20G Fever!
Sep 26, 2005, 11:20 AM
#47
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Originally Posted by atlvalet
Here's a question. Would stroking an engine (thereby allowing more air into it) help with compressor surge? Or will surge be there no matter what?
If you drive the car properly you will never even feel the surge - you just have to keep the revs over 4500 at all times to avoid it 100%
When it happens its not bad and I have seen it on a lot of cars - especially the subarus with the 20g I mentioned
Sep 26, 2005, 11:22 AM
#48
Originally Posted by NocturnalEVO
is there any way to fix this 'surge' problem?
Ultimately, you have to increase volumetric efficiency at this rpm range. This can be achieved by porting the cylinder head or using higher lift cams to gain some efficiency.
You can also increase displacement. This will change volumetric efficiency as well, by triggering spoolup a bit earlier and increasing volume.
You can also try to tune it out with some cam gears, but caveat emptor on that one, as the inexperienced will find out what an exact science that is.
Regards,
Sep 26, 2005, 11:25 AM
#50
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Originally Posted by 4G63>OOOO
Typically, you can go about this a couple different ways:
Ultimately, you have to increase volumetric efficiency at this rpm range. This can be achieved by porting the cylinder head or using higher lift cams to gain some efficiency.
You can also increase displacement. This will change volumetric efficiency as well, by triggering spoolup a bit earlier and increasing volume.
You can also try to tune it out with some cam gears, but caveat emptor on that one, as the inexperienced will find out what an exact science that is.
Regards,
Ultimately, you have to increase volumetric efficiency at this rpm range. This can be achieved by porting the cylinder head or using higher lift cams to gain some efficiency.
You can also increase displacement. This will change volumetric efficiency as well, by triggering spoolup a bit earlier and increasing volume.
You can also try to tune it out with some cam gears, but caveat emptor on that one, as the inexperienced will find out what an exact science that is.
Regards,
Maybe David has tried that already
Sep 26, 2005, 11:27 AM
#51
That's another way to do it as well. Don't the Evo400 boys over in the UK have a 4" antisurge cover that they're using? Could be worth getting in touch with them as they've btdt.
Let us know how you make out.
Regards,
Let us know how you make out.
Regards,
Sep 26, 2005, 11:33 AM
#52
Originally Posted by 4G63>OOOO
Triny,
Nice explanation, but the way I understand it is a little different.
Think of things not in terms of pounds of boost, but mass air. You have this turbo compressing this mass of air and trying to stuff it into 2000cc's of engine volume. At a certain rpm range, the motor just can't take in this amount of air and it gets backed up, so to speak. If your diverter valve isn't soft enough, it will get "backed up" all the way back to the compressor wheel and either slow it down or stall it. At higher rpms, the engine's volumetric efficiency is such that it can digest this volume of air compared to its capability at lower rpm's.
Think of it in terms of fluid dynamics and it makes a lot more sense.
Nice explanation, but the way I understand it is a little different.
Think of things not in terms of pounds of boost, but mass air. You have this turbo compressing this mass of air and trying to stuff it into 2000cc's of engine volume. At a certain rpm range, the motor just can't take in this amount of air and it gets backed up, so to speak. If your diverter valve isn't soft enough, it will get "backed up" all the way back to the compressor wheel and either slow it down or stall it. At higher rpms, the engine's volumetric efficiency is such that it can digest this volume of air compared to its capability at lower rpm's.
Think of it in terms of fluid dynamics and it makes a lot more sense.
now that i think about the definition of stall should be this: the situation where you lose rejoined flow such that the breakway causes an unhealthy pressure differential causing drag and loss of desired aerodynamic characteristics. sooo... with that said... the situation you described can also happen. the pressure differential instead generated by backed up air instead of oversped air. both actually happen, it's not to say that surge doesn't happen in the way that i described, but the increasing displacement arguement would help this "volumetric stall" that you described. tho raising displacement causes a whole lotta other flow characteristic changes as you already said.
so i guess in conclusion there are at least three types of compressor stall. one being the normal oversped air stall, the volumetric stall and the purge stall. the volumetric can be tuned by using the proper sized turbo on the proper sized engine and the purge stall is done away with a proper bov. the oversped air stall is generally the hardest which is why i mentioned garrett does lots of testing for it.
Originally Posted by 4G63>OOOO
Typically, you can go about this a couple different ways:
Ultimately, you have to increase volumetric efficiency at this rpm range. This can be achieved by porting the cylinder head or using higher lift cams to gain some efficiency.
You can also increase displacement. This will change volumetric efficiency as well, by triggering spoolup a bit earlier and increasing volume.
You can also try to tune it out with some cam gears, but caveat emptor on that one, as the inexperienced will find out what an exact science that is.
Regards,
Ultimately, you have to increase volumetric efficiency at this rpm range. This can be achieved by porting the cylinder head or using higher lift cams to gain some efficiency.
You can also increase displacement. This will change volumetric efficiency as well, by triggering spoolup a bit earlier and increasing volume.
You can also try to tune it out with some cam gears, but caveat emptor on that one, as the inexperienced will find out what an exact science that is.
Regards,
you may be right about increasing efficiency, as i recall br kept raving about how the 20g on his car is now surgeless, i believe he has all the goodies on his car... so maybe that's why.
answers please!
Last edited by trinydex; Sep 26, 2005 at 11:40 AM.
Sep 26, 2005, 11:39 AM
#55
EXCEPT that the volumetric stall (when you're trying for 100% or close VE) will never be 100% gone due to the fact that airflow requirements for 100% VE at 7k rpm will not necessarily (read:almost never) get you something surge-free down low in the rev range.
Like anything else, maximizing VE is a compromise, like anything else you modify on your car.
Regards,
Like anything else, maximizing VE is a compromise, like anything else you modify on your car.
Regards,
Sep 26, 2005, 11:45 AM
#57
it's all about very very meticulous tuning (choosing). you put a huge turbine on a huge engine with a small compressor you will get boost taper and possibly oversped surge.
you put a big everything on a small engine and you get the volumetric surge and prolly problems with your bov holding things down and being able to release.
you gotta get the babybear solution... just right for everything, which is really sodding hard.
but then you could just deal with the surge... if you have a race car a lil burp after launch aint' a big deal... if you live above 5000 all the time... again... no big deal... it's only for the daily driven ultimate street car where the surge becomes a problem
you put a big everything on a small engine and you get the volumetric surge and prolly problems with your bov holding things down and being able to release.
you gotta get the babybear solution... just right for everything, which is really sodding hard.
but then you could just deal with the surge... if you have a race car a lil burp after launch aint' a big deal... if you live above 5000 all the time... again... no big deal... it's only for the daily driven ultimate street car where the surge becomes a problem
Last edited by trinydex; Sep 26, 2005 at 11:48 AM.
Sep 26, 2005, 01:28 PM
#59
Originally Posted by Pruven
1 - I like the 20 G the best as it feels stock like and makes big power
2 - Sti with 20 G makes 390 tq and 425 whp on pump gas - (at least one I tuned did) Seems that the evo will hold more power after 6,000 than the sti will but the sti will kill it in low end tq. An evo with a 2.3 L would be a even match
3 - Yes - its good for 28 - 30 psi
4 I dont like the 3071 or 3076 at all
I would either do a TME or 20 G or go with the GT35R
AL on Dan's computer by mistake
2 - Sti with 20 G makes 390 tq and 425 whp on pump gas - (at least one I tuned did) Seems that the evo will hold more power after 6,000 than the sti will but the sti will kill it in low end tq. An evo with a 2.3 L would be a even match
3 - Yes - its good for 28 - 30 psi
4 I dont like the 3071 or 3076 at all
I would either do a TME or 20 G or go with the GT35R
AL on Dan's computer by mistake
thanks Al, i really appreciate it. here is my situation, i would love to get the 35r but my elevation is making it tough(6000ft). local people with the 3076r are getting full boost at 4400-4600rpm in 3rd gear. i figure that the 35r would be pointless.
a friend of mine is getting the 20g for his sti and of coarse there is competition between us so i want something that can help my car perform better. the 2.3 is possibly in my future plans. what set up can you recommend in my situation? for tuning, i am really hoping for a custom tune from you if you come out to Denver.
Sep 26, 2005, 01:35 PM
#60
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Originally Posted by Nez136
i would like to hear some more opinions on drivability....20g owners please come out!
I was told that a road racining customer Jim Potts drove the RS and was finding the compressor surge very annoying
I dont find it to be any difficultly
I mention it becuase I want to remain credable and make sure that no one buys this unit without being aware or the condition
IMHO its a minor sore spot and this turbo represents huge performance opportunities at a bargain price