Have a 901CC two troke engine running a GT28 60 turbo. Works great turbo is sized about perfect for 5-14lbs of boost. Looking to run a quick spool valve system with the single pipe and run a twin scroll turbo.

Now the hard part what twin scroll turbo is going to fit my needs. I want faster spooling with the same top end power if not a little better. NOTE I have a small electric oil pump so I need to keep a turbo like the GT28 that does not need a ton of oil.

So how much gain do you think I will get I spool up or start to build boost at 5000rpm now at about 1.5lbs and ramps up very fast from there I would like to be spooling at 4000rpm at a higher 2-3lbs of boost.

My turbo specs now are below many thanks for those who can help me out in this area. THANKS!!

COMPRESSOR TURBINE

Turbo CHRA
739548-1 446179-66
Wh Dia Trim A/R
Ind Exd
47.2mm 60.0mm 62 0.60
Wh Dia Trim A/R Type
53.8mm 76 0.86 Wastegated

 

I guess being 2 stroke its nearly 2 ltr to compare with 4 stroke engine ??

 

Not sure on the exact airflow of the motor but yes it moves allot of air for the small size. Mostly interested in a faster spoolup the faster the better. Top end is allready great.

 

Can you fit a tighter trim exh wheel ??

 

I can yes.

So how does a guy go about trying to figure out a good trim combo?? Is there more info that I need to get you guys to help me out??

 

Can we get some more information: snowmobile..... watercraft... bike? Is it a twin or a triple? Whats peak rpm? Single or multple pipes? How much hp n/a? A 2860 is small for 900cc, that is a popular turbo for a 700cc. What is the turbine a/r? We run a t3/t4 50 trim on a SkiDoo 700 twin asphault racer that makes boost @ 5500 with a .63 a/r. I would think a 900 with a 2860 would make boost @ 4500 or less, but be very restrictive up top. Have you ever checked your exhaust backpressure? A 3071 would be a good choice if it is a twin, and you can get that in a .78 a/r twin scroll t3 flange. I never seen this tried, and am very interested in the results.

 

The problem I see is you already have about the best turbo for the combo. If you like the power then going bigger is going to do nothing much increase lag. To get better spool you would need a tighter exhaust that would lose you some power. Since this is a ball bearing turbo already, I don't know what your options would be to keep the power the same but spool better. I would imagine a 2860RS ball bearing turbo is going to spool as fast or faster than anything else in the power range.

 

Raises an interesting question.... If you assume that all of the other factors stay the same (VE etc) - do you simply double the airflow/RPM when using the standard 4 stroke math model? I would think that you would - but don't know enough about how typical 2-strokes work to be sure... Thoughts?

 

Twin Cly was used in a snowmobile at one time.

NA HP is 165ish

I want to use a quick spool valve system and a twin scroll turbo snce I allready have a single pipe system so in my way of thinking I can use a twin scroll with one trim being for fast low end spool then as the valve would it would use the other trim wheel as well for top end power.

 

What type of transmission are you using? Still using snowmobile cvt system?

 

Yes, 900cc moves as much air as 1800 cc 4 stroke assuming equal ve. Its pretty common to plot for the center of the center island of the map.... the one advantage of the cvt transmission. Ive also been told you need more compressor because of the crankcase volume. Exhaust bp is important.... seems like 5-7 psi above boost is a good setup, much more and they tend to eat pistons. There are a few 800cc twins around here running hx35's, and seem to work pretty well.

 

So if I was to go to a GT3071R turbo what trims would work best for me with the twin scroll and is this turbo a good turbo to start with??

 

I say the 3071 is the turbo to run. .82 exhaust The 2871 would be fine too but the 3071 will make more power per pound of boost than the 2871 will and there should be no lag difference because of the cvt. should be fine with the single pipe, have a good y pipe on there though. most of the two stroke stuff I have seen like this use a sigle scroll tang tial stainless housing.

 

Any updates? I didnt see what your peak engine rpm was... what rpm range does it run in? 2 strokes are inherently peaky, and sensitive to exh back pressure, and the turbo motors seem to follow that same powerband. Have you thought about compound turbos.... not for the high pressure ratio, but for a broader power curve? I'm very curious to see how the engine reacts to boost at lower rpm. If your still running the cvt, there is a lot of gain to be had there..... well worth your time.