So after reading this thread I decided to take my stock box cover off and take a drive for lunch.

Comments: It's louder and meaner sounding but not as much louder as I was expecting. It "sounds" smoother now which might be adding to the feeling of smoothness so I like it. I did notice that when coming to a stop and dropping to neutral from a 2,000rpm decel the rpms don't dip down as fast as they did with the box intact. They hover at 1200 for a second before settling down to 800-900 like normal.

But, I agree with thomsbrain....there is no way that it's better to run with it off from an intake temperature standpoint.

 

^^^^This X2

 

i hope you took in to account for windchill.. moving air generally tends to read colder.

to properly read temperature you need to shield the probe from moving air.

hence.. if you put the probe in the box it's gonna read hotter then if you put it behind the radiator.

There was a test done on a civic measureing air temperature through out the engine compartment. result ... 1-2 degree difference on all spots of the engine bay once the car is moving.

 

Wow, 30-40° hotter goes against everything I've ever read from others that have recorded temps from the car. Without knowing what conditions you were testing in, I wonder if your numbers are correct since they out-lie other data I've seen.

From all other reports I've seen by other S2000 owners, the intake temps (not airbox temps) will be 10-20° hotter with the lid off when you are driving. Idling, intake temps increase faster because the hot air more easily gets into an open air box, and airbox temps do not drop as quickly when the lid is off, but do "normalize" at ~10° hotter when moving. I'd like to know your testing methodology as I'm always interested in new data sets.

 

I don't think probes were used - he used a Scangauge so it is piggybacking of the OBDII system in the car and seeing what the car sees as intake temps. In any event, if the recording method is the same, it wouldn't make a difference since you want to see differences, not absolutes in this case.

 

Taking the airbox lid off is why I bought an intake. The Fujita CAI sounds quite a bit better than the airbox lid off IMHO, but it's the same type of sound, and that gets into personal preference more than anything. I liked that sound enough for it to be well worth the $200, so it was a great purchase.

On power gain or loss, who cares? A loss or gain of 2hp or 5hp is a change of 1% - 2.5% of the power of a stock car. So the airbox loss or CAI gain produces the staggering change of [sqrt(1+(%%))-1] = [0.5%-1.2%] times your acceleration rates compared to stock. But hey, every 1% counts, right?

 

I don't think the minor power loss is an issue, I think most people just want to know if it is detrimental to the car in any way besides performance, which it is not. Its an inexpensive way to change the S2000's aural nature without doing any damage to the car.

 

Ah, well then I'm with you 100%.

I can understand not liking bog--fine. But when I hear heat soak is so terrible for power I just don't get it. It's worse than stock, sure, but having a full tank of gas is even more detrimental.*

To anyone who has never tried taking the airbox lid off and is curious, TRY IT! Nothing will break, and from what I've seen, most people prefer the sound of the car without it, YMMV. If you like it, think about an intake. They can sound a little better still.




*For anyone who cares, 13 gallons * 6.175 lb/gal = 80lbs = 2.7% of the car and driver's weight. That negates over 5 whp to balance the P/W ratio on a stock S2000.

 

I think heatsoak can yield a hp difference much more than 5 whp, no?

 

It was hardly a scientific experiment in a controlled environment! But morning temps in my area are a pretty stable 40 degrees or so (I live near the ocean), and I enjoy watching my intake temps on the Scangauge and comparing it to the ambient temps reported on the instrument cluster (among other data), so I've logged a lot of informal seat time thinking about this particular issue. I generally leave for work in the morning, climb a 2000 foot high freeway mountain pass, then coast down the other side over my 35 mile morning commute. So I have a fairly unique opportunity to watch temps over extreme conditions, which exaggerates the results and makes the behavior much more clear.

By the time I reach the summit with the lid off, intake temps were consistently over 100 degrees, sometimes over 110 degrees (ambient around 40-50 degrees). This is a sustained heavy-load situation on the engine because of the steep grade. With the lid on, I read 60-70 degrees (same ambients). So that's a 30-40 degree difference under high load, high speed conditions.

The behavior on the downhill side is the opposite. With the lid off, the intake temp DROPS the longer I coast in gear (fuel shutoff mode). It can be as low as the high 80's by the time I reach the bottom. With the lid on, temps RISE the longer I coast in gear (fuel shutoff mode means very little cool air being drawn into the system and the tubing gets hotter). Lid-on intake temps at the bottom of the mountain have usually climbed to the low 80's. Keep in mind I am essentially coasting for close to 10 miles straight. So under low-load, high-speed conditions, the temp difference is small, maybe 5-10 degrees.

When I reach the bottom and get back on the gas, lid off results in temps climbing slowly, while the lid on results in temps dropping rapidly, returning to a larger differential between the two options.

Sorry to go against popular opinion, but when idling, temps increase faster with the lid ON, not off. With it off, the fact that you aren't moving is likely counter-balanced by the fact that you aren't dumping as much heat from the radiator (because the engine isn't producing as much heat). Temps stay in the 100-110 range when I reach my freeway exit and sit at the stoplight. Lid off obviously takes all its air from the engine bay. Because those temps hardly change whether you are driving or not, you can deduce that engine bay temps don't change very much whether you are driving or not.

So now we know engine bay temps are staying roughly the same regardless of the situation and that the heat of the engine bay would obviously heat up the intake tubing. The harder you run the engine with the lid ON, the more cool air is sucked into the intake tubing from outside the engine bay. So at idle, there's very little cool air and a pretty steady amount of hot air on the other side of the tubing. In high-load situations, there's a lot of cool air with roughly the same amount of hot air on the other side. The result is that idle warms up the intake charge, and heavy throttle cools it down.

The point either way is that with the lid off, the heat you are producing from the engine and radiator is what largely determines your intake temp. More heat = higher temp. With the lid on, the rate at which you are sucking air is what largely determines your intake temp. More throttle = lower temp. Since we only care about power when we are hard on the throttle, I'll happily put my money on the lid on making more power since it gets cooler in that situation instead of hotter.

I know some people on this forum have said otherwise. I disagree with them.

For the record, I much prefer the sound with the lid off (very throaty!) and the car is still fun to drive that way, it's just a trade-off of where the fun is coming from. There's no right or wrong for how people want to run their own cars. I'm not even particularly sold on doing it one way for my own car.