Compound boost not as expected

[englertracing]

another
https://youtu.be/A48PTg4UKQM
https://www.youtube.com/watch?v=IIMkmfFvL0A

hmm 1250hp with no lag

[ptuomov]

So, outside racing classes with specific rules, when is twin charging better than just increasing displacement of the base engine in a normal turbo system? I’m thinking that maybe if you Miller cycle it, and don’t run a too high of a pressure ratio with the supercharger, this might work.

[craigory]

My main reason for keeping it smaller cc was for economy. I know this isnt much of a concern to most, but the way my twincharge engine is setup now I can commute to work and mostly avoid boost and get 28-30 MP (Canadian) G
Once I get to 75% tps its all go then though.

[ptuomov]

My main reason for keeping it smaller cc was for economy. I know this isnt much of a concern to most, but the way my twincharge engine is setup now I can commute to work and mostly avoid boost and get 28-30 MP (Canadian) G
Once I get to 75% tps its all go then though.

It's usually hard to get a small mechanically supercharged engine to give better fuel economy than a large normally aspirated engine, except when the cams are implementing the Miller cycle. That's my understanding of it anyway.

(It's true that 300hp 2L normally aspirated engine is a nightmare to drive in every way, while 300hp supercharged 2L engine can be docile and economical.)

[craigory]

I may be running a slight Miller effect as my cam is retarded by 4 degrees.
If i ever get a cam ground for this specific application its gonna need thought..

[craigory]

Anyone care to comment on a cam spec for this engine?
I'm guessing a wide lsa.. Not much on the shelf stuff for a compound Twincharged

[user-23911]

Just a "normal " cam.

No such thing as a special turbo cam, not unless you sell such things to make money, then they cost extra.

[ptuomov]

Anyone care to comment on a cam spec for this engine? I'm guessing a wide lsa.. Not much on the shelf stuff for a compound Twincharged

Where are your intake and exhaust manifold cycle average pressures? I'm thinking narrow LSA like in a normally aspirated engine. Isn't the ability to run a lot of camshaft overlap the whole point of twin charging with a turbo and a belt-driven supercharger? If you want to "Miller cycle" it, then I guess you retard everything a lot. Just a reminder, I don't know what I'm talking about, just thinking out loud!

[Wolf_Tm250]

I've daily driven turbo cars with a power band like that. They are nice, I actually like that it's just a normal car under 4k, kinda of jekyll hyde ish. Have you driven a blower car? The response is just not comparable, even in boost modulating the throttle is completely different. Not to mention any low speed turns you are going to be out of boost and a 4k turbo would get absolutely destroyed in those hill climb events if you watch some of the excruciatingly slow speed corner exits.

I don't see any evidence a 35r range turbo would even be in the same league as that twincharged evo for the type of racing he does.

https://youtu.be/9x-pkymzDOA
i dont know turbochargers is a gt3076r ancient school, old school, current, or new tech?
look at the dyno chart there is a difference of 150HP at 2300rpm.............
why wouldnt you want that? why are you so opposed to superchargers?
do you not enjoy immediate throttle response?
do you like to use throttle to correct under steer?

I simply don't understand your opposition?
the cons are what? 35 extra lbs of weight?
I guarantee you that is more fun to drive with the supercharger except to maybe a novice that finds the boost coming on late and suddenly amusingly scary and would be afraid to floor it with the supercharger.

I dont care how advanced the turbocharger is, but i suppose you can downsize the supercharger the better the turbo is. To me its an efficient, quiet reliable, FAST, anti lag system with a small weight penalty.

perhaps I am biased towards superchargers in the way that you are biased towards turbochargers, If a twin charge system is too complex, then just leave off the turbocharger . I am going to build a 2500cc-2800cc 4 cylinder with a whipple 510R twin screw supercharger, targeting 700hp on e85 for something like a street legal hill climb car. That way you really get to hear the exhaust , No lag, and pretty simple, consistent 2d throttle response, off idle power, ability to change boost with pulleys

Tim, englertracing,
yes I drove supercharged cars and I'm not against them in principle.
What I love is that turbochargers take advantage of a lost energy, the exhaust gasses one, so they are more efficient and don't rob power from the crank.
Furthermore the newer ones, smaller, better design, with lighter wheels, give you the instant boost you love in your supercharged cars and, yes, you can also correct understeer with throttle... you just have to stay over the spool up rpm threshold.... but that's really easy as you have just to run to the red line, change gear up and you'll always be over the spool up threshold, so in an instant boost region.
About hill climbs slow speed turns, there always is anti-lag to help.

PS: GT3076R is a very laggy old school (52.5 lbs/min flow - PR of 3 @ 28lbs/min) , the newer GTX3076 gen2 spools faster (PR of 3 @ 22lbs/min) and is a 62 lbs/min flow at the same efficiency (that's 100hp more)
PS2: GTX3582R gen2 is 82 lbs/min flow at 60% efficiency, so potentially an 800 hp turbo
PS3: I never wrote a compund system won't have more power than a same power single turbo somewhere in the powerband....

[ptuomov]

Do any of the modern turbos have an internal wastegate that is sufficiently high flow to use as a circuit for a second turbo in a sequential system?

[Big Al]

ptuomov: Actually no if you go for like +600hp. My friend had to build a custom exhaust housing for the big turbo on the triple turbo setup.
If you build like a 2-stage with ~400hp there are options on turbos with internal WG that could work.

[Big Al]

Wolf_Tm250: What's the difference between Gen 1 and Gen 2 GTX? other measurements?
I havn't actually looked at Garrett for "ages" because when the GTX came there was nothing new ... the 11 full length blade compressor is one that they had many years sooner but now they made it in billet and called it new. And the turbine had still bad measurements and spools with a bang. So I recommend people who ask for a turbo everything else then a Garrett.
So I hope they have actually made improvements on these Gen2

[craigory]

[/quote]


Tim, englertracing,
yes I drove supercharged cars and I'm not against them in principle.
What I love is that turbochargers take advantage of a lost energy, the exhaust gasses one, so they are more efficient and don't rob power from the crank.
Furthermore the newer ones, smaller, better design, with lighter wheels, give you the instant boost you love in your supercharged cars and, yes, you can also correct understeer with throttle... you just have to stay over the spool up rpm threshold.... but that's really easy as you have just to run to the red line, change gear up and you'll always be over the spool up threshold, so in an instant boost region.
About hill climbs slow speed turns, there always is anti-lag to help.
[/quote]



Having the turbo above the spool threshold is the way forward but you still interupt it with closed throttle events during gear change and over run.
A positive displacememt charger still gulps the same volume at closed throttle events at any rpm.. So the turbo basically gets to keep going with no interaction with a BOV.. Its hard to describe or even explain how mad this thing is at higher rpm.
Its like the turbo gets to freewheel but in a controlled environment and not over spinning like it would if vented to atmo. This is why i think venting (recirculating) to before the turbo is better than venting to after... Venting after will have similar properties to a turbo only set up...
Boost doesn't build its like opening a high pressure valve right to the throttle body.

As i stated before, I was having bypass issues that ive now addressed. But during problematic times my FMIC has a bulge on the bottom row... What kinda pressure would do that..

I'm getting the high boost from turbo and the instant boost from charger at the same time. Apart from the parasitic draw this seems to be working not too bad.

[craigory]

I also perceive the parasitic draw to be not much more than it would be if pumping atmo air. The boost from turbo will actually be helping it turn.

[Wolf_Tm250]

Wolf_Tm250: What's the difference between Gen 1 and Gen 2 GTX? other measurements?
I havn't actually looked at Garrett for "ages" because when the GTX came there was nothing new ... the 11 full length blade compressor is one that they had many years sooner but now they made it in billet and called it new. And the turbine had still bad measurements and spools with a bang. So I recommend people who ask for a turbo everything else then a Garrett.
So I hope they have actually made improvements on these Gen2

Really don't know what's new inside them, except the advertised "new comp wheel aero", anyway these are some comparisons between gtx gen1 and gen2





So as the gen2 area are wider, then it seems to be a better choice... not to mention the jump we already had between GT and GTX gen1:



.... and over the "ancient school" T series:



So that's why I pretty understand you had to compound boost a T series in the good ol' days....