wicked_95z

iTrader: (8)

Alright, 918 beehive springs coil bind @ 1.140". Now if the springs are installed @ 1.740" with a .628" lift cam at max lift the spring is compressed to 1.112" which is .028" lower than coil bind. If I install these springs @ 1.800" that will put me at about .032" above coil bind. First of all, is this correct. Secondly, if it is right will I be okay to run up to 7K rpm with the valves setup at 1.800"

Adrenaline_Z

With those numbers, the math looks good.

Don't forget to account for any shims and lifter pre-load in your clearance.

GOaT Cheese

You are gonna need more than .032 clearance before coil stack. I would recomend at least .050. I speak from experience, I had exactly .030 at max lift with a .600 solid roller. Like clockwork at 6400 rpm's I crash valves, below 6400 everything was fine. I cut the spring pockets on the heads .020 to give me .050 before stack and that extra .020 curred the problem completely.

SStrokerAce

iTrader: (2)

Yes that will be fine in terms of installed height and room to coil bind. The 918's can coil bind lower than 1.140" so check them before you install them and even at a tight clearance they work fine.

I would just be worried that its not enough valve spring for them, 130lbs on the seat is a little weak for most stuff going to 7000rpm.

Bret

skipperbisket

iTrader: (4)

so Bret speaking in ls1s what would be the most suitable seat pressure for a hyd cam with mild to high lift and still keeping those higher rpm ranges?

wicked_95z

iTrader: (8)

Just so I understand completely. What is the difference between seat pressure and open pressure?? Also, installed height is inversely proportional to seat pressure correct??

Adrenaline_Z

The seat pressure is the closed pressure at the specified install height.

Open pressure is the value at max valve lift.

Seat pressure and open pressure reduce as install height increases.

vettenuts

iTrader: (4)

Seat load = (Free length - Installed height) X stiffness

or if the load is only given at 1.8"

Seat load = Load at 1.8" + (1.8 - Installed height) X stiffness

Open load = Seat load + (Installed height - valve lift) X stiffness

So as the installed height decreases, seat load increases. Since stiffness is for the most part linear, the open load will go up by the seat pressure increase.

For 918's, stiffness = 313 lb/in, load @ 1.8" = 130 lb

So for your installed height of 1.74"

Seat load = 130 + (1.8-1.74) X 313 = 148.78 lbs

Open load = 148.78 + 0.628 X 313 = 345.344 lbs

wicked_95z

iTrader: (8)

Bret, what pressure do you recommend for seat and open for a .606 and .628 cam and 15psi.

Thanks guys for the calculations, good info

SStrokerAce

iTrader: (2)

Depends on the lobe, the rest of the parts in the system and the RPM range.

Bret