Originally Posted by davidbuschur

The new turbo has more surge than the old style 35r. BUT when we tested the HTA35r it had no ported shroud on the compressor. Now it does, that is why it was sent out. It's in this thread actually saying all this.

Originally Posted by davidbuschur

The turbos are not ready yet but this is not going to be a long wait.

PM me if you have a turbo kit you JUST bought and is NOT on the car yet. I would take back the normal GT35R and some cash for the new one. DON'T do anything yet though, I don't know what the price difference is, no idea at all. It may not be worth it to you.

This car was obviously run on C16, atleast obvious to me. So no this is not pump gas.

Why do I shut it off at 7,000 rpm. Let me explain briefly. How many dyno runs are on YOUR car? Mine has hundreds. How many other shops do anything like this other than me? Uh, basically none. I am on the dyno beating the **** out of my own stuff constantly. So now for the actual explaination. Two things wear an engine out quickly, boost and RPM. Seeing as how I am constantly dyno'ing this car, driving it and racing it I really have no desire to swap engines on a regular basis. How high do you want to see a dyno graph, 10,000 rpm? The engine will do it. If I did it for the last 100 dyno runs, the track runs and every time I drove it it would simply wear out. I have no desire to do that. If you'd like higher RPM results please bring your car by, we'll put the parts on your car and I will rev it as high as you like as many times as you like I ran the car higher a few of the runs. The curve goes flat just as you can see it doing at 7,000 rpm so there is no need to go higher, it is at it's maximum power there and stays at the same point.

I swear no matter what I take time to do I get ****ng harrassed here. It will be interesting to see what the Subaru guys think of my testing on the Subi's.

Originally Posted by 240Z TwinTurbo

Always good to see new wheel combinations and the results look good. Question, how do your reduce backpressure(besides clipping) when the turbine wheel/turbine housing remain the same?



Here is where I get excited, an opportunity to learn. Again, regarding the backpressure, how can you reduce backpressure without changing turbine housing or turbine wheel?

Originally Posted by 240Z TwinTurbo

Intuitively, this condition will create the double whammy. If we think of the turbine wheel as a pump, if you were to reduce the shaft speed you effectively reduce the flow. The reduction in shaft speed(flow potential) should cause additional increase in backpressure on top of the fact you are making more power, thus generating additional exhaust flow and increased backpressure.

I would agree that with increased compressor efficiency you can potentially decrease shaft speed and generate additional efficiency/flow. However, without touching the turbine side you have not increased the total efficiency of the turbo.



I know you are just quoting, but as I read this I say to myself, "Am I learning something new or did I just lose 3 IQ points?" I am not familiar with his reference to "pressure head" although I know those words and their meaning individually. I even passed this by my turbo guy and he is at a loss. If you truley observed this occurance then their should be a plausible explanation. I will do some digging and post my findings.

Originally Posted by 240Z TwinTurbo

Again, I agree this is not a scientific community, but it is a "Technical" forum. I personally have not asked for any information regarding the compressor wheel nor do I plan to. It is clear that even Buschur doesn't understand how backpressure was reduced as he quoted his "Turbo Guy." If Buschur wants to come on the technical forum to sell product and make certain claims, then it is to be expected that "Technical" questions are asked based on those claims. Otherwise post in the classified section.

Originally Posted by discopotato03

Hi all , just thought I'd air my thoughts on compressor wheels and how they effect a turbo's boost threshold .

Most people agree that using a larger diametre and or trim compressor wheel makes for a higher capacity pump . So pumping a greater mass or weight of air means that the wheel has higher power demands than the previous lower capacity pump . So this now means for a given exhaust gas speed the rotating assembly spins slower which adds up to extra turbo (turbine) lag . With exhaust gas velocity rising and the turbine speed not rising as fast as it could/should I reckon gasflow throught the turbine housing would have a little more restriction .

I believe its possible to go the other way with some turbos and use a slightly smaller trim version of the same family compressor wheel which basically gives the existing turbine (and available exhaust gas energy) a little less workload so the whole rotating assembly tends to want to accelerate more easily and the transients should improve as well .

Some will have noticed that amongst the Garrett GT BB range there are optional compressor trims of basically the same theme ie 48/52/56 trim GT2871R's and GT3076R/GT3037S's and the GT2835 series also in 48/52/56T .
The GT3582R (AKA GT3540R) I believe has only been sold in two forms ie the HKS spec GT3240R and the Garrett marketed GT3582R .

The GT3240 appears to have a cropped GT35 turbine to get it approximately GT32 turbine dimensions . Its compressor wheel is the 54 trim version of Garretts 82mm GT40 or BCCW-18C . The GT3582R uses the 56 trim version of this compressor family .
As far as I can tell it has been available in 50/52/54 and 56 trim sizes from turbos like Garrett GT4082 and HKS GT3040 (50T) , Garrett GT3782 (52T) , HKS GT3240 (54T) and the GT3582R and GT3782R I believe use the 56T wheel .

If I was trying to get a little better response from a "GT3582R" I would be trying the 52 and possibly 54 trim versions of this same wheel family . To make it really punchy it would be very easy to take a HKS GT3040 and exchange the turbine/heatshield/turbine housing for the GT35BB bits . The compressor bore would need to be reamed because the GT30 turbine shaft is slightly smaller than GT35 (where the compressor fits) so would need to be resized and balanced .
A problem exists if you use the bush bearing 50 and 52 trim wheels because their bore is larger than the GT35 BB turbine shaft so may need to be bushed which is not easy , also backspacing is different so machining required .

Also its just possible that Garrett may be making an 82mm version of the C117 series compressor ie same family as the GT4088R uses but in 82mm instead of 88mm . The Cummins upgrade turbo (GT37R Stage 1) I think uses a C117 series compressor in I think 82mm 50 trim . These wheels are 7/14 blade designs and usually in smaller trims ie 50/52 rather than the GT40's 56 trim . I suspect that the extra pair of blades and smaller trim sizes have a lot of say in the workload/shaft speed/airflow stakes .

Food for thought .

Originally Posted by 240Z TwinTurbo

Compressor efficiency and shaft speed
It is possible to have a more efficient compressor that will increase flow with a reduced shaft speed. This concept was a given for me.

Term "Pressure Head"
There are several formulas/meanings of "pressure head" as it applies to fans, compressors, etc., but in this case it can only be applied to the compressor wheel and "pressure head" does not translate or affect performance on the turbine side as nothing on the turbine side was changed.

You can easily do a google search or pick up your old physics book to better understand this concept as it applies to this scenario.

HP and BackPressure
With all else remaining equal, an increase of hp will generate additional exhaust flow and only have the potential to increase backpressure.

Shaftspeed and backpressure
With all else remaining equal, reduce shaft speed and you reduce the flow. Not a hard concept to understand. Turn a turbine faster it flows more, turn a turbine more slowly and it flows less.

=========================

Based on the scenario and information presented, the reduction in backpressure does not appear to be plausible.

The turbo gods have spoken

Originally Posted by MalibuJack

Spoken like a true engineer.. This is the difference between learning from experience and from textbooks... There are always situations where the math says something shouldn't work.. And it does.. I'm more inclined to believe David's trial and error data before someone with an unknown reputation.

David does admit when something he is testing isn't working out as planned. Only nobody has waited long enough for his final results.

I've learned over the years that people who are very caught up in terminology and math, have very little actual experience doing this sort of work. At least in forums, its very easy to rattle off a bunch technospeak if your talking over the heads of your peers. He may be onto something, he may not, but he feels that he has something new to offer, and we'll learn about it soon enough. I'm more inclined to believe his results over your googled quotes.

What have you offered the community?

I don't mean to be harsh, but I consider myself a redneck engineer most of the time. I doubt many people would argue that I do understand what I'm talking about even though I treat everyone as a peer and not talk over their heads whenever possible. Dave is the same way.

Originally Posted by 240Z TwinTurbo

My mother always told me it isn't polite to tease the animals at the zoo. I guess I should stop throwing rocks at the monkey cage.

As far as turbo gods, we called the head engineer at Garrett and explained the scenario as well as read your response. They were at a loss to explain how you could have decreased backpressure without changing a single thing on the turbine side. Backpressure is created by the restriction on the turbine side and none of that was changed. Even more at loss to do this while decreasing shaft speed, which further restricts the turbine side. Anyway, I read your explanation and choose not to drink the punch.

Here is how I would suggest that you market this turbo...
GT3582PHT (PHT=Pressure Head Technology)

Originally Posted by sparky

Here we applied a somewhat broader definition of backpressure as being any restriction of airflow which causes reversion within the system.

Originally Posted by trinydex

you have a doctorate in engineering and you don't know the answer?

more efficient comp wheel means you flow more air at a lower shaft speed. refocus to lower shaft speed on turbine side. build up of air due to more hp as you said. spin turbine faster, more horsepower on the comp side as it's able to flow because it's more efficient. the turbine is under LESS LOAD BECAUSE IT'S MORE EFFICIENT!!!!!! (this is where lowered back pressure comes in) efficient compressor is NOT JUST flow more... it's FLOWS EASIER. this is something entirely to do with matching both sides.