[badcobra]

If I wanted to run +1mm valves, do I need larger seats? Does it make sense to go +2mm if I need the larger seats anyway? Does the shrouding in the chamber need to be layed back some if the valves are that much larger? These heads are being ported and going on a .020" overbore. Thanks for the info.

 

[roadwarriorsvt]

My heads are +1mm both int. & exh. I was told 4.6s can go +1mm, 5.4s can go +2mm.

 

[blacksnake305]

My heads are +1mm both int. & exh. I was told 4.6s can go +1mm, 5.4s can go +2mm.

I'm not calling you out (just applying logic), but I can't see why a 5.4 could run any larger valves than a 4.6. The bore is the same and hence logic dictates that the surface area available is the same. Dont forget that the valve shrouding issue is the same problem in both as well...

 

[XR8TED]

I think 2mm is the largest you can go.... I would recomennd seat for anything bigger then stock....

 

[badcobra]

So we have two differing opinions here. If I need to do seats, I would just do the +2mm size since I am trying to flow enough air to make well over 1000 HP. If I could do the +1mm without seats I would prefer to just do that.

 

[roadwarriorsvt]

I'm just repeating what the shop told me. After looking at my valves/chamber, +2mm would really be squeezing it. I'm just guessing that the 5.4 combustion chamber must be larger?? If +2mm can be done on a 4.6, larger seats are a must, if it can be done.

Blacksnake brings up a good area of concern, valve shrouds. I've heard several times that unshrounding the valves will greatly increase the flow, so don't overlook this option.

 

[E. Green Cobra]

While some shops do put plus size valves in the stock seat, Al Papitto says no way. Plus sizes valves require new seats. I asked about a 37/31 arrangement, and was told a 37/32 setup would be better, but not for a mild n/a setup. Its on the corral I believe...

 

[4vMn12]

I think a big bore is a better option, but both would be the best, helping to unshroude the valves, and ehance flow with the larger bore.

 

[MP-John]

Oversize

We install the +.025" without changing seats. That is the limit (safe) Anything over that wil required new seats. PERIOD.

We have run 37/32 with great success.

 

[yellow46gt]

thats not even a millimeter, what is the advantage of puting a 0.635mm larger valve in as opposed to just stepping up to a +1mm. Please help me understand. Not trying to thread jack, just trying to understand.

 

[ATOMonkey]

IMO, new seats are cheap insurance. You're going to have to cut the head anyway. Might as well put in seats while you're there. If you're shooting for 1,000 HP is this going to be turbo or super chargerd? You're going to probably want a hardened exhaust seat either way.

 

[badcobra]

thats not even a millimeter, what is the advantage of puting a 0.635mm larger valve in as opposed to just stepping up to a +1mm. Please help me understand. Not trying to thread jack, just trying to understand.

I agree. A +1mm valve is .039" larger. Who makes an oversize valve less than 1mm, and why would anyone even bother? Thanks

 

[ATOMonkey]

Well, youngsters... Back in the day before the metric system infiltrated it's way into our lives, pretty much all automotive specs were in .025, .030, .060 increments. Older manufactureres still make oversized valves this way.

Sometimes you could also grind down an .025 valve to meeting the BP max limit for valve OD for all those racing is Sportsman Stock classes.

 

[badcobra]

That would be awesome if we weren't dealing with Modulars. I am 34 and still prefer standard measurement myself, but we go by what is presented to us. Everything is metric on these cars nowadays!!!!

 

[ATOMonkey]

I prefer that to the 80s and 90s when only half the car was metric. What a pain that was!!!

 

[badcobra]

You got that right...

 

[RED 97 COBRA]

1 mm larger valve can be run on the stock seats, depending on engine usage and valve job dimensions. That is the maximum allowable size. More that this will place the valve seat into the aluminum of the head. My suggestion is that you consider if your airflow demand to reach the desired power level requires a larger valve. Just putting a larger valve in without the proper port work to the intake runner and valve bowl will reduce airflow. The air will now have a larger obstruction (the valve head) it must get around to enter the combustion chamber.Unshrouding the valve will benafit any cylinder head. Even more so if bigger valves are fitted as this places the edge of the valve closer to the quench area or squish pads of the cylinder head due to it's physicaly large size now.
As far as 4.6 and 5.4 engines go the cylinder bore dimensions are the same as is the cylinder head and valve design. Now i'm not talking about the specifics of combustion camber volumes, compression, intake volumes. So what applies to a 4.6 for valve size requirements, also appiles to a 5.4.
1000hp can be obtained using stock dimension valves diameters depending on engine configuration. So airflow requirement will determine if largers valves are needed, and only if the cylinder head will flow the extra air volume to support this, not how much power.
As far as being cheap insureance as stated above, it is not cheap. you need to determine if you indeed realy need this level of modification. The old seats must be removed by a machine shop, then the seat register enlarged. The seat material you are after is berllynium along with bronze manganese valve guides. Most machine shops do not have the proper cutters and reems to handle these materials. It generly requires a diamond hone. One the parts cost $4.00 per guide x 32. $6.00 per seat x 32=$320.00 in parts. When I had mine done, machine shop rate was $10.00 per guide and I don't remeber cost to do the seats, but the valve job cost more due to the harder seat material. Start adding this up and you can see that to this modification properly is getting very costly.
I am not tring to discourage you from anything just inform. Changing parts just because can some times be detrimental to the ultimate goal.

 

[badcobra]

Well the real reason I was looking at larger valves was because I had damage to the valves in 2 cylinders and needed to replace them. Plus I wanted to run stainless steel valves. So I have purchased the +1mm size valves. My bud porting my heads is accomodating for this with the chamber work he is doing.

 

[ATOMonkey]

Why not use Ni-Al-bronze seats or even ductile iron seats? The beryllium seats are for top dollar race only applications generally used with titanium valves so as not to gall the face. An A286 seat would probably even be ok. Ductile iron has been used forever in aluminum heads and stainless valves.

 

[RED 97 COBRA]

The Ni-Al bronze seats are also a very good choice, as most of the cost is in the machine work. Ductile iron seats would be a waste of money. All of the time and effort in changing out the seats will only gain you the ability to run the larger valve. You would be gaining nothing in durability. If you are at a point where you truely need valves large enough to move the air volume of 2mm larger valves, then you already have a race engine.