:5-bolt housings, but not by a considerable amount. The biggest difference is the wastegate: 25mm vs. 20mm
:The turbine I am using is the same dimensions in both exducer and inducer diameters as that of the GT2860RS (they are both a GT28 turbine, 76-trim) but it has that extra blade and the profile of the blades are slightly different: the trailing edges of the blades in my turbine are slightly more curved. So what you're saying is that your turbine is designed for maximum reponse, at the expense of slightly less maximum flow. This is basically the same tradeoff as going to a smaller housing. So not only do you have the smallest turbine housing, but also the most responsive (and most restrictive) turbine wheel. The housing has been bored out for this larger wheel - it isn't an OEM diameter T22 turbine. The differences between my turbine and the GT2860RS's turbine is small, the housing's A/Rs are similar too, but this is notably changing how the compressor is responding. The manifolds are likely improving that as well.
:Also consider: you are suggesting that my manifolds flow better, which I would agree with. This would mean higher VE, yet, I make more boost: this is contradictory to Scott's original statement that you 2nded. Overall VE is only as good as your worst bottleneck, which in your case is your turbine and housing. :I think the term VE has been used a little too loosely in these exchanges, at least, by Seb. Perhaps we should just use the term "efficiency" and discuss the components.
:An example of this is clear in your statement suggesting that Seb's car has higher VE because of the better flowing .86 turbine housing. I agree that the larger housing flows more air more freely, which will mean higher VE, however, his car makes less power. This is because of the fact that the housing is too free-flowing and too much exhaust energy is passing through the scroll area, compromising flow to the nozzle. So, without the compressor being able to generate higher pressures, you aren't going to make more power although the turbine housing flows better. It is all a balancing act between the components and the .86 is simply too large for our engines (BTW, the disco potato was initially designed for the 2.0L 4-cylinder platforms, which have considerably more exhaust gas flow than our 1.5L banks - the .86 housing works really well on 2.0L engines from what I've been told) I agree that it is indeed a balancing act. I think we need to consider VE both with and without the turbo in the system. It is important to maximize the volumetric efficiency of the system so that when the turbo is added to the equation, it is the only significant bottleneck. Restrictions upstream of the turbine will only serve to lessen the available flow to the turbine. You're correct in saying that it is a balancing act, in that we want the engine to flow, but at the same time we need sufficient pressure drop across the turbine to power the compressor to facilitate this flow. :You made a comment that flow is more important than pressure, which I strongly disagree with: the fact is, you must have both - they are equally as important. Flow and pressure are somewhat correlated, in that you must have pressure drop across the turbine to maximize flow. As we have both agreed upon, it is a balancing act. You can't have maximum mass flow rate without having pressure. Pressure is easier to measure, but what we are really trying to maximize is mass flow :Although his turbine housing flows air more freely, that extra flow is compromising the turbine's capability of generating the higher shaft speeds required to bring the compressor to these greater PRs, and the net effect is that the car has slower boost response and limited peak boost capability. Seb saying that it is all about volumetric efficiency is far too loose of term to use - the real reason is due to the effectiveness of the turbine housing he is using.
:Perhaps this is what he meant, but I didn't get that impression as he seemingly disagreed with my explanation about what is really the cause of his lack of boost - he just generalized and said it is about VE and that I'm missing something. Regardless, I know that I am not missing anything.
:~90% of the differences that we see between these three cars is mostly due to the turbine and housing that are used. There are obviously other components that are different between these cars as well, but their effect is considerably smaller.
:My car made the same power as Dee's car, but, I was running some 28psi of boost and Dee's car did the same power at 26psi of boost. My slightly smaller turbine section is boosting bottom end and midrange performance, but at the sacrifice of some top-end performance. While this is true, I'm perfectly content in giving up a little bit of top-end performance to get better streetability as I built the car specifically to have that kind of response: it isnt like I drive on racefuel all the time anyway so I rarely see the drawback and mostly enjoy that benefit. Sounds like a reasonable tradeoff to me Seb's car using the .86 housing is clearly just a poor match of housing to the engine - that .86 housing was designed for a 2.0L engine. I don't disagree with this
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