pistonsuk

First of all, I already know all the opinions on the SSAC mantel piece, so save it.

The twin scroll idea makes alot of sense. I have explained the theory here:

http://usu.edu/~jgastrich/TwinScrollDesign.doc

I hope this will allow me to retain the spool of my current setup ( 60-1/0.84 hotside) after installing a GT4088 w/ maybe an 0.94 or even better a 1.19 A/R.

Here are pics of the latest work done. It sucks I won't be able to test it until later this summer...something about graduating first...then back home to my car..Yeah!





I plan on actuating it with the factory S4 turbo wg diaphram.

Justin

tdazmansFD

iTrader: (1)

Wow man. I really like the idea, but would be a little hesitant to use it. would'nt the increase at low RPM's be minimal since ther'es no adjusting the sizing or flow of the Hot side? What I mean is, the air may flow faster through 1 scroll but you still need to fill the entire housing and flow as much air as possible to the blades. (Hope fully you understand what I'm trying to say)
Anyway, good luck with it, I hope it works!

dubulup

don't some TII's have this? How'd Mazda's try end up?

pistonsuk

This is exaclty what the twin scroll flapper does. It halves the size and diverts the flow to one of the two scrolls in the Hotside.

Yes the housing will still "fill" with pressure. I'm a little confused.

All flow is not created equal! Read the word doc I posted, this might help.

Thanks for the questions/thoughts, keep'm coming.

Justin

pistonsuk

Yes the S4 T2's. This technology is ancient. Even the third gens have a version of this. They pipe all of the exhaust to one turbo (halving the flow area) at low rpm, then switch over to the dual turbos at high rpm (additional flow, less resriction).

Justin

pistonsuk

btw... that pic of the manifold was before I was done building-up/grinding the flange area to mate with the flap flange.

Justin

dubulup

So, why'd Mazda ditch it for the S5's???

and...

ah yes, I remember all the seq stuff sitting in a box after I ripped it all out

pistonsuk

Good question. Complexity maybe?

The S5 has a fully divided manifold with dual wastegates. This has the advantage of supplying individual exhaust pulses (not one canceling the other) to the turbo to aid in spooling. Maybe these benifits paired with fewer mechanisms needed for the twin scroll made it more desirable from a design standpoint.

Justin

RotaryResurrection

iTrader: (8)

Dude, I dont think that's going to work.

For one, the flapper seems to be thin, and I'm not sure it or the arms it's mounted on can withstand 1500+*F of rotary exhaust heat for very long. Not to mention the high pressure the exhaust exerts when revving the engine up and building boost.

For 2, and most importantly, you're blocking flow to the entire rear rotor. Once the exhaust fills the length of the rear runner (which is blocked off) where will it go? You'll have an even higher amount of pressure buildup there, like putting a potato in someone's muffler. You'll start getting more exhaust dilution in the engine just like an egr valve, and lose power.

Note that mazda's twinscroll design had both chambers joined, not seperate, and the flapper blocked off the turbo scroll itself, not one individual engine runner. So all the pressure from both runners was forced into one scroll of the turbo.

EVen if you make the claim that the gases in the blocked off runner will revert through the wastegate tube and eventually back over to the other runner, this will make for **** poor flow on both sides, interrupting flow on the open runner as well.

I think if it were me I'd put it back like it was. Or, if I HAD to make it work, I'd join the 2 runner passages just behind the flapper, cut a passage there for air to flow around the flapper and force all the air from both runners to go into the open scroll.

Turbo II-FB

well doens metak expand under heat? If so it looks like it will get stuck

NESpeed

How do you figure its blocking the flow from the rear rotor? I think you need to look at the picture alittle closer.

tdazmansFD

iTrader: (1)

Let's say it does make for **** poor flow. Won't it still accomplish the goal? Because of the lower rpm's? (less flow)
then at higher rpm's after the second scroll opens up, allowing it to flow normally again with the top end power.

RotaryResurrection

iTrader: (8)

Yeah I guess you're right...sorry about that. I was looking at it on the shop computer before and the lighting on that monitor isn't as good as this one. I can see that there is now a small chamber for exhaust to flow around the flapper, which should be okay I guess.

I still have reservations about whether that flapper and armature will hold up to the heat and pressure, but I give it an A+ for effort. It'd be interesting to make pulls with the flapper functioning, with it wired open, and without the flapper at all, with all else being equal, and compare the results to see if it's doing anything.

pistonsuk

Kevin, I think your missing some of the key points. Take a quick look at the word doc I posted about the systems operation. You concerns about the composer of the flap under load and heat are valid.

I did un-divide the manifold.

It is 304 SS. It has a melting point of 2550F, so melting won't be a problem. I dont know how ductile it becomes at ~1800F. So bending under high heat and load from the exhaust gases might be problem.

As far as thermal expansions go... I figured the the worst case would be a hard boost run on a "cold" (~400F) manifold, and assume the flap becomes the temp of the exh. gas (~1800F). The CTE of 304 is 10.4 µin/in-°F. So the flap would grow is 0.015" more than the flange. I plan on putting more gap than this between the flap and the flange.

Justin

pistonsuk

I plan on doing this. Probably be g-tech runs, but never the less a comparison.

Justin

pistonsuk

This ^ is the idea.

Turbos in general make for "**** poor flow". Turbos are a nozzle! That is the last thing you would ever want to put in your exhaust.

However, "****-pooring" your flow a little can have advantages as all turbo cars have shown. The amount that you restrict your flow changes the useful operating range of your turbo. The idea of the twin scroll is to make your turbo useful over a wider range.

Justin

pistonsuk

Coating the flap with this CBX ceramic coating I just ordered for my rotor faces will also help with the thermal expansion issue.

http://techlinecoatings.com/BulkEngine.htm


Justin

pistonsuk

Hey if any of you have an FD SSAC on your FC help me out with this. My car is not with me now so I can't take these measurements.

Is there enough room below/behind the turbo flange to mount the actuator without hitting the motor mount or frame/sub frame as shown in the pic?








I want to kind of tuck it up under the upper wg tube. I plan on heatsheilding it and wrapping the manifold. I am using the actuator from an FD OEM manifold.


Justin

pistonsuk

I just tacked a few things together yesterday. I still have to make positive stops for the arm and port the flange-manifold interface some.

Vid: http://usu.edu/~jgastrich/TwinScroll.mov

A few Pics with the FD actuator:

pistonsuk

Well I finished it up yesterday. I still plan on welding in studs for ther turbo, heat wraping it and drilling/tapping the wg flange for the racegate.

I heated the flap only to about 1200F and made sure that at this temperature difference the thermal expansions were not great enough to cause it to stick. I had to do some hand filing to get it to work here. I figure the temperature difference should never get this worse thatn this under running conditions.










Justin

signofinfinity

nice piece of bench fitting!!! innovative!

We need some trials on this......

Good luck and nice work!

George

Speedworks

you're trying to build a really simplified version of a VGT turbo (variable turbo geometry).
which is the answer to bigger turbo's spooling faster (see most european diesel engines and new Porsche turbo)

I also think your setup will not withstand the heat from the exhaust gasses and be aware that when it breaks apart, it will destroy your turbo.

Maybe a 'slide-venturi' (see Mazda's 787 intake system) would be an option to go for. Though it would require quite some investigation

pistonsuk

Yep. Twin scroll, VGT all the same theory.

This is the answer to any turbo spooling faster. All turbocharged vehicles can benefit from this.

The Melting Point of Stainless Steel is: 1400 - 1420 °C, 2550 - 2590 °F

I have never logged above 950C EGT's. How do you think it will fail?

Yep, this would suck.

Justin

mwatson184

Sorry if I missed it, but will the actuator be activated by boost or RPM?

dubulup

boost would be the better answer