MMS Spring Pressure/Lifter questions 150lb seat/370lb open
05-14-2002, 10:29 AM
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MMS Spring Pressure/Lifter questions 150lb seat/370lb open The last set of MMS springs I had, one broke.
I just got my "revised" MMS (941 direct replacement) springs pressure tested at the Machine Shop.
Set at 1.750 yields 150lbs (seat pressure)
Full open .558 valve lift yields 370 lbs. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />
Will I have a problem with the lifters getting flattened? I thought the 941's were 130 lb. seat and 340 open?
Some of the guys at the machine shop said I could have lifter problem (too much spring pressure) causing spring breakage.
The above numbers sound kind of high compared to the 918 springs that were tested by the same shop, same machine. I believe the 918 had just over 300 lbs full open (.561 lift) and 125 lb. seat. I'll get the exact info from them today.
I just got my "revised" MMS (941 direct replacement) springs pressure tested at the Machine Shop.
Set at 1.750 yields 150lbs (seat pressure)
Full open .558 valve lift yields 370 lbs. <img border="0" title="" alt="[Eek!]" src="gr_eek2.gif" />
Will I have a problem with the lifters getting flattened? I thought the 941's were 130 lb. seat and 340 open?
Some of the guys at the machine shop said I could have lifter problem (too much spring pressure) causing spring breakage.
The above numbers sound kind of high compared to the 918 springs that were tested by the same shop, same machine. I believe the 918 had just over 300 lbs full open (.561 lift) and 125 lb. seat. I'll get the exact info from them today.
05-14-2002, 01:24 PM
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Re: MMS Spring Pressure/Lifter questions 150lb seat/370lb open As a comparison a Comp 941 spring
had a spring pressure of 126 seat @ 1.770 and 380 @ 1.200
Seat pressure will not hurt the lifter, but provides better stability at higher rpm. Higher seat pressure will help prevent valve bounce at higher rpm. The two main components of stability are cam ramp rates and valve mass.
You can use the 918 springs, but I don't feel there is enough open pressure to keep the valvetrain stable with some of the more aggressive lobe designs currently available, especially coming over the top of the lobe. This is where open pressure is most important. It's similar to a roller coaster. If you don't have enough force to hold you in your seat then you will not stay in the coaster on the first big drop. Also the heavier the person, then the more force required to keep that person seated. If you are running a cam only with stock valves then the demand on the spring is much less than running an aftermarket 2.08 or larger. Personally I would limit the max rpm to 6600 unless it is the mildest of lobes available with the 918 springs.
Some of the older generation lobes didn't exert the same forces as we see today. They also didn't perform as well as what's available. The quicker ramp rates have improved power and torque and have greatly improved the idle and driveability also.
had a spring pressure of 126 seat @ 1.770 and 380 @ 1.200
Seat pressure will not hurt the lifter, but provides better stability at higher rpm. Higher seat pressure will help prevent valve bounce at higher rpm. The two main components of stability are cam ramp rates and valve mass.
You can use the 918 springs, but I don't feel there is enough open pressure to keep the valvetrain stable with some of the more aggressive lobe designs currently available, especially coming over the top of the lobe. This is where open pressure is most important. It's similar to a roller coaster. If you don't have enough force to hold you in your seat then you will not stay in the coaster on the first big drop. Also the heavier the person, then the more force required to keep that person seated. If you are running a cam only with stock valves then the demand on the spring is much less than running an aftermarket 2.08 or larger. Personally I would limit the max rpm to 6600 unless it is the mildest of lobes available with the 918 springs.
Some of the older generation lobes didn't exert the same forces as we see today. They also didn't perform as well as what's available. The quicker ramp rates have improved power and torque and have greatly improved the idle and driveability also.
05-14-2002, 01:58 PM
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Re: MMS Spring Pressure/Lifter questions 150lb seat/370lb open Mike thanks for the reply.
Any input on the open pressure and lifter problems?
Someone suggested too much open pressure could cause lifter bleed down at high rpm. The lifter goes solid (collapses?) and the spring breaks shortly after.
Know one seems to know exactly why these springs keep breaking. Coil bind is not a problem. Clearance was 0.080 at 1.192 (max. valve lift for me).
Any input on spring breakage? I have broken a 941 after 20k and one MMS spring after 7k miles.
I understand your above explanation compeletly. So would you use the same springs on a (MTI T1) 221/221 .558 and say your 229v3 cam?
How does valve bounce and/or float look on a dyno plot? Are there any other ways to identify those two conditions?
Any input on the open pressure and lifter problems?
Someone suggested too much open pressure could cause lifter bleed down at high rpm. The lifter goes solid (collapses?) and the spring breaks shortly after.
Know one seems to know exactly why these springs keep breaking. Coil bind is not a problem. Clearance was 0.080 at 1.192 (max. valve lift for me).
Any input on spring breakage? I have broken a 941 after 20k and one MMS spring after 7k miles.
I understand your above explanation compeletly. So would you use the same springs on a (MTI T1) 221/221 .558 and say your 229v3 cam?
How does valve bounce and/or float look on a dyno plot? Are there any other ways to identify those two conditions?
05-15-2002, 04:00 PM
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Re: MMS Spring Pressure/Lifter questions 150lb seat/370lb open Mike thanks for the reply.
Any input on the open pressure and lifter problems?
It's a combo of RPM, oil pressure, ramp rates. I don't know exactly the limits of the 'R' lifters, but I'd guess it is good pressure into the 400+lb range.
Someone suggested too much open pressure could cause lifter bleed down at high rpm. The lifter goes solid (collapses?) and the spring breaks shortly after.
When the lifter collapses, you are effectively removing lift and duration from your cam. It wouldn't cause spring breakage since there is less lift at the rocker.
Know one seems to know exactly why these springs keep breaking. Coil bind is not a problem. Clearance was 0.080 at 1.192 (max. valve lift for me).
Any input on spring breakage? I have broken a 941 after 20k and one MMS spring after 7k miles.
Unfortunately there is no clear answer. What we found out with our springs that with previous setups, we were getting some harmonics. We found the 1.750" worked well to shift the harmonics above the engine operating RPM while maintaining an appropriate amount of pressure. We weren't concerned about the seat pressure since that is less critical to lifter function, but the add'l pressure would keep the valve from bouncing at higher RPM.
I understand your above explanation compeletly. So would you use the same springs on a (MTI T1) 221/221 .558 and say your 229v3 cam?
These springs will work on all the cams out there under .600" lift since they are less aggressive than ours. We've really focused on good driveability and idle quality with our profiles. You will find that our 224 cam idles better than equivalent spec'd cam because of this lobe design.
How does valve bounce and/or float look on a dyno plot? Are there any other ways to identify those two conditions?
It can show up in different ways. Two things to look for is a sudden drop in power or a drop then recovery. This will usually happen above 6000 rpm. Then we get into different valve sizes which can change the equation too, but that is a generality.
Any input on the open pressure and lifter problems?
It's a combo of RPM, oil pressure, ramp rates. I don't know exactly the limits of the 'R' lifters, but I'd guess it is good pressure into the 400+lb range.
Someone suggested too much open pressure could cause lifter bleed down at high rpm. The lifter goes solid (collapses?) and the spring breaks shortly after.
When the lifter collapses, you are effectively removing lift and duration from your cam. It wouldn't cause spring breakage since there is less lift at the rocker.
Know one seems to know exactly why these springs keep breaking. Coil bind is not a problem. Clearance was 0.080 at 1.192 (max. valve lift for me).
Any input on spring breakage? I have broken a 941 after 20k and one MMS spring after 7k miles.
Unfortunately there is no clear answer. What we found out with our springs that with previous setups, we were getting some harmonics. We found the 1.750" worked well to shift the harmonics above the engine operating RPM while maintaining an appropriate amount of pressure. We weren't concerned about the seat pressure since that is less critical to lifter function, but the add'l pressure would keep the valve from bouncing at higher RPM.
I understand your above explanation compeletly. So would you use the same springs on a (MTI T1) 221/221 .558 and say your 229v3 cam?
These springs will work on all the cams out there under .600" lift since they are less aggressive than ours. We've really focused on good driveability and idle quality with our profiles. You will find that our 224 cam idles better than equivalent spec'd cam because of this lobe design.
How does valve bounce and/or float look on a dyno plot? Are there any other ways to identify those two conditions?
It can show up in different ways. Two things to look for is a sudden drop in power or a drop then recovery. This will usually happen above 6000 rpm. Then we get into different valve sizes which can change the equation too, but that is a generality.
