Turbo Dump Design (Split wastegate vs Not)

[SillyCarS]

separation = screamer

[Rex_Kelway]

Some sharing of the Rex way of thinking:

From what Rex has read is seems that a gas flowing down a tube will naturally begin to swirl, not unlike water going down a drain.

This is not particularly quick as you may have guessed. For a given length of exhaust the gas may end up having to flow several times this distance depending on the exact 'swirls per inch' or whatever the correct measurement is.

The gas flowing out of the rear of the turbo is already swirling meaning its not moving away from the housing nearly fast as it could potentially be.

So the Rex way of thinking is to have a large mouth/opening (not necessarily circular) immediately after the turbo to try and break up the swirling motion and allow the gas move away from the area as quick as possible. The wastegate discharging into this area helps with this also.

To use the old sink or bathplug analagy, you'll notice that water swirling its way down the drain seems to take longer than if that swirling motion is disrupted.

On the percentage gains front. remeber your baseline or starting point is just as important as the result:

...15% better than great is excellent but 15% better than garbage is just mediocre...

For those that need it spelling out, IE 15% improvement over stock is nowhere near as impressive as 15% improvement over the best on the market.

Rex is by no means a thermodynamics engineer, but it's what His instincts tell Him, not marketing...

[Dieseltrain]

I gotta agree with Rex on some of this. I must be the ONLY person NOT using SPlit wastegate dumps on a 1JZ that i have read about or know of ... Everyone laughs at what i use or question it, but the results speak for themselves .

Ive driven a mates car with split wastegate dumps @ the drags for him . His car had programmable ecu and both adj cam gears over my mods. HIs car runnin 20psi boost . Slightly lighter car also as pov pack, no abs or luxury stuffs...

Not only was his car 3-4mph lower than mine, But no way could i get as good a 60ft out of it as i could in mine... Same stock convertors and stock boxes with shift kits . Best i could do in his was 1.74 . I can run high 1.6's in my setup, and have gone a best of 1.60 . Both cars on ET streets same size also...

And those who have driven my car, comment on how responsive it is.

[seamonsta]

I made twin 2.5" dumps for my 1J cressida and I don't recommend doing it, prick of a job! I am not an exhaust/fabricating guru and although I got there in the end I would recommend buying some from Sasha at Canak Autosport, he has a jig for the cressida/1J combo and they fit.
My 2C worth.

[Gary]

rex theres a few flaws in that way of thinking, the idea of swirl doesnt apply in the same way for zero pressure fluid drains as it does for high pressure gas exhausts

the theory behind split dumps is as the gas that passes through the wastegate (hence, around the turbo) is typically hotter, it tends to flow faster than gas exiting the exhaust turbine. i dont get it completely myself, but i think its just about keeping them seperate from each other until the wastegate gas cools enough that its similar in terms of dynamics as the gas coming through the turbine. so normally the gases from either source merge and cause a certain bit of turbulence that impedes flow, but having a split dump creates a new merger, that reduces the level of turbulence that occurs and it should all flow better

I gotta agree with Rex on some of this. I must be the ONLY person NOT using SPlit wastegate dumps on a 1JZ that i have read about or know of ... Everyone laughs at what i use or question it, but the results speak for themselves .

Ive driven a mates car with split wastegate dumps @ the drags for him . His car had programmable ecu and both adj cam gears over my mods. HIs car runnin 20psi boost . Slightly lighter car also as pov pack, no abs or luxury stuffs...

Not only was his car 3-4mph lower than mine, But no way could i get as good a 60ft out of it as i could in mine... Same stock convertors and stock boxes with shift kits . Best i could do in his was 1.74 . I can run high 1.6's in my setup, and have gone a best of 1.60 . Both cars on ET streets same size also...

And those who have driven my car, comment on how responsive it is.

ive never seen split dumps for stock CT12a's, other than the pics i posted above obviously

id thought perhaps people didnt do it just to keep it simple, as quite a few people who make them for 1J's and 2J's arent exactly specialists in the field. sorta just people who know how to weld and can knock a few good looking sets together for people that want em

[wagonist]

There are lots of reasons to have a split dump. All have to do with reducing turbulence.
1. the air coming from the turbine is spinning, where the air from the wastegate will be smoother. Differing flows hitting each each other.
2. there is a sudden transistion from the spinning into hitting the "transistion". While it has been shown there should be sudden increase in area, this only goes for the turbo flow.
3. differential in temp causes differences in flow.

if you're making a split for the dump, make sure you build it so it goes upto the turbo face, and see if you can make it so it fits the shape of the turbine & wastegate. I once saw one with a simple straight piece in there. It would have had some effect, but if you're going to the trouble, may as well do it properly.

[w0n0matic]

delete this post

[Dieseltrain]

Lew Radbourn from MArlew Performance in QLD ( has closed his doors but is looking at working from home and possibly in another workshop ) Used to sell his SPlit dump designs through the Soarer Clubs for years to suit 1JZ soarers... Even with a jig setup, he said they took 8-10hours to make each set. They were designed to bolt up to the stock exhaust down next to the bellhousing. And retailed for about $950-$1100 .

[Gary]

awesome, good to hear someones bothered!

ill need to read up a little to make sure it wont be more of a restriction than simply having a single path for both, but other than that i'm gunna make a set and see how they go. i can always make a single 2.25" set afterward if i'm not happy, having to do them with the engine in the car will be good punishment for possible previous stupidity

wagonist that'll be the key, one can simply knock up a single dump for each turbo and be messy about it and still get good results, but if im doing a split system i'll need to be careful and do it properly. will take me a while but i dont mind

on another note, i read screamers for internal wastegates arent so cool - given internal gates are rarely full closed or full open, there's no high rpm roar like you get with external gates, just a reasonably constant shit sound similar to having a colossal exhaust leak

thanks for the contributions has made decision making easier

[JZA70 R]

[PsyCo]

I'd love to buy sasha/canak twin dumps but just cannot justify the expense. At $800 it's nearly half the amount of coin required to convert to a single. Seems like a waste to me. I'm in the same boat as you gary. Might have a shot at it myself.

[Gary]

IMG

thats the easier way out, ja

getting closeup pics of dumps is tricky sometimes though, thanks for the thought

[Gary]

I'd love to buy sasha/canak twin dumps but just cannot justify the expense. At $800 it's nearly half the amount of coin required to convert to a single. Seems like a waste to me. I'm in the same boat as you gary. Might have a shot at it myself.

damn right hey, when you step back and actually look at what you're buying, most of the prices set by people that make em up are quite astronomical! once youve got a jig going and have made a set or two, surely it doesnt take nearly enough time to justify that sorta cash

the cheaper ones have poor collectors and really dodgy welding, so its not as though thats an option either. makes me want to undercut the expensive chaps something fierce, for no other reason than principle. some of the CES dumps ive had a look at spring to mind

[Dieseltrain]

IM running Unique Autosports Dumps . They cost me $395 and i installed them myself. Had to get the front pipe modified to suit, which cost me $90 at the time . So for $485 they were done

[richzx]

Daniel the UAS one won't bolt on for cressida conversions. I have the UAS dumps on mine and they took a shitload of cutting and welding to get them to fit around the steering rack etc. Also I don't think the quality is all that to be honest mine split, the faces weren't flat and they also sloped inwards slightly, mine might have been a bad set though, who knows. I'm certainly happy with the response of the smaller pipes and it's got to be better than the factory dump!