When do Valves and Pistons Burn? WOT or almost closed throttle???

svx_commuter · #1 06-01-2007, 04:44 AM

I am looking for a little help in this area.

I do know that valves and pistons can burn if an engine runs too lean. So I am wanting to know if this problem is more prononced at a particular engine load. I want to know if it is thottle setiing dependent. In other words I do not know if it is more common at wide open throttle WOT or a very slight throttle openings. You know, as when the car is being driven to get good gas mileage.

So yes I am thinking if it is possible to lean out an engine SOME at light throttle settings without causing any high temperature piston and valve damage.

Comments will be greatly appreciated.

Take care,
John

svxfiles · #2 06-01-2007, 06:23 AM

Are you doing this to get better gas mileage?
You would be safest if you get a wideband, ($350) to see for yourself what the A/F ratios are.
And then a Subaru Select moniter ($350) to keep track of timing.
If you lean it out, the ECU will pull timing, dropping power, requiring more throttle.

You might do better freeing up the exhaust flow and going with high pressure mileage tires.

cdvs · #3 06-01-2007, 06:30 AM

From what I've read here and on ECTune, the factory has these running much leaner than would historically be considered good.

Some other suggestions:

1. Make sure all of your stuff is working properly.

Most avoidable losses occur where the rubber meets the road:

2. Maintain tire pressure. Buy a good pressure gauge and use it at every fillup.

3. Get non-sport, low rolling resistance tires.

4. Get skinny tires. 205/55 work well on stock rims. They maintain accurate speedometer reading. Some traction is lost at the outside of the envelope, but they actually do better in snow.

5. Experiment with higher tire pressures, but make sure to maintain the same front/back radius on AWD. Judging from tire wear, factory recommendations are compromised for comfort, not performance. I'm thinking plus 10% will be fine.

Driving style can be costly or pay off:

6. Don't show anyone how fast your SVX is.

7. Avoid using the brakes as much as possible.

8. Careful use of the manual shift could improve results, or make them worse, depending on your skill.

That's all I can think of right now.

Charl

p.s. The SVX will learn to run on 87 octane, but I've not found any reliable cost/benefit data.

TomsSVX · #4 06-01-2007, 12:49 PM

they burn when the a/f ratio runs lean... Dangerously lean... Considering the higher the load the higher the heat, at WOT the engine will run considerably hotter than at lower load. SO if you could lean it out wot is not recomended... Actually, I wouldn't recomend it at all

Tom

svxfiles · #5 06-01-2007, 12:59 PM

You COULD buy LAN's chip, and hook up the Red wire, and run the cheaper 87 octane.

If you are looking to save money in the long run.

XT6Wagon · #6 06-01-2007, 01:26 PM

Its not so much "dangerously lean" as lean enough to spike egts, but rich enough to spike egt's.

you can more or less run many engines designed for turbochargers all day long at insane boost levels at 14.7:1 or leaner since they are moving alot of air, and not alot of fuel. AKA how diesels operate with cheap valves, cheap turbos, etc. Alot of air, not alot of fuel for low EGT's.

Now the problem is that what happens if you want 11.5 and don't get it, but it doesn't go all the way to 14.7:1 or leaner. NOW you are screwed. 12.5-13.5 is just perfect for cooking stuff off. Even worse when EGT's get high, turbos will start to lose boost control. I've seen someone with a turbo kit wire open the wastegate and wonder why it was making 22psi. His EGT's were so high that it was operating as a jet engine with the STi engine as the start of the fuel burn. Putting timing back in and adding a bit of fuel made it settle right down.

jeffast · #7 06-01-2007, 05:03 PM

Quote:

Originally Posted by XT6Wagon

Its not so much "dangerously lean" as lean enough to spike egts, but rich enough to spike egt's.

you can more or less run many engines designed for turbochargers all day long at insane boost levels at 14.7:1 or leaner since they are moving alot of air, and not alot of fuel. AKA how diesels operate with cheap valves, cheap turbos, etc. Alot of air, not alot of fuel for low EGT's.

Now the problem is that what happens if you want 11.5 and don't get it, but it doesn't go all the way to 14.7:1 or leaner. NOW you are screwed. 12.5-13.5 is just perfect for cooking stuff off. Even worse when EGT's get high, turbos will start to lose boost control. I've seen someone with a turbo kit wire open the wastegate and wonder why it was making 22psi. His EGT's were so high that it was operating as a jet engine with the STi engine as the start of the fuel burn. Putting timing back in and adding a bit of fuel made it settle right down.

you have it backwards

Crazy_pilot · #8 06-01-2007, 06:03 PM

Speaking sticktly from my flying experience:

Airplane engines are generally run between 14 and 15:1. Anything richer for a prolonged period of time tends to lead to fouled spark plug. But then, we do run leaded fuel. Piston planes actually have a mixture control in the cockpit, allowing manual control of the a/f mix. The basic way to tune the mix in is to run full rich and then lean till the engine starts getting cranky (ie; almost dies) at this point the mix is enriched a tad. The fancy way is if the plane has an EGT guage. Lean the mixture for max EGT's, and then back of a bit.

Plane engines aren't much like the EG33 though. The 6-cyl boxer engines I've used in planes run about 200-300 HP, with a displacement of 6-9L. They also have two spark plugs per cylinder and are carb fed, running on 100 octane leaded fuel.

This was my only experience with A/F mixture before signing on here, so seeing numbers like 11 or 12:1 had me scratching my head at first.

svx_commuter · #9 06-02-2007, 05:35 PM

Quote:

Originally Posted by svxfiles

Are you doing this to get better gas mileage?
You would be safest if you get a wideband, ($350) to see for yourself what the A/F ratios are.
And then a Subaru Select moniter ($350) to keep track of timing.
If you lean it out, the ECU will pull timing, dropping power, requiring more throttle.

You might do better freeing up the exhaust flow and going with high pressure mileage tires.

Yup I am looking for better gas mileage.
What is the wide band? A/F monitor?
Where can I get the Suby Select Monitor fro $350?
Well How do I get the ECU to leave the A/F alone?

I ahve been getting 27mpg average and I got the tires pumped up to 40/36.
I am not in the market for new exhaust yet. Thanks
I want to try and lean it out some if possible.
Can the select monitor be used to reprogram the ECU?

Thanks

svx_commuter · #10 06-02-2007, 05:44 PM

Quote:

Originally Posted by cdvs

From what I've read here and on ECTune, the factory has these running much leaner than would historically be considered good.

Some other suggestions:

1. Make sure all of your stuff is working properly. >> Everything is as good as it gets. All sensors working fine.

Most avoidable losses occur where the rubber meets the road:

2. Maintain tire pressure. Buy a good pressure gauge and use it at every fillup. >>> Yup I run higher pressure 40/36

3. Get non-sport, low rolling resistance tires. No Way!!! I got the FalKens, great in the rain and okay in the snow.

4. Get skinny tires. 205/55 work well on stock rims. They maintain accurate speedometer reading. Some traction is lost at the outside of the envelope, but they actually do better in snow. >>> not yet

5. Experiment with higher tire pressures, but make sure to maintain the same front/back radius on AWD. Judging from tire wear, factory recommendations are compromised for comfort, not performance. I'm thinking plus 10% will be fine. >>> I have done this I think it helps

Driving style can be costly or pay off:

6. Don't show anyone how fast your SVX is. >>>>>Ha Ha I think I get better MPG when I blow out the intake valves at least once a day

7. Avoid using the brakes as much as possible. >>>> Yup I just love to coast in teh SVX and keep my foot of the brake and gas. This works

8. Careful use of the manual shift could improve results, or make them worse, depending on your skill. >>>>>>I think that using 1, 2 or 3 and keeping the engine rev's around 2000 to 2400 may help UNLESSSS the SVX is over 45 mph and the TC locks up.

That's all I can think of right now.

Charl

>>>>> Thanks Charl

Also the route I drive is important. Going down hill is better than up hill when the engine is cold. Satying away from stop n go helps too.

p.s. The SVX will learn to run on 87 octane, but I've not found any reliable cost/benefit data.

Yeah I tried that too not cost advantage.

svx_commuter · #11 06-02-2007, 05:53 PM

Quote:

Originally Posted by TomsSVX

they burn when the a/f ratio runs lean... Dangerously lean... Considering the higher the load the higher the heat, at WOT the engine will run considerably hotter than at lower load. SO if you could lean it out wot is not recomended... Actually, I wouldn't recomend it at all

Tom

I am think lean at light throttle, low intake pressure, maybe a vacuum switch and then normal A/F at higher intake pressure. But I do not know how to get the ECU to let it go lean..........

{{{I also get it to stay in TC lock-up more when cruise control is not used.}}}

Okay Tom looked at this way.... recommend the lean burn and if I burn up a few valves you can help me replace them!!!!!!

My SVX is not like yours tom. It is not "show room" rare condition. Even if it was with 306k miles on it, my SVX would still not be worth much to anyone but me.

Take care,

John

PS the oil leaks are not so bad now. I think the new oil filter design from Suby had helped and lower viscocity oil.

svx_commuter · #12 06-02-2007, 05:55 PM

Quote:

Originally Posted by svxfiles

You COULD buy LAN's chip, and hook up the Red wire, and run the cheaper 87 octane.

If you are looking to save money in the long run.

Yes I did think about this and the pay back was a long time for me. Even with all the miles I drive.

Take care,

John

svx_commuter · #13 06-02-2007, 05:58 PM

Quote:

Originally Posted by XT6Wagon

Its not so much "dangerously lean" as lean enough to spike egts, but rich enough to spike egt's.

you can more or less run many engines designed for turbochargers all day long at insane boost levels at 14.7:1 or leaner since they are moving alot of air, and not alot of fuel. AKA how diesels operate with cheap valves, cheap turbos, etc. Alot of air, not alot of fuel for low EGT's.

Now the problem is that what happens if you want 11.5 and don't get it, but it doesn't go all the way to 14.7:1 or leaner. NOW you are screwed. 12.5-13.5 is just perfect for cooking stuff off. Even worse when EGT's get high, turbos will start to lose boost control. I've seen someone with a turbo kit wire open the wastegate and wonder why it was making 22psi. His EGT's were so high that it was operating as a jet engine with the STi engine as the start of the fuel burn. Putting timing back in and adding a bit of fuel made it settle right down.

Is there an exhaust gas temperature monitor?

I read somewhere that more accuarte temperature is right under the spark plug flange to the head. This head temperature is much more reliable indicator of combustion temperature.

Take care,

John

XT6Wagon · #14 06-02-2007, 08:36 PM

yes, there is many EGT sensors on the market. While many people put them close to the head, I have a small aversion to doing this given I started on ford SHO's back in the day that could suck cat "sand" up a foot or more vertical on a high rpm engine braking. So I don't like anything that fits in an exhaust port that close to said exhaust port. Second is the bad history of the OEM WRX egt sensors getting cooked, weak, and thus break off and blow the turbo. While the OEM sensor is far easier to break this way, I still like the EGT back off the heads some to reduce the EGT peak and for a smalller swing in EGT's between each exhaust pulse.

That said, read up on what the temp probe you have in your hand is rated for and base placement on that. Also decide if you want to place it far enough to see a whole bank, or just one cylinder.

And as far as the person who said I was wrong on EGT's... I've messed around with ALOT of wrx's and STi's including doing the tuning myself. Play with them a while and you can tell roughly the A/F ration by listening to it. 14.7:1 is fairly distinctive sound when on boost, its smooth and kinda highpitched. Hard to describe without hearing it. 12.5-14:1 or so usualy is distinctive with surging boost, detonation, random timing, etc. basicly its not so much as a sound as the ECU on the modern subarus throwing a complete fit. 12.5 is the most dangerous since its usualy just clean solid detonation going to town on your pistons and rings. 10.5-11.5 is a deeper, and a hit of "watery" edge to the exhaust note. 9.5-10.5 is the range where it gets very watery in the sound. Richer than 9.5 you will start getting "detonation" issues. Its really a rich misfire, but many tuners will have trouble with this since many widebands after a while of use are really off in this A/F range and it has all the signs of detonation. Also I advise to NOT run richer than 10:1 thanks to seeing a couple motors puke due to the extra fuel washing out the rings.

This assumes that you are using gasoline or nearly straight gasoline. E85 will require different A/F ratios given its a very different fuel. If you want to get exotic and run something like nitromethane, you need A/F ratios down around 2:1 IIRC. If runing more than normal gasoline, DO THE RESEARCH on modifying the fuel system for these fuels. Its kinda not a good idea to find out that E85 melts your aluminum fuel tubing and your rubber lines are going to dry out and crack quickly. Anything more exotic than Alky get some very expert advice. Nitromethane is very dangerous stuff.

As far as running lean at low loads, its perfectly fine. Whats even more interesting is that detonation at low cylinder pressures can do nothing at all given the peak cylinder pressure during the detonation will be very low. The old 4L v6 pushrod explorers had some serious issues with tuning and would detonate like mad at altitude during the summer. Which didn't matter since the cylinder pressures were very low under these conditions. So if you end up with some detonation at low rpm, low/moderate load, you should get the tuning fixed, but don't sweat too much that your motor is getting shattered. If you get some detonation on boost, ah absolutely 100% avoid those conditions till you can get the tuning fixed.

In short a egt sensor is good to see if you are breaking stuff. a wideband is good for tuning stuff, but your ears and eyes are the best bet for keeping a modified car in one piece. A gauge you don't see doesn't help you. A trained ear will catch when things are not right with the car.