Plane Silly

i have read some past threads on this but I didn't find a real solid answer. I have a Whippled 496 with a forged bottom end, Raylar cam, ported stock heads and Lightning headers. It has an EGT gauge off of the #2 cyl tapped into the exhaust port on the head. Just cruising it runs around 1350 but when I push it it starts to climb above 1400 and I back out of it. Can someone tell me if above 1400 is safe. I have bumped up the fuel press a bit but it didn't seem to made a difference. The plugs look good.

What is the best way to reduce EGT's? Does high octane fuel (race gas) help?

JRider

Aluminum can melt @ 1220*. I would say 1350 is high.

stevesxm

and you would be correct ... especially in this case if it happens very quickly as implied.

Plane Silly

This is why I am confused. I've read other post with motors have no problems at 1500*.

JRider

Even though the EGT reads a certain temp, only a percentage of that transfers to the piston/heads etc. There are far more qualified people than me that could give you specifics on what is safe.

SB

During running, the combustion chamber (ie: head comb chamber, piston top + rings/ cylinder wall) will have a boundary of air/fuel that protects the metal surfaces. This is caused by proper a/f ratio and the metal surfaces being cooler. Therefore, combustion temp can, and is, be much higher than the melting point of the surface metals.

When you run too lean, all of/or part of the boundary layer can disappear and that's when parts melt.

Kind of fascinating stuff huh. Always amazes me too.

Plane Silly

Does anyone know if race gas or 100ll would lower the egt's. Also, how big of an affect does water temp(motor) have on it?

stevesxm

yes and no on the fuel. in a lab setting, a 100 octane low lead like avgas will burn more slowly and give you a small incremantal reduction in egt. but that isn't a solution in general and certainly NOT a solution in your case.

the observation is made above about egt vs what is actually happening inside a combustion chamber. with out getting into the nitty grity of it, that observation is essentially correct. but having said that, there is a lifetime of empirical data that says that when you are seeing 1400 f, 2" out of the port early on in the load profile then you are serious asking for trouble almost immediatly... and thats on a normally aspirated motor. while my experience with superchargers is limited my experience with turbos is pretty extensive and i can tell you that if i was seeing data from the car that suggested 1400 before the extreme end of the longest straight then i would be putting a LOT more fuel in it pretty quick because that motor would not survive for the length of the race.

as for fuel... your selection of fuel type is very specific relative to the configuration of the piston tops and combustion chambers and comp ratio . those define the burn rate and that is a function of the fuel chemestry. the upshot being that you select the fuel first to suit the motor THEN you adjust the fuel curve to suit the load profile and gives you good af ratios at your desired revs.

now im sure there will be 86 posts now that describe how people run over 1400 ALL the time for hours on end with no ill effect. fine. be my guest

all im saying that it would not ever occur to me to do that on a forced induction motor.

Plane Silly

Thank you for your input!

I have just been running hard for short burst due to the high temp. But I would like to get it addressed so I can see how fast she will go. I'll try adding some more fuel and see how it responds.

H2Xmark

you said 1400 was on port 2, it might be a little higher or lower on a different cylinder. maybe add a intercooler would be best option if you dont have one