Downpipes Upgrade, Worth it?

[TMac]

The truth is no one knows exactly how much the downpipes are worth. The best info is from @UNBROKEN at 2/10s, but as I understand it, he did those and exhaust without testing in between. I've posted before that the stock exhaust does not pose any significant restriction to 500 or more HP. This is based on the area size even if you consider the 2 1/4 restriction in the midpipes. They still have more area than a muffled (Magnaflow) 3" system which you can find numerous online dyno results at 750+ HP. A 3" system has about 7.06 sq in of area, a dual 2.25 has 7.95 sq in of area. So, if it made 2/10s on his system, they're probably worth that much. As I posted before, I wouldn't do downpipes unless I was also doing turbos.

 

[UNBROKEN]

The truth is no one knows exactly how much the downpipes are worth. The best info is from @UNBROKEN at 2/10s, but as I understand it, he did those and exhaust without testing in between. I've posted before that the stock exhaust does not pose any significant restriction to 500 or more HP. This is based on the area size even if you consider the 2 1/4 restriction in the midpipes. They still have more area than a muffled (Magnaflow) 3" system which you can find numerous online dyno results at 750+ HP. A 3" system has about 7.06 sq in of area, a dual 2.25 has 7.95 sq in of area. So, if it made 2/10s on his system, they're probably worth that much. As I posted before, I wouldn't do downpipes unless I was also doing turbos.

But I have dual 3”. lol
Still…I think the stock DP’s are worth swapping after the usual IC/tune stuff is done. It’s the next logical step and there’s improvements in ET to back it up.
The stock exhaust with high flow DP’s I firmly believe will still show a good improvement. All the available DP’s are 3” to the mid-pipes…I’m no fluid dynamics guy but I’d bet the exhaust is cooled enough at that point the 2.25” stuff won’t make much different. The Thermal 2.5” mid-pipe would probably work well if someone wanted to step down pipe diameter gradually.

 

[DetroitST]

So it's safe to say if I went tune/intercooler and then added let's say meth or upgraded fuel system, my gains would be limited by the bottleneck of the downpipes? The stock cats are the culprit? Again I only ask and am being as thorough as I am is because of my last car, the cost and difficulty of the downpipes were pretty nuts and plenty of people who never did the downpipes had similar 1/4 miles times as I did. So at the end of the day I can confidently say adding 3" downpipes on the 2.7L wasn't worth it. And by not worth it, I do mean no gains. I dyno'ed before and after I installed mine with no difference. So for the $1400ish and like 15 hours it took me to install them I don't want to repeat that kind of rabbit hole. My understanding of a bottleneck is that no more additional power (air) can be pushed out of the engine due to the restrictiveness of our stock downpipes after a tune and intercooler is added. If you got .1-.2 from the mod, that implies a 10-20hp gain and potentially opens the door for more gains the more modifications you add down the road. Please correct me if I'm off base.

Also off topic but @UNBROKEN I did read your 34 page build log last night and wow you are quite the trend setter on this forum so I appreciate your input. I hope I am not coming off as too challenging, just trying to do my diligence as well as provide information to others curious.

 

[UNBROKEN]

I definitely wouldn’t do them first. They’re expensive and very labor intensive. I wouldn’t even attempt it without a lift because you damn near have to drop the subframe and lower the trans to get to the passenger side bolts. Either that or fight for hours to rip off the welded on heat shield. I know I don’t event wanna install another set.

 

[DetroitST]

Haha, I hear that, I did my 2.7L on the floor in my garage the first time around, then when I upgraded my turbos I had a shop do the work, no way was I stressing like that again. Ok so expensive, difficult, possibly not the bottleneck we need to address as a 3rd modification? Is that the general consensus?

 

[twin001]

I definitely wouldn’t do them first. They’re expensive and very labor intensive. I wouldn’t even attempt it without a lift because you damn near have to drop the subframe and lower the trans to get to the passenger side bolts. Either that or fight for hours to rip off the welded on heat shield. I know I don’t event wanna install another set.

Uggghhhhh……not what I want to hear! This is my next mod and I’m a DIY kinda guy. Guess I should just buy a lift.

 

[MattJ716]

Once you do downpipes you then look further at the inlet... you usually want the pressure ratio to match if I'm not mistaken

 

[TMac]

I’m no fluid dynamics guy but I’d bet the exhaust is cooled enough at that point the 2.25” stuff won’t make much different. .

Yep.

 

[DetroitST]

Sorry to bring up an old thread but with everything said, now that I'm over 500whp and dyno tuned, let's say my downpipes and exhaust are restricting future gains, if I were to upgrade one or the other, would I need to get retuned or would the car just make more power because it can breathe easier? More important question, can I harm anything by NOT updating my tune?

I've read that 2.25 dual exhaust is only good for ~460hp. I clearly have more than that, thoughts?

 

[TMac]

Sorry to bring up an old thread but with everything said, now that I'm over 500whp and dyno tuned, let's say my downpipes and exhaust are restricting future gains, if I were to upgrade one or the other, would I need to get retuned or would the car just make more power because it can breathe easier? More important question, can I harm anything by NOT updating my tune?

I've read that 2.25 dual exhaust is only good for ~460hp. I clearly have more than that, thoughts?

I have covered this in various exhaust threads on this site. A dual 2.25 exhaust has more flow area than a single 3" exhaust. You can find scores of turbocharged vehicle dynos on the internet with a single 3" exhaust making 700+hp. Flow requirements are different between N/A and supercharged vehicles as opposed to turbocharged due to higher exhaust velocity.

 

[DetroitST]

I have covered this in various exhaust threads on this site. A dual 2.25 exhaust has more flow area than a single 3" exhaust. You can find scores of turbocharged vehicle dynos on the internet with a single 3" exhaust making 700+hp. Flow requirements are different between N/A and supercharged vehicles as opposed to turbocharged due to higher exhaust velocity.

Take away is... stock exhaust can flow 700hp+? Increasing diameter on downpipes or exhaust will not help gain power?

 

[TMac]

Dual 2.25 pipe can flow that. Certainly the stock muffler components would reduce that somewhat. But if you're at 520, that's probably 580 or so crank, so you're pushing 600 with stock components.
Check out my exhaust thread https://www.explorerst.org/threads/...-a-performance-exhaust-system.2775/post-33847

 

[DetroitST]

That was a good read. The last comment kind of contradicted your basis though and wasn't refuted.

Still, probably likely that changing anything post turbo won't net gains.

Let's say I do turbos next, which is likely, I still don't think I will be making more than 650ish whp, so all things considered, if 2.25" duals can handle 700hp, I don't think I should make the investment on downpipes or exhaust.

Sound accurate?

 

[TMac]

It wasn't refuted because it was silly, and I didn't think anyone would take it seriously, nor am I going to argue across the internet with someone who has no idea. Do you know of anyone in the world, even in the racing world running no exhaust on their turbine housing? I guess they're all less informed than that poster! There are also things going on from a dynamic point of view- having a properly sized exhaust increases the inertial energy which enhances turbine response during up-shifts. Finally, the flow is enhanced by moving it from the spiraling, chaotic exit of the turbine with a properly sized transition to move to laminar flow.

 

[Cruising68]

While I'm no rocket scientist I do know that a properly configured exhaust can have a significant impact on performance.

 

[Rugrat2553]

That was a good read. The last comment kind of contradicted your basis though and wasn't refuted.

Still, probably likely that changing anything post turbo won't net gains.

Let's say I do turbos next, which is likely, I still don't think I will be making more than 650ish whp, so all things considered, if 2.25" duals can handle 700hp, I don't think I should make the investment on downpipes or exhaust.

Sound accurate?

If you're doing turbos you'll already have the hardest part of downpipes done...why not go ahead and do them at that point so you only have to take them off once

 

[Cruising68]

If you're doing turbos you'll already have the hardest part of downpipes done...why not go ahead and do them at that point so you only have to take them off once

Agree with that. At that point you might as well do them.

 

[Chrisicle]

My concern wouldn't be about power gains from high-flow downpipes as much as my concern would lie with the turbos longevity. Personally I believe (and have been told) that any thing you can do to reduce back pressure on the turbos will help with its life span. Since I bought the car to own for 10 years the first thing I did was reduce back pressure before introducing more pressure through the inlet side. I personally have no plans to upgrade the turbos, but ideally I don't wanna replace them either.

 

[DetroitST]

My concern wouldn't be about power gains from high-flow downpipes as much as my concern would lie with the turbos longevity. Personally I believe (and have been told) that any thing you can do to reduce back pressure on the turbos will help with its life span. Since I bought the car to own for 10 years the first thing I did was reduce back pressure before introducing more pressure through the inlet side. I personally have no plans to upgrade the turbos, but ideally I don't wanna replace them either.

Holding breath... it's a lease.

 

[TMac]

My concern wouldn't be about power gains from high-flow downpipes as much as my concern would lie with the turbos longevity. Personally I believe (and have been told) that any thing you can do to reduce back pressure on the turbos will help with its life span. Since I bought the car to own for 10 years the first thing I did was reduce back pressure before introducing more pressure through the inlet side. I personally have no plans to upgrade the turbos, but ideally I don't wanna replace them either.

The factory cats aren't the same as those on cars from 20-30 years ago. They are not that restrictive. Second, the pressure between the exhaust valves and the turbine is WAY higher than after the turbines. Third, are you road racing? How much actual time are you spending at max boost at 5000+ rpm? Finally, those turbos are less than $600 brand new, so they're not that expensive. Spending $1000 plus installation for "high flow" cats to save turbos is pointless and not money well spent.