wastegate design effect boost and power
 

I was wondering on am external wastegate setup how the wastegate exit effects the power and boost. I know some people dump it and some people have it merge back in for sound. How does it effect boost and power?
Also for a twin wastegate setup, how does it effect the power if you were to merge the 2 exits? It doesn't seem that many turbo setups want scavenging

I think its not so much like an NA system.

If you did incorporate scavenging into your wastegate(s) then you will get more wastegate flow and turbine speed will drop, boost will drop and wastegate(s) will close some for less wastegate(s) flow so boost can increase back up to wg spring pressure.

Doesn't seem like that achieves much.

If you were trying to stop boost creep and for some obscure reason you couldn't take the easy routes of increasing priority of flow to the wastegate(s) with a better position on the manifold or putting a larger wastegate(s) on, then you might investigate how to scavenge the wastegate(s).

Easiest way is like you say, merge your wastegate flow into your turbine flow at an angle to induce scavenging if you are confident your wastegate(s) are flowing less than your turbine (big turbo system).

In any case combining your wastegate(s)'s flow into your turbine flow will help with boost creep (even if you aren't getting a scavenging effect) since you will be raising the post-turbine backpressure by increasing the volume of exhaust flow through the turbine exhaust route and so lowering the turbo exhaust side efficiency (same as running a smaller diameter exhaust or another type of restriction).

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Okay, one thing I can think of regarding wastegate design that is along the lines of what you are thinking.

In the case where you are running a dual scroll divided turbo manifold and cannot put two wastegates on the manifold due to cost or space constraints (to make it truly pulse divided for better spool)-

you can try to make your wastegate runner lengths pulse tuned or at least long enough up to the single wastegate that you are not interfering with the divided pulse tuning through the manifold runners to the turbine wheel (because the runners to the single wg provide communication between the manifold runners).

Another Idea I had regarding saving money by purchasing one wastegate was to get a larger wastegate and have a plate to split the 2 sides all the way to the wastegate valve. The only issue was that the plate splitting the 2 sides would take away some of the flow, so I was thinking of a big 60mm wastegate, which costs the same price as about 2 45mm wasteagates.

I posted this more out of curiousity. I drive on the streets so sounds would be an issue. I also have 91 octane, so I can't boost much either. Call me stupid , but my next engine build will be a 9.4:1 compression with goals in the 350whp range on 91 octane, focusing on response.

I currently have a kidney up on ebay so I can do an EFR setup. Another thing I forgot to mention is if the EFR IWG would be enough to do low boost applications, like 10 psi. I saw a few comments in different posts about the efr that the wastegate was best for applications with 12psi or more. Now, add higher compression to that factor

Another Idea I had regarding saving money by purchasing one wastegate was to get a larger wastegate and have a plate to split the 2 sides all the way to the wastegate valve. The only issue was that the plate splitting the 2 sides would take away some of the flow, so I was thinking of a big 60mm wastegate, which costs the same price as about 2 45mm wasteagates.

No, this doesn't work well on the rotary in my experience- I did this twice with poor results.

I had a 60mm external WG on a modified S5 TII stock hybrid. I ported the WG runners huge with flow priority to the WG and then ran a stainless sheet divider between the two WG ports all the way to the WG valve.

It tore the stainless sheet between the WG runners.

I misunderstood what happened and thought it was heat expansion forces that broke the spot welds and then exhaust forces bent and tore the plate while it was out of position in the WG tube.

Version two was a floating arrangement with a 3/16" stainless sheet welded to the turbo back plate and then welded to a floating ring at the WG end that could expand/contract along its length.

It lasted fine for a year or so (with just one mishap where the divider was too close to the WG valve and so welded itself to the valve causing WG to stick shut)- but then I started autocross racing.

Almost immediately after starting racing the 3/16" stainless WG divider tore like paper inside the WG extension tube. This time I could clearly see the tear was from the differential exhaust pressure/pulsation between manifold runners/WG runners. Part of the 3/16" stainless divider piece was still intact welded to the turbo back plate and the other divider piece still in tact welded to the ring. The two pieces had a tear dividing them from constant wiggling back and forth.

Maybe I could have cut the WG extension tube in half and welded the divider in and then welded the halves back together to keep it divided and support the divider against movement with pulsation- but that sounded like a lot of work and I noticed something else in the mean time.

Without the divider there was a very very very little bit less boost response in the 1,000rpm to 2,000rpm range and no other discernible difference. Like ~2psi boost by 2,000rpm instead of ~3psi boost on my set-up.

You can see the manifold runner porting up to the WG passages here if you are familiar with stock S5 turbos.
https://www.rx7club.com/attachments/...t-dsc00520.jpg
Here is the WG porting.
https://www.rx7club.com/attachments/...t-dsc00531.jpg
Here is the backplate with V2 of the WG divider. The lower piece stayed welded to the backplate, the divider tore inside the tube. You can see the floating ring at the top that can slide with thermal expansion on this V2.
https://www.rx7club.com/attachments/...t-dsc00527.jpg


I posted this more out of curiousity. I drive on the streets so sounds would be an issue. I also have 91 octane, so I can't boost much either. Call me stupid , but my next engine build will be a 9.4:1 compression with goals in the 350whp range on 91 octane, focusing on response.

I currently have a kidney up on ebay so I can do an EFR setup. Another thing I forgot to mention is if the EFR IWG would be enough to do low boost applications, like 10 psi. I saw a few comments in different posts about the efr that the wastegate was best for applications with 12psi or more. Now, add higher compression to that factor

Well, if you have a problem with boost creep with IWG or a small single WG from poor manifold design- its easiest to fix the boost creep with an exhaust restriction.

Run small 3" exhaust, or run a "highflow" cat in the exhaust or put a restriction at the very end of the exhaust where it won't affect spool.

I should have just run my 3.5" downpipe/midpipe to 3" RB turbo back where boost did not creep instead of all that work to the turbo to run full 3.5" turbo back. But I hated the though of restriction...

I was so worried about boost creep with the EFR 7670 turbo set up I built to replace that stock hybrid that I put two 44mm wastegates on with high priority to flow.

Friend read my the old Tial WG spring chart online to me when I put the springs in and I ended up with a 6psi WG spring selection at first.

Well, it held 6psi no problems to redline...

Overkill on the wastegate$$$.

Thanks for the info!

Btw, did you make that gasket from manifold to turbo? I need a gasket for my custom bell mouthed dp

I did make that copper gasket- but don't do it.

All the Copper gaskets I used got pushed out between the bolt areas to where they leaked. It seems like the thicker the copper or further between bolts the faster it happens (more area for exhaust pressure to push gasket out).

I switched to using multi layers of thin stainless sheet[/B] and zero problems. Stainless does not get so soft with heat like Copper.

Easier to make as well as you can cut the thin Stainless with good scissors or sharp tin snips without it bending all up.

For the turbo to manifold gasket pictured I just used the stock S5 multi-layer Stainless gasket and cut the fire ring out (ported with carbide to manifold/turbo size).

Absolutely no problems with the Stainless multi-layer. Many years of auto-x/hillclim/sprints racing and probably ~ 50 dyno pulls.

I actually sagged out that front turbo runner at the runner divider on the stock cast turbo manifold (front runner center divider got pushed out toward rear runner from exhaust pressure), but the gasket is fine.

On my EFR 7670 I bought cheap thin Stainless gaskets and stacked them up- no problems putting the hurt on it racing with 26psi and another ~50 dyno pulls. That turbo glowed in broad daylight when dynoing and racing.

http://www.susan-parker.co.uk/images...ld-v-temp1.gif


http://t3.gstatic.com/images?q=tbn:A...YfEP2p_PJmd0zQ

https://www.rx7club.com/attachment.p...1&d=1430181665

this is the wastegate routing I went with... older Tial 44mm into 3 inch custom downpipe

which stainless did you end up going with? the 316?

I like how the pipe was flared out and then welded!

i am running this setup now, on a 60-1 compressor, T3 P-trim undivided hot side. the manifold is tubular, short runner, divided up to the turbo flange

ATP TURBO - The Premiere Provider of Turbocharging Components

http://www.atpturbo.com/Merchant2/gr...-023_1_450.jpg

http://www.atpturbo.com/root/release...-wgt-023_3.jpg

with no creep on a 28mm wastegate hole. well, it initially creeped until i ported the wastegate hole from 25 mm to about 28 mm. maybe it works in this case because it isnt a divided housing, so there is some turbulence right at the wastegate to help interrupt the flow to the turbine wheel.

but i think it goes to show wastegate position and how the exhaust flows around the wastegate is more important than actual wastegate size. or how a giant wastegate is just a bandaid for poor flow through the wastegate. it always bugs me how external gates have an abrupt 90 deg angle in their design, you would think that affects flow as well.

i dont have any solution to a fully divided setup, just throwing some ideas out

What are your turbo specs? I know almost everyone says to run a t4 with a .91ar or larger. How much power are you making? dyno? powerband?

its a .78, it doesnt spool particularly fast, it hits 10psi by 3500, but i suspect its because of the undivided housing. i havent had it dynod, its down at the moment due to cracked clutch fork, but once it get it back together and tuned i can get it on a dyno