HP Per Pound Of Boost

WyoBoy1000 · Jul 15, 2011

The bigger turbo works with less lag because the 2 stoke spools so fast and like gus said, its all about leverage, with the bigger wheel the exhaust has more leverage and will spin it easier and faster. The reason it hasn't been used is because the turbos that where used first are tuned to the point that most don't want to screw with a good thing, and at the time everyone thought a bigger turbo was slower to respond, but many have found putting different turbos together ie bastard turbos it works like a champ.

YETIms · Jul 15, 2011

That doesn't make sense at all.
Bigger turbo with less lag? We are still talking about M8? less then 400cc per Chamber?
Also a bigger wheel can not spool faster and quicker, that doesnt make sense, then to spool that huge wheel you need masive air volume. And a two stroke simply do not have that volume.

WyoBoy1000 said:
The bigger turbo works with less lag because the 2 stoke spools so fast and like gus said, its all about leverage, with the bigger wheel the exhaust has more leverage and will spin it easier and faster.

gus bohne · Jul 15, 2011

Like myself and Twisted have PROVEN Yetims.
the 2 stroke needs a compressor large unuf to flow BELOW boost.

2 strokes need and MOVE double the air as a 4 stroke for a loose comparison.Much more than a prehistoric 4 stroke, the gulp factor is something that we are addressing for all to benefit from, this gulp factor is what drives the need for a larger compressor wheel..even for moderate airflow.

The tighter hot side bleeds less around the wheel and spins it quicker. Physics

2 strokes tend to be leaky ,,, they need lots of air on the intake side Before they can build boost...

2871 has 2 psi at 3800 ish rpm
2876 has 2 -3 psi at 2700 ish rpm

my testing is on the 800 Doo twins
Twisted testing is on the 800 cats.

Both of us found boost to come up 1000 rpms quicker with the larger 76 compressor..

the twisted kits now come with 2876's m8

Another smart student of mine and OVS is on the newer course of the tighter hot side a/r and again finding HUGE gains in response and transitional power as well as peak gains too..

Unlike a 4 stroke we NEED exhaust backpressure to build before we can build Intake pressure.

typically 3 psi in the pipe to see the first 1 psi on the intake side..

after 22 yrs of this I still learn every season ..

FWIW.. on the dyno I still see power climbing at 10 psi over boost ( exhaust backpressure )..

2 psi over in the pipe is 23% down on power vs 5 psi over boost backpressure.

to date BSP is at 209 hp per 400cc of displacement,, safely..

Wheel House Motorsports · Jul 15, 2011

a very wise man right there... ^^^

for those who thing that smaller turbos will spool quicker.. keep telling yourself that and enjoying cranking the boost and heating your charge temps way up to play ball.

the "gulp" factor is also so huge even with very good fueling and a well designed systems i have seen firsthand the benefits of the larger turbo, it makes the power so much more linear where the smaller ones act very on/off and react slow as they cant breathe with the turbo blocking the intake... the big turbo's move so much more air at lower turbine speed that you get a LOT more power right out of the hole. it would blow some folks away how much more managable the powerband gets when you step UP in turbo size. it rides much more like a stocker with HUGE legs on top.

another benefit, again with going from a 2871 to a 3071 with the .64 exh housing on an 800. dropping from 8 to 4.5# of boost to make the same power, charge temps are going to be a fair bit lower meaning gains like longer read life. heck, i imagine the whole motor appreciates a lot less heat being forced into it.

knifedge · Jul 15, 2011

--Seems like a 2876 would work better than a 3071, with the smaller exhaust side offering more back pressure and the larger compressor offering more air.

ACMtnCat · Jul 15, 2011

knifedge said:
--Seems like a 2876 would work better than a 3071, with the smaller exhaust side offering more back pressure and the larger compressor offering more air.

The new ProClimb has a bigger pipe exhaust outlet than the '11 M8. Maybe the 3071 will be the ticket on the ProClimb.?????

Wheel House Motorsports · Jul 16, 2011

knifedge said:
--Seems like a 2876 would work better than a 3071, with the smaller exhaust side offering more back pressure and the larger compressor offering more air.

friend with the setup is running a 3071 with the .64 exhaust housing which flows almost exactly the same as everyone who runs the .86ar 28 series. BUT the compressor on the 3071 is different then the 2871, so it flows more.. different ar on the compressor side. there are tons of little difference between each of them besides just the overall numbering.

WyoBoy1000 · Jul 16, 2011

Personally in my mind I think the 2 stroke cycles more than 2 times the amount of air, when the piston is down all the ports are open which allows the boost to clear the cylinder as well, so not only is it firing twice as much because of the 2 stroke instead of the 4 stroke it flows through the engine more without valves shutting.

I'm still not quite putting this together completely(i might be but want to be sure), from what I understand they are taking the 2876 which is the 28 housing on the hot side and a bigger intake side. But when you say .64 I have no idea. between the 2876 and 3071 could someone list what it is, i e which side you are referring too, then the stock size vs the modified size, so if your saying .64, what was it before and are you changing the inside only or the whole housing. Get specific with all numbers and changes so I can piece it together in my mind and know I understand. If someone would do this I would greatly appreciate it. I don't have the option to get hands the way I need to.

I even thought people where starting to use the 3076 on the m1000

KMOD · Jul 16, 2011

turbobygarrett.com has some good info also.
Kevin

WyoBoy1000 said:
Personally in my mind I think the 2 stroke cycles more than 2 times the amount of air, when the piston is down all the ports are open which allows the boost to clear the cylinder as well, so not only is it firing twice as much because of the 2 stroke instead of the 4 stroke it flows through the engine more without valves shutting.

I'm still not quite putting this together completely(i might be but want to be sure), from what I understand they are taking the 2876 which is the 28 housing on the hot side and a bigger intake side. But when you say .64 I have no idea. between the 2876 and 3071 could someone list what it is, i e which side you are referring too, then the stock size vs the modified size, so if your saying .64, what was it before and are you changing the inside only or the whole housing. Get specific with all numbers and changes so I can piece it together in my mind and know I understand. If someone would do this I would greatly appreciate it. I don't have the option to get hands the way I need to.

I even thought people where starting to use the 3076 on the m1000

Pure Logic Tuning · Jul 16, 2011

People need to also understand the 2876 larger compressor wheel supplies more air to the engine at the same Rpm than the 2871 with the standard compressor housing. The other thing people should be aware of all turbo builders do not use the same compressor housings on the 2871. OVS uses a different compressor housing than other Kit builders. This makes the 2871 achieve boost at a lower RPM like a 2876 but also keeps the pressure ratio of the 2871 to make more power at high altitude at high boost levels. The 3071 with the smaller .64 housing does not spool as fast but does make more midrange and top end power. The customer needs to understand there are gives and takes with with larger turbos and they need to deside what is best for them individually. There is a new Hybrid Garret turbo that OVS is offering for those customers that want the best of both worlds. This turbo flows the the same flow rate as the 3071 compressor with the quick response of the 2871 that customers love to ride.

WyoBoy1000 · Jul 16, 2011

So what is it,

Mine is a 2871-2, its a little slow to get up. Installed new in 09 buy twisted, now they are saying go with the 2876

Wheel House Motorsports · Jul 16, 2011

take a bit out and read on the garrett site, it will open your eyes a lot to what is going on.the .64 is the exhaust housing. on the garrett website it explains exhaust housing .ar sizing much better then i feel like trying to. in general its the overall shape of the housing. the 28 is going to be your wheel size but how the housing is shaped greatly affects flow. a 28 series with a .86 ar exhaust housing is rated at a VERY similar flow to a 30 series with a .64 housing. (bigger wheel, tighter housing) so they act very similar, but not the same. the one i have played with has an optional upgraded compressor on the 71mm compressor wheel, so again it acts different then some.

knifedge · Jul 16, 2011

--Yep, lots of variables here.

http://www.turbobygarrett.com/turbobygarrett/products/turbochargers.html

--At least 8 different 2871 variations from Garrett to choose from and a couple variations for the 2876.
--Add to that, any mix and match combos you may want to try.

WyoBoy1000 · Jul 17, 2011

It is sounding to me like the 2876 with the right housings or what ever is prob the best turbo for get up and go. I ride mine with the 2871 around 8-10lbs on average and it does the job but laggy off the bottom. So on the ho motor and the 2876 up to 12lbs should be the best back country, boonedocking, tight tree combo. Or would the 3071 be better, What do you guys think.

Pretty much I want a new 800 and want to be able to run around 8-12lbs with instant bottom end.

knifedge · Jul 17, 2011

--Read the above post my PURE LOGIC

--Basically they are offering a new "Hybrid" turbo combination that flows like a 3071 and spools like a 2871. The best of both worlds. Then you can add the Tial wastegate on top of that. So if you have the flow and the spool, sounds like a great match. Sounds like the "Hybrid" may be the way to go for boondocking, powder, and even most hillclimbing. I believe the "Hybrid" pulls very strong off the botom also.

--Maybe email them for more detailed info. Definetly do not want to have an outdated turbo kit on a new sled.

WyoBoy1000 · Jul 17, 2011

I did, ovs uses a 2871 hybrid, they say it builds boost at low rpm like the 2876. So why not use the 2876. Twisted claims there 2011 m8 with a 2876 will pull a m1200 out of the hole and keep pulling, also said it will pull similar to a TM1000 up to 10lbs.

knifedge · Jul 17, 2011

--Good to hear that different setups seem to work well.

--OVS claims 7hp more and quicker spool off the bottom with the 2871 hybrid than the 2876 they tested with their setup. Also claim to outpull the M1000 off the bottom and midrange.

--This does not necessarilly mean OVS setup out-pulls and out-spools the Twisted setup or vica versa, although it very well may, especially with the Tial external wastegate.

--Sounds like if either OVS or Twisted performs as claimed, a person couldn't go wrong. Just research(what we are doing now) the specific features and performance of each setup, pick a setup, and go for it.

WyoBoy1000 · Jul 18, 2011

I don't know exactly what twisted's setup is so it might be a hybrid of some sorts but I know my current 2871 is laggy on bottom and great on top. I wish we could do a demo ride with all these options and decide what was best for our riding style.
I don't care for the tail, it just seems like extra unneeded stuff, if I where going for the most power and boost it would be an option but the way I ride you can't even run full throttle at 12lbs but for a few seconds. It might be a little better off bottom though, I wouldn't know. I just like the simplistic less is more nature of the twisted kits.

Hey "J almont", Why the bad rep

knifedge · Jul 18, 2011

-- I like the Tial external wastegate due to the relatively uninterupted exhaust flow over the turbine wheel. Apparently this allows to run 3lbs less boost for the same power compared to a non-Tial(Tial 8lb = 11lb non-Tial). Tial = more power per lb of boost plus quicker, more efficient spool. So less boost = same power = less heat = less octane = less money for high grade fuel. I like simplicity of some of the kits also.

Eli · Jul 18, 2011

Here is a couple links related to the 2871. One is the larger housing and the other is an upgraded compressor wheel. I am wondering if the hybrid that ovs uses is Garretts GTX compressor wheel on the 2871?

http://www.ringer-racing.com/product.sc?productId=178

http://www.atpturbo.com/mm5/merchan...tp&Product_Code=ATP-HSG-138&Category_Code=GCH

HP Per Pound Of Boost

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