Topic: Exhaust question... (Read 1122 times)

mjohnson · « **on:** July 28, 2009, 09:10:35 PM »

So I was reading a diy a little while ago that involved showing the inside of a downpipe, to where you could see the flex pipe. The flex pipe on the 2.5" dp had almost swollen shut. There was about a 1/4" hole where exhaust could pass through to the rest of the pipe. I then started to think about the exhaust on my bro's chev 350 and it doesn't have a flex pipe, it's all rigid. This got me thinking, is it REALLY necessary to have said flex pipe? If not, it would save me a lot of money in completing my new exhaust project. Instead of buying a new 3"dp, I'd just cut the flange off my stock exhaust (where ever that rascal went to) and weld 3" pipe on it and run it all the way back to the new muffler.

I'm sure it would have to do with how much power/torque a person is dealing with and whether or not the motor/tranny mounts had been swapped from stock to something more stiff, like hockey pucks! (since I like cheap, but effective

).

Lay it on me gents!!

101stvet · « **Reply #1 on:** July 28, 2009, 09:18:42 PM »

well i'm don't have a turbo but my 84 rabbit has a euro 4-2-1 style exhaust/down pipe to my cat then a full techtonics exhaust the rest of the way back no flex pipe in my sytem and seems fine my jeep is the same way

Giggidy · « **Reply #2 on:** July 28, 2009, 09:58:31 PM »

You will need a flex pipe, otherwise, all the torsion that builds up between the frame flex and engine torquing will have nowhere to dissapate, and leave you with some serious issues I.E. numerous broken exhaust hangars, etc.

Smokestack · « **Reply #3 on:** July 28, 2009, 10:02:36 PM »

RWD V8s lift up on the exhaust while FWD anything twists. There's usually some joint (cup and ball) or flex pipe built in to take that twist.

mjohnson · « **Reply #4 on:** July 29, 2009, 09:22:55 AM »

Good to know. I will definitely being taking this all in to consideration for my next exhaust...

Barry · « **Reply #5 on:** July 29, 2009, 12:35:14 PM »

also.... what kind of mounts are you running? If you have something alot more rigid than stock mounts, the flex wont affect the exhaust the same way

mjohnson · « **Reply #6 on:** July 29, 2009, 02:57:57 PM »

Well, right now the motor mounts are stock, but the tranny mount has been swapped for the ecs one.

Barry · « **Reply #7 on:** July 29, 2009, 03:00:55 PM »

change out the motor mounts, and trash the flexpipe

mjohnson · « **Reply #8 on:** July 29, 2009, 03:04:15 PM »

that's what I was thinking, but I just wanted a second opinion. The easy method would be to go with vf, but I REALLY don't like the $600 price tag. I haven't really seen anything else out there. Is there any way to rebuild the stock ones with hockey pucks???

Barry · « **Reply #9 on:** July 29, 2009, 03:09:06 PM »

i am sure there is..... I know on mkIII's it's super easy...

Oh... BTW.... my mkII vrt had stock mounts, and no flex pipe.... and I am willing to bet that at 25 lbs, it was producing more torque, and engine twist than your 1.8T..... downpipe was 7 years old and no cracks

mjohnson · « **Reply #10 on:** July 29, 2009, 03:13:26 PM »

Oh Barry, don't let the 1.8 power house fool you like that. haha

I'll look in to it. The only issue now is having some hockey pucks shipped out here. I highly doubt any store is going to carry them in lower alabama, but I suppose I'll check.

scurvy_bandit · « **Reply #11 on:** July 30, 2009, 03:18:54 AM »

to flex pipe

MileHighAssassin · « **Reply #12 on:** August 08, 2009, 03:25:00 PM »

If you are building your own downpipe, make sure there is a smooth transition from the turbo outlet to the pipe. Going from say a 1.5" outlet to a 3" pipe is going to create a lot of turbulance. Match the port outlet on the flange and then expand the pipe up to your desired size.

mjohnson · « **Reply #13 on:** August 08, 2009, 10:29:31 PM »

mm. good to know

formulanerd · « **Reply #14 on:** August 09, 2009, 12:24:03 AM »

fuck building one... not when 1.8t shit is so cheap.

mjohnson · « **Reply #15 on:** August 09, 2009, 12:36:48 AM »

Quote from: formulanerd on August 09, 2009, 12:24:03 AM

fuck building one... not when 1.8t shit is so cheap.

Yes and no. I've gotten in good standings with an exhaust shop out here and if I provide the muffler (already priced it for $90), the owner will fab and install the full 3" setup for $65. $155ish for a full 3" exhaust, installed, is REALLY hard to pass up.

scurvy_bandit · « **Reply #16 on:** August 09, 2009, 10:14:40 PM »

is it mandrel bent or crap bends?

mjohnson · « **Reply #17 on:** August 09, 2009, 10:54:18 PM »

formulanerd · « **Reply #18 on:** August 10, 2009, 10:34:05 AM »

you'll find very few small shops that can mandrel bend 3"+, the equipment is very very expensive.

and when i said buy vs build, i was actually just talking about the downpipe

mjohnson · « **Reply #19 on:** August 10, 2009, 11:01:47 AM »

ahh ok. Yeah I've seen mandrel bent 3" dp on ebay for about 100 bones including shipping. Perhaps I might go that route. Having said that. Is is going to make THAT big of a difference having the 'cat back' portion mandrel bent as apposed to not?

MileHighAssassin · « **Reply #20 on:** August 22, 2009, 03:45:31 PM »

I would bet these bends are not mandrel bent or if they are they are not stainless. Probably aluminized which is junk. I am building a cat-back and possible down-pipe if I can find the right flanges for my TDI. The bends alone with a discount in 304 stainless cost more than what you are talking.

formulanerd · « **Reply #21 on:** August 23, 2009, 12:02:47 AM »

Quote from: MileHighAssassin on August 22, 2009, 03:45:31 PM

I would bet these bends are not mandrel bent or if they are they are not stainless. Probably aluminized which is junk. I am building a cat-back and possible down-pipe if I can find the right flanges for my TDI. The bends alone with a discount in 304 stainless cost more than what you are talking.

mass production in china can really bring costs down.

mjohnson · « **Reply #22 on:** August 28, 2009, 10:58:17 PM »

Today I decided to order up the dp and muffler to finish my exhaust.

I went with a $100 flea bay special, 3" mandrel bent dp. It comes with step downs, but those won't be necessary and will be chopped off. It does have a flex pipe, but I will leave it on for now until I get a chance to stiffin up the motor mounts. I'll have the shop bend up some 3" pipe that will run catless to the magnaflow muffler and have 2x 2.5" tips coming off. I haven't decided if I want the tips to come back through the valance like stock, or if I wanna have them turn down and find a valance w/o an exhaust cut out.

This video is similar to how it'll sound.

<a href="http://www.youtube.com/v/atwJNINlTuo&hl=en&fs=1&" target="_blank" class="new_win">http://www.youtube.com/v/atwJNINlTuo&hl=en&fs=1&</a>

I'll take some pics and video clips when the parts come in and are installed

scurvy_bandit · « **Reply #23 on:** August 29, 2009, 09:22:29 AM »

Quote from: mjohnson on August 28, 2009, 10:58:17 PM

Today I decided to order up the dp and muffler to finish my exhaust.
I haven't decided if I want the tips to come back through the valance like stock, or if I wanna have them turn down and find a valance w/o an exhaust cut out.

I'll take some pics and video clips when the parts come in and are installed

turndowns and no tip FTW.

MileHighAssassin · « **Reply #24 on:** September 12, 2009, 02:05:17 PM »

Just get rid of the muffler altogether. That's my plan.

scurvy_bandit · « **Reply #25 on:** September 12, 2009, 07:52:11 PM »

jeff?
raceland -148$

supersprint- 707$

yokust · « **Reply #26 on:** September 13, 2009, 03:24:08 PM »

Techtonics and do it right

Some of those short headers like that are no better than manifold and dp

mjohnson · « **Reply #27 on:** September 14, 2009, 05:08:26 PM »

Quote from: MileHighAssassin on September 12, 2009, 02:05:17 PM

Just get rid of the muffler altogether. That's my plan.

I've been rockin a straight pipe for a while. It started as 2.5" TB w/ high flow cat and an electronic exhaust cut out after the front wheels. I lose too much power going with the cut out open (dyno proven) and then I threw it back on the dyno when I lopped the muffler off (still 2.5" w/ hiflo cat) I gained some power over the cutout being open but still not like when I had the muffler on. I decided to go w/ 3" TB w/o a cat in to a magnaflow muffler and 2x 2.5 out. I know it's going to sound sick, but as far as power goes, we'll see.

MileHighAssassin · « **Reply #28 on:** September 14, 2009, 05:12:22 PM »

Quote from: mjohnson on September 14, 2009, 05:08:26 PM

Quote from: MileHighAssassin on September 12, 2009, 02:05:17 PM
Just get rid of the muffler altogether. That's my plan.

I've been rockin a straight pipe for a while. It started as 2.5" TB w/ high flow cat and an electronic exhaust cut out after the front wheels. I lose too much power going with the cut out open (dyno proven) and then I threw it back on the dyno when I lopped the muffler off (still 2.5" w/ hiflo cat) I gained some power over the cutout being open but still not like when I had the muffler on. I decided to go w/ 3" TB w/o a cat in to a magnaflow muffler and 2x 2.5 out. I know it's going to sound sick, but as far as power goes, we'll see.

That doesn't make any sense. On a forced induction car you shouldn't lose power from losing the muffler or having a cutout. How far apart were the dynos done? Could it have been something else, maybe conditions, temp, etc?

mjohnson · « **Reply #29 on:** September 14, 2009, 05:37:11 PM »

I've gone to the dyno 3 times and this is how I did my pulls.

Jan 08 col spgs:
session 1 pull 1 - cutout closed w/ muffler and stock (modified airbox) [base]
   pull 2 - cutout closed w/ muffler and stock (modified airbox) [another base]
   pull 3 - cutout open w/ muffler and stock (modified airbox) - whp & tq less than pulls 1&2

Feb 08 same dyno:
session 2 pull 1 - cutout closed w/ muffler and cone filter (clamped directly to the maf housing)
   pull 2 - cutout open w/ muffler and cone filter (clamped directly to the maf housing) - whp & tq less
   pull 3 - cutout open w/ muffler and stock (modified airbox) - whp & tq higher
   pull 4 - cutout closed w/ muffler and stock (modified airbox) - whp & tq higher yet

Aug 09 dothan AL:
session 3 pull 1 - cutout closed w/o muffler and cone filter (clamped directly to the maf housing)
   pull 2 - cutout open w/o muffler and cone filter (clamped directly to the maf housing) - whp & tq less
   pull 3 - cutout open w/o muffler and stock (modified airbox) - whp & tq higher
   pull 4 - cutout closed w/o muffler and stock (modified airbox) - whip & tq higher yet

I'd post numbers but 1: I don't feel like looking for them, 2: the exact numbers shouldn't be relevant since the pattern of power loss/gain should speak for itself.

As you can see I tested the different variations each time I was at the dyno so I highly doubt conditions played a factor. Especially since the power loss/gain patterns were very similar and as predicted in each session.

MileHighAssassin · « **Reply #30 on:** September 15, 2009, 02:59:59 PM »

That is seriously strange. There is no way in hell you should have better numbers with a muffler and more restrictive exhaust on a turbo motor.

The numbers might shift up a bit but you should still have better numbers

scurvy_bandit · « **Reply #31 on:** September 15, 2009, 04:01:59 PM »

Something else to consider is the exhaust turbulence.

mjohnson · « **Reply #32 on:** September 15, 2009, 06:27:42 PM »

Quote from: scurvy_bandit on September 15, 2009, 04:01:59 PM

Something else to consider is the exhaust turbulence.

as far as?

mjohnson · « **Reply #33 on:** September 15, 2009, 06:41:28 PM »

Got the car back from the exhaust shop today. Alls good, except that he said he couldn't bend the 3" around the axle, so he did as much as possible 3" and over the axle 2.5" I was kind of disappointed because I know people have fit 3" through the whole thing (at least that's what people have said). Could it be because of the style of bends? He doesn't have a mandrel bender.

I digress.

I started the car...then thought to myself "didn't I just start the car?" I was so used to straight pipe or cutouts that I didn't recognize the quietness of a brand new muffler. Sounds too prissy for me (at idle). Can't wait for it to be broken in. It does sound nice under load though. The 3 gave it a much nicer deeper growl instead of the slightly raspy growl of 2.5.

I must say though. A piece of me was tore out when the cutout was removed $:-\$ I've grown attatched to bleeding ears at the touch of a button...

yokust · « **Reply #34 on:** September 15, 2009, 07:30:57 PM »

Quote from: MileHighAssassin on September 15, 2009, 02:59:59 PM

That is seriously strange. There is no way in hell you should have better numbers with a muffler and more restrictive exhaust on a turbo motor.

The numbers might shift up a bit but you should still have better numbers

This has been proven time and time again. It is all based on your ecu tuning.

If your ecu is meant to have a cat in it, removing the cat can cause lower power levels EVEN on a turbo car. By opening his exhaust boost levels came in harder, faster, and HOTTER. By having the hotter air charge the stock ecu will cut boost and timing levels to get back to what it thinks is normal. Even more so on a stock intercooler that is barely capable or functioning on a fully stock car.

The ME7 Bosch ecu also needs to see the same exhaust flow and temps on both O2 sensors. Surprising or not the ME7 ecu the rear O2 sensor has overall main control of fuel mixture and timing maps. The front O2 only controls short term fuel mixtures and settings.

mjohnson · « **Reply #35 on:** September 15, 2009, 08:03:36 PM »

so could a person theoretically just move both sensors in front of the cut out and trick the ecu? or how about resistors? Obviously going standalone is the way to go, and I likely wouldn't do the resistor part, but I'm just tossing ideas out there, trying to learn a thing or two.

scurvy_bandit · « **Reply #36 on:** September 15, 2009, 10:28:27 PM »

I think he meant by hotter faster air, it was in reguards to the pressurized air entering that tiny throttle body.

About the turbulent air, when hot air expands say.... as much as just a cutout allows it, the result is the loss in streamline of airflow. The air is flowing down a nice smooth path from the turbo then into the open. Think of it like throwing a rock in a pool, the pulses of exhaust gas also help to pull themselves out of the way of the fresh hot pulses. If you just have everything going to open atmosphere eventually the ripples probably disrupt the smooth air flow from the turbo. (why nobody runs an open turbo without some type of DP) Think even race drag cars have some nice pipe exiting somewhere..

yokust · « **Reply #37 on:** September 16, 2009, 08:20:03 AM »

Quote from: mjohnson on September 15, 2009, 08:03:36 PM

so could a person theoretically just move both sensors in front of the cut out and trick the ecu? or how about resistors? Obviously going standalone is the way to go, and I likely wouldn't do the resistor part, but I'm just tossing ideas out there, trying to learn a thing or two.

That only fixes half of the problem, but would help somewhat. You still have an issue with the tune in the ecu not meant for what you are doing. And other items you would need to upgrade in order to make it function correctly

Quote from: scurvy_bandit on September 15, 2009, 10:28:27 PM

I think he meant by hotter faster air, it was in reguards to the pressurized air entering that tiny throttle body.

I meant both as well.

To do it right with an open exhaust/cutout you would need supporting mods. ECU tuned for open exhaust, and intercooler capable of handling higher intake temps made by turbo.

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