15-20% downpipe rule?

[forcefed86]

So I hear the basic rule is 15 to 20% larger than the diameter of your turbine exhaust. My turbine outlet is 2.5".

Currently I'm running a 2.5" downpipe with a pretty nasty angle straight out of the turbo. Then 2.5" all the way back to a 3" dynaflow turbo muffler. I'm sure I'm losing all kinds of hp with this setup. But I don't have alot of room and i like quiet exhaust. Do you think a small 38mm wastegate placed just downstream of the turbo would flow just as much as a larger 3" downpipe? I'd assume this would out flow a full 3" exhaust system and act as a cheap exhaust cutout.

Here is my down pipe/exhaust and 02 setup. Could maybe even mount the WG on the 02 housing...

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Idea for WG

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[agentorange313]

http://www.dsmtuners.com/forums/app...rged-8-9-cut-out-bypass-13.html#post151912112

 

[TJCTalon]

You want to mount the wastegate on the downpipe? I dont understand what your trying to accomplish here

 

[gats0101]

I'm not sure what you are looking for either bud but if you search for 3in down pipes with electric cut outs you can see some slick setups. I was planning on running a setup like that with the stock catback so you cruise in silence but open up for track use or for fun on the street.

 

[forcefed86]

I'm know all about electric and WG actuated cutouts. I actually own cars with them installed. That's not the point. It's not my problem you can't see outside the box and grasp a simple concept.

How is a WG different than a cutout? Hmm... opens under boost....adjustable...was designed to seal exhaust tightly, and is cheap. Why the hell not use one? Does it not do the same thing? I suppose an inline straight through butterfly similar to the electric cutouts would flow a bit more. But how much flow is really necessary? A wide open 44 or even 38mm WG will still cause a huge pressure drop in the system. I was looking for a way to calculate the difference between say a full 3" exhaust system and down pipe VS a 2.5" pipe with a cutout.

To do this one would have to mount a press transducer on the downpipe and measure the current 2.5" back pressure. Then measure it with a the "dump" open, then add a 3" exhaust system and measure that back pressure and compare.

Obviously not something most of us have the time and money to do. Just wondering if anyone knew of a formula or has heard of race teams calculating this kind of stuff. My google search came up with zilch.

 

[TrystanGST]

It's not like 3" DPs are expensive. I wonder if it wouldn't be easier (and cheaper) to bolt one of those up rather than fab up the WG you're suggesting. Unless you have them lying around, of course.

 

[gats0101]

I would keep searching then bud but honestly I think you are thinking to hard on it. I would also think you would have fitment issues with having a wastegate that low. One topic that I thought was very interesting I was reading about was discussion of an internal baffle inside a downpipe that was boost activated. I think ultimately though it was decided it was a little complex for the guys setup. Your idea is an interesting thought though. Good luck

 

[WillRaceForBeer]

Basically the OP want's to run a external WG as a means of boost controlled cut out. The only issue I can see is turbulence at the point where the WG is attached. Is there some reason you don't want to just run a dumped WG from the manifold? Dumped WG's do have the advantage you are looking for without the chance of turbulence in the exhaust.

 

[forcefed86]

It's not like 3" DPs are expensive. I wonder if it wouldn't be easier (and cheaper) to bolt one of those up rather than fab up the WG you're suggesting. Unless you have them lying around, of course.

Your right, 3" aftermarket DP isn't that expensive. (more than a WG still) But I can't just replace the down pipe I'd have to do the whole system. I could have a 6" downpipe, but if I bottle neck it down to 2.5 from the "cat back" It won't flow any better than 2.5" pipe.

A cheap china WG is $60. Would work fine for this application. If it were to fail etc, its not like it would damage the motor.

I would keep searching then bud but honestly I think you are thinking to hard on it. I would also think you would have fitment issues with having a wastegate that low. One topic that I thought was very interesting I was reading about was discussion of an internal baffle inside a downpipe that was boost activated. I think ultimately though it was decided it was a little complex for the guys setup. Your idea is an interesting thought though. Good luck

The image quickly made was just to get the point across. It's not to scale. The WG is as big as the exhaust pipe in that pic... A mini 38mm WG is smaller than most of the cutouts I've seen and I wouldn't install it low hanging like that image.

Basically the OP want's to run a external WG as a means of boost controlled cut out. The only issue I can see is turbulence at the point where the WG is attached. Is there some reason you don't want to just run a dumped WG from the manifold? Dumped WG's do have the advantage you are looking for without the chance of turbulence in the exhaust.

Turbulence will effect the pressure drop a bit. But should still drop total pressure across the exhaust system a butt load... same concept for boost control. I run a manifold dumped WG already. But I'm pushing 30lbs through an HX40 pro turbo and I know a 2.5" exhaust system is holding me back.

 

[turboglenn]

If the wastegate or cutouit is meant to be further down the exhaust and not on the area where it would be used for controlling boost you can get away with a few other options that may be cheaper and or easier to work with getting a large diameter of flow than a wastegate would provide (doller per flow amount anyway)

What i'm talking about is ..wait for it ...... a throttle body You can make a flange up pretty easily from mild or SS and "Y" that off your current exhaust and use a wastegate actuator from an internal setup to open and close the butterfly (this is something i've thought about quite a bit for cheap exhaust that's quiet and can open up anhd really flow) But being in an area past the oil pan towards the rear of the car the temps are low enough that you can run aluminum exhaust and there for an aluminum throttle body woud be fine as well.. The conceot is exactly the same as that of a normal cut out, just thought i'd toss that out as food for thought

 

[forcefed86]

If the wastegate or cutouit is meant to be further down the exhaust and not on the area where it would be used for controlling boost you can get away with a few other options that may be cheaper and or easier to work with getting a large diameter of flow than a wastegate would provide (doller per flow amount anyway)

What i'm talking about is ..wait for it ...... a throttle body You can make a flange up pretty easily from mild or SS and "Y" that off your current exhaust and use a wastegate actuator from an internal setup to open and close the butterfly (this is something i've thought about quite a bit for cheap exhaust that's quiet and can open up anhd really flow) But being in an area past the oil pan towards the rear of the car the temps are low enough that you can run aluminum exhaust and there for an aluminum throttle body woud be fine as well.. The conceot is exactly the same as that of a normal cut out, just thought i'd toss that out as food for thought

I've seen it done a few times. Several DIY threads with pics on the honduh sites. No different than the electric cutouts really. (cheaper I suppose) The TB will have all the flaws of the typical butterfly valve cutouts though. They will never seal as tightly as a waste gate, and are prone to sticking. Also the farther down you put the cutout the less effect it will have on your total back pressure. I'm not saying there is anything wrong with that idea or the standard electric cutouts. Just that a WG is actually designed to operate in hot sooty exhaust conditions and can be had very cheaply these days. No doubt it won't relieve as much pressure as a huge throttle body. Just that it may free enough power to be practical and out last the electric valves.

I ran a 4" cutout on my turbo sc300. It worked well for the first two months. Although it never sealed air tight. Then would stick occasionally, then a back fire bent the butterfly valve open . Still it was fun and worked ok.

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[turboglenn]

Another point about butterfly type assemblies. If you've ever seen older aircraft that used turbocharged engines a lot of them had wastegates that were nothing more than butterfly type flapper assemblies much like tha tpiece in your pic.

Reason i know this is my stepfather was a marine and knew a bunch of older guys that restored "out of service" aircraft (you can't own anything the military currently uses as far as that goes) and one time over there helping out I picked up a piece and said "what's this throttle body off of?" to which he replied "that's a helicopter's wastegate" I was stunned and then became more curiouse (he's the guy who gave memy love of metal working)

but either way, if military avaition used the setup/idea, aside from the leaks and such i would imaging that it would serve a good life..sticking is probably limited to the power of the actuator moving the butterfly anbd the amoutn of leverage it has on the pivot.. most e-cut-outs have crap motors and some have no gearreduction making them even less poerfull to overcome a sooted up joint

not trying to convince you just adding to the conversation

 

[forcefed86]

Another point about butterfly type assemblies. If you've ever seen older aircraft that used turbocharged engines a lot of them had wastegates that were nothing more than butterfly type flapper assemblies much like tha tpiece in your pic.

Reason i know this is my stepfather was a marine and knew a bunch of older guys that restored "out of service" aircraft (you can't own anything the military currently uses as far as that goes) and one time over there helping out I picked up a piece and said "what's this throttle body off of?" to which he replied "that's a helicopter's wastegate" I was stunned and then became more curiouse (he's the guy who gave memy love of metal working)

but either way, if military avaition used the setup/idea, aside from the leaks and such i would imaging that it would serve a good life..sticking is probably limited to the power of the actuator moving the butterfly anbd the amoutn of leverage it has on the pivot.. most e-cut-outs have crap motors and some have no gearreduction making them even less poerfull to overcome a sooted up joint

not trying to convince you just adding to the conversation

All good points. I have actually seen them. I'm an aircraft mechanic and started out in general aviation. Those valves are pretty heavy duty compared to a TB or typical electric cutout. There is a reason the WG design was changed though.

I had always thought about using some heavy duty SS industrial food grade valves. You can get them used on ebay for around $50-75 and many come with V band flanges ready to go. These use some nice thick plates for the valve blades as well.

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Any of these things will work...but I'm going with the WG idea to be different.