What's the reason for Torque dip in BRZ Dyno ?

[WingsofWar]

Originally Posted by Dimman

There doesn't sound like there is any actual 'switching' of port and DI. There is continuous changing fueling of both from the sounds of it. Like they have 2 simultaneous, continuously changing fuel maps that run together.

Yeah, sorry what i meant by switching was the cylinder environment. Direct injection is on all the time...while port fuel supplement is on at 0-3000rpm and around 6800-7400rpm. Making DI the primary source of fuel giving off a consistent weak strat across the revboard. Didn't mean it like a on and off switch...

I think the issue here is how ignition timing is effecting the two fuel maps especially at the "switch" when port comes off. Especially since DI loves lots of retarded timing, and that there are really different cylinder pressure differences between the two maps.

[arghx7]

Has anybody hooked up current probes and taken data on the injection timing yet?

[YukiHachiRoku]

Originally Posted by Memphis

I think it will be fixed with tuning so nobody needs to worry about it. It has been said by Tada I believe that they could have released it with 220bhp from the factory but had to dial it back because of emissions.

We have already begun to see how corked up this engine is from recent dynos from Perrin and other companies with aftermarket exhausts being manufactured that it is going to be quite easy to get power down the road.

How many NA engines do you see gaining 7whp from a cat back exhaust upgrade alone? Thats not even including the mid pipe as they have not even shown that dyno yet.

There is a dyno supposedly showing a 30hp increase from just an exhaust and what many speculate as a tune.

The point is the engine is being held back more than was first expected and the dip while part of the reason is nothing to worry about as it will be fixed in due time.

I wonder when complete bolt ons from header all the way to cat back, will I fail emissions test?

[Symbiont]

Originally Posted by Dimman

There doesn't sound like there is any actual 'switching' of port and DI. There is continuous changing fueling of both from the sounds of it. Like they have 2 simultaneous, continuously changing fuel maps that run together.

The other thing to keep in mind is from the dyno graphs, that 'dip' is ~ 85% of peak torque. The low rpm peak and the high rpm peak are very close to BOTH making peak torque.

It isn't so much that there is a horrible dip, but that the motor manages to create a LOT of torque in the 2500-3200 rpm range. (Name another 2.0L NA motor that makes ~150 lb-ft @ 3000 rpm...)

While this is true (and impressive), I really am interested in seeing how some tuning can smooth that out. Whether it is handled by bolt-ons or a remap, this would be worth quite a bit to me, as long as it is CARB legal. Fuel mileage isn't as much of a concern to me as feeling uninhibited in my shift points.

[noAE86]

Originally Posted by Dimman

There doesn't sound like there is any actual 'switching' of port and DI. There is continuous changing fueling of both from the sounds of it. Like they have 2 simultaneous, continuously changing fuel maps that run together.

The other thing to keep in mind is from the dyno graphs, that 'dip' is ~ 85% of peak torque. The low rpm peak and the high rpm peak are very close to BOTH making peak torque.

It isn't so much that there is a horrible dip, but that the motor manages to create a LOT of torque in the 2500-3200 rpm range. (Name another 2.0L NA motor that makes ~150 lb-ft @ 3000 rpm...)

exactly what i think too,
im more inclined to say, "toyota/subaru found more low end TQ" rather then "oh they lost some TQ in the middle,

reminds me of the arguments i have about open stack trumpets on quad throttles,
can i have long trumpets = yes but you loose some power at high rpm,
oh then can i have best high hp = yes but you need very short stacks,
can i have high hp but with long trumpets = NO
why = helmholtz resonance....20 minutes later

[Matador]

Originally Posted by serialk11r

I never said DI had anything to do with it, and I don't think it does, although it's possible it does.

What I think is that the cams have peak efficiency at 6000 or whatever, and the intake has peak efficiency at like 2500, so you get 2 peaks. The drop isn't that bad really, as a percentage of peak torque. But these are all guesses.

Also keep in mind that the rev range here is 7500 rpm, so it's natural to see more variation in torque than when the rev range is only 6000.

...... -__-

[serialk11r]

Originally Posted by Matador

...... -__-

Honest question, what are you thinking? I'm confused

[Matador]

Originally Posted by serialk11r

Honest question, what are you thinking? I'm confused

Just giving you a ribbing for panning me in perrin's thread mate

[Motordyne]

As so many others have mentioned above, there are so many different possible reasons for the hump its hard to say without a whole lot of experimentation.

I get the impression its related to resonance tuning of either the intake manifold or the headers. It looks like an out of phase portion of the resonance tuning.

Its not completely unusual though. Here are 2 different intake manifolds on the Nissan 350Z. One with shorter intake runners, the other with longer intake runners.

None of these are completely flat and both have different dips due to their respective manifold resonance characteristics.

[serialk11r]

Originally Posted by Matador

Just giving you a ribbing for panning me in perrin's thread mate

I could tell But what's wrong with my post?

[arghx7]

I spoke to an industry person who is an expert on such matters as this, a person I greatly respect whose knowledge exceeds my own. He in essence agrees with Dimman:

Originally Posted by Dimman

It isn't so much that there is a horrible dip, but that the motor manages to create a LOT of torque in the 2500-3200 rpm range. (Name another 2.0L NA motor that makes ~150 lb-ft @ 3000 rpm...)

It's not so much a "torque dip" as it is a "torque bump" under 3500rpm. This is caused by aggressive scavenging from high overlap--lots of intake and exhaust cam phasing combined with the characteristics of the manifolds.



it would take, at minimum, changes in the intake and exhaust system to add torque around 4000rpm. Like any other resonance tuning, when you improve one area there's a chance you will hurt another.

It seems unlikely that you could just reflash the ECU on a stock car with merely a catback and "get rid of" that dip without lowering torque somewhere else. There are a lot of engines with conventional port injection and cam phasers that have a similar dip.

[Dimman]

Originally Posted by arghx7

I spoke to an industry person who is an expert on such matters as this, a person I greatly respect whose knowledge exceeds my own. He in essence agrees with Dimman:



It's not so much a "torque dip" as it is a "torque bump" under 3500rpm. This is caused by aggressive scavenging from high overlap--lots of intake and exhaust cam phasing combined with the characteristics of the manifolds.



it would take, at minimum, changes in the intake and exhaust system to add torque around 4000rpm. Like any other resonance tuning, when you improve one area there's a chance you will hurt another.

It seems unlikely that you could just reflash the ECU on a stock car with merely a catback and "get rid of" that dip without lowering torque somewhere else. There are a lot of engines with conventional port injection and cam phasers that have a similar dip.

The boost range looks like it is timed to the length of the primaries (at 14-16" via my eyeball) and an effective cam duration of ~200ish degrees. Haven't looked to see if there is something that corresponds on the intake side, but I think the 'sound tube' may actually be playing a role with this too...

[ahausheer]

Wonder if this resonance theory has anything to do with the fact that there are 5 intake resonators (including sound tube as branch resonator)

[MANDALAY]

Originally Posted by Dimman

There doesn't sound like there is any actual 'switching' of port and DI. There is continuous changing fueling of both from the sounds of it. Like they have 2 simultaneous, continuously changing fuel maps that run together.

The other thing to keep in mind is from the dyno graphs, that 'dip' is ~ 85% of peak torque. The low rpm peak and the high rpm peak are very close to BOTH making peak torque.

It isn't so much that there is a horrible dip, but that the motor manages to create a LOT of torque in the 2500-3200 rpm range. (Name another 2.0L NA motor that makes ~150 lb-ft @ 3000 rpm...)

A TOYOTA ENGINE thats 15 years ago

[arghx7]

Dude that's in Newton meters.

[AlmostMDD]

Originally Posted by MANDALAY

A TOYOTA ENGINE thats 15 years ago

I think Dimman's point stands, not quite 150 ft lbs at 3000rpm. But isn't the FA20 engine dyno somewhat conservative compared to what people are observing on chassis dynos?

[czar07]

Originally Posted by arghx7

Dude that's in Newton meters.

190NM = 140 lb-ft

[arghx7]

Originally Posted by czar07

190NM = 140 lb-ft

Yes. Notice how 140 isn't 150.

[Dimman]

And at 3000 rpm it's just a touch over 160 Nm ~120 lb ft.

And 120 isn't even close to 150.

[old greg]

Originally Posted by Dimman

And at 3000 rpm it's just a touch over 160 Nm ~120 lb ft.

And 120 isn't even close to 150.

You're reading it wrong.

[Dimman]

Originally Posted by old greg

You're reading it wrong.

Ack... PS, kW, N•m, kgf•m...

Two different power scales on the left and torque on the right. Oops. Metric is simpler...

And that is the motor that I thought the FA20 would be an even torquier version of anyways thanks to D4-S and more compression, plus reduced friction.

[HunterGreene]

Originally Posted by Dimman

Ack... PS, kW, N•m, kgf•m...

Two different power scales on the left and torque on the right. Oops. Metric is simpler...

Measurements in factors of 10? Craziness!

Seriously, though, good thread. I have been seeing mentions of this "power drop" around the forum, good to see the discussion condensed in one thread.