a bend much smaller you effectively diminished its ID or...Inner radius....radius. decrease the radius you decrease the flow...its a DIRECT CORRELATION.

Poiseuille flow


The important feature of this equation is the sensitive dependence upon the pipe radius a. For instance, for a pipe with a fixed pressure gradient, a 20% reduction in the pipe radius leads to a 60% reduction of the flow rate! This clearly has important flow implications -- small amounts of protrusion in the ID of tubes can lead to very large reductions in the rate of air flow.

so eat a dick, I know my ****.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ~RTErnie~ &raquo;</TD></TR><TR><TD CLASS="quote">excuse me sir but I do know what im talking about. I'm 10 credits from my BS in Mathematics and Applied Physics(double major). You WILL change the ID of the pipe by making pie cuts and you WILL loose flow. </TD></TR></TABLE>


I can't compete with those credentials. However, I took pictures so you can explain how pie cuts reduce the inner diameter of the pipe thereby reducing flow.


This is a piecut:




The measurement of the cut:



Measurement of the original pipe:




However my original question was do you have proof that using pie cuts for a downpipe will reduce HP compared to using a mandrel bend that has the same radial sized bend? I mean in theory communism works, I'm just asking for real proof.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by The Original Whitey &raquo;</TD></TR><TR><TD CLASS="quote">


I can't compete with those credentials. However, I took pictures so you can explain how pie cuts reduce the inner diameter of the pipe thereby reducing flow.


This is a piecut:


</TD></TR></TABLE>

I love the degree in the background of the picture.

Anyways, piecuts do come in handy in some cases. If a mandrel can be used, I'll use one. But if I need a bend that's even tighter than a donut, then expletive it, what other option is there. Sure, a good fabricator will design something so that you'll never have to be in the position to use piecuts, but what if you're stuck with an Ebay manifold that the customer wants to use with a turbo that's just way too big to fit in the engine bay. I know I'm going to use piecuts, because the other option (no exhaust ) is going to get you nowhere really fast.

Here's a 1995 Mitsubishi GSX that the customer wanted an intake/exhaust made for it. He supplied a superb XSPower turbo/manifold which obviously had the best fitment in the world. So I had to make a 3" downpipe that wouldn't end up burning up the alternator or oil filter (read: I used piecuts for the initial few bends coming out of the turbo! )








Modified by backpurge at 11:22 PM 1/28/2006

 

for Christ-sake, we are not bulding a F1 race car or a 1500HP race car. this is not critical, pie cuts are fine for this application.

these guys in Japan pushing over 700hp on their twin turbo 240z and pie cut the hell out of their piping and they're fine with that.

 

ohh yea pie cuts are fine and used all the time.. i like the look as well. Lets also not forget this is a DOWNPIPE.. try not to get so critical. I def want to see some pics of your progress thow.. any updates ham ?

also, most of this cars exhaust is all pie cuts. I think its the greatest exhaust i've seen
http://www.dupontregistry.com/...nkey=


Modified by GarageAlchemist at 3:33 PM 1/28/2006

 

tube/pipe ID and bend/elbow CLR(center line radius) are two different things. pie cuts/cheated bend allow a tighter CLR than is possible with mandrel bending or the ability to fab a bend to your specs from straight if you dont have any bends. generally the tightest CLR available from a mandrel bend is 1D (1 times the OD of tube)....pie cuts can be tighter.

 

pie cutting contest 06.. 2 weeks to make the coolest pie-cut !... lol

 

they could maybe use pie cuts because they are using titanium, and it seems it might be more cost effective to pie cut then to bend titanium which could be difficult to bend. just a thought here

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by GarageAlchemist &raquo;</TD></TR><TR><TD CLASS="quote">pie cutting contest 06.. 2 weeks to make the coolest pie-cut !... lol</TD></TR></TABLE>
think we've already got the winner here. Tigcraft.they make high-end Ti systems for sportbikes.as said above about the car pictured,i think the main reason these guys are using pie cuts is because they're using thin gauge titanium,and bends probably aren't really an option.










but anyway,to the original subject.i think the bottom line is that the pie-cut will inhibit flow some IF:
-it makes the radius of the bend too tight/sharp.as you can see above,pie cuts can be just as smooth as a mandrel bend.

and/or

-the weld protrudes into the inside of the joint.too much penetration will lower the diameter of the piping.poor fitment can also cause turbulence.

both of those will obviously reduce flow,but can be avoided.
i think the bottom line is poor planning and execution is going to give you problems regardless of how you make the downpipe.pie-cuts aren't going to cost you flow just because they're pie-cuts ....a well thought out downpipe with pie-cuts will cost you no power over a mandrel bend setup.

chris

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by TeamNextGenChris &raquo;</TD></TR><TR><TD CLASS="quote">

i think the bottom line is poor planning and execution is going to give you problems regardless of how you make the downpipe.pie-cuts aren't going to cost you flow just because they're pie-cuts ....a well thought out downpipe with pie-cuts will cost you no power over a mandrel bend setup.

chris</TD></TR></TABLE>

just costs you time...and time is $...so im guessing the above pieces must be pretty expensive

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by Full-Race Javier &raquo;</TD></TR><TR><TD CLASS="quote">

just costs you time...and time is $...so im guessing the above pieces must be pretty expensive </TD></TR></TABLE>
definitely big money.
obviously in the applcation we're talking about,there's no reason at all to make a whole DP out of pie-cuts.my point is just that if you have to,doing it properly should not present any measureable loss.if you have some kind of turbo/mani setup that leaves you no room to have proper radius bends,you're screwed regardless.i cringe every time i see turbos with those really tight 90* elbows welded on the outlet of the compressor
chris