Turbo Kit

CrBoy

I know this is a NON Audio related but I don't know the right place to post it so here it is...

This question popped in my head this morning...

What would be the impact on Fuel Economy if I put a Turbo Kit in a car like a Jetta (2.0L, 96 model) or something around those lines. Is it doable/recommendable?

I know I should specify a lot more details but I don't know much about turbos. I'm sure there are many polkies here with good knowledge about this matter...

Please chime in!

skydeaner

It is doable/recommendable, those engines handle turbo applications well. But a turbo forces more/more-compressed air into the engine and as the amount of air increases, so does the need for fuel. So the higher boost on the turbo you would be running the more fuel the engine would throw in for compensation. Your gas milage that you are seeing right now would go bye bye unless you drive extremely conservatively.

PolkThug

skydeaner is correct!

audiobliss

Turbos are for going fast! Do it!

But I'm not sure exactly how it would affect your gas-mileage.

CrBoy

How bad will be the gas mileage? 15MPG? Lower?

PolkThug

CrBoy wrote:

How bad will be the gas mileage? 15MPG? Lower?

Shouldn't be that bad. Depends on how often you engage the turbo.

CrBoy

PolkThug wrote:

Shouldn't be that bad. Depends on how often you engage the turbo.

I usually drive very conservatively but I would like to kick some **** from time to time (too many modified Honda ricers around here)

CrBoy

PolkThug wrote:

Depends on how often you engage the turbo.

Can somebody explain me how that works? Please...

PolkThug

There is a blow-off valve (BOV) that lets the compressed air exit the system when you are not putting your foot down. When you put your foot down, the blow-off valve closes, then keeps all that extra air in the system.

Sami

PolkThug wrote:

There is a blow-off valve (BOV) that lets the compressed air exit the system when you are not putting your foot down. When you put your foot down, the blow-off valve closes, then keeps all that extra air in the system.

I believe that would be wastegate, BOV does something different.

CrBoy

So if I push the pedal half way the turbo will not kick in, right?
What size of Turbo will be adequate for a Jetta... 15Psi... more... less...?

PolkThug

Sami wrote:

I believe that would be wastegate, BOV does something different.

Wastegates are on the exhaust end.

PolkThug

Where's Jstas!!!!!??

Sami

PolkThug wrote:

Wastegates are on the exhaust end.

Maybe I understood you incorrectly, I thought you were referring to the use of the turbo. Anyway, wastegate is what regulates boost level.

http://www.automotivearticles.com/Turbochargers_Design_and_Related_Parts.shtml

WASTEGATE:

In the most basic of terms, a turbo system is self-feeding. That is, as the system creates more boost, it also creates more exhaust flow. This exhaust flow is what powers the turbocharger, so if left unchecked the turbo system will quickly spiral out of control. Now it takes time and a specific amount exhaust flow to start creating boost, but once this point is reached (called boost threshold), either exhaust flow to the turbine is regulated, or the system keeps building pressure until something gives, usually a hard part in the engine. Which is where the wastegate comes in.


Controlled by vacuum signal from the manifold (or more correctly, positive pressure in the manifold), the wastegate’s job is to re-route exhaust flow around the turbine wheel to control boost levels. Remember, the turbo creates boost by extracting energy from exhaust gas flow, so this is the prime location to regulate turbocharger RPM, and therefore boost levels. What a wastegate does is provide an alternate path for exhaust gasses to flow through that doesn’t cause them to contact the turbine wheel. This prevents the exhaust gasses from contributing to boost production, thus regulating boost to preset levels.


There are also two main types of wastegates, internal & external. Both are there to perform the same task, the only difference is location and effectiveness. Internal wastegates are located inside the turbine housing itself, and although effective at re-routing exhaust gasses around the turbine wheel, they can impart a good bit of turbulence to the exhaust flow path. This increases exhaust system pressure and hurts performance. The external wastegate, the true performance choice, has provisions made for it’s mounting before the turbo on the exhaust manifold. An entirely alternate flow path is created where exhaust gasses skip going through the turbine housing altogether, contributing much less to turbulence in the system. They also tend to be more accurate at controlling exhaust flow and turbo boost; combine these two attributes and you have a recipe for superior performance.

BLOW-OFF VALVE:

This is both the insurance policy of the turbo system, and it’s protector. Two things are governed by the blow-off valve; maximum boost levels and pressure spikes in the intake tract. While the first job is primarily handled by the wastegate, in the event of a big enough overboost, the blow-off valve will vent excess pressures to help maintain safe levels of boost. Basically, the blow-off valve is a springloaded poppet valve contraption that will bleed off and excess pressure that builds up in the intake system. This can occur due to either boost creep or a sudden closing of the throttle body when boosting (such as during full throttle, high RPM shifts), but either way it’s the blow-off valve’s job to prevent pressure spikes in the intake tract. This serves two functions: one, to prevent serious engine damaging overboosts, and two, to prevent airflow from reversing direction into the turbocharger itself. The second one is it’s principle job, to keep the intake tract from building up large pressures during sudden lift throttle situations (such as shifting). When the engine is at full boost and full song, the turbo is spinning madly to supply air to the intake system. The momentum of air and turbocharger are not easily stopped on a dime, so when the throttle body is suddenly slam shut, things tend to get interesting in the intake system. There is an immediate pressure spike between the turbo and throttle body, putting great stress on the compressor wheel which is still trying to pump air into a closed system. To keep the turbo’s RPM up and the pressures in the intake tract down, the blow-off valve vents this excess pressure for maximum performance and reliability.

neomagus00

i have a 4-cyl turbo and i can easily pull 35 mpg on the highway if i keep it sane... the turbo will always be running, it's hooked up directly to the exhaust line, but as sami's posted, a wastegate will limit your boost, though this doesn't help you on the highway (it's unlikely you'll be hitting 7 psi of boost in cruise)... a bov is essentially so you don't wreck your turbo when you lift off the gas, but the end result is basically the same no matter which you have (i have an external wastegate, and it's performed admirably... the only reason i'd want a bov is for the 'whoosh' sound )...

yes, a turbo is likely to reduce gas mileage, especially in the city, but on the highway, the difference should be negligible...

CrBoy

neomagus00 wrote:

yes, a turbo is likely to reduce gas mileage, especially in the city...

I'm still wondering how low the MPG will go...

Sami

CrBoy wrote:

I'm still wondering how low the MPG will go...

With just a turbo, low pressure, it's like it is right now; depends on how heavy your right foot is.

CrBoy

What's consider a low pressure turbo?
what does it take to put a nice turbo on a car? What parts need to be redone or mod?

Sami

CrBoy wrote:

What's consider a low pressure turbo?

Maybe 5 PSI or so.

CrBoy wrote:

what does it take to put a nice turbo on a car? What parts need to be redone or mod?

Talk to a reputable local shop if you seriously plan to do this.

CrBoy

the car is in the very near furture (15 days or so), and the turbo kit is in the not-so-near future (6 months or so)... Audio equipment goes first!

neomagus00

sami's pretty much right, it's probably a lot easier to have a quality machining shop do the installation for you... it requires pipe bending (mandrel bends, please!) and welding, plus the fabrication of mounting brackets...

i'd reccommend thoroughly researching turbos and their application before you buy, because little things you wouldn't have thought of will appear... for example, did you know you have to grind and polish away any imperfections the welds may make inside the pipe? any little bump will screw with the turbo...

as far as setting the pressure on the turbo, this varies according to whether you choose a BOV or wastegate, and the specific turbo you buy... a larger turbo will generally provide more boost but with more lag...

you also should consider what will happen to your ECU - you may need to get a new one or get this one remapped, because while it can handle a little bit more performance than stock, it probably won't be able to handle 7 psi more of pressure... same goes for your fuel delivery system (pump and injectors) - you may have to upgrade one or both of these...

these are all good reasons to try and find a kit from a good volkswagen-specific company that has taken all this and more into account, because they'll have chosen a turbo that flows well for your car and they'll know what pitfalls to watch out for...

PoweredByDodge

i would not run more than 4 - 6 pounds of boost... any more and you have to start considering whether the bottom end of the motor is built well enough to handle the extra "umph".

its not a matter of build quality... but a matter that you are doing something to the engine that it was not intended to do... now i'm not telling you not to - it's a good modification - but if you start doing too much you can damage your motor... start running 15 pounds of boost and you better be damned sure positive that your crank and rods can take it... also - consider what effect this will have on the valve train... will you be aiming for higher rpms? -- if so, you may need a different cam, etc etc...

CrBoy

What kind of HP/Torque increase can be expected from a 6 psi turbo...?
I'm willing to change/mod everything if it's necessary... cams, valves, fuel injectors, fuel pump... even re-inforce the engine block...

audiobliss

Man...money's no object for you, huh? LOL

Changing cams, valves, valve springs, lifters (do ohc engines have lifters?), fuel rail, injectors, pistons, piston rings, connecting rods, wrist pins, crankshaft,...you're talking a lot of money!

CrBoy

audiobliss wrote:

Man...money's no object for you, huh? LOL

Changing cams, valves, valve springs, lifters (do ohc engines have lifters?), fuel rail, injectors, pistons, piston rings, connecting rods, wrist pins, crankshaft,...you're talking a lot of money!

I know but the deal is that that kind of things are not so expensive here... it is a lot of money, but the question is... is it worth it? If not I'll jus save up the money and get a better/newer car down the road...

neomagus00

well, manufacturers of turbo cars usually put a lot of time and effort into selecting and integrating a turbo for that particular vehicle, and then ensuring the engine and drivetrain can handle their chosen turbo for 200,000 miles...

what i'd do is a cost-benefit analysis (so econ 101 wasn't a total waste!)... add up the price of parts and labor for a major engine rebuild (probably all or most of the parts bliss listed, some of which may have to be custom-manufactured, in addition to a good engine computer and some dyno time), and compare that to the price of a new turbocar with the same approximate performance (factor in the sale price of your current car, too, if you'd be selling this one to help pay for the new)... whichever is cheaper in the end, do that...

CrBoy

^ That's I wanted to do at the beginning but then I thought about modding an older car which should be a lot of fun........ or I can put all the money towards audio equipment but I don't really want/need 3000 watts on my car.

The Turbo Kit was kinda like a project for me, something to keep me busy over the weekends. The money for the new car is coming from my savings (I've saved some money for the last 5 months)... I'm tired of driving a Metro :eek:

audiobliss

My word...I would be too!!!

If you just want to mod something, I'd start with something besides a Jetta 'cause 1) there's not a lot of potential there, I don't imagine and 2) you'll be working in the tight, cramped area of a very securely sealed German automobile's engine compartment; not nearly as much fun (or as easy or even inexpensive) as working on *most* American automobiles.

Certainly a hard vehicle to make stuff fit and work with, much less to start out on!

neomagus00

i second that... vw's are very well-engineered vehicles, but their engines are not built to handle overpowering (my mom's stock passat gets very very angry above 3500 RPM... try turboing that!)... and as an owner of a european car, i can tell you that the tank-like nature of those vehicles precludes easy engine modification...

Sami

CrBoy wrote:

What kind of HP/Torque increase can be expected from a 6 psi turbo...?

In theory, it's roughly your hp * (15+6)/15 = 1.4 * hp. A 40% increase. I wouldn't do that to a Jetta though, at least get something RWD.

neomagus00

sami - where'd you get that equation? what theory? it sounds terribly interesting...!