Turbo Sizing

[utah_sledder]

I know this is like asking which snowmobile is the best but I am interested in hearing the size of turbo you are using, elevation, Compressor Trim and A/R, and Exhaust trim and A/R. I am just trying to learn a little more here. I am kinda curious about how changing a/r's and trims will affect the response of the system. Some builders say GT2871 some say 2860 I see some cats are running 2854's and 2876's. I have been told that 2871's will have more lag than a 2860 but is that really true? Come on TEACH ME!

Currently I am running:

Garrett GT2860rs (cold Side .60 a/r, 62 trim, hot side .86 a/r 76 trim).

I ride 7-10,000 feet, 7-8 lbs of boost. Great bottom to mid response, pulls hard on top. Seems to build a lot of heat. '08 TXP 163 stock motor.

 

[Wheel House Motorsports]

go into the t-cat section, this has been chatted about a LOT.. thread should be decently high on the list.


2860= waste of time on an 800.. 2871's hit harder and make more top end.. they do even better with the compressor side of the 3071 attached to the 28 exhaust side. its the same diameter, just different trim

basically.. the bigger turbo's run awesome on 800's. buddy also has a precision turbo that is a 28 exhaust side of a garrett and a then has a billet wheeled compressor side that is right around a 71mm... should be on the snow rather soon and ill report back how that compares to the same sled with a 2871.

 

[knifedge]

--OVS now sells a 2860 TIAL for the ProClimb. They stated their primary reason to sell this size setup was to basically meet market demand for the flatlanders, as the 2860 seems to work ok down there...whatever, it sounds like a money maker, that's cool.

http://www.ogdenvalleysports.com/theirs_vs_ours_93.html

--Read info in the above link--

--Basically what you will eventually find out is, a 2871 .70 a/r compressor Hybrid or 2876 works well at altitude. TIAL exhaust housings work better. Billet comp wheels work even better if setup correctly. --New offerings for CAT this year are oiless bearings, billet comp wheel, 70 A/R housing, TIAL exhaust 2871.

--There are other good setups out there, I believe each builder tunes to what they believe which turbo size works best, and they optimize that setup for that size turbo. You will get different opinions. Properly setup 2871 or 2876 TM8 pull harder than mod M1000 off the bottom and mid. Does yours?

--800 2 strokes need to breathe, 70 a/r housings allow for that

--Spend some time in the CAT TURBO forum, and scroll around--CAT has been #1 turbo sled for years now.

 

[swrev]

Currently I am running:

Garrett GT2860rs (cold Side .60 a/r, 62 trim, hot side .86 a/r 76 trim).

I ride 7-10,000 feet, 7-8 lbs of boost. Great bottom to mid response, pulls hard on top. Seems to build a lot of heat. '08 TXP 163 stock motor.

I thought you had switched your XP to an oil less Precision setup? Is it back to the Garrett? How are you judging the heat? I'd like to put a sensor in for charge temps but haven't looked into it yet.

For what it's worth, the fastest responding two stroke turbo I've been around is a 2860 on a Cat, w/ an intercooler. It seems to work great at all boost levels.

 

[utah_sledder]

Yep I put a Comp Turbo ceramic bearing oil-less 2871 (CT3 .86 turbine, .60 compressor) in it this year, but that still doesnt quench my desire to learn more about turbo sizing. Since I have not been able to ride it yet I am just trying to learn about how different turbo sizes affect performance.

I put 2300 Mountain miles on the 'ol GT2860 last year with killer performance! But after sucking a piston through on my last ride (June 10th) it got me thinking about changing the turbo. I went with the comp turbo mainly to get rid of the oil tank, pump, oil in the intake etc.

It's really expensive to go buy a bunch of turbos and see which one I like the best so my next best option is to learn as much as I can and then make an educated guess on which one will work the best for me.

So pretty much the everyone agrees that you need a .86 AR turbine housing and a .60 compressor, so really it just comes down to trims.

Anyone out there know the pressure ratio and corrected flow for a doo 800r motor?

 

[madmini660]

I thought you had switched your XP to an oil less Precision setup? Is it back to the Garrett? How are you judging the heat? I'd like to put a sensor in for charge temps but haven't looked into it yet.

For what it's worth, the fastest responding two stroke turbo I've been around is a 2860 on a Cat, w/ an intercooler. It seems to work great at all boost levels.

haha cat is faster to spool 2860 but xp pulls harder on topend 2871 thats the differents pretty shur swrev has a 2871 on his xp

 

[knifedge]

--Not everybody agrees 2860 is the way to go. It may work ok, but I personnally am leaning toward a 2871 70 a/r billet wheel, .56 trim(I think), oiless Comp, Tial wastegate. Tial also gives quicker spool, among other advatages as well.

 

[gus bohne]

Anything smaller than a 71 wont even WORK at sealevel.
ie. 2860 @ 15 psi on 800 rev = 221hp
2871@15 psi = 243
2876 @ 15 psi = 305 hp

The 2860 IS a bogging dog, the 71 is real good, the 76 is on boost @ 2800rpm.
Now YOU figure it out.

At sea level we have a denser charge so the theory of a smaller turbo looked good.. in reality it created a heat soaked bogging dog.

NOT 1 cat turbo is alive out here in new england, even a 1200 cat turbo detoed 4 times in under 4 miles of riding.. heat soaked !! they gave up as did OVS Dan on all the turbo cats for good out here. 2860's on the little cats and a punny 3071 on the HUGE AIRFLOWING 1200 ???

If they had stuck it out till I showed them what was on ours it may have been different for them.

When I get to DTR with the e torch turbo testing ALL 3 sizes will be done.
I hope NOT to destroy the engine when we test that rediculous 2860.

The charge temps on the 2860 in the field were 177 degrees at 10 psi.
the 71 was 130 degrees
the 76 was 112 degrees.

thats allot of heat friends...

Gus

 

[swrev]

2860 @ 15 psi on 800 rev = 221hp
2871@15 psi = 243
2876 @ 15 psi = 305 hp

The 2860 IS a bogging dog, the 71 is real good, the 76 is on boost @ 2800rpm.


The charge temps on the 2860 in the field were 177 degrees at 10 psi.
the 71 was 130 degrees
the 76 was 112 degrees.

thats allot of heat friends...

Gus

Gus, w/ the 2876 building boost so early, would that make the TPS sensor/boost actuator (or whatever it's called that Boondocker has this year)setup a bit of a waste? It seems boost would tend to be more progressive w/ RPM naturally if you never really had to build any rpm to start seeing boost.

For curiosity, what was the air temp when you were measuring the charge temps?

Could be wrong, often am , but based on the horsepower numbers and charge temps, I would do an intercooler or even some sort of water to air cooler, before changing a 2860 to a 2871. If I ever loose the turbo, 2876 is looking good. 305 vs 221, that's impressive.

 

[gus bohne]

The boondocker ebctps would just be opening the wastegate sooner and at a faster pulse width.
When cruising out here on the flats, boost creeps up at 1/3 throttle really easy. Thats my pet peave,, the ebc tps is what the flatlander needs to stay alive wth a 2 stroke turboed... especially carbed,,sklides are low, fuel flow is ?? LOW.


The airflow increase at lower tip speed of the wheel is such a charge temp reducer alone its a good comparison to what you see with a good intercooler. the density of the chrge would increase too.

The in field difference I do not know, we did not test the 76 IN field without the shaman cooler. the boost build rpm of 2800 is WITH the shaman.
3 '' in and out barrel .

outside temps was 34 degrees, on the ice..

Coolant temp is another funny indicator of how close you are to deto ..
with the 60 comprs@ 22 psi the sled left the line @ 74 degrees coolant.
returned to pit at 187 ish..

with the 76 @ 24 psi leaving at 72-74 degrees again, pit temp is 135 !!!
That alone is the indicator of heat in the combustion chamber ,, Josh has oh so much more room before deto is seen..
We run c 14 period, not a trace of deto, 130 psi comp, 15 degrees timing @ 8200-8900 rpm.

Doing a new set of cylinders for it, has been running stock 03 non ho cyls . They smoked the ho cyls in the field really bad. humiliating.

going to dtr next week wth a triple Polaris 1080cc with a 3582 and HTG tripl pipes. MSD, 44 mm carbs..will let you know how she does..

Gus

this is a 660 ft drag run, shutdown of 1100 feet then drive back to pit total of 2700 feet of run distance.. of course the trip back is off boost !! LOL

 

[knifedge]

--2871 with a 70 a/r housing seems to be a good combo for spool and boost--4 inch inlet and 2 1/2 inch outlet flows just fine. Then add Tial, oiless, billet comp wheel.

--2871 Hybrid 70 a/r or 2876 -- whatever --- good choice either way -- billet 2871 comp wheel will spool faster though and flow equal or more than 2876 standard, just physics and efficiency

--The 2871 70 a/r and the 2876 have similar size housings --maybe flatland riding 2876 would be the way to go. Both work well in the Mtns.

 

[brycter]

What shaft speed are you seeing on the 76 over the 2871? You still need to take that into consideration when sizing s that you know if your trim is right. Faster the shaft speed the better.

 

[Octanee]

curious, when you talk of the sizes 2860, 2871,2876, is the "60" 71" "76" the compressor size? or the exhaust??

 

[utah_sledder]

Yep I agree with what has been said. Lots of guys over on the cat forum are leaning toward the 2876 with .64 ar on the turbine over the .86. Seems that the bigger .70 ar and 48 trim on the compressor will flow a fair amount more air than the 2871 with .86 ar turbine. It would be fun to have a couple different turbos to test with.

I spoke with Comp today to verify the turbo that I received. My comp turbo has .60 ar compressor with 48 trim, .86 garrett turbine housing with 76 trim. It is almost an exact match to a gt2871 but comp's 48 trim starts at 48mm inducer 71 mm exducer where the garrett is 49.2 mm ind and 71 mm exd.

Comp also mentioned that they have developed a motorsports specific turbine wheel that is designed for super quick shaft speed. It is an 11 blade turbine vs. the 10 blade turbine that comes standard.

Can't wait to test!

 

[utah_sledder]

curious, when you talk of the sizes 2860, 2871,2876, is the "60" 71" "76" the compressor size? or the exhaust??

If i'm not mistaken those numbers relate to the exducer on the compressor side.

 

[utah_sledder]

What shaft speed are you seeing on the 76 over the 2871? You still need to take that into consideration when sizing s that you know if your trim is right. Faster the shaft speed the better.

Bryce, don't they have medication for that?

Is there any way to know what kind of shaft speed the turbo is producing? Obviously fast shaft speed means lots of air movement, so how does one go about picking the turbo size or trim to acheive the greatest shaft speed?

 

[Octanee]

ah, i got for a good deal so i had taken this turbo up, but its hybrid, i cant remember exactly, but i was looking into sizing a while ago there, and basically it has a compressor of approx a 3082 would?? but its exhaust side is a 2860 essentially, should be a good turbo?

 

[knifedge]

-- Do not use 60 a/r turbine housings on the 800 for 28 size turbos. You'll burn up the motor

--Use 80 a/r or greater for turbine housing and 70 a/r for 71 and 76 compressor housing

--There is no way a 2860 hybrid will flow as good or better than a 70 a/r compressor housing 2871. It has a 4 inch inlet and 2 1/2 outlet like the 2876 for starters.

--Maybe a 2860 Hybrid may come close to flowing like a standard 60 a/r 2871, but why not just get a 2871 Hybrid

--This is about flowing volume and boost, not just building boost. Bigger 70 a/r housings do both

 

[gus bohne]

ATTA BOY KNIFEDGE !
right on the money.

makes me smile.

gus

 

[utah_sledder]

I have been snooping around the garrett site quite a bunch. I am liking the thought of a gt2876. Can anyone tell me what the actual corrected airflow of a ski-doo 800r motor is? I can somewhat deduce that it must be somewhere around 30-35 lbs/min thus the 2860 is out or dang close to the edge of the compressor map, but that would put the 2871 in the island and the 2876 on the 76% line. Am I getting close?