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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...
 

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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?
 

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The Toad
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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.
 

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

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The Toad
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I have plenty of both...

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)
 

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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...
 

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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.
 

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Super Duper Mod Man
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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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The Toad
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There are just...

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!
... too many variables to make any accurate generalizations.

My rule of thumb for gas engines is: "If you want more HP get a bigger engine." Turbos just introduce too many problems. That's what happened with the turbo bikes the Japanese introduced all those years ago. Why put a turbo on a 750 to get 1000 performance? Just get a 1000.

Anyone who thinks they need a turbo on a Hayabusa is welcome to the problems.
 

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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 not talking insane compression, here. More like the type you get out of your standard superstock 1000cc-1400cc bike. You can run an easy 8-10ftlbs of boost out of a stock Busa motor and get hp figures in the 240 area pretty easy without burning up to motor. But in a V-Twin application, running 7-9ftlbs of boost will trigger a torque curve that should stay above 100ftlbs from about 2500rpm (or so) to 6000rpm, usually peaking in the 130 range in or around the 4500rpm range.
I've seen v-twins running flat-top weisco pistions with 8.5to1 and get solid 150hp ranges all day and night. I know a Busa owner that does his own mapping with a stock motor hit the 260 range. He's never dropped a piston and as far as I know only runs premium 93 octane pump gas. I'm not expert, either, but If you run FI motors and have a laptop you may be in pretty good shape if you know fuelling. I don't. I'm just giving my take from what I've experienced. Personally, I'd go blower. Much more consistant air pressure in application.
 

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Super Duper Mod Man
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I'm not talking insane compression, here. More like the type you get out of your standard superstock 1000cc-1400cc bike. You can run an easy 8-10ftlbs of boost out of a stock Busa motor and get hp figures in the 240 area pretty easy without burning up to motor. But in a V-Twin application, running 7-9ftlbs of boost will trigger a torque curve that should stay above 100ftlbs from about 2500rpm (or so) to 6000rpm, usually peaking in the 130 range in or around the 4500rpm range.
I've seen v-twins running flat-top weisco pistions with 8.5to1 and get solid 150hp ranges all day and night. I know a Busa owner that does his own mapping with a stock motor hit the 260 range. He's never dropped a piston and as far as I know only runs premium 93 octane pump gas. I'm not expert, either, but If you run FI motors and have a laptop you may be in pretty good shape if you know fuelling. I don't. I'm just giving my take from what I've experienced. Personally, I'd go blower. Much more consistant air pressure in application.
Busa's have low compression compared to the other Supersports ,which is why they are so popular to turbo. Much easier to turbo a Busa at 8-10 lbs., which is low boost. Go any higher than 10 and you would need a spacer and octane boost, or some type of intercooler. The way your friend is set up is fine for an occasional blast, but any extended high-speed run, and he might end up with a motor for lunch.
 

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Super Duper Mod Man
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... too many variables to make any accurate generalizations.

My rule of thumb for gas engines is: "If you want more HP get a bigger engine." Turbos just introduce too many problems. That's what happened with the turbo bikes the Japanese introduced all those years ago. Why put a turbo on a 750 to get 1000 performance? Just get a 1000.

Anyone who thinks they need a turbo on a Hayabusa is welcome to the problems.
At the boost levels the OEM's ran the turbo was more of a marketing scheme than a performance booster. The reason most guys run turbos compared to buying new or building the motor is expense and ridability. Build a non-boosted 200+ hp Busa, and you lose rideablity AND it costs an arm and a leg. With boost you retain stock rideability until the turbo spools and then hang on! I have heard of 500 HP streetable Busa's out there. Crazy!
 

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The Toad
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Not quite.

At the boost levels the OEM's ran the turbo was more of a marketing scheme than a performance booster. The reason most guys run turbos compared to buying new or building the motor is expense and ridability. Build a non-boosted 200+ hp Busa, and you lose rideablity AND it costs an arm and a leg. With boost you retain stock rideability until the turbo spools and then hang on! I have heard of 500 HP streetable Busa's out there. Crazy!
If you lower the compression on a boosted engine you lose performance until you are on boost. My brothers old Merkur was a very irritating car to drive because it was gutless until it was on boost. So you were either poking along or pressed back in your seat. It was a rush that got very fatiguing after a while. That and the fact that the POS quit running at random moments and had to be towed. I got very tired of driving 25 miles to pick him up on the side of I-5. LOL!
 

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Super Duper Mod Man
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If you lower the compression on a boosted engine you lose performance until you are on boost. My brothers old Merkur was a very irritating car to drive because it was gutless until it was on boost. So you were either poking along or pressed back in your seat. It was a rush that got very fatiguing after a while. That and the fact that the POS quit running at random moments and had to be towed. I got very tired of driving 25 miles to pick him up on the side of I-5. LOL!
Which is why there are so many turbo Busas running around with stock compression and 10 lbs of boost. 250 hp with stock drivability for not a lot of cash. I was considering doing it myself until my license took a couple of hits from the friendly state troopers.
 

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I don't know why so many people have this screwy idea that torque and hpr are somehow seperate things. They're not.

Hpr = torque * rpm

So oviously since a turbo increases your power but doesn't make your engine rev higher it increases torque, it might not increase it at the peak though, it might increase it after the peak in the higher rpm range.

That's the equation. When taking about acceleration what actually accelerates you is rear wheel torque. But rear wheel torque isn't = to engine torque it's related to engine hpr since there's a gear box in between. What I mean is rear wheel torque is higher the lower the gear (hence harder acceleration)

Hpr is ALWAYS a better measure of acceleration potential since it factors out the gearing.

Basically in the end torque is a stupid marketing gimmick. because take this scenario - One engine makes 50 lbs of torque at 10,000 rpm another makes 80 lbs of torque at 5,000 rpm the one that spins to 10,000 is going to have 20% more power. If you gear it down to 1/2 what the 5,000 engine is geared for it will accelerate harder and make more rear wheel torque, even at the 'mid-range'
 

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A lot of people have this mistaken idea that good low RPM power meas "Torque" and good high RPM power means "Horsepower". It's all horsepower. Torque is just the force reading we take to compute the power out of the engine over time.
 

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I think the formula is torque x rpm /5252 = HP. Or HP / rpm x 5252, which is why the formulas always cross at 5252. Others here have said it, if you make more HP, you will make more torque at that particular RPM, it may or may not change the HP you are making at the peak torque RPM, which would affect your peak torque number. In plainer language, trading low RPM HP for high RPM horsepower will typically lower peak torque, but you'd need to chart it to be sure. This is why you'll often find a Harley making 65 hp at 4K has higher torque than a 600cc sportbike making 100 hp at 11K (about 85 vs. 48 ft. lbs).
 
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