Go Back   Motorcycle Forum > Motorcycle.Com General Discussion > Motorcycle General Discussion

Reply
 
Thread Tools
Old 10-18-2007, 10:13 PM   #1
tripleripple
Founding Member
 
tripleripple's Avatar
 
Join Date: Jun 2007
Location: Lightly Fortified Compound (apartment): Chicago, IL
Posts: 421
Default 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...
tripleripple is offline   Reply With Quote

Sponsored Links Remove Advertisements
Motorcycle Forum
Advertisement
Old 10-19-2007, 05:55 AM   #2
The_AirHawk
Founding Member
 
The_AirHawk's Avatar
 
Join Date: Jun 2007
Location: Leanin' Tower O' P-P-P-P-POWAAAAAAAAA!!!!
Posts: 11,491
Default

Quote:
Originally Posted by tripleripple View Post
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?
__________________
Parfois, on fait pas semblant
Sometimes, it's not pretend
Oderint Dum Metuant
Let them hate so long as they fear
политики предпочитают безоружных крестьян
Politicians Prefer Unarmed Peasants
Nothing to see here, Citizen. Move along now...
The_AirHawk is offline   Reply With Quote
Old 10-19-2007, 06:36 AM   #3
seruzawa
The Toad

 
seruzawa's Avatar
 
Join Date: Nov 2001
Location: 8501 ft.
Posts: 17,461
Default

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.
__________________
"Make no mistake, Communism lost a big argument - one we know today as the 20th century."

Last edited by seruzawa : 10-19-2007 at 07:46 AM.
seruzawa is offline   Reply With Quote
Old 10-19-2007, 06:58 AM   #4
sarnali2
Aging Cafe` Racer

 
sarnali2's Avatar
 
Join Date: Jun 2007
Location: Sittin' down by my window, lookin' at the rain.
Posts: 8,719
Default

So was the little turbine spinning in your Oxygen Destroyer Bomb spinning for volume or velocity?
__________________
"Carpe` Throttelum -Loud Suits Save Lives"

"He said he's farting because of his medication"...
sarnali2 is offline   Reply With Quote
Old 10-19-2007, 07:49 AM   #5
seruzawa
The Toad

 
seruzawa's Avatar
 
Join Date: Nov 2001
Location: 8501 ft.
Posts: 17,461
Default I have plenty of both...

Quote:
Originally Posted by sarnali2 View Post
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)
__________________
"Make no mistake, Communism lost a big argument - one we know today as the 20th century."
seruzawa is offline   Reply With Quote
Old 10-19-2007, 07:56 AM   #6
vermicious
Registered Member
 
vermicious's Avatar
 
Join Date: Jun 2007
Location: New Orleans, LA
Posts: 553
Default

Quote:
Originally Posted by seruzawa View Post
...to go with your pink armchaps
hehe, pink armchaps
vermicious is offline   Reply With Quote
Old 10-19-2007, 07:56 AM   #7
mscuddy
MODERATOR X

 
mscuddy's Avatar
 
Join Date: Jun 2007
Location: Next to my still checkin the temp.
Posts: 5,447
Default

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...
__________________
A gun is a tool, Marian; no better or no worse than any other tool: an axe, a shovel or anything. A gun is as good or as bad as the man using it. Remember that.
mscuddy is offline   Reply With Quote
Old 10-19-2007, 08:01 AM   #8
sarnali2
Aging Cafe` Racer

 
sarnali2's Avatar
 
Join Date: Jun 2007
Location: Sittin' down by my window, lookin' at the rain.
Posts: 8,719
Default

Quote:
Originally Posted by vermicious View Post
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.....
__________________
"Carpe` Throttelum -Loud Suits Save Lives"

"He said he's farting because of his medication"...
sarnali2 is offline   Reply With Quote
Old 10-19-2007, 08:13 AM   #9
acecycleins
Founding Member
 
acecycleins's Avatar
 
Join Date: Jun 2007
Location: North Georgia
Posts: 4,129
Default

Quote:
Originally Posted by seruzawa View Post
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.
__________________
"Slack" - a state of being in which everything flows smoothly.....a frame of mind so at ease that the universe naturally cooperates.
acecycleins is offline   Reply With Quote
Old 10-19-2007, 09:09 AM   #10
longride
Super Duper Mod Man

 
longride's Avatar
 
Join Date: Nov 2001
Location: Anywhere they let me
Posts: 10,479
Default

Quote:
Originally Posted by acecycleins View Post
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!
__________________
I'm a knucklehead
longride is offline   Reply With Quote
Reply


Thread Tools

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

vB code is On
Smilies are On
[IMG] code is On
HTML code is On
Trackbacks are Off
Pingbacks are Off
Refbacks are Off