When do we know that the problem is in the air?

[MetalMania80]

Hello.

If it comes to fuel, it seems quite simple. Bad quality- ignition timing correction. Not enough- high trims, bad AFR, fuel pump pressure drop.

But what can tell us the engine needs more air? New big mouth snorkels, new intakes, bigger intercooler and so on?
Is there something in the logs that would say it to us? Is there really a need to install snorkels, intakes, bigger air filters and so on?

 

[Thomby]

I don't know that the engine will ever "need" more air, in the sense that the intake system is throttling it to the point of a bottleneck. You could say that any engine that doesn't have its fuel system fully maxed out is airflow-limited (since if it had more air, it could add more fuel), in the same way that any car that isn't power or traction limited must be gear limited.

But in terms of when a less restrictive intake system will make a non-negligible difference in how the car breathes, I guess you could either hook your intake up to a flow bench like they use to test cylinder heads, or swap it out for air filters mounted directly to the turbos and see what the difference is on a dyno.

 

[MetalMania80]

Ok, but shouldn't we see any difference in max boost (ECU) duo to turbo performance?

I'll take some 60-130 MPH with different setups, too costly and time-consuming to go for dyno.

 

[Thomby]

Ok, but shouldn't we see any difference in max boost (ECU) duo to turbo performance?

I was assuming by "more air" you meant "freer flowing intake" based on the mods you described, at a given level of boost. And I think the answer is that the convoluted stock routing probably has some restriction that any open airbox (or sealed box + snorkels) eliminates. If there were further room for improvement, you can't beat a cone filter on the turbo itself.

If you're asking more generally if the engine is limited by the amount of air, that's easy: if you aren't fuel limited (quantity or knock), you're air limited. But that really means turbo limited (either via self-imposed boost limit, or thermally...not a physical restriction between turbo and engine).

So if your logs show zero timing corrections, you're "air limited" by your conservative boost limit. If you have mild corrections, you're air limited by your octane. And if you ran BEF+E85+CPI/WMI with the turbo cranked to the max, you'd be air limited by the size/efficiency of the turbo itself (and exhaust manifold restriction).

 

[Corleone1]

There is always a limit at both sides. For us its mostly fuel and turbosize. If you do things that facilitates airflow at intake side, it will be a benefit, also if you do it at exhaust side even more. Backpressure kills power. In our case we have small turbos but also cats, DPs and the rest of exhaust will take down power as long as the turbos is enough. In the GTRs we have built we do 100 more whp if we demount exhaust after downpipes, of course this is when turbos isnt the limit.

If you ease up both sides engines VE (volumetric efficiency) will increas, it means that you can have the same power to the turbos max at like 18 psi instead of 22. At the end power are always comes from the amount of cylinderpressure but you again can kill it with backpressure after.

 

[MetalMania80]

Ok. I don't want to mess too much with my exhaust. If so, mayby catback. Comfort is important for me to.

If it comes to logs, mayby I'm wrong,but wouldn't wastgate valve go higher on this same boost when intakes flow is limited?

 

[Corleone1]

If intake side is limited, turbo need to close wg more to reach the asked boost or airmass, same with the exhaust side, more resistant it takes more turbo rpm to produce the air that asked power takes.

 

[MetalMania80]

So, when I see JB4 logs with WGDC 98-99 I can assume I'm air limited?

Do You think only cat-back gives some noticeable improvement?

 

[Corleone1]

If wg = 0 it will be fully open and if it is 100 (and the max figures are = 100 in JB, I dont remember) it will be fully open and do what it could as the in and out are sluggish. If you free up, both or either side turbo can produce what is asked with lower energy from the exhausts. If you run Ethanol that burns with lower temp it can be a need for more closed but as also the temp/volume is less the backpressure will be lower, a real benefit.

 

[MetalMania80]

So, I asked differently. I hit a 20-22 psi boost with Ign 18-19 deg. I don't want to go higger with that. WGDC is 80-90.
Am I air-limited? Would changing intakes/exhausts give me more power/torque? I do not want to upgrade my turbos.

Yes, I'm running E30-40.

 

[Corleone1]

Probably same power with less boost and less wg

 

[Thomby]

In the GTRs we have built we do 100 more whp if we demount exhaust after downpipes, of course this is when turbos isnt the limit.

You're saying exhaust dumps net you 100hp? That's wild, I used to always wonder about putting dump valves as far up the exhaust as possible to have the best of both worlds (quiet stock for cruising, open headers better than any aftermarket exhaust during fun times), but didn't think it would give that much power. Is the GTR exhaust just that restrictive?

So, I asked differently. I hit a 20-22 psi boost with Ign 18-19 deg. I don't want to go higger with that. WGDC is 80-90.
Am I air-limited? Would changing intakes/exhausts give me more power/torque? I do not want to upgrade my turbos.

Yes, I'm running E30-40.

Remember that pressure (psi) is really resistance to flow. We use it as a proxy for flow (amount of air) because for a given turbo and setup, over a narrow range, it's roughly linear. But just like how upgrading to a bigger (more efficient) turbo will give you more flow at the same or lower psi, lowering the resistance to flow between turbo and engine would mean more flow at a given pressure.

I don't think the same applies to resistance upstream of the compressor or downstream of the turbine...those should impact spool-up and maybe temperature indirectly (like when our exhaust manifolds become a bottleneck to more flow).

 

[Corleone1]

GtRs... yes but this is when power is more Tha 1100 whp. Stock is really restrictive, better DPs and 3,5" makes from 40 whp on a stock tune

 

[MetalMania80]

Correct me if I'm wrong, but I'm not a mechanic.

1. The psi that our turbos generate impact on pressure in the combustion chamber. Power = pre-ignition pressure + pressure generated during fuel burning.
2. When we lower resistance to flow/ improve delivering systems, we can burn more mixture, and generate more power with lower psi but by the cost of heat. At some point, the temperature can damage the engine/ exhaust system.
3. We can increase the output power by advancing ignition with this same psi/ amount of fuel/air mixture.
4. More advanced ignition timing/ psi, more knock, so we need better fuel ( higher octane rating).
5. We can't increase psi above some point even when fuel lets us do so, because we damage the engine. (Max psi for us is 22-24?)
6. By improving intakes/ exhaust we generate this same power with lower pressure but higher temperature (more burned fuel).
7. The real gain is with better intakes/ exhaust and high psi- the coast is incresed temperature.

Is my thinking correct?
Is there any difference in torque when we have lower/ higher pressure?

 

[Corleone1]

So, I asked differently. I hit a 20-22 psi boost with Ign 18-19 deg. I don't want to go higger with that. WGDC is 80-90.
Am I air-limited? Would changing intakes/exhausts give me more power/torque? I do not want to upgrade my turbos.

Yes, I'm running E30-40.

I think you stress engine with 22 psi, turbos efficiency go down a lot, inlet temp much up, by that more risk of ping (knock). As I said before, my car isnt faster with 22 psi than 19 and dropping of over 5500 rpm to like 17-18. Yes, it can feel like its faster/stronger as you take out more torque also at midrange but when you go gear by gear I really dont think it will be faster.

I dont think you can express your Q "If you are air limited" as all is a combination of the airflow = better a suction side = more power, more free after turbo = more power but always something that will be the limit first. Fuel and timing = no problem. I prefer safe 18 degrees timing with E+gas blend, 19 with full E85, more will be near "MPC" = Max cylinder pressure that increase risk A LOT for headlift/studs/gasket, pings and also a big load on pistons and rods and... power will NOT increase over 19 so why aim for to high timing? I have blown one engine as the EWGs did stuck in close so boost was +2 bar = 30 Psi, it did cost KIA $35 k

You can try this with air in+out by put a restriction in filterboxes and a plug in exhaust end tips. I promise you notice quite a difference.

1. The psi that our turbos generate impact on pressure in the combustion chamber. Power = pre-ignition pressure + pressure generated during fuel burning.
And how easy it can pass both into the compressor and also out thru the turbo´s hotside, always the biggest restriction

2. When we lower resistance to flow/ improve delivering systems, we can burn more mixture, and generate more power with lower psi but by the cost of heat. At some point, the temperature can damage the engine/ exhaust system.
More efficiency with cooler air, higher flow speed = denser air takes more fuel = more power

3. We can increase the output power by advancing ignition with this same psi/ amount of fuel/air mixture.
Yes, with E content there is a slower burning of fuel, thats why you have to increase timing between 5-10 degrees depending of where it is from beginning and how sensitive to pings. Modern engines have a pretty high timing and let the ECU´s knock system take care of the environment like temp, fuel quality and so on, this to have a good fuel milage and low emissions. And when you test timing for max power you always needs to back of 1-3 degrees from there at higher rpm and even more at midrange as heavy torque stress engine mechanical more than higher revs.

4. More advanced ignition timing/ psi, more knock, so we need better fuel ( higher octane rating).
Yes, inlet temp also lower ping level. Full E85 is the thing, around 104-107 RON and runs with cooler exhaust = allowed more air before limit = more power

5. We can't increase psi above some point even when fuel lets us do so, because we damage the engine. (Max psi for us is 22-24?)
Yes, fuel isnt the limit for us or its easy to make it enough. Hardware like inlets, turbos, IC, exhaust is the things that can make engines VE (Volumetric efficiency) higher when you have reach other limits. VE increases with flow, lower temps, less backpressure

6. By improving intakes/ exhaust we generate this same power with lower pressure but higher temperature (more burned fuel).
Cooler air, easier flow and suction, less backpressure

7. The real gain is with better intakes/ exhaust and high psi- the coast is incresed temperature.
There is always a point when efficiency of the different parts has its limits. If you go higher boost, pressure drop over IC will increase = heavier for turbo = less turbo efficiency = more backpressure and also all other parts will affect

8.
You can also increase power with higher revs as power is from torque x rpm but for us... we shift early at 5800 rpm just as the turbo/flow/efficiency going so bad over that and power will decrease over 57-5900 rpm depending of hardware and tune. The only shifts that maybe can be a bit higher is 1 to second gear (6000) but also questionable as shifts take a bit longer at higher revs

Conclusions:
Every part works together and for a +600 hp Stinger you need a full rebuild with:
- Line/ar bored engine block/crank
- Better rods
- JE pistons or similar
- ARP head studs both at head and block bottom
- Cometic headgasket
- Camshafts
- Separate pipes exhaust manifold
- Bigger turbos
- Big DPs + free exhaust
- Bigger IC and all pipes
- Another ECU stand alone so its possible for tuners to do a full tune

Even with that there could be limits like in heads valve size, intake channels and so on.

I estimate a build like that to around $40-50 k

 

[MetalMania80]

Thanks for the complete explanation !!! It's very didactic.
There are many ways to make power/ torque, and many things to consider. Is there an exhaust gas temperature sensor in stock Stinger or do we have to install an aftermarket one?

I don't need 600hp. I would be happy with 500hp/ 700-750 Nm torque
I run JB4 Race BEF ( ign 18deg ) with map 4/5, and sometimes map 6 (up to 20-21 psi) with E30.

I'm pretty happy with that, the car feels great.
I don't want to mess up too much, I want to gain some practical knowledge about tuning

One more time, thanks for explanations

 

[Corleone1]

Thanks for the complete explanation !!! It's very didactic.
There are many ways to make power/ torque, and many things to consider. Is there an exhaust gas temperature sensor in stock Stinger or do we have to install an aftermarket one?

I don't need 600hp. I would be happy with 500hp/ 700-750 Nm torque
I run JB4 Race BEF ( ign 18deg ) with map 4/5, and sometimes map 6 (up to 20-21 psi) with E30.

I'm pretty happy with that, the car feels great.
I don't want to mess up too much, I want to gain some practical knowledge about tuning

One more time, thanks for explanations

Thanks!

No exhaust temp is there. Garret Turbos can handle almost 1000 degrees C at short time but its wise to stay at max 950. To solve this high temp, just get a bigger hotside...

I think you should stay at that level. If you go max for longer run, like 1 km at WOT you are in the twilight zone that some will happen.

If I should recommend something to guys here it it to run full E85, more safe in every aspect, nicer to drive as more timing. Problem with E85 is when you drive your Stinger at winter here in Europe it needs a hole other tune to get started under +10 degrees. My car start now at even -10 but took a lot of tests to be there. E85 runs about 30% more fuel than gas but in cold you have to add up to over 100%. I think the tuners soon have solved that.

 

[oddball]

All of these things are interlinked with each other and there's not really a straight or simple answer to any of them.

For example, as proven on Engine Masters multiple times, an engine can make MORE horsepower with LESS psi of boost! That's counter-intuitive, but the point is there's a lot of things happening and they all impact each other.

As for being "air" limited, it would really take a tuner looking at how the engine is reacting to different changes to determine the limiting factor. In the Stinger case, the turbo's ability to move air is limited by its size, and that ceiling appears to be in the 500-600 HP range. Other things start falling apart at that level, including fuel delivery, and pretty soon after that the head bolts and engine deck.

 

[MetalMania80]

Do you have any data on where the stock exhausts "power" limit is? How much we can have using JB5, BEF and intakes without any exhaust change?

 

[Thomby]

Do you have any data on where the stock exhausts "power" limit is? How much we can have using JB5, BEF and intakes without any exhaust change?

If by "exhaust" you mean catback, gains are minimal as it's not a big bottleneck. The issue is upstream of the turbine, in the combined exhaust manifold / turbine housing.

According to Tork (video below, start around 3:40), it necks down to about quarter sized or 1.1-1.2", which probably helps a lot with that 1300 rpm spool, but when you're trying to go north of say 600hp, you get a ton of heat & pressure backing up in the cylinder that even a more efficient turbo can't fully mitigate.

Nor can the wastegate since the restriction is upstream of that...I think in this same video he discusses adding a wastegate ahead of the restriction to at least vent the excess pressure, but the real fix would be to expand that necked down area. One of the turbo upgrade companies claims to port it, and another guy on here is trying to, but it's not clear how much the diameter can be expanded in the stock piece.