SAAB advice: lug the engine (from 1982)
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Hi,
do you want to be bored by more data or is this thread done?
IMHO the 1-3-5 scenario is an excellent one most of the time and I have used it for decades. Once mastered for the vehicle you are driving it lives well!
Doug
do you want to be bored by more data or is this thread done?
IMHO the 1-3-5 scenario is an excellent one most of the time and I have used it for decades. Once mastered for the vehicle you are driving it lives well!
Doug
I disagree. If genuinely comparing apples to apples (same hp curve, same operating speed range, both turbocharged, pump fuel, etc.) a Diesel-cycle engine will require fewer cubes to do it in my experience. This is due to the massively higher compression of a diesel engine and the requirements of preventing detonation in the Otto-cycle.
you miss the point... I'm talking about taking the G35 engine, slapping a 4:1 reduction unit on it and installing it in a class 8 truck. in this application you'd have a 280HP/1080tq powerplant which would pull the load just fine at hwy speeds. if you slapped the gear reduced engine into a g35 sedan.. it would self destruct within seconds.
my point is that hp is a number derived from torque and RPM.. HP is not measured, it is calculated
My comparison was naturally aspirated. Modern naturally 4 stroke gas engines put out about 1 lb-ft/in^3. Naturally aspitrated 4 stroke diesels are doing good to put out 0.8 lb-lt/in^3.
0.8 < 1.0
Part of the reason for diesels having a lower specific torque/power output is that the smoke limit for these engines is substantially short of stoichiometric.
They can never get their full compliment of fuel in, and thus make proportionally less torque/power.
They can never get their full compliment of fuel in, and thus make proportionally less torque/power.
That's what I said about 7 posts up, although I wasn't as eloquent as you, you silver tongued devil.
An excellent example of how choosing one's apples carefully will result in supporting one's point, regardless of what that point is.
Nevertheless, if we remove the artificial constraint of natural aspiration (as is the case in the open market), my assertion is verified not only by my experience but also by the fact that most tractor engines stopped being gasoline-powered in most of the world over half a century ago. The same is true of heavy truck engines. If it was as simple as beefing up/slowing down a gasoline engine to make it live as long as a diesel and that would increase specific output, you can bet that's what would be done.
Hi,
Bret Chase - you said;
"my point is that hp is a number derived from torque and RPM.. HP is not measured, it is calculated"
Perhaps you could explain this
Regards
Doug
Bret Chase - you said;
"my point is that hp is a number derived from torque and RPM.. HP is not measured, it is calculated"
Perhaps you could explain this
Regards
Doug
The big reason that diesels took over in the commercial market is that they are more fuel efficent. It had nothing to do with torque for a given sized engine. The change to diesel was made before turbocharging was used in trucks and tracters.quote:
Originally posted by bulwnkl:
An excellent example of how choosing one's apples carefully will result in supporting one's point, regardless of what that point is.
Nevertheless, if we remove the artificial constraint of natural aspiration (as is the case in the open market), my assertion is verified not only by my experience but also by the fact that most tractor engines stopped being gasoline-powered in most of the world over half a century ago. The same is true of heavy truck engines. If it was as simple as beefing up/slowing down a gasoline engine to make it live as long as a diesel and that would increase specific output, you can bet that's what would be done.
"I'm talking about taking the G35 engine, slapping a 4:1 reduction unit on it and installing it in a class 8 truck. in this application you'd have a 280HP/1080tq powerplant which would pull the load just fine at hwy speeds."
I'm talking about the low rpm torque being needed for moving a load from standing start, maybe up a hill, as the very high torque produces 'adequate' hp at low rpm. Eventually you need to get the load up to highway speed, where the similar peak hp of the gas engine should work as well, on paper, as the almost 4x bigger diesel. The steep hp curve on the gas engine means that you'd need to run it in a very tight rpm range, otherwise if you hit a hill or stiff headwind and the rpm drops, the load carrying capability drops dramatically and the hp does too.
I'm talking about the low rpm torque being needed for moving a load from standing start, maybe up a hill, as the very high torque produces 'adequate' hp at low rpm. Eventually you need to get the load up to highway speed, where the similar peak hp of the gas engine should work as well, on paper, as the almost 4x bigger diesel. The steep hp curve on the gas engine means that you'd need to run it in a very tight rpm range, otherwise if you hit a hill or stiff headwind and the rpm drops, the load carrying capability drops dramatically and the hp does too.
Thinking of another example that might be closer to home as few of us have seen 3 liter gas engines in class 8 trucks, consider road racing bikes from the 60s/early 70s. Triumph and Harley were running 750s while Yamaha was running a 350cc 2 stroke twin. I recall one article, in Cycle I believe, where the author was given the opportunity to ride the 'giant killing' Yamaha, and he said that he proved unable to ride it as it had such a peaky powerband. It was either producing almost no usable power or it was accelerating pretty much uncontrollably, with the front wheel was climbing in the air.
Putting a G35 engine into a class 8 truck might be similar, although now we're talking about just moving as opposed to doing wheelies.
Putting a G35 engine into a class 8 truck might be similar, although now we're talking about just moving as opposed to doing wheelies.
I've determined that shifting 1-3-5 at 2200RPM allows me to accelerate as fast as, if not faster than, most other drivers so I'm not holding anyone up.
Had a play with the technique, as today I had to do a repeat of the exact same trip as we did on the weekend (left some keys/important stuff at a motel 200km away.
In spite of heavier traffic today in the city portion (being a weekday), mileage was up 8%. Filled at the same bowser as yesterday, same time of day, same excess speed on the country roads/freeways.
In spite of heavier traffic today in the city portion (being a weekday), mileage was up 8%. Filled at the same bowser as yesterday, same time of day, same excess speed on the country roads/freeways.
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