Motortrend's Carlos Lagos reviews 2015 M3

[BhamDavid]

Originally Posted by mlhj83

I understand flow. But when you said ram effect, I understood it as pressurisation above atmospheric pressure, but I'm purely referring to starvation as the NA engine is consuming air faster than atmospheric pressure alone can adequately replenish.

But you have the whole underside of the hood area, a rather large area, with lots of air available to replenish a supply to the underhood area.

If you believe this, never vacuum a small room in your house. You might suck your eyeballs out.

[CanAutM3]

Originally Posted by mlhj83

I understand flow. I still think that the NA engine is consuming air faster than atmospheric pressure alone can adequately replenish.

I am sorry, but you don't seem to understand flow based on your comments.

On pure ram systems, the vehicle velocity will only very slightly increase pressure over athmospheric at road speeds, hence will have little impact on flow. Further, since the S65 airbox is vented on the hood, that effect is entirely negated.

[mlhj83]

Originally Posted by BhamDavid

But you have the whole underside of the hood area, a rather large area, with lots of air available to replenish a supply to the underhood area.

If you believe this, never vacuum a small room in your house. You might suck your eyeballs out.

It is the rate of replenishment that is insufficient. I'm not saying that there isn't air available to replenish.

If you had a powerful enough vacuum cleaner in a room, you can still generate negative atmospheric pressure even if you had a very large window.

[BhamDavid]

Originally Posted by mlhj83

It is the rate of replenishment that is insufficient. I'm not saying that there isn't air available to replenish.

If you had a powerful enough vacuum cleaner in a room, you can still generate negative atmospheric pressure even if you had a very large window.

I think your problem is that you have over-estimated the mount of flow to the engine. Also remember that as you try to pull a vacuum on a volume of space, you lower the air pressure which in turn increases the driving force for air to replenish the volume.

The amount of air required, ever at high engine speeds, is just too small to reduce underhood pressures given the large area of flow area to replenish.

Underhood air pressures are going to be a function of aerodynamic flows of air under the body. The affects of the intake are minuscule in comparison.

[scutts]

Originally Posted by CanAutM3

This is the video version of the Motortrend dyno run thread.

On the video, it is now clear that the cars were run on a 4WD dyno with all 4 rollers running, as I previously suspected. This will significantly increases losses (tire rolling losses, hub friction, tire and wheel inertia). This is probably the most significant reason for the low numbers of this test. Further, E92 was run in 5th gear while F80 was run in 4th. The higher equivalent speed of E92 will translate to more losses too.

I followed a bit on the previous thread about this particular dyno comparison and I remember you bringing up the 4WD dyno. It makes sense and it's clearly running all 4 rollers. Nonetheless, F8X seems to have been underrated.

Thanks for your perspective.

[mlhj83]

Originally Posted by CanAutM3

I am sorry, but you don't seem to understand flow based on your comments.

On pure ram systems, the vehicle velocity will only very slightly increase pressure over athmospheric at road speeds, hence will have little impact on flow. Further, since the S65 airbox is vented on the hood, that effect is entirely negated.

I understand what you are saying. I'm certainly not referring to ram effect resulting in the build up of pressure above atmospheric pressure, which definitely won't be the case especially with the hood vent like you said.

I'm just referring to the maintenance of sufficient air within the intakes. The intake of the S65 (with increasing engine speed) is not being replenished fast enough when the car is immobile. While the intake design may not generate ram effect, the flow of air into the intakes (when the vehicle is moving) is able to replenish air quicker than a static vehicle relying on negative pressure alone.

[BhamDavid]

Originally Posted by mlhj83

I understand what you are saying. I'm certainly not referring to ram effect resulting in the build up of pressure above atmospheric pressure, which definitely won't be the case especially with the hood vent like you said.

I'm just referring to the maintenance of sufficient air within the intakes. The intake of the S65 (with increasing engine speed) is not being replenished fast enough when the car is immobile. While the intake design may not generate ram effect, the flow of air into the intakes (when the vehicle is moving) is able to replenish air quicker than a static vehicle relying on negative pressure alone.

One more post on this subject and I'm out:

You do realize that the dyno runs are made WITH THE HOOD OPEN.

[Fuman]

The N54 motor with the JB4 tune, flash, FBO, inline LPFP, Meth and e85 fuel is over 450 whp and over 500 lbft torque. It's not a surprise what this S55 motor can do, and also more that can be done given it's baseline. This is a key reason why I am getting impatient waiting for mine - and perhaps many others too.

The sound of the high revving V10 M5 was to me a significant change. IMHO, V8 sound is really not much of a biggie when there's a straight 6 turbo flying past a pricey ride - sorry if I upset any V8 die-hard fans. But it was also good to know that a C63 owner recently posted that he liked the sound of the S55 motor.

The shots of brake rotors turning red was a key take away from this as there was another article on less brake fade than e92s while on track.

[mlhj83]

Originally Posted by BhamDavid

One more post on this subject and I'm out:

You do realize that the dyno runs are made WITH THE HOOD OPEN.

No need for aggression.

If you can show me numbers that clearly show that the rate of air replenishment of the air intake from atmospheric pressure alone matches that of engine air consumption, then I'll digress.

[hwelvaar]

Originally Posted by Powaup

Funny how he's talking about a 155 mph speed limiter. We were pulling 165.9 km/h on the Autobahn lol

A case of speedometer read-out (usually too high) vs 'real' or GPS speed ?

[Powaup]

Originally Posted by hwelvaar

A case of speedometer read-out (usually too high) vs 'real' or GPS speed ?

It would never be that much. German speed limiter is higher than US speed limiter. Once car gets back to the US I'll have a speed limit of 155 mph

[utenigma]

Originally Posted by Ghetto2315

It was sooo fast that you couldn't even see it!

lol the OP just mislabeled his post. I am sure he meant to say "E92" and not "E90".

Yup - went by so fast in the video didn't notice it had 2 doors - fixed it

[bradleyland]

Originally Posted by mlhj83

No need for aggression.

If you can show me numbers that clearly show that the rate of air replenishment of the air intake from atmospheric pressure alone matches that of engine air consumption, then I'll digress.

How about this. How about you show the numbers supporting your argument?

Originally Posted by mlhj83

If you blow air into a syringe at the same rate as the plunger is being pulled, the syringe will fill up faster than relying on a negative air pressure alone.

That's true, but it's not what you're suggesting. What is the pressure generated at the intake for the E92 M3 at 100 MPH? You're the one positing the theory, so back it up. Do some googling on "ram-air effect". You'll find that even with an optimally designed intake, the effects of ram-air are dubious at best. Then consider that the intake on the E92 is on the horizontal hood surface. If anything, increased air flow over the hood is going to create additional vacuum, not pressure. If you don't understand why, then you should check out of this conversation.

[chiplee]

Originally Posted by BhamDavid

One more post on this subject and I'm out:

You do realize that the dyno runs are made WITH THE HOOD OPEN.

Lol, I had already gone "out" without announcing it and you lured me back in with your matching sentiment. Blast! There is some serious nuking going on here and I'm doing my best to bite my tongue and be patient while the M3 world comes around to a turbo way of thinking. However, having built and ran a 380wtq turbo 4 cylinder at roughly 20psi boost for the last 20 years, I'm getting a little overwhelmed by all the misinformation and desk testing. I had to go through it, too though, so I guess I'll be patient.

[Wild_Will]

Originally Posted by EndBosS

or you can get a new one, and when there is a Mid Life refresh, get that one...

If you can afford to do that then that's a solution then!

[FreekinMedic]

I picked mine up on Friday. Break-in service is scheduled for this Thursday!!

[Yay-Z]

Originally Posted by CanAutM3

The S65 airbox is vented on the hood, so there is no benefit from RAM effects.

Further, if you do the math, you will find out that RAM effect is negligible for the speeds of road cars.

Sucking hot air from the dyno room is usually the culprit for reduced power due to poor ventilation.

Feel like I'm back in fluid dynamics class

[FreekinMedic]

I picked mine up on Friday. Break-in service is scheduled for this Thursday!!

[uhn2000]

Badass car..

[pearlwhites]

All this fluid dynamic thread jacking has made my head hurt. Please stop. Dynos are good for before/after tests and internet fighting

[PhillyNate]

Originally Posted by pearlwhites

All this fluid dynamic thread jacking has made my head hurt. Please stop. Dynos are good for before/after tests and internet fighting

^^This. The F8x M3/4 is MORE THAN LIKELY underrated. The E9x M3 was more than likely properly rated...which isn't a bad thing. End thread.

[05Mdriver]

What an incredible leap for BMW M.