Question about Boost and Temperature

[Smokie]

I have now enjoyed my Kit since May and in Florida the weather usually is hot and not as hot. I had always noticed that boost under WOT would go between 9-10 on the gauge so it is exactly what I expected from my base kit.

Today is the first time since May that I have been out for a drive with morning temps around 60 degrees and low humidity 42%. The gauge during several test runs went over 10 psi every time and to 10.5 once when I had enough room to let the rpm's rise a bit.

The car felt much stronger than usual, do you guys that have this set-up in colder air see an increase in psi readings or the do you think my gauge is wacko???

[King Fubar]

It does feel different, I haven't watched my boost gauge but you have to take into consideration not only is the air colder it's dryer, with the less humidity the air is more than likely slightly thinner than it is during the summer months.

That may have something to do with it.

[TripleTransAm]

I'm not familiar with the details of the supercharger setup (plumbing, location of sensors, etc.). So here's my wild-a$$ guess...

Could it be a case of colder denser air being ingested and then subsequently being heated to expand to a greater overall pressure once inside the intake or wherever the boost gage sender is located? In other words, the colder very dense air expands to a higher pressure once heated to a certain temp as opposed to slightly warmer less-dense air heated to the same temp?

[Smokie]

??????????

[TripleTransAm]

If that was directed to me, let me change my wording...

I think if you took hot air and put it into a hotter bottle and sealed it, the air would expand to result in a certain in-bottle pressure. If you took cold dense air and shoved it inside the same hot bottle, the air would expand to result in a higher in-bottle pressure.

In this case, the bottle is the plenum or intake plumbing, which is at a certain temperature related to the engine block's operating temperature. However, the colder denser air has more molecules per unit volume and hence would result in a higher in-plenum pressure once heated.

Like I said, just a wild a$$ guess...

[Hotrauder]

Smokie,
Save about 6 of those ? for me. I don't have a clue except that my car has always run better the cooler it is. Especially now and a few degreesa seems to make a difference. These lower humidity days are good to. Perhaps I just feel better myself and am more into the car on those good days but I really think the car does indeed run better. I read posts of members wishing for cool weather to run in. ?? My S/C experience is to new to note pressure changes but I will made a scientific study every time I get a chance and report back:D Dennis

[DEFYANT]

My boost guage also shows *more* boost when the temps are cold. It is normal

[Smokie]

If that was directed to me, let me change my wording......

Thank you, I do appreciate the input. I tend to agree with your explanation, I thought maybe some Trilogy owners could say "yes my boost increases about 1 psi when it's cold and dry"...or... "no it does not happen to me, your gauge is wacko"

[Haggis]

I'm not familiar with the details of the supercharger setup (plumbing, location of sensors, etc.). So here's my wild-a$$ guess...

Could it be a case of colder denser air being ingested and then subsequently being heated to expand to a greater overall pressure once inside the intake or wherever the boost gage sender is located? In other words, the colder very dense air expands to a higher pressure once heated to a certain temp as opposed to slightly warmer less-dense air heated to the same temp?
Thank you Steve for hitting the nail on the head.

[Smokie]

My S/C experience is too new to note pressure changes but I will made a scientific study every time I get a chance and report back:D Dennis

Dennis, I knew I could count on you.:beer: Be safe during your scientific studies.:burnout:

[Kennyrauder]

Kennyrauder says it's the cooler weather that results in denser air being drawn into the intake system whih results in more HP & more boost pressures. In Northern Ontario Canada you would not believethe difference in performance. Try 10 F !!!!

[SergntMac]

Kennyrauder says it's the cooler weather that results in denser air being drawn into the intake system whih results in more HP & more boost pressures. In Northern Ontario Canada you would not believethe difference in performance. Try 10 F !!!! Which is why wise, more northern owners, like HwyCruiser, install a larger pulley creating less boost in very cold temps.

[dwasson]

When it gets cold enough you can feel the difference in a NA Marauder. The denser air requires more gasoline to reach the stochimetric ratio. More gas and air = more HP.

By the time I parked mine for the winter I had driven in on a couple 30 degree days. It ran like a scalded dog.

[BillyGman]

Hmmmm, I never noticed the boost gauge in my Marauder going any higher during WOT in colder temperatures. But it isn't like I'm ever watching it all that close anyway. I look at it every once in awhile. Maybe I'll check it out again tomorrow during a WOT blast since it's been in the lower 40's here lately.

[jdando]

I will look at my gauge this weekend also. Our temps are highs of 20F and lows of 8F. That should be worth some psi :cool:

Maybe I can tear the carcasses of my snows when it gets to -20F in two months:D

jeremy, quality of life in minnesnowta

[BillyGman]

....Maybe I can tear the carcasses of my snows when it gets to -20F in two months:D

I can relate to that. ;) ..(just watch out for that sand thrown on the road......once you hit it, it's like your car is on marbles, and it just won't stop until it hits something despite the anti-Lock brakes......don't even ask me how I know that :rolleyes: )....

[spiders]

For us in the eastern states it's a black ice week. Last night I watched two rodders playing on a side street, they both hit the ice none of us could have seen, then both ended up in the shoulder ravine in heartbeats... a mess, but a reminder that it isn't always as good an idea in that cold air to play too much and definitely not on roads where they'd had light rain in the preceding hours... thankfully they were both later model camaros (affectionately called commodes around here) so no painful losses...and yes, people were fine, even if stupid, too young, and wholly unworthy of v8's due to lacking driving skills. What are we doing with the kids these days????

[BillyGman]

I hear ya. I usually don't play around once the temperatures get below 40 degrees, since there's always a chance of black ice lingering around once the temps fall into the 30's (especially when the sun goes down).

BTW, the high temps around here were again in the low 40's today, and I hammered on the gas pedal three separate times to see what the boost gauge read during WOT, and all three times it read the exact same thing that it does during 80 degree temperatures.

[DEFYANT]

Maybe I see more than the advertised boost because I have the JLT? If I remember correctly, after the JLT on the stock pully, I saw a solid 10lbs on cool days.

[Hotrauder]

Dennis, I knew I could count on you.:beer: Be safe during your scientific studies.:burnout:

Smokie, Very controlled scientific tests over the past 2 days have confirmed your suspicions...More boost pressure on cooler days..up to 10.5 to almost 11 yesterday. If I can just get the temps down to -244*F this car is a killer!Dennis:beer:

[BillyGman]

Maybe I see more than the advertised boost because I have the JLT? Yep, that could be.

[Smokie]

Maybe I see more than the advertised boost because I have the JLT? If I remember correctly, after the JLT on the stock pully, I saw a solid 10lbs on cool days.

Keep in mind, my original question was based on a noticed boost increase when the temperature/humidity dropped (an increase of nearly 1 psi) I've had a PHP air box since the day the Kit was installed.

So what I am asking is: does your boost increase when the temperature drops? if it does, what number does it change to? My usual psi is XX, when is cold my psi is XX.

That is the kind of feedback I was hoping to get, of course if you notice no change whatsoever, I am also looking for that type of response.

I also am aware that here in Florida some of our T-Kit owners have observed between 10-11 psi right out of the box with their BASE kit on 100% OEM exhaust, that to me suggests that a free exhaust would show a lower psi than a stock one.*

*or the gauges have fairly large margin of tolerance.

[SergntMac]

*or the gauges have fairly large margin of tolerance. Yes, the do.My Autometer gauge reads 14 PSI of boost, the MAP sensor reports 17+. Don't know which is correct, but I'll side with the sensor until I know more.

[Tallboy]

There is definetly quite a variance in guage readings. Carfixer and I have researched this thoroughly and "test-swapped" more guages than I can remember. The guage is more like a "ballpark" reading, IMO. However, once you get used to what your guage reads, you can tell if it's reading higher than "normal". In short, both Smokie and Mac are correct.

[QWK SVT]

Keep in mind, my original question was based on a noticed boost increase when the temperature/humidity dropped (an increase of nearly 1 psi) I've had a PHP air box since the day the Kit was installed.

So what I am asking is: does your boost increase when the temperature drops? if it does, what number does it change to? My usual psi is XX, when is cold my psi is XX.

That is the kind of feedback I was hoping to get, of course if you notice no change whatsoever, I am also looking for that type of response.

I also am aware that here in Florida some of our T-Kit owners have observed between 10-11 psi right out of the box with their BASE kit on 100% OEM exhaust, that to me suggests that a free exhaust would show a lower psi than a stock one.*

*or the gauges have fairly large margin of tolerance.


It's Lightning information, but very applicable to the situation:
On very warm days (80* and above) I see measure boost of 12-14lbs
On cool days (55* and below) I easily see 15 and sometimes 16lbs

Freeflowing exhaust will reduce the amount of boost measured, in most applications. This is most typically seen with headers and cats, not just a cat back. As boost is only a measure of backpressure, a more efficient process can result in less measured boost, with more airflow and more resultant power. The more air and fuel that you can get into the cylinder the more power you will make.

[MikesMerc]

Colder air produces more boost pressure.

The colder the ambient air temps, the denser the air charge, the more air molecules per CF (cubic foot).

Because the compression process heats the charge to "similar" range of temps regardless of ambient temps (due to the intercooler), the more boost you will see when colder ambient air is used to begin with. At any given temperature, the "space" between air molecules is fixed. So, when you start with more air molecules to begin with, and heat it to the same temps, you created the need for more space. And when the space if constant, you get more pressure.

[BillyGman]

There is definetly quite a variance in guage readings. Thanks for that info Chuck, but even though those boost gauges aren't incredibly accurate, aren't they repeatable? if so, then we can still use the guage we have for air temperature comparisants at WOT. And my guage reads the exact same thing at WOT at 80 degrees than it does at 40 degrees.

[Tallboy]

Thanks for that info Chuck, but even though those boost gauges aren't incredibly accurate, aren't they repeatable? if so, then we can still use the guage we have for air temperature comparisants at WOT. And my guage reads the exact same thing at WOT at 80 degrees than it does at 40 degrees.

Yes. I agree they are repeatable.

As fas as boost levels at 40 degrees, you'll just have to show me.

Again.:D

[SergntMac]

Funny, I never thought of boost as being a static, specific, or exact number. I've always looked at it as an "-ish" number.

For example, my 3.48 pulley on my Vortech V2 S Trim produced 9.5 PSI of boost on my MM, but that same blower and pulley on another MM only makes 8 PSI, and another MM makes 10 PSI. This doesn't surprise, nor, disappoint me, I've always thought that was just the way it is.

Kind of like the difference between a digital clock, and an analogue clock, one tells you it's 2:50 PM, the other shows "ten to three." I've always thought of pulleys and PSI as producing boost "in the neighborhood of X".

At least this is the way I hear it when listening (or, reading) other's accounts. LOL, when folks ask me, I must sound specifically vague.

[Tallboy]

My guage doesn't seem to be reading noticeably higher in the colder weather.

I'll keep my eye on it, though.

[BillyGman]

okay, for what it's worth.....yesterday it was merely a cold 18 degrees with the sun shining and the roads were nice and dry, so I stomped on it on the open highway (yes Chuck, I was going north ;) ) and I glanced quickly at the boost guage during full throttle, and it read 11 PSI, and that was a first for my car. I know that the boost gauges aren't always super accurate, but like Chuck and I have stated earlier in this thread, atleast they probably are repeatable, which is all that's needed for a comparisant of boost changes in various air temperatures.

For whatever reason, I guess it takes some extremely cold weather for my car to have extra boost, because during temperatures in the lower 40's, I haven't seen enough of a change in the boost pressures for it to register on the boost gauge.

[Marauderjack]

My thoughts.....

Colder/Denser air simply makes more power....More power makes quicker revving.....Quicker revving makes higher 1-2 shift point by 50-100RPM's??:bows:

This and the fact that the mechanical blower is stuffing more (denser) air into a finite space equals increased realized boost??:rolleyes:

Try the same run in 100* air and see what happens?? Maybe 7-8 PSI is what I would expect?? Am I wrong??:confused:

I have had a couple of WOT runs yielding 12 PSI and I was shocked!!:help: Dave at Injected Racing said that was not unusual with air in the 50* range!!:bows: Scared me though??!!:(

Marauderjack:burnout:

[Smokie]

I won't see 18 degrees here, when I started this inquiry I thought temperature alone was the greatest factor, but I think humidity also played a role, my original findings were on a day were the temp. was about 60 degrees/42% hum. Last night it was 59 degrees/86% humidity and the gauge did not go past the 10 psi mark as before.

Not scientific but I think both temp and humidity combine for the higher boost readings.

[TripleTransAm]

The increased humidity must lubricate the sender. :)

(yes, I'm kidding...)

[Tallboy]

okay, for what it's worth.....yesterday it was merely a cold 18 degrees with the sun shining and the roads were nice and dry, so I stomped on it on the open highway (yes Chuck, I was going north ;) ) and I glanced quickly at the boost guage during full throttle, and it read 11 PSI, and that was a first for my car. I know that the boost gauges aren't always super accurate, but like Chuck and I have stated earlier in this thread, atleast they probably are repeatable, which is all that's needed for a comparisant of boost changes in various air temperatures.

For whatever reason, I guess it takes some extremely cold weather for my car to have extra boost, because during temperatures in the lower 40's, I haven't seen enough of a change in the boost pressures for it to register on the boost gauge.

[I'm smiling as I read this] Sounds like fun! See you in a few weeks...:burnout:

[RF Overlord]

The increased humidity must lubricate the sender.Note to /Steve: this is not an oil thread. Words like "lubricate" are not allowed in regular threads.

by Official Proclamation of the RF Oil-Lord...