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Track FD Air Temp Sensor Heatsoak

Old 01-26-05, 06:06 AM
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Track FD Air Temp Sensor Heatsoak

After doing many (if not all) performance-racing mods, and using the search tool, I have not found a clear answer or opinion on the following:

1. the car is a track car only which is road raced in a hot (90F) climate.
2. Everything possible has been done to isolate fresh air through the signal lamp provision - lamp removed - to the filter which is boxed not to receive radiator air(factory headlights changed to fixed type - Rotary extreme).
3. AIT reading at the Power FC climbs to a max of about 87C after about 8-10min of all-out racing, after 80C (prev. raised already) timing retard occurs and power is lost and misfiring starts.
4. Now my concern is how much of the 87C is really due to hot air in the intake track and how much is really sensor heatsoak from the surrounding metal parts.
5. Other threads address only the heatsoak from rest to starting the car again and the damage due to cool air etc., etc., etc. I'm interested only in the racing approach.
6. My concern is that DURING RACING and only if the higher AIT temp is due to sensor heatsoak then retard is totally unnecessary. BUT I don't want to blow the engine during trial & error...
7. Is anyone racing with a relocated sensor to the Greddy elbow and has noticed different AIT reading behavior, or anything that may indicate a previous factory location heatsoak reading vs real air temp. (or same behavior just 10C cooler, if so, then the relocation is totally useless for racing purposes)
8. I've been holding on the relocation due to the fact that I also have a WI system installed at the Greddy elbow and that will only complicate the real temp reading...
9. On race gas what is the highest AIT you guys are using prior to the start of the timing retard sequence.

Again, how much is heatsoak reading vs. actual air temp reading ???

Thanks in advance for your comments
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Old 01-26-05, 11:10 AM
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Gustavo,

I recall you run 17-18 psi on a GT3540, with PFS version of M2 large smic.

Stock sensor location will converge on about correct air temp while lapping, although it does have some lag. Peak will actually be a little higher than what you see on PFC. Is 87C with water inj'n? usually about 10-15% of fuel flow is req'd, so at your power level that's a lot of water. I'd expect more like 60-70C air with large smic and proper water inj'n.

The small inlet on the large smic duct limits airflow and IC efficiency during sustained high power runs. SCC tests with fast response sensors at the IC output showed 70C air temps at the end of a strait, at 12-13 psi on stock twins, with an M2 IC, on a 90+F day.

Your set up should work well. Your coolant temps are below 100C, iirc. The water inj'n should make up for the limited airflow to the large smic, which should have low pressure drop.

If necessary, a cross flow 2 pass rad (like nascar) could be used, with a Mod'd IC duct inlet that goes across the top of rad .. goal inlet area would be 40% of IC face area which is about 200 sq in. Bad news is coolant temps would go up with less air flow to rad. Another option is convert what you have to a V-mount. But 1st try to get water inj to work right ... easiest fix ... cooling in a refillable bottle.

Also, make sure the large PFS IC has a low pressure drop (early M2's were high).
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Old 01-26-05, 12:00 PM
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Hi Kevin

Yes, 87C is without water injection.
I'm trying to work with a modified duct to feed more air into the IC somehow.
I just keep trying to make the set-up as effecient as possible without relying on WI to cool, although, I may switch it on during the last laps of a heat when AIT sensor driven retard kicks in.

Based on your response, I should undersand that the relocation is not necessary since the reading is correct at the stock location and not due to sensor heatsoak.

Any comments on the highest temp at which to start the retard sequence based on your experience.

PS: with WI (using the same maps and boost level) I get 380rwhp and without 400rwhp, therefore, I'm just using WI as a last option at the end of the time trial heat when retard will do obviously worse...
I can't give you temps with WI at the track since I really have not used it much while trying to make the set-up work without WI (BUT I'm very close to giving up and start focusing on WI tuning).

Thanks again
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Old 01-27-05, 10:26 AM
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Can't advise on timing maps ... I think there is a datalogic/PFC egroup that you could join that might be usefull.

To get max hp benefit of water inj, timing must be advanced, and/or mix leaned out. Agree that to rely on water would require some automated safeguards .... monitoring injector duty cycle and water supply pressure, etc.

For track car, I'd consider tilting the rad down, and going with a new top tank that is more triangular .... this would provide a nice gap along the top or rad for duct inlet.

Note that I use a 1/8" grid metal screen that generally fronts and is parallel to the radiator core, to reduce rock and bug damage to rad on track.
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Old 01-27-05, 08:10 PM
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Any pics on the tilted rad and IC duct.

Please post or PM. Thanks.

Have experienced the impact between high presurre drop large SMIC vs the newer low pressure more efficient designs? I suppose PFS is old plate type.
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Old 01-27-05, 08:11 PM
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I meant have you experienced .....
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Old 01-27-05, 09:23 PM
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I have my ATS mounted in the FMIC outlet neck. Living in Houston was my reason for a FMIC and the relocation was for accuracy. During 80-90F outside air temps and a few repeated 4th gear tuning runs, my air temp will go up to about 42C. That was with the stock turbos and 15PSI boost.

Almost no heat soak in slow traffic. After parking then driving, the air temps will come down to normal in about 3 miles of freeway driving.

A friend uses his water injection to cool his system down between runs or after heat soak. His ATS is in the Greddy elbow.

You will have to do a little tweeking of your Air Temp vs INJ map with the change.

You can slowly grind away the black outer cover of the sensor tip untill you see clear or blue plastic or something else. This will increase the sensor's sensitivity to temperature changes. I had a spare sensor and had decided to experiment.
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Old 01-28-05, 11:25 AM
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Like Chuck, my AIT sensor is in the SMIC IC outlet pipe. The worst I've seen is 48 in traffic and 42 at a slow track in 90F temps. Generally it's about 10C above ambient.

Regarding radiator relocation and IC ducting, I made some plates to fit on the sway-bar mounts which drop the radiator abbut 1.5 inches (you must cut off the existing rad mounts). Then relocated the relay box and made a duct which can now run the entire length of the IC. It has made a huge difference.
Attached Thumbnails Track FD Air Temp Sensor Heatsoak-ait.jpg   Track FD Air Temp Sensor Heatsoak-front.jpg   Track FD Air Temp Sensor Heatsoak-duct1.jpg   Track FD Air Temp Sensor Heatsoak-duct2.jpg  
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