Fuel economy vs gas prices

[Series8217]

I've only ever seen what Nashco describes... they just coat the part thats exposed in the combustion chamber. Imagine taking a spray can to the combustion chamber with closed valves. That's it. I guess you could technically do that.. keep the valves closed, then apply the coating to the whole chamber including the valves.. turn the valves slowly as its curing so the coating doesn't form a bond between the valve and chamber..
Someone on here or Old Europe was offering ceramic coating services. I think it was indy or bryson.. can't remember.. I think I saw some pistons they did.

[Nashco]

so you think they can't insulate? how far can a foam coffee cup spread the heat? yes, it gets warm, but it never gets to 212 degrees F, no matter how hot the coffee. Ceramics insulate. Sorry, your theory isn't perfect, nor complete, nor accurate.

BTW, the cup will most definitely get to 212 degrees if everything around it is 212 degrees for long enough. Similarly, a valve will get to the same temp whether it's coated or not...it just takes longer. Actually, if there was enough cooling at the stem/seat, it would stabilize at a slightly lower temp, but I'd guess that it would be a negligible difference. In reality, though, we don't develop maximum heat forever, we only do it in short bursts. Unless you're running 12:1 compression with 2.88:1 rear gears on a boat with an overdrive trans, regular gas, and SBC chambers. Nobody is that crazy though, right Will?

Like I said, I'd like to learn more about it if anybody knows of some reliable info out there.

Bryce

[Atilla the Fun]

NOONE coats the stems. The only part of the stem it is possible to coat is the part that gets undercut for flow on good valves. I'm not sure I'd coat that, as that part of the valve cannot cause preignition. Just more weight and less flow. The sharp edge being in the chamber, yes.

[Nashco]

NOONE coats the stems. The only part of the stem it is possible to coat is the part that gets undercut for flow on good valves. I'm not sure I'd coat that, as that part of the valve cannot cause preignition. Just more weight and less flow. The sharp edge being in the chamber, yes.

Sure they do, I just saw it earlier when I was researching it. Some people even coated valve springs. Most were just coating the faces though.

Bryce

[Series8217]

Coated valve springs? That's something entirely different..

[teamlseep13]

I have seen ceramic coated valve faces, the backsides of the valves but as far as the stem that actually contacts the guide, the only coating i have seen is an anti friction coating for obvious reasons.

The only real reason to coat the backside of the valve is to keep heat in the exhaust gases for optimal velocity. If you are doing that they you are coating the exhaust ports as well.

Most competitive turbocharged motors have the entire exhaust tract coated, made of a poor heat conductive material such as 321 SS or are wrapped with a thermal barrier.
A few experimenters in the 80's Group B rally cars tried to coat the inside of their exhaust manifolds and turbine housings but no coating could stand up to the heat without flaking.

As far as valve springs, most companies coat with a thermal dispersant which basically improves the heat transfer of the valve spring to keep them running at a cool temperature and therefore increasing fatigue life. I have seen claims of up to 200% longer life before the springs go "soft:.

I would just coat the combustion chamber surfaces, ie. valve faces, piston crown and cylinder head combustion chamber. Obviously indexing the plug is a must along with a a complete debur of the exposed threads and electrode.

[The Dark Side of Will]

The only real reason to coat the backside of the valve is to keep heat in the exhaust gases for optimal velocity.

I disagree.

To a first order approximation, the exhaust valve should get no hotter than the intake valve. This is obviously not the case, so there's more to it than the first order approximation.

The first order approximation: The heat flux into the FACE of each valve through the entire cycle of the engine is the SAME. The faces are exposed to the same temps for the same duration for both valves.

Second order approximation: Given that the heat flux into the face of each valve is the same for each valve, the difference in valve temps is accounted for by the fact that the intake charge COOLS the BACK and STEM of the intake valve and the exhaust charge HEATS the BACK and STEM of the exhaust valve.

Third order approximation: When the valves are closed, they shed heat to the cylinder heads through the valve seats. The heads are somewhat cooler on the intake side than the exhaust side, so intake valves shed heat more easily than exhaust valves.

Because of the second order effect above, I think that the back and stem of the exhaust valve should be the FIRST things coated because the heat flux into the BACK of the valve is the DIFFERENCE in heat flux between the intake valve and the exhaust valve. The coating will reduce (but will NOT eliminate) that flux. Conversely, for keeping valve temps down, the back of the intake valve should NEVER be coated.

As I said before, once the back of the valve is coated, the seat needs to be ground so as to facilitate heat shedding to the cylinder head.

[teamlseep13]

I agree that when you coat the backside of the valve, obviously the seating area needs to be coating free to allow heat transfer into the valve seat.

What I was getting at was that when you coat the backside of the valve, you will reduce the flux of heat through the valve by keeping the heat in the exhaust stream, which keeps the valve temp down and exhaust gas temperatures up.

[The Dark Side of Will]

Yeah, you were going at it from the point of view of keeping the charge hot, and I was thinking of keeping the valve cool... Potayto(e) vs Potahto(e).

But now I am intrigued by the idea of having some coating work done to the cylinder heads. I hadn't included that in the initial budget, but there may be some slop depending on what I find out about conversion lifters.

If the conversion roller lifters really are $500 for the set, then it wouldn't be that much more to throw down for a set of Roller-X lifters ($700, IIRC).
But if the conversion lifters can be had for $200 like the article says, then that frees $300 for other things.

[The Dark Side of Will]

I'll probably just build the engine with coated pistons and see how it does without any coatings on the heads. It's a PITA, but I can always pull the heads and have them worked with the engine in the car.

One thing about coatings and compression... The coatings reduce the amount of heat flowing through them. This means that less heat goes from the charge into the engine. This means that MORE heat stays in the charge. I would think that at a given compression ratio, coating EVERYTHING in the chamber would make the engine MORE prone to detonation, since the coatings are keeping that much more energy in the chamber. It's the same effect as aluminum heads vs. iron... at a given compression ratio, an iron head engine is more suceptible to detonation than an aluminum head engine because the iron conducts less heat from the chamber than aluminum and results in a higher chamber energy density.

Does anyone have any experience (full chamber coatings vs. detonation) that would indicate I am wrong?

The HRM 347 used 1.6 rockers. These shouldn't have any affect on DCR because DCR is determined by the .005 lift point, which shouldnt change enough to worry about with changing rocker ratio.

[AntiCooter]

Will, FWIW I used the coatings, but on a smaller scale. I coated the piston crown, combustion chamber and valves on a kart race engine. It ran strong for about 8 laps of the 10 lap race and then started knocking and quit. The noise turned out to be pre-ignition and it hit so hard that the steel flywheel key broke. When I tore the engine down, everything looked nice and clean, but the spark plug had got so hot that the ground and center electrode was blue. I swapped to an uncoated head and did not have any more problems.
If I had been running alcohol, it might have been okay but at the time we were running the pump gas class and the temps must have been pretty high for an 8 to 1 compression engine running premium fuel to go into uncontrolled ignition mode.

[Kohburn]

Will, FWIW I used the coatings, but on a smaller scale. I coated the piston crown, combustion chamber and valves on a kart race engine. It ran strong for about 8 laps of the 10 lap race and then started knocking and quit. The noise turned out to be pre-ignition and it hit so hard that the steel flywheel key broke. When I tore the engine down, everything looked nice and clean, but the spark plug had got so hot that the ground and center electrode was blue. I swapped to an uncoated head and did not have any more problems.
If I had been running alcohol, it might have been okay but at the time we were running the pump gas class and the temps must have been pretty high for an 8 to 1 compression engine running premium fuel to go into uncontrolled ignition mode.

sounds like the coatings did the job of trapping the heat in the cumbustion chamber. but the added heat built up in the spark plug and it couldn't take it acting like a glow plug instead. needed a different heat range on the plug and you probably would have been fine.

[The Dark Side of Will]

Will, FWIW I used the coatings, but on a smaller scale. I coated the piston crown, combustion chamber and valves on a kart race engine. It ran strong for about 8 laps of the 10 lap race and then started knocking and quit. The noise turned out to be pre-ignition and it hit so hard that the steel flywheel key broke. When I tore the engine down, everything looked nice and clean, but the spark plug had got so hot that the ground and center electrode was blue. I swapped to an uncoated head and did not have any more problems.
If I had been running alcohol, it might have been okay but at the time we were running the pump gas class and the temps must have been pretty high for an 8 to 1 compression engine running premium fuel to go into uncontrolled ignition mode.

I'll agree with Kohburn on the plug getting too hot. What heat range were you using? Could you have gone colder?

It didn't hole the piston?

What was the duration (time) of the race? I imagine the cart was at or close to WOT for most of the race.
Auto OEM's have routines in production ECM's which richen the mixture significantly after a certain time (usually in the 20 second range) at WOT in order to keep things like that from happening. I don't expect that the engine I want to build will be used that way, but I don't want it to be fragile either...

Someone remind me of the rule of thumb for advancing or retarding the cam in a pushrod engine. Does advancing give you better low end and retarding better high end?
With variable cam phasing, the DCR can be varied. I'm not sure what the optimization parameters are on, say a 3500 VVT, but it occurs to me that if you're not worried about power and only go by BSFC, you could probably come up with some interesting results by playing with the VVT.

[Kohburn]

[Someone remind me of the rule of thumb for advancing or retarding the cam in a pushrod engine. Does advancing give you better low end and retarding better high end?

other way - advancing at high rpm gets a more complete combustion due to the slight delay in time it takes for the stark to form and ignite the mix. at low rpm it can cause premature ignition.

[The Dark Side of Will]

Not following your description.

[Kohburn]

at time it takes the spark plug to generate the spark and trigger combustion translates to a greater rotation of the crank at higher rpm. so advancing the timing so that is starts earlier at higher rpm can allow ignition to happen at the same point in the stroke as a retarded timing at lower rpm.

so retarded timing at low rpm provides a smooth idle and good torque without pinging

advanced timing at high rpm improves combustion and produces more power.

atleast thats how i always understood it - but I just looked at MSD's site and they seem to have timing control devices that retard for low rpm then advance it to a point then pull timing back for high rpm. no sure what thats about

[Aaron]

atleast thats how i always understood it - but I just looked at MSD's site and they seem to have timing control devices that retard for low rpm then advance it to a point then pull timing back for high rpm. no sure what thats about

MSD primarily caters to the SBC crowd, who are traditionally plagued with poor ignition characteristics because of the cylinder heads. While once the SBCs get built to the point where their VE is high, or if they are using forced induction, they may pull timing at high RPM to fend off detonation, since high RPM is where there will be the most air and fuel in the cylinder. This isn't much of a concern for us, since our heads and stock ignitions provide us with excellent burn qualities.

For example, the MSD ignition on our blown 406 pulls 1.5* for every pound of boost, and this is where the engine likes it. On my 3.4 DOHC, I'm not pulling any timing throughout the boost curve.

[The Dark Side of Will]

I was talking about CAM timing.

My idea for using VVT was to set the engine up with too high a SCR to run at WOT on pump gas, but play with the variable cam phasing to tailor the DCR.

The VVT would advance the cam at part throttle to increase DCR and cruise efficiency, then retard the cam at WOT to reduce DCR and stave off detonation.

Not caring too much that this would probably cost a few ponies due to cam phasing not optimized for power. I'd be looking for gas mileage with such a schema.

[Kohburn]

lol - woops

i thought low end high end was more of cam overlap than both advancing or retarding.

[AntiCooter]

Good point about the heat range of the plug. Its been a while, but I remember it being a non-resister race plug. So, it was probably a 'cold' plug already. As far as the mixture, it would be lean- you start off with a fat mixture to get the kart rolling and once up to speed, lean it up for more power. I am sure things got pretty toasty in the couple of minutes that it was at WOT.