Port Injection & Coated Intake Valves

[NewbVetteGuy]

A fairly random and specific question:

My understanding is that with most/ all? port injection systems fuel is actually sprayed on the back of a closed intake valve and the fuel spray hitting the back of a hot valve causes the fuel to finely atomize and that this is an important process with port fuel injection. -Now I'm wondering whether coating intake valves would significantly drop back-of-the-valve temps and inhibit this process and cause issues...


So: When coating chambers and valves for a port-injection system, is it better to leave the intake valves uncoated or is there no meaningful impact either way?


Thanks!
Adam

[MadBill]

If tuned correctly, hotter un-coated valves could potentially provide slightly better fuel economy and emissions but from a power standpoint, intake valves transfer substantial heat to the mixture, reducing charge density. David Vizard reports looking down the dead-straight intake runners of a high power Midget 4 cyl in a darkened dyno cell and seeing the valves glowing dark red. Coating them top and bottom gained a little over 1% power.

[Smoke ring]

Another question would be if everything in the combustion area is coated except the intake valve, how much extra heat will it absorb? Will the intake valve be subjected to absorbing extra flash heat temperature because everything else is protected?

[user-612937456]

I'm under the impression that you are looking for a target chamber temprature. This can be manipulated from various infleunces (including using your intake valve as a heat sinc) with a certian molicule size for the fuel as a specific end product just before ignition. Application specific of course.

If you can achieve this already and you add more heat potential you could be shooting yourself in the foot if your end chamber temprature goes 50 degree's beyond detonation. Or your fuel atomization is so fine it slows flame travel or it ignites before the spark.

I post this with expectations of clarification of what may be some misconceptions of mine. Please try to make since of my thoughts

[modok]

Reducing or increasing the intake valve temp may have some influence on knock limit as well.
I don't know the answer but I have wondered about it.
Darn good question.

[user-23911]

It's going to do nothing because the original statement was wrong.


Yes an injector will spray onto the back of a closed intake valve.
If you've got a hot cam you've got ?? deg duration?
I've got (a bit over 300) 250deg (to be easy) out of 720 total deg.
30 ish %
So if you're at an IDC of about 30% you might be spraying on the back of the valve all the time.
If your IDC gets out to 99%, it won't be.

As for coating the valve?
Isn't it just the face.
You're not going to coat the part that seals to the seat. Nor the back. But the valve will be a bit cooler. Maybe?
No different effect from coating a valve on a carby engine.

[digger]

ive heard some say that they like to inject when inlet port speed is highest not at a closed valve but probably depends on the load and rpm of the engine and the engine itself and what its used for and where the injector is located. these days you can do whatever you want.

personally i think even with a coated valve its still going to be very hot and hot enough to vaporize fuel these coating are not miracle treatments

[modok]

Timing to fire when the valve is closed was common in OLDER systems, but it was not so much an ideal as it was a lesser of evils. They did not have enough drivers and/or sensors to fire each injector at the ideal time.

[stealth]

Keep in mind ..... OEM's do this for one reason....FUEL MILEAGE! ..(which is their MOST important priority)

Not the best place to spray fuel from a HP stance...

[user-23911]

So the pretty red things?
They've got a coating on them.
Valves get hot, they need to have a conduction path to cool them which is usually the seat and the stem.
The seat is insulated so it's going to run hotter and be a potential source of pre ignition?
Nor will it seal properly so it'll end up burning out.


But they DO look pretty?
Can you do mine too?

[digger]

The seat isn't insulated it's bare metal, just not the clearest pic