We're these outlets flow tested? To me they don't look restrictive but I'm no expert. If they were flow tested you could compare the tests, stock, silicone, vs aluminum?
VTT
- Thread starter buster84
- Start date
We're these outlets flow tested? To me they don't look restrictive but I'm no expert. If they were flow tested you could compare the tests, stock, silicone, vs aluminum?
Don't mind Rob he's been on a VTT bashing roll lately 
Rob@RBTurbo
Lieutenant
Buster,
It doesn't take a flow bench (or a rocket scientist) to understand that two 1.5" tubes merging into a single 2" (or 2.25") tube and THEN tapering to a 2.5" tube is going to pose a restriction over one that is two 1.5" tubes merging into a single 2.5" tube (ie. PSP). These things only takes basic understanding of performance design.
FWIW the OEM outlet tubes are about 1.5" with a semi-reasonable merger into a single 2.4x" tube- the biggest improvement would be in optimizing the merger (not the opposite).
Rob
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Just an FYI @Chris@VargasTurboTech & @Rob@RBTurbo, credibility goes down not up with these kinds of posts. Same for sales.
Filippo
Filippo
Rob@RBTurbo
Lieutenant
Filippo,
Just as FYI for the future we (RB) literally care zero about how these kinds of posts come off, so if John Consumer does not like the truth (as obvious it otherwise should've been) it is what it is... and rest assured for every one who doesn't agree there is another 2+ who do and appreciate the information.
Rob
Just a side bar - there is no way I could ever expect to be successful as an IT consultant with the level of "honesty" some vendors out here have. I do love the bravado and the set of balls these guys have, but damn..... It's like Coke having a commercial that says "Pepsi sucks"...
welcome to the N54 scene. you'd be hard pressed to find a vendor who doesn't do this, they are few and far in between.
it's gotten to the point where if I ask for a product recommendation and a vendor comments, I ignore them and bump the thread.
Rob@RBTurbo
Lieutenant
It's more like Pepsi finding out a batch of their own product was made from Horse Piss, and rather than tossing it out they decide to label it and sell it anyway. Then Coke finds out and tries to warn others about it, and some decide to observe closer and intelligently pass while some others say "I trust Pepsi" and decide to drink it anyway.
These guys are not dummies and they both clearly know this was a very poor design. It's not even part of their prototype as seen here:
https://bmw.spoolstreet.com/threads/2018-vtt-new-product-release-thread.2791/
Unfortunately when you deal with outsourcing overseas many times what you send in as a sample/drawing/idea/etc is NOT exactly what you get back, it can be very consuming in time/money to do the rounds to get it all ironed out. So it is most likely their first batch was a bum deal and something they'd decided to pass along as product to the consumer rather than pushing it back. Honestly we'd be willing to bet it has already been a discussion piece for them with the manufacturer. In conclusion you can mark these words: You will see that taper disappear in future batches...
Rob
The nerd in me wanted to work out the math on outlet diameter rather than just "bigger is better" or "these are good enough". Take all this with a grain of salt though as there are some assumptions.
I'm far from an engineer, so if someone has better assumptions for some of this, please correct it. I found that the ideal speed to stay under is .4 mach, or 304 mph to prevent the air from getting too turbulent and losing efficiency.
The speed in the pipe is affected by its size, and CFM. Using the 1.5" pipe, we find that the .4 mach limit is reached at 330CFM of airflow. Using a ballpark 15CFM per lb/min, we arrive at 22lb/min. On Ethanol fuels, you can typically achieve 10whp per lb/min, so 220WHP per turbo. This would mean that 440whp is about the limit of where efficiency lies with 1.5" outlets.
Moving to 2" inlets, .4 mach is reached at 585CFM, or 39lb/min. per turbo, or 780whp total. It appears that there is a benefit (however much that is could be questionable though) to running larger diameter outlets.
The assumptions/generlizations made are also for a smooth pipe with few bends, i.e. "ideal conditions."
I would think most hybrid twin setups would benefit from 2" outlets.
I'm far from an engineer, so if someone has better assumptions for some of this, please correct it. I found that the ideal speed to stay under is .4 mach, or 304 mph to prevent the air from getting too turbulent and losing efficiency.
The speed in the pipe is affected by its size, and CFM. Using the 1.5" pipe, we find that the .4 mach limit is reached at 330CFM of airflow. Using a ballpark 15CFM per lb/min, we arrive at 22lb/min. On Ethanol fuels, you can typically achieve 10whp per lb/min, so 220WHP per turbo. This would mean that 440whp is about the limit of where efficiency lies with 1.5" outlets.
Moving to 2" inlets, .4 mach is reached at 585CFM, or 39lb/min. per turbo, or 780whp total. It appears that there is a benefit (however much that is could be questionable though) to running larger diameter outlets.
The assumptions/generlizations made are also for a smooth pipe with few bends, i.e. "ideal conditions."
I would think most hybrid twin setups would benefit from 2" outlets.
You're kidding right?
They look perfectly fine to me, stacking is spaced correctly and the bead is even. Armchair welder much?
You're kidding right?
They look perfectly fine to me, stacking is spaced correctly and the bead is even. Armchair welder much?
What do you think of the weld on the inside of the merge?
Rob@RBTurbo
Lieutenant
The only upgrade we see is that it is powder coated black- which is pretty neat. Performance wise a total waste IMO as the OE merger looks much better, compare yourself with the pics attached.
Rob
Attachments
Rob@RBTurbo
Lieutenant
There is always going to be something to dispute with sizing along with conversions, etc.; but if you go right off your beginning 330cfm per 1.5" pipe @ .4 mach limit and use this calculator below each pipe should be good for about 475hp (950hp for 2 1.5" tubes).
https://www.gregraven.org/hotwater/calculators/airflow-hp
Now surely this is a bit optimistic, but it is likely your ballpark conversions are not quite accurate either. IMHO primary sizing somewhere between 1.5" and 1.75" is most ideal with smooth bends and a nice merger for this application, while it is certain that 2" is way overkill. This is based mostly from studying other production turbochargers, their outlet sizes vs. power ranges, etc.
Rob
We can agree to disagree, but the calculator you linked and the CFM ratings you are using look like they are for cylinder head flow, and usually NA. I recall a general formula for cylinder head CFM to Horespower that I used back in the ole NA V8 days as (max head CFM * .25 * # of cylinders. Using the 330CFM value, that calculator you linked would be accurate for a 6 cylinder NA engine.
While CFM is airflow and lb/min is mass flow rate, you can convert between the two when using some assumed values. The general multiplier is .069, so 330cfm is 22lb/min. You've got some wicked tricks done to those RB turbos if you're getting 950HP from 44lb/min, that's for sure. Can we agree that you aren't getting 950HP from 44lb/min? Maybe not, but if my assumptions are not quite accurate, your aren't even in the same league, much less same ballpark.
If so, then we could possibly agree that you need ~ 60lb/min for 600whp, assuming 10whp for every lb/min, which is ballpark for ethanol. So you need 30lb/min per turbo, or 434CFM, which is past the 330CFM point of turbulence with 1.5" outlet pipes.
That's not to say that 1.5" pipes won't work, just that 2" pipes would be more efficient at the higher power levels.
The .4 mach assumption is also with ideal flow, few bends, transitions, etc. So you'd want to lower that number for pipes that don't meet that criteria. Since that's unlikely in any scenario, it's better to upsize earlier.
Rob@RBTurbo
Lieutenant
Have lots of turbo orders to fill and not enough time to argue online about google calculations but if you are looking for 1000+rwhp on a twin setup, then would agree that 2" outlets per turbo would be about right. On these cars with ~1.1" compressor housing outlets especially, 1.5" is quite sufficient. Those N54 setups with the Native TD04 Compressor housings (such as RB EVO's), even then 1.75" is beyond capacity and otherwise perfect.
Would suggest looking less into google calculators and more into some of the big dog setups, ie. AMS/GTR/Porsche, etc. These setups are built by accurate calculations and more importantly much experience.
Rob
Do you even science bro?
Seriously - If you like em, buy em. If you dont its for a reason. Im RHD so these aren’t an option Probably just make my own TBH. It’s not that hard.
Seriously - If you like em, buy em. If you dont its for a reason. Im RHD so these aren’t an option Probably just make my own TBH. It’s not that hard.
I'm really wondering how much velocity loss from say the 2" outlets would matter when people have 3" inlets and outlets at the intercooler and 3" charge pipes. I'd just look for the best merge personally.
