CAM and Valve Springs Question
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Teching In
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From: Denver, CO
CAM and Valve Springs Question I am new to a lot of this so bear with me. I have a LH6 new engine, never run that has an upgraded CompCAMs 11-457-11 CAM. (.610/.617, 223/231, LSA 112). My application is an aircraft. Max power is 300 HP at 4500 RPM (my max RPM). This is too much CAM. As is the engine will produce 350 HP at 4500 RPM. Keep in mind the exhaust and transmission losses will be minimal here in contrast to a automobile. The exhaust will be around 36" long and the transmission is 1 gear. When the CAM was put in the springs were also upgraded. Moving to a milder CAM (.457/.466, 191/190, 115.5). I have been advised to replace the springs as well as the upgraded springs will just generate lots of wear and heat.
Option 1: Stock LS6 springs (Seat Pressure 90, Open Pressure 265, Install Height 1.800", Open Height [1.800-[b].466 = 1.334], 375 lb/in springs, cost $70-$100 each)
Option 2: Trickflow springs Part Number: TFS-16306 (Seat Pressure 108 [estimated], Open Pressure 318, Install Height 1.800", Open Height [1.800-.[b]466 = 1.334], 450 lb/in springs, cost $150 each )
Part of the rational for Option 2 is better seat pressure and more stable valve train.
Does this make sense, am I clueless in my analysis? Is there an option 3 that is better?
Rick
Option 1: Stock LS6 springs (Seat Pressure 90, Open Pressure 265, Install Height 1.800", Open Height [1.800-[b].466 = 1.334], 375 lb/in springs, cost $70-$100 each)
Option 2: Trickflow springs Part Number: TFS-16306 (Seat Pressure 108 [estimated], Open Pressure 318, Install Height 1.800", Open Height [1.800-.[b]466 = 1.334], 450 lb/in springs, cost $150 each )
Part of the rational for Option 2 is better seat pressure and more stable valve train.
Does this make sense, am I clueless in my analysis? Is there an option 3 that is better?
Rick
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From: Central Cal.
You're putting a stock truck cam back in, so a set of stock LS6 springs will do very nicely.
They are plenty stable for that cam. Keep in mind their normal application is in C5 Corvettes with a 400+ HP engine. No sense spending money on anything different
They are plenty stable for that cam. Keep in mind their normal application is in C5 Corvettes with a 400+ HP engine. No sense spending money on anything different
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Please note: "cam" is not an acronym or something. (in this case anyway... there is of course "Computer Aided Manufacturing" but that's not what this is) The word "cam" in this context, short for "camshaft", is NOT an all-caps deal. 
Seeing it typed that way is REALLY annoying, it's as though you are SHOUTING or even SCREAMING the word at us.
That said, I agree with G Atsma, the LS6 springs are "adequate" for a stock LM7 cam. Personally, over the years though, I've found that you can NEVER go wrong with upgrading the springs, to a point. I have PAC 1218 springs in my stock LM7 ATM. Seat pressure is what's important; open pressure not as much. "Valve float" is almost always a function of the valves bouncing off the seat as they close, not "valve toss" where they launch into space at the top of the cam lobe profile. Especially not with a stock cam. Although, for an aircraft, it could be argued that some very mild double spring might be better than any of those, as it gives a backup in case one breaks.
Seeing it typed that way is REALLY annoying, it's as though you are SHOUTING or even SCREAMING the word at us.That said, I agree with G Atsma, the LS6 springs are "adequate" for a stock LM7 cam. Personally, over the years though, I've found that you can NEVER go wrong with upgrading the springs, to a point. I have PAC 1218 springs in my stock LM7 ATM. Seat pressure is what's important; open pressure not as much. "Valve float" is almost always a function of the valves bouncing off the seat as they close, not "valve toss" where they launch into space at the top of the cam lobe profile. Especially not with a stock cam. Although, for an aircraft, it could be argued that some very mild double spring might be better than any of those, as it gives a backup in case one breaks.
Please note: "cam" is not an acronym or something. (in this case anyway... there is of course "Computer Aided Manufacturing" but that's not what this is) The word "cam" in this context, short for "camshaft", is NOT an all-caps deal. Seeing it typed that way is REALLY annoying, it's as though you are SHOUTING or even SCREAMING the word at us.
That said, I agree with G Atsma, the LS6 springs are "adequate" for a stock LM7 cam. Personally, over the years though, I've found that you can NEVER go wrong with upgrading the springs, to a point. I have PAC 1218 springs in my stock LM7 ATM. Seat pressure is what's important; open pressure not as much. "Valve float" is almost always a function of the valves bouncing off the seat as they close, not "valve toss" where they launch into space at the top of the cam lobe profile. Especially not with a stock cam. Although, for an aircraft, it could be argued that some very mild double spring might be better than any of those, as it gives a backup in case one breaks.
Seeing it typed that way is REALLY annoying, it's as though you are SHOUTING or even SCREAMING the word at us.That said, I agree with G Atsma, the LS6 springs are "adequate" for a stock LM7 cam. Personally, over the years though, I've found that you can NEVER go wrong with upgrading the springs, to a point. I have PAC 1218 springs in my stock LM7 ATM. Seat pressure is what's important; open pressure not as much. "Valve float" is almost always a function of the valves bouncing off the seat as they close, not "valve toss" where they launch into space at the top of the cam lobe profile. Especially not with a stock cam. Although, for an aircraft, it could be argued that some very mild double spring might be better than any of those, as it gives a backup in case one breaks.
Thread Starter
Teching In
Joined: Nov 2011
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From: Denver, CO
Well this is interesting. Thanks for the input and guidance, especially on CAM vs cam.
Further info.. My Option 2 Is a double spring and I had thought/hoped it provided a level of redundancy. So I it looks like a better choice given my application. It's not a huge increase in spring pressure so I am not increasing wear and generating tons of heat. But better seat pressure to minimize/mitigate valve float which is what I was hoping for.
Option 2: ption 2: Trickflow springs Part Number: TFS-16306 (Seat Pressure 108 [estimated], Open Pressure 318, Install Height 1.800", Open Height [1.800-.[b]466 = 1.334], 450 lb/in springs, cost $150 each )
Thanks for the feedback!
Further info.. My Option 2 Is a double spring and I had thought/hoped it provided a level of redundancy. So I it looks like a better choice given my application. It's not a huge increase in spring pressure so I am not increasing wear and generating tons of heat. But better seat pressure to minimize/mitigate valve float which is what I was hoping for.
Option 2: ption 2: Trickflow springs Part Number: TFS-16306 (Seat Pressure 108 [estimated], Open Pressure 318, Install Height 1.800", Open Height [1.800-.[b]466 = 1.334], 450 lb/in springs, cost $150 each )
Thanks for the feedback!
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From: Wilmington, De
I would not be concerned about valve float with a stock cam and stock springs turning a max of 4500 RPM.
I don't think you'll be gaining anything in regards to redundancy going to a dual spring, either. It's not like the inner spring is going to keep things together long enough to get to the nearest airport if the outer spring breaks.
I don't think you'll be gaining anything in regards to redundancy going to a dual spring, either. It's not like the inner spring is going to keep things together long enough to get to the nearest airport if the outer spring breaks.
I would not be concerned about valve float with a stock cam and stock springs turning a max of 4500 RPM.
I don't think you'll be gaining anything in regards to redundancy going to a dual spring, either. It's not like the inner spring is going to keep things together long enough to get to the nearest airport if the outer spring breaks.
I don't think you'll be gaining anything in regards to redundancy going to a dual spring, either. It's not like the inner spring is going to keep things together long enough to get to the nearest airport if the outer spring breaks.
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This is a very weird feeling for me to say this, but I would only go with a dual spring in the combo, regardless of camshaft. This is an airplane, not a car. At least if an inner our outer breaks, you may be given a little extra run time to make an emergency landing. This isn't as easy as popping into neutral and pulling over waiting for a tow.
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From: Central Cal.
This is a very weird feeling for me to say this, but I would only go with a dual spring in the combo, regardless of camshaft. This is an airplane, not a car. At least if an inner our outer breaks, you may be given a little extra run time to make an emergency landing. This isn't as easy as popping into neutral and pulling over waiting for a tow.
A redundancy factor weighs BIG in an aircraft situation.
If he can find dual springs with equivalent total spring forces to the LS2/3 beehives, it would be ideal.
This is a very weird feeling for me to say this, but I would only go with a dual spring in the combo, regardless of camshaft. This is an airplane, not a car. At least if an inner our outer breaks, you may be given a little extra run time to make an emergency landing. This isn't as easy as popping into neutral and pulling over waiting for a tow.
Turns out some of the early AFR 225 heads installed height had been set up about .080"-.100" too short!! Springs were REV, but probably not their fault......Last edited by grinder11; Sep 28, 2023 at 08:42 AM.
Probably the closest he will find is PAC-1204X. I don't believe anyone makes a less aggressive dual spring.
We wouldn't sell to an aftermarket aircraft engine manufacturer due to the FAA requiring a "guarantee" on valve springs. That is something that 99.99% of the VS wire out there cannot do. The one (only one that I am aware of) that can, cost an insane amount of money, and i believe they even leave a fudge factor in their specifications for inclusions.
We wouldn't sell to an aftermarket aircraft engine manufacturer due to the FAA requiring a "guarantee" on valve springs. That is something that 99.99% of the VS wire out there cannot do. The one (only one that I am aware of) that can, cost an insane amount of money, and i believe they even leave a fudge factor in their specifications for inclusions.
Thread Starter
Teching In
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From: Denver, CO
Grinder11, thanks for the response and insight and everyone else's as well!!!
TurboBuick6: The springs I was thinking of using are Trick Flow® by PAC Racing Dual Valve Springs TFS-16306. My max camshaft lift is 0.466. Heads are stock 799/243 heads with 1.7 ratio rockers, to my knowledge no trunnion upgrade. Below is some information I gathered on 4 different valve springs.. I also found the PAC-1904 as a possible candidate.
The 4 springs outlined below are: PAC-1204X or TFS16306 or PAC-1904 or Stock GM springs (19420455)
One other question.... Do I need to lap the valves? The engine is new, never run.
Rick
TurboBuick6: The springs I was thinking of using are Trick Flow® by PAC Racing Dual Valve Springs TFS-16306. My max camshaft lift is 0.466. Heads are stock 799/243 heads with 1.7 ratio rockers, to my knowledge no trunnion upgrade. Below is some information I gathered on 4 different valve springs.. I also found the PAC-1904 as a possible candidate.
The 4 springs outlined below are: PAC-1204X or TFS16306 or PAC-1904 or Stock GM springs (19420455)
- All are Standard Dual springs except the stock that is beehive/single. The engine currently has standard springs.
- All have an OD of 1.290 except TFS16306 @ 1.275. The springs currently in the engine are 1.320. Is this an issue?
- ID of Inner springs are .694/.675/.694/unknown.
- Seat Pressure is 145/150/150/90. It is my understanding that the rockers stock rockers can handle 175 lbs of seat load and 450 lbs of open load (OnAllCylinders.com)
- Spring rates are 369/450/370/375
- Open loads were calculated at .466 to be 317/356/322/265.
One other question.... Do I need to lap the valves? The engine is new, never run.
Rick
Grinder11, thanks for the response and insight and everyone else's as well!!!
TurboBuick6: The springs I was thinking of using are Trick Flow® by PAC Racing Dual Valve Springs TFS-16306. My max camshaft lift is 0.466. Heads are stock 799/243 heads with 1.7 ratio rockers, to my knowledge no trunnion upgrade. Below is some information I gathered on 4 different valve springs.. I also found the PAC-1904 as a possible candidate.
The 4 springs outlined below are: PAC-1204X or TFS16306 or PAC-1904 or Stock GM springs (19420455)
One other question.... Do I need to lap the valves? The engine is new, never run.
If you go with a dual spring, you will need to change the locator, seal and retainer. You can re-use the locks. The 1904 is a great spring and is based off the 1204X. The difference is the 1204X was manufactured for dedicated racing, so it does have a little processing advantage over the 1904, however, either is a good choice. Even though the TFS springs are great, the PAC branded options are going to be a better option for you application in an airplane.
Rick
TurboBuick6: The springs I was thinking of using are Trick Flow® by PAC Racing Dual Valve Springs TFS-16306. My max camshaft lift is 0.466. Heads are stock 799/243 heads with 1.7 ratio rockers, to my knowledge no trunnion upgrade. Below is some information I gathered on 4 different valve springs.. I also found the PAC-1904 as a possible candidate.
The 4 springs outlined below are: PAC-1204X or TFS16306 or PAC-1904 or Stock GM springs (19420455)
- All are Standard Dual springs except the stock that is beehive/single. The engine currently has standard springs.
- All have an OD of 1.290 except TFS16306 @ 1.275. The springs currently in the engine are 1.320. Is this an issue? No, not an issue
- ID of Inner springs are .694/.675/.694/unknown.
- Seat Pressure is 145/150/150/90. It is my understanding that the rockers stock rockers can handle 175 lbs of seat load and 450 lbs of open load (OnAllCylinders.com) Yes, more than that IMO
- Spring rates are 369/450/370/375
- Open loads were calculated at .466 to be 317/356/322/265.
One other question.... Do I need to lap the valves? The engine is new, never run.
If you go with a dual spring, you will need to change the locator, seal and retainer. You can re-use the locks. The 1904 is a great spring and is based off the 1204X. The difference is the 1204X was manufactured for dedicated racing, so it does have a little processing advantage over the 1904, however, either is a good choice. Even though the TFS springs are great, the PAC branded options are going to be a better option for you application in an airplane.
Rick
My goodness!!! I just realized you said the cam has only .466" lift!!! I'd listen to TurboBuick6, as he works at PAC. I will say I can't think of a dual spring that wouldn't stay intact for many years with only .466" lift......
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From: Central Cal.
Hey, as I mentioned, it's a stock LM7 truck cam. A stretched door spring would work with that cam. But aircraft guys can't be TOO careful....
Agree on can't be too careful. I've seen some airboats with old Continental aircraft motors that use twin distributors. Would imagine the Lycomings are the same.... TECH Addict
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Yeah I seem to recall that those Lycoming 4-cyls have 2 magnetos... a "distributor", with its requirement for external battery power, has always been considered inadequately reliable for aircraft. With yerbasic automotive engine like a LS series though, I suppose that requirement can't be avoided.
The rockers shouldn't really care too much about seat pressure; really, only the max they are subjected to, which would be at full open, would be an issue.
The rockers shouldn't really care too much about seat pressure; really, only the max they are subjected to, which would be at full open, would be an issue.
Hmmm.....Probably not the forum for discussing merits/faults of a Lycoming engine, but I've been told they are one of the greatest aircraft engines ever designed. Anyway, thanks for joggin' the noggin about the dual magnetos. I believe Continental also used dual mags. Anyway.......