why do cobras turn 6800 from factory?
Banned
Joined: May 2007
Posts: 4,064
From:
RE: why do cobras turn 6800 from factory?
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
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
5th Gear Member
Joined: Nov 2005
Posts: 4,412
From: MN
RE: why do cobras turn 6800 from factory?
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.
4th Gear Member
Joined: Jul 2006
Posts: 1,007
From: Az
RE: why do cobras turn 6800 from factory?
ORIGINAL: Stone629
5spd Machs do have forged cranks, Auto Machs have cast cranks. Reason being, the Auto trans can't turn 6800rpms safely...according to Ford.
ORIGINAL: defconfire
I am not positive but I dont think mach's have a forged crank.
I am not positive but I dont think mach's have a forged crank.
6th Gear Member
Joined: Jan 2004
Posts: 12,575
From: United States
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.
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.
4th Gear Member
Joined: Jul 2006
Posts: 1,007
From: Az
RE: why do cobras turn 6800 from factory?
ORIGINAL: 2000GT4.6
I have always heard, espcially with a FI car, that RPM on a 2v = death. On the other hand, we have had more than a few members setting the limiter to 6500 RPM.
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.
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.
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.
5th Gear Member
Joined: Nov 2006
Posts: 3,569
From: So Cal
RE: why do cobras turn 6800 from factory?
I thought for sure someone would've gotten this one by now....
It's thelow tension springs. Spinning them much faster than 5800 causes "valve float". Since I don't have the energy to put it in my own words, here's Wikipedia's:
"Valve float is an adverse condition which occurs when the poppet valves on an internal combustion engine valvetrain do not remain in contact with the camshaft lobe during the valve closure phase of the cam lobe profile. This reduces engine efficiency and performance and potentially increases engine emissions.
Valve bounce is a related condition where the valve does not stay seated, due to the combined effects of the valve's inertia and resonance effects of metallic valve springs that effectively reduce the closing force, and allow the valve to re-open partially.
Stiffer valve springs can help prevent valve float and valve bounce, but only at the expense of increased friction losses. Various techniques have been used to offset the effect of stiffer springs, such as dual-spring and progressive-sprung valves, roller-tipped tappets, and pneumatic valves."
It's thelow tension springs. Spinning them much faster than 5800 causes "valve float". Since I don't have the energy to put it in my own words, here's Wikipedia's:
"Valve float is an adverse condition which occurs when the poppet valves on an internal combustion engine valvetrain do not remain in contact with the camshaft lobe during the valve closure phase of the cam lobe profile. This reduces engine efficiency and performance and potentially increases engine emissions.
Valve bounce is a related condition where the valve does not stay seated, due to the combined effects of the valve's inertia and resonance effects of metallic valve springs that effectively reduce the closing force, and allow the valve to re-open partially.
Stiffer valve springs can help prevent valve float and valve bounce, but only at the expense of increased friction losses. Various techniques have been used to offset the effect of stiffer springs, such as dual-spring and progressive-sprung valves, roller-tipped tappets, and pneumatic valves."
I ♥ Acer
Joined: Jan 2007
Posts: 2,214
From: Laguna Hills, CA
RE: why do cobras turn 6800 from factory?
ORIGINAL: POISND U
I thought for sure someone would've gotten this one by now....
It's thelow tension springs. Spinning them much faster than 5800 causes "valve float". Since I don't have the energy to put it in my own words, here's Wikipedia's:
"Valve float is an adverse condition which occurs when the poppet valves on an internal combustion engine valvetrain do not remain in contact with the camshaft lobe during the valve closure phase of the cam lobe profile. This reduces engine efficiency and performance and potentially increases engine emissions.
Valve bounce is a related condition where the valve does not stay seated, due to the combined effects of the valve's inertia and resonance effects of metallic valve springs that effectively reduce the closing force, and allow the valve to re-open partially.
Stiffer valve springs can help prevent valve float and valve bounce, but only at the expense of increased friction losses. Various techniques have been used to offset the effect of stiffer springs, such as dual-spring and progressive-sprung valves, roller-tipped tappets, and pneumatic valves."
I thought for sure someone would've gotten this one by now....
It's thelow tension springs. Spinning them much faster than 5800 causes "valve float". Since I don't have the energy to put it in my own words, here's Wikipedia's:
"Valve float is an adverse condition which occurs when the poppet valves on an internal combustion engine valvetrain do not remain in contact with the camshaft lobe during the valve closure phase of the cam lobe profile. This reduces engine efficiency and performance and potentially increases engine emissions.
Valve bounce is a related condition where the valve does not stay seated, due to the combined effects of the valve's inertia and resonance effects of metallic valve springs that effectively reduce the closing force, and allow the valve to re-open partially.
Stiffer valve springs can help prevent valve float and valve bounce, but only at the expense of increased friction losses. Various techniques have been used to offset the effect of stiffer springs, such as dual-spring and progressive-sprung valves, roller-tipped tappets, and pneumatic valves."
6th Gear Member
Joined: Feb 2007
Posts: 11,302
From: North Carolina
RE: why do cobras turn 6800 from factory?
ORIGINAL: jEEd
exactly! david knows what hes talking about.
ORIGINAL: POISND U
I thought for sure someone would've gotten this one by now....
It's thelow tension springs. Spinning them much faster than 5800 causes "valve float". Since I don't have the energy to put it in my own words, here's Wikipedia's:
"Valve float is an adverse condition which occurs when the poppet valves on an internal combustion engine valvetrain do not remain in contact with the camshaft lobe during the valve closure phase of the cam lobe profile. This reduces engine efficiency and performance and potentially increases engine emissions.
Valve bounce is a related condition where the valve does not stay seated, due to the combined effects of the valve's inertia and resonance effects of metallic valve springs that effectively reduce the closing force, and allow the valve to re-open partially.
Stiffer valve springs can help prevent valve float and valve bounce, but only at the expense of increased friction losses. Various techniques have been used to offset the effect of stiffer springs, such as dual-spring and progressive-sprung valves, roller-tipped tappets, and pneumatic valves."
I thought for sure someone would've gotten this one by now....
It's thelow tension springs. Spinning them much faster than 5800 causes "valve float". Since I don't have the energy to put it in my own words, here's Wikipedia's:
"Valve float is an adverse condition which occurs when the poppet valves on an internal combustion engine valvetrain do not remain in contact with the camshaft lobe during the valve closure phase of the cam lobe profile. This reduces engine efficiency and performance and potentially increases engine emissions.
Valve bounce is a related condition where the valve does not stay seated, due to the combined effects of the valve's inertia and resonance effects of metallic valve springs that effectively reduce the closing force, and allow the valve to re-open partially.
Stiffer valve springs can help prevent valve float and valve bounce, but only at the expense of increased friction losses. Various techniques have been used to offset the effect of stiffer springs, such as dual-spring and progressive-sprung valves, roller-tipped tappets, and pneumatic valves."
6th Gear Member
Joined: Feb 2007
Posts: 11,302
From: North Carolina
RE: why do cobras turn 6800 from factory?
ORIGINAL: 2000GT4.6
I have always heard, espcially with a FI car, that RPM on a 2v = death. On the other hand, we have had more than a few members setting the limiter to 6500 RPM.
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.
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.
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.
4th Gear Member
Joined: Mar 2007
Posts: 1,148
From:
RE: why do cobras turn 6800 from factory?
I havespun mine up to 6500rpms almost every time i take it out,for a year+ now and still going strong for now.Knock on wood lol.And i have put about 20,000+ miles on mine(plus 6 botttles of 150 shotnitrous)since i have moved my rev limiter up.