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-   -   Turbo = HP or lbs.ft?? (https://www.motorcycle.com/forum/motorcycle-general-discussion/6580-turbo-hp-lbs-ft.html)

tripleripple 10-18-2007 10:13 PM

Turbo = HP or lbs.ft??
 
If anybody can help a gearhead who actually knows very little about gears, I got somethin' bugging me. Just saw a car commercial that trumped a turbo charger as adding torque (It was an MB diesel). Question from the less than mechanically competent: Doesn't a turbo, whether bike or car, only kick in at high rpm? And if so, isn't that the definition of bhp? I concede I may be completely wrong here but I've never heard of anybody adding a turbo to any engine to increase TORQUE. Wish I knew a good engineer...

The_AirHawk 10-19-2007 05:55 AM

Quote:

Originally Posted by tripleripple (Post 171439)
Doesn't a turbo, whether bike or car, only kick in at high rpm? And if so, isn't that the definition of bhp? I concede I may be completely wrong here but I've never heard of anybody adding a turbo to any engine to increase TORQUE. Wish I knew a good engineer...

If there is exhaust-gas flowing through the turbine, that turbo is spinning. You can make a well-balanced turbo spin by merely blowing-through it.

As to when it "kicks in" - that's all relative to compressor and turbine vane size ("trim"), pitch, weight, the bearing assembly (ball-bearing turbos turn more-freely than plain-bearing, hence "spool" more-quickly) and the compressor and turbine housing inlet to outlet ratios. It's almost more guesswork than science choosing a turbo.

As to the torque question: the reason big-cube engines (usually) make so much torque is because, due to displacement - they're moving a lot more air (and consuming a lot more fuel) relative to a small-displacement engine. If you "stuff" more air (and fuel!) into a small-displacement engine via a turbo or other supercharger (or Nawz, Baby!), what do you suppose happens to the torque-output of that engine?

seruzawa 10-19-2007 06:36 AM

It's kind of hard to increase one without increasing the other.

"Tuning for torque" is sort of misleading because in that case you are not increasing the torque as much as you are just widening the rpm range of the usable torque. You get less peak torque when you widen the torque band and lower the peak HP. However the motor feels stronger because the torque is more available.

So to answer your question, "Does adding a turbo increase the hp or the torque?" Yes.

None of these rules are absolute. you can always find exceptions so they are just general rules of thumb.

BTW there are no good engineers here. If you are looking for a good engineer I hear there is one on the CW forums who knows everything.

sarnali2 10-19-2007 06:58 AM

So was the little turbine spinning in your Oxygen Destroyer Bomb spinning for volume or velocity?

seruzawa 10-19-2007 07:49 AM

I have plenty of both...
 
Quote:

Originally Posted by sarnali2 (Post 171446)
So was the little turbine spinning in your Oxygen Destroyer Bomb spinning for volume or velocity?

.. volume AND velocity.

And you would too if you got one of these nifty new Harley credit cards to go with your pink armchaps and EZ leaker. Sign up today. don't waste a second. (offer not valid where anyone has a clue)

vermicious 10-19-2007 07:56 AM

Quote:

Originally Posted by seruzawa (Post 171452)
...to go with your pink armchaps

hehe, pink armchaps

mscuddy 10-19-2007 07:56 AM

Cubic inches + compression ratio = HP. Take the 1969-1970 series 472 cu.in. Cadillac V8. The HP peaked at 3800 rpm @ 365 HP, but at 4000 rpm the torque peaked at 500 ftlbs. So it has a lot to do with cam profiles, valve size, timing, etc.

Generally a turbo-supercharger (like ones on Detroit 2 stroke diesel v8's) that stack a turbocharger on top of an axial blower, produce tons of low end grunt, for big rigs, prison buses, etc...

So, to answer your question, yes and no...

sarnali2 10-19-2007 08:01 AM

Quote:

Originally Posted by vermicious (Post 171454)
hehe, pink armchaps



They're NOT PINK, the arm chap part is "light red" and the fringe is white!

I wish you'd learn to read that colorwheel Longride sent you.....

acecycleins 10-19-2007 08:13 AM

Quote:

Originally Posted by seruzawa (Post 171442)
It's kind of hard to increase one without increasing the other.

"Tuning for torque" is sort of misleading because in that case you are not increasing the torque as much as you are just widening the rpm range of the usable torque. You get less peak torque when you widen the torque band and lower the peak HP. However the motor feels stronger because the torque is more available.

So to answer your question, "Does adding a turbo increase the hp or the torque?" Yes.

None of these rules are absolute. you can always find exceptions so they are just general rules of thumb.

BTW there are no good engineers here. If you are looking for a good engineer I hear there is one on the CW forums who knows everything.

Compression plays a role. High Compression motors will turn better over-all hp numbers but you may have peaks and valleys in the torque curve because the motors are alrady tuned for hp. If you have lower compression you will usually run lower boost but in doing so you will have a flatter, fatter torque curve or line as it were.

longride 10-19-2007 09:09 AM

Quote:

Originally Posted by acecycleins (Post 171457)
Compression plays a role. High Compression motors will turn better over-all hp numbers but you may have peaks and valleys in the torque curve because the motors are alrady tuned for hp. If you have lower compression you will usually run lower boost but in doing so you will have a flatter, fatter torque curve or line as it were.

Not that I am a turbo expert, but you can't run much boost with a high-compression engine without burning holes in the pistons. The first step for running high-boost turbo applications is a cylinder spacer to lower compression and then usually C-16 gas to control detination. If you are pinging on boost, you will have a motor meltdown sooner, rather than later. Low boost and mild cam timing, and high rpm's is what makes a turbo go. Like I said, I am not an expert, but high-compression and high boost = BAD!


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