Topic: Finally (seriously) considering turboing my 4-banger

[Jeffy]

why would downshifting to 4th would be affecting 5th? not sure how that works (i don't understand the mechanics behind it)

The problem has to do with the retaining ring that hold 5th gear on the shaft.  The gears are made with a helical cut and the forces applied to the gear change when in motion.  When the engine is driving the gears it pulls the gear into the next.  When downshifting the forces applied changes and the gear move in the opposite direction which puts more stress on the ring and causes it to rotate and chew off some splines.  When it chews enough metal, the retainer rotates and falls off.

[Tsd]

What are the benefits of a turbocharger over a supercharger? I mean, which one is better for our 4bangers and why?

[Jeffy]

What are the benefits of a turbocharger over a supercharger? I mean, which one is better for our 4bangers and why?

It depends on what you want to do really.  In short, a root supercharger will make power very low and continue up the RPM range.  Centrifugal are a bit more bell-shaped, like a turbo.  Superchargers are usually belt driven and rely on the engine's power to turn it.  A turbo requires a lot more piping as it relies on exhaust pressure to turn it.  This also means you will need to shield other parts from the heat as well.  Unlike the supercharger the turbo uses free energy though.  Superchargers can use up to 1/3 the power the engine produces.

For a 2.5L, a centrifugal SC or turbo would drive like normal at low RPM's.  Once you get the engine up to speed, usually around 3500RPM or so then you'll get boost.  The 2.5L makes enough low-end torque so as not to feel too anemic when you're not producing boost.

Other then mounting and piping, you'll still have to deal with the same boost and fuel requirements.

[sharpxmen]

It depends on what you want to do really.  In short, a root supercharger will make power very low and continue up the RPM range.  Centrifugal are a bit more bell-shaped, like a turbo.  Superchargers are usually belt driven and rely on the engine's power to turn it.  A turbo requires a lot more piping as it relies on exhaust pressure to turn it.  This also means you will need to shield other parts from the heat as well.  Unlike the supercharger the turbo uses free energy though.  Superchargers can use up to 1/3 the power the engine produces.

For a 2.5L, a centrifugal SC or turbo would drive like normal at low RPM's.  Once you get the engine up to speed, usually around 3500RPM or so then you'll get boost.  The 2.5L makes enough low-end torque so as not to feel too anemic when you're not producing boost.

Other then mounting and piping, you'll still have to deal with the same boost and fuel requirements.

actually both the turbo and the s/c use the same amount of power (or very close) - if you look at the BSFC rating for both is about the same (that's the actual efficiency of the engine, how much HP produces per quantity of fuel used). I am not talking roots supercharger but screw supercharger which is lot more efficient than the roots. A good approximation is 0.5 BSFC for normally aspirated and 0.6 for supercharged or turbo, i think the Jeep comes to something like 0.47 for n/a and 0.57 for a well tuned forced induction - that means about 20% loss in efficiency but that is only when you actually are in boost. It is also related to how you size the supercharger (and the pulley ratio) or the turbines in the other case. Also you have to consider that you are not in boost all the time, even with a supercharger if you don't open the throttle your bypass valve will stay open so there will be lot less loss in the unit as it will free spin and not produce boost. In many places you'll find supercharged engines rated at a BSFC of 0.55 to 0.60 and turbocharged at 0.60 to 0.65 (which would tell you the turbo is actually less efficient) - but bsfc is very much related to engine load, so while the turbo is actually acting as a constant restriction in the exhaust even at a low engine load the supercharger will free spin when the MAP reading is below the atmospheric pressure, but at a various loads the BSFC is also different so those numbers are just an approximation at the RPM, throttle position and boost where your engine produces the peak power.

[jfrabat]

I have blown fifth just cruising down the highway lol.. was driving then all of a sudden and rotational crunch crunch crunch went to 4th silent went back to fifth crunch crunch crunch hummm going back to 4th silent humm guess were driving home in 4th lol

Mine already has that crunch crunch crunch issue...  I may just go to an AX15 (if I can scavange the parts) and call it good.

Oh, and the reasons for me to go to turbo instead of SC is that (1) it would be cheaper to find a used turbo and pipe the whole thing than it would to either buy or manufacture a SC kit (like Sharp is doing; by the way, Sharp, how's taht project going?), and parts would be easier to find for a turbo down here than they would be for a SC (import duties here in Costa Rica are DIDICULOUS!  sp?).  But I would want my boost to start before 3500 RPM.  I would like to start having SOME boost at around 2,000 RPM, as the jeep rarely gets up to 4500 RPM, and typically cruises at 2500~3000 RPM's.

[RT]

jfrabat, what gears do you have?

[jfrabat]

jfrabat, what gears do you have?

4,88

[RT]

how long has it been since your last rebuild? because depending on how tired your motor is you could blow it up with a turbo....I could be retarded here but if you have a high mileage motor (without rebuild) I'd stay away from a tc or sc IMHO. But i'm also kind of a noob so idk

[RT]

http://www.novak-adapt.com/catalog/kit_b150gm.htm heres a tranny kit that could help you btw

[sharpxmen]

Mine already has that crunch crunch crunch issue...  I may just go to an AX15 (if I can scavange the parts) and call it good.

Oh, and the reasons for me to go to turbo instead of SC is that (1) it would be cheaper to find a used turbo and pipe the whole thing than it would to either buy or manufacture a SC kit (like Sharp is doing; by the way, Sharp, how's taht project going?), and parts would be easier to find for a turbo down here than they would be for a SC (import duties here in Costa Rica are DIDICULOUS!  sp?).  But I would want my boost to start before 3500 RPM.  I would like to start having SOME boost at around 2,000 RPM, as the jeep rarely gets up to 4500 RPM, and typically cruises at 2500~3000 RPM's.

that project is on hold until i get the Jeep on it's wheels - had some other priorities so the Jeep has to wait for now.

yes, a turbo will be easier to put together, not sure if cheaper but less hassle + you have an A/C so that kind of takes away some of the mounting option. You'll get boost at 2000 like you want so that should cover your requirements, response will be a bit slower at that rpm but once the turbine gets enough spin you'll have boost.

[Jeffy]

that project is on hold until i get the Jeep on it's wheels - had some other priorities so the Jeep has to wait for now.

yes, a turbo will be easier to put together, not sure if cheaper but less hassle + you have an A/C so that kind of takes away some of the mounting option. You'll get boost at 2000 like you want so that should cover your requirements, response will be a bit slower at that rpm but once the turbine gets enough spin you'll have boost.

If he went with a Centrifugal he could mount it outside the AC unit.  Even with a roots type he could still mount it like that as well, like how my York is mounted.  I don't really think it will be much cheaper unless you're lucky and find a turbo that doesn't need to be rebuilt.  Or else you'll be rebuilding it afterward in which case you'll still want to leave some money for that.   Unless you have a tube bender, you'll have to source that out as well.

The only problem I see with setting the boost so low is that it's going to be spooling up and dumping a lot more often as you'll be shifting pretty close to that in every gear.  Keep in mind most OEM applications start around 32-3600 RPM.  I think if you're wanting to be boosting that low you would be better off with a SC.

Also don't expect to get one out of a Neon SRT or a PT Cruiser GT as they are integrated into the manifold.

[jfrabat]

how long has it been since your last rebuild? because depending on how tired your motor is you could blow it up with a turbo....I could be retarded here but if you have a high mileage motor (without rebuild) I'd stay away from a tc or sc IMHO. But i'm also kind of a noob so idk

Engine has about 130K miles on it, but compression is fine (this is where there could be a problem if you put a trubo on it), so I am not worried about this blowing up on my face.

If he went with a Centrifugal he could mount it outside the AC unit.  Even with a roots type he could still mount it like that as well, like how my York is mounted.  I don't really think it will be much cheaper unless you're lucky and find a turbo that doesn't need to be rebuilt.  Or else you'll be rebuilding it afterward in which case you'll still want to leave some money for that.   Unless you have a tube bender, you'll have to source that out as well.

The only problem I see with setting the boost so low is that it's going to be spooling up and dumping a lot more often as you'll be shifting pretty close to that in every gear.  Keep in mind most OEM applications start around 32-3600 RPM.  I think if you're wanting to be boosting that low you would be better off with a SC.

Also don't expect to get one out of a Neon SRT or a PT Cruiser GT as they are integrated into the manifold.

Keep in mind labor in CR is cheap, but parts are expensive.  Finding a used turbo in good working condition is also not that difficult, but finding a used SC is more rare (less cars here with SC vs turbo).  I

And I think I mis-explained myself; I want SOME boost at 2~2.5K, but not ALL boost at that range.  If boost starts out at 3,600 RPM, I have no use for it, as I rarely get  up there.  I would probably set MAX bost to around 5K (maybe a bit less), but I want to have some more power for cruising down the highway without havng to shift.

As for the trany, I doubt 5th will take the boost (it's already acting up in 5th; I already have that CRUNCH CRUNCH CRUNCH sound when cruising in 5th), so I got to consider a tranny swap into the cost...  I am thinking a AX15 with the didge bellhousing, but I have not checked the ratios yet...

[neale_rs]

The AX 15 has a 3.83 first vs 3.93 in the AX5.

[Jeffy]

As for the trany, I doubt 5th will take the boost (it's already acting up in 5th; I already have that CRUNCH CRUNCH CRUNCH sound when cruising in 5th), so I got to consider a tranny swap into the cost...  I am thinking a AX15 with the didge bellhousing, but I have not checked the ratios yet...

The noise is usually associated with the upper rear driveshaft U-joint.  Grease it and see if it goes away.

I'd be sure to have the turbo rebuilt.  Check it for play in the bearings and make sure the veins are OK as a minimum.

[jfrabat]

The noise is usually associated with the upper rear driveshaft U-joint.  Grease it and see if it goes away.

I'd be sure to have the turbo rebuilt.  Check it for play in the bearings and make sure the veins are OK as a minimum.

I'll regrease it again, but I regreased all U-Joints when I had the Jeep in Costa Rica last time, and the noise was stilll there.