Help Choose Turbine HSG for 250 Ci L6

[cameljockey]

Hi everyone!
I am getting ready to purchase the Turbo!!!!!
I have included a detailed description of my build below and I wanted your input.

I would like to drive this car every day and take it to the strip every now and again.

+Turbo: Garrett GT3582R:

I need help choosing the Turbine sizing 0.63, 0.82, or 1.06 I am definitely using an external waste Gate.

I've already run this build by Will and I tend to agree with his suggestion because it is based in real world experience but I also asked a number of vendors about the appropriate turbine housing and they differ, and I would like as many opinions as possible

I won’t say what Will has suggested so as not to taint your thought processes.

I have done the Sizing math and the compressor is optimally sized for the air flow requirements of this build but the Turbine housing comes in three A/R ratios and I want to size it so that I don’t lag too much when I’m on the street. I don’t want to make more than 10 lbs of boost for the time being until Mike gets Cometic MLS gaskets at which time I will turn up the boost.


Bearing in mind that I want a fuel injected daily driver here
I have completed the following engine work:
Engine: Ford 250 cid L6
+Block: 0.030” over decked to 9.440”
+Pistons: Ross Racing Forged Al 8.7:1 Compression, Spiro-Locks, Full Floating Pins
+Crank: Turned 0.010 & 0.010 and Cryogenically Strengthened, Machined rear snout and rear main cap to accept 1 piece rear main seal from ’89 mustang 5.0.
+Rods: Cunningham 2 piece forged I-beam Bronze bushed for full floating Chevy pins
+Comp Cams: Dur @ 0.050
Int:224° Exh:218° LSA: 115°
Gross valve Lift:
Int:0.494 Exh:0.447
+CI Al Head & Cast Al IntakeThe head is being done by Mike's shop as of this writing)
-street / strip porting option 1.56” Exh Valve
-Viton seals
-64cc chamber
+Transmission: Ford Racing T-56 and associated Mcleod Industries Clutchery (TBD on the tranny here I like the idea of two overdrives and a shifter being farther back)
+Rear end: 3.70:1 Detroit Tru-trac worm gear posi, 31 spline axles,
+Tires: 245/45/ZR17

I really need some help with the Turbine housing size and any input is greatly appreciated and I eagerly await your arguments!
Keep Sixn'
Daniel Hanna

 

[StrangeRanger]

Have you ever seen any equations, charts or nomograms for sizing the turbine?
It seems that sizing the compressor is all science and sizing the turbine is all a Black Art

 

[cameljockey]

Have you ever seen any equations, charts or nomograms for sizing the turbine?
It seems that sizing the compressor is all science and sizing the turbine is all a Black Art

You are correct sir.
I interned at Garrett Turbo chargers back in 2006 for about 3 months and there IS some numerically iterative math that is involved in choosing a turbine housing but ultimately experience is the best (and unfortunately most expensive) teacher.
Ultimately you have to take into account the desired driving characteristics and as such the operating range. The rule of thumb is a larger housing is great for High RPM pulls which is great for L.S.R. or auto cross and drifting but lousy for drag strip runs and street driving while a smaller housing is great for street driving but becomes a restriction at higher RPMs when you want to flow more. Think of it like the comparison between free flowing race headers and a log manifold.

The Mathematics of it requires some empirical knowledge about the operational characteristics of the engine and the ambient conditions during that operation because the primary reason for wanting to size the turbine correctly at least IMHO is to achieve good transient response i.e. "no lag". Modeling that with computers is the stuff of PHD thesis's (PHD just means Piled Higher and Deeper in the Engineering world lol j/k ) It's a very complex problem of heat, mass, and momentum transfer where the amount energy being put into the system does not always increase or decrease after a linear fashion and simplifying assumptions get made just so your computer won't crash trying to converge on a solution. Transient problems are nothing new neither are they very complicated but its the complication of the system that we try to apply transient methods to that requires the iterative numerical approach that really makes this all difficult.
There ARE lots of good computer models these days but the average shade tree mechanic (myself especially) doesn't have access to these models much less know how to use them appropriately (really now are definitely talking about me ). perhaps one day there will be a user friendly numerical program that can take inputs from users to narrow down selection of turbine housings but like all programs it would follow the rule of GIGO.

On the Compressor side of things there are lots of nice assumptions that simplify things greatly and the matter is further simplified by the fact that you are not adding a whole lot of thermal energy to the system on that side(depending on the adiabatic efficiency of your compressor)(compared to the Turbine side I mean don't go and touch your compressor discharge tube after a drag strip run that heat you feel is mostly the energy that the Tube extracted from the flow inside it REALLY HOT! isn't skin friction drag just great?! :x ) Thermal energy can sill enter the compressor side through other avenues as well e.g. heat soak back from the turbine side, ambient heat in the engine bay, elevated atmospheric temperatures (i.e. hot days), and (I'm not sure about this one) an improperly sized inter-cooler

Hope you all enjoyed my butt talking again I welcome any thoughts on this and encourage any corrections / objections to what I have written above.

Best Regards,
Keep Sixn'
Daniel Hanna

 

[StrangeRanger]

One minor correction about application: for autocross, you need instant throttle response and as much mid-range as you can get. You spend so little time at high revs that you trade it for mid range in a heartbeat.

 

[wallaka]

That is pretty much a perfect turbo choice IMO. The ball bearings will help it spool, but I think that a .82 housing would be a bit big for the street and the 1.06 undriveable. Hmmm. The .63 should spool quickly, but I don't know how much of a restriction it would be. Depends on how high you plan to rev it. On the other hand, an engine this small rarely needs a large A/R unless it revs to the moon.

I think that the sizing rule for A/R is like primary header tubes or camshafts: If in doubt, go for the slightly smaller size. You MIGHT leave a little power on the table, but I'll take driveability and low-end/midrange torque over 20 peak hp anyday.

That's my thoughts on it, anyhow.

 

[drag-200stang]

What size waste gate are you planning? I'm not familiar with the turbine wheel that the new Garrett's are using but if its typical TO4P trims my guess would be something between the .63 and the .82. So I personally would error on the larger housing because if you're pleased with the performance your fuel mileage will be better and it will be easier to get a handle on your tune up. The .63 may be a little rude to start off with trying to tune. No one ever gets these right the first time. Just plan on change. Should be able to swap with someone else.

What are your plans for your exhaust system? Sizes?

I would recommend that you tap your turbo header for an 1/8" pipe thread so you can take a TIP (turbine input pressure) reading. A cheap oil pressure gauge with metal line is all you need and you only need to check it once or if you make a change. It will give you an idea what your turbine AR and exhaust system is doing. Of course boost creep would be an indication that your waste gate is too small or your AR is too small.

It sounds like your build is sound and really should fly.

 

[cameljockey]

My plans for the header thus far are up in the air because I haven't figured out my motor mount situation quite yet which will have a big influence on space and geometry.

As for your waste Gate questions I just assumed to go as large as possible right? I've never heard any one complain about a waste gate being too big. What are the criteria besides boost creep in choosing the appropriate sized Waste Gate? I'll throw that into the debate here lol

 

[drag-200stang]

The biggest problem with a larger waste gate is cost. But if you get too large a waste gate for your application it can be harder to keep boost steady because slight movements of the valve can dump too much boost and create a see-sawing action. They have some pretty good electronic boost controllers that make this not too much of an issue. I'm thinking a 44mm or maybe a 50mm should work for what you're doing. Lower boost requires a larger waste gate and you can get by with a smaller waste gate for higher boost. The reason being you need a larger valve to flow the same amount of exhaust at a lower boost pressure and not as much exhaust will be used to propel the compressor. Hope this make sense... I must be tired. I'm going to try running a 38mm on my new build - cheaper and to save weight. But don't plan on running less than 15 lbs boost.

 

[fast64ranchero]

I used a P trim wheel with a .82 housing, a 38mm waste gate, I had no problems controlling boost and any RPM, and was making full boost by 2700rpm, my buid was different then yours, so with that said I'd use a .63 housing, stage 5 wheel and a little bigger waste gate on yours and hold on!!!

 

[XFlow_Fairlane]

Just my opinion......skip the "Cool" factor of the T56. they have a VERY step first gear (2.95) in them and are closely spaced gears (remember 4th is still a 1:1) you end up HAVING to run a 3.73 or such gear in it. I put one in my S10. with stock 3.08 gears I could do 50mph in first (before hitting rev limiter). I now have 4.10's and that gives me the same final drive in 6th (.5:1) as the old 5 speed (.73:1) first gear is about the same (2.67 in the T56 vs 4.02 in the 5speed) so all I gained was a loss of 1mpg, 40 more pounds of transmission, and one more gear to shift through all the time. The T56 is a pig of a transmission (huge and heavy) I run alot of highway driving so the closer (more gear choices) is more annoying than anything. with the taller ford 1st gear you can run a shorter final drive like a 3.2X or 3.50 but then your .5 OD in 6th will be killer (better have some lowend) I cruise at 65 in 6th with 4.10 gears at 2500rpm (I have mustang bullits on it right now) drop down to a 3.50 gear and rpms will drop a good chunk too.

I would consider a Tremec 5 speed (not a T5) cost is cheaper, lighter, STRONGER. much easier to swap in. not as wide, uses a standard T5 bell or toploader bell, shifter is not AS far back (farther back than a 3.03 shifter is)


Now for the turbine. I would check around and see if I could find a used one or two in different sizes. It looks to me like you got alot of money in this motor so I would start out with the smaller housing and work my way up as the boost comes up in the tuning process. for daily driving fast spool is alot of fun. it will hurt you at the strip on top end but will get you out of the hole fast. being a stick you can't load up a convertor so faster spool will be better.

Just use some antisieze so if it doesn't work you can get it apart and step up a size.