Used cars, does the math work?

[ERD50]

I think those older turbos hold up due to the relatively low boost that they are pushing, maybe 5-7 psi? I run 19 in mine. Thinking about a bigger tmic and header so I can go 25psi or so on e85

Could be, I don't know how much boost mine provides. But if I remember to do it, I can find out and report back.

I have one of those bluetooth dongles that plugs in the OBDII port, and an app ("DASH") on my tablet that provides all sorts of real time data on the engine in addition to any failure codes, and I was looking at the boost pressure last time I used it, but I don't recall the numbers.

What driving condition would you expect max boost? Flat out acceleration from a stop, after enough time for the turbo to spin up?

I'll try to get it to record it to a file so I don't need to try to monitor it while driving.

-ERD50

 

[Big_Hitter]

Could be, I don't know how much boost mine provides. But if I remember to do it, I can find out and report back.

I have one of those bluetooth dongles that plugs in the OBDII port, and an app ("DASH") on my tablet that provides all sorts of real time data on the engine in addition to any failure codes, and I was looking at the boost pressure last time I used it, but I don't recall the numbers.

What driving condition would you expect max boost? Flat out acceleration from a stop, after enough time for the turbo to spin up?

I'll try to get it to record it to a file so I don't need to try to monitor it while driving.

-ERD50

depends on the tune - max boost is usually 4k rpms I think.

yes, if you run a log you can check max psi

 

[ERD50]

I think those older turbos hold up due to the relatively low boost that they are pushing, maybe 5-7 psi? I run 19 in mine. Thinking about a bigger tmic and header so I can go 25psi or so on e85

Could be, I don't know how much boost mine provides. But if I remember to do it, I can find out and report back.

I have one of those bluetooth dongles that plugs in the OBDII port, and an app ("DASH") on my tablet that provides all sorts of real time data on the engine in addition to any failure codes, and I was looking at the boost pressure last time I used it, but I don't recall the numbers.

What driving condition would you expect max boost? Flat out acceleration from a stop, after enough time for the turbo to spin up?

I'll try to get it to record it to a file so I don't need to try to monitor it while driving.

-ERD50

Yes, I tried cranking ti up, within limits of traffic and the law, and I got 5.9 psi on one try, and 6.2 and 7.6 (holding it in 2nd gear) on two others. The app might not catch the peak though, and I couldn't safely/legally spend more than few seconds all out.

But I'm sure it would go no where near 19.

I drive fairly conservatively most of the time. My poor old 16 year old S-40 probably didn't know what to make of this abuse!

-ERD50

 

[Big_Hitter]

I didn't think they ran that much boost. On my e85 map I go over 20psi at WOT.

 

[aja8888]

Yes, I tried cranking ti up, within limits of traffic and the law, and I got 5.9 psi on one try, and 6.2 and 7.6 (holding it in 2nd gear) on two others. The app might not catch the peak though, and I couldn't safely/legally spend more than few seconds all out.

But I'm sure it would go no where near 19.

I drive fairly conservatively most of the time. My poor old 16 year old S-40 probably didn't know what to make of this abuse!

-ERD50

How do you accurately measure turbo boost with an electronic device when most boost gauges are indicating pressure within the turbo intake tubing? Is it some kind of electronic interpolation?

On my turbo diesel, I have a pipe tap in the plumbing to the intake where a pressure gauge is installed. I also have a boost valve that limits my boost to 18 PSI to protect the turbo and in the event of overboost condition. Of course this is on a tuned turbo diesel and it's running a variable vane turbo with no wastegate.

 

[Big_Hitter]

my cobb AP can measure boost

 

[ERD50]

How do you accurately measure turbo boost with an electronic device when most boost gauges are indicating pressure within the turbo intake tubing? Is it some kind of electronic interpolation?

On my turbo diesel, I have a pipe tap in the plumbing to the intake where a pressure gauge is installed. I also have a boost valve that limits my boost to 18 PSI to protect the turbo and in the event of overboost condition. Of course this is on a tuned turbo diesel and it's running a variable vane turbo with no wastegate.

It is just something reported back through the ODB2 port. I use a bluetooth dongle and the "Dash" app on my tablet, and it does the magic.

I have no idea if it is accurate, but since I'm not getting any ODB2 fault codes, and it runs well, I think it's probably right.

Tends to run ~ -10 PSI when I'm decelerating. Not sure what it was at idle, maybe -4? Do those numbers make sense?

https://www.amazon.com/Bluetooth-Di...0051CAE1C/ref=cm_cr_arp_d_product_top?ie=UTF8

-ERD50

 

[aja8888]

It is just something reported back through the ODB2 port. I use a bluetooth dongle and the "Dash" app on my tablet, and it does the magic.

I have no idea if it is accurate, but since I'm not getting any ODB2 fault codes, and it runs well, I think it's probably right.

Tends to run ~ -10 PSI when I'm decelerating. Not sure what it was at idle, maybe -4? Do those numbers make sense?

https://www.amazon.com/Bluetooth-Di...0051CAE1C/ref=cm_cr_arp_d_product_top?ie=UTF8

-ERD50

Unless the engine control system has some way to measure boost pressure (with a sensor) and covert it to an electrical signal, it's probably being estimated. Usually, at idle, most turbos aren't operating in boost mode at all. I don't know what those numbers represent.

 

[Big_Hitter]

those are vacuum mode numbers. no biggie.

 

[ERD50]

Unless the engine control system has some way to measure boost pressure (with a sensor) and covert it to an electrical signal, it's probably being estimated. Usually, at idle, most turbos aren't operating in boost mode at all. I don't know what those numbers represent.

I don't know. It could be calculated. But I would think the engine control system would need to know manifold pressure/vacuum. So maybe there is a sensor?

In the quick search I did between innings, I didn't find anything.

Go Cubbies (grand Slam - yeaaaahhhhhh!) 7-0 bottom of the 3rd

-ERD50

 

[ERD50]

This:

https://en.wikipedia.org/wiki/MAP_sensor

seems to indicate it is a hardware sensor, available over ODB2 port.

-ERD50

 

[aja8888]

This:

https://en.wikipedia.org/wiki/MAP_sensor

seems to indicate it is a hardware sensor, available over ODB2 port.

-ERD50

This is what you have with a gasoline powered engine:

Common confusion with boost sensors and gauges

MAP sensors measure absolute pressure. Boost sensors or gauges measure the amount of pressure above a set absolute pressure. That set absolute pressure is usually 100 kPa. This is commonly referred to as gauge pressure. Boost pressure is relative to absolute pressure - as one increases or decreases, so does the other. It is a one-to-one relationship with an offset of -100 kPa for boost pressure. Thus a MaP sensor will always read 100 kPa more than a boost sensor measuring the same conditions. A MaP sensor will never display a negative reading because it is measuring absolute pressure, where zero is the total absence of pressure. Vacuum is measured as a negative pressure relative to normal atmospheric pressure. Vacuum-Boost sensors can display negative readings, indicating vacuum or suction (a condition of lower pressure than the surrounding atmosphere). In forced induction engines (supercharged or turbocharged), a negative boost reading indicates that the engine is drawing air faster than it is being supplied, creating suction. The suction is caused by throttling in spark ignition engines and is not present in diesel engines. This is often called vacuum pressure when referring to internal combustion engines.

In short, most boost sensors will read 100 kPa less than a MaP sensor reads. One can convert boost to MaP by adding 100 kPa. One can convert from MaP to boost by subtracting 100 kPa.

My diesel need a boost gauge because it's not normally aspirated.

 

[ERD50]

This is what you have with a gasoline powered engine:

My diesel need a boost gauge because it's not normally aspirated.

OK, but if the only difference is an offset, then it's not a significant difference to the end user, the software just accounts for that offset when it displays the number.

I can't see how DASH labels it, I have to start the car to see that display.

-ERD50

 

[DrRoy]

Since my first car in 1981, I have bought new. I try to wait for model year close outs, when the incentives peak to move the old ones off the lot. Over the years I have gotten 15-25% off sticker. My last car was a 2006 Pontiac G6 that I bought for $16K, drove 190K miles until Jan 2015, and replaced with a nicely equipped Chevy Malubu for $21.5. I have helped my sons find used cars several times over the last 5 years or so and most of them were trouble in a short while. New works for me.

 

[Senator]

I always thought a new car was cheaper. The first 3 years are $0 for repairs, due to the warranty. Tires and brake are 100%. When you buy new, you are paying a bit extra for the factory warranty.

A used car, even under warranty, might have only 50% brake and tire life left. It need may need an oil change almost right away. Everything, including ball joints, windshield wipers, seats, tie rods, etc. are worn.

Factor in that you do not know why it is being sold, or if it was abused, and new makes more sense.

 

[Koolau]

I always thought a new car was cheaper. The first 3 years are $0 for repairs, due to the warranty. Tires and brake are 100%. When you buy new, you are paying a bit extra for the factory warranty.

A used car, even under warranty, might have only 50% brake and tire life left. It need may need an oil change almost right away. Everything, including ball joints, windshield wipers, seats, tie rods, etc. are worn.

Factor in that you do not know why it is being sold, or if it was abused, and new makes more sense.

I don't disagree with most of your premise. I think we would have to have some figures and comparisons to really know which gives the best cost per mile. Clearly, the new car gives the most "trouble free" miles (unless you buy a lemon.)

My experience suggests that if you buy an older "cream puff" (low miles, one owner, well maintained) you come out far ahead. BUT you are correct - it's not a guarantee of lower cost miles. That has just been my experience since the last time I bought new in 1991.

My "ideal" car would be one that came from a dealer's lot after a hail storm "totaled" it. Buy it from the insurance company. Fix the glass and drive your $4K "new" car with all the dings for the next 200K miles. But, now were dreaming. YMMV

 

[brett]

We bought a three year old full loaded V6 Honda Accord w/ 25K miles on the clock in 2009. It was $12K less expensive than the new model even with a $500. reserve fund for misc. repairs.

Buying used definately worked for us. We had our last import for 19 years. Based on our experience to date, we expect the same service from this one.

 

[Senator]

I don't disagree with most of your premise. I think we would have to have some figures and comparisons to really know which gives the best cost per mile. Clearly, the new car gives the most "trouble free" miles (unless you buy a lemon.)

The most valuable miles are the ones under warranty. I am not sure how much more they are worth. A used car, still under warranty, should not have significant issues, but will have wear and tear. At least if something goes wrong, you can get it fixed.

I buy at invoice price from my dealer. No haggle in the fleet sales department. Hopefully that is a cheaper way to go than negotiating directly.

 

[GTFan]

I always thought a new car was cheaper. The first 3 years are $0 for repairs, due to the warranty. Tires and brake are 100%. When you buy new, you are paying a bit extra for the factory warranty.

A used car, even under warranty, might have only 50% brake and tire life left. It need may need an oil change almost right away. Everything, including ball joints, windshield wipers, seats, tie rods, etc. are worn.

Factor in that you do not know why it is being sold, or if it was abused, and new makes more sense.

And I've seen 2015/2016 Sonatas on sale in the paper recently for $13k with less than 40k miles on them. These are $20k+ cars, still under warranty.

You can't beat that kind of deal on cars that depreciate a lot in the first couple of years. Prius is another car with heavy depreciation because of cheap gas. There is a tradeoff, sure, but you can save a TON of money on recent used cars if you're willing to shop around and not be obsessed on make/model (at least here in the ATL, that is).

New does not make more sense, financially speaking (in general). But I can understand why folks want to spend the extra for peace of mind and new car smell.

 

[aja8888]

I always thought a new car was cheaper. The first 3 years are $0 for repairs, due to the warranty. Tires and brake are 100%. When you buy new, you are paying a bit extra for the factory warranty.

A used car, even under warranty, might have only 50% brake and tire life left. It need may need an oil change almost right away. Everything, including ball joints, windshield wipers, seats, tie rods, etc. are worn.

Factor in that you do not know why it is being sold, or if it was abused, and new makes more sense.

These days, brake pads last 100,000 miles (except for heavy trucks), oil changes are $50 and good for 7,500 miles, ball joints and other front end/suspension parts are good for well over 100,000 miles +, etc. What I am pointing out is that cars with 50,000 miles or less usually have a long way to go before significant maintenance costs are encountered.

As an example, a 2003 VW Jetta with 296,000 miles on it I bought for less than $1000 to putt around in earlier this year, needed struts and rear shocks. The ones on it were original and for $1500 I had the whole suspension rebuilt. That included struts/shocks, lower control arm bushings, sway bar bushings, ball joints, tie rods and an alignment.

In my opinion, lightly used modern cars, if bought properly, seem to be a better deal that paying for new. Even if they need light maintenance (tires, oil changes, etc) you spend way less than the 30+% you eat in front end depreciation with a new car.

 

[aja8888]

New does not make more sense, financially speaking (in general). But I can understand why folks want to spend the extra for peace of mind and new car smell.

If you really want the new car smell..

 

[Totoro]

In my opinion, lightly used modern cars, if bought properly, seem to be a better deal that paying for new. Even if they need light maintenance (tires, oil changes, etc) you spend way less than the 30+% you eat in front end depreciation with a new car.

=> If carefully bought, 30% depreciation losses aren't the norm anymore. Precisely because the common wisdom has become "buy lightly used modern cars".

As always though, your mileage will vary

 

[meierlde]

Note that if you can find a copy of the warranty manual for used cars you may discover some parts that have longer warranties than the default 3/5 year. in particular emssion control systems warranties (this is gms 2016 emission control warranty for 8/80 "For 8 years or 80,000 miles,
whichever comes first:
‐ If the catalytic converter,
vehicle powertrain control
module, transmission control
module, or other onboard
emissions diagnostic device,
including emission-related
software, is found to be
defective, GM will repair or
replace it under the Federal
Emission Control System
Warranty.
Thus some computer parts (emission related) have an even longer warranty than 5 years. One might check this also before buying a used car.

 

[EvrClrx311]

I ran into something very similar when I was in the market for a new car a couple years ago. I'd never bought a new car before, always believing that the major depreciation came in the first couple years... so getting a 2-3 year old used car seemed obvious for someone like me who drives a car for at least a decade before getting a new one.

What I found, was that the car I wanted to purchase only cost about 7-8% less per used year... leaving me scratching my head thinking why on earth I'd opt to save just 15% of the cost of the car in order to get something that is two years old with 30K miles on it. The math almost worked out as thought the user car was more expensive (odd huh?) when I looked at keeping it till it was aged 10 years or 150,000 miles.

I chalked this up to the extreme discounts car manufacturers give on the trailing end of new model years (I was buying a 2015 car in September of 2015). If you're smart about when and where you buy new... it can be a smart thing to do. Also the peace of mind knowing I'm not getting a car (usually someones leased leftovers) that was run into the ground knowing they were just trading it in after two years for another new car. I think the leasing market is really what is making new car buying cheaper. So many people lease, that the car companies are getting more and more excited about anyone who actually wants to put down cash just to move a car off their lot and inflate their monthly sales numbers.

 

[aja8888]

I ran into something very similar when I was in the market for a new car a couple years ago. I'd never bought a new car before, always believing that the major depreciation came in the first couple years... so getting a 2-3 year old used car seemed obvious for someone like me who drives a car for at least a decade before getting a new one.

What I found, was that the car I wanted to purchase only cost about 7-8% less per used year... leaving me scratching my head thinking why on earth I'd opt to save just 15% of the cost of the car in order to get something that is two years old with 30K miles on it. The math almost worked out as thought the user car was more expensive (odd huh?) when I looked at keeping it till it was aged 10 years or 150,000 miles.

I chalked this up to the extreme discounts car manufacturers give on the trailing end of new model years (I was buying a 2015 car in September of 2015). If you're smart about when and where you buy new... it can be a smart thing to do. Also the peace of mind knowing I'm not getting a car (usually someones leased leftovers) that was run into the ground knowing they were just trading it in after two years for another new car. I think the leasing market is really what is making new car buying cheaper. So many people lease, that the car companies are getting more and more excited about anyone who actually wants to put down cash just to move a car off their lot and inflate their monthly sales numbers.

I would bet that the 15 - 20% yearly depreciation is realized as a price given to you if you attempted to trade in a 1 - 2 year old car to the dealer or sell it outright to Carmax or some reseller.