408, Small or Big Block? Need EGT Info

-
What? Are you actually reading your EGT?

To the OP, as others have mentioned EGT is not the ideal way to tune. The only guys I've seen that used egt's were running alcohol or gas and a LOT of nitrous on very fast drag cars.
Not to tune, but to keep my pistons from melting
 
I have a 408, not sure if that is classified as a small or big block, it is a big small block, lol
Distributor in the back, small block regardless of cubes. Distributor in the front is big block. This is generally speaking for A, LA, B, and RB engines.
I have an EGT gauge, but don't know what the readings should be. I have TTI 3 step headers, 10:1 compress. and a pretty good cam, not the biggest, Eddy RPM heads. I need to know what normal, cool, and hot readings are. The sensor is located about 2 to 2-1/2 inches from the exhaust port, or header flange on the pass rear cylinder, should be 8 if I remember my cyl #'s correctly. If I need to post in Big Blocks, please just let me know.

Thanks
 
EGT readings are WORTHLESS. Unless you have very expensive thermocouples (and then it’s still not that good) they react way too slow to give you any meaningful data. Where you mount the EGT in the pipe makes a HUGE difference in what the temperature reading will be.

Learn to read plugs. I watched guys go seven different ways of wrong looking at EGT’s and trying to tune. If you think the EGT’s are high, what on the tune to do you change? What if the EGT’s and the plugs don’t jive? Then what? Trust the EGT or the plugs?

There is no reason to use EGT for much of anything unless you can data log it and have a point of reference for the temps. And even then, it’s a crappy way to tune.
 
I didn’t treat you like an ignorant child but I can if you want. It would be pointless since you want to be hard headed and stick to your guns on what your doing which would be *** backwards. If your EGT’s sky rocket to the point of burning up an engine, you sure did something wrong that you could have avoided with ether an 02 or spark plug readings.

Well, have fun then. I’m out.

I apologize Rob. I am under an extreme amount of stress, and even little things knock me over. I misinterpreted your intent, and was frustrated. Sorry
 
EGT readings are WORTHLESS. Unless you have very expensive thermocouples (and then it’s still not that good) they react way too slow to give you any meaningful data. Where you mount the EGT in the pipe makes a HUGE difference in what the temperature reading will be.

Learn to read plugs. I watched guys go seven different ways of wrong looking at EGT’s and trying to tune. If you think the EGT’s are high, what on the tune to do you change? What if the EGT’s and the plugs don’t jive? Then what? Trust the EGT or the plugs?

There is no reason to use EGT for much of anything unless you can data log it and have a point of reference for the temps. And even then, it’s a crappy way to tune.
That’s exactly what the OP is doing
 
EGT readings are WORTHLESS. Unless you have very expensive thermocouples (and then it’s still not that good) they react way too slow to give you any meaningful data. Where you mount the EGT in the pipe makes a HUGE difference in what the temperature reading will be.

Learn to read plugs. I watched guys go seven different ways of wrong looking at EGT’s and trying to tune. If you think the EGT’s are high, what on the tune to do you change? What if the EGT’s and the plugs don’t jive? Then what? Trust the EGT or the plugs?

There is no reason to use EGT for much of anything unless you can data log it and have a point of reference for the temps. And even then, it’s a crappy way to tune.

I appreciate your input Yellow. The sensor for my EGT is 2-1/2 inches from the head in the primary tube of the header. That seems to me to be a lot faster read than the plugs. Seems to be that the probe would be an instant read, and the plug would take time to change to reflect the temperature of the engine. Now I am not an expert, you probably know a lot more about this than me... but if you read post #23, and still feel this way, then how can I be sure I am not going to burn a valve or what have you in the first few seconds of WOT? I doubt it would melt a piston really, I just want to catch the over heating of my cylinders before it is too late.

The only thing I can gather, from what you have posted, is for me to make runs with the engine tuned, as I have done, it is tuned. Now run one pass up to 60mph WOT, which won't take long by the way : ) Then check the plugs? Then make another 60 mph pass and check the plugs?? And do this about 10 times to see if it is getting too hot? Now if it gets hot, what would the plugs look like? That is my next question. I don't know what a plug experiencing excessive heat would look like. But then, make 10 passes up to 80 mph, checking the plugs after each pass with the modification. All of these would be with the modification on. I can watch my gauges between runs if I need to, but then take it up to 100 10 times read the plugs after each pass. Is "That" what you guys are saying? I am concerned about pass one and two, not 30 passes down the line. That is what I am saying. I want to be sure the first pass isn't too hot for the valves, etc. I would think the valves would go before the pistons. I think I understand you better than the other posters. Maybe it is just sinking into my thick head, IDK. But I am not sure you guys understand what I am saying. What about the first WOT, am I overly concerned about burning a valve? How long does it take to burn a valve? What does a plug that got too hot look like?
 
I appreciate your input Yellow. The sensor for my EGT is 2-1/2 inches from the head in the primary tube of the header. That seems to me to be a lot faster read than the plugs. Seems to be that the probe would be an instant read, and the plug would take time to change to reflect the temperature of the engine. Now I am not an expert, you probably know a lot more about this than me... but if you read post #23, and still feel this way, then how can I be sure I am not going to burn a valve or what have you in the first few seconds of WOT? I doubt it would melt a piston really, I just want to catch the over heating of my cylinders before it is too late.

The only thing I can gather, from what you have posted, is for me to make runs with the engine tuned, as I have done, it is tuned. Now run one pass up to 60mph WOT, which won't take long by the way : ) Then check the plugs? Then make another 60 mph pass and check the plugs?? And do this about 10 times to see if it is getting too hot? Now if it gets hot, what would the plugs look like? That is my next question. I don't know what a plug experiencing excessive heat would look like. But then, make 10 passes up to 80 mph, checking the plugs after each pass with the modification. All of these would be with the modification on. I can watch my gauges between runs if I need to, but then take it up to 100 10 times read the plugs after each pass. Is "That" what you guys are saying? I am concerned about pass one and two, not 30 passes down the line. That is what I am saying. I want to be sure the first pass isn't too hot for the valves, etc. I would think the valves would go before the pistons. I think I understand you better than the other posters. Maybe it is just sinking into my thick head, IDK. But I am not sure you guys understand what I am saying. What about the first WOT, am I overly concerned about burning a valve? How long does it take to burn a valve? What does a plug that got too hot look like?
Your location for the sensor is spot on.
I would venture to say that the readings were very close to real time .
 
I appreciate your input Yellow. The sensor for my EGT is 2-1/2 inches from the head in the primary tube of the header. That seems to me to be a lot faster read than the plugs. Seems to be that the probe would be an instant read, and the plug would take time to change to reflect the temperature of the engine. Now I am not an expert, you probably know a lot more about this than me... but if you read post #23, and still feel this way, then how can I be sure I am not going to burn a valve or what have you in the first few seconds of WOT? I doubt it would melt a piston really, I just want to catch the over heating of my cylinders before it is too late.

The only thing I can gather, from what you have posted, is for me to make runs with the engine tuned, as I have done, it is tuned. Now run one pass up to 60mph WOT, which won't take long by the way : ) Then check the plugs? Then make another 60 mph pass and check the plugs?? And do this about 10 times to see if it is getting too hot? Now if it gets hot, what would the plugs look like? That is my next question. I don't know what a plug experiencing excessive heat would look like. But then, make 10 passes up to 80 mph, checking the plugs after each pass with the modification. All of these would be with the modification on. I can watch my gauges between runs if I need to, but then take it up to 100 10 times read the plugs after each pass. Is "That" what you guys are saying? I am concerned about pass one and two, not 30 passes down the line. That is what I am saying. I want to be sure the first pass isn't too hot for the valves, etc. I would think the valves would go before the pistons. I think I understand you better than the other posters. Maybe it is just sinking into my thick head, IDK. But I am not sure you guys understand what I am saying. What about the first WOT, am I overly concerned about burning a valve? How long does it take to burn a valve? What does a plug that got too hot look like?
Very white insulator even a yellowish glaze,detonation,spots can indicate metal chunks
 
Thanks Brooks. I used to be working with a stock motor which everything is different on. I went performance mode and am in a little over my head. I don't mind learning, and the Duster has 2x the hp about, which is great. I guess I will just have to as the Gauge mfger what the normal, hot and too hot readings are. No one seems to know. lol
 
Thanks Brooks. I used to be working with a stock motor which everything is different on. I went performance mode and am in a little over my head. I don't mind learning, and the Duster has 2x the hp about, which is great. I guess I will just have to as the Gauge mfger what the normal, hot and too hot readings are. No one seems to know. lol
Google egt temps there’s plenty of info out there
 
Very white insulator even a yellowish glaze,detonation,spots can indicate metal chunks


Lets hope we never get so far as to see spots!! I don't want it to get that far. But I can't seem to get the other people here to understand that I want to know what it is "When" I am on the floor, not after I get it home. If it starts to get hot, I will back off, you know what I mean? Make some adjustments, add fuel, retard timing, then incrementally work back up to the same WOT speed. Geeze, is this that complicated?
 
Some what of an idea. 355 SBC dirt oval , check out the A/F at different rpm's. EGT's to the right of screen
101 (2).JPG
102 (2).JPG
 
my first thought was asking what egt's 'should' be (as a starting point) surely won't have any relevance to your tuned motor. there are way too many variables on motor spec's, tune etc to take a guess at what it 'should' be.
 
my first thought was asking what egt's 'should' be (as a starting point) surely won't have any relevance to your tuned motor. there are way too many variables on motor spec's, tune etc to take a guess at what it 'should' be.

What temp is too hot for the valves?
 
again, with valves being made from different materials that can 'handle' different temp's there are many variables. as mentioned above i'd rather work from afr readings.

So just keep the AFR around 12.5 to 13, maybe 13.5 outside? Never 14, back off throttle at 13.8 and add fuel? What are the outside parameters of the AFR reading?
 
Last edited:
How much are you currently spraying and how fast are you going? What's the most you've sprayed in the past?

Well, this is the entire reason I am asking. I have a brand new engine, never taken it over 3k RPM. Never to the floor. I have 74's in the front for jets, 85's in the back, 32 shooter in the front 35 in back w/a 4.5 PV

I just got this combo to sit pretty at 12.5 AFR cruise, idle bounces between 12.2 and 12.9 or 13, usually rides in the 12.5ish zone. AFR Seemed to dive at 3,000 RPM on highway @ 65-70 mph though. I think I have my secondaries opening too soon. I have no idea what the EGT top end will be, but I don't want to burn a brand new valve, on a brand new motor that I have been waiting 3 years to drive. A calculator said 120mph is at 5,200 RPM in 3rd. 3:23 gears w/24" tires. I need to be careful taking it up to top end. Just broke it in about a month ago, the diff was broken in about 2 weeks ago. I am waiting on an 800hp rated driveshaft, had to save $$ for it. But could possibly get it this week. Everything is new. Trans too, but only a 2,500 stall.
 
Well, this is the entire reason I am asking. I have a brand new engine, never taken it over 3k RPM. Never to the floor. I have 74's in the front for jets, 85's in the back, 32 shooter in the front 35 in back w/a 4.5 PV

I just got this combo to sit pretty at 12.5 AFR cruise, idle bounces between 12.2 and 12.9 or 13, usually rides in the 12.5ish zone. AFR Seemed to dive at 3,000 RPM on highway @ 65-70 mph though. I think I have my secondaries opening too soon. I have no idea what the EGT top end will be, but I don't want to burn a brand new valve, on a brand new motor that I have been waiting 3 years to drive. A calculator said 120mph is at 5,200 RPM in 3rd. 3:23 gears w/24" tires. I need to be careful taking it up to top end. Just broke it in about a month ago, the diff was broken in about 2 weeks ago. I am waiting on an 800hp rated driveshaft, had to save $$ for it. But could possibly get it this week. Everything is new. Trans too, but only a 2,500 stall.

You're rich at cruise.
 
I got this off Google:

The absolute maximum safe EGT range is debatable. Our universal rule of thumb, regardless of engine make/model/year, is to not exceed 1250° F and not to operate in the 1200° F - 1250° F range for an extended period of time.

My EGT Stays pretty consistent. I understand there are a lot of variables that determine EGT, but I reason that they had to make an EGT for a reason, that reason I assumed was to prevent burning valves. This tells me that 1,200 is the danger range. If I start getting near 1,200 I will see what I can do to bring it down, but this is what I was looking for.
 
-
Back
Top