Question about Custom Exhaust

I recently had a custom exhaust installed, which was supposed to be 3" to 2.5." I think I assumed would mean 3" piping until AFTER the split before the mufflers, but I noticed that it goes from 3" down to 2.5" BEFORE the split.

 

Is that right? It seems like you wouldn't want that restriction until after the split. Was this lazy or cost-costing on materials? I did ask for a quieter tone, could that have anything to do with it? I thought that would be more to do with the muffler selection (Vibrant).

 

Just wanted get opinions. Another issue I see is that the muffler tips are really poorly aligned with the bumper cutouts.

Sounds like a trip back to the installer is in order.

 

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Do you agree on the piping being wrong?

depends on what the estimate says? unless you specifically said where the 3" ended and the tips are to be centered/aligned, you'll want to consider money spent already vs cost to fix.

 

3" into the oem split isn't going to help you much. did you upsize the dp too?

Not sure what you mean by 3" into the oem split.

 

It's a 3" Invidia catted downpipe, then custom piping all the way back to new Vibrant mufflers.

 

I guess I didn't realize I needed to "specify" this. I was sold on a "top of the line custom exhaust" and "we'll take care of everything, you'll be very happy with it." As far as the tip alignment, they're not even mirrored from each other, meaning that if you stand behind the car, one is off center by a certain amount, and the other is off center by a different amount. On the passenger side it's nearly touching. There is maybe a quarter inch of clearance.

 

In any case, the tip alignment was an aside. My real question is what is the best practice for transitioning from 3" to 2.5". Is it normal to do this before the split, or is that nonsensical?

 

It certainly seems like it would be less restrictive to step down after the split. Would power be effected?

if they told you "you'll be happy ", id be banging on the door because you're not happy.

 

The oem system has splits just after the rear axle into two pipes. Its not 3", or 2.5"; but it is sized for the oem system. If they didn't upsize that split from oem, then you kind of wasted your money.

 

That said, a 3" exhaust doesn't really become a requirement until you're over 400hp. Upgraded mufflers are done mostly for noise changes. If you didn't dyno before and after, you won't actually know if you have improved your power output.

I run a Cobb DP and an SPT CATBACK. there is a 2.5” neck-down at the end of dp. My car makes about 375hp/415tq at the wheels. I doubt that the pipes will cost you much power.

my invidia catless dp necks down from 3" to 2.5" at the end of the dp, too. The rest of the exhaust is oem. My first dyno run was 369tq on a mild build.

 

be careful of assuming fixes for other car brands work the same on Subarus. For the most part, until you get into high power builds, the oem setup is enough. ymmv

Yup your not leaving any power on the table with this set up unless you’re trying to put down big power. More than anything, a “high end custom” should at the very least have properly aligned tips. That’s part of the “custom” I’d take it back for sure, that’s weak sauce from the shop

1 measured a 1 whp difference after removing the 2.5" restriction at the DP flange (Cobb CBE in a 08 LGT SpecB making 400whp) and "upgrading" to 3" pipe and flange.

 

 

 

Where the neck down is basically makes no difference. You can only flow as much as the smallest restriction, no matter where it is. It was most likely far easier to fabricate/weld the split at the y-pipe the way they did it. Maybe they had prefabricated "y's" in 2.5".

 

 

 

As for aligning tips in the cutouts, dont even get me started. Without a fixture it is impossible. With a fixture it is almost impossible. Bumpers do flex and move you know. So does the exhaust that is swinging on hangers. Plus, moving a pipe or flange 1/8" of an inch at the DP can result in 1" of movement at the bumper.

 

 

 

Regardless, if you are not satisfied I would respectfully bring it up with the shop.

As others have said, not much, if any difference past the Dp.

 

I have had a number of different 3" exhaust on my wagon. It currently has the OEM mid pipe from my 2009 Spec B to MagnaFlow knock off mufflers to the 4" double wall DynaMax tips I had put on those mufflers back in 2013.

 

The car has had a 3" to 2.5" Pro Lab Tuning exhaust for a few years, the Q300 exhaust which is currently on the Spec B. Was dynoed with a catless Dp back in 2011. I switched to a Catted Dp a couple years back. I had no changes to the tune after talking with my Tuner about it.

 

No real difference in the tune. I will say, I think I have a bit more throttle response with the OEM mid pipe. My heads also have some mild port work down where it matters.

I get what everyone's saying, that 2.5 inches after the down-pipe is plenty, but I can't agree with the following:

 

Where the neck down is basically makes no difference. You can only flow as much as the smallest restriction, no matter where it is.

 

This doesn't make sense. If the neck down is before the split, you're going down to a smaller pipe when there is only one pipe to flow through. This is a much smaller restriction than if you stay at 3" until after the split when there are two pipes to flow through.

 

Once you're flowing through two pipes, going down to 2.5" is less restrictive because you only need to flow half the exhaust through each pipe at that point. Maybe the difference is not significant at stage 2, but there certainly is a difference. I won't be staying at stage 2 forever, and if you've gone through the trouble of running 3" all the way from the down-pipe to the rear axle, why negate the benefit inches before the split?

 

Maybe they had prefabricated "y's" in 2.5".

 

I paid a premium for this, so I wouldn't be happy if they compromised anything to use up what they had lying around.

 

I will bring this up respectfully, but this isn't the only issue I had with this shop. I had other work done and found loose nuts and bolts, half seated hoses, hoses with no clamps, low coolant, etc. I even found damaged breather hoses reused and two washers on the oil plug, both causing oil leaks.

Edited November 11, 2020 by puddles

Beside the alignment woes, how does it sound?

Haven't you ever heard of "restrictor plate" races in NASCAR. They forced all the teams to put the same size orifice plate under the carburetor. It slowed the cars down on the faster/high speed tracks.

Haven't you ever heard of "restrictor plate" races in NASCAR. They forced all the teams to put the same size orifice plate under the carburetor. It slowed the cars down on the faster/high speed tracks.

 

In our cars, the exhaust from the midpipe back, doesn't effect HP.

I get what everyone's saying, that 2.5 inches after the down-pipe is plenty, but I can't agree with the following:

 

 

 

This doesn't make sense. If the neck down is before the split, you're going down to a smaller pipe when there is only one pipe to flow through. This is a much smaller restriction than if you stay at 3" until after the split when there are two pipes to flow through.

 

Once you're flowing through two pipes, going down to 2.5" is less restrictive because you only need to flow half the exhaust through each pipe at that point. Maybe the difference is not significant at stage 2, but there certainly is a difference. I won't be staying at stage 2 forever, and if you've gone through the trouble of running 3" all the way from the down-pipe to the rear axle, why negate the benefit inches before the split?

 

 

 

I paid a premium for this, so I wouldn't be happy if they compromised anything to use up what they had lying around.

 

I will bring this up respectfully, but this isn't the only issue I had with this shop. I had other work done and found loose nuts and bolts, half seated hoses, hoses with no clamps, low coolant, etc. I even found damaged breather hoses reused and two washers on the oil plug, both causing oil leaks.

 

 

Wait, all these issues in the past and yet you're still taking your car to them? Dang...

There is a lot more to air flow. I "dumbed it down" but the info is valid.

 

If the shop has a history of poor workmanship, why keep going back??? Smh.

Beside the alignment woes, how does it sound?

 

It does sound good. Invidia down-pipe and Vibrant mufflers, so I'm pretty happy with it as far as the sound goes.

 

I haven't taken my car to them multiple times, only once. It was supposed to be a reputable shop. There was some mechanical work done at the same time as the exhaust and I found all sorts of problems under the hood, which makes me question the exhaust work as well.

 

I used to work as a mechanic years ago, but I told myself "my life is too busy to do all this right now. I don't have access to a lift and other tools. I can afford to pay for it. Etc., etc. etc." Now I'm feeling like a fool, and kicking myself for trying to throw money at it instead of just rolling up my sleeves and doing more of the work myself.

 

This kind of thing makes me feel like the only way to get something done right is to do it yourself. I feel like I re-learned this lesson the hard way. I ended up having to put in the time to fix a bunch of issues anyhow.

 

So anyhow, I'm trying to figure out what to do. I'm trying to decide if I should just cut my losses and move on, ask for a refund on some of the labor, or give them a second chance and ask them to fix anything (I've already fixed most of it myself, but I'm not a welder).

If your happy with the sound, happy with the way the mufflers and tips are aligned.

 

Move on.

 

Some of the breather hose don't have clamps from the factory. You can zip tie them with black ties.

The further away from the exhaust ports on the heads the gases cool and contract , Hence the narrower pipe going into the muffler doesn't slow things down. The 2.5 pipe at X temp gases moves as much volume as the 3 " DP at higher temp gases.

bdcvg, that also makes sense. From what everyone said, it makes sense that the neck down before the split is not a problem. I talked to the owner of the shop and he also said that it would help with noise, as I asked that that it not be excessively loud.

 

Given all this, I agreed that the location of the neck down was not an issue and asked only to have the muffler tips better aligned with the bumper cutouts. He offered to do this free of charge along with some other things, given the issues I found under the hood, and will be overseeing the work personally.