quick question. How hot would be regarded as too hot for an intake temp?
I installed a homemade grill block in my 2007 ford ranger (I know not the ideal mpg vehicle). Intake temperature used to be close to ambient before the block, now it runs about 20 to 25 degrees C hotter than ambient. This will be fine in the winter but that is about 130 degrees F on a warm day. The coolant temp is fine (scan gauge to monitor both).
I have yet to make a trip test over ay distance so not sure of any mileage benefit at this point.
If the air is too hot, there could be some pre-ignition. The knock sensor will pick this up (maybe even before you hear it) and then the ECU may richen the mix and/or retard the timing. This would lower your mpg.
I don't think that 130 F is that terribly hot- I would think that 150 F would be a little too warm. If your mpg goes down, perhaps you could make a duct that draws in cooler air from the lower rear part of the engine compartment.
I had a K&N intake on my 2008 Civic Si. During the summer, with ambient temps of 100-105 degrees, I saw between 138-144 degrees on my intake air temp, according to my Scangauge. I had no preignition, but my car also had variable valve and ignition timing.
I have one on my car and with the weather change, I am running around 155F. During the summer my water and intake ran close to the same temperature. I don't notice a big power loss but I have been running the intake so long, I may have just gotten used to it. Mileage isn't super but every bit helps.
I think my max IAT was around 184 or so.
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When I had my 1998 Saturn SC1 I installed a HAI. I saw the biggest MPG gains with intake temps around 150 degrees F. Once intake temps exceeded this, power drastically dropped as I saw ignition timing nose dive. I saw intake temps as high as 190 degrees one summer day and the car had lost so much power that it was difficult to accelerate to get on the highway.
However, every car will respond differently. The best thing to do is to monitor ignition timing without the grill block. Then install the grill block and see if ignition timing drops a lot when intake temps increase. Keep working on hotter intake temps until your ignition timing starts to really drop, at which point try to keep intake temps a bit cooler than that point.
I've been trying to determine the right temp for my '00 RAV4. My mileage increases around +7 MPG if I go from 70F to 130F intake temp. BIG difference.
But I'm getting pre-ignition. No codes (CEL does work), The pre-ignition seems to lessen some when I lower the intake temp. But even at 80F there's some pre-ignighting going on. I'm wondering if there isn't some other issue there?
I asked a Honda/Toyota/Subaru expert if he knew a good temp to stay below for mechanical/wear & tear reasons. He wasn't sure, but said there are some Honda cars that have a sensor for AIT. When it gets to 120F it starts cooling it down. He suggested staying below that.