What boost pressure will lift the valve?

G

Gun512

New member
Joined
Jul 4, 2009
Messages
6
My truck is an 04.5
stocker/s400
100hp nozzles
bag-o-parts(Industrial injection 33% on the way)
studs
smarty TNT


I have a 60psi gauge and have buried it on several occasions. Typically at WOT it is around mid 50psi. I have read several threads on the forum with individuals saying you need springs at 40psi to you do not need them at all.



My question is, what PSI will the stock spring on an 04.5 truck lift?

I am looking to hear from individuals with real data. Not someone who melted a truck down cause they have 200hp sticks on a stock truck and kept there foot in it for 20mins straight.

Thanks for the help guys!
 
Last edited:
Surface area of the valve x seat pressure is a starting point for the window of possibilities. Remember, RPM and the effects of valve-train inertia play a role as well. Its not necessarily what pressure will it take to lift the spring at rest, but what pressure will delay its closing.

I didn't want to worry about it, so I swapped mine out. Sorry, I have no practical experience playing matchmaker of pistons and valves.
 
Amish Elegance said:
Surface area of the valve x seat pressure is a starting point for the window of possibilities. Remember, RPM and the effects of valve-train inertia play a role as well. Its not necessarily what pressure will it take to lift the spring at rest, but what pressure will delay its closing.

I didn't want to worry about it, so I swapped mine out. Sorry, I have no practical experience playing matchmaker of pistons and valves.
Click to expand...


All good info....i have a set of hamilton 110# springs sitting at the house but only a couple days between getting back from afghanistan and taking a trip to FL. looks like i will take the time to put them in. :thankyou2:
 
I blocked off an exhaust port with a drilled plate and pumped up the port to see when the spring would lift and right at 60psi the exhaust valve started opening and leaking by... And that does not take into account any valvetrain weight or rpm's... so I would say a running engine at 3000rpms or so would would start leaking by the valves way before 60psi...
 
This is a subject a lot of people disagree on. I have pressured up different combinations to see what happened on the bench and found it to leak at mid to upper 50's so you are almost dead on to what I found.

There are thoughts defending heavier springs and lighter. I choose to have pretty high seat pressure on our combinations. In the past cylinder heads did not flow that well so people had to jack up boost to get the air into the cylinder. THis created more than a few issues. One thing that a lot of people fail to take into account is if you have a single charger at 60 psi, your drive pressure is going to be 80psi plus. On the intake stroke as the intake valve is open, with 80psi drive pressure and stock springs, you will be filling the cylinder with exhaust because you blew the exhaust open with drive pressure.

Jeff Garmon put some of our #175 12v springs in a few months ago and found 10hp over the 60# (really 145#)springs he was previously running. According to some he should have lost power from the heavier pressures.
 
All great info guys....i get home on the 3rd and drive to FL on the 6th. So i have the 4th and 5th to put on springs, re-torque studs, rebuild kit for stock turbo, new pump, GM Govenor solenoid.

Plus....different forward controls on the bike, bars, grips, risers, wrap the stock pipes...

Few busy days but i am sure i will be happy with the hamilton's. Heard nothing but good from them and i dont expect to experience any difference.

So you can do any two cylcinders that add up to 7 right? Like 1 and 6..2 and 5 at the same time?
 
You must log in or register to reply here.
Back
Top