Ouestion about displacement
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Junior User
Joined: Jan 2008
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From: Baton Rouge, LA.
Ouestion about displacement
I read an ad the other day about Volkswagen diesels, they generate more HP & almost as much torque as my 7.3 & they do it with a small 4 cylinder engine, my mother has a nissan sentra ( 4 cylinder ) small displacement that has as much HP as my diesel, the V8 in my gmc is 4.8L ( 292 cubic inchs ) & it is 270 Hp. So here is the question, what happened to the idea that displacement equals horsepower? in the old days you were doing good if you could get 1HP for every cubic inch of an engine. My 7.3L is about 446 cubic inches but only 184 HP, what happened to the HP?
Elder User
Joined: Feb 2009
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From: Edmonton AB
A diesel motor isn't about horse power. If you want big horse power go buy a gas motor.
Diesel's are all about torque and longevity. As far as your concerned about smaller diesels out performing your 7.3l, well your Motor is really old technology, and there are a lot of new diesel's with smaller displacements that can out perform an IDI. 90% of people on here have IDI's because there a cheap dependable workhorse, the other 10% because the love the motor for one reason or another. If you don't fit in two either of those two catagories, there are some other diesel's out there for you like a cummins, or a duramax.
Diesel's are all about torque and longevity. As far as your concerned about smaller diesels out performing your 7.3l, well your Motor is really old technology, and there are a lot of new diesel's with smaller displacements that can out perform an IDI. 90% of people on here have IDI's because there a cheap dependable workhorse, the other 10% because the love the motor for one reason or another. If you don't fit in two either of those two catagories, there are some other diesel's out there for you like a cummins, or a duramax.
Lead Driver
Joined: Nov 2003
Posts: 6,900
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From: Campbell River, B.C.
Newer engines often rely on overhead variable timing cams and multi valve heads to get those performance numbers. In the case of smaller 4cyl engines, that often means a rubber band instead of a timing chain, or timing gears like our engines. All of that makes the engine capable of putting out more and more Hp per CID.
Something else we need to define is "peak horse power" verses "constant rated horse power".
Good luck getting that VW engine to hold up for more than about 60 seconds pumping out those numbers. Our diesels being a commercial design can hold steady at thier rated horsepower for days at a time (pre production testing was for several weeks).
Something else we need to define is "peak horse power" verses "constant rated horse power".
Good luck getting that VW engine to hold up for more than about 60 seconds pumping out those numbers. Our diesels being a commercial design can hold steady at thier rated horsepower for days at a time (pre production testing was for several weeks).
Senior User
Joined: Sep 2007
Posts: 317
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From: Snohomish, WA
Horsepower is a function of torque multiplied by engine speed, as detailed:
Horsepower - Wikipedia, the free encyclopedia
So, if you make the same amount of torque at a greater engine speed, you will effectively increase the horsepower. This is how a diesel engine that produces gobs of torque, but does not rev high, can produce a lower peak horsepower number than a small high speed engine.
Horsepower - Wikipedia, the free encyclopedia
So, if you make the same amount of torque at a greater engine speed, you will effectively increase the horsepower. This is how a diesel engine that produces gobs of torque, but does not rev high, can produce a lower peak horsepower number than a small high speed engine.
Postmaster
Joined: Dec 2002
Posts: 3,594
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From: Southern Oregon USA
I read an ad the other day about Volkswagen diesels, they generate more HP & almost as much torque as my 7.3 & they do it with a small 4 cylinder engine, my mother has a nissan sentra ( 4 cylinder ) small displacement that has as much HP as my diesel, the V8 in my gmc is 4.8L ( 292 cubic inchs ) & it is 270 Hp. So here is the question, what happened to the idea that displacement equals horsepower? in the old days you were doing good if you could get 1HP for every cubic inch of an engine. My 7.3L is about 446 cubic inches but only 184 HP, what happened to the HP?
As everyone has said, torque is where it is at. The only one that would compare is the Vortec 4.8. Those new GM engines are impressive, but they won't last under a heavy load like an IDI will. But that is comparing 25 year old technology. Look at the gasoline engines in the IDI era and nothing was making close to 1 hp per cubic inch.
The latest generation of diesels do it all. Plenty of horsepower, loads of torque and decent fuel mileage on top of it.
Jason
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yes true they do all that, i can rebuild my engine like dave s engine for the same as a set of duracrap injectors and a repair bill
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Postmaster
Joined: Dec 2002
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From: Southern Oregon USA
Jason
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From: Campbell River, B.C.
Only other engine I can think of is the touareg V10 TDI. I feel ashamed to admit that I might be intrigued by the idea of a V10 turbo diesel.
Although this 3L V6 TDI still beats the stock IDI's numbers peak for peak CanadianDriver 2009 Montreal International Auto Show Clean-diesel VW Touareg shown in Montreal
I think I'll pass on anything that has a **** water injection system though.
Postmaster
Joined: Dec 2002
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From: Southern Oregon USA
They aren't as complex as you would think. People tend to make them harder to work on than they actually are, mainly because you don't see all of the components that make them function as you do with a mechanical engine. But if you have a shop manual and a little understanding of electricity and basic automotive computers, most things are easily repaired. The internet is a valuable resource when it comes to repairing and modding, just like this forum is for the IDI.
On that thought, I recently overhauled the injectors on my neighbors '99 PSD. Once I got to the valve covers to get them off, everything was pretty simple. Just a couple of different steps to follow than replacing an IDI injector. The worst part of the job was getting the air to air tubes out of the way and the fact that the engine is half buried under the dash on the Super Duty.
Jason
On that thought, I recently overhauled the injectors on my neighbors '99 PSD. Once I got to the valve covers to get them off, everything was pretty simple. Just a couple of different steps to follow than replacing an IDI injector. The worst part of the job was getting the air to air tubes out of the way and the fact that the engine is half buried under the dash on the Super Duty.
Jason
