interesting. where does rockerratio play in this? .715 x 1.7?
<----also wants to learn.

 

NO

NO ............................Phuck.....Oh yeah, for sure,,...............maybe....

 

yeah, basically its your cam(.715) x rocker ratio(example 1.7) =1.215"
then subract your lash for net lift. hers where i got this
http://www.circletrack.com/techarticles/ctrp_0611_rocker_arm_valvetrain_geometry/photo_06.html
losta good info here -Jas

 

Hey hot rod, The cam spec you are listing being .715 lift of valve off the seat. On that cam the acctual or net amount of lift at the cam would be .420. The rocker factors in as the lift at valve. Therefore .420 x 1.7 = .715. Here is a double check for you. .715 devided by rocker ratio. A dial indicator at each ind of the rocker tells these numbers. Lastly a cam of that size wants a minimum .040 coil clearance. YOU MY FRIEND ARE IN THE DANGER ZONE!!!!!!!!!!!!!!! I don't know if you have purchased your'e rockers yet but if you do the math with the info above a slower ratio rocker is a easier fix. IE .420 x 1.6=.672 lift at valve. Very good spec cam.IMO M

 

Ol guy is right, and that would be a VERY tight combination, best dealt with by less lift, one way (different cam) or another (lower ratio rockers).

 

ok not to hijack but to understand, my cam is .680 lift how would i know what rocker to use to atchieve that lift would it be in the part number?

 

Hey bord, not knowing the motor Ford or chevy it's a hard call But the stock ratio is the factor the cam grinder comes up with for the lift at the valve,Chev uses a 1.70 rocker so the lift at cam is .400. Ford 429-460 uses a 1.73 rocker so the lift at cam would be .393 Then you multiply by rocker ratio and that determines the lift at valve. Again the cam grinders design cams to work with stock ratio. then its up to the motor builder to take some lift out or add some by rocker ratio changes. I was racing a 429 ford and would order my cam choice knowing I was going to machine the head for chevy 1.70 rockers, The chevy valve train is much easier to play with and less costly in the long run. Hope this helps. M

 

ah ha! beautiful. thanks for clearing that little mystery up. i looked at a cam i have here and said to myself there's just no way those lobes are .700 tall,lol. i'll keep that 1.7 in my mind. -jasdevil

 

That's a bit tight and would likely be a problem. Depending on the application, you may be able to buy +.100" longer retainers to give you a bit more room. You'll likely need different springs to get proper seat/over the nose spring pressure. Likely cheaper than new valves.
If I can, I like to set my spring height about .100" taller than my valve lift. This gives you room to shim the spring if it starts to get a bit soft and still allow enough room to avoid coil bind. Good luck.

 

Someone might add the insignificant fact that valve spring PRESSURE may not be correct for the application. Required pressure is dependant on lobe profile (how radical the ramps are), application, rpm's it regularly sees, valve weight, etc.
You need .060" minimum before spring coil bind. Just because a spring is spec'ed at .700 has little to do with how much lift it will handle before coil bind. Different manufacturers (of springs) rate their springs different (before coil bind). (I don't even think that sentence made sense)
But, what do I know.
Wags

 

tHIS DOESN'T EVEN WARRANT A RESPONSE!!! I'll just back out and say listen to wags Good luck guys. P.M. me If you want My thoughts. Instant balls just add a keyboard. M

 

If the heads came as a package from say Brodix for example, and the spring package was for .700 lift, this would typically be .075-.100 from coil bind. You say your cam has a gross theoretical of .715, factor in a typical lash of .020, plus valve train deflection (with some decent parts) and you will be lucky if your getting .650 actual at the valve.
I would say you will be more than fine, but need to check the heads to make sure they are indeed set-up for .700 lift (coil to coil bind and seal to retainer clearance) and are of the proper pressure for the cam.

 

more info

Valvetrain. I'm looking at a set of Merlins, 030620-3, assembled, new, recomended for a solid roller cam, max valve lift .700

Originaly I was going to go with 030620-4 with a max valve lift of .800, but unfortunately the Summit Credit Card doesn't have the balance for that.

My cam is .715 lift with a 1.7 rocker arm ratio.

 

I wasn't trying to bust anyones balls. Sorry if I offended you Ol guy..
Just adding pressure is something that needs to be taked about. It seemed to get off track talking about lobe profile, lift and rocker ratio
I am no expert..like most of the engine guys on the internet.
Wags

 

Back on track.
Yes..the math works out on paper. As warpt said, there will be some deflection.
Yes, you need to check everything..always.
You could replace valve springs. You could switch to a +.050 installed height keepers (if pressures are still up to what you need).
Increasing installed height will lower pressures.
You also could machine the spring pockets deeper (depending upon the head).
You could regrind the cam.
You need .060" according to most manufacturers. In the pleasure world, or bracket world, there is not usually a reason to run so close to coil bind. So many springs available..it just isn't necessary...especially with a .700 lift cam. Once you get above about .825..spring choices are cut in half..and there are still many dozens that will accomodate that lift.
Hope that answers questions..on track..and not pissing on anyones cheerios.
Wags

 

O.K. this may really screw things up, but I will throw this out there to see if anyone has tested this. Does a spring working near coil bind create more heat than a spring that has a higher lift rating?

Paul

 

Good point FC!!!

No, a spring that is running near coil bind (.050-.060) will typically run cooler due to the lower amount of "spring surge" vs. a spring ran at say .150 from coil bind.
Heat is caused by the spring "cycling" or being compressed and released. Spring surge is stored energy from the spring being compressed, then released. This energy has no were to go so it bounces back and forth through the spring from the retainer to spring seat and back. The further you are from coil bind, the more of a "running start" this surge can get before it hits the spring pad and returns up through the spring to the retainer. The spring will continue to surge back and forth until the rocker moves it again and starts the process all over again. This whole time the spring is moving it is creating heat.
When running a spring close to coil bind it effectively shortens this "running start" or "takes up excess room" for surge to magnify, thus adding stability to the valve train, and increasing spring life through shortening duty cycles (less heat).
In the past this has been the case only in high dollar, high rpm race engines, but as cam lifts in the .700-.800+ range are becoming the norm, this applies to the lower speed boat and street/strip engines. Remember, it isn't engine speed the valve spring is fighting it's valve speed!devil

But FC, you already knew this didn't you?!?

 

You also need to find out if that spring has the right psi rate(s) for your application. 'Roller Spring' does not mean that it will work for all roller cams.
Plus, is it some low grade cheapo that won't last long in your application or ????????

You need to find all this out before you buy.

Since you haven't bought the heads yet, have you given the Dart Iron Eagle's some thought?

 

You also need to find out if that spring has the right psi rate(s) for your application. 'Roller Spring' does not mean that it will work for all roller cams.
Plus, is it some low grade cheapo that won't last long in your application or ????????

You need to find all this out before you buy.

Since you haven't bought the heads yet, have you given the Dart Iron Eagle's some thought?

Yes I looked at the Dart Iron Eagles, they looked slightly better for the money. The Dart's have a 308 cc runner vs. 320 cc runner for the Merlins which I think the velocity would be better for a jet boat app. The Dart's (Dart 15100112) have a "Spread" exhaust location and I don't know what that means, but it sounds like different headers would be required. Plus the Dart's have a max lift of .690. .010 less than the Merlin's. Sounds like that's not an "issue" for me anymore as most people seem to be trying to steer me to buying unloaded heads and loading them for my app instead of relying on a "generic" valvetrain set-up from Merlin or Dart.

 

It seems like I have a ton of options and only a few of them are "correct". I think I need to go back to school to figure it all out, or get a second job so I can pay someone else to figure it all out.

 

I have a inside hook up for Pro Comps, about $500 a pair (edit: each) loaded (not loaded for my cam), but I've been told I should go with iron heads for a lake/river hot rod, and that Pro Comp heads are crap. ? . I don't know enough information to form a decision on iron vs. aluminum, or enough information to determine valvetrain components for my app.. (yet)

 

I'm with you FC, was definitely suspecting that the behavior would be oposite, but, wasn't about to claim any kind of info to it, just "the way it seemed it should be".

Thx for the info here too WS.

 

Warp has this nailed down. The old school thought was to run a spring that didn't get close to coil bind and it would live for ever. Then cams got a little more aggressive and the springs started jumping up and down on their seats (oscilating/surge) and they found that the closer the spring gets to coil bind the less this happens because the there isn't enough room and the spring pressure is higher(for a given spring rate) running a .600 lift cam on a .850 spring just doesn't get it done. Scooter Brothers(Comp Cams) wrote an article on this a while back and basicaly said the spring needs to get within about .090 of coil bind to work as designed, even if that means shimming it and letting the seat pressure rise. I no longer set by springs just by seat pressure but also by how far I am from coil bind.