HP Per Pound Of Boost
- Thread starter WITHERS
- Start date
There are sooooo many variables to this. Air temp, volume, density (read: elevation), type of fuel/oil and corresponding burn times, etc, etc, etc. Just thinking of the number of things that would have to be included in such an equation to make it accurate makes my mind hurt at this time of night....
But, x2 on it being cool to know if someone has spent a nice chunk of time figuring it out...
But, x2 on it being cool to know if someone has spent a nice chunk of time figuring it out...
W
WITHERS
Active member
I understand what your'e sayin with all the variables,just lookin for a rough number. Say for example an M6 should make somewhere between 4-7 hp per pound depending on variables. An M8 should make between 6-9.An M1000 should make between 8-11. This is the kind of answer I'm looking for.There are sooooo many variables to this. Air temp, volume, density (read: elevation), type of fuel/oil and corresponding burn times, etc, etc, etc. Just thinking of the number of things that would have to be included in such an equation to make it accurate makes my mind hurt at this time of night....
But, x2 on it being cool to know if someone has spent a nice chunk of time figuring it out...
very good answer.
There are sooooo many variables to this. Air temp, volume, density (read: elevation), type of fuel/oil and corresponding burn times, etc, etc, etc. Just thinking of the number of things that would have to be included in such an equation to make it accurate makes my mind hurt at this time of night....
But, x2 on it being cool to know if someone has spent a nice chunk of time figuring it out...
Just to give a number (taking into consideration the comments above), the most common one I see used in regards to the M8 is 8hp/psi. I feel that on my setup (2860) the gain is minimal from 5 to 8, then increases greatly from 10 to 14. so, just to give an idea, that from 5 to 8 I think I see about 6 & from 10 to 14 I think I see about 10. (just as an example, NOT accurate numbers, just what I see in my cutler stage II setups trying to set them up for different PSI levels.)
The 8hp number is also what I heard from Zollingers, who I feel avoid spewing incorrect data, so it's likely a good baseline example.
The 8hp number is also what I heard from Zollingers, who I feel avoid spewing incorrect data, so it's likely a good baseline example.
On my 800 it feels like anything less than 6lbs is weak then every 2lbs after that just seems to double.
I also wondered about the turbo sizing. Given two commonly used turbos, I assume that the bigger turbo at 10psi might be more efficient than the smaller turbo at 10psi(on the same motor). Therefore make more HP at the exact same boost level??? Is that correct?
Sorry to hijack, but it seems to be a big part of the equation??????
K
knifedge
Well-known member
--For the M8, OVS uses the 2871 and Twisted uses the 2876
--Apparently the bigger compressors are better able to supply the volume of air off the bottom and thru out the rpm range that 2 strokes need.
You can search the forum and also check this interesting thread
http://www.snowestonline.com/forum/showthread.php?t=269008
--Apparently the bigger compressors are better able to supply the volume of air off the bottom and thru out the rpm range that 2 strokes need.
You can search the forum and also check this interesting thread
http://www.snowestonline.com/forum/showthread.php?t=269008
But is there a specific range where one will be more efficient than the other? IE: 2860 is efficient from 8 to 12, falls off after that...2871 is more efficient from 9-14, and 2876 is best from 12-15? (examples only here)
Then there's the push turbo... which is a whole different beast as well.
I would assume that these would each have a "sweet spot" and I wonder how they compare in that respect. On mine (2860's) it seems to be 10-14, never used any of the other turbos to compare though.
The 2876 is the best from top to bottom. The bigger turbos will produce more power at lower boost. Thats what I've been told.
The 2871 has been the tried and true for OVS, but they have been running bigger turbos on some sleds for a couple of seasons. They took the 2876 off my TM8 and we have been running a different turbo since the start of the season with some amazing results, and the 76 was no slouch. That is why I think 10 psi is not 10 psi is not 10 psi.....LOL
Yeah... but if JUST a bigger turbo was all it takes, we'd be running 3 series compressors on the 8, and we know that doesn't work... not very well anyhow.
i just know that a 3071 on 4.5# pulls what a 2871 on 8# will for clutching on the exact same sled, no changes besides switching turbo, so its NOT a simple equation or even close, build a good kit and it will stomp others at far less boost. pressure is just a matter of restriction, horsepower is how much air and fuel you can burn in the motor(safely)... something to think about.
not every turbo produce same air volume at same boost.
10psi on gt30xx if much more air volume then 10psi on a gt26 series. even if the boost level is the same.
there is no turbo kit actually available on the market with a real life air volume calculation. I know that MCX has done some calculations for their Yamaha 4 Stroke kits and they use those turbos out of the Volvo cars then they produce the necessary air volume for the engine.
for two stroke it is a bit different calculation, then there are so many things that need to be calculated.
10psi on gt30xx if much more air volume then 10psi on a gt26 series. even if the boost level is the same.
there is no turbo kit actually available on the market with a real life air volume calculation. I know that MCX has done some calculations for their Yamaha 4 Stroke kits and they use those turbos out of the Volvo cars then they produce the necessary air volume for the engine.
for two stroke it is a bit different calculation, then there are so many things that need to be calculated.
Actually, you will see some very smart turbo builders who tested the tighter .64 30 series on the 800 and found even better drivability and instant response to throttle..
funny how that old leverage thing works, larger diameter wheel with a tighter housing is quicker to react AND outflow the smaller diameter larger leak ( a/r) 28 housings.
Some of the 800's have really high port timing and will not work as well without adjustment but you will see these 3071 .64's in use on 800cc sleds.
Gus
Gus,
I think I get what you are saying but still not 100%, so there taking the 3071 and changing the housing to a .64, which housing, or could you explain it a little better. I am a hands on person and until I see it its hard for my mind to put together, or at least to be sure I am putting together the right pieces in the right order. What about fueling, hows that working out.
I think I get what you are saying but still not 100%, so there taking the 3071 and changing the housing to a .64, which housing, or could you explain it a little better. I am a hands on person and until I see it its hard for my mind to put together, or at least to be sure I am putting together the right pieces in the right order. What about fueling, hows that working out.
It's amazing when you get into turbos... when you think you're SOMEWHAT knowledgeable... how you find out you know NOTHING!
So why the heck aren't we all using the larger turbos then? What kept that from happening? I know the 3071 is common on the 1000, but the AR on the one that works for the 1000 is different I'd assume than the 64?
So why the heck aren't we all using the larger turbos then? What kept that from happening? I know the 3071 is common on the 1000, but the AR on the one that works for the 1000 is different I'd assume than the 64?
D
diggerdown
Well-known member
Usually the larger the turbo volume the slower responce time is. Horsepower to psi readings will have so many variables it would be hard to calculate. I'm sure setting on a dyno and adjusting the pressures could give a pretty fair idea. If that has a direct corralation to adjusting for altitude would be the next step. If the M8 put out 160 hp at 10,000' with 10lbs. of boost it would be 3% increase for every lb. of boost. However I doubt it would be a constant figure.
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