Peak Power vs Redline

[Chapel]

Does anyone think its kind of weird that peak horsepower is at 6000rpms yet it runs out of revs 500rpms later?
Im hoping new software will open another 1000rpms reliably

[*Jedimaster*]

Why do you want it to rev higher? Personally, one thing I don't like aobut my WRX is that you have to rev the shit out of it to get it to move out. I like engines with more torque.

[Chapel]

I like torque, but I also like engine range.
plus, only tapping peak just shy of cutoff seems silly.
Id want to hold the gear at least until 7k

[SUBE555]

Ever driven a 2.5L SOHC Phase II engine, it runs out of steam around 5500rpm and the redline is 6250. They say it has better power delivery than the Phase I's, but the Phase I's rev to 6500 redline and carry good through at least 6000.

It all depends on how it is tuned. I was hoping for the same 7000 redline like the STi, but if it's more responsive, 6500 will do alright. 7000 would have made for some great racing ability (if tuned right), considering 2 shifts in the 1/4 would have netted some great times for mag racers and the actual track racer. A little more headroom for AutoX too. :)

The big question is, what is the limiting factor for revs? Cams, valvetrain including springs, buckets? ECU tune? There are a couple of things it could be, or a combination of them. If it's as simple as an ECU reflash, great, if not, it'll be cost of cams and any valvetrain changes + potential labor OR swapping heads. We just don't know the differences.

To get a good idea how the ratios run in comparison to speed and rpm, I suggest you check out the gear ratios thread in this GT section. That may afford you a few answers. :)

[Th3Franz]

Could the lower red line be due to the fact that the STi and Legacy GT have slightly different engine blocks? I thought I heard this but at the same time they have the same heads? Correct me if I am mistaken.

[SUBE555]

I would imagine it would have to do more with heads and/or engine management tuning than the short block itself.

[Chapel]

somehow, I think the AVCS head is capable of 7000rpms.
7000 is not that high, and I dont think I've ever seen a car that isn't capable of at least 7000rpms with factory bits.
Most valve springs are good for 7000 and so are most lifters.
If it can't handle at least 7000, its an inferior design.
Most manufacturers give themselves a bit of a valvetrain safety net in the odds of a mis shift
My stock 325i had 6200rpm redline
now its a 6900rpm redline
I've seen some people with a 7200rpm redline on stock bits. Most catastrophic top end failure in that car occur at 7500rpms with the stock bits.
And knowing that there are 2.5 Turbo Subarus that have a higher redline, it wouldn't cost that much more to just use the same valves and lifters even if the cams are different.

Now, this car is a true quad cam design, yes?

[SUBE555]

It has 2 cams per head, 2 heads, therefore 4 cams. ;)

It's likely in the cams mostly as the tune, though you may be able to garner a little more with AVCS, you'd likely need revised cams to take advantage of the larger rev range, make it able to breathe up higher or its just running out of steam.

[Chapel]

I'll have to look
the nice thing about electronic valve control is that sometimes you dont even need new cams. You can retard cam timing with software to work better with more boost.
We'll see how it comes along
and with forced induction, you dont necessarily need more cam... just more boost to make up for the top end :)

[SUBE555]

We'll have to see, I haven't really heard much on that end with engine management tuning and the AVCS setup really being able to increase that end. Your description seems very rudimentary in comparison to the complexity of the system, particularly on the side of redline in which was the dubject of the thread.

We just won't know until they start tuning this new setup.

[SteVTEC]

If you don't make peak horsepower until redline, you'll never be able to take full advantage of all of the power. Personally, I like an engine that makes peak horsepower backed off from redline a bit since you don't have to flog the shia out of it to get everything out of the engine. Tweaking an engine to make peak horsepower at redline ultimately involves compromising performance at other RPM's (low-end and mid-range). Variable technologies minimize the compromises, but you're still compromising.

As for "if it can't handle at least 7000 rpm it's inferior", I'll have to disagree on that also, lol. What do you need to handle high RPM's? Ultimately you need stiffer valve springs or maybe a dual-rate setup. That means more friction, lower power in the low-end and mid-range, and reduced fuel-mileage. Power used to turn the valvetrain is lost power, so the less of it you need the better. With a high-RPM setup you can get more peak horsepower sure, but again you're compromising something to get it.

Nothing in engineering is without compromise. :D

Steve

[SUBE555]

Will be interesting to see the day when cams in themselves are gone and it is just an oil actuated system, similar to that of AVCS and AVLS, but completely computer controlled for an extremely variable setup, valve by valve. It would be more complex from the electronics standpoint, but the heads, intake manifold, and other components could be smaller, lighter, and have the ability to be more efficient.

The technology is here, making it next to 100% reliable is the biggest thing.

I think if that technology was incorporated, it would also give to potential for variable compression as well with the ability of certain parts to articulate more.

Hmm, that brings in a whole new set of applications. *scratches chin and wonders* :P

[apexjapan]

Ah - just remember, it's possibly nothing to do with valves, cams, rotational mass of a 2.5 vs. 2.0, or whatnot. It could simply have to do with intake air flow and exhaust flow.

Cheers,

Paul Hansen

[Drift Monkey]

People that want higher redlines are likely ex-Honda drivers who feel inadequate w/o a ridiculous redline. :P

So find the motor's weak point, someone must first push the engine to the point where it breaks. Any volunteers?

[outahere]

Most valve springs are good for 7000 and so are most lifters.
If it can't handle at least 7000, its an inferior design.
Most manufacturers give themselves a bit of a valvetrain safety net in the odds of a mis shift
My stock 325i had 6200rpm redline
now its a 6900rpm redline
I've seen some people with a 7200rpm redline on stock bits. Most catastrophic top end failure in that car occur at 7500rpms with the stock bits.


What is so special about 7000rpm? That is slow. If you want revs, do what the F1 boys do, and run at 18,500rpm. All it takes is money. You could run the quarter mile with only one shift. :)

[outahere]

People that want higher redlines are likely ex-Honda drivers who feel inadequate w/o a ridiculous redline. :P

HaHa, some truth to that. You don't need a lot of revs to make power.The turbocharged 16 cyl diesel engine in a locomotive will max out around 1000rpm, but will make 4400hp all day long, day after day. Of course it helps that the displacement per cylinder is over 700 cubic inches.

[firedawgs]

Why do you want it to rev higher? Personally, one thing I don't like aobut my WRX is that you have to rev the shit out of it to get it to move out. I like engines with more torque.

Than you should have bought a V8. I think that the 2.5 w/ 250 hp and 250 torque is awesome for a H4.

[Deer Killer]

high revs=unreliable. Honda's got the advantage because they possibly have the most reliable engines on the planet, but still.

How often are you cruising the highway at 7000rpm? It doesn't pay to produce power there. The average driver would be more than content if their engines only rev'd to 4000 rpm but produced massive torque.