LSx Twinscroll Turbo Design Analysis
09-04-2011, 06:23 PM
#41
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I really wanted to reply to this post, and I had to shorten your original to cover some key points. I am not for sure if you are going for a daily driver or HP monster, but the same advantages that 2.5 liter 4 bangers take advantage of can be had with the LS motors as well. I am using a twinscroll turbo on my rearmount GrandAM GT (has a quickspool valve) and on a front mount turbo Firebird V6. From personal experience, the most important thing (without getting too technical) to remember is that as long as you keep the exhaust pulses separate to each turbine volute you will take advantage of faster spool, higher top end, less heat, less backpressure and more timing to run with a twinscroll on an LSX motor. Guess what? Better mileage too! Basically, the scavenging effect is still going on! Naturally equal length primaries are a good thing to start with, but they are not 100% necessary. As long as the firing order is separated by each cylinder bank you will still get stonger, more focused pulses to hit the turbo wheel and boost faster. You will get more HP for the same given amount of boost of a single scroll. Any losses by not having variable valve timing, or superior head design are going to be quickly dissipated by engine displacement 
In a nutshell, if you slap together a good sized twinscroll setup with two wastegates and decent flowing manifold you will still reap the benefits that the smaller motors are getting.
In a nutshell, if you slap together a good sized twinscroll setup with two wastegates and decent flowing manifold you will still reap the benefits that the smaller motors are getting.
My only thought is variable valve timing (in my experience) can be used to spool turbos quicker. But must watch out for melting things with too much exhaust advance, things like that.
09-04-2011, 06:53 PM
#42
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so i hope you wont mind me cluttering this thread with them
Oval port flanges welded into D-port shape
starting mock up
V-bands
inside the collectors
welds
welded while bolted to an aluminum block heat sink
re-surfaced the flanges after welding
merge pipe
divided wastegate
testing fit
more wastegate stuff
4.5 inch downpipe (up?)
flex sections installed
finished hot side
intake piping and hat, and overview
4.5 inch exhaust to dual 3 inch over the axle duals
finished piping
09-04-2011, 08:29 PM
#44
Staging Lane
Thread Starter
Incredible build!!!!!! Where do you live (how far do I have to ship the car to get that kind of quality)?
What would you charge to build the hotside portion of that build, heads to tail pipes? (just for reference sake
)
Going to look for your thread to get details of the turbo and the performance.
What would you charge to build the hotside portion of that build, heads to tail pipes? (just for reference sake
)Going to look for your thread to get details of the turbo and the performance.
09-04-2011, 09:32 PM
#45
I've contributed more to this sight in any one of my threads than you have in total so please don't take it too personally when I ask you to kindly go **** yourself.
This bullshit thread does nothing but confuse the guys that are just starting out and does not apply to v8's at all.
This bullshit thread does nothing but confuse the guys that are just starting out and does not apply to v8's at all.
Gee I'm sorry I did not realize you were so tough on the internet.
Again another useful post. I never said or implied that you have not given some useful posts and build threads on this site. (I just don't have time to post here multiple times per day) I was just saying that particular post was not useful and really was not needed. If this was a web site that prides it self on flaming like Yellow bullet then by all means flame away. If you had a real reason why this should not be discussed then say it. How will talking about twin scroll steer a new ls1tech member in the wrong direction?
I have my doubts about twin scroll too, but that does mean I should automatically shoot it down. Hell I remember when I was at the track with a 4cyl turbo and every body with a V8 just didn't get it. Why not just run a blower or spray it is what I would get, Now Turbo V8's are everywhere. The point is nothing progresses if no body ever thinks outside the box.
And telling someone to go **** them self over the internet? really?, Grow up. In no way what I wrote warrant that response. I guess you took a little Icon that rolls its eyes personally, lol
I'm done with the conversation I have already wasted more time than I would like on this.
Alright Back on track.
Last edited by Professor_speed; 09-04-2011 at 09:48 PM.
09-04-2011, 10:10 PM
#47
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that may have made sense 20 years ago, but most modern and properly engineered setups operate on roughly a1:1 PR, which mean the engine runs much like it would N/A (which, from what i can tell, is one of the points he's trying to convey)..
09-05-2011, 11:49 AM
#49
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Sorry for coming off as arrogant. Unfortunately there's no way I can hold my own 1 against 100 as it is without setting some ground rules, that I'm not going to dedicate another two hour of my life to this thread when I, actually all of us, should be spending time outdoors, with family actually DOING something. I'm sure you understand no one wants to spend their whole life typing, which would easily happen if unchecked. Furthermore, please understand that this is a thread I started, about a very specific topic, with very clear boundaries (because I know how threads tend to go to crap), and please take notice that others came in here, read a little portion of what I wrote, skimmed the rest, then attacked me from the angle of what's best for their drag racing endeavours, without noticing that I had already stated earlier this wouldn't work well for drag racing. So call me arrogant, that's fine.
09-06-2011, 12:52 AM
#50
Second, pressure ratio has nothing to do with scavenging. Scavenging has everything to do with actual exhaust back pressure which is not the same as pressure ratio as the intake pressure differential doesn't even become a factor until the very end of the exhaust stroke when the intake valve starts opening IF there is overlap. You are mixed up with reversion.
09-06-2011, 02:24 AM
#51
If you can get a 1:1 Exhaust manifold presure (EMP) to intake manifold presure you are doing VERY well indeed! Most OEM setups are anywhere from 2-4:1 from what i have heard. I think compound setups can get below the 1:1 raitio but not really seen any testing done so that might be BS! lol
Chris.
Chris.
09-06-2011, 08:17 AM
#52
Interesting thread Climber. We are actually working on a road race ls powered single turbo suby right now, but it is mainly going to come down to simplicity. We discussed ts for it, but it came back to simplicity and space in the bay as well as time and cost. In the end we are not too worried about it due to running a smallish bw 9179 turbo with a T4 turbine housing on a 5.3 liter. My main fear at this point is choking the motor up top.
That being said, on a large single T6 turbo this could be useful!
That being said, on a large single T6 turbo this could be useful!
09-06-2011, 01:25 PM
#53
Staging Lane
Thread Starter
Interesting thread Climber. We are actually working on a road race ls powered single turbo suby right now, but it is mainly going to come down to simplicity. We discussed ts for it, but it came back to simplicity and space in the bay as well as time and cost. In the end we are not too worried about it due to running a smallish bw 9179 turbo with a T4 turbine housing on a 5.3 liter. My main fear at this point is choking the motor up top.
That being said, on a large single T6 turbo this could be useful!
That being said, on a large single T6 turbo this could be useful!
)... alright enough of my childish drooling on myself. Will save the rest for the big unveil.Back to topic, 9179 sounds like a great road race turbo! I hear you on simplicity. True twinscroll would tripple the cost of my own header build, all so I can make more boost quicker between what, 1000 and 2500 rpms? Wish I knew... Bigger turbo would make twinscroll more worthwhile if driveability is of concern.
If the 9179/9180 you're looking at has the stock .91 divided or .88 undivided, you can upgrade to the 1.00 divided... which is a lot bigger than a S200SX 1.00 because of the ratio... though if it's still not big enough, or if you have doubts, you know who to call (Geoff) and he can probably get closer than anyone else. I don't think the A/R or divided/undivided is the choke point if you're looking at high RPM power. I think the whole turbo is too small for that goal. Why not an S400SX...
91-79:
Top 2.5liters are pushing 400g/s, and you would be doubling the displacement so 800g/s minimum for best possible top end... quick dirty probably inaccurate due to VE differences and the 10 other things I mentioned earlier, but still ballpark calculation. Nonetheless, I think it's a mistake to walk away from twinscroll for a road race car. It will do very little to change costs if you do left bank/right bank split. 1.00 divided vs .88 undivided, you really think you're going to make any significant gain with the .88 up high? I don't, but then your team probably knows a lot I don't, and I would LOVE to hear what you end up going with and your results!
P.S. Other people, where do you guys get these numbers... 1:1 pressure ratio is only going to happen with the most efficient header design that matches the rest of the system, like what a racing team would do since their goal is to maximize EFFICIENCY for the best possible result from the build. I see people accomplish 1:1 routinely, but that's people who have the money and attention to detail to do things right. 1:4 is OEM log manifold territory, though OEMs have been getting a lot better than they use to be. Remember, OEMs determine a power goal and power band that accommodates gas mileage and emissions requirements and a BIG safety factor, and they do the build cost MINIMUM to achieve those goals. So they don't care how crappy their pressure ratio is as long as they meet their goals. Marketing the pressure ratio won't sell any more cars. No one cares.
Last edited by ClimberD; 09-06-2011 at 01:55 PM.
09-06-2011, 02:00 PM
#54
Staging Lane
Thread Starter
Sarg, have you seen Frank_ster's Buick 3.8L swap into his Legacy? He has so much room to the sides of the motor that it's just funny. Running a HX35, tons of driveability...
09-06-2011, 03:28 PM
#55
We actually have 2 cars that are undergoing the swap. The roadrace car is getting the single 9179 with a .91 divided. I am sure we will split it bank 1 and bank 2, but that is not really a good pairing, so in effect it won't really be a true twinscroll...but better than nothing. That is getting a T56 rear wheel drive with a R180 rear diff.
The other will be getting twin 9179's and going for top end with a solid axle rear end and an automatic rwd. Primary will be drag racing
The other will be getting twin 9179's and going for top end with a solid axle rear end and an automatic rwd. Primary will be drag racing
09-06-2011, 04:12 PM
#56
Staging Lane
Thread Starter
We actually have 2 cars that are undergoing the swap. The roadrace car is getting the single 9179 with a .91 divided. I am sure we will split it bank 1 and bank 2, but that is not really a good pairing, so in effect it won't really be a true twinscroll...but better than nothing. That is getting a T56 rear wheel drive with a R180 rear diff.
The other will be getting twin 9179's and going for top end with a solid axle rear end and an automatic rwd. Primary will be drag racing
The other will be getting twin 9179's and going for top end with a solid axle rear end and an automatic rwd. Primary will be drag racing
09-06-2011, 08:34 PM
#57
Spent some time with it tonight. It is going to be hard enough to snake a 2.5" pipe over and then the 3" back without having to do dual 2.25-2.5 inch cross over pipes over and back. The other thing is real estate at the collector location. We plan to do this while retaining AC (it gets stupid hot and humid here in Georgia). That would mean sneaking 2 pipes around the AC compressor rather than one. I am not saying that it is not a cool idea, just going to be a lot of piping going over and back. Here is one we did on a Subaru. We had around 30 hours in the headers and up pipe!
09-07-2011, 02:05 AM
#59
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OK, first, most turbo systems do not run at true 1:1 pressure ratio in competition or otherwise at max effort. I'd go one further and say that it's a very small percentage.
notice how i use the word roughly?
Second, pressure ratio has nothing to do with scavenging. Scavenging has everything to do with actual exhaust back pressure which is not the same as pressure ratio as the intake pressure differential doesn't even become a factor until the very end of the exhaust stroke when the intake valve starts opening IF there is overlap. You are mixed up with reversion.
notice how i use the word roughly?
Second, pressure ratio has nothing to do with scavenging. Scavenging has everything to do with actual exhaust back pressure which is not the same as pressure ratio as the intake pressure differential doesn't even become a factor until the very end of the exhaust stroke when the intake valve starts opening IF there is overlap. You are mixed up with reversion.
BUT i will while it may over complicate an engine bay, its obvious TS has its advantages.. it may not be feasible in most chassis, or fun to work around, but with some creative thinking i think it MAY be worth someones time, depending on what they're planning on doing with the car.
09-07-2011, 06:02 AM
#60
Nope, no build thread yet. We are still amassing parts. We both have our engines and transmissions of choice, but still selling off subaru parts to help raise funds for this project.
Back to TS thread though, if our are making a single TS kit and making your own manifolds it really would not be terrible. You could more than likely run both pipes right next to each other. Extra expense but not a ton really.
Back to TS thread though, if our are making a single TS kit and making your own manifolds it really would not be terrible. You could more than likely run both pipes right next to each other. Extra expense but not a ton really.