TOPIC FOR DISCUSSION... HIGH-COMPRESSION, LOW BOOST TURBO FOR 2 STROKE... HMMM.

[o2bncamo]

I am assuming MH is just using the map 17.7 for a reference. A high compression turbo system at sea level is 12.5 to 1. But at 8000 to 11000 feet 12.5 to 1 is very low compression (lazy). I rarely drive my turbo at low elevation but the difference in low end response and spool is dramatic. I see two kits if your looking for high compression low boost, one for low elevation one for high. a 14-1 head at low elevation is just overkill IMO. At elevation at nice upgrade, a way to get some of the low end back.
I would like to hear from somebody that has tried this high compression turbo. Do you gain significant low end grunt? Or does boost come on so early with proper clutching there isn't much to be gained.

"You can do this by putting a butterfly valve in front of the turbo inlet and still getting the higher boost numbers on pump gas with the great throttle response. Valve in front of the turbo intake lets the turbo remain spooled up. And then you have the power on top with full spool up. This discussion is like anything with a traditional turbo set-up...what do you want to trade? Also, typically, one gets the best throttle response with lower octane on a standard motor. So why not just accommodate that as opposed to upping compression?"

This is a great point, like Yamaha does on the new sidewinder. Maybe the future of aftermarket turbo systems.

 

[Daltech]

I am assuming MH is just using the map 17.7 for a reference. A high compression turbo system at sea level is 12.5 to 1. But at 8000 to 11000 feet 12.5 to 1 is very low compression (lazy). I rarely drive my turbo at low elevation but the difference in low end response and spool is dramatic. I see two kits if your looking for high compression low boost, one for low elevation one for high. a 14-1 head at low elevation is just overkill IMO. At elevation at nice upgrade, a way to get some of the low end back.
I would like to hear from somebody that has tried this high compression turbo. Do you gain significant low end grunt? Or does boost come on so early with proper clutching there isn't much to be gained.

"You can do this by putting a butterfly valve in front of the turbo inlet and still getting the higher boost numbers on pump gas with the great throttle response. Valve in front of the turbo intake lets the turbo remain spooled up. And then you have the power on top with full spool up. This discussion is like anything with a traditional turbo set-up...what do you want to trade? Also, typically, one gets the best throttle response with lower octane on a standard motor. So why not just accommodate that as opposed to upping compression?"

This is a great point, like Yamaha does on the new sidewinder. Maybe the future of aftermarket turbo systems.

I dont think the sidewinder does have any butterfly valves. They do have a resirculation valve, that is mentioned in the promo video like it was the next new innovation from yamaha. Truth is this has been used for 30 years in automotive industries. Nothing breaking news with the sidewinder engine.

But, Push turbo does use this approach with a singel TB before turbo. The idea is that the turbo speed is maintained when tb is closed.

More here: http://www.pushturbo.com/home/polaris-section/pro-800/

 

[mountainhorse]

There are plus's and minus's to TB before the compressor.

It has been tried in many racing apps.

I see that Push has used it on some of their turbo kits...and knows about them... but chose not to use in in their new kit for AXYS.



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[roni87]

Turbo heads

What is different on the combustion area on like the turbo heads that rktek markets? I believe they are around stock compression though...wondering if there is much to gain with them?

MH. Would a 2008 cfi head work for your higher compression thought...I have a 2012 motor now

 

[briand]

What is different on the combustion area on like the turbo heads that rktek markets? I believe they are around stock compression though...wondering if there is much to gain with them?

MH. Would a 2008 cfi head work for your higher compression thought...I have a 2012 motor now

I have a 12 800 pro with RKTek dropin kit and BD turbo with the 12.1 turbo domes. ran turbo with both turbo dome 12.1 and 13.1 regular domes with turbo. Biggest difference in design is the turbo domes have bigger bowl area. The 13 domes have smaller but deeper dome area and wider squish area. Performance wise the 13 domes under 8 pounds of boost at 7000 ft have a slightly better topend power where as the 12.1 turbo domes have slight less topend power (Guessing here but maybe 5 hp) but way better bottom and midrange power great for riding in the tress. under same settings as with the 13 domes. really like the turbo domes from RKtek.

 

[mountainhorse]

I'm still pretty convinced that this would be a great setup

100% AV-Gas 100LL

14.5:1 static compression (maybe special dome shape?)

3 lbs at sea level (equal to 7.2 lbs at 10k feet)

No intercooler.

No supplemental injectors

Excellent throttle response.

Better bottom end and transitional power for WOT/Chop/WOT/Chop kind of technical riding... The Added compression would change the character of the engine for sure... and be very consistent in giving rock solid performance to all but those that need more than say 200 hp from their turbo sled.

The 100LL (103 MON)... would be needed for this high compression... and higher cylinder pressures in general to stay off Deto.

I still have not found someone that has run a similar setup to this in say the last two years... sure... I've "heard' of some 'back in the day'... but nothing recently with someone detailing the build with vid, or direct commentary.




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[Sunvang]

Justin,
6 - 7 LBS [Gauge] at what??? 10k feet on pump fuel... thats 16.7 - 17.7 PSIa MAP (what I referred to as '3 lbs at sea level... 17.7 PSIa MAP).

At 6-7 lbs (20 PSIa MAP) at lower elevations.... say 3K feet...Too high for pump gas without pulling timing (performance detractor) or pulling compression (performance detractor).

I dont know about the fuel quality you have over in the US, but here in Norway we run 6 LBS boost on straight 91 pump fuel at 2000ft and no detonations on the MTNTK kits, stock compression and no pulled timing.

On a 50/50 mix of 91 and 100LL we ride at 10 LBS boost no issues. Will try higher boost later on.

 

[JesseJames]

I think what you are looking for Mountainhorse is a smaller turbo that will be spooled up a little at engagement.

I have wanted something just like you are talking about for a long time, minus the Av gas. Always thought if I could just bring 180hp to the mountains, you would really have something fun to ride.

You could have all that on pump gas with a smaller turbo that spools faster so you are making power at engagement, and still making 180-190hp on the big end. I think it would be fun to ride, and only running 3-7lbs of boost, you wouldn't need a charge air cooler. Or perhaps a turbo with variable vanes that acts like a small turbo at spool up, and can still make the power on the big end other people are looking for.

 

[JesseJames]

If it was spooled up a little at engagement rpm, you would have the low end power a guy likes, without the need for high compression.

 

[mountainhorse]

OR...

A turbo that has a much lighter spool ... like the groundbreaking EFR's from BW... with the gamma-ti turbines that are about 1/2 the mass of comparable turbos turbines ...

But still.... I'd want the high comp for the bottom end and transitional torque.
The same 'character benefits' that a NA sled gets from higher comp.

I think what you are looking for Mountainhorse is a smaller turbo that will be spooled up a little at engagement.

I have wanted something just like you are talking about for a long time, minus the Av gas. Always thought if I could just bring 180hp to the mountains, you would really have something fun to ride.

You could have all that on pump gas with a smaller turbo that spools faster so you are making power at engagement, and still making 180-190hp on the big end. I think it would be fun to ride, and only running 3-7lbs of boost, you wouldn't need a charge air cooler. Or perhaps a turbo with variable vanes that acts like a small turbo at spool up, and can still make the power on the big end other people are looking for.

 

[mountainhorse]

I'll digress a 'hair'... related to the topic though.

A sincere question that I hope those answering can put some effort into.

An IQR 600...pick a year.... what HP does a properly tuned one make on Race-Gas (with race-gas head & pipe)?
What does that same engine/sled make, HP-wise, on lower-compression head & pipe w/91 octane... properly tuned of course? (Say that a seasoned/vet factory level mechanic is tuning these).

Then.... MORE importantly.... What is the 'character' of these two scenarios (hi-comp/race, lower-comp/pump-91) on the same sled... HOW do they run differently? (eg throttle response, rpm recovery, acceleration etc)... the PRO and CON for each side would be nice as well.




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