Cheap Over-rev Insurance!
09-05-2014, 07:41 AM
#31
Drifting
09-05-2014, 09:15 AM
#32
Race Car
You do realize that for the turbo to produce boost, the exhaust system must have notably higher pressures than the intake, don't you? Granted, the intake valves are bigger, so the pressure has a greater area, meaning manifold pressure can create a greater force. But the lowest pressure in the cylinder occurs when you are opening the intake, anyway, meaning the delta P across the valve face will be greater on the exhaust side. Finally, what is typically the biggest factor in over revs is usually valvetrain kinematics, meaning that mass is of greater importance than pressures, anyway. Are the exhaust valves heavier? I don't recall if they are inconel or not, but since they are smaller, if the densities of the materials are close, the lighter exhaust valve will be more likely to float (and I'd note that the sodium filling is VERY light).
09-05-2014, 09:29 AM
#33
Addict
Rennlist Member
Rennlist Member
MM is one of the most value per post users here. Also stuff he sells is usually trick stuff for bargain price , not generic used parts.
The thing I find funny in this thread is that there is debate about more stress to the valvetrain and in the same time almost nobody runs stock boost level which automatically means XX% more stress to complete drivetrain. Is that stress less damaging than stiffer inner valvespring? Doubt it.
The thing I find funny in this thread is that there is debate about more stress to the valvetrain and in the same time almost nobody runs stock boost level which automatically means XX% more stress to complete drivetrain. Is that stress less damaging than stiffer inner valvespring? Doubt it.
09-05-2014, 10:34 AM
#34
Racer
Join Date: May 2008
Location: Encinitas, ca PCA National DE instructor PCA San Diego chief driving instructor
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You do realize that for the turbo to produce boost, the exhaust system must have notably higher pressures than the intake, don't you? Granted, the intake valves are bigger, so the pressure has a greater area, meaning manifold pressure can create a greater force. But the lowest pressure in the cylinder occurs when you are opening the intake, anyway, meaning the delta P across the valve face will be greater on the exhaust side. Finally, what is typically the biggest factor in over revs is usually valvetrain kinematics, meaning that mass is of greater importance than pressures, anyway. Are the exhaust valves heavier? I don't recall if they are inconel or not, but since they are smaller, if the densities of the materials are close, the lighter exhaust valve will be more likely to float (and I'd note that the sodium filling is VERY light).
I was having a brain fart thinking about only the intake valve seeing more back pressure as my most recent land speed effort was a supercharged design.
In any event, stiffer valve springs in otherwise stock valve trains are a worthwhile mod for any engine that sees the track.
09-06-2014, 09:32 AM
#38
Three Wheelin'
You do realize that for the turbo to produce boost, the exhaust system must have notably higher pressures than the intake, don't you? Granted, the intake valves are bigger, so the pressure has a greater area, meaning manifold pressure can create a greater force. But the lowest pressure in the cylinder occurs when you are opening the intake, anyway, meaning the delta P across the valve face will be greater on the exhaust side.
With typical street application ratio between intake and exhaust is easily 1:1-5-2, but a well engineered performance oriented system aims for 1:1 or even less...
09-07-2014, 08:38 AM
#39
Rennlist Member
Getting back to the original thread topic, I can tell you that I have first-hand experience using Michael's inner valve springs, and they certainly saved my engine.
At the Lime Rock PCA race this spring I was coming out of the Downhill turn (track out at 100MPH) in 4th gear, was chasing a competitor for a podium finish, went for 5th gear... But missed and got third!
My dash lit up like a Christmas tree... All the rev limit lights were on and flashing, the shift light was blazing and the over-rev alarm was flashing. I was pretty sure I was screwed.
To make a long story short, my data acquisition shows I hit 7,900 RPM - for an engine that has a stock red-line of 6,400. But NO HARM WAS DONE! No valve float, no piston-to-valve collisions and no bent valves. I even went on to win the race!
I think these are worth it at twice the price.
At the Lime Rock PCA race this spring I was coming out of the Downhill turn (track out at 100MPH) in 4th gear, was chasing a competitor for a podium finish, went for 5th gear... But missed and got third!
My dash lit up like a Christmas tree... All the rev limit lights were on and flashing, the shift light was blazing and the over-rev alarm was flashing. I was pretty sure I was screwed.
To make a long story short, my data acquisition shows I hit 7,900 RPM - for an engine that has a stock red-line of 6,400. But NO HARM WAS DONE! No valve float, no piston-to-valve collisions and no bent valves. I even went on to win the race!
I think these are worth it at twice the price.
09-12-2014, 02:52 AM
#41
Rennlist Member
Thread Starter
Getting back to the original thread topic, I can tell you that I have first-hand experience using Michael's inner valve springs, and they certainly saved my engine.
At the Lime Rock PCA race this spring I was coming out of the Downhill turn (track out at 100MPH) in 4th gear, was chasing a competitor for a podium finish, went for 5th gear... But missed and got third!
My dash lit up like a Christmas tree... All the rev limit lights were on and flashing, the shift light was blazing and the over-rev alarm was flashing. I was pretty sure I was screwed.
To make a long story short, my data acquisition shows I hit 7,900 RPM - for an engine that has a stock red-line of 6,400. But NO HARM WAS DONE! No valve float, no piston-to-valve collisions and no bent valves. I even went on to win the race!
I think these are worth it at twice the price.
At the Lime Rock PCA race this spring I was coming out of the Downhill turn (track out at 100MPH) in 4th gear, was chasing a competitor for a podium finish, went for 5th gear... But missed and got third!
My dash lit up like a Christmas tree... All the rev limit lights were on and flashing, the shift light was blazing and the over-rev alarm was flashing. I was pretty sure I was screwed.
To make a long story short, my data acquisition shows I hit 7,900 RPM - for an engine that has a stock red-line of 6,400. But NO HARM WAS DONE! No valve float, no piston-to-valve collisions and no bent valves. I even went on to win the race!
I think these are worth it at twice the price.
09-12-2014, 06:29 AM
#42
Three Wheelin'
Fitting stiffer inner springs to prevent mechanical failure from an over rev will put additional stress to the valve train when the engine is running in its normal RPM band without providing any gain in performance, so because you think you may accidentally over rev the engine you are going to affect the longevity of your valve train because of increased valve spring stiffness. The pros are therefore not a lot more obvious than the cons. The only racers that may hit the rev limiter at each and every opportunity are Drift guys. It's up to you whether you consider Drift "real" racing.
