Can anyone either point to a reference or explain the decision points(in laymans terms) when using EGT as an indicator of F/I engine function?

 

my opinion: put it in the manifold 1" from the port or dont even put it in.

 

EGTs do not really help you tune much. Wideband A/Fs are what you use for tuning. EGT gauges can give you an idea of things occasionally... but you cannot use them to judge 100% what is happening in the cylinder.

During repeated runs or sustained runs the EGTs can go much higher then normal. Where you put the sensor is a HUGE factor in the readings... if its in the collector of a short manifold, i would expect it to read a tad hotter then if its only reading from one port. If its after the turbo, I dont even pay attention to it, regardless of any speculation, not only will it read incorrect, but it will not even have the same temp curve in some situations.

How hot is too hot? If your seeing 1900-2000F expect things to break within a couple runs. If your seeing 1250-1350F I would also wonder wtf is going on. Typically WOT operating range of a turbocharged engine will be 1400-1800F. On your average turbo car you can see 1450-1500F under full throttle, and there is pretty much always a climb towards redline. On very high HP engines its not rare to see peaks of 1650-1750F by redline. These are temps you would not want to sustain for more then a moment.

Different people might have different experiences with it... this is just what I Have seen on several cars... some tuned by me, some not tuned by me... Just observations I have seen on the dyno.

If your EGTs are getting very hot by redline... the ways to cool it would be advancing ignition timing, or adding in some fuel. For the sustained abuse I put my personal cars thru, I would use the adding fuel method to cool my EGTs down... but that is because I feel that any more timing would cause problems. I would only use timing to cool EGTs if the timing is far off.

The turbo systems we are using on our Z's is going to promote high EGT... since we have what are considered smaller turbos than if you were going to try and compare your EGTs to say a single turbo supra.

 

I disagree somewhat. Each type of car can safetly run differenet EGT's. For instance, Supras typically like and can tolerate hotter EGT's than many cars.

1800F is going to break something almost right away......much too hot for the type of fuels, CR, and engine/turbo characteristics in the VQ.

1350F measure from a thermocouple device, even one mounted 1inch from the manifold, directionally tells you how hot the burn is getting. But the temps inside the combution chamber are MUCH hotter than the temps seen on an EGT gauge.

I agree with Charles, in that an EGT gauge alone is not an effective tuning device. But IMHO, you really need both a wideband and an EGT to tune safely. It can be done with AF only...and we do it all the time, especially on moderately boosted cars. When once you start pushing past 500whp, where you margin for error is decreased, the EGT becomes a critical tool. There are many instances were your AF ratio can be spot on, but your EGT's exceptionally hot. That's why I like to cross reference both of them. I also find that EGT's make it easier to dial in ignition timing with a little more precision.

 

On DSM's we tapped the EGT hole with car running to blow out most of the shavings. Any that made it through wouldn't hurt the turbo b/c it wasn't spinning at idle. Will this be the same case with a turbo VQ?

I was going to try it on mine before I put on my single turbo. Is it possible to even tap the manifold on the car up by the cylinder head? If not I'll just tap the piece that puts the right and left stock manifolds together.

 

Turbos will be spinning at idle...they are always spinning when the engine is running. Honestly, a few small metal shavings will likely do no damage, but its just easier to do when the manifolds are off of the car.

Based on the unscientific comparo that Booger and I did, I am not overly concerned that there are material differences in EGT's if you are using cast manfiolds.

 

1800F definatly will not break anything right away unless the engine is already in disorder. I have hit 1800F countless times on countless engines, especially when doing intial tuning.

And its not each particular car that can handle different EGTs... its each particular engine, and that means my VQ, your VQ, and his VQ, are completely different.

Plenty of high HP cars will run in the 1600s to 1700s for a breif spike by redline, even if they run in the 1500s during most of the powerband. Sustained temps of over 1550-1650 I might worry about... the hotter it is then the less time you want to spend there... but once again, often times you will not see a steady EGT all the way to redline, spikes of higher EGTs on top are pretty typical. In some applications, depending on the engine and the way its built, you will experience high EGTs towards redline, even when your running very rich... but when you try to increase advance to get rid of it, you start getting some ping.. every engine is very different... the way it likes to be tuned is the way it likes to be tuned. If the car ends up with hotter or colder EGTs then another by the time its tuned and happy... then that is just where it is. If your particular setup runs hotter or colder, then sometimes its outside of the tune that is really causing it... just causr you can use tuning to correct it, doesnt always mean that it was ever a problem in the tuning to begin with. Many other factors have play in EGTs besides just your ignition timing and fuel tuning... and with those tuning their Z on just a piggyback... the only thing you have to work with are those 2.

Edit: Ultimatly, your exact setup will determine your EGTs. Sometimes the car will just end up with higher EGTs, especially with very high output. This is the reason why there are higher temperature resistent parts available, such as exhaust valves. The reason people find needs to upgrade to these components are to withstand the increased temps... I recommend using upgraded exhaust valves in any high HP build up... because melting valves is something I wouldnt want to worry about. Typically a valve will melt before damage to the valve seat is done, because the valve seat has much better cooling thru dissappation then the valve, and less surface area exposure than the valve.

 

phunk, Sharif@Forged.....thanks for the comments!

 

good stuff guys...keep it coming...i just got back from street tuning my car with Brody (speedlab)...we got it dialed in pretty quickly to 10.8:1-11.0:1 in 5th gear pulls...
the tuning scenario was a street tune with about 90% 101 octane and 10% 91 octane...i figure 97/98 octane at best (wanted to street tune with a bit more safety--i plan to run 91 daily)
14psi...
originally, we were seeing 11.7:1 at about 5500rpm and up...injector duty cycle was at 95%!!! and the fuel pressure at idle was around 52-53psi
we were out of time for tuning, so i filled up the rest of the tank with 91 (figured this would lean out the tune even moreso....so i chose to pull some timing up top to see the effect (we were only pulling 6 degrees of timing above 5500rpm (as opposed to the 13 degrees of timing being pulled at 4200 ish right before the huge torque peak)

so, after pulling 2 degrees of timing up top (and filling with 91) this richened up the top end (i didnt want to go much higher in fuel pressure, although i might...and i havent checked what the duty cycle is at now...i should, but i just got home and am about to go out and eat with the lady)

we checked several loads (only have access to a dynojet-non-load based)...and i have personally concluded that this method of tuning is more exact than simply doing 30-40 passes in 4th.5th gear on a dynojet....

 

please specify....tuning with 101...then running 91 will lean the tune, correct?

 

no offense todd... but WTF does any of that have to do with EGTs?

 

I agree somewhat... that is if your tuner is riding shotgun. On the street you can hold load points longer in a higher gear easier then on an inertia dyno... however the situation is less controlled... but if you have good datalogging and good traction, then by all means tuning on the street can be a little fun.

 

i know, sorry to hijack, should have started my own thread...ijust knew this would be visible to you and sharif...two of the brightest...take it as a complement

 

yah, brody was riding shotgun..as far as getting the A/F logged, he watched it on some software that displays a graph..able to monitor boost, throttle position, and rpm, and fuel map....(i admit, not at super high resolution, but it proved accurate)

 

Subscribing

 

What about the egt on my car??

 

your car has no EGTs at the moment engine and trans is mounted back in there and we are hooking it all up, slowly but surely! check your email in the morn for an update.

-Charles

 

Tuning is all about experimenting, practice, and following some general guidelines. Everyone is going to have their own techniques. As a general guideline, I would never take a street car to 1800F...ever. Granted, we havent tuned any cars with upgraded valves....but 1800F puts you very close to the surface temps needed to melt aluminum pistons. 1800F EGT is well over 2000F in the combustion chamber. And AL melts at 1200F....

 

I added mine on the LHS exhaust manifold, about 1-2 inches from the head. Here are some pictures of it:

http://www.science.uottawa.ca/~paul/.../G35TT088.html
http://www.science.uottawa.ca/~paul/.../G35TT125.html

Later,

 

Looks good Madelinot. Can I ask, what was the turnaround on getting your parts coated?