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High revving, small displacement V8 engines

TheRobSJ said:
You really shouldn't hit the limiter in any modern car with an auto. Just about every computer in a vehicle is programmed to perform a full throttle up shift about 2-300rpm short of the redline. Put the shifter in "manual" mode? Ok, it can happen. But even with that many cars will force the up shift anyways because the manufacturer doesn't trust you enough to give you full control.

So what happened? My guess is that perhaps you broke traction and either the computer closed the throttle (or immediately reduced power in one form or another) which can sometimes feel like hitting a rev limiter. Or since it broke traction, engine was able to spin up so fast, it bounced off the rev limiter for a moment before the transmission was able to react and physically perform the up shift.

If it is that, then I'd say something is wrong and I hope it's still under warranty.
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Well, she didn't say how fast she was going, the rev limiter is there somewhere, though I would guess an AMG would hit the speed governor before running out of revs.
 
TheRobSJ said:
You really shouldn't hit the limiter in any modern car with an auto. Just about every computer in a vehicle is programmed to perform a full throttle up shift about 2-300rpm short of the redline. Put the shifter in "manual" mode? Ok, it can happen. But even with that many cars will force the up shift anyways because the manufacturer doesn't trust you enough to give you full control.

So what happened? My guess is that perhaps you broke traction and either the computer closed the throttle (or immediately reduced power in one form or another) which can sometimes feel like hitting a rev limiter. Or since it broke traction, engine was able to spin up so fast, it bounced off the rev limiter for a moment before the transmission was able to react and physically perform the up shift.

If it is that, then I'd say something is wrong and I hope it's still under warranty.
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thanks so much. can't recall if i broke traction or not (was kinda mindlessly punching it). i immediately backed off, hesitated for a moment, and then hit it again, and all was well. it was just weird, and i didn't know what to make of it. will probably err on the side of caution and take it in for a checkup (presumably the computer can detect any anomalies).
 
bpw said:
Well, she didn't say how fast she was going, the rev limiter is there somewhere, though I would guess an AMG would hit the speed governor before running out of revs.
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hadn't thought of that, but you may be right. the burst where i experienced the phenomenon was followed by more measured speed.

edit - on second thought, no way i hit even a regulated top speed - unless it's set at a stupid low triple digits.
 
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littlebeast said:
hadn't thought of that, but you may be right. the burst where i experienced the phenomenon was followed by more measured speed.
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I was being a bit tongue in cheek, I think the limiters kick in at 186 mph (300 kph)
 
bpw said:
I was being a bit tongue in cheek, I think the limiters kick in at 186 mph (300 kph)
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yeah - see my edit. not even close to possible. just am taken back by driving a car that behaved so differently than what i would expect (or what i have experienced previously).
 
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TheRobSJ said:
There are these guys from Dearborn who just made a 5.2L V8, flat plane crank just like a Ferrari V8, and tachs up to 8000rpm. And it sound fantastic too. Better than a Ferrari V8 too.
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Ehhh, for 5.2l that's not really impressive. Might sound cool and be different but that's about where the benefits stop.
 
Didn't really read OPs post correctly yesterday, probably has to do with the drinking. There's a reason that every type of heads up racing has a cubic inch maximum limit, and it's not because it's easier to make power with a smaller motor. Assuming the bores are the same size you always take the cubes.
 
bpw said:
Well, she didn't say how fast she was going, the rev limiter is there somewhere, though I would guess an AMG would hit the speed governor before running out of revs.
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Yep. My E63 AMG is goverened to 155mph but will do over 190mph if that's removed.

It's also got a 6.2L V8 that will rev to 7200rpm.
 
bpw said:
I was being a bit tongue in cheek, I think the limiters kick in at 186 mph (300 kph)
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I believe the new M-Bs have a limiter at 155mph. You have to get some kind of "performance package" and/or the Black Series (either way is pretty rare) to get a 186mph limiter.
 
Jalopyshoppe said:
The higher an engine revs, the faster it tears itself apart. High rpm engines require higher spec valve trains, stronger internal components, and more expensive manufacturing processes.
Also, if you look at an engine as an air pump, you end up moving similar amounts or air to make similar power. You don't gain much efficiency by spinning a small engine faster. There is a small gain by having less rotating mass creating parasitic loss, but it doesn't offset the increased maintenance and manufacturing costs.
The answer is forced induction and direct injection.
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this.

6000 rpm and 12000 rpm valve trains are not remotely similar, except in basic design. The valves have to be with smaller stems, lighter, and with lighter springs and retainers. The cams have to have more lift, putting more wear on the valve train. The seats wear faster due to the valves hitting them so many times, as does the face of the valve that hits the seat. They wear out. The cranks have to be better balanced. The rods have to be lighter yet strong so that they don't come apart at 12000 rpm. Everything wears faster.
 
afm199 said:
this.

6000 rpm and 12000 rpm valve trains are not remotely similar, except in basic design. The valves have to be with smaller stems, lighter, and with lighter springs and retainers. The cams have to have more lift, putting more wear on the valve train. The seats wear faster due to the valves hitting them so many times, as does the face of the valve that hits the seat. They wear out. The cranks have to be better balanced. The rods have to be lighter yet strong so that they don't come apart at 12000 rpm. Everything wears faster.
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Not to mention the more cylinders, the more compounded all of the above becomes to manage. Not practical in a street production car, but where money is no object? Meh

Look at the history of Formula One engines. Right now they are restricted to 1.6 litres (small) V-6, 15,000 rpm :)wow).

you can get any amount of power out of just about any configuration where money is not the limiting factor. The less moving parts, the less risk of failure.
 
All the above, money and longevity are the factors. They do sound great though. The small V8 F1 motors from the early 70's were at the historic this year and sounded just indescribably amazing. A fairly modern ferrari V8 sounds pretty good IMHO: the 355. Its a short stroke, small displacement V8 with 5 valves per cylinder. Revs to about 8500 I think. One of theist sounding "street" cars out there.
 
Cost: 33% more cylinder/ignition related parts than 6 cylinder.
Size: A V8 is going to be longer than a 6 cylinder car. Not going to fit in the tight engine compartments, especially if FWD.
Technology: Smaller/Faster parts have to be cooled more, which makes the cooling requirements much more complex.

From a manufacturing/sales standpoint, it's a lose/lose, the number of people willing to pay the extra $$$ to buy then maintain the vehicle aren't going to outnumber the people who will pass on paying the extra $$$.
 
Climber said:
Cost: 33% more cylinder/ignition related parts than 6 cylinder.
Size: A V8 is going to be longer than a 6 cylinder car. Not going to fit in the tight engine compartments, especially if FWD.
Technology: Smaller/Faster parts have to be cooled more, which makes the cooling requirements much more complex.

From a manufacturing/sales standpoint, it's a lose/lose, the number of people willing to pay the extra $$$ to buy then maintain the vehicle aren't going to outnumber the people who will pass on paying the extra $$$.
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Assuming you meant that a V8 will be longer than a V6?

The straight six in my Jeep is longer than the V8 in my Chrysler.
 
JesasaurusRex said:
they're almost always the weirdest fucking speeds too, so weird
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I think my Acura says no more at 123mph. Or maybe it was 127. Either way, the H-rated (130mph) tires dictated that situation because it certainly has the horsepower go go much more than that.
 
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