Turbo Sizing

[knifedge]

--2871 HYBRID 70 a/r and 2876 flow similar

--2871 hybrid 70 a/r will spool quicker than 2876 if setup properly, but both have the necessary volume so spool may not be as critical as with a lower volume 2860 or 2868.

 

[turbo800]

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?

From Garrett's site:
"◊ Mass Flow Rate

Mass Flow Rate is the mass of air flowing through a compressor (and engine!) over a given period of time and is commonly expressed as lb/min (pounds per minute). Mass flow can be physically measured, but in many cases it is sufficient to estimate the mass flow for choosing the proper turbo.
Many people use Volumetric Flow Rate (expressed in cubic feet per minute, CFM or ft3/min) instead of mass flow rate. Volumetric flow rate can be converted to mass flow by multiplying by the air density. Air density at sea level is 0.076lb/ft3
What is my mass flow rate? As a very general rule, turbocharged gasoline engines will generate 9.5-10.5 horsepower (as measured at the flywheel) for each lb/min of airflow. So, an engine with a target peak horsepower of 400 Hp will require 36-44 lb/min of airflow to achieve that target. This is just a rough first approximation to help narrow the turbo selection options."


From what I can calculate its 34@sea level, 31.5@4500', and 25.6@10K' based on 20* air temp.

I would say your assumptions are reasonably close

 

[milehighassassin]

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

How is the smaller turbo taking longer to spool?

Also are those number given without an intercooler?

What are you using to measure charge temps?


Heat = inefficiency folks

 

[Wheel House Motorsports]

How is the smaller turbo taking longer to spool?

all of them are running the identical turbine wheel.. thus, getting the shaft spinning should be virtually identical between 3.. obvisouly a bigger compressor takes a hair more to spool, but its close enough.. spin a tiny pump vs a big pump at the same speed. which one is gonna fill the space faster?

 

[milehighassassin]

I understand the difference in volume vs pressure. Just normally a smaller turbo will spool faster than a larger turbo.

I myself would rather have faster spooling lower horsepower setup than a long spooling big horsepower setup. Of course I do more tree riding than I do hill climbing. Nothing is worse than hitting the throttle knowing you are too low in your RPM range for any real power.

I ask this everytime but has anyone ever used a VNT turbo on a sled or a veined turbo?

 

[gus bohne]

Thanks dooinit..
you speak of rpm range for boost pressure,, is 2800 rpm to low for you ?

instead of asking ,, try it and make your decision.. speculation is pointless.

Twisted, and all the guys who have learned by trying the larger comp wheels on the garretts are proof enough ,, must be causing a ruccusss.

Reminds me of trying to convince the masses of the TURBO 2 stroke in the 80's.. sometimes the only thing that works is time..




Good riding
Gus

 

[knifedge]

--When using a 70 a/r comp housing on the 2871 or 2876, your are flowing more volume AND building boost, so absolute spool time is not as critical for the engine to breathe like on the smaller turbos. On smaller turbos, you must spool quickly to build boost to make up for limited volume.

--2871 70 a/r housing, billet comp wheel, Tial wastegate, oiless would be a setup I would recommend. A well setup 2876 Tial is recommended also. In the flatlands or dragracing , a standard wastegate probably works just fine.

--Limited volume turbos = more boost pressure needed = more heat = more octane = less dense of a charge due to heat = intercooler = more difficult to tune

--High volume 70 A/R 2871 and 2876 = less boost needed = less heat = less octane = denser charge = easier to tune

 

[utah_sledder]

So can the turbine housings be "swapped out"? Can I just unbolt my .60 ar housing and bolt on a .70 ar housing? If the trim of a 2876 is a 48 with a .70 ar housing couldn't you just swap housings with a 48 trim 2871 (.60 ar) and basically have a 2876?

Is there more to the housing/compressor wheel than I am not thinking about?

I would assume that same would go for the turbine side too. If I want to put a .64 turbine housing on my 2871 that already has an .86 could it be done?

 

[gus bohne]

No on the comp side.
yes on the turbine side.

comp wheel size is different so housing swap is a no .
turbine wheel is the same, just the housings are different so YES.

you get it..
Gus

 

[knifedge]

--The compressor wheel radius on the 2871 is 71mm outside diameter and is fitted to a 71mm comp housing. The 2876 compressor wheel is 76mm OD and fitted to a 76mm comp housing. A 5mm difference in diameter for comp wheels. You can get a 70 a/r 2871 comp housing for .56 trim wheel, 4 inch inlet, 2 1/2 inch outlet.

--Keep the .86 turbine housing as the .60 is too small for 800.

 

[motoxracer42]

good info guys. you guys should get some videos up this winter

 

[utah_sledder]

Here's one for ya!

Turbo XP

 

[madmini660]

do these pistons look heat soaked ran on a 2860 at 12lbs for three years and I watch my charge temps never over 137 degrees on long pulls with intercooler I dont think a 2860 is a waste of time great turbo for what it is

 

[Octanee]

do these pistons look heat soaked ran on a 2860 at 12lbs for three years and I watch my charge temps never over 137 degrees on long pulls with intercooler I dont think a 2860 is a waste of time great turbo for what it is

curious, what engine where they from? or sled?, but 3 years on those ,and to my eye they look pretty good, very top of the piston looks like maybe some heat? but it could be carbon discoloration any how,

 

[turbo800]

The pistons are in OK shape, 3 years is pushing it though. I would like to see the bottom side of them for heat marks.

 

[madmini660]

here is the bottoms I dont think there heat soaked not for three year old pistons not alot of blueing like I've saw on heat soaked motors has some brown/black crap on it you can scratch off with your fingernail and I lost my injectors once when we where way back in a hole and ran pretty dry on fuel

 

[madmini660]

and these pistons are out of a cat 800

 

[turbo800]

I'd say ya, they've seen some heat. Don't know the thickness of the cat pistons but, I normally have a dot the size of a quarter or smaller. Yours extends all the way out to the edges. It's a tan color and could be carbon from your fuel/oil, maybe being the difference being a case reed vs cyl reed design. I don't know what case reed pistons normally look like under there...

 

[Eli]

How about a shot of the underneath side?


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[Eli]

Sorry, missed the pics. See them now!


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