thom000001

Nice,

Looks ilke the 2 biggest dogs will be rolling the same time...Vlad's Sedan just hit the streets last week......

C'mon Mike.......can't Sharif work on a sunday for ya????????

tom

ttg35fort

iTrader: (2)

PM me your e-mail address. I'll send the spreadsheet to you that I use for all of my calculations.

EDIT: In the spreadsheet, I use Garrett's published data for the turbine diameter and A/R. Then I assumed the same value for the turbine housing wall thickness and gap between the turbine blades and the wall. The rest is all based on calculations. You will see when you look at the spreadsheet.

XKR

iTrader: (1)

Lol....... I will ask him why he is not working on my car on Sunday....

ttg35fort

iTrader: (2)

Tom, this is your ticket:

http://www.xtrac.com/pdfs/386%20Gran...ox%20Jun07.pdf

Transfer weight from the front of the car and get it over the rear wheels. Not only will it help straight line traction, it also should help handling. With the turbo kits, our cars get a little nose heavy. A transaxle will balance it out a bit.

Dog gears are a little rough on the street, though. One of the British companies makes an H-pattern synchromesh transaxle that will work too.

Then again, you can always get hold of one of those Getrag twin-clutch jobs like they use in the Ferraris.

I know, they are all big, big bucks, but if I ever hit the lotto transaxle here I come.

str8dum1

iTrader: (11)

twin 67mm turbos should make a TON of power. well north of 1300. How wide of a slick can that car fit? a 12"x28+" slick would be awesome!

ttg35fort

iTrader: (2)

Garrett finally got back to me, which changes the entire analysis... I updated the post.

Essentially A is the inlet area, but the formula only works in INCHES, while all of their dimensions are specified in mm.

Using A as the area of the inlet (in inches), I computed the turbine inlet areas by converting to inches, performing the calculations, then converting back to mm (only in America do we have to go through this BS - even the British have dropped the British measurement system, for the most part).

Summary is that the T25 flange will work perfectly fine on the turbos we use, even the GT3582R turbos.

XKR

iTrader: (1)

If Sam/GTM was a nice person...he could have saved you all this trouble..

GreenGoblin

iTrader: (6)

^ lol

ttg35fort

iTrader: (2)

I wonder if he even new that A/R was a ratio that would only work in inches??? I doubt most people even think too much about this. I didn't until the question about whether the T25 flange was going to be a bottle neck came up. After all of the analysis, it is pretty clear that it won't be. The analysis would have been much faster and easier if Garrett had been more accurate with the information on their website, though.

In fact, Garrett's technical support didn't even immediately know why the A/R ratio was not working. They sent me an e-mail on Friday saying that they needed time to look into the issue. The e-mail I received today indicated that you must use inches for the ratio to work.

It would be helpful for them to update their website with this, considering all of their published dimensions are in mm. Considering their reputation, you would think they would be a little less sloppy about these things.

str8dum1

iTrader: (11)

interesting about the calculations.

i guess we'll just have to wait for more real world data becuase if the T25 housing isnt causing excessive backpressure, no one has really even maxxed out the smallest gt3071 yet (which should be around 900 on a dynojet)

rcdash

iTrader: (18)

900 on a DJ from what sized motor? 3.5L low compression? Twin GT30s I presume. GTM got 855 whp with APS extreme, which is likely well over 900 chp (yes, I know that was on the stroker).

ttg35fort

iTrader: (2)

The area of the T25 flange is 1.55 times the size of the GT3582R (0.76 A/R) turbine inlet, and the distance between the flange and the inlet is only a couple of inches. Even if you use a T4 flange, there is going to be a bottleneck at the turbine inlet. Note, that the turbine inlet area calculation has changed significantly for this particular turbine housing since Garrett actually confirmed what they mean by A/R. On my turbos, the numbers did not change much. It was pure coincidence that for my turbos diameter measured in mm made the A/R value work. (Just my luck - it made me waste a bunch of time).

Moreover, a good wastegate/dump should help to reduce back pressure. Once the pressure that is needed to spool the turbines for the desired intake manifold pressure (MAP) is reached, the wastegates will open. You will know they are adequate if you don't experience boost creep. If boost creep occurs, then you need a larger wastegate.

To get any realizeable benefit out of the T3 or T4 flange, you will need a header style manifold with large tubes. As we discussed, this may not be a viable option for those of use who intend on road racing our cars. As Mike and Roger at Japtrix will attest, SS header style manifolds start to sag over time when used in road racing. Both of these people steared me toward using cast iron manifolds for road racing.

For street and 1/4 mi. use, the SS header style manifolds are the way to go. Still, you need a good wastegate/dump setup because there is always going to be a bottle neck at the turbine inlet.

Also, as you increase the volume of the manifolds, you decrease turbo response (i.e. increase the response time). pV=nRT. So, p=(nRT/V). Assume that nRT is relatively constant at a given moment in time; as V increases p decreases. So R has to increase, which takes a little more time, in order to get the same pressure (R is number of moles of gas). In other words, you need more exhaust gas to build up in the manifold to reach the same pressure. In actuality, T will be slightly lower in a larger manifod because there is more surface area to thermally conduct heat out of the exhaust gases into the engine compartment. So that adds a little bit of time to the spool up as well.

The additional time can be computed based on the amount of air/fuel mixture being combusted and the rate of thermal exchange between the manifold and the ambient air in the engine comparment. Considering, though, that we usually have a fairly large intake systems with all of the piping and the intercooler, the additional turbo lag caused by a bigger exhaust manifold is farely insignificant in the overall scheme of things, and may not be too noticable, if at all. I only went through the logical steps to help increase understanding of the thermodynamics involved for those that are interested.

str8dum1

iTrader: (11)

ok so the inlet is ok, what about the outlet?

ATPs custom t25 housing uses a T3 outlet.
http://www.atpturbo.com/Merchant2/me...egory_Code=GTH

any idea there on measurements of the t25 housing outlet?

ttg35fort

iTrader: (2)

I just checked the turbine outlet dimensions for the GT3071R. On the models that I looked at, the turbine outlet that is used on non-internally wastegated turbos is a standard "3-inch 4 bolt" outlet. This is the same outlet used on the GT3582 models that I checked which used the T3 and T4 flanges (they don't list the T25 flange for this model):

http://www.turbobygarrett.com/turbob...T3071R_new.pdf

The cross sectional area is 4070 mm^2.

The models with the T25 flange are internally wastegated, so the outlet is a completely different shape. It is a "5 Bolt" outlet:

http://www.turbobygarrett.com/turbob...2_3_20_new.pdf

I just did a very quick estimate of the cross-sectional area, but it looks like it is right about the same size.

Note that GTM has disabled the internal wastegate because it does not work as well as an external wastegate.

If anyone wants to take the time to compute the actual cross-sectional area of the 5 Bolt outlet, please do so. It is a relatively complex shape and will take a bit of time. From my perspective, it is a moot point as my estimate will be pretty close. It may turn out that the 5 Bolt outlet is slightly bigger or slightly smaller, but it won't be by much. It appears that Garrett tried to keep the same cross-sectional area as the 3" outlet.

EDIT: Also note that the cross-sectional area of the wastegate will come into play once the desired MAP is acheived. Any excess pressure beyond that which is needed to get the desired MAP will be relieved through the wastegate, assuming the wastegate/dump is large enough to prevent boost creep. Essentially, once the pressure at the turbine reaches the point to give the desired MAP, the wastegate will open and route any additional exhaust gases to the dump.

In summary, the only way a T3 or T4 flange will make a noticable difference is if the size of the exhaust manifold tubes also are increased. Then the net back pressure will be lower. For a log style manifold, it won't make much of a difference.

With respect to the turbine A/R, a smaller A/R will need a bit more pressure to get the same MAP as a turbine with a larger A/R because of the difference in the direction of the exhaust gas flow. Other than this, the wastegate and dump should act to equalize any differences between the turbine housings. A larger A/R will provide more boost potential. However, if a smaller A/R will get you to the boost you need, it is probably a better choice given that it will be more responsive. The pressure differences at the exhaust valves will not be that different among the different A/R turbine housings unless the bottleneck creasted by the exhaust manifold itself is decreased.

Even more summarized, if you have a log style manifold, go with the lower A/R turbine housings and the T25 flange. If you have header style exhaust manifolds with large tubes, go with a T3 or T4 flange. Then you should get a noticable benefit with a larger A/R in terms of lower back pressure at the exhaust valves, as well as greater total boost potential. The cost of this is more turbo lag.

ttg35fort

iTrader: (2)

Have I earned my PhD yet?

str8dum1

iTrader: (11)

NIce thorough academic review.

1 more week and we'll know more for sure!

Resmarted

iTrader: (2)

Dude that is just flat out insane. Major props.
You better go out and hit the intranetz like VRA.... hell you two should race.
Seriously, a bit more inter manufacturer respect for the VQ is due.

GreenGoblin

iTrader: (6)

Terry you sir are a maniac lol!!! Its great tho...

RudeG_v2.0

iTrader: (1)

They were out of diplomas... so we got you this shirt.

thom000001

So Mike......did she start yet???????? Today was a work day and all....

tom