Does externally gated with dump increase effective exhaust size under boost?

[4gfun]

If I am running an e316g turbo that is externally gated with an exhaust dump, does that mean that while I am boosting my exhaust size is effectively bigger than 2.5 inches?

I ask because I have a 2.5 inch exhaust from essentially the turbo downwards. I also have a pre cat 2.5 inch manual cutout that I am sick of hearing.

I never stopped to think whether or not an external wastegate dump makes my exhaust effectively larger under boost.

Probably a dumb question, but I don't understand how it works so I figured I would ask.

Thanks

 

[ed1380]

Yes. With the external dump you're not forcing as much exhaust through the exhaust piping

 

[tin_tin13]

Also the gains are not that noticed(on a small frame turbo) On a Miata forum I have seen back to back test on a dump vs recir and there was a 30whp difference between the two, cant recall how much the car was pushing but it was around the 500whp mark.

 

[4gfun]

...but wait...

I just thought about it and the answer should be NO right...since the wastegate won't be open until after target boost is exceeded.

I don't want to be right....I really don't want to be right but I think I am

 

[ed1380]

target boost is usually achieved before 4000rpm. Higher rpm=more airflow=when you want a bigger exhaust. So the wastegate opens at the same time as you need the extra airflow capability

 

[4gfun]

This is starting to make sense...and I am glad that you are right because this might preserve my wallet, my hearing, and my ability to make a freaking phone call.

So when the dump is open, I am running the equivalent of a 4 inch exhaust? I really don't care if it amounts to being that big. So long as it is 3 inches or greater I would be happy to close my cutout and live in peace.

Thoughts?

Still digesting this, but thank you!!

target boost is usually achieved before 4000rpm. Higher rpm=more airflow=when you want a bigger exhaust. So the wastegate opens at the same time as you need the extra airflow capability

 

[dsmcurse]

target boost is usually achieved before 4000rpm.

Oh how I miss those days...

If you have a 2.5" downpipe than its still gonna be a 2.5" downpipe if wastegate is doing its thing or not. From my own expierence I'm gonna have to say exhaust is the same size through out. Your external dump is still a "internal-wastegate" but your O2 housing is aftermarket external dump on the WG huh? Ya, your 2.5" downpipe and exhaust is still a 2.5" exhaust, just the baby lil wastegate hole above your hot-wheel opens up "maybe like 30mm hole?" in the turbine housing and it dumps out of your after-market O2housing

There are other ways to make your 2.5" downpipe magicaly become a 3" equivelent when you need it.

E-bay 60mm external wastegate mounted in your downpipe right after your turbo used as a boost activated exhaust cut-out. Alll sealed up and not loud or noisy, but opens up and let's it breathe when the time is needed

 

[4gfun]

Hmm....yep I am familiar with that arrangement but I am trying to avoid it if possible.

Ok, so let me ask you something. I realize that the restriction is the 2.5 inch downpipe (actually I had forgotten about it), but is the external dump (when open) equal to the cutout being open pre cat?

If so, I am content to let it rest.

Thanks

target boost is usually achieved before 4000rpm.

Oh how I miss those days...

If you have a 2.5" downpipe than its still gonna be a 2.5" downpipe if wastegate is doing its thing or not. From my own expierence I'm gonna have to say exhaust is the same size through out. Your external dump is still a "internal-wastegate" but your O2 housing is aftermarket external dump on the WG huh? Ya, your 2.5" downpipe and exhaust is still a 2.5" exhaust, just the baby lil wastegate hole above your hot-wheel opens up "maybe like 30mm hole?" in the turbine housing and it dumps out of your after-market O2housing

There are other ways to make your 2.5" downpipe magicaly become a 3" equivelent when you need it.

E-bay 60mm external wastegate mounted in your downpipe right after your turbo used as a boost activated exhaust cut-out. Alll sealed up and not loud or noisy, but opens up and let's it breathe when the time is needed

 

[dsmcurse]

Just a quick question for you real fast. When you say external wastgate, explain this further? You mean external dump internal wastegate? You made mention of a 16g turbo, theyre obviously mitsu flange in and mitsu flange out, and they're internal wastegate. The flapper that's built into the wastegate on that turbo is about the size of a quarter. That's what's breathing pressure off the exhaust side of your turbo controlling boost.

Now if your set up is like what I'm picturing, than you have a 16g turbo with a aftermarket external dump O2 housing. Then you have a 2.5" downpipe breathing the back-pressure (which is fine given the turbo size) all in all, when your wastegate dump opens and gets loud, look back to the source, it came out of a quarter sized hole in your turbine housing. So to compare it to a 4" exhaust isn't quite doable

 

[ZenkaiRacerDsM]

Yeah a external dump is going to be a little more efficient. But either way, a bigger exhaust is going to be better.

Also a bigger exhaust most definitely will affect spool times.

 

[forcefed86]

You can't say "2.5 pipe" has a set resistance value.

Depending on the length of the pipe and the amount of bends, restriction will go up. So the closer you vent the pressure to the turbo, the lower the over all resistance will be. In the case of a 16g internal gate you'll be dumping exhaust before it even hits the piping, so a large opening isn't needed to vent quite a bit of exhaust pressure.

Easiest way to check if your exhaust system is up to par is to put a pressure gauge on it and watch it at boost.

I'm tired of guys making 300hp max thinking they need 5" exhaust sytems. If theres no back pressure in the exhaust system, going to larger piping does nothing!

Heres my setup for cheap performance exhaust. Run a stock exhaust system so it's quiet and nice to drive and run a cutout or WG straight off the downpipe. Simple/cheap and supports 500hp with or without a "dumped" gate.

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[4gfun]

Sorry, went to sleep right after my last post. The setup is the latter of the 2.

Gotcha on comparing it to a 4 inch exhaust. I had this explained to me on another forum at about the same time. However, the poster did feel that I would meet or exceed a 3 inch exhaust at that time. The poster is intelligent like yourself so I am inclined to believe them.

What do you think?

Thanks

Just a quick question for you real fast. When you say external wastgate, explain this further? You mean external dump internal wastegate? You made mention of a 16g turbo, theyre obviously mitsu flange in and mitsu flange out, and they're internal wastegate. The flapper that's built into the wastegate on that turbo is about the size of a quarter. That's what's breathing pressure off the exhaust side of your turbo controlling boost.

Now if your set up is like what I'm picturing, than you have a 16g turbo with a aftermarket external dump O2 housing. Then you have a 2.5" downpipe breathing the back-pressure (which is fine given the turbo size) all in all, when your wastegate dump opens and gets loud, look back to the source, it came out of a quarter sized hole in your turbine housing. So to compare it to a 4" exhaust isn't quite doable

I am only targeting a 3 inch exhaust size to meet the status qo for an E316g on pump at 25 psi. Really trying to figure out if the EWG dump combined with the 2.5 inch exhaust meets this so I can close the open cutout call my losses and not spend any more money in that area.

Yeah a external dump is going to be a little more efficient. But either way, a bigger exhaust is going to be better.

Also a bigger exhaust most definitely will affect spool times.

 

[gofer]

DSMCurse is correct. An open atmosphere wastegate dump, internal or external, isn't going to effectively increase the size of your exhaust when it's open. The exhaust gases that escape out the wastegate port never even see the turbine wheel, it's the exhaust gases used to spool the turbo that make their way into your o2 housing outlet/dp.

Dumping exhaust gases to atmosphere help with the turbo's efficiency because there's less back pressure in the exhaust after the turbo outlet caused by the exhaust gases routing back in from the wastegate port.

This is how Paul runs his cutout, immediately after the o2 housing it branches off the DP.

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[4gfun]

Thanks for your help. To me it seems like DSMCurse says it is going to increase exhaust diameter effectively but you say it won't increase exhaust diameter at all correct?

If this is the conclusion, I need to work on getting the end of my open cutout to flange to work with perhaps an electric cutout. I am not even sure how to begin that task. Maybe I could trace it and send it to the cutout manufacturer?

I always overpay for welding for some reason (just my opinion relative to what others tell me they pay), so I like to avoid it like the plague.

Thanks

DSMCurse is correct. An open atmosphere wastegate dump, internal or external, isn't going to effectively increase the size of your exhaust when it's open. The exhaust gases that escape out the wastegate port never even see the turbine wheel, it's the exhaust gases used to spool the turbo that make their way into your o2 housing outlet/dp.

Dumping exhaust gases to atmosphere help with the turbo's efficiency because there's less back pressure in the exhaust after the turbo outlet caused by the exhaust gases routing back in from the wastegate port.

This is how Paul runs his cutout, immediately after the o2 housing it branches off the DP.

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[dsmcurse]

I never said your wastegate was gonna "increase" the size of your exhaust. I said your wastegate dumping exhaust comes from a hole in your turbine housing about the size of a quarter. this "bleed off" of exhaust is only for controlling boost pressure. (all exhaust in turbine housing will be full boost as much as she can go, wastegate opens to bleed off exhaust is a form of boost controll) What i did say, was using a E-BAY 60mm external wastegate as a cut out AFTER your turbo will act as a much friendlier cut-out.

The wastegate in the down-pipe trick is similar to a electric cut out (essentially does the same thing) but the wastegate is pure automatic, no wires to get burnt and crispy, no flapper plate to crust over and get stuck, no forgetting to "flick your switch" the wastegate just does it at X-amount of boost.

My down-pipe is 3", i wish it could be a 3.5" but fittment issue's and a tight clearence in my engine bay restrics me to a 3" down-pipe. My wastegate used as a "boost activated exhaust cut-out" comes on at 15psi boost. so under normal driving and not much boost theres no cut-out in my exhaust and she stays quiet. But when i go over 15psi boost my wastegate in my down-pipe opens and I magically get a 60mm hole in my exhaust. Think about 60mm, our throttle-body is 60mm, nearly a 2.5" hole automatically apears in my down-pipe to releive back-pressure.

What i said was, THIS TRICK can make my 3" down-pipe a 3.5" equivelent, or better.

your internal gate 16g with a external dump direct bolt-on O2 sensor housing is doing nothing to "magically" increase your exhaust size. all your doing there is bleeding off the exhaust air that creates boost air. Why do you think a BOOST CONTROLLER hooks up at the waste-gate?

If you wanna do the magic trick to increase your down-pipe size, bring your cut-out as close as possible to the turbo, make sure she breathes straight down at the ground, you dont wanna crisp-ify your oil sending wires

 

[gofer]

Some track events don't allow electric cutouts, especially of youre running in street class where you need exhaust that reaches the rear axle. The way around this is running a 60mm wastegate off of your DP, like DSMCurse explained, so you get the same result with a lot less moving parts and you can pass tech too.

You can "shut-off" the DP cutout wastegate by unplugging it's boost source pressure line to it and it won't open up. If I were building a cutout this is exactly how I'd spend my money, I wouldn't waste my time with an electric cutout.

 

[rEclipserGST]

-gofer-

Wouldn't the 60mm wastegate still open depending on the spring pressure rating? Or is it too far away from compressed air to act on its own?

I know my external WG works based on the spring, with or without a boost source.

 

[4gfun]

Very cool posts, I now completely understand this.

Thank you!

 

[boost97gst]

-gofer-

Wouldn't the 60mm wastegate still open depending on the spring pressure rating? Or is it too far away from compressed air to act on its own?

I know my external WG works based on the spring, with or without a boost source.

The 60mm wastegate "cutout" will open depending on the spring. If its an 8lb spring then as soon as the exhaust system has 8psi and up, it will open thus acting like a cutout. Its best not to think of it in the traditional sense of Wastegate. Those are used pre turbine wheel. Thats the way i see it anyway.

Btw, i think it was boostdriven who first showed this idea off and i gotta say, i think a ton of dsmers are gonna be looking into it. Its so cheap and has to be far more reliable than an electric. And way less complicated.
A big thank you to whomever came up with this idea, im sure its been used in other platforms but still, cool to see it on a dsm.

 

[gofer]

Usually I'm one of the last to hear of anything new and a buddy presented this idea a few years ago, saying that a big name DSMer, I think it was Jeff Bush but I'm probably wrong, installed a 60mm external wastegate as a exhaust cutout to pass tech where specific exhaust lengths were required and exhaust cut outs weren't allowed. You can buy boost activated cutouts with a butterfly valve controlled by a wastegate actuator but they aren't cheap, which is why 99% of the cutouts you see are electric.

VES system

Boost Activated Exhaust Cutout

SP EXHAUST CUTOUT 3"

Fabricating a DP to accept a 60mm external wastegate as a cut out definitely has the best sleeper status and it's cheaper in the long run, no one would be the wiser even if they could pop the hood and see it.

 

[GSXftw]

Also remember that the hotter the exhaust is, the less dense it is and the easier it flows... a 2.5" downpipe hurts you way less than a 2.5 muffler, so the farther upstream you relieve restriction the better. You need to stop thinking about what SIZE the external dump makes your exhaust, just know it takes some load off the rest of the exhaust flow and will help if the 2.5" was a restriction with the WG dumping inside.
Since you have a dump on there theres really need to wonder anything... do the atmospheric dump if you want, run it at the track, then do a run with the cutout open. If you didnt pick up any time then youre not restricted. If you are save for 3" or live with the cutout open

 

[dsmcurse]

A s far as I know it was boostdriven that fiirst explained this trick. I was there when he installed the first one, and I first hand witnessed a 50+ whp gain with a before and after test at COBB TUNING SURGLINE. After proving its success, we installed one on my car, I installed one on my friend Justins first gen automatic, I've seen awesome results everytime with this trick. Also consider a diesel boost gauge (does not read vacuum) installed in your exhaust mannifold befor your turbo, you can see back pressure changes when messin with the cut-out

 

[Boostdriven]

I know I might be repeating few things some of you have said but I wanted add my 5 cents to this discussion Yes not running the wasted gases from the wastegate back in to the exhaust will help, but I think it will only work well to a certain point. With a small frame turbo like 16g when you start pushing that turbo to its limits running high boost (26-27+) most likely the wastegate isn't going to be open much at higher rpms due to higher drive pressure requirements to maintain high boost. So in high boost situation external dump probably isn't going to help you as much as a bigger exhaust or a cut-out but nevertheless is a better setup for peak performance.

Assuming an external dump wastegate, in my opinion if you're making close to 400 HP then I would say you need a 3" exhaust or a cut-out on a 2.5" exhaust. If you're making over 500 HP and reving to 8000 rpms then I would suggest using a cut-out, custom 3.5" exhaust can get a little spendy if you're not building it yourself. Big wastegate like 60mm or an actual electronic/mechanical cut-out either one will work, its nothing more then a self appearing hole in the side of your exhaust an actual cut-out might cost you more then the wastegate setup.