240Z TwinTurbo

iTrader: (25)

Great, I get to spend more money on a Tial BOV. I went to the hardware store and purchased a 3/4" pipe end cap for $0.35 and shoved it into the BOV tube. It fit snug so I was sure it would stop any boost from getting to the BOV and then reassembled everything. Well, results are below....

CO_VR4

iTrader: (83)

That's the practical result because the waste gate is primarily diverting flow from only one cylinder and the other cylinder is not getting diverted much, if at all. That affects the back pressure in both -- one will be "over diverted" and have more "negative" pressure, while the other will have little or no "relief" and have the maximum back pressure. The "overdiverted" cylinder will have much less backpressure to cope with (while the wastegate is open) and will have a corresponding comparable "lean" condition because it will get more air for the same amount of fuel. The "underdiverted" cylinder can get the opposite effect -- higher backpressure causes (1) reversion of exhaust gas, (2) more difficulty in scavenging the exhaust out of the cylinder and (3) more difficulty in getting the new intake charge into the cylinder during overlap. That's the basis for the AFR differential comment. How much it will change can only be measured if you had pressure sensors in both, or O2 sensors in both, but it is well known that individual cylinders can and do run different mixture ratios, and many sophisticated ECUs on race cars monitor this and modify fuel to equalize for it.

That's not a knock on the OP at all -- it's just an effect of the geometry that was chosen for this particular fitment.


You can look at any fluid dynamics text and see that if you introduce one (or in this case, two) cross flows across the main flow it will disrupt the smooth flow of fluid down the downpipe. The greater the angle of cross flow, the more disruption of the flow out of the turbine, and the greater the effect on the backpressure before the turbine as the result. That's why a dump tube which is not recirculated generally gives greater horsepower, and also why (generally) the further away from the turbine a recirculated dump tube rejoins the downpipe, the better...

sparky

iTrader: (1)

I agree with the above and the reasoning behind it. Thanks for illuminating, CO_VR4! .

03whitegsr

iTrader: (8)

Looks like the BOV might have been your HP wall that got you to build the manifold?

The before and after is looking pretty good. Maybe it's just the difference in the manifold alone and not a twinscroll vs. single scroll issue...but it's showing what a few have been saying about TS setups for a while now. People ***** about torque drop up top on TS setups, but the TS setup makes more peak torque at a given boost level and then similar top end. Yes, torque drops more relative to the peak torque value, but the whole curve is higher then the single scroll setup.

sparky

iTrader: (1)

I have more difficulty getting onboard this train of thought. You are referring specifically to the gating of cylinders 1 & 4, correct?

Supposing that the gate is positively closed, the internal pressure within each of the two runners should be identical. Are you suggesting that once the gate opens, the pressure loss across the two manifold runners would not be equal?

So, in your opinion, once the gate opens, would only the rate of loss be unequal? Or would the lowest level of pressure reached, also be different between the two runners?

sparky

iTrader: (1)

He could test out the leaky DV theory by either inserting a block off plate between the base of the valve and the flange, or simply by flipping the orientation of the DV.

03whitegsr

iTrader: (8)

Automotive manifolds are not a constant pressure system. They deal with pulses, just because two runners are connected to the same collector DOES NOT mean they have the same back pressure in them when it actually matters (blow-down and during overlap conditions).

During high wastegate flow conditions is likely when there would be the biggest issue as exhaust from cylinder #4 is likely going to try and go up runner #1 to the wastegate. This leads to exhaust gas with inertia heading straight back to cylinder #1. Like I said earlier though, crank up the boost and dial out the overlap to avoid reversion and let the turbo do the work. That HTA compressor is good to like 4.5:1 PRs, it can handle it.

sparky

iTrader: (1)

Hmmm? Wouldn't it be just as likely that exhaust gases exiting the gate would be traveling toward an area of lower pressure altogether, such as the DP?

sparky

iTrader: (1)

Should we then make a distinction between equal length manifolds as opposed to manifolds incorporating different runner lengths? Does this hold true for all manifolds in general, and if so, in what way does the manifold in this thread differ from manifolds in general?

Is the pressure differential due solely to the differences in distance from the exhaust valve to the wastegate? Or, is the directional flow path to the collector also a factor?

03whitegsr

iTrader: (8)

Absolutely. If the wastegate didn't offer a lower pressure outlet, exhaust wouldn't flow that direction at all. With pulse flow though, you have inertia to go with the mass flow. If you had 2 cylinders moving air at a consistent rate into this manifold, you wouldn't have flow from #4 trying to go up #1 runner past the wastegate as you'd reach a steady state condition that minimized energy and going up the runner doesn't minimize energy.

With pulse flow though, minimum energy some times means air going the wrong way up #1 when the exhaust valve is closed. It's not just pressure pulses either, it is mass flow. Dynamic energy eventually changes to potential energy as the exhaust from #4 crashes into the closed exhaust valve of #1. Potential energy being pressure. If it arrives at a time when #1 exhaust valve is just starting to open, or when it is closing during overlap, that pulse is going to have a negative impact on the in cylinder conditions in #1.

Don't think this only happens with this issue though. This is how motors work either way. Difference being the degree to which the exhaust ends up backflowing up the runner.

Equal length doesn't make the manifold equal pressure.

Really, all automotive manifolds operate some where in between being constant pressure and pulse-flow. A log manifold is pretty close to constant pressure. A long tube, equal length, shallow angle merge collector setup is pretty close to a pulse-flow manifold.

I would say the manifold in this thread leans towards the constant pressure side. However, it is the wastegate placement that is the topic of interest, not the runner/overall design. If the wastegate was off the collector, there would be less concern (to a degree) of exhaust reversion.

eTiLiKo

iTrader: (1)

240Z, what's the spec of your engine?

sparky

iTrader: (1)

To dispel , or verify the alternate assumptions and postulations(mostly my own crackpot material) as set forth above, we would need to measure and compare the pressure at the exhaust port outlets of port 1(A) & port 4(B) at the cylinder head with the pressure at the waste gate exit(C), comparing the pressure drops from points A & B to those at point C. I am pretty sure that no one is going to do this just to satisfy my idle curiosity.:

240Z TwinTurbo

iTrader: (25)

IX Stock long block, stock cams, stock intake, stock tb

DIY COP, IC Pipes, 24x12x3.5" Garrett IC by MP FAB, 3" exhaust with CAT, Perrin Intake filter, custom intake tube

short runner TS tubular header (large runner - 1.5")

eTiLiKo

iTrader: (1)

Thanks. Not to bad in spool on a IX, curious to see how it reacts on a non MIVEC evo.

240Z TwinTurbo

iTrader: (25)

Thanks and definitely a good question. I think the big question that will remain unanswered for some time...what is the real benefit of this setup. Will the 1.06 a/r T4 TS outflow other comparable turbochargers for higher boost applications on built motors based on seemingly good spool characteristics? I think the other potential advantage is that I now have a platform for future turbo upgrades based on a t4 TS platform. Of course this will be limited by compressor housing sizes, but I can fit fairly large wheels in a T04S housing.