Go ahead...ask those car questions you were always afraid to ask...

[StormChaser]

Why does the AC go from cold to warm when I drive aggressively or use WOT? It's not just this car, several cars I've owned have done this. Heat soak? Some sort of WOT cut out for the compressor? Why? Annoying!

[MAG58]

Most cars have the compressor shut off a grand or so before redline (some more some less), or when you open the car up to WOT. It's done to reduce parasitic drag on the engine as well as keeping the compressor for overspeeding.

[efrie]

Why does my F150 squeak when I go backwards? All new brakes, everything is good to go.

[Assle]

Probably because one of the caliper bolts is seized. This is what happened to me. The squeak would only happen when backing up, then when only turning left and backing up, then would start happening all the time.

[spitfire1]

most cars turn off the ac at wot, was told from a vw instructor its to free up hp and reduce drag on the engine

[spitfire1]

question regarding intake temperature and octane

i was told on another forum that decreasing the engine bay temp, leading to lower intake temps gives you a theoretical octane boost

can anyone confirm/ deny, or explain?

engine bay temp has nothing to do with engine internal temp. plus temp has nothing to do with octane. lower intake air temp will give you more hp because the air is denser than hot air.

[TwoLitreVW]

Why does my F150 squeak when I go backwards? All new brakes, everything is good to go.

where's the noise coming from?

how old is the truck?

when was the last brake job?

what shape are the ball joints and bushings in?

[efrie]

Wow, didn't think anyone would respond.

Ball joints and other bushings are in okay shape for the age of the truck, it's a 1996 with 160,000 miles on it, 4x4.

I just replaced the pads on the front, the caliper bolts seemed fine, as in, no pad was worn worse than the others. Took off the drums to change the shoes and they still had tons of pad left, so I just tightened out the rear brakes.

I'm kind of thinking it's something in the rear, probably the drums, it's not anything major enough for me to really care about. It's a 16 year old vehicle, if it doesn't make noises it means it's not going down the road.

[Snake Hips]

To which are you referring? I've never seen a positive displacement style setup running blow through carbs. There are generally benefits and drawbacks of each, but draw through is usually run on a positive displacement supercharger and doesn't really require much carb modification over a re-jet since it's still seeing atmospheric pressure. The issue with draw through setups is that they can only live so far away from the intake valve since keeping fuel well atomized and distributed throughout the intake is fighting a losing battle. Also IMO it's a poor decision to run a draw through and an intercooler. You've basically created a phenomenal combustion chamber for if (when) the engine spits back through the intake valve. Blow through carbs are most often run on centrifugal superchargers and intercooled turbo setups (though the VW air cooled turbo guys LOVE draw through carbs). The benefit to a blow through setup is that you can pressurize and intercool the charge before you add fuel and you have a much shorter length of 'wet' intake. The downside is that you cant just run any ol' carb. The carb needs to be modified and setup for blow through forced induction. As far as a blow-through roots setup, the ENG-Tips forum seems to agree that there is increased pumping losses at part load and fuel consumption issues. IANAE so I wouldn't be able to detail out what exactly would cause those pumping losses, though I do believe Corky Bell thought a blow through roots could increase the polytropic portion of putting fuel in the intake tract i.e. it will cool off the pressurized charge more.

I wasn't referring to either because I wasn't really aware both types of induction existed in the car world. I work on airplanes, and airplanes are simple, much (MUCH) simpler than cars; all of my car knowledge basically comes from here. Airplanes: intake > carburetor > supercharger > cylinder. OR: intake > turbocharger > carburetor > cylinder. So I wondered why in cars the supercharger came before ("upstream of") the carburetor. I wasn't aware both setups were used in cars. So thanks for all the info, it was really pretty enlightening!

[Mayerz]

I just did a 2200km trip from montreal QC to moncton NB and back so i had a long time to think and wonder stuff.

If i have half a tank of 91 octane gas, and put another half a tank of 94 octane gas, does it become 92.5 octane?

[saron81]

I just did a 2200km trip from montreal QC to moncton NB and back so i had a long time to think and wonder stuff.

If i have half a tank of 91 octane gas, and put another half a tank of 94 octane gas, does it become 92.5 octane?

Yes... infact, 91 octane gas from the pump is just 89 and 93 mixed together. They only have two storage tanks. Regular, and premium.

[helement2003]

I just did a 2200km trip from montreal QC to moncton NB and back so i had a long time to think and wonder stuff.

If i have half a tank of 91 octane gas, and put another half a tank of 94 octane gas, does it become 92.5 octane?

Essentially, yes.

People do this frequently to get higher octane. Mix some 100 with 91 to get a good 93-94 in the tank, etc.

There are even mixed octane calculators out there:
http://www.wallaceracing.com/octane-mix-calc.php

[Mayerz]

Cool thanks!

[Tourenwagen]

Assuming a 350 mile per week commute - would it be cheaper to own/run a diesel car than it would a petrol car? For purposes of this question I'm looking at a used '09/'10 Jetta.

[envy.]

What are those red things behind the grille on all the modified turbo cars I see?

[adrew]

Hella SuperTone horns

[adrew]

Assuming a 350 mile per week commute - would it be cheaper to own/run a diesel car than it would a petrol car? For purposes of this question I'm looking at a used '09/'10 Jetta.

Looks like most TDIs average around 40 MPG on Fuelly.

TDI: 18,500 miles/year ÷ 40 MPG = 462 gallons/year
Gas: 18,500 miles/year ÷ 30 MPG = 616 gallons/year

So, at $3.70/gallon, the TDI will save you $570 a year. Is that worth it to move to different car? Keep in mind when buying used that you will not get complimentary service and TDIs have pricier oil changes and a timing belt you'll have to do every 5 years, eating up some of the fuel savings.

If you go from a 30 MPG car to a 50 MPG Prius, you will save $900± a year.

[envy.]

ah HA! I always figured it had something to do with turbo setups since I only ever saw them on STI/WRX/MS3/EVO/etc cars.

surely you can see now why I was "always afraid to ask"

[StormChaser]

Assuming a 350 mile per week commute - would it be cheaper to own/run a diesel car than it would a petrol car? For purposes of this question I'm looking at a used '09/'10 Jetta.

Not sure about used, but for a new Jetta, the ROI (return on investment) is at about 75,000 miles. That means you don't even make up the extra cost for 75,000 miles...then you start seeing savings. If you provide the price of the car you are looking at and the price of an equivalent car with a non-diesel engine, we can calculate the ROI.

[Air and water do mix]

Not sure about used, but for a new Jetta, the ROI (return on investment) is at about 75,000 miles.

Does this include increased worth at trade-in time? If the car is worth $1,000 more than an equivalent gasser at $75,000 miles, how does that effect the calcultations?

I don't know their KBB numbers used and haven't run the numbers, I'm just playing devil's advocate.

[FissionMailed]

Guessing the answer is no on this, but worth asking:

The US spec Honda CRZ comes with two worthless and bizarre seat-shaped storage bins behind the front seats.

The JDM Tyte edition comes with two equally worthless actual seats and seatbelts.

What if somebody were to acquire SuperHella JDM Extreme OEM+ backseats from a JDM HellaTight CRZ and throw them into a US spec CRZ? Legal?

[StormChaser]

Does this include increased worth at trade-in time? If the car is worth $1,000 more than an equivalent gasser at $75,000 miles, how does that effect the calcultations?

I don't know their KBB numbers used and haven't run the numbers, I'm just playing devil's advocate.

No, it didn't include value differences at trade in because value for a used car varies way to much to be consistant.

[Tourenwagen]

Looks like most TDIs average around 40 MPG on Fuelly.

TDI: 18,500 miles/year ÷ 40 MPG = 462 gallons/year
Gas: 18,500 miles/year ÷ 30 MPG = 616 gallons/year

So, at $3.70/gallon, the TDI will save you $570 a year. Is that worth it to move to different car? Keep in mind when buying used that you will not get complimentary service and TDIs have pricier oil changes and a timing belt you'll have to do every 5 years, eating up some of the fuel savings.

If you go from a 30 MPG car to a 50 MPG Prius, you will save $900± a year.

Very comprehensive answer, thank-you. The TDI still makes for an attractive commuter option since I am looking to pick something up used as an additional vehicle versus trading what I have.

[Tourenwagen]

Not sure about used, but for a new Jetta, the ROI (return on investment) is at about 75,000 miles. That means you don't even make up the extra cost for 75,000 miles...then you start seeing savings. If you provide the price of the car you are looking at and the price of an equivalent car with a non-diesel engine, we can calculate the ROI.

Appreciate the offer but this is early research. Assuming I would be somewhere between $15k and $20k though for both vehicles depending on mileage, condition etc.

[WD-40]

Very comprehensive answer, thank-you. The TDI still makes for an attractive commuter option since I am looking to pick something up used as an additional vehicle versus trading what I have.

It's not all about economy and ROI... For a commute vehicle, range and the associated convenience are huge benefits for the TDI.


So we take adrew's numbers:

TDI: 18,500 miles/year ÷ 40 MPG = 462 gallons/year
Gas: 18,500 miles/year ÷ 30 MPG = 616 gallons/year

and divide those by the 14.5 gallon gas tank size, and you're looking at a minimum of 32 fillups on diesel, and 43 on gas, assuming you run the tank 100% empty (which you wouldn't do). That's an extra 11 times that you don't have to stop at the gas station.


Looking at it from a different angle, if the weekly commute is 350 miles, that's more than the gas Jetta's 326 mile range for a full tank (you'll be filling up more often than once a week)... whereas it's comfortably less than the TDI's 431 mile single-tank range. So with the TDI, you could have a weekly routine ("Get gas on the way home from work every Thursday"), with 80 miles of wiggle room, whereas the gas Jetta would leave you filling up at odd times because you had to or you would run out of gas.

[SoTxBill]

The Greenstuff pads are not super aggressive, so it shouldn't throw out the bias by any noticable amount. I wouldn't bother until the rears are due to be replaced.

Do you get along with your better half?

[FreshBaked 24 7]

If my car has TPMS and I put rims on it that don't have TPMS sensors, my cluster will read that "tire pressure low"

Is there anyway to fix that without having to rebuy wheels that have sensors?

[One_Off_Volk]

Could I put an intercooler behind the grill to keep the stock front bumper instead of getting an aftermarket Corrado bumper? Is it possible to do that so it mounts behind or in front of the radiator?
Stupid question :/

[DarkNeo]

If my car has TPMS and I put rims on it that don't have TPMS sensors, my cluster will read that "tire pressure low"

Is there anyway to fix that without having to rebuy wheels that have sensors?

Disable TPMS via VCDS

[MrMook]

Could I put an intercooler behind the grill to keep the stock front bumper instead of getting an aftermarket Corrado bumper? Is it possible to do that so it mounts behind or in front of the radiator?
Stupid question :/

This isn't a turbo-building thread, but I'll play:
If you mount it in front of the radiator, you're compromising the radiators cooling capabilities, if you mount it behind, the IC is limited now, as well. This is why FMIC's are typically mounted low in the bumper. Part of building a turbo car is solving fitment issues like this. Get creative, and go read other build threads for inspiration.

[ohsnappe2]

why not wrap the whole car in clear bra?
why not powdercoat the metal pieces instead of paint?

[StormChaser]

2. If my car has TPMS and I put rims on it that don't have TPMS sensors, my cluster will read that "tire pressure low"

2. Is there anyway to fix that without having to rebuy wheels that have sensors?

1. Yes
2. No, not unless you find a way to totally disable the system. Maybe find/pull the fuse? But it may be on the circuit for other things. Or see if the OBDC system in the car can turn it off.

[StormChaser]

why not wrap the whole car in clear bra?
why not powdercoat the metal pieces instead of paint?

The answer is the same for both...cost.

[MrMook]

why not wrap the whole car in clear bra?
why not powdercoat the metal pieces instead of paint?

Bra: You could. In fact, many do wrap their entire cars in vinyl. But as mentioned, it ain't cheap.

Powdercoat: Some pieces are powdercoated from the factory (lots of suspension parts). Body panels are not because the finishes are not as lustrous as paint, it's heavier, and repairs are difficult, because you can't just "spot coat" and blend like you can with paint. You'd have to strip the whole panel and go through the whole process again.

[saron81]

Could I put an intercooler behind the grill to keep the stock front bumper instead of getting an aftermarket Corrado bumper? Is it possible to do that so it mounts behind or in front of the radiator?
Stupid question :/

Lots of cars and trucks package the intercooler in front of the radiator (some even put the AC condenser in front of both.) The airflow through the intercooler will still be enough to cool the radiator effectively. The air in the intercooler will be much cooler than the coolant. I have this setup pictured in my XR4Ti with electric puller fans behind the radiator. I usually see air intake temps <100* on cooler days (or about 20* warmer than ambient) while coolant temps run around 212*. You wouldn't the intercooler behind the radiator because of heat transfer. Not a stupid question.