Turbo Dump Design (Split wastegate vs Not)

[wilbo666]

I'm doing up turbo flanges for myself at the moment.

And I am quite interested in the benefits of a split wastegate dump vs a common wastegate & turbine dump on an internally gated turbo....

Just thinking about it quickly...

Thought
With a common dump area the wastegate air is going to try and join up with the post turbine air... if the flows are pretty well going the same way; which they are?, wont the wastegate air try and drag the post turbine air away? I would expect the wastegate air to have a higher velocity that the post turbine air...

I guess there is a trade off between straightening the wastegate air and adding restriction to the wastegate air? (more restriction = less suction effect from the wastegate air?)... (or am i incorrect in the flow type and this idea doesn't hold?)



Random Ramblings:
The post turbine air will have some velocity; if the difference in velocity between the pre turbine air (that is going to get diverted out the wastegate) and the post turbine air is large then I would guess that the angle of the wastegate air would be large....(the slow post turbine air allows the wastegate air to dominate, and expand (diffuse)...)?

**questions (i'll do some research when I get home from work and see if I can't answer soe of these myself...) **
-What is the velocity of the exhaust gas pre turbine?
-What is the velocity of the exhaust gas post turbine?
-What angle does the wastegate gas exit into the dump pipe at? (I imagine this will be dependant on the velocity / pressure differential...)

Well that prbly doesn't make any sense at all! But if anyone has ideas I'm more than open them to them Back to back tests would also be very interesting (split wastegate vs common)...

Cheers
Wilbo

["Z" UTE]

When I sold my 1JZ-GTE VVTi Celica, I mentioned to the guy that he might like to have a split dump made up.

He finally had it made up and fitted. Last dyno day, he recorded 213.8rwKw, an improvement of at least 10Kw. A few dollars well spent.

cheers Chuck.

[Norbie]

Not sure if this is relevant but you can pick up external wastegates on eBay pretty damn cheap these days...

[wilbo666]

Not sure if this is relevant but you can pick up external wastegates on eBay pretty damn cheap these days...

Not revlevant

Turbos involved in this plan have internal gates and there isn't room to add an external gate pre turbos (adapter plates).



Cheers
Wilbo

[jfallen]

there are advantages, but they aren't huge.

if you canget a gate and let it scream
Jordan

[JustenGT8]

Do it if you have the room, you will see gains...how much depends on a whole swag of variables but the flow separation will net you a gain.

WRXs commonly see approx 15rwkw from this mod. My old 18RGT saw gains but no numbers, just a very obvious improvement in response. The GT8 saw the most dramatic gain from separating the wastegate flow.....err completely. This was worth nearly 50rwkw at the same 13psi boost!!

[wilbo666]

Seems pretty overwhelming the thing to do is to split them.

Pretty sure I will have the room so will design my flanges for that.

My next question is who far should I aim to keep them split for? (I won't be running screamers!)

I was thinking about 150mm atm depending on room...

Cheers
Wilbo

[JustenGT8]

Again, the answer is as long as you can...there will be a point of no additional gain but if you can get something like 300mm in there try for that. The critical issue is to merge the wastegate pipe in at as gentle an angle as you can to minimise turbulence as the 2 flows meet.

[wilbo666]

Easy, thanks guys!

Cheers
Wilbo

[love ke70]

my exhaust guy said 18" if not your wasting your time.
i think it will do something before this point, but how much more could it do if it is 18" ?

[wilbo666]

At this rate I'll be running a separate exhaust system for the wastegates all the was to the rear (it keeps getting longer each time...)

I guess the idea is the longer the better so will aim for that

Cheers
Wilbo

[love ke70]

At this rate I'll be running a separate exhaust system for the wastegates all the was to the rear

Cheers
Wilbo

cant see why not

[Gary]

yeah old thread i know

getting into exhaust system design at the mo for my 1J cressida. the plan was twin dumps through to a nice catback, catback is sorted design wise but now time for dumps, hoping someone can either support the idea swimming around in my currently tired and hungover head, or shoot it down so i can just do it the easy way instead

initially i was happy just using 2.5" mandrel bends off each turbo (ie bent into a weird oval shape, and an extra bit tacked on to close it up over near the wastegate flap), kept independent for 650mm or so, then merged into a shallow 3" collector and away. then once i got my hands on the turbos it became obvious that in theory 2.5" sounded nice but in reality it would do little more than just provide for more volume to fill - not so bad for top end flow but not so good for low down response. so it was to be 2.25" to reduce volume and keep things a bit tighter

now after some more thinking, the inevitable split dumps thing popped up (). so for my engine, each turbo would have its turbine diameter and wastegate flap diameter (the rough circle cast into the exhaust housing around the wastegate flap anyway) matched with independent lengths of piping; ~47mm diameter piping for the turbine side(so 50mm i/d piping would be closest), and ~37mm diameter piping for the wastegate flappy thing side (probably 40mm i/d). these two pipes will be attached to a flange obviously and closed up, with an extended bit between the two pipes to act as a seperator of the two different temp/flowing gas paths. id leave the two pipes seperated for as long as i could (maybe 500mm or so? just a rough number to give you an idea) before theyd merge, just before the 3" collector joining each turbo

i'm a backyarder, the effort involved in doing this over the simple 2.25" dumps is negligible for me. if there's gain to be had without drawbacks, even if its small, thats more than enough for me to do it

any boffins happy to hazard a guess if this is worth doing? the possible problems im imagining with the design is the potential for greater loss of heat (lots more surface area to transfer and hence extract heat out of the system), which might be able to be combatted with either ceramic coating or if room permits, header wrap (depends on design i spose)
the other possible drama is perhaps as the turbos are as small as they are (factory ct12a's), the benefits of seperating the hotter wastegate flow from the cooler turbine flow are negligible?
lastly, as i'd be matching the turbine diameter, im thinking pipe friction might act as a sort of choke point? smarter to go something larger in diameter to help that situation? im trying to get my head around fluid mechanics, very slowly getting there

appreciate any input

[love ke70]

my understanding with turbos was that the less restriction after the turbo the better, as all the backpressure in the exhaust is provided by the turbo. i may be wrong though?

[Gary]

guess so, removing or reducing whatever impedes the turbine

i found a saltlake basher powered by a 1J with some pics as to how he did his dumps;




the builder of which seems a man after my own heart, amatuerish builder whacking bits together so he can go racing