spazzytroy

iTrader: (1)

I wanted to post this after I had done a bit more research, but the timing of arghx's exhaust sleeve vs. manifold volume post has prompted me to ask ahead of schedule. Is it worth giving up the ability to control manifold volume to implement a semi-divided one?

Options I'm considering:
1) Semi-divided (beautiful piece, similar to the one designed by bewtew)

2) Collected pre-turbo, equal length + QSV (similar to the one designed by CMonkar)

3) Collected pre-turbo, unequal length + QSV (similar to the one designed by Banzai)


I've also been unable to find anyone that has tried to do a comparison of 13b divided single WG (semi-divided, without the WG sealing the runners) vs double (fully independent) WG performance. Do you think this would approximate a divided 20b manifold test vs a "fully divided" theoretical 20b manifold?

Any input is appreciated

arghx

iTrader: (3)

I voted for unequal length + QS valve (like pic #3). This is based on "book knowledge," not firsthand experience.

I have basically read all the Mazda papers and technical manuals on the turbo rotaries that are available in English. I find it interesting that equal-length designs are conspicuously absent from every bit of literature I've ever seen from Mazda. It's all about the absolute length (i.e. shortest possible for low-end torque), diameter, and straightness of the piping.

A-Spec Tuning

Ideally, equal length collected is optimal but it honestly depends on numerous things and is relative. Relative being the application it is used in.

1)RE I believe uses this design. This manifold is a good choice if you don't mind the complications of fabbing it up. (I believe I went through this conversation with BewTew at one point)I think it is a well thought out compromise of getting three runners to work on a split pulse turbine housing. The down side is the bends involved, though they aren't poorly executed they would almost certainly need to be equal or there almost is no point to it.

2)This is ideal for making a peak power level. (I spoke at length with him on this set up) People scream "equal length" all the time and while it is ideal the bigger concern often over looked is equal length for the application. Usually the packaging envelope limits this and so while equal in length, it may not be the length you want or need. Simple examples are runner diameter and length. The diameter essentially sets the velocity through the runner, the larger the diameter the slower the velocity along with slower response to get to peak torque, losing bottom end basically. Smaller diameter will increase velocity getting you to peak torque quicker this will also choke overall flow at some point causing lose of power up top. Runner length will effect power before or after peak torque, adding length will help increase power below peak torque, reducing runner length will help increase power above peak torque. When you think of all that you have to then say, "How many "equal length" manifolds people sell actually put the math down to get where they "wanted" or "needed" to be versus what the packaging envelope allows?", myself included by the way. (Though I did make some really sweet headers for a cobra kit car that all the math was done and perfect equal, stepped, proper length primaries and secondaries blah blah blah, only to find out we now needed to step up the carb again.)

3)This manifold is similar to what many use in Aus. as well as RX7specialties in canada.
Unequal length gets a bad rap and while it is not ideal it has benefits one being a broader torque curve. However to be done correctly you need to be stepping the runner lengths within a given range to make it work properly. That would mean say ideal runner length is 12" the middle runner would need to be 12" and the rear runner 14" front runner would be 10". (these number mean nothing it's just a frame of reference) This means each runner will hit it's peak spread out evenly. Most are just made to fit figuring unequal is just unequal so who cares and at that point just made to fit.


On the QSV, I ask why? I'm sure BewTew and Chris and certainly I would tell you if you size the turbo well enough a 20B has enough oomph down low to not need boost that much sooner. It will spool a good sized turbo rather well. Hop into a Viper or ZO6 and see what instant oomph gets you. The ZO6 we had here with just long tubes, intake, and reflash became almost pointless because you can't really get on it or you just burn up tires. It's fun but I hate having to feather a throttle or worry all the time about it.

If the turbine housing your going to run is divided BewTew's setup is ideal, If it is not Chris's may work best for ease of cost and packaging. If you have to run a divided turbine on a undivded manifold you need to cut the divider back .5" minimum don't knife edge it just cut it back in the shape of a U or C this will help balance flow into the housing.

~S~

rarson

Personally, I think the best manifold is the shortest one. Heat (and pressure) is the primary motivator of the turbine wheel, so the less pipe the exhaust has to travel through before getting there, the better. It also tends to make packaging easier.

t-von

iTrader: (8)

It's always hard to figure the best route with subjects like this because no one ever dynos different manifolds on the same set-up in a controlled environment. Now since were talking TURBO and larger displacement 20b, In terms of power, I feel manifold design isn't gonna be too much of a big deal because the 3 rotor is so capable when you add ANY amount of boost. You build a shitty manifold for a 20b and still manage to get 20psi boost though the intake with a large enough turbo, your still gonna make a **** load of power (more than what you could probably use on the street). Now how long it last and or is it capable of allowing a wastegate to properly control boost levels is a different story.

I feel smaller engines need better designs to help manipulate things vs larger displacement engines. To me the more power your trying to make, then I feel the design is more important if your trying to squeeze every single bit of potential out of the set-up. This is pretty much dyno gueen territory or drag cars. If your doing this, your basically running your turbo to the raged edge. Aside from material choice, I feel PRIMARILY overall smooth transitions to reduce drag/turbulance and proper wastegate location are key to getting a manifold it's do it's job for 98% of the STREET cars on the road. Then there is runner diameter and length if your trying to manipulate the power band.

A-Spec Tuning

Only to a point, start getting too short and you run into BP issues. The engine does need some room to breath and your heat loss is almost minimal in a thick wall stainless manifold over a couple of inches. Meaning you'll see little to no difference in the turbine being driven from say 8" to 12" but you can see better breathing from the engine. Usually packaging dictates what you have to work with though.

RZMotorsports

I use a equal length non divided turbo and i got good power, great torque and quick spool its all about the entire combo, turbo, manifold, exhaust housing, and exhaust. everything need to work together. I know bewtew and my car spools quicker, about same amount of power but mine had 100 more in torque. So its all about the entire combo everything has to work together.

bewtew

iTrader: (7)

when i had my old set up i had a undivided and not equal length manifold and it was alot laggier. i switched to equal length,divided, twin scroll and the difference was day and night. the responsive of the turbo was a lot better and so was the spool time.

Mini, i think those torque #'s are wrong .

t-von

iTrader: (8)

See this is what I'm talking about and why it's so hard to figure out what works. How do we know that the twin scroll isn't making the most difference in your spool times all by itself? Before you had unequal length and undivided manifold the response was laggy. Now you have equal length, divided manifold, AND TWIN SCROLL and are now getting great response. You see what I mean? It's really hard to tell what's making the difference here with all your changes. Now the overall set-up does help with the intial starting point when it comes to figuring our HOW someone wants to build their set-up.

spazzytroy

iTrader: (1)

Exactly.

I suppose I should have included this earlier for completeness in this thread but goals for the car are:
500-550rwp on pump gas
Probably 80% Street / 20% AutoX usage
BW S400SX3 (75mm inducer, 83mm turbine exducer I believe) on the 1.00 T4
Stock intake ports
Port matched exhaust ports with S6 turbo sleeves

I'm actually kind of leaning towards doing the unequal length QSV just to add another data point for the community. Perhaps someone can ship me a semi-divided manifold for some testing once my rig is complete. =D

As a side note, I've used solidworks before, but never tried any of their CFD simulations. I would be guessing at pretty much every variable (exhaust gas velocity out of the port, which gas to use to model with, temp effects, BP from the turbine etc) Additionally, I'm not sure I'd know how to interpret the results. Do you guys think it would be worth it to try and get some virtual comparisons going as far as manifold design?

Also, thanks everyone for putting your thoughts out.

arghx

iTrader: (3)

That might be fun to play around with for a little while but I wouldn't let it have much influence on any decisions for your build. You don't have the proper proprietary data to have an accurate model. OEM's have entire teams of engineers putting together CFD models. That's how all the rapid development is done now. You have a team of guys putting together the CFD model, and then another team that punches in the data/variables.

I will send you a paper that may shed light on how CFD is used in a real-world application.

RZMotorsports

the car was slipping on the dyno so the torque numbers should have been higher.