valve spring pressures on a SFT cam

[Bluefish]

Whats enough and whats really needed for a SFT cam with a .403/.410 lobe lift using a 1.6/1.5 combo rocker and a dual spring? With .020" lash I figure its at .625/.595 actual lift at valve. 7000RPM limit
(302/308)270/276@50 on a 110 lsa.

 

[LemonWedge]

I run Engle 594/595 dual springs. 160 seat and 360 open lbs on 1.875 installed ht. Cam is an Engle KV3 lobe with 1.6 rockers. Lift @ .594 after .018 lash. I shift at 6300; trap at 6500. Cam has been happy for 10 years now.

 

[Bluefish]

I run Engle 594/595 dual springs. 160 seat and 360 open lbs on 1.875 installed ht. Cam is an Engle KV3 lobe with 1.6 rockers. Lift @ .594 after .018 lash. I shift at 6300; trap at 6500. Cam has been happy for 10 years now.

which one is more important, the seat or the open pressure?

 

[LemonWedge]

which one is more important, the seat or the open pressure?

I think that’s a loaded question. I’ll start by making it readily clear that I’m not an engineer. But my thought is that the relationship between the two is the biggest factor to consider. It would seem that the most imperative job of the spring is to (A) keep the lifter on the lobe on the way down the backside of the lobe. Then (B) keeping the valve from bouncing when it shuts. So most of job (A) involves the spring-stroke between seat and nose pressures. Job (B) involves only seat pressure. Nose spring pressure needs to be stiff enough to hold the lifter down as it reaches max-lift too, without being so heavy that it damages the cam-lobe.
What this all means to me is that all aspects of the spring are equally important.
I think the best practice when choosing springs is to simply follow the cam manufacturers recommendations.

 

[Bluefish]

I think that’s a loaded question. I’ll start by making it readily clear that I’m not an engineer. But my thought is that the relationship between the two is the biggest factor to consider. It would seem that the most imperative job of the spring is to (A) keep the lifter on the lobe on the way down the backside of the lobe. Then (B) keeping the valve from bouncing when it shuts. So most of job (A) involves the spring-stroke between seat and nose pressures. Job (B) involves only seat pressure. Nose spring pressure needs to be stiff enough to hold the lifter down as it reaches max-lift too, without being so heavy that it damages the cam-lobe.
What this all means to me is that all aspects of the spring are equally important.
I think the best practice when choosing springs is to simply follow the cam manufacturers recommendations.

Todd at competition wedge engines contacted me and offered to test a few springs for free. no charge. Gonna box some up and send them out to see what I have. Thanks

 

[383man]

My solid flat tappet cam is .585 & .592 lift and it has about 150 on the seat and 350 with valves open. They been in the car over 8 years now and its still running the same 10.70's and 10.80's. Ron

 

[stage3]

Whats enough and whats really needed

when i had my comp cams solid roller set up i went by what the rpm range of the heads flowed would be....we reduced the valve spring pressure at both ends....both closed and open...instead of say appx 300 closed and 650 open,,,we reduced that to 195 closed and 495 open...this was not a random deal,,,we based it upon older set ups that was well documented on head flow vs cam specs,,,no sense in over stressing valve train gear on cam manf lawyer approved settings....superstock march 1975,,tightnuts article,,running a crane cam,,reduced valve spring pressure because there motor wasn't going to run 8500 rpm's.....ran consistant 10.70's...max wedge with roller cam....thats what i based mine upon..same specs as above.

 

[66Satellite47]

I have always looked closely at the manufacturers recommendation to gauge what their opinion of open pressure should be to keep the lobe from flattening and then the seat pressure. I tend to add about 10-15# more seat pressure. Also make sure what RPM range they are talking about for the specific grind you are using. If you plan to operate on the high end of the recommended operating range, you may want to be at or a little extra pressure at max lift. As stage 3 said, you don't need to go bigger on the spring pressure if it's not needed.

 

[Bluefish]

Gonna pull the heads for machining , so I will be getting all springs checked and or replaced with proper pressures. Thanks