Torque dip common to NA boxer engines?

[P@ul]

I took a look at some dyno charts for Caymans and they have similar dip, which is also solved by an aftermarket header. Here's an article with dynos from European Car magazine.

Here's another photo from Fabspeed for their headers:


Porsche's will never feel as bad because they have a lot more displacement and also variable intake manifolds. That's what you get when you pay another $40k.

The short answer on the header is emissions. Another important factor is assembly; engines are fully assembled and installed by inserting it from below the car between the frame rails. That's a hell of a different story than someone installing a header by hand on their own sweet time. Hand assembly doesn't cut it for the cycle times required for high volume manufacturing. I know this is will come as a shock to some of the disciples of Automotive Jesus, but you didn't buy a hand built Ferrari.

An aftermarket header can take advantage of packaging space that is not normally allowable for an OEM. Either it doesn't fit within dynamic range of engine movement, serviceability, skid plate clearance, or clamshell heat shields clearance. Also note the lack of flex joints on most aftermarket headers; your OEM catalytic converter has a federally mandated 8 year 80k mile warranty (our cat is welded to the header so it has the same coverage).

I'm sure there quite a few folks on this forum that are a million times more qualified than myself to fill you in on the insane level of detail that goes into parts like this. Our cars have an impressively wide torque band; it's just that the dip occurs in at part of the midrange torque that is very noticeable in daily driving.

The billet power blocks showed that longer intake runners deliver more midrange torque, and arguably better driveability, at the cost of peak power. In a conversation with a friend, he made a good point that Toyota probably sacrificed midrange torque to make sure the car could hit 200 peak horsepower for marketing purposes. Hence the saying that "Horsepower sells cars. Torque wins races."

If you can do a better job, well then get on it because you can MAKE SOME MONEY! Have fun with your Ali Baba Powertrain Engineering team during Golden Week! Pray to the God of Direct Injection, I hope your seals over the rival!

[DarkSunrise]

Originally Posted by s2d4

I commend you for pulling those numbers out of that graph, I couldn't do it as the error would have been way too large due to the lack of resolution.

It artificially flattens the graph by using double the scale required.
There are 3 dips visible and there was no baseline run to compare it to as reference.
On top of that, he'd been running unichip.
For these reasons, I don't believe that 3rd party dyno provides substantiated data to actually draw values for valid comparisons.

Would be nice if someone stepped up and posted a cleaner, untuned dyno. Personally I think this header may resolve most of the torque dip, but ultimately won't make as much peak hp as uncatted headers.

[major quicknap]

Originally Posted by P@ul

Our cars have an impressively wide torque band; it's just that the dip occurs in at part of the midrange torque that is very noticeable to some people in daily driving.

Fixed

[major quicknap]

I get the impression that some people would prefer a power curve like the black line as opposed to the red line.

[s2d4]

Originally Posted by DarkSunrise

Personally I think this header may resolve most of the torque dip.

Only question is how for reasons as stated earlier.
I have no idea how stock ignition/vvti timing can automatically make more power in a specific region but not on either side of that region.

Originally Posted by major quicknap

I get the impression that some people would prefer a power curve like the black line as opposed to the red line.

hell no, captain snooze.

[major quicknap]

This is Mrs Snooze. The Captain is unable to post atm. He will be back later. He has asked me to keep him informed of what is going on here. He sends his regards.

[wparsons]

Originally Posted by P@ul

I took a look at some dyno charts for Caymans and they have similar dip, which is also solved by an aftermarket header. Here's an article with dynos from European Car magazine.

Here's another photo from Fabspeed for their headers:

Man, I would be PISSED about having that as a dyno result after buying headers for a Cayman. For every place it gained power, it lost as much (or more) somewhere else. Look at the dip it created from ~4800-5700 rpm!

[OrbitalEllipses]

The answer is terbo

[Boxer486]

Originally Posted by P@ul

I took a look at some dyno charts for Caymans and they have similar dip, which is also solved by an aftermarket header. Here's an article with dynos from European Car magazine.

Here's another photo from Fabspeed for their headers:
Porsche's will never feel as bad because they have a lot more displacement and also variable intake manifolds. That's what you get when you pay another $40k.

The short answer on the header is emissions. Another important factor is assembly; engines are fully assembled and installed by inserting it from below the car between the frame rails. That's a hell of a different story than someone installing a header by hand on their own sweet time. Hand assembly doesn't cut it for the cycle times required for high volume manufacturing. I know this is will come as a shock to some of the disciples of Automotive Jesus, but you didn't buy a hand built Ferrari.

An aftermarket header can take advantage of packaging space that is not normally allowable for an OEM. Either it doesn't fit within dynamic range of engine movement, serviceability, skid plate clearance, or clamshell heat shields clearance. Also note the lack of flex joints on most aftermarket headers; your OEM catalytic converter has a federally mandated 8 year 80k mile warranty (our cat is welded to the header so it has the same coverage).

I'm sure there quite a few folks on this forum that are a million times more qualified than myself to fill you in on the insane level of detail that goes into parts like this. Our cars have an impressively wide torque band; it's just that the dip occurs in at part of the midrange torque that is very noticeable in daily driving.

The billet power blocks showed that longer intake runners deliver more midrange torque, and arguably better driveability, at the cost of peak power. In a conversation with a friend, he made a good point that Toyota probably sacrificed midrange torque to make sure the car could hit 200 peak horsepower for marketing purposes. Hence the saying that "Horsepower sells cars. Torque wins races."

If you can do a better job, well then get on it because you can MAKE SOME MONEY! Have fun with your Ali Baba Powertrain Engineering team during Golden Week! Pray to the God of Direct Injection, I hope your seals over the rival!

Great response. Your friend is spot on about the 200hp for marketing. Remember when the Honda Civic SI got in trouble claiming 200hp for the same reason and the SAE had to revise testing protocols for the industry and made Honda drop the figure below 200 to I think 194 or 197, can't remember which. Emissions, CAFE, marketing, and assembly process are the final determinants of your torque curve.

[arghx7]

I have responded in other threads that the torque dip (or even just a flat spot) is common on N/A direct injected engines. It's more on performance-oriented engines with a higher revving character, and it's not limited to just boxer engines. Here's the published torque curve for the FA20:



Here is the Lexus IS350 with D-4S 2GR-FSE engine:



Here is the Audi 12 cylinder engine n/a previously available on the A8:



Here are the n/a boxer engines available in the current Porsche 991



and here is the torque curve for the GM 3.6 DI version, originally released in the Cadillac CTS and now found in a bunch of other vehicles:



So a torque dip is not a universal aspect of n/a DI engines (look at the Hyundai Sonata and Honda Accord 2.4 n/a DI engines), but it's hardly an unusual thing as you can see above.

[zdr93523]

Good info

Sent from my LG-D800 using Tapatalk

[clintavo]

The Toyota 2ZZ has a noticeable dip before hitting lift. Feels like it is running out of breath, then gets a second wind.

[P@ul]

Originally Posted by arghx7

I have responded in other threads that the torque dip (or even just a flat spot) is common on N/A direct injected engines. It's more on performance-oriented engines with a higher revving character, and it's not limited to just boxer engines. Here's the published torque curve for the FA20

....

BUT WAI!??!?!?!?!??!?

[Trettiosjuan]

Originally Posted by arghx7

So a torque dip is not a universal aspect of n/a DI engines (look at the Hyundai Sonata and Honda Accord 2.4 n/a DI engines), but it's hardly an unusual thing as you can see above.

Yes there is a tendency there but DI is not enough to explain the SEVERITY of the FA20 dip (as I wrote before).

All the other examples above have a dip of around at most 10 Nm when climbing the curve, often on top of a much fatter curve. So the dip amounts to a FEW percent of the total torque before they climb again.

On the FA20 the dip is, in reality (ignoring published), sometimes more than 40Nm or 20% of total torque. That is more than a small "did you feel that?" hick-up. Feels like some lifts off for you!
The DI tendency is augmented by the acoustic characteristics of the header design. Stock mapping suggests that the engine developers are fighting the dip but fail. That is why a header design can change it so much as then this strategy to advance timing can succeed.

And because I keep getting slated for no reason before: this is the opinion of a 35 year old automotive professional engineer that however does not claim to be an expert (i.e. one of few in the country) unlike others that love to completely dismiss others...