Feel of HP & Torque

[Tony D]

I'll add another subjective butt dyno anecdote so you can see just how ill it really is:

 

I had changed from the large HKS style plenum to the small box Corky Bell style plenum like everybody else here in the USA seemed to be using. I immediately did not like the response I was getting. At 110 (indicated) the car no longer planted me in the seat like it did with the larger plenum with a built-in diffuser.

 

After getting a fix-it ticket, I found I had an ATROCIOUS speedo error.

 

Long story short: What I thought was poor performance at 110mph, was actually complaining that the car no longer 'planted me' at 137mph when I tromped on it.

 

Speed, Torque, and it's feeling is something you get "used to"---some call it 'velocitization'---the phenomenon of thinking hyperperformance is actually mundane and in some form or way middling in performance.

 

When I took the turbo off, I almost committed suicide the car was so gutless! I went from 350 to 140 in 1/2 hour. No torque compared to what I was used to having. No more romping it in 5th to pass people at 80+ effortlessly. Now I had to downshift to 3rd to get decent passing, and then only to around 90mph. No more merging on a short ramp at 120+...

 

This was a striking revelation for me. I seriously was complaining that the car didn't plant me at 110 (which in fact was 137mph due to speedo error).... I didn't know how good I had it!

 

Beware the butt-dyno. It lies to us all!

[Zmanco]

I'll add one more element that Daeron and Tony D touched on and that's the noise, vibration and harshness (NVH) of the car. Do 0-60 mph in a Lexus sedan with the AC on in 5-6 seconds and it doesn't feel like much, mostly because it's so quiet, smooth, etc. You barely hear the engine rev and the shifts are smooth and refined. Do that in my 240Z with the windows down when it had a header, triple webers, tokico's, etc and it felt/sounded much more impressive. Yet the acceleration numbers were more or less the same.

 

Like Tony D said, our butt dynos are inherently subjective and influenced by things that have nothing to do actual speed and acceleration.

[Tony D]

Hell, you want the ultimate NVH Experience, take the Shinkansen from Tokyo to Hiroshima!

I looked down at my GPS and went HOLY SH*T! 268kph? I was walking around. You want to talk about velocitized---hell they are going 100mph till right up to the station. And some express trains on the 'middle track' come running through the stations full out, you feel the compression wave off the front of the train, and then the push at your back by the vacuum as it exits---it's the reason for the 'yellow line' on the floor---so an unsuspecting person isn't knocked off balance and allowed to fall on the tracks.

 

You don't really get ANY sensation of speed AT ALL on that thing. Until you look at your GPS and go HOLY SH*T! Or stand ready in a station because you feel the rumble. If the camera isn't already on and focused---the most you can hope for is to catch the last 8 cars of a 16 car train when it comes through. By the time you hear it coming, it's already going!

[ozconnection]

Hell, you want the ultimate NVH Experience, take the Shinkansen from Tokyo to Hiroshima!

I looked down at my GPS and went HOLY SH*T! 268kph? I was walking around. You want to talk about velocitized---hell they are going 100mph till right up to the station. And some express trains on the 'middle track' come running through the stations full out, you feel the compression wave off the front of the train, and then the push at your back by the vacuum as it exits---it's the reason for the 'yellow line' on the floor---so an unsuspecting person isn't knocked off balance and allowed to fall on the tracks.

 

You don't really get ANY sensation of speed AT ALL on that thing. Until you look at your GPS and go HOLY SH*T! Or stand ready in a station because you feel the rumble. If the camera isn't already on and focused---the most you can hope for is to catch the last 8 cars of a 16 car train when it comes through. By the time you hear it coming, it's already going!

Impressive speeds on those trains alright! Ya just wanna make sure the engineer who services them didn't forget anything!

 

V-max doesn't have any associated acceleration. All depends on what part of the pendulum swing we're talkin' about. High school physics 101.

[Gollum]

I'll throw in my 2 cents.

 

 

I've driven several B16 CRX's, and it's amazing that though all of them were probably within .5 of a sec in the 1/4 mile they all felt SO different. Some of the key things was that the fastest FEELING one had SOLID engine mounts (4 instead of 3) and also had OLD OEM suspension that was very tired. Bushings were pretty much shot to hell. It also had a YS1 tranny that would have you into vtec at about 70mph. That thing was a SCREAMER. It felt like it was putting you into your seat in 4th gear at 110mph, with a measly torque number, but it was flat.

 

And then comparing that to a stock 88' GT, the mustang felt like it'd be slightly faster, but it was actually slightly slower. And compared to a 93' cobra, the SVT was way, way faster but only felt a little quicker than the 88 GT... odd eh? Both mustangs had similar torque numbers, but the cobra had stiffer suspension.

 

Now, one of the scariest cars I've ridden in, was a modded NSX. That thing sure put you in your seat, but what was scary was knowing how much car was behind you, how much it gripped, and how fast you were traveling. I'd never ridden in something (at that time) with so much cornering power, and when the driver floored it in the middle of a turn I thought for sure we were going sideways but it just stuck and pushed hard. But in the 1/4 mile, it's by far one of the fastest cars I'd been in.

 

But I'd say that consistantly, the cars that have "put me into the seat" the most are high displacement engines. Even more so is high displacement force induced engines. Even the turbocharged small engines I've experienced still felt different, and I think that's more to do with the torque curve than anything else. I think if you took a low powered 4 cylinder like the KA, with a fat torque curve that's low reving, and force induced it there's a chance it'd put you in your seat like a V8.

 

Who knows. Lots of variables.

[Tony D]

Since Gollum Necro-Posed to this one, it gives me a chance to comment on something said earlier:

 

"Exactly, its not just engine torque, its the torque at the wheels. 4.62 gears, 275 ft. lbs. in my old 2,100 lb. NA race car pushed me and my passengers back in the seat very well from 4,000 to 7,500 rpms."

 

Cheap narrow-seat buying, short belted SOB! Not this prospective passenger it didn't!

[johnc]

Since Gollum Necro-Posed to this one, it gives me a chance to comment on something said earlier:

 

"Exactly, its not just engine torque, its the torque at the wheels. 4.62 gears, 275 ft. lbs. in my old 2,100 lb. NA race car pushed me and my passengers back in the seat very well from 4,000 to 7,500 rpms."

 

Cheap narrow-seat buying, short belted SOB! Not this prospective passenger it didn't!

 

Cheap! Cobra Imola Pro S seats were $750 back in the day and I even bought the GT (wide butt) model for the passenger side. I offered to grease your ass up so you could slide into it but you demurred.

[Tony D]

Hey I FIT in the seat, those damn non-adjustable belts set up for Spadanoesque midriffs is what did me in.

 

Ask Steve McQueen: The Blob chased him places he NEVER thought it would fit, but DID!

 

Same with me, I fit in stuff, but generally restraint devices defy me...

[Midnitz]

Comparing a new Nissan 4 valve per cylinder engine to an older L series engine isn't fair....

 

Low end torque requires displacement and the ability to fill those cylinders at lower valve heights.(high VE%) The Nissan Titans 5.4 has heads that flow well

at a reasonably wide powerband, the 4 valve per cyl heads have this characteristic.

 

The valves are smaller but there are more of them...and the ports behind the valves are also more in number....this is good for high port velocities at low engine speeds and because there are two intake ports per cylinder....the engine can also breathe well at higher rpms.

 

My comment is oversimplified but I hope it makes sense.

 

If we could get our hands on 4 vale per cyl heads on our L series engines.....forget it...we'd be making some serious power.

[JMortensen]

Comparing a new Nissan 4 valve per cylinder engine to an older L series engine isn't fair....

 

Low end torque requires displacement and the ability to fill those cylinders at lower valve heights.(high VE%) The Nissan Titans 5.4 has heads that flow well

at a reasonably wide powerband, the 4 valve per cyl heads have this characteristic.

 

The valves are smaller but there are more of them...and the ports behind the valves are also more in number....this is good for high port velocities at low engine speeds and because there are two intake ports per cylinder....the engine can also breathe well at higher rpms.

 

My comment is oversimplified but I hope it makes sense.

 

If we could get our hands on 4 vale per cyl heads on our L series engines.....forget it...we'd be making some serious power.

I don't think 4 valves or 2 valves has as much to do with torque as the cam. You can have higher port velocities with a 4 valve head, but if you have a cam that breathes well at higher rpm it's going to open the valve farther, reducing the port velocity and it's not going to have much torque. Likewise you can have lower port velocities with a smaller cam and a 2 valve head and it won't breathe as well up high but it will have a lot of torque. What would work best would be adjustable valve lift so that you could have low lift and duration at low rpms and high lift and long duration at high rpms. I know they have experimented with electrostatic valves, but I haven't heard anything lately on that front, but that's the holy grail of valve operation IMO. If it were possible to program whatever lift and duration at whatever throttle position and load is present at the time, then I think you'd see a real revolution in the internal combustion engine.

 

It may be true that 4 valves is better than two, but I don't think the 4 valve head is so far superior that "we'd be making some serious power" with one but we can't with a 2V head. Just look at some of the threads on max hp. You'll see things like Electromotive getting 1100 hp out of the L engine with a 2 valve head back in the early 80s. Maybe you could get more with a 4 valve head, but at some point it's going to be more of a hindrance than a help to overall speed unless you're talking about drag racing on wrinkle wall slicks, and then you have much better engine choices than the L, regardless of what head you put on it.

[Leon]

I don't think 4 valves or 2 valves has as much to do with torque as the cam. You can have higher port velocities with a 4 valve head, but if you have a cam that breathes well at higher rpm it's going to open the valve farther, reducing the port velocity and it's not going to have much torque. Likewise you can have lower port velocities with a smaller cam and a 2 valve head and it won't breathe as well up high but it will have a lot of torque. What would work best would be adjustable valve lift so that you could have low lift and duration at low rpms and high lift and long duration at high rpms. I know they have experimented with electrostatic valves, but I haven't heard anything lately on that front, but that's the holy grail of valve operation IMO. If it were possible to program whatever lift and duration at whatever throttle position and load is present at the time, then I think you'd see a real revolution in the internal combustion engine.

 

It may be true that 4 valves is better than two, but I don't think the 4 valve head is so far superior that "we'd be making some serious power" with one but we can't with a 2V head. Just look at some of the threads on max hp. You'll see things like Electromotive getting 1100 hp out of the L engine with a 2 valve head back in the early 80s. Maybe you could get more with a 4 valve head, but at some point it's going to be more of a hindrance than a help to overall speed unless you're talking about drag racing on wrinkle wall slicks, and then you have much better engine choices than the L, regardless of what head you put on it.

 

While valve lift is somewhat dependent (metallurgical/physical issues) on duration, I don't see why you'd want lower lift at lower rpm unless maybe you factor in some mixing processes (tumble/swirl). Ideally, you'd have maximum valve lift over the duration of the valve's open period, or essentially very fast ramp rates in order to increase cylinder filling (VE).

 

A lot of people put too much focus into port velocity. The main function of port velocity is to keep the mixture distributed and the fuel atomized in a carburated or throttle-body fuel injected engine. There are kinetic effects that occur at higher speeds that are slightly dependent on port velocity, but really you want those ports to be big.

 

Cam duration (along with port and manifold design) is what really controls VE over the operating range of the engine, given a high enough valve lift. At lower speeds, you want lower duration because longer durations encourage gas reversion, where exhaust pressure is higher than cylinder pressure or cylinder pressure rises above intake pressure. At high speeds, you want longer duration since gas speed is higher which increases both intake kinetic energy as well as exhaust scavenging, making longer durations more efficient.

 

A cam is really designed for one operating point where it is most efficient. Being able to alter this point as the engine accelerates is a huge bonus. Changing it continuously would be even better. Many modern engines already do this.

 

If I had a choice of constantly varying a part of the valvetrain, variable valve duration would be on top! Although variable lift is cool as well, especially when the intake valve doubles as the throttle, like BMW!

 

I think I've digressed a bit, but it's an interesting topic! I've had some free time to dig into Heywood's IC Engine Fundamentals...