I was hoping to get a better answer in this forum from a technical side of things.

My hotside is built as the following... Stock forward facing manifolds with a 1 7/8" diamter outlet. This feeds into a short piece of 2" ball flange, and steps up to 2.5" for the rest of the hot side. The two hot sides merge together right at the turbo. There is only a 3/8~1/2 area where the division wall of the two hotsides stop, and the division wall of the T6 housing begins.

Unfortunately due to packaging, I really can't get the wastegate feed right at the merge. It will end up being approx 4"~6" down stream on the passenger hotside pipe only. I should be able to get a decent approach angle at that point. I will be using 2.5" to feed a 60mm Xo2 wastegate. My question is'¦ how can this effect the system?

I am an engineer, but NOT a turbo/turbine/thermodynamics expert at all'¦ My view is this'¦

The turbo works off mass flow (not so much pressure differential). If mass flow is bled off only one side of the engine, the total mass flow to the turbo is still reduced. My guess is that the turbo doesn't even really know where the mass flow was lost upstream, it just "see's" less over all mass flow. In this case I don't think it would really effect the turbo at all. The only thing I could see is that if you needed to wastegate off MORE then just one full bank of gas, then you may not be able to control low boost levels.

But I can't believe that I'd have to wastegate such a huge amount of mass flow would I?


My other concern is how this would effect the tuneup. In this case, the passenger side may have a lot lower backpressure in the system with the wastegate only on one side. I'm wondering if this will allow one bank of the motor to run leaner then the other bank? (less residual exhaust gas trapped from lower backpressure/better flow)?

I know this is pretty technical'¦ but that's what this forum is for right?

 

I've seen some people say an imbalance of piping caused issues, which I'm not too convinced about, but at the same time I ran dual 1 3/4" pipes to my 60mm wastegate for a nice balanced setup and it seems to work just fine.

 

That's what I'm trying to understand. I've seen people say it before too, so I'm just wondering if there is any truth to it or not.

Thanks for the suggestion of running two WG pipes to a single WG. I might just do that...

 

Im sure its not the proper way to do things , but I tried it on my capri ( 351w s475 ) and it works just fine! It will hold a steady 6psi. up to 6k I havent seen any boost creep.

I thought about starting a tubo mythbuster thread about my car... vented one side wastegate, twin 3in. downpipe under the stock k-member, chinese wg and bov ect... but I dont have time to argue with everyone, Im always out driving my car.

 

1) It IS possible to have cross talk between Turbos feeding into a common plenum. This is more of a Compressor Side issue with one turbo not getting the same mass flow discharge as the other turbo due to plumbing issues on the inlet side, etc.

2) You can sometimes "fix" the cross talk by how you plumb the discharges into the plenum/ throttle body.

But back on the waste-gate question.

Agree that exhaust mass flow will go down from any opening in the system. If the plumbing is a consistant size for both units to the waste-gate, it should not be an issue. We had a car years ago Monza with SB Chevy that would run 8.40s and it used a single large wastegate on the passenger side of the engine with a cross-over of exhaust from the driver's side. No issues. The waste-gate(s) is/are also controlled by manifold pressure on the intake for the most part so a small difference in the exhaust pressure on the underside of one of the waste-gate valves will typically not be noticed.

Just my observations, after 34 years of doing this stuff.

Tom Vaught

 

I have been told that if its not balanced, the motor can wear unevenly, as one bank is making more power than the other (probably more significant in higher hp apps).

 

It is true that one bank will make more power than the other, but I'm hesitant about the "wearing unevenly" part, at least to a level that is of any concern whatsoever. Every piston in every engine, as well as each bank, rod journal, any way you slice it, makes different power than its brethren, due to compromises in intake piping (especially low-rise dual plane types, which sport significantly different flow and fuel distribution characteristics runner-to-runner), exhaust piping, different clearances between parts, etc.
If the gate is placed on one bank or the other, and they merge a foot or so later, I really doubt the backpressure will be more than a couple psi different between the two. I don't think that difference is enough to cause a significant imbalance in engine wear.
Maybe if you drove the turbo solely off one bank, and just stuck a regular header on the other side.
I'd be interested to see some backpressure datalogs for a biased-wastegate setup, one for each bank.
I think it is a good goal to strive for symmetry between the banks, as well as individual runners - but it isn't a requirement.

 

I was really wondering more if it would effect the tuneup too? If the backpressure is different, then the residual exhaust gas in the chamber is different, and the fuel required on each bank is probably different.

i know E85 is pretty forgiving anyway, I was just wondering in general if it was a big deal or not though.

 

95mm Renegade tore his motor down (after his first build) and it was worn unevenly due to drastically different hot side pipes on each bank......If you making 2000hp, and one bank is only making 800, the other one has to be making 1200hp.....I'm pretty sure 1200hp wears a lot faster than 800hp.

 

Worn how? The rod bearings on one side were all worn more than the others? Pistons took a worse beating on one side?

The only way I could see one side of a motor wearing worse than another side is if, on a twin setup, with twin wastegates and no cross-over tube - something was really wrong with one turbo or one wastegate. Or, like Tom said, if you had one really FUBAR'd charge pipe (creating a horrendous restriction undue to the other side, and ultimately a restrictive side of the motor, and then building destructive heat). I think this would be pretty hard to do, but not impossible, of course.

Outside of something like that - like Tom brought up, the intake manifold draws from the same source....the mass entering each cylinder is about the same (unless there was a REALLY bad backup, and you'd know pretty quickly if there was - ever driven a car with ONE rounded exhaust lobe or a broken exhaust rocker?). The mass of the exhaust gas must then also pretty much be the same (from cylinder to cylinder) on its way out. Since motors have a hard time creating matter (like the rest of the universe), one side of a motor can't produce more exhaust gas than the other. On a single setup, once you're out of the scavenging zone (say, a few inches past the header collector), the WG can go wherever you need it to be - the pressure will equalize inside the pipes.

 

This was his hotside setup trying to make 2000+ hp. I'm not sure which side of the motor was more wore out or how, but here was his old hotside:

#ad


And his newest hotside which is almost perfectly symetrical:

#ad

 

If *destructive heat* is being built in one pipe vs. the other because of a combination of being at the limit of 3" pipe (?) AND a pile of tight 90s on the driver's side AND an almost dead end of a merge at the turbo, which is causing stuff on one side to nuke faster than the other, then okay, makes sense. But it's not because "one side of the motor is making 1200HP and the other is making 800."

 

To the O.P., here's the "money where my mouth is" - Mike's WG is located just past the passenger side header collector, for mega convenience / clearance. No troubles at all holding down 7psi on the street or running 146mph (so far) out the backdoor.

https://www.theturboforums.com/smf/index.php?topic=108794.0

 

Re: Re: How does Wastegating only one side effect the system?

No offense but you're really comparing apples to oranges. Phil's car is trapping at least 60 MPH higher in the quarter. I really don't think any kind of accurate conclusion can be drawn when comparing a 900 hp car to an 1800 hp car. I would assume that his issue was due to backpressure differences from one bank to the other. As far as the old merge, it was far from perfect but it was considerably smoother than how it looks in that picture.

Regardless, I really don't think it's going to have any noticeable effect on a typical setup. Phil's car still ran an amazing number with his old setup and as far as I know it never grenaded the motor due to the turbo system, it just wore unevenly.

 

Re: Re: How does Wastegating only one side effect the system?

None taken, but - are you saying you're on board with the "1200/800" theory? And that the laws of physics somehow change when you start making over 1000RWHP? Someone had better call NASA.

And what does everyone keep talking about with the uneven wear? Worn guides? Wrecked rings? What was "worn?" Again, any "wear" would be from destructive heat and not because the motor is "half and half." If the "1200/800" scenario were somehow true, what would happen to the air/fuel ratios between banks? What would 200HP worth of missing air, or extra fuel, do to a motor? (Unless you were able to tune each cylinder individually, in which case you'd know for sure you had a problem.)

 

Re: Re: How does Wastegating only one side effect the system?

No, I'm not on board with the 1200/800 theory. I can't remember exactly what the wear was, I think it was bearings. Maybe more wear on the rod bearings on the bank that had higher backpressure? I don't know, I guess it's a possibility. Again, this is only in a max effort deal and it wasn't like it was so severe it trashed the motor. The car was tuned with BS3 so it's possible it was tuned cylinder to cylinder. Could it have been a fluke? Sure, but it could also have a real, preventable cause. Either way, I wouldn't be concerned about it in anything but a full blown, max effort race car where things are more easily packaged. In a street car, just do what's easiest.

I think he's a member on here, maybe he'll jump in and explain what really happened.

The more I think about it, the only thing I can come up with for a cause is a backpressure difference.

 

Cool. Hey, do you have a RWHP build? I'd like to check it out.

 

*a link to your own 1000 RWHP build - sorry, on my phone

 

Re: Re: How does Wastegating only one side effect the system?

Nope, never had a car with anywhere near that much power. My only turbo car made around 500 and all bearings were virtually identical when pulled apart. The hotside was far from symmetrical and the wastegate was on the short side of the crossover. I'm in the middle of an LSx in a Tbird build now that should make close to 1000 but I'll just have to wait and see. I'm not even slightly concerned about symmetry or wastegate location on this either.

I had no intention of starting a pissing match or argument over this, you've built much more impressive cars than I have. I was simply trying to say that it's possible that it could potentially have a negative effect, although probably nothing worth worrying about on this particular build. There has to be some explanation of why wear was different from bank to bank on that motor but it probably doesn't make a discernible difference in something that's not on the ragged edge all the time. With a goal of 600 to the tire, as posted in his other thread, just set everything up in the simplest, cleanest way, it's not going to make a bit of difference.

 

I am confused why a WG on one side changes the backpressure a cylinder will see from bank to bank. Why would the pressure differ? Wouldn't the pressure be the same anywhere in the system?

The pics posted looked to me to have a tight bend right off the collector and tougher route into the turbine than the other.