tim99ws6

iTrader: (31)

How much seat pressure do you guys run on your valvetrain open/closed in a hydraulic setup with cars making 800 or more? I'm beginning to question mine as the heads are at the machine shop right now. The car see's 20+ psi on a 408ci motor. Is there such a thing as too much seat pressure?

Morel lifters, titanium intake valves, sodium filled exhaust, stock Ls3 rockers.

slow67

iTrader: (2)

Too much seat pressure will bottom out the lifter, effectively making it a solid lifter. As too how much is too much, might want to ask your engine builder.

tim99ws6

iTrader: (31)

Lifters are Morel's, so they'll take the abuse better than a stock lifter anyways.



I was more asking what people are shimming up their springs to ensure the valvetrain stay's stable and also holds the valves closed under moderate boost.

chris@hps

Yes you can have to much seat pressure, especially on a hydralic roller setup.
On a hydralic roller around 170-175lbs on the seat. You can go a little higher but then risk the chance of bleeding out the lifters.

Chris

Phil99vette

iTrader: (11)

That that boost level factoring in backpressure, it is probably a good idea to go solid roller.

tim99ws6

iTrader: (31)

Not the first to recommend that and I'm probably going that route in the near future.

Sometimes I hate your recommendations, haha. They are usually $$$.

Phil99vette

iTrader: (11)

Can you get it done with a hyd setup, yeah probably but you will have limitations and will be on the ragged edge. A solid will probably help spoolup and make 50-100 more HP.

tim99ws6

iTrader: (31)

Thats honestly exactly where I am at right now: maximizing seat pressures without destroying my lifters.

Sarg

iTrader: (6)

I think it also depend on the cam more than anything. Boost by itself is not going to radically change the pressure you must run on your springs. I mean think of it...they are only having to withstand 20 psi trying to push them open....not a lot really.

Nitroused383

iTrader: (10)

20psi of intake pressure but probably double that on the exhaust valves. What style cam lobes are you running? HUC lobes are very smooth / stable for high rpm. I think most turbo setups float the exhaust valve while trying to stay seated. It's not 20 lbs of pressure either you have to multiply pressure x surface area. Here is a great post explaining the math https://ls1tech.com/forums/14657390-post4.html

tim99ws6

iTrader: (31)

Exactly, it's valve size, weight, lobes(to an extent) and pressure/back pressure.

My cam is a virginia speed vtc4

Sarg

iTrader: (6)

Ok so 50 lbs of pressure....still not a huge deal. Don't forget you will also have exhaust back pressure as well. I would think that asking the guys that made the cam would be the best idea I am sure they have an idea.

Phil99vette

iTrader: (11)

What is the surface area of a 1.60" valve x 50# of force per square inch?

Phil99vette

iTrader: (11)

Sorry got tired of waiting.... A 1.60" circle is 2.01, 2.01 x 50 = 100.5# of pressure. I understand that number is not going to be exact but by the time you subtract the stem area plus the backside of the valve is not flat, its close enough. So your reducing the pressure of the valve springs by 100#.

Sarg

iTrader: (6)

From the link, 15 psi on a 2.05" valve:

2.05" intake valve, then the radius = 1.025"

So the Area = 3.1415 X (1.025" X 1.025")

or

3.1415 X 1.05 = 3.3 (rounded up a tad)

So if you are running 15 psi of boost, then the extra force on the face of the intake valve is 3.3 X 15 = 49.5 pounds.


Now back to your example:

So if you take that on the exhaust valve: 1.60 radius is .80 so area is 3.1415x (.80x.80)= 2.01

2.01x15 psi= 30 ish lbs. So you are reducing your spring pressure by 30 lbs, not 100.

Let's go one step further and imagine that you are running a TINY turbo and backpressure is double boost (not unheard of) That would at more be 60#. A good bit more, but still not 100#.

Phil99vette

iTrader: (11)

From above...

Intake valves are not the problem
Backpressure is not 15# @ 15# of boost on most of these setups.
Its not turbo size that dictates backpressure, its turbine efficiency.

Sarg

iTrader: (6)

Just saying the math here was not exactly correct

Phil99vette

iTrader: (11)

Can you please tell me the correct answer for 2.01 area and 50# of backpressure? Funny, you calculate it the same way.....

Sarg

iTrader: (6)

No and I agree...but a lot of people run a turbo that I would consider to be a bit small and a turbine housing that is generally way too small for a good performance motor. I tend to size the turbine a bit bigger in hopes of getting close to a 1:1 backpressure or less. That is one reason why I am still considering running dual T4 turbos or a single T6.

Sarg

iTrader: (6)

That would be assuming 50# of boost on the intake valve? Seems a bit much for these engines! Maybe on a diesel motor! But that would be about 160# if you were to run 50 psi of boost!

Edit:
Ah, you are talking area, not the size of the valve. My bad. Are you really seeing 50# of back pressure in your turbo set up?!?