sabastian458

iTrader: (25)

I am looking into getting a spare head build for my Evo 8 but I can not find specific enough answers to my questions. (I have been searching for about 2 hours and 77 pages of results)

What I am wanting to know is this;
1a) What is the benifits in increasing the valve sizes? (I see standard, +.5, +1, & +2mm size valves)
1b) What is the effect on turbo spool and engine torque?

2a) What is the advantages in going to Iconel exhaust valves verses Nitrided valves?
2b) What is the advantages in Nitrided intake valves verses Stainless valves?

3) I have read in a thread that the valve guides need replaced when going to oversized valves. Why is that?

4a) Are the solid lifters required if dual valve springs are utilized, or are the factory lifters sufficent? (daily driver useage)
4b) Does the valve spring seat need to be replaced with dual valve springs?

5) How much lift is available to be utilized on and engine setup that has had .015 milled off the block and head, using a factory head gasket? (totaling to .030 milled off. I know there isnt any valve clearance issues using BC280's with BC springs but I want to know if I can use a cam with more lift)

I know that is alot of questions, but hopefully a few of the big guys could help out with answering them. Thanks to anyone who help!

sabastian458

iTrader: (25)

so far I have recieved 1 PM saying that a high HP (900+) Evo ran stock lifters for 1/2 season.

Any other information guys?

Ted B

iTrader: (6)

Increasing the valve size may or may not be of benefit, depending upon the port itself and the realistic power target of the application.

The effect on spool and low speed response is entirely dependent upon how much flow velocity is lost as a result of the port job.

If you're not involved in endurance racing or other extended high heat, high rpm stress, exotic valve alloys are of limited benefit to you.

There are better valve guides than the factory ones, which is why they are typically replaced in better prepped heads (except Cosworth).

Solid lifters are neither required nor desired.

Dual valve springs are advantageous in some cases, again, depending upon the hardware and application.

Milling the head and block solves nothing and potentially creates problems. Avoid this wherever possible.

Precision

iTrader: (1)

However, if the head or block needs to be milled you should have it done. For a good head gasket seal a virgin mating surface is best. Besides a head that has been hot enough to warp over .015" is probably needing to be replaced. When a head gets that hot it changes the angle of the seats to the guides a decent amount. But I digress, you can always get a thicker head gasket. to make up the difference.

sabastian458

iTrader: (25)

my head and block are already milled. i am running a 2.3l & 3076, possibly going to a hta35r. im wanting to be in a 450ish pump gas area. i already have a ported intake mani & 65mm throttle body and looking into increasing the air flow thru the head.

so far im gathering that i dont need the iconel valves? ( when my head was built last i had replaced the sodium exhaust valves with i think stainless valves. i will check tomorrow)

Ted B

iTrader: (6)

Why are the head and block milled?

Another potential issue with milling (aside from possible valve clearance and quench issues) that affects some engines is that it shortens the distance between crank timing gear and the cam gears, which can cause a cam/crank timing issue, depending on how the tensioner reacts. One would be wise to check all timing marks with the crank squarely at TDC.

icantdrive75

iTrader: (8)

You really can't go wrong with more lift. But as far as how much you can run, it depends less on your lift and more on your cam timing. You could theoretically run an inch of lift(I'm still waiting to see a prostock evo), assuming you open the intake valve incredibly late. So I don't think there's an issue with your P to V, as long as you degree the cam properly and don't just line up the dots. Adjustable cam gears would be a given. If there is indeed an issue with your P to V(I think somewhere around 10* ATDC is the most likely point for P to V issues on the intake side, so check there), you will have to open your intake valve later, and possibly run into some problems bleeding off compression.

Quick question, what cam are you considering with more lift? I think I remember seeing one in the cam sticky, but for the most part all I saw stayed pretty much with a standard.

sabastian458

iTrader: (25)

head was milled due to prior owner being a complete idiot. kept driving on a blown head gasket. it kinda melted the head between cylinders 3&4.

block was decked 1 year later during my stroker build for a freash surface and to bump the compression up a tad ( used 8.5:1 pistons )

icantdrive75

iTrader: (8)

Have you ever checked the quench on one of these motors? I'm interested to know if someone has taken the time to measure it.

sabastian458

iTrader: (25)

i am currently running brian crower 280's with brian crower single springs.

i am looking into running either s2's possible s3's or brian crower stage 3 288's

Ted B

iTrader: (6)

I haven't, but I'm going to change that to settle my curiosity as well when I make some changes in the very near future. I made a point to see that the pistons I use presently are designed with this in mind.

icantdrive75

iTrader: (8)

Quench is an often over looked problem in these motors, not to mention the fact that there's really not much area for it in the chamber. The rule of thumb I've heard from my teacher is .045-.050 quench on a steel rod, but no where between .060 and .070. Accepted theory, is that having tight quench, along with the usual benefits, will not leave enough gas in the space to allow cooling. Anything over .070 will allow such a quantity of gas that it will not allow cooling. But between .060 and .070 it will cool and be detrimental to flame propagation. So say you take a motor and throw a thicker gasket on it to reduce compression. In the process you put your quench in this "no-man's land" and actually detonate sooner than you would with higher compression and good quench.

SOEuro

iTrader: (29)

why PMs...i need to read this stuff as well

POST IT,good info so far

Ted B

iTrader: (6)

Which is exactly why I cringe when thicker head gaskets are suggested as a 'fix' for what is actually a larger problem.

sabastian458

iTrader: (25)

i did post what was in the pm.



i am going to have my spare head built and the combustion chamber is going to be reworked ( had small chips in it when a ring land broke) so therorically that should help compensate and make the quench area larger ( closer to where it was before the mill work was done)