When you click on links to various merchants on this site and make a purchase, this can result in this site earning a commission. Affiliate programs and affiliations include, but are not limited to, the eBay Partner Network.
I am quite familiar with Bournouli's Principle. Enough that I understand the operation of a pressure differential system as it also pertains to the turbine. & you're right the housing & wheel determine the required back pressures at certain compressor flow rates.
Distinction here is it is a principle that measures flow differential, not energy.
Link to build thread is in my sig. It's a long one!
I don't' follow this at all? What "differential" are you talking about exactly? List the 2 things we are comparing... And what do you mean by "required back pressures"? The bottle neck determines the system pressure... period.
Originally Posted by gtfoxy
We seam to each have our own experiences.
I've done my own testing as well and once upon a time had a twin system running 2.5" connector pipes off the headers. EGT's were not where I wanted them on pump gas from where I thought they should be, so I went up to 3" connectors & EGT's dropped 150*, went faster & it spooled up faster.
Maybe had I went to larger turbine & maintained the exhaust velocity it sure would have worked out close to the same.
It really mostly matters where you land in the flow & pressure islands on the turbine so it is working efficiently.
For very long piping yeah I agree. You need to maintain a certain velocity, but at a point shortly before the turbo you can transition into a surface area that is closely equivalent to the surface area of the turbos inlet.
I am curious what your combination consists of. I'll check out your build thread.
What kind of power are we talking here? I find it more than a little hard to believe that you maxed out a 2.5" hotside (per bank!) to the point that 3" piping would lower EGT's and improve spool time. I'd have to question the test procedures and equipment.
Guys are literally making 2800++HP 2.5" collectors and a 2.5" hotside piping going to the turbos.
Quillens pontiac is a good example. 482 pontiac, Twin 91mm @ 40+lbs of boost and 8000+ rpm. Note the 2.5" collector, 3" charge pipe, and 90mm TB. 2800 hp. It's the highest HP and fastest pontiac powered car in the world. The way I see it, if there were any HP or spool improvements to be had here with 3" pipe they would run it. Piddly setups like ours should use small diameter pipe IMO.
I checked out your build. Very nice. You have quite a light-weight performer.
The pressure differential i am talking about is the pressure drop across the turbine wheel. That is how it creates lift in the turbine: pressure differential due to flow creating lift. Just like a wing.
The engine was about 650HP on T4 turbos. P-trims if I remember correctly. Old school stuff. All I can say is it worked in that application.
Don't get me wrong, I have always been a proponent of smaller exhaust piping, to a point, back when Korky was making log manifolds for mustang set-ups. Had some good conversations with him.
But maybe Morris should have ran 2" pipe to their turbos on the v-16 rather than the 3" they used.
Light weight is what I was hoping for! With 100lbs of ballast I'm just under 3100lbs race weight these days, no less than most mustang LS builds.
Ok, so we are talking about the pressure differentials across the turbine blade... I still don't see how larger piping would assist in spool? The way I see it, larger piping would slow the flow of air traveling over the blade. This would then create less lift and more induced drag. Just like a plane traveling at slower speeds. This would result in less power/velocity driving the turbo...
As far as I know the ONLY reason to run larger piping is if the exhaust gasses are traveling fast enough to create turbulent air flow. If the air speed goes sonic, it could create enough drag in the pipe to decrease performance. Making the pipe the new bottle neck in the system.
I agree with most of your logic and I am aware of exhaust velocity benefits.
The same benefits on turbo systems still hold true on NA cars. Something a lot of people don't realize is you want the smallest exhaust pipe diameter you can run without increasing back pressure on a NA setup as well. The faster the exhaust is moving, the better the scavenging effect.
So while going to a smaller diameter pipe will help with heat retention, scavenging effects, and spool time due to less exhaust pipe volume to fill, it will not increase exhaust velocity where it matters; at the turbo. What matters leading up to the turbo is not velocity, but volumetric flow rate. The cross sectional area and volumetric flow rate at any given point inside the turbine housing is what will dictate the velocity, not the velocity leading up to the turbo.
However everything you say still holds true about the benefits of smaller diameter piping due to heat retention and less volume to fill, but not because of increased velocity within the exhaust piping prior to the turbo.
I do appreciate your insight and experience in the field. If I can twist my buddy's arm to weld me up a 2" exhaust I will per your recommendation.
Originally Posted by Forcefed86
Like I mentioned earlier, remote mounts tend to be laggy to start with. What people can't grasp is you don't want large piping. It's not an exhaust system, don't think of it as one. 3" piping is way too large IMO and will slow the exhaust velocity WAY down. low velocity gas = slow spool times.
If the factory "Y" is 2.75" it's too large as well. Like I said 2" pipe off each manifold to a 2.25" "Y" then a single 2.25" into the turbo. You want to extend the 2.25" pipe as far into the turbo as you can. Then Slap some 1/8 or 1/4" steel with a 2.25" hole over the back of it weld it all up. The result will be a much faster spooling turbo. Larger pipe pre-turbo isn't flowing anymore than smaller pipe.The turbo is the bottle neck in the system, whether it's in the back or the front doesn't matter. 1 2.25" pipe to the turbo will support 600whp on that setup.
I get wanting to use factory equipment though. If that's what you have and don't want to get involved in making a better system, go for it. Wrapping helps, but you defiantly don't want to go larger that the OEM piping.
You have done a great job. You're getting the converter loosened up aren't you?
Look at it like this, some wings make lots of lift at lower air velocities while others create lots of lift at high air speeds. You don't run an old 40's bomber wing at mach 1 air speed.
On a side note I am fixing to buy my wastegates. I want to run two ebay wastegates (in case one fails). Does anybody know which off brand ones have interchangeable springs and diaphragms with the name brand ones?
I think $300 is fair. Also different areas vary a ton. I ended up driving to Kansas City for engines and transmissions the last couple times. 3 hours drive is worth saving some cash.
I am planning on buying one of those oil filter adapters for the oil feed. does anyone have any suggests on which to buy or maybe a different way to pump oil to the turbo?
Forgive me of im wrong, but don't you want a sandwich adaptor that's not thermostatic? Otherwise it's only going to provide oil at a certain temp range right?
Here is a little update. I have purchased most of my turbo build parts. The parts that I still need to purchase are a map sensor, oil hard line, cold side charge piping, tuning software (most likely HPtuner pro), and a wideband 02 sensor. I will post pictures of the welded hot side and various other parts tonight.
