Will 3.5L valves, seats & guides fit in a 2.5L head?

[SicSE]

I'm thinking about going with bigger valves and just for sh*ts, checked out the specs on the 3.5L's. The valve heads are slightly larger than the 3L's, 37/31, as opposed to 35/30. However, the stems are 0.5mm smaller in diameter, and I can't find the length. Too skinny should be able to be remedied by appropriately-sized guides, valve retainers, etc... but there's no fix for too short. Anyone know the valve length, and/or if this could actually work?

I just checked 05-06 LS V8 specs, (trying to look at all 4-valve engines), and I'm expecting that 44mm intake valves would be overkill... if they would even fit! Plus, the stems are 1.0mm smaller in diameter, so that might present some problems.

4.6L 4-valve valves are 37/30, but again, not sure of length. Also, the stems are 1.0mm diameter thicker in diameter, so I would expect that to definitely present some problems.

Cost will not be an issue... but I'll be using Ford OEM parts, or not doing it.

Can anyone think of any other possible options for putting larger OE valves in OE 2.5L, or maybe 3L heads?

Please, no haters. :laugh:

Input appreciated.

 

[Rara]

Cost will not be an issue... but I'll be using Ford OEM parts, or not doing it.

Based on this qualification, you won't be doing it. The things you are considering to try to accomodate the different stem diameter, length, retainers and keys can open up several cans of worms and barrels of monkeys all at the same time.

If you really want larger valves, you will need to have custom valves made with the larger head size. You will also need the heads machined with larger seat insert pockets, and locate new seat insert blanks to use (this would probably be the easiest part, even though you need to pick the correct material). You will also need to increase the spring rates to accomodate the increased mass of the valves. Since you won't be able to run complex valve studies, its better to err on the conservative side with much stiffer. Unfortunately, no stiffer valves exist that the regular 3L springs, and no the ST220 springs are not actually stiffer, I've personall spoken with an engineer from the OEM spring supplier that told me the rates are the same for all the 3L spring part numbers. Basically this means you will need custom wound springs as well.

This all assumes there is enough room, center to center to actually fit both valves on the intake side. Don't forget to account for the seat inserts and the pockets to accomodate them.


I guess what I'm saying is that it could be done if you REALLY wanted to; but I don't think the benefit is there. When using the 3L valves, they have never been the limit for making more power NA or boosted with the D25/D30 engine family. Your $$ and effort is better spent elsewhere.

 

[SicSE]

I guess I got caught up in the numbers. The LS & 3.5L are a flat-tappet style, which I'm guessing is why the stems can be smaller. I doubt it would be a good idea to mix-n-match valves between the two types... even if they COULD be made to work... probably too short anyway. And extra weight as you mentioned, would be ugly with the 4-valve 4.6L valves... and I hadn't thought about the needed increased spring pressure. :blackeye:

Looks like I'm sticking with the 3L's if I do this. I'm definitely not getting into the custom stuff that I can't do myself.

Thanks Rara, you're the man.

 

[Rara]

Thanks Rara, you're the man.

Fortunately, this happens to be a specific area where I am particularly experienced and knowledgable. Glad I could help.