If the S4 was

B5 S4/ RS4
#22

yeah the airflow capability is going to limit the upper end, but pressure losses due to airflow restrictions will decrease the air density in the cylinder well the valves close and the air stagnates (basically the restriction will slow down the gases)

also higher compressor outlet pressures may push the compressor out of its efficiency range (or it may push it into it), but without a compressor map its tough to say

depending on where you are measuring your boost it can be indicative of a restriction… so if it takes 40 psi to push 48lbs/min of air while a different setup can move that 48lbs/min with only a 30psi differential you may have something between the pressure tap and the tailpipe of the car causing significant backpressure/restriction

air flow makes the power, but inefficiency will chip away at that max output that that airflow can achieve… inefficiency can be flow issues, improper timing curve, poor combustion, etc

#23

Right, good stuff. So where and how do we find a middle ground? Spool (power curve) and power. What you have referenced seems to be worst case scenario. I don’t think we have experienced that extreme yet. How do we avoid it on say, a car that aims to make 900whp.

#24

how do you avoid the discussion around efficiency? Very well.

#25

If you owned a B5 what would you do? I’m not avoiding I’m asking for opinions and stating concerns. Overall efficiency can create laggy situations. I guarantee the RS6-R car has unefficiencies in it. That is a car you seem to respect. All I am asking for is suggestions. I am aware as we all are that you disagree about how I am going about it. So why don’t you give it a go. It seems to me all you are doing is criticizing while never giving solutions.

#26

I don’t know anything about jay’s build…or those turbos. For whatever reason the info leaked about their time and they posted a video. Not their style…they usually share all kinds of info in one big shot.

I don’t disagree about how you are going about it. I just think a massive power build B5 S4 should address the exhaust mani, the downpipes, the catback, the cooling, and of course tuning and fuelling…and a million little things. I’d strengthen up the axles since they have a propensity to give up when you really hammer the car from a stop. If I just dropped $20,000 I wouldn’t skimp on the last $2000. If I just dropped $5000, sure I’d skip that $2500 if I could. I don’t get the impression you’re a $5,000 build kinda guy though. I also think you’re taking my criticisms of AMD way too personally. Unless they now have 3 employees, you don’t work there. You’re an actor.

I could be dead wrong. Of course a few folks have long before posted what I am saying. (I’m no researcher, I’m just repeating wise words that have been shared with me in the past). You just appear to not like it when I say it. Understandable, I’m annoying that way. Then again, you and Jason could be dead wrong. You could be hurting performance, hurting your turbos, and hurting your engine. That doesn’t sound like a really good idea.

#27

With NA its all about increasing efficiency as much as possible to free up hp, so it seems very counterproductive to say you want some inefficiency to help create additional pressure/heat/restriction b/c of the fear that it might not get to X psi fast enough.

If you were saying each primary on the exhaust manifold was 3", then yes, that would most likely not be beneficial, just as saying each primary being less than .5" is not beneficial. But to say X turbo needs to be at a certain psi to operate properly, so we’ll just make sure it’s bottlenecked before the turbo to create that seems backwards. It possibly goes back to the faults at the beginning and selecting a PSI for a turbo rather than working through efficiency & cfm goals and allowing psi to be the end result of all other components, not the beginning.

It makes me think of the theory of making 500whp at 40psi, vs 500whp at 30psi.

(not directed at anyone, just observation of many B5 conversations and/or builds)

#28

There is a correct combination of air flow and velocity. If you don’t strike the balance you will be losing power somewhere. Velocity in the manifold helps spool the turbo and (power under the curve). Like we all have said too little of an opening doesn’t create much more velocity and creates harmful back pressure problems. Does anyone have access to stock manifold flowbenh numbers?

#29

nitrous, give it some juice to light the turbos and then back it off… it’d be cool to add in a MAP input to a nitrous control in addition to the wot and rpm controls… i.e. determine the size of the shot based on the boost youre making and taper it off until you are at full boost.

but really though I’m not familiar enough with the 2.7T to say where exactly that is

#30

That’s the plan on my yellow car. Nitrous express makes a controller called “instaboost” it’s pretty much exactly what I would need.

#31

[/quote]
Sorry your 110% wrong especially on the larger dia tubing equaling slower spool. I bet if you take 770 turbos an run them on those manifolds they will spool faster, make more power at less boost etc. restriction causes slower spool as back pressure is adding weight to the turbine wheel ie slowing it down

#32

Sorry your 110% wrong especially on the larger dia tubing equaling slower spool. I bet if you take 770 turbos an run them on those manifolds they will spool faster, make more power at less boost etc. restriction causes slower spool as back pressure is adding weight to the turbine wheel ie slowing it down
[/quote]
go look at gearhead’s 770 dyno charts v.s. any other 2.7L with 770s. It has the vast log manifolds. They were larger and didn’t make anymore power than stock manifolds that are 3/4 inch smaller.

#33

flow bench numbers really don’t tell the full story. If you want a quick test to see how well the stock manis perform without going through all the flow bench b.s. take the manifold, grab your air compressor and just put 15lbs in the furthest runner from where the turbo mounts. After you do this pretty basic test you will see 15lbs of air coming back out the other 2 runners as well. Thats back pressure and the major problem with those log manifolds. If you do this very same test on those merge collector manifolds they won’t have hardly any back pressure at 100psi

#34

go look at gearhead’s 770 dyno charts v.s. any other 2.7L with 770s. It has the vast log manifolds. They were larger and didn’t make anymore power than stock manifolds that are 3/4 inch smaller.
[/quote]
Exactly “log manifold”

#35

^^^^Those turbo’s are 770’s,

but at what psi did gearhead make his power

#36

The same, and those are 2868, same center sections, different hotside and comp covers. Big difference in flow of that tial V-band hot-side.

#37

Exactly “log manifold”
[/quote]
You never said anything about changing to an equal length. I just said larger diameter doesn’t work better in every scenario. Gearhead’s was a great example. He had to run very similar boost to yield similar power as the stock manifolds.

#38

You never said anything about changing to an equal length. I just said larger diameter doesn’t work better in every scenario. Gearhead’s was a great example. He had to run very similar boost to yield similar power as the stock manifolds.
[/quote]
Doesn’t need to be equal length, a lot of times you will have to add ft more tubing to acheive equal length and at that point your going backwards.Just needs to have proper diameter runners with a proper merge collector

#39

As long as you keep your setup on the simple side you will have one of the best setups out but if you want the best than add the new Garrett GTX2863 turbos to your kit and sell the 2868 turbos. Skip the nitrous you wont need it.

#40

I’m not going with 2868s anymore. I’m going with a 2873 the only thing I’m utilizing is my V-band hotside cover. It flows more than the 2863 and spools faster than a 2871.

#41

Sorry to chime in so late

I think that you could make 2-2.5hp per cubic inch easily in a built motor that was n/a and if you really push it you can make 3 + or - .35

I think that you could take a 2.7L FULLY built with 15.1 compression and 116 octane and make 3-400 wheel hp with the correct heads cams intake and open headers.
I also think that you could make 225-275 wheel with out much problem… all it takes is money

Now I think that without going into the engine you would be shy of 200 wheel i agree there…

my 2Cents