why do cobras turn 6800 from factory?
10-16-2007, 08:37 AM
#21
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RE: why do cobras turn 6800 from factory?
I did spin mine to 6500 when it was n/a and pi swapped with upgraded valve springs and cams. I was just wondering why tim set my limiter back to 6200 when he tuned it for the procharger.
10-16-2007, 09:36 AM
#22
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RE: why do cobras turn 6800 from factory?
ORIGINAL: amoosenamedhank
This explanation doesn't really work because the 96-98 cobras used the same rods as the GT's. The only difference is the forged crank and you can spin them to 6800 all day long. So the rods aren't making the difference in this situation.
Has anyone actually blown up there 2v stock short block from moving the rev limiter to 6500rmps? With the right cam the car can pull that high no problem.
ORIGINAL: banned
well lets clear some things up
the 2v can spin 8k or more if it was built for it... the real problem is the rods, and the valve train are not made to turn that high... i know plenty of stock crank, forged internal turbo GTs spinning almost 9k on a stock crank... it can be done, ive actually never seen a stock crank give out, but the forged crank is cheap insurance
now the older cobras i believe could spin 7200-7500 redline... the new ones have a lowered red line due to the m112, which can over spin, like any other twin screw blower, so i think now the redline is what 6800?
but basically if you built your motor you can spin those rpms, but like they say you need FI to make power there and built heads
well lets clear some things up
the 2v can spin 8k or more if it was built for it... the real problem is the rods, and the valve train are not made to turn that high... i know plenty of stock crank, forged internal turbo GTs spinning almost 9k on a stock crank... it can be done, ive actually never seen a stock crank give out, but the forged crank is cheap insurance
now the older cobras i believe could spin 7200-7500 redline... the new ones have a lowered red line due to the m112, which can over spin, like any other twin screw blower, so i think now the redline is what 6800?
but basically if you built your motor you can spin those rpms, but like they say you need FI to make power there and built heads
Has anyone actually blown up there 2v stock short block from moving the rev limiter to 6500rmps? With the right cam the car can pull that high no problem.
10-16-2007, 10:05 AM
#23
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RE: why do cobras turn 6800 from factory?
ORIGINAL: Chris98Gt
I did spin mine to 6500 when it was n/a and pi swapped with upgraded valve springs and cams. I was just wondering why tim set my limiter back to 6200 when he tuned it for the procharger.
I did spin mine to 6500 when it was n/a and pi swapped with upgraded valve springs and cams. I was just wondering why tim set my limiter back to 6200 when he tuned it for the procharger.
The more RPM you make on a FI car the more boost you make too... gotta limit the numbers your making or your gonna make too much and kiss the SB goodbye.
10-16-2007, 11:19 AM
#25
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RE: why do cobras turn 6800 from factory?
A real question should be something along the lines of, "does anyone know what would cause a 2V, with the stock rev limiter, to bend a valve?"
Im in this boat right now, and hopefully when the valve covers come off I see some kind of doomed valve spring, and not perfectly fine ones that would indicate something else is wrong.
Has ANYONE else here seen/heard or/experianced a bent valve in their near stock Mustangs? *96-04 preferrably?*
As for the valve float, that makes sense, basically the cam is spinning to quickly, that the valve seperates itself from whatever it is connected to that draws it back up. Essentially it 'floats' away and might be left in the path of the piston as it approaches the top of its stroke.
But, again, anyone with bent valve experiances?
Im in this boat right now, and hopefully when the valve covers come off I see some kind of doomed valve spring, and not perfectly fine ones that would indicate something else is wrong.
Has ANYONE else here seen/heard or/experianced a bent valve in their near stock Mustangs? *96-04 preferrably?*
As for the valve float, that makes sense, basically the cam is spinning to quickly, that the valve seperates itself from whatever it is connected to that draws it back up. Essentially it 'floats' away and might be left in the path of the piston as it approaches the top of its stroke.
But, again, anyone with bent valve experiances?
10-16-2007, 02:17 PM
#28
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RE: why do cobras turn 6800 from factory?
ORIGINAL: 2000GT4.6
And it has nothing to do with the trans. Its an issue of rotatting assembly strength. Not only that, but as mentioned the cam profile on a stock 2v won't make any power up there anyway.
And it has nothing to do with the trans. Its an issue of rotatting assembly strength. Not only that, but as mentioned the cam profile on a stock 2v won't make any power up there anyway.
But guys, a lot of you have part of the answer, but are missing other importantthings that allow the 4V's to rev higher.
First, just as 2000GT4.6 said, the reason the 2V can't spin as high as the 4V'sis an issue of rotating assembly strength. The main thing that allows the 4V'sto spin that high is the forged crank.The crank of the 2V isn't as strong, and will eventually fail permaturely from being revved so high. It simply can't take the prolonged stress.
Second, again just as 2000GT4.6 said, is the cam profile. The stock 2V cams aren'tdesigned to make power that high in the RPM range. Therefore, they don't. As most of you know, peak power ison a stock motor 2V is madeat 5,250RPM. After about 6KRPM, power starts to fall off quickly. The stock cams were designed to work with the flow of the stock heads. Therefore, power is made a lot lower in the RPM range.
The third factor that allow the 4V's to be revved higher is the heads. The 4V heads flow VERY well. The stock 2V heads don't flow well enough to make power that high. Even if a 2Vhad aftermarket camsspec'd outto rev as high as a 4V and made usable power in the higher RPM range, there still wouldn't bea huge benefit (or at least as much as there could be) because of the stock2V heads (they can only flow so much).Cams designed to do so would definitely help, but only if you're continually making usable power.Usually,most of the usable power gained in the higher RPM range come from a good heads and cam combination. The limited flow capabilities of the stock 2V heads and cams don't allow it to make goodpowerhigher in the RPM range.
With all that being said, the stock 2V motorcanbe spunto 7K. But unfortunately,itwon't makeany morepower than taking it to the stock redline, and there is a high risk of hurting the motor.
With cams and a good setof heads,you could spin the stock 2V motor to 7K and make usable power. But then, there's still the risk of doing damage to your motor, especially the valves and crankshaft. Those would be the first to go.
On a stock 2V motor, there aren't any advantages of taking the motor that high. Holding the gear longer, especially when there isn't any usable power left,is not worth the risk of doing damage.
Alright guys, It took me a while to sit here and type all this andmake it understandable. Lol. I hope this answers some of you guy's questions [8D]
10-16-2007, 02:19 PM
#29
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RE: why do cobras turn 6800 from factory?
ORIGINAL: banned
but your rods cant take it...
but your rods cant take it...