Well I have finally got my new motor in the car and it seems to be OK, nothing great but serviceable. While the car was down, I installed the post turbo EGT. As you know I have two thermocouples installed in the exhaust manifold runners of my Apexi kit.

The engine is a extreme streetport with 3mm seals from Atkins automotive.

Now for the results.

1. Pre-Turbo EGTs are uniformly and approximately 200 F hotter than post turbo EGTs across the entire operating range.

2. TRE thermocouples are extremely fast and responsive when compared to Autometer thermocouples.

3. Under boost, my pre-turbo EGTs max out at about 1750F = 950C

4. Under boost, my post-turbo EGTs max out at about 1550F=843C


Now for the questions

1. Can anyone else comment on the temperature differences they have seen pre-and post turbo?

2. Can anyone confirm whether the 900C operational limit for EGTs is measured pre or post turbo?

 

Yes, that has been my experience as well.
I get about a 100C or 200F difference.
I've seen 1000C max on stock ECU, but that's under extreme conditions.
Messing with ultra-lean cruise, I've hit 1150C max.
You really don't want to see EGT's hit that kinda temps.


-Ted

 

Thanks Ted.

1150C??? OMG that's hot!
I am assuming that the 1000 and 1150 C numbers are pre-turbo confirming the ~900C guideline as a post turbo limit. Until I get things sorted out with the WB and some time, I am going to dump some extra fuel in all ranges.

All these new toys and so much to do just getting the new engine back to where the old one was before it lost the coolant seal. I feel like an FD virgin.

 

1000C was seen on stock ECU FC turbo running 14psi for about 15 seconds.
Yes, I was about 130mph+ at the time.
The car got up there quick, and I didn't have time to look at it until at speed.
The car was running the stock top-mount IC, so it's most likely heat soak!

The 1150C was done on a customer's FC turbo trying to tune ultra-lean cruise at 4,000RPM.
Yeah, we were cruising at around 80mph at the time in 5th gear.
This car was a built 13BT, GReddy FMIC, GT3540, controlled by a Haltech.
I kept leaning it out just to get some gas mileage back, but 1150C was getting a bit too hot!
We were running the new Mazda OEM 2-piece 2mm apex seals, and they didn't warp even with a brief trip to 2000F!

Yes, both cars had EGT probes pre-turbo.


-Ted

 

Man that says alot about the Mazda seals. Mental note to self, M-A-Z-D-A seals.

Thanks again for taking the time to respond.

 

hi jeff,

thanks for sharing your observations and also for posting the invaluable egt schematic. i will be building and installing 2 of them to monitor my two to4s over the winter layup.

have you yet logged your egts? if so what time offset if any are you finding?

as to temps... during the 6 seasons i raced rotaries in gt3 i tuned my weber exclusively by jetting for 1750 in top gear near the end of the straight... my motors ( built be roger mandeville and daryl drummond) were 12a bridgeport, na and were rules restricted to 38 mm chokes (2) produced 259 hp flywheel). since they had such a small restrictor they had to be really revved... my powerband was minimum 7000 to 10,0000. one motor failure in 6 seasons of 12 races plus a week of runoffs.

obviously a turboed 13b making tons more hp is a different proposition.

do keep us posted on further observations and thanks for your egt help. and Ted, thanks for your commentary which is always insightful.


howard coleman

 

I am amazed at the difference in temps from sensor to sensor. Mine read around 600C to a peak of 700C during 3rd and 4rth gear pulls.I can't believe my temps are ctually that much lower than yours. My sensor is located midway down the downpipe. Have you figured out how to log the EGT guages yet?

 

Howard
Good to hear from you and I am glad you are planning to do the AD595 converter build. That thing is just terrific.

Here are some more interesting findings:

1. I have not actually done a keeper log of anything yet as I am waiting to finish reinstalling all the goodies on the motor and position the new AFR system. I am just afraid I would reveiw the logs and start trying to tune stuff before I am really ready. I really have no self control. I am, however, using the monitor function of the Datalogit to monitor the EGTs.

2. Response time with the unsheathed end TRE racing thermocouples is incredibly fast when compared with the sheathed thermocouple supplied with the Autometer gauge. Under load, the preturbo egts reach their peak almost before I can shift my gaze to the monitor. Under the same type of load, I can watch the Autometer guage climb to the peak. It is SO much different that I can't really comprehend why anyone would use a sheathed end when the unsheathed are so durable and quick. I know that the sheathed end is preferred by turbo users for preturbo applications because they claim the ends are less likely to melt off and go through the turbo. I am not certain that this is accurate. If the sheath ever does fail it is much more mass about to go through the turbines. But such is the risk you take with anything pre-turbo.

TRE claims a .18 sec/100° F response time offset. Most fast unsheathed TCs claim .30 sec/100° F and sheathed types have reaction times as high as .70 sec/100° F. For a hard run between say 1000° F and 1800° F you are looking at the TC reporting the top EGT in around 1.4 seconds. While that is clearly too slow to rely on to avoid a bang, you are going to start noticing the fast moving trend almost immediately as opposed to the slow reaction time of others contenders.

This when coupled with the durability and accuracy factors make me a happy camper when using these TCs:
Accuracy: +/- 14°F @ 1400°F.
Max continuous temp: 1785°F.
Max temp: 2200°F.


3. Since I installed the new engine, I have seen differences between the front and rear chambers of between 50°F. and 75 °F.. This is considerably different than the old motor which showed some much higher differentials. I attribute those higher differentials to the problems with the old motor. I next intend to swap the TCs and see how much, if any, of the differential is due to the individual characteristics of the TC.

Well that's it for now. I promise to keep posting my results as long as anyone is interested. Good luck with the electronics build and feel free to drop me a line or call anytime.

Regards
Jeff

 

Ryan

I would not attribute all the differences to the sensors. K-type thermocouples are required to meet certain parameters and there are very small differences that are acceptable.

As to the difference between your results and mine, there are a number of possibilities:

1. No 2 cars are identical (porting, timing etc etc etc all matter)
2. My sensor is placed less than 3 inches from the exhaust side of the turbine while yours is considerably downstream. Note that in the 6 or 7 inches between the exhaust mainifold TCs and post turbo TC my EGTs drop close to 200 degrees, some of that is attributable to the turbine and cast iron snail acting as heat sinks, but a bunch of it is just the number of inches from the exhaust port.
3. My car is just not tuned yet.


Regarding logging the gauges, as you remember, I had a post on how to build a circuit for taking the raw TC data and setting it up for use with the datalogit

https://www.rx7club.com/showthread.p...&highlight=egt

This is the way I am doing it now, although there are still the options of opening up your gauge and taking the 0-5vOut and hooking it to the datalogit use input.

Drop me a line if you need further info

 

Now that you know the difference between pre and post turbo egt's you should pull that post turbo sensor out and move it to the other exhaust port. I want to put 2 bungs on each runner so I can move the wideband and egt back and forth to check for consistancy instead of putting it in the dp. Its in the dp now and that just reads averages, a 11.5 a/f could be one running 11 and the other running 12. You just dont know unless you test them both seperatly.

Anyway, just thought I'd throw that idea out there incase you havent already thought about it.

Good luck with the tuning!!!
Stephen

 

Hi Stephen

Actually my current configuration is one TC in each exhaust manifold runner and one post turbo. I LOVE the idea of having a WB O2 sensor bung in each exhaust runner and since I have two WB controllers (one post turbo and one for tuning other people's cars) , I could constantly monitor the situation. I actually had not thought about that but it sounds deliciously extravagant and I may well be doing that before the end of the year.

Thanks for the idea

Jeff

 

Can the O2 sensor stand the heat though?

Your dual EGTs should already be able to tell you if there are differences between rotors.

Motec wants $199 to amplify thermocouple output to 0-5v. $109 for the thermocouple.


FJO has just come out with a dual channel wideband though.

 

Tyson
Good point about the operating temps for the O2 sensor. If I remember right the body temp of the Bosch LS4 has be maintained below 800 C and the NTK L1H1 is unreliable above 900C. In either case, the temps seen by the manifold runner positions may be too high for the sensors. Thanks for the reminder.

"Motec wants $199 to amplify thermocouple output to 0-5v. $109 for the thermocouple"

Look back at the thread I referenced in this thread for the schematics for an Type K TC amplifier/conditioner/linearizer which amplifies TC output to 0-5v. Total cost for the building materials for a DUAL channel amp would be around $45-$50 even if you paid top dollar for the AD595 ICs. Single channel amp would cost about $30. TRE thermocouples are available from Teamrip for $45 each.

 

Any success getting the fuel economy back? And does those high EGT's effect apex seals? What is the AFR at those temps? I'm also trying to lean out my mixture to get back some mileage at cruising power levels. Currently running a Microtech.

Thanks!

 

Yep, but we lowered the max EGT to 1050C.
1150C is like 2000F, and that's a bit too hot!
We were only able to get the engine to lean out like this cause it was around 4,000RPM.
If you try and shoot for this ultra-hot lean burn at lower RPM's, the engine hesitates too much, and the car becomes very uncomfortable to drive.
At lower RPM's, the EGT stabilizes at 1050F without bucking too much, so this was the ceiling EGT we shot for this particular vehicle.
The mileage came back up to 15mpg roughly with us trying to tune the car.
This includes boosting about 40% of the time, so we felt this was decent.
Upper cruise only freeway driving was getting 20mpg easily.


-Ted

 

Jeff, thanks for sharing this information. I now have some ball park figures to work from.

I have just gone single and the headers were already for EGT sensors. About an inch into the header.

Fish

 

Thanks for the info. I've been getting about 15 to 17mpg mixed driving (about 85% highway). I don't have an EGT so I have to rely on the O2 sensor for an approximation. In 5th gear, it's running about 15 to 16.5 AFR at about 3000-4000 rpm's with 10-15 inches of vacuum during cruise. Would that indicate too high of an EGT?

 

Are we talking about a wide-band or a narrow-band O2?


-Ted

 

It's a narrow-band O2 sensor.

 

That's basically useless.
Don't try and read AFR's off a narrow-band.


-Ted

 

For what it is worth, here is a 2.7 second clip of a WOT run with all three TCs (Front and rear rotor preturbo and 1 post turbo) reporting to the Datalogit. The preturbo TCs are .18 sec/100 degree F units while the post turbo unit is more like a .89 sec/100 degree F unit.

By the way. The max post turbo egt is incorrect on the jpg. It actually reads 1365 degrees F.

 

I would expect there to be a temperature difference pre and post turbine, as well as with points downstream. I don't think anyone mentioned this, but the primary mechanism causing this is simply the expansion of the gases. Even at these temps, the gases will cool as they expand through transitions and into the downpipe, for example. And as was mentioned above, some portion is also conducted and/or radiated away.

It is more complicated in case of the turbo's because a certain amount heat is recovered--converted to mechanical energy in the turbine--as the gas expands through the turbine. This may seem counter intuitive, but it occurs even though these are considered impuse turbines. I will submit that the greater the temp differential across the turbine, the better the design is in converting waste heat back into motion to drive the compressor. (Theoretically this would require less mechanical energy to be extracted from the exhaust gases in order to achive the same amount of power at the compressor, and therefore, would require less impedance to the flow of the exaust gas. This = more HP.)

Just something to think about.