Exhaust Temp numbers how hot is safe ?

[saltracer1]

just checked my data logger records from last year. I also run a flathead with supercharger, XF/BGALT at about 140 mph 1571egt. This is being monitored kind of down stream. 12.33 afr. Engine did not run hot, but I have to mention we did have a blown head gasket (probably at this time).

[Stan Back]

1571 downstream, after curling around and out, sounds plenty warm to me.

[saltracer1]

ok, so that leads to my showing my ignorance. I can make a couple of  guesses on how to lower the egt 1. increase carb jet sizes 2. change to colder heat range on plugs 3.lower boost 4.back off on timing 5.

[Stainless1]

SR1, that really sounds hot.... were you burning a lot of your mix in the exhaust after it left the cylinder?

[hotrod]

colder plugs will not really change the EGT much, they mostly help prevent detonation/pre-ignition by not getting red hot at the tips, they do not significantly cool the combustion process.

Increasing jet size (making the mixture richer) can raise or lower your EGT.
If you are on the lean side of the EGT curve (ie lean of max EGT) adding fuel will make it run hotter, if you are on the rich side of peak EGT it can cool the EGT.

Burn speed of the fuel also effects EGT.
If you are using a fuel that burns too slowly for your application a lot of fuel will still be burning as the exhaust valve opens significantly increasing EGT (and risk of burned exhaust valves).
Race fuels that have very high proportion of toluene and similar slow burning components, although high octane can burn too slow to finish the burn before the exhaust valve opens in some engines.

Lowering boost will almost certainly lower EGT. That might be a first step to create a little cushion in your tune while you figure out what the real cause of high EGT is.

Timing likewise can go both ways depending on where you are compared to where you need to be.

If you have too much advance so that the piston is still rising when peak burning takes place it can make cylinder pressures and temperatures skyrocket.
You want peak cylinder pressure to occur about 14 degrees after TDC (plus or minus a bit depending on engine design).

If you're not sure of what is going on, I would back off the boost a little and get some dyno time so you can figure out if you really have ideal timing and mixture. Once you get those dialed in then you can work up your boost pressure. As boost pressure goes up, your safety margin gets very slim very quick near max performance.
Much easier and safer to find best timing and mixture just a little bit on the safe side of maximum boost.

For a given engine design, fuel choice and fuel air mixture there is only one ideal ignition timing at peak power rpm.
Changing fuel air mixture will change the burn speed slightly so as you get your fuel air mixture dialed in, you need to keep tweaking your timing slightly to keep it at peak power with minimum timing.

A safe rule of thumb for tuning is to tune the engine for peak power then back off the timing until you can just detect a power drop.
That ensures you are on the safe side of the timing curve running the minimum ignition advance that will get you peak power. Most people tend to use too much ignition advance when tuning.

As boost goes up you generally see burn speed increase too, so higher boost will generally need a little less timing to be in the same sweet spot of ideal timing than a lower boost all else being equal.

The other option is to change fuels. Some fuels produce more heat than others. Some fuels have fuel components which cause significant evaporative cooling of the air charge and burn cooler or as mentioned above burn faster so they complete the burn cycle earlier for a given timing advance. You might want to talk to ERC to see what they say about your fuel choice and the EGT you are seeing they might recommend a different fuel with burn characteristics more suited to what you are doing.

[jl222]

Not sure if theres a good way of asking this but is there a safe temp number I should be looking for when using my exhaust temp gauge? The gauge high point is 1500 degrees I run bown on gas the motor is a flathead not an easy combination to play with.  But as we all know if we want easy Land Speed Racing would not be what we would do. To date I have run the mile and mile and a half so any ideas?  

An intercooler would help but might be a problem with added blower height. Front mounted blower into intercooler if room.

  Water injection might be simpler. Turbocharging book by Hugh McGiness [ HP BOOKS] explains a lot. Chart in same book by Ricardo should make you a believer.

  Also talks about 3 stages of turbos in superstock tractor pulling, that's 2 blowers into another blower into another blower, multiplying boost at each stage and ending up with 250 lbs boost

  with all those blowers no room for intercoolers so 3 gal min of water injection

   Also a centrifugal supercharger would lower your intake temperature a lot depending on how much boost, about 100 degrees at 14 lbs boost 70 degree day and 12.5 lbs atmosphere

  We have had problems running water injection in past, make sure cylinders are water free after run, we have had rusting and eching of cyl walls even after spraying a bunch of WD40 into intake after a run with motor running.
 
 We now remove spark plugs and give about 3 good squirts of motor oil in each cylinder and turn motor over with starter.

            JL222


                                                   
 

                                      

[Bob Drury]

  Okay gang, Lets start by looking at the facts.  Aluminum melts at 1221 degrees fahrenheit. Any higher temp in the combustion chamber will result in 100% leakdown in short order. The higher temps shown by EGT's are due to unburnt fuel in the combustion chamber which is instead burning in the exhaust pipes.  So as was mentioned earlier where the EGT probes are located has to be taken into consideration.
  Unburnt fuel means lost horsepower.
  This can be dealt with in several ways.  One is using exhaust reversion  with step headers, merge collectors  tubing size and length. The trick is to not have the exhaust suck the unburnt fuel out but you still want it to scavenge well enough to help bring the intake charge into the cylinder.
  Another is by camshaft design and timing, involving lobe centers lift and duration.
  A third way is by controlling spark duration in the combustion chamber.  If you look at a Fuel Dragster they run two forty four amp magnetos usually timed slightly apart and firing two sets of spark plugs per cylinder.
  Think back to the old dual point distributors which were developed to allow longer dwell time of the points.
  MSD has recently come out with adjustable electronics to widen the dwell time with their electronic ignitions and magnetos so in the future a Top Fuel car may not need two magnetos or two sets of spark plugs, just one eighty eight amp magneto (enough to weld with or fire the 115 gpm fuel pump(s) delivery.
  The longer the spark is lit the less fuel will exit into the headers and not only will the EGT readings by lower, but the horsepower will be higher.
  Just my two bits worth...............................One Run

[RansomT]

EGTs are a precarious thing.  So many factors, so little information.  For what it is worth, a mainly stockish Hayabusa (with an all aluminium engine with that melting point of 1221F) tuned with 0.2 AFR richer than peak power with the correct timing (MBT) can see north of 1400F Naturally Aspirated.  Add nitrous to the mix, and everything goes through the roof.

I've been battling high EGTs now for a couple of years without much solutions.  Getting information from the drag racing world is of little help because my EGTs claim as long as I am on the throttle.  The first 1/2 mile is always golden for me, it's on down the track that gets me in trouble. 

Each engine and combo is different. I know that my engine will survive as long as I don't go above 1650F, but other folks can and do melt down long before then.

[manta22]

Bob;

"Think back to the old dual point distributors which were developed to allow longer dwell time of the points."

The longer dwell time only allowed the coil magnetic field to still build up at high RPM-- it didn't increase the spark duration.

Regards, Neil  Tucson, AZ

[JoshH]

You want peak cylinder pressure to occur about 14 degrees after TDC (plus or minus a bit depending on engine design).

Could you provide examples to this statement? I’m curious.

With cylinder pressure transducers becoming more available to amateurs I’m wondering if any LSR participates actively use them for dyno work or otherwise.

I’m also curious about how people dyno tune for this. I've participated in a heavily loaded 30 second pull to observe the EGTs but I’m not sure its enough to capture the full picture.
 

[Dynoroom]

Another factor related to EGT on the dyno vs. Bonneville involves the thermocouple design itself. In the automotive world we normally use "K" type thermocouples, but there are many different types. Starting with diameters. In many racing applications we use 3/16" or 1/4" in the exhaust with the smaller dia. responding faster. Most are "shielded" for durability as they will degrade over time. This shielding also makes for a "lag" in response time especially on a dyno test so we use "open tip" T-couples to get faster response and more accurate data when testing. When I test intercooler effectiveness or intake manifold temps I use 1/16" open tip T-couples again for even faster response during a test. Lastly I NEVER tune via T-Couple information, it is used as an aid in tuning, after spark plug reading, and O2 information. Spark plugs will tell you everything you need to know, you just need to know how to look at them.     

[JoshH]

Good point on EGT types.

tune - poor choice of words on my part... If you had an engine that was tuned correctly (optimized) but was still running dangerously high EGTs during passes (long course) what would you do? This may seem a bit oxymoronic but I could see a case where you have to dial it back to make it live. In some ECUs you can set up fuel or timing adders (even boost) in order to not exceed or at least try to control EGTs, just thinking functionality like this could be beneficial for survival as long as you know what variable to tweak. This might be a bit of a corner case; stout engine, power adders, and changing environmental conditions. I guess the other issue here is you need to know what temperature is terminal for certain combinations.

[Bob Drury]

  Manta, I meant to use that reference more as a reference model to picture in ones mind.  Sorry about the confusion.
  p.s.  A friend of mine added a second ignition and a  set of Brodix Buick (Chevy) heads, added  a second set of spark plugs between the rocker arms, and achieved exactly what I mentioned it my previous post.
  His EGT's dropped over 200 degrees (4" from the exhaust ports) and he subsequently blew away the existing BB/A NHRA record with a 300" gas burning 14.71 blown small block running 7.30 at almost 180 mph five years ago.
  The new motor is going to a racer in Texas who now holds the record and My friend tunes.  The last four National Events it ran resulted in one win and three runner-ups in Comp Eliminator.
  He just designed a improved version and Brad Anderson (BAE) built a set of Billet Water (Yes, Water) heads with the dual plugs to go on top of a new Billet (water) block which he is assembling currently.
  I shot a bunch of pictures of it last week and as soon as I manage to corner  4 Barrel Mike to coming over I will post them.
  The entire thing should be put in the Smithsonian.                              Bob

[ronnieroadster]

Thanks everyone lots more good information. Considering everything so far it looks like each combination has their own variables. With the flathead getting close to the port for a reading is impossible so there may be a higher reading caused by the added distance from the port.
  SR 1 reading 1571 EGT on the supercharged flathead with only a blown head gasket tells me the readings might be higher than expected on a flathead.   

[hotrod]

Could you provide examples to this statement? I’m curious.

It shows up in many college level engineering texts and other resources. As mentioned it varies due to engine design. The object is to have maximum conversion of cylinder pressure to mechanical power. If the peak cylinder pressure happens too early it expends most of its effort trying to push the crank out of the bottom of the engine rather than turning it. (sort of like standing on the peddle of a bicycle when it is nearly straight up. You expend a lot of force but not much useful work is accomplished).

If peak pressure happens too late a lot of force is used as friction as the piston tries to push into the cylinder wall away from the crank throw. "Mechanically" ideal compromise between those two situations happens about 14 degrees after TDC on average but it varies a lot due to construction details of the engine, such as con rod stroke ratio, bore, rpm and all those other things. Then you have all the variables due to uneven mixture, spark scatter etc. slight variations in true mechanical compression ratio and cylinder filling efficiency due to cam grind port shape and such.

In the industrial engine world they actually tune engines cylinder by cylinder to get them each to work at their optimum efficiency. If a stationary engine has a "lazy cylinder" that is not doing its share of the work it not only lowers the power available but increases the odds of detonation in the next cylinder to fire as it has to pickup the slack and ends up under higher load than cylinders that follow efficient cylinders.

This link touches on this cylinder variation issue:
http://www.autospeed.com/cms/A_109725/article.html?popularArticle

I would  have to dig through some books to find you specific references.

This image shows a pressure trace for a typical spark ignition 4 cycle engine, note that peak pressure occurs about 14 deg ATDC.

http://www.maintenanceresources.com/referencelibrary/ezine/images/engbal5.gif

This image shows the cylinder pressure on a 2 cycle engine at lean, normal and rich fuel air mixtures. (Lean is the high spike, normal is the middle, and rich is the lowest peak cylinder pressure)

http://www.maintenanceresources.com/referencelibrary/ezine/images/engbal7a.gif

Source article for these images is :
http://www.maintenanceresources.com/referencelibrary/ezine/enginebalance.htm

Good article but mostly deals with the issues of balancing cylinder pressures by tweaking ignition and fuel air ratio cylinder by cylinder.

http://www.rodandcustommagazine.com/techarticles/0604rc_ignition_timing/   <----- this article specifically mentions the ideal timing range.


http://www.ni.com/pdf/csma/us/361574a1.pdf

By observing the measured in-cylinder pressure and the location of the peak pres-
sure with respect to the top-dead-center piston position (TDC), the engine
operator can quickly tune the engine for optimum performance. Most conventional
engines exhibit optimum performance when the peak pressure occurs 12 to
15 deg after TDC and the combustion event occurs during the nearly constant
volume condition near TDC, as indicated by the mass fraction burned.

http://tfxengine.com/SuperchargedEngineData.html