str8dum1

iTrader: (11)

Ya, the t25s push the powerband to the left which is great for that mid 600 car. But for the guys with true gt30 or bigger turbos, you have to wonder how much that limits the potential. Goes back to the old saying - pick the smallest turbo that does the job. I think that the 3071s might be the biggest you can go with a T25 and not have much left in them when you string them out. Of course, thats my nonscientific guess

I think a large gt40 framed turbo with a quick spool valve would be the deal. Biggest set back is the fabrication costs to essentially making a custom single kit and the sacrifices involved (removed radiator support, maybe lose accessories...).

In the end, you might still have a car with similar dyno curves to a pre-fabbed twin kit but at alot higher cost.

rcdash

iTrader: (18)

Don't get Terry started! I bet he's thinking how hard it would be to machine and port match that cast iron manifold outlet and turbine inlet. lol.

ttg35fort

iTrader: (2)

That looks like a sweet setup.

ttg35fort

iTrader: (2)

I already hit Roger up with that. He laughed.

ttg35fort

iTrader: (2)

Yes, GTM uses the T25 flange on their exhaust manifolds.

Mike, it does not appear that Garrett makes the GT35 turbos with the T25 flange. I think the smallest is the T3 flange. What exhaust manifolds are you running?

XKR

iTrader: (1)

Guys.....clearly understand what you all are saying about T25,T3 and T4.

I could have went with SFR or SP turbo kit instead of GTM.. But my car will be a multi-task setup.....not drag racing. I will drive it on the road with AC on....then drive it to a road race track and also high speed runs.

I am well aware what a T4 setup with an extended NON Log manifold does....I also know how much i have to rev it to get it back on the track......I went from GT3 ( Log Manifold) to GT1 setup .....so I am well aware.

For what I am looking for ...GTM prove to be the best for ME.

Now for making 1000 whp. Do you guys understand that if I make anything over 850whp on sharif's dyno ...that will get me to 1000whp or more on the DJ I use here in town.... which was 14-15% more at the time I did my run to 800whp with the 850bb??

Why do I care about 1000whp???? I really dont.....I believe in having 200-300whp more than I need......a car that can run 700whp or more on pump gas...

So as good as SP and SFR setup is...its not for my needs.

GTM Manifold.......I am sure Sharif will post up that info

str8dum1

iTrader: (11)

Terry, pretty sure its a 64/82 compressor but with a 60mm gt30 turbine to fit the t25 housing.

ya, all this talk is purely theroretical. The GTM kits are prefect for basically everyone that wants some streetability. The smaller housings are perfect for quick spooling beefy midrange.

Definitely not questioning why you went with that kit, more just dreaming about 'perfect world scenarios'

you car and the next 3.5L gt35 kit Sharif is going to do will be a great indicator of what really is the max anyone can run on pump gas. You contribution to the greater knowledge of the group will be awesome!

XKR

iTrader: (1)

Dont get me wrong....I agree with what you guys are saying.....just explaining my reason for going about the build this way.

ttg35fort

iTrader: (2)

I just did some analysis using the compressor housing A/R values provided by Garrett to determine the turbine Inlet Area at the position indicated in the picture below:



When computing this, I assumed that there was 1 mm of clearance between the turbine blades and the housing wall. This was a SWAG on my part.

Remember that the area of the T25 flange is 1735 mm^2. Now, here are the computed values for the inlet area at the position indicted in Red in the figure:

GT3071R w/ 0.64 A/R:

Turbine Inducer Dia: 56.5 mm

Radius R1 of Turbine Inducer: 29.25 mm (adding 1mm to the radius for spacing between the turbine blades and the wall)

Radius R2 of the Inlet Area: 2.54 mm

Total Radius R (R1 + R2) from center of turbine to center of red inlet area: 31.79 mm

Inlet Area: 20.3 mm^2 (based in Pi*R2^2)

To confirm that I have computed R2 and the Inlet Area correctly, take the computed area and divide that by R.

A/R = 20.3/31.79 = 0.64 - This is precisely the A/R value listed by Garret. There might be some deviation from my computed inlet area to the actual one based on my assumption of 1mm clearence between the turbine blade and the wall, but it should not be significant, maybe a few percent.

Based on this analysis, the bottleneck will lie in the red inlet area indicated in the picture. 20.3 mm^2 is a very small fraction of the size of the T25 flange opening (1735 mm^2). Thus, I do not think changing from a T25 flange to a T3 flange or a T4 flange will make a significant difference in the overall back pressure.

I have ran the numbers for other turbos as well.

GT3071R 0.86 A/R: The Inlet Area = 27.7 mm^2

GT3582R 0.76 A/R: The Inlet Area = 28.9 mm^2

These are all way, way smaller than the opening in the T25 flange.


EDIT: I HAVE AN E-MAIL INTO GARRETT TO FIND OUT IF THERE IS A FACTOR (E.G., 100) THAT NEEDS TO BE THROWN IN HERE SOMEWHERE. THEY CERTAINLY HAVE NOT INDICATED ANY SUCH FACTOR ON THEIR WEB SITE, BUT AS RAJ HAS INDICATED, THESE INLET AREA VALUES SEEM AWFULLY SMALL.

ttg35fort

iTrader: (2)

It also strikes me as being very funny. I sent an e-mail to Garret asking if there are any factors in their A/R ratio not being published.

For example, is it really 100*A/R?

When I hear back from Garrett I'll update the post. Nonetheless, based on Garrett's published data, the above calculations are correct. The question is whether their published data is lacking some information. I'm speculating that there is a factor of 100 to be thrown in there somewhere that they failed to mention in the tech session where they describe the A/R ratio.

Even if there is a factor of 100 missing, the inlet area still will be significantly smaller than the flange area.

rcdash

iTrader: (18)

Well you caught my ninja edit! So I might as well post in full (I was going to calculate the true opening based on the physical dimension specs in the Garrett catalog)...

Where did you get R2 value from? That's a diameter of 0.2 inches! You back calculated from R1? Something does not seem right - I don't see how you are accounting for the entire diameter of the housing up to the midpoint of the inlet. The R in the A/R ratio is measured from the center of the turbine to the midpoint of the exhaust gas inlet. Suppose the cast iron housing is 5 mm thick. Where is that represented in your calculations? Plus you've got all that space between the turbine blade and the top of the cast iron in the turbine housing (not really depicted well in your diagram):



Basically you haven't accounted for the 2nd lower red arrow in the diagram below (and in that diagram it looks like it is about the size of the radius of the turbine blade itself)...



All restrictions to total airflow will be cumulative (e.g. for a pipe, diameter important along with the length that that pipe is constricted over). The question is what percentage of the total flow restriction will be flange related.

ttg35fort

iTrader: (2)

I applied basic Algebra.

I did account for it. As you will see. I will update this post in a few minutes with the derivation.

Here is the derivation:



Given in Garrett's published data for GT3071R - 0.64 A/R version:

A/R = 0.64
D = 56.5

Where A is the inlet cross-sectional area, R is the radius from the turbo centerline to the centroid of the area A, and D is the inducer diameter.

Defined: R = R1+R2

R1 = D/2 + 1 mm, assuming 1mm gap between turbine blades and turbine housing. The size of the gap is fairly insignificant to the overall computation.

A = Pi* R2^2

==> A/R = Pi*R2^2/(R1+R2)

Let X = A/R

==> X = Pi*R2^2/(R1+R2)

==> R2^2 = (X/Pi)R1 + (X/Pi)R2

==> R2^2 - (X/Pi)R2 - (X/Pi)R1 = 0

Apply the quadratic formula to solve for R2:

==> R2 = ((X/Pi) +/- ((X/Pi)^2 + 4XR1/Pi)^0.5)/2

Plug in 0.64 for X and 29.25 for R1, and you get two solutions for R2, either 2.54 or -2.34. Of course, as we have defined it, R2 cannot be negative, so the correct value of R2 is 2.54.

rcdash

iTrader: (18)

You are applying a ratio with the A/R but you only really know the turbine wheel diameter. You know nothing about the housing (without additional physical dimensions). You don't know A and you don't know R. You are attempting to use the ratio to back calculate but you're missing a dimension.

The true R = turbine radius (R1) + radius of exhaust inlet (R2) + physical space between edge of turbine wheel and start of exhaust inlet (R3).

A= R2 * R2 * PI

R1 = 56.5 / 2 = 28.25 mm

R2 * R2 * PI / (28.25 + R2 + R3) = 0.64

Let's assume R3 is 5 mm (guessing).

R2 * R2 * PI / (28.25 + R2 + 5) = 0.64

R2 * R2 * PI / (33.25 + R2) = 0.64

R2 * R2 * PI = 0.64 (33.25 + R2)

R2 * R2 * PI = 0.64 (33.25 + R2)

R2 * R2 * PI = 21.28 + R2

R2 * R2 * PI = 21.28 + R2

PI*R2^2 - R2 - 21.28 = 0 is a polynomial equation that may have more than one root but I must admit my solving skills are a bit rusty...

This would be a lot easier if someone could just measure it! lol. Just using a rough estimate of 3 mm does seem to work to approximate R2. Which is still really, really small. Wierd. R3 must be bigger than 5 mm.

RudeG_v2.0

iTrader: (1)

ttg35fort

iTrader: (2)

Raj, Garret provides the turbine wheel diameter on their website, as I indicated. For that turbine it is 56.5 mm. HERE IS THE LINK:

http://www.turbobygarrett.com/turbob...R_700382_3.htm

Now, I indicated that I made an assumption that there was a 1mm gap between the turbine blade and the housing (2 mm overall diameter). How much more space could there be and still have the turbine work properly? Even if the gap were 3mm it would not change the calculation by that much.

I will send another e-mail to Garrett to confirm the exact gap between the end of the turbine blades and the inner wall of the turbine housing. Still, the result won't change much.

EDIT, I'll say it again because it is worth repeating. I think Garrett will come back with an answer that there is a factor of 100 they forgot to publish in the explanation of A/R. Once they respond, I will adjust the numbers to correspond with whatever they come back with.

rcdash

iTrader: (18)

LOL Rude. I'm not sure why everyone except Terry and I went off track. Yah Terry I'm thinking something is waaay off in their specs or maybe it really is that small. I'm dying to have one in my hands now!

ttg35fort

iTrader: (2)

LMAO

I'm guessing that they are computing area in cm^2 and radius in mm. That's where I came up with the factor of 100. Hopefully I'll here back tomorrow.

Earlier today I found some other discrepencies in their technical section that I let them know about. They replied right away.

ttg35fort

iTrader: (2)

Here is the definition of "A/R" as published by Garrett:

"A/R (Area/Radius) describes a geometric characteristic of all compressor and turbine housings. Technically, it is defined as:

the inlet (or, for compressor housings, the discharge) cross-sectional area divided by the radius from the turbo centerline to the centroid of that area (see Figure 2.)."


However, after doing more research, I have found other peaple who define the term A as the diameter of the of the inlet, As shown in the pictures you posted (but one still calls it area?). That certainly would provide much more realistic numbers. Perhaps Garrett just got their definition wrong???

str8dum1

iTrader: (11)

I love intelligent thought provoking topics. Mike's thread delivers!

In 2 weeks, we'll have some real world data to compare to paper data!

XKR

iTrader: (1)

Just to calm RudeG down.....let me ask Terry a question.... Have you ever looked at a GT35r & GT30 side by side ???..... It's VERY easy to see the difference.

Your calculation does not reflect the true difference between both turbo's. Part of the puzzle is missing.