Cam and spring decisions

[NightTrain66]

LOTS of things go into if a spring will work or not.

Seat pressure, open pressure and coil bind are all measurable and any machine shop can take a spring and give you the info.

2 things to consider is if this is a dbl springs (putting the load on 2 different springs and with 2 different frequencies) and the quality of the wire that is used (that's not really something you can measure or look at).

There can be springs with the same seat pressure, open pressure and coil bind that range in price from $60, $120, $180, $250 and $350 for springs only (not springs, retainers, locks, locators, seals, etc).

Those $100 Alex springs are OK for the $$$ but once you break down that you are getting springs AND retainers, locks, locators and seals all for $100, you can see it is probably a $60 spring or so with everything you are getting for $100. These are OK on some of the slower ramp speed cams like 210-mid 220 duration Comp Magnum lobes in the .520-.560 lift range (based on a 1.6 rocker) spinning 6300 RPM or so but they have NO BUSINESS being on a Voo Doo, XFI, etc and DEFINITELY NOT on any "aggressive" lobe or ANY lobe that will wanna spin 6500+ RPM.

Not picking on these springs because for $100, you are not gonna get a better spring, retainer, lock, locator and seal package, they just severely limit what lobes you can use and expect them to live and if you want a "real cam" you really need to buy a better set of springs.

Obviously the more expensive springs are gonna be made with the better wire and the less expensive are the cheaper wire.

The cheaper quality springs are just gonna lose pressure sooner under the same conditions compared to the better spring.

Every spring (at least the ones most on this board are gonna reference) will lose a lil pressure (3-5 lbs) when you first start it up and heat cycle it a few times and maybe a lil more after the first 1000 miles or so (another 3-5 lbs).

You can get some $350-450 Isky Tool Room, nice PAC or PSI MLS springs that will NOT lose any pressure but most reading this are not gonna shell out that kinda $$$ for springs and for the most part they can get a set of Lunati 73925 K2 dbl spring kit that will handle any cam most are really gonna need.

Even if you have everything right and the correct quality/rate springs at correct set up ht with correct rocker geometry and correct PR length you can expect a lil pressure drop from most springs.

As long as everything above matches up, the springs should stay there for a while before losing any more pressure.

If the lobes and springs do not match or if the person doesn't have proper rocker geometry (rockers not centered on all valves "side to side"), doesn't have correct PR length (how many "really measure"), etc, the springs are gonna continue to lose pressure until they can not control the valve trane any more. At that point you are getting valve trane problems and valve float. That is basically like "wheel hop" in your valve trane with slack getting in between all parts and then they get a running start at crashing back into each other and "SOMETHING" is gonna break. Might be a lobe, lifter, pushrod, rocker, valve, spring, retainer or whatever but the springs will keep losing pressure until SOMETHING breaks.

Most will blame it on the pushrods or rockers or valves, etc, (or what ever part actually broke first) and never understand that it was the spring/cam choice all along.

If you ever try to remove the springs and compress the retainer and have to hammer them down with a socket or tap with a hammer to get them to break loose, look at the back of the locks and you can see some "etching" where the retainers have been walking around and moving. This is caused by valve float. Most that have disassembled stock LT1 heads have done this to get the valves out. The car might not bang or pop and might feel fine running thru the gears at high RPM but that is a sign of some valve trane problem. If you ever have to remove a spring like this, MAKE SURE and use a flat file and remove any sharp edge from the lock groove ion the valve before sliding it through the guide so the guides are not damaged.

Lloyd

[NightTrain66]

Not all lobes are the same and I guess they can be broken down into 4 groups just for this educational on a hyd roller LT1. LOTS of things go into the shape of the lobe and how fast it yanks the valve off the seat, how long it is in the mid lift range, how long it is in the high lift range, how long it is in the mid lift range on closing side and how fast it slams the valves back into the seat on closing and how well it transitions In between all of these. With out working at a cam company and looking at each lobe and understanding all of this you are kinda stuck and have to go by what your cam guy tells you.

The most common way to see the "ramp speed" of a lobe id by looking at the Adv duration, @ .050 duration and @ .200 duration #'s and comparing them. There is A LOT more to it but this is at least one way for the average person on this forum to have "some idea' about lobes and differences.

Most people still reading and learning will find the below info useful.

1-LAZY lobes - these are cams with 60 degrees or more between the Adv (.006) duration and @ .050" duration Example - 281 Adv, 220 @ .050, 134 @ .200

The Hot Cam, CC 305, etc all fall in this category. They open slow, spend a lot of time getting to mid/max lift and then close slow as well. These are EASY on parts and as long as you stick with 220 duration or less, can usually get by with cheep springs, $30 pushrods (sometimes stock even), cheep rockers, etc. 125-130 lbs on seat will control these lobes with no problem.

The CC 306 uses Lazy lobes as well but at ANYTHING over 230 duration in an LT1 has the RPM capability to spin 6400-6800 RPM in an LT1 so even though it has LAZY lobes, I would get descent springs, pushrods, rockers, etc and NOT the cheep parts I mentioned above.

2-Moderate/medium lobes. These have between 54-58 degrees between the Adv and @.050 duration #'s. Example Adv 280, 224 @ .050, 144 @ .200.

130-135 lbs on the seat will control these lobes with EVERYTHING correct (rocker geometry, PR length, rocker adjustment, etc). The more things you have wrong or off, the more pressure needed to control them. Also remember if you want the springs to have 130-135 lbs on the seat after 1000 mile of street driving, I would set them up 140-145 lbs when assembling them since they will lose some pressure.

3-Moderately aggressive - These will have 50-53 degrees between Adv and @ .050 duration Example - 280 Adv, 230 @ .050, 154 @ .050.

Lunati VooDoo lobes, XFI lobes, etc are more aggressive than the above 2 groups of lobes but still pretty fluid in motion so even though they are more aggressive than the previous listed lobes, they are actually not much harder on parts. Just make sure and get better springs like a good dbl spring with 155 lbs on the seat (remember, it will be down to 145-150 lbs in 1000 miles or so).

I would use $200-330 rockers, $90-135 PR's with these lobes.

4 -They make more aggressive lobes but as mentioned, anyone reading and learning from what I read here has no business going more aggressive than what is listed if they are in control of the build. If you call a cam company they will probably not get you a cam with this kinda lobe because they know it needs GOOD parts and EVERYTHING must be right. The extra 8-15 HP made from these lobes are NOT WORTH the average customer bad mouthing them when their cheep springs, rockers, lifters, etc broke and destroyed the cam.

I cant state enough that there is more and more to cams and springs than I could possibly type but after reading the questions posted in this thread, I thought this would be helpful to lots of people and give them a better understanding of what parts are needed and why I suggest certain cams when a customer calls up and already has the springs picked out. The most important part is for the valve trane to live and NOT beat itself to death (how much HP is the engine making with a dropped valve . . . . . ZERO HP). Once I know what springs are being used and the life expectancy (cust wants them to live 100K, 50K, 30K, 15K miles) I have a much better idea about how aggressive of a lobe we can use.

The duration and LSA is more tied to the cubic inch, compression, vehicle weight, gear, stall, shift RPM, emissions, etc and the spring/valve trane parts selection is what will limit/dictate how aggressive the lobes are.

Lloyd Elliott
972-617-5671
Elliottsportworks.com

[firebird_1995]

And that ^ my friends, is why Lloyd is THEE man for the job when you need a cam or set of heads done. Now I need some aspirin....

[englundjd]

Thank you Lloyd you are the man! that was very informative

[NightTrain66]

Just a crash coarse to help some people posting in that thread to shed some light on why a ".600 lift spring" is not really a useful term when ordering a camshaft.

The cam guy really needs a lot more info than that.

Lloyd

[englundjd]

@NightTrain66 not to take the thread off course but how long will my valvetrain hold up with the 231/239 109lsa and lunati dual spring kit? I forgot to ask you that before I ordered.

[NightTrain66]

I have customers with 30K miles on that set up with no problems.

Just make sure they are set up at 1.760-1.780". and they will live a long time.

You could probably test a spring after 30K miles and see if it is low and then shim it another .030" and get the pressure back up for a while longer or swap springs and be safe.

OBVIOUSLY driving style has a lot to do with it and 30K miles of street driving and occasional track time is different than a bracket car getting 200 passes a year at 1/4 mile at a time and expecting 30K+ miles.

Most bracket guys consider springs a part that wears and understand that they will be replaced every 1-3 years depending on shift RPM, # of passes, etc.

If you beat on it a lot you can expect them to live less than a guy that never beats on his stuff and keeps the engine in lower RPM more often (of coarse).

Those Lunati 73925's are good wire (for the $$$).

Lloyd

[MI6TA]

Wow, I feel enlightened. Thank you very much for the crash course Lloyd! I'm always wanting to learn more about motors and really the heads in general is a new playground. I get how they function but not the specifics. I definitely understand more now though; and am more glad than ever that you're building my cam haha. I will follow up in E-mail about my situation. I went with the cheap alex springs mainly for the price, I fully expect that I will get what I paid for, but at this time my priority is to get the engine back together so I can stop borrowing my girlfriends car lol. In the future when the springs need replacing I will put a longer lasting combination on there but at this time budget is holding me back.