How to manipulate egt's??

[Gigaherz]

There are alot of variables that affect egt's and I've been trying to get a grip on them to better tune my car for lower egt's. I think I have most of them covered but it would be nice if you guys could steer me where I'm wrong or add some info.

so far I've read a bunch of varying opions through searches on the net and this is the info I've got. Of course every car is different but for the most part in general tell me if these statements hold true.

Fuel Ratio

richen the a/f to drop egt's in general
however go too rich and the unburnt fuel will cause high egt's in your exhaust. Your combustion chamber temps may be lower than the temps your exhaust sees. While this is good for the engine it is not good for your manifold and turbo obviously.

lean out the a/f and your egt's will go up in general
however if you lean out to a higher than stochiometric ratio your egt's will go down. I would think this would be only at part throttle and light loads.

You will have the highest egt at stochiometric or 14.7 afr.

Ignition Timing

Increase the timing advance to lower egt's in general
Decreasing the advance will raise egt's because the lower you go the more likelyhood the fuel mix will burn up in the exhaust than in the chamber. Hence why the anti-lag strategy for turbo cars is to dump extra fuel in with very low timing so it explodes in the exhaust creating crazy egt's and fast spool up as long as the turbine blades are still there that is!! It's very destructive to the turbo and manifold.

Compression

higher compression lowers egt's because it creates a faster burn of the mix
lower compression raises egt's at part throttle until you are into boost and increasing the effective compression ratio with the turbo.

Exhaust Backpressure

The more exhaust backpressure you have in the system wether it be before or after the turbo will increase the egt's. Going to a bigger downpipe/catback or exhaust housing will lower your egt's usually.

Cam timing

???????
I'm guessing advancing overall cam timing will lower egt's???

Octane rating of fuel

???????????
Ie: does going to 100 octane actually increase egt's??


Don't know what else affects egt's really but this is what I think to be true and makes sense to me. If any of you guys know better please tell me what is correct.

Also what are acceptable egt's? It seems 1400-1500 is dangerous territory when measured at the manifold about an inch away from the exhaust port.


Man, thank god I copied this before I hit submit new thread.

[CWCZX3]

AHHH!!!!! Now i see it.

[LornesBored]

I think when your accepatble EGT is about 1400 fully warmed up and on the throttle, if it spikes to 1600, then your in deto territory and it must be fixed ASAP.

[Gigaherz]

Egt doesn't necessarily correspond to deto does it? At 1600 I think I would be more worried about my alluminum pistons and head melting. I could have no deto but my engine would still destroy itself. No?

At cruising and light loads it goes above 1400-1500 on my car and that is where I'm trying to lower it. It might even go higher but I usually let off the gas or gun it whenever it hits 1400 and it drops right away.

[BUR_ZX3]

yah I'd never heard that EGT was a cause of deto.... possible symptom... but high EGTs are bad things for aluminum engine parts like we've got.

[LornesBored]

^^ I meant symptom

and spikes to 1600 (or higher) like for a flash and then drops back down.

to clarify

[Tobyboom]

Originally Posted by Gigaherz

At cruising and light loads it goes above 1400-1500 on my car and that is where I'm trying to lower it. It might even go higher but I usually let off the gas or gun it whenever it hits 1400 and it drops right away.

That is the exact same problem I am having. I hate it because this is what keeps burning up my head/manifold gaskets. Its only under light load and part throttle that I see anything over 1300. As soon as I floor it, the EGTs drop back down to around 1100-1200. I've talked to Tom til I was blue in the face about this, and we havent been able to correct it yet. My short term fuel trims and timing are all where they are supposed to be. The only thing that I havent tried to fix it is dumping a little more fuel in it. I might give that a try to see how it works.

[Gigaherz]

what size exhaust housing do you have toby? I have a .48 housing and I'm thinking it might be related and creating too much backpressure.

[Ray]

Gig - please stop breaking the internet.

Thank you.



nice post btw, i'm going to add this to the reference thread.

[Hocky]

Originally Posted by Tobyboom

That is the exact same problem I am having. I hate it because this is what keeps burning up my head/manifold gaskets. Its only under light load and part throttle that I see anything over 1300. As soon as I floor it, the EGTs drop back down to around 1100-1200. I've talked to Tom til I was blue in the face about this, and we havent been able to correct it yet. My short term fuel trims and timing are all where they are supposed to be. The only thing that I havent tried to fix it is dumping a little more fuel in it. I might give that a try to see how it works.

Have you tried running more timing? That is going to make the biggest difference in EGT.

[Gigaherz]

I was using the stock spark tables and was worried about increasing them since I figured they would be too high already. Today I increased most of the spark in the borderline knock table by a few degrees and my egt's are dropping. My j&S isn't showing and indications. I rarely went over 1400 and now for the most part at cruise I'm around 1350-1400. Gonna add even more spark till my j&s lights up and then I'll back off. I can't believe how much timing I'm running!! I think maybe all the combustion chamber re-working I did is now paying off! WOOHOO!! Hehe, feels good to keep making progress.

[P-51]

Good question. Directionally speaking, most changes that makes more power, or is more fuel efficient, will lower EGT.

Here's my take:

Fuel Ratio:

I have heard the bit about being too rich making the EGT's go up, but have not found this to be the case. The Zetec stops firing around 8:1, and I never saw the temps go up by this point. I think this is an old wives tale, or related to something else not understood.

EGT's will go up as you approach stoich, then drop off.

I've also heard that the EGT will go up with a lean mixture, because it burns slowly or something stupid... again, not the case. I cruise at 16-17:1, and the EGT's are around 1200. For reference, they're around 1400 at 0 boost and ~13:1, and 1550 at full boost.

Ignition Timing, correct.

Compression Ratio

High compression ratio decreases EGT's because the engine is operating more efficiently. At the root of it, the Otto cycle increases efficiency as compression ratio goes up.

Backpressure: Correct. Low backpressure allows the gas to expand faster as it comes out of the head. PV=nRT, the gas drops temperature as it expands.

Cam timing....

Advancing the exhaust cam should send EGT's up. Because you're opening the exhaust valves earlier in the power stroke, the gas won't have given up as much work to the piston.

Intake timing? No clue.

Octane, in and of itself should not make any difference. Contrary to popular belief, octane has no bearing on combustion speed. At least not of a magnitude that would result in measurable EGT changes.

Oh, and for the record, I run up to 1550F on track, with no ill effects so far. The tollerance of the engine depends on a few factors. Really the biggest threat is burning an exhaust valve. Longer duration cams will increase the risk, as the valve spends less time on the seat where it can dump heat into the head. Multi-angle valve grinds do the same thing, as they reduce the area of contact with the valve seat, thusly reducing heat transfer.

[Gigaherz]

sweet, good to see that I'm on the right track for the most part. Thanks for the explanations.

About the temps, I have an spi and they are known to drop valve seats when overheated. So, melting or warping aluminum and dropping seats is my biggest fear. I had better seats put in and I'm running inconel exhaust valves so hopefully my valves should hold up. (crosses fingers) It seems that with the timing on the borderline like I have it now my egt's won't go over 1400 anymore and hover in the 1200's most of the time. I'm pretty relieved and boy does it pull now!!

[Lee Martinez]

When I first was turbo'd I had a boost leak that I couldn't figure out, and so I just bypassed the turbo and drove the car home in NA mode.

Cruise EGTs were 12-1300F and floored, it didn't go above 1400F but I only reved around 4500rpms since the turbo was still spinning, just venting all boost.

I wouldn't mess with timing too much to lower EGTs because too much timing and you'll blow the motor.

[Tobyboom]

Originally Posted by Gigaherz

what size exhaust housing do you have toby? I have a .48 housing and I'm thinking it might be related and creating too much backpressure.

I'm also running a .48 exh housing. I dont think that too much backpressure would be the cause here though. Maybe if we were using Aerochargers...

[Tobyboom]

I'd just like to add that my EGT probe is about 4" into the downpipe and not in one of the runners itself. This might be a reason my EGTs are getting such a high reading.

[LornesBored]

I thought the closer to the head would be the hotter readings?

[Gigaherz]

If the egt is 4" after the turbo then it should be cooler. If it was in the collector right before the turbo inlet then it would be hotter than an individual runner, but not after the turbo in the downpipe.

[P-51]

Originally Posted by Gigaherz

If the egt is 4" after the turbo then it should be cooler. If it was in the collector right before the turbo inlet then it would be hotter than an individual runner, but not after the turbo in the downpipe.

Oh really! That's interesting. How so?

Mine is in the collector, and it's a little hotter than I'd like, but the engine is fine. Maybe this is why?

[Gigaherz]

All the exhaust gasses are meeting at that one point and at that point you are getting four exhaust pulses per cycle instead of one like in an individual runner. It is in maximum boost under manifold design. That's why alot of times in pics you see manifolds glowing at the collector but not at the runners or the collector glows first before the whole manifold turns cherry red. I guess how big of a discrepancy (sp?) depends on what type of manifold and how long the runners are.

[EJ20T]

Originally Posted by P-51

Good question. Directionally speaking, most changes that makes more power, or is more fuel efficient, will lower EGT.

Here's my take:

Fuel Ratio:

I have heard the bit about being too rich making the EGT's go up, but have not found this to be the case. The Zetec stops firing around 8:1, and I never saw the temps go up by this point. I think this is an old wives tale, or related to something else not understood.

EGT's will go up as you approach stoich, then drop off.

I've also heard that the EGT will go up with a lean mixture, because it burns slowly or something stupid... again, not the case. I cruise at 16-17:1, and the EGT's are around 1200. For reference, they're around 1400 at 0 boost and ~13:1, and 1550 at full boost.

Ignition Timing, correct.

Compression Ratio

High compression ratio decreases EGT's because the engine is operating more efficiently. At the root of it, the Otto cycle increases efficiency as compression ratio goes up.

Backpressure: Correct. Low backpressure allows the gas to expand faster as it comes out of the head. PV=nRT, the gas drops temperature as it expands.

Cam timing....

Advancing the exhaust cam should send EGT's up. Because you're opening the exhaust valves earlier in the power stroke, the gas won't have given up as much work to the piston.

Intake timing? No clue.

Octane, in and of itself should not make any difference. Contrary to popular belief, octane has no bearing on combustion speed. At least not of a magnitude that would result in measurable EGT changes.

Oh, and for the record, I run up to 1550F on track, with no ill effects so far. The tollerance of the engine depends on a few factors. Really the biggest threat is burning an exhaust valve. Longer duration cams will increase the risk, as the valve spends less time on the seat where it can dump heat into the head. Multi-angle valve grinds do the same thing, as they reduce the area of contact with the valve seat, thusly reducing heat transfer.

Saying that higher octane will not lower combustion temps and lean a/f ratio will not increase egt temps at the cylinders is wrong IMO. My understanding is that fuel acts as a coolant in the combustion chamber and the higher the octane the cooler the egts @ the cylinders.

I don't know much about the Ford Focus other than the fact that they do pretty good at the track bone stock and that it's a great WRC car but in the Subaru community we don't think this way. I am in no way an expert on egt manipulation or a/f ratios but I've done a lot of research and everything I've read contradicts your theory.

I'm not trying to stir the pot, I'm just hoping for a better explanation to your claim.

[EJ20T]

Originally Posted by Gigaherz

All the exhaust gasses are meeting at that one point and at that point you are getting four exhaust pulses per cycle instead of one like in an individual runner. It is in maximum boost under manifold design. That's why alot of times in pics you see manifolds glowing at the collector but not at the runners or the collector glows first before the whole manifold turns cherry red. I guess how big of a discrepancy (sp?) depends on what type of manifold and how long the runners are.

Interesting, all this time I've thought my readings would be lower since I have mine tapped at the collector rather than 4" away from the cylinders but now you have me second guessing myself.

Has anyone ran a 4 channel egt setup on a focus? Just wondering if you guys have a cylinder that runs hotter than the other 3. This is a problem with the WRX when you run the oe exhaust and manifold.