MadMike 97 Z28

iTrader: (3)

so i got a call from the shop that is reconditioning my heads and he said im going to have high seat pressures with my setup and wanted to know if i still wanted to run stock valves is there any reason i should be concerned about stock valves if my setup is as follows

-GM847
-1.52 rockers
-918 springs
-and +.50 locks

any help is appreciated

BattleShip

I would trust the machinist who is setting up the heads. He is sounds worried that the seat pressure is above what he feels is 'comfortable' for the stock valve to handle. I would listen, but verify...

To know what the seat pressure is determine your spring's installed height, and calculate the seat pressure. This should be close to what is needed for your cam, be less than recommended for a stock valve, have sufficient margin to avoid coil bind at full lift, etc...

Good luck

Formula350

iTrader: (3)

Well, if you're running a fairly big cam (I assume "little" in your sig is sarcasm heh) then I don't see any downside to running bigger valves, more-so if the seat pressure IS high. Better safe than sorry, no?

BattleShip

It sounds like the machinist is concerned about running his pressures on a stock valve because stock can not take high seat pressure. For larger cams often you need to change to a 'one' piece valve. The one piece may or may not be the stock 1.94"/1.5"

Formula350

iTrader: (3)

I know Hence the "better safe than sorry" and "get bigger valves" portion of my post lol 2.00/1.58 fit nice in our heads.

Formula350

iTrader: (3)

My understanding, is it goes on the OUTSIDE of the valve where it (heh) meets the seat, and could collapse it. Otherwise it would be called High Stem/Shaft Pressure, no?

MadMike 97 Z28

iTrader: (3)

ya the cam is a 847 not small by any means.

so you guys think i should go with one piece valves what size valves should i get and how much will it run me for them to put the larger valves in?

Formula350

iTrader: (3)

No idea on cost, but like I mention, 2.00/1.58 fit in very well and don't require heavy work. I believe they come from LS2s or something.

EDIT: here's some 1.58s but no listing for which motor -_- http://store.summitracing.com/partde...5&autoview=sku

I'll leave them there, but screw them. Here's Manley's stainless ones for SBC
2.00 (8)
http://store.summitracing.com/partde...5&autoview=sku
1.575 (8)
http://store.summitracing.com/partde...5&autoview=sku

BattleShip

Check what machinist says your seat pressure is, stock valve stems can't take alot. The seats can take a ton if not you would need different seats when using a large cam. Most large rollers need HI seat pressure.

It is the valve stem he is concerned about. Larger valves need to have head work done but if you are using large cam large valves might be worth it along with related porting.

BUT iron heads will cost ALOT less to go to 2.02/1.6 than aluminum will. Ask machinist to price options

Good luck

BattleShip

What are specs on that cam? You want to match the heads to cam port etc
One piece valves in stock 1.94/1.5 are cheap insurance especially since he says he has a concern

Formula350

iTrader: (3)

Going to re-tract my current assumption on seat pressure. I was thinking that it was the valve seat in the combustion chamber (like when you get a sunk valve). Unless that is it, and now I'm thinking of the spring seat :\

Battle, want to clear this up for me? heh As I said in the other thread, it's always fun the learn and get correct info.

BattleShip

Well the pressure IS proptional to area of valve like you said. Larger will 'distribute' the presure in a larger valve seat area.

BUT all the pressure will be 'carried' in the valve stem. Stock are 'two piece'. They are fine to there design limit...

That I think was machinist 'concern'. I have been shown them 'broken' in two by macinist friend.

96capricemgr

iTrader: (1)

Not like everyone and their brother has already run those springs on stock valves.
Oh wait yes it is exactly like everyone and their brother has already run this combination.

How many problems are you guys aware of from too much spring on stock valves???

Sounds like your machinist is a couple decades behind the times, good luck.
Just because someone gets paid to do something does not mean they have a clue what they are talking about.

Only tuliped LT1 valve I know of was caused by a lean nitrous shot on a friend's car.

BattleShip

The stock valve is two piece and weak. Increase spring pressure and rev motor and yes the valve can become two pieces. BUT I used stock valves on a 224/232 .540/.550 and revved to 6800 with no problem..it is all how lucky you feel.

His machinist is not making money putting in a one piece valve he believes it is money wisely invested. How much does that insurance cost with heads on bench? The valves are ~$80 at competition products.


Also remember you get what you paid for, and you are getting free advice.
You won't ever worry about dropping a one piece valve, and saving the $80 might cost you >$2,000

So you decide.

Good luck

96capricemgr

iTrader: (1)

I am basing my comments on the 8 years of experiance and observation I have with this application. The stock valves are not a weak point though yes a quality aftermarket one is stronger.

Yes advise is free, posters would be well advised to spend some time here and see who knows what they are talking about and who is just talking before the start asking questions(not targetting you just a good general statement) because there are a lot more ignorant kids trying to answer questions than there are knowledgable guys.

This specific thing has been done, lots of guys running 918s on stock heads.

If anyone is aware of any problems with the stock valves please post links or share stories so we can try and see if there have been any spring pressure related issues, if it is a genuine concern I think it would be very good for us to discuss.

I just hate seeing guys spend money on "problems" that don't exist.

I also think it very possible that concerns about stock valves may have been well founded in the past but that does not mean it applies here.

BattleShip

I think we agree...I can't disagree with your assessment.

Only change is I tend to be cheap and never bought 918 I buy cheap $50 springs from Competition products and they are good for .570". And use their valves when I change them.

MadMike 97 Z28

iTrader: (3)

thanks for the info guys i know just like you guys have said that many people run the 918's on stock valves i just figured it was worth double checking my setup and asking if any of you knew of any problems. I know one piece valves would be insurance but im kinda on a tight budget now.