Parallel Turbocharger Manifold Design

[SammyDaFish]

I'm designing a parallel twin turbo setup for an inline 6 engine. I've been searching for information about wastegate placement and manifold design, and unfortunately, I've yielded few results. The car will be a street car, so maximizing power below 6k rpm is the goal. I've tried to find images of some header/manifold designs to get some ideas from, and also come up short. I plan to use external wastegates. I'm wondering about the pros and cons of running a single wastegate verses two. The application is a Toyota 7M engine. Greddy/Trust made a twin kit for this engine years ago that utilized a single external wastegate. There are a few kits for the famed Toyota 2JZ engine that use two external wastegates, but most designs I've seen have had a manifold connecting the two collectors. Like in this photo (I know it's a little hard to see, the flex section is actually not bolted in)

http://store5.yimg.com/I/supra_1770_14474140

I'd like to do all I can to maximize the pulse effect on the turbines. I can imagine that equalizing the pressure between the two manifolds would be beneficial to equalize the two turbos, but is it really necessary? It's not usually done for v engine setups that run twins. Would equalizing the headers sacrifice the effect of the exhaust pulses on the turbines? None of the books I have even mention the scenario of wastegate placement or header design in a twin turbo setup, and I have no experience designing a twin turbo setup, so I'm completely in the dark here.

I'm interested in how race teams might have run a setup like this. I know in race trim a single turbo is usually more desirable, but I'm sure there have been some teams that have run twins on an inline 6 before. I've also tried finding some aftermarket designs for the infamous RB26DETT, but no luck there either. It seems people don't fancy posting pictures of uninstalled parts on the internet to much.

Any input or direction to information is greatly appreciated.

 

[SammyDaFish]

Here are some more images of a manifold with both banks combined.

http://www.exvitermini.com/pics/extrsid.jpg

http://www.exvitermini.com/pics/extrbot.jpg

http://www.exvitermini.com/pics/tr2311.jpg

http://www.exvitermini.com/pics/rt2111.jpg

 

[patprimmer]

If I were designing from scratch, I would do a simple manifold with cylinders number 1,2&3 merging into a slightly larger pipe, via very short pipes.

I would repeat this for cylinders number 45&6. The primary pipes would be very slightly larger cross sectional area than the port exit flange. The secondary pipes would be very slightly smaller than the turbo exhaust inlet flange.

I would have a balance tube between them, that was the same size as the secondary pipes.

I would put one large waste gate between them.

I would run the two dump pipes into a merge then into a very low restriction silencer.

I would run the waste gate into a small bore and very effective silencer. I would then run it into the main silencer.

I would run a merge between the compressor outlets then run a single pipe to the intercooler, then back into the stock 7M-GTE inlet manifold.

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[SammyDaFish]

Thanks Pat, knew you'd be one of the 1st to respond I'd like to know why you suggest a single wastegate. Besides being easier to plumb, is there any benefit to running a single wastegate instead of two. I guess boost control would be easier also. I plan to achieve a relatively high total horsepower output on the engine (600 - 700 rwhp) so if I were to run a single wastegate, it would likely need to be quite large. Is there any disadvantage to running a single large wastegate as opposed to two smaller units?

The plan is to run 1.5" primaries from 1,2&3 ->turbo1 and 4,5&6 -> turbo2

On the induction side, mandrel-tubing equal to the size of the compressor outlet will run from each turbo to the split inlet tank intercooler with radiuses leading edges. Then pipe equal to the throttle body diameter (75mm in this case) will run to a custom from facing long runner manifold (similar to those found on the JZ-GTE engines).

The goal is to create a very powerful, yet very drivable car. The peak horsepower goal is not nearly as important as the area under the curve. The car will be street legal and I'll build two downpipes for it, one using catalytic converters, and one not. Trying to maximize efficiency in every possible way is the goal of this project.

My largest dilemma here is that I don't understand any of the concepts behind wastegate placement or sizing. All the information I've found basically says make it smooth and big enough. Far from an engineer's point of view. Does anyone know where I can find some test results of different wastegate placement? Does the distance from the collector mater? How will the effect of exhaust pulses affect the flow of exhaust as the wastegate begins to open? Should the distance be calculated similar to the way header length is?

Sorry I have so many questions. I can't seem to find information anywhere.

 

[patprimmer]

I suggest one large waste gate to keep it simple and I suggest it be in the middle of the balance pipe because that will be a relatively stable area re pressure fluctuations and will have equal effect on both turbos.

It will also be an area least effected by pressure changes due to gas velocity and inertia.

I guess you intend replacing the stock 7M-GTE injectors, as they only flow enough fuel to support about 10 lb boost with the stock set up.

I have no hard data to support most of the above (except the stock injector flow capacity).

Regards
pat pprimmer@acay.com.au
eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

 

[Proxses]

For wastegate placement, the optimum setup is to have the pipe from the manifold to the wastegate to be at the least angle possible. This will flow best, you don't want to have the gasses making a right turn to exit out of the manifold. It is easier to balance manifold pressure with one wastegate. Distance from the collector is not a big issue. Since it is only venting pressure, and not helping to create more power. Wastegates are there so you don't overspin the turbo, or shove too much air into the engine.
You could try to look for Corky Bell's book, Maximum Boost. This could be a good resource. It describes how to make your own turbo system.
The only downside I can see from using only one wastegate, is the pipes that extend from each manifold to the wastegate may eventually crack from heat expansion, were they join. Easily avoided.
I hope this helps, I know more about supercharger than turbos. Good Luck