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Old 06-22-2002, 11:06 AM   #31
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Quote:
Originally posted by 454Casull

What you've just described is valve float. It can happen at any speed, depending on the stiffness of the springs.
yes, but also at high speeds the camshaft may not be able to keep up with the pistons or most likely vice versa.
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Old 06-22-2002, 08:40 PM   #32
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The camshaft can't keep up with the pistons? really? how does that happen?
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Old 06-22-2002, 09:23 PM   #33
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The camshaft can't keep up with the pistons? really? how does that happen?
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Old 06-23-2002, 12:26 AM   #34
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Quote:
Originally posted by ivymike1031
The camshaft can't keep up with the pistons? really? how does that happen?
touche

i was tired as hell, thats what happens when i get on here late at night with nothing to do :P
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Old 06-23-2002, 10:27 AM   #35
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You don't need a better gearbox just because you're using higher revs. Engine torque is what destroys a gearbox.

The easiest way to change the rev. limiter is just to modify the software in the ecu.

The most common way to blow up an engine by over reving is by changing to a lover gear when the engine is going at max speed. Mechanical failure is a other way, but if the engine is original this practicly never happends.

When gearchanging for maximum performance you should always go over the engine power peak, there can of course be situations when gearshifting at lover engine rpm is to prefer.

If higher revs is wanted it can be smart to use stiff valve springs, short stroke, light pistons, light, stong and long conrods and use mechanical valvelifters.

Lets compare the stresses caused by engine speed in an original engine (in this case a Saab B234R with 225 hp) with the BMW M10 formula one engine which have over 1000 hp.
The engine specs are, the saabengine has 90mm stroke, rev limiter at 6500 rpm and 153 mm long conrods, the bmw engine has 65 mm stroke gives it best at around 12000 rpm (don't know the max speed), don't know the conrod length but say 150mm (this is over 2,3 times the stroke, which is very long conrods).

Original engine:
average piston speed: 19,5 m/s
max acceleration (at TDC): 26981,8 m/s^2
max piston speed at 75,2 and 284,8 degrees after TDC, max speed is 31,84 m/s

F1 engine
average piston speed: 26 m/s
max acceleration (at TDC): 62441,7 m/s^2
max piston speed at 78,5 and 281,5 degrees after TDC, max speed is 41,7 m/s

The max accelerations are i G, 2747,6 and 6358,6, this means that is the piston and crankpin weights 500 grams they will cause stresses in the conrods which are comparable with the stress caused by 1370 kg and 3180 kg weight hanging in them. And this stress is only caused by engine speed, not the combustionpressure.
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Old 06-26-2002, 06:58 AM   #36
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oops, 60mm is the stroke in the F1 engine.

and this gives

average piston speed: 24 m/s
max acceleration (at TDC): 56848,9 m/s^2
max piston speed at 79,3 and 289,7 degrees after TDC, max speed is 38,4 m/s

this gives a acceleration of 5789 G, and the stress caused by a 500 gram piston and pistonpin is comparable with 2895 kg.
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Old 06-26-2002, 09:59 PM   #37
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yes yes... thanks for the great details
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Old 07-05-2002, 12:28 AM   #38
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Quote:
Originally posted by SaabJohan
You don't need a better gearbox just because you're using higher revs. Engine torque is what destroys a gearbox.



The engine specs are, the saabengine has 90mm stroke, rev limiter at 6500 rpm and 153 mm long conrods, the bmw engine has 65 mm stroke gives it best at around 12000 rpm (don't know the max speed), don't know the conrod length but say 150mm (this is over 2,3 times the stroke, which is very long conrods).

I believe it's 17500 rpm, I haven't heard the M10 code, but I heard 17500 rpm for the latest Williams BMW.


Okay another question here, I also recently started driving standard, no real problems just wanna make sure that I can do everything well.

So the question is, My shifts are jerky, and how can I correct this, is it just the matter of tapping the gas with the clutch in, to keep engine momentum matched with the car's? (IE the clutch is turning at the same speed as the engine is ?)
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Old 07-05-2002, 01:00 AM   #39
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Quote:
Originally posted by Porsche


I believe it's 17500 rpm, I haven't heard the M10 code, but I heard 17500 rpm for the latest Williams BMW.


Okay another question here, I also recently started driving standard, no real problems just wanna make sure that I can do everything well.

So the question is, My shifts are jerky, and how can I correct this, is it just the matter of tapping the gas with the clutch in, to keep engine momentum matched with the car's? (IE the clutch is turning at the same speed as the engine is ?)
well if you shift quickly you're likely to jerk. unless you're REALLY good (where you shift, push in the clutch let off the gas at the same time, then engage the clutch and get on the gas at the same time very precise and perfect). You can shift slowly and smoothly: just be smooth in your foot work and take it easy. It's slower to shift but if thats what you want when you're not racing it should be fine.
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Old 07-08-2002, 01:00 PM   #40
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Shifting smoothly should be a goal of yours. Smooth shifts make the ride for you and your passengers much more comfortable. After driving a stick shift for a while you will figure out the best speed and time to shift. When i drive my car i have goptten it so that when i shift by the time i have moved the shifter and am just about to release the clutch the RPMs are perfectly matched up. Now, obviously when i am getting on the highway or driving like an asshole my shifts are much harsher but there is no way around that. Just work on smoothing everythjiong out and eventually it will click.
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Old 07-10-2002, 03:00 AM   #41
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You will learn to shift smoothly with time. I did it in about a month, with a bad clutch. It's just a matter of varying the cluth position and throttle position at the same time, in the right proportions.

On this whole thing about high RPM breakdowns, redline is not the magic point where the engine explodes for reasons unknown. My engine will run nearly 2000 RPM over redline to no ill effect (Nissan engineering) with stock internals. It's all a matter of how the engine is built and how timid the engineers are when it comes time to set the rev limiter. Valve float doesn't usually become a problem until you are waaay over redline anyway, plus some small engines (about the only ones you can get to high enough speeds for this) are non-interference type anyway.

The pistons can only move faster than the crankshaft if the con rods all break at the same time (and fling the pistons into the valves), or if someone puts a Voodoo curse on your car.

Your gearbox is not likely to suffer any harm from higher revs, although your clutch is. Remember, it has to bridge the gap between the crank speed and the input shaft speed. Now imagine you've just let the clutch out and are rapidly accelerating to 8000 RPM. Polished clutch, anyone? Of course, you have to have tons of power and accelerate very fast for this to be a problem, but it's still a legitimate concern.

As for the effect on the valvetrain, you will wear things out faster. In my opinion, the first (and maybe only) thing to attack here is the valves. If you can find titanium valves, buy them. If you can't, pay to have some made. The reduced valvetrain mass will take a lot of stress off of the valve springs, not to mention let you accelerate faster and keep making significant power further on up the tac. I can't stress this enough, Ti valves are great (good enough to convince a lot of people that they don't need a new cam)!

See, I don't need to quote anyone to make an obscenely long post!
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Old 02-03-2009, 03:54 AM   #42
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Re: learning to drive a manual (5 speed)

[quote=iwantlancergsr]ok where do i began.i a new driver to a 5 speed i to was taught with automatic.but the past few days i have been searching for a car.been alot of places seen alot of junk.then i come across a 1997 acura 2.2 cl.its a sweet car.but its a 5 speed i was scared to buy it but a few days later i sucked up and bought it.i let it sit a few days because i was scared of it.but this is what i did to learn it u dont have to do the same but here is something that will get u boosted to drive one.i started by every night when no traffic was out and i drove it around the block.u know so i could practice stoping at stop signs. and taking off i stalled alot i even threw it it the wrong gear cause i was trying to speed shift.lol....then after 2 days of doing that i was driving by myself with no one in the car and out in traffic.one thing my instructor taught me was to find the g spot of the clucth and always clucth and brake when coming to a stop.u can either put it in neutral are downshift.with shifting down u will have to clucth are the car will stall.with it in neutral u can just use your brake.my first time on a hill i spun my tires so dont worry and good luck.
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Old 02-03-2009, 09:41 AM   #43
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Re: learning to drive a manual (5 speed)

Whoa, baby... this thread is 7 years old. Don't ressurect old threads, they smell bad.
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