Impulse axys

mountainhorse · Jan 4, 2017

How does this really help?

mountainhorse said:
The mock ups look nice...
What is the reason for routing the Wastegate directly out the side of the sled?

skibumm said:
Wastegate... clean and reduces bog in deep snow conditions

I'm still having a hard time wrapping my head around the external dump WG.
And could use some input on this. (this is a sincere question for discussion and not a bash... to be clear)

If the sled is bogging from deep snow conditions plugging the exhaust outlet of the sled... if this is alleviated by uncorking the WG....Then you are spilling exhaust energy and slowing the spool assembly... If the exhaust exits from the WG dump... it is not turning the spool.

I get that the engine may not "Bog" ... but with that much exhaust leaving before it can turn the turbo... I can't see this as a net positive in the 'big picture'....

AND... I am open to learn here.

...

skibumm · Jan 4, 2017

mountainhorse said:
I'm still having a hard time wrapping my head around the external dump WG.
And could use some input on this. (this is a sincere question for discussion and not a bash... to be clear)

If the sled is bogging from deep snow conditions plugging the exhaust outlet of the sled... if this is alleviated by uncorking the WG....Then you are spilling exhaust energy and slowing the spool assembly... If the exhaust exits from the WG dump... it is not turning the spool.

I get that the engine may not "Bog" ... but with that much exhaust leaving before it can turn the turbo... I can't see this as a net positive in the 'big picture'....

AND... I am open to learn here.

...

So generally speaking external wastegate turbos are more efficient by Design. Quite simply, they spool up quicker. In wide open throttle or at least 3/4 throttle, extra boost will be expelled out the wastegate. For example if you want 10 pounds and you get a 12 pound Spike some of that is let out of the wastegate. In a situation where the snow is deep and there is a clog in the exhaust, some of that clog might be alleviated through the wastegated exhaust. The reason for the external wastegate on this setup is not to help it alleviate this situation, it is to create a more efficient system. One of the side benefits, perhaps is that it might help a clog in certain scenarios. The location has more to do with clean setup and eaze of installation.

skibumm · Jan 4, 2017

I will let this guy explain it, he's way smarter than me.

https://youtu.be/pn-uCAgB4H8

skibumm · Jan 4, 2017

I couldn't have said it better myself ;-)

Snowmow · Jan 4, 2017

All of the external wastegate turbos that I've ran. (OVS and boondocker). Have had the external wastegate plumbed into the outlet portion of the exhaust. So a In dump of pressure on the backside of the turbine, greater than than the pressure of the compressor during a throttle chop could create a turbo stall. You would have to route the waste gate of the exhaust side of the turbo to the inlet exhaust stream not to see a pressure dump in the system.

Snowmow · Jan 4, 2017

Like the BRV valves on the cat 1100T. That system reroutes the cold air side boost back into the intake of the turbo.

Snowmow · Jan 4, 2017

That actually seems and sounds somewhat efficient. I don't see how routing the externally wastegated exhaust gas from somewhere in the muffler section of the exhaust or to the atmosphere would make much of a difference. Unless the pressure created from the wastegate upon opening on the down stream of the exhaust would actually cause the turbine to slow down.

Snowmow · Jan 4, 2017

In that case, a wastegate like impulse is using, To the atmosphere instead of being reintroduced into the down stream exhaust, could be a benefit

skibumm · Jan 4, 2017

Snowmow said:
In that case, a wastegate like impulse is using, To the atmosphere instead of being reintroduced into the down stream exhaust, could be a benefit

Just like the video explains.

gmustangt · Jan 4, 2017

If I understand you correctly , it wouldn't matter internal or external. The energy is wasted and going around the turbine wheel. Wether it is going to atmosphere or inside the housing via internal wastegate it's not driving the wheel.
Keep in mind wastegate is controlled from compressor side. So if your target boost is reached , it's diverting energy.

mountainhorse said:
I'm still having a hard time wrapping my head around the external dump WG.
And could use some input on this. (this is a sincere question for discussion and not a bash... to be clear)

If the sled is bogging from deep snow conditions plugging the exhaust outlet of the sled... if this is alleviated by uncorking the WG....Then you are spilling exhaust energy and slowing the spool assembly... If the exhaust exits from the WG dump... it is not turning the spool.

I get that the engine may not "Bog" ... but with that much exhaust leaving before it can turn the turbo... I can't see this as a net positive in the 'big picture'....

AND... I am open to learn here.

...

gmustangt · Jan 4, 2017

One benefit not usually mentioned is the external turbine housings have much better geometry because they are not limited to incorporating a flapper.
Take a look down a tial and you'll see.

skibumm · Jan 4, 2017

gmustangt said:
One benefit not usually mentioned is the external turbine housings have much better geometry because they are not limited to incorporating a flapper.
Take a look down a tial and you'll see.

Exactly right! That is why we use Tial housing on all the kits. Also makes for easier install and maintenance.

Snowmow · Jan 4, 2017

gmustangt said:
If I understand you correctly , it wouldn't matter internal or external. The energy is wasted and going around the turbine wheel. Wether it is going to atmosphere or inside the housing via internal wastegate it's not driving the wheel.

Keep in mind wastegate is controlled from compressor side. So if your target boost is reached , it's diverting energy.

Yes. I don't see how a drive pressure dump into the exit side of the exhaust would help keep the turbo spinning. Now if you could
Dump the compressor side boost back into the inlet stream maybe you could see a benefit.

Snowmow · Jan 4, 2017

Or I suppose if you could do the same with the exhaust. Dump the excess boost back into the expansion chamber.

mountainhorse · Jan 4, 2017

Thank you for the info (sincerely)

My take... and more food for discussion.

My quandary does not come from external vs. internal WG functionality. It lies with the claim that the location of the WG exit from the sled helps with snow-restricted exhaust scenarios.

IF dumping the WG to a different location (free air) 'uncorks' the engine in deep powder... The exhaust stream from the turbine is choked off... and the WG is dumping to atmosphere... the Turbine is not getting any of that energy that exits the WG... simply put...if the WG is dumping enough to 'uncork' the exhaust it's not turning the spool.

When the exhaust is corked-up from deep snow on the Impulse units... the Boost control is not directing the WG to open... it is opening because the exhaust back-pressure becomes greater than the seat pressure of the WG valve/spring and the WG is PUSHED open by the exhaust backpressure.

Regardless of WHERE the WG dumps... it is still diverting energy from the turbine.

With a WG that returns it's 'dump' back to the exhaust DOWNstream of the turbine... the WG can't be blown open by exhaust back pressure.

I hear the impulse works well.... which is why it still makes me wonder about the deep snow advantage of a separated dump location. Keeping the exhaust from getting plugged in the first place makes the most sense.

I'm very familiar with how a waste gate works... and the benefits that some external can have over some internal wastegated turbos.

How the ext WG is mounted also has a lot to do with the efficiency... an ext WG mounted at a right angle to the exhaust flow will have a disadvantage in terms of efficiency to one that is mounted for more laminar flow from the exhaust. Most external WG mfgs (TS, Tial, Turbonetics etc) recommend NOT mounting their WG's 90˚ to the exhaust stream.

The new Borg EFR turbos are very efficient with their well designed/routed internal WG....Contrasted with the Garrett internal WG's that were designed originally for diesel engines, I believe, from the 1970's.

Also...Travis... are you working for Impulse?

.

Jaynelson · Jan 4, 2017

I wouldn't get too hung up on the 90 degree gate placement itself. There are some serious high HP automotive exhaust manifolds with the gate mounted 90 degrees off the flow, dumping to atmosphere. And we're talking 1000hp-1500hp 40psi++ ...so if it's working there, I'm sure it's good enough for a turbo sled.

mountainhorse · Jan 5, 2017

Kinda my point.... I'm not worried that an internal OR External WG that is functioning well is detracting from, or adding to, the performance of a kit on an 800cc two stroke twin.

.

gmustangt · Jan 5, 2017

If the downpipe get blocked off , the work on the turbine decreases, shaft speed slows, boost drops, wastegate closes.
Does boost drop 1:1 with back pressure. Typically not, depends on the setup.
I know with my Tial wastegate I was able to put more backpressure on the spring than it is rated for before it pushed open, so thats a guessing game.
So IMO the wastgate does not get pushed open by backpressure , considering a reduce in intake pressure.
The increase in back pressure would effect cylinder filling and potential bog , this is boondockers big thing with tunnel dump.

All the info out there for the external wastegate is based on 4 stroke cars, its a little different with 2 stroke sleds.

Good topic.

mountainhorse said:
Thank you for the info (sincerely)

My take... and more food for discussion.

My quandary does not come from external vs. internal WG functionality. It lies with the claim that the location of the WG exit from the sled helps with snow-restricted exhaust scenarios.

IF dumping the WG to a different location (free air) 'uncorks' the engine in deep powder... The exhaust stream from the turbine is choked off... and the WG is dumping to atmosphere... the Turbine is not getting any of that energy that exits the WG... simply put...if the WG is dumping enough to 'uncork' the exhaust it's not turning the spool.

When the exhaust is corked-up from deep snow on the Impulse units... the Boost control is not directing the WG to open... it is opening because the exhaust back-pressure becomes greater than the seat pressure of the WG valve/spring and the WG is PUSHED open by the exhaust backpressure.

Regardless of WHERE the WG dumps... it is still diverting energy from the turbine.

With a WG that returns it's 'dump' back to the exhaust DOWNstream of the turbine... the WG can't be blown open by exhaust back pressure.

I hear the impulse works well.... which is why it still makes me wonder about the deep snow advantage of a separated dump location. Keeping the exhaust from getting plugged in the first place makes the most sense.

I'm very familiar with how a waste gate works... and the benefits that some external can have over some internal wastegated turbos.

How the ext WG is mounted also has a lot to do with the efficiency... an ext WG mounted at a right angle to the exhaust flow will have a disadvantage in terms of efficiency to one that is mounted for more laminar flow from the exhaust. Most external WG mfgs (TS, Tial, Turbonetics etc) recommend NOT mounting their WG's 90˚ to the exhaust stream.

The new Borg EFR turbos are very efficient with their well designed/routed internal WG....Contrasted with the Garrett internal WG's that were designed originally for diesel engines, I believe, from the 1970's.

Also...Travis... are you working for Impulse?

.

Jaynelson · Jan 5, 2017

Perhaps I'm missing something ...but wouldn't the obvious benefit for the atmosphere wg dump be more accurate boost control?

If wg is plumbed back in to the exhaust downstream of the turbo, and you have some blockage with deep snow ....you are potentially affecting both exhaust flow and the wg being able to control boost. Now, a partially plugged exhaust is likely to affect boost anyways....but by eliminating the potential for a partially plugged wg, you are allowing the wg to do its thing properly; regardless of what the exhaust exiting the turbo is doing. It also sounds BA

I can't really comment on the internal gate - all of my turbo knowledge stems from auto stuff, and no one I'm aware of uses an internal gate turbo in a high performance application. Some OEM turbo cars do...but I would guess more for NVH reasons, and also very low boost levels with a high level of sophisticated computer control.

gmustangt · Jan 5, 2017

Jaynelson said:
Perhaps I'm missing something ...but wouldn't the obvious benefit for the atmosphere wg dump be more accurate boost control?

If wg is plumbed back in to the exhaust downstream of the turbo, and you have some blockage with deep snow ....you are potentially affecting both exhaust flow and the wg being able to control boost. Now, a partially plugged exhaust is likely to affect boost anyways....but by eliminating the potential for a partially plugged wg, you are allowing the wg to do its thing properly; regardless of what the exhaust exiting the turbo is doing. It also sounds BA

I can't really comment on the internal gate - all of my turbo knowledge stems from auto stuff, and no one I'm aware of uses an internal gate turbo in a high performance application. Some OEM turbo cars do...but I would guess more for NVH reasons, and also very low boost levels with a high level of sophisticated computer control.

Yes like mentioned above the boost can be effected by the plugged exhaust in the first place.

Everyones talking about a plugged downpipe , what happens if the external wastegate pipe gets blocked? Boost creep, over rev , potential damage...
Just to look at the other side of things...

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