germeezy1

truly the only thing that can make up for no torque even with agressive gearing is light weight. If you don't believe me drive a Celica GTS and drive an Elise you will swear that its not the same lethargic no torque engine out of the already lightweight Celica.

Louie83

iTrader: (3)

I'll jump in here and stick up for both sides.

Mike is correct, a lot of people associate weak torque with DOHC engines. That really is not a problem with DOHC engines, they can breath great, especially when they have 4 valves per cylinder. The torque numbers are small when the engine is small, no matter if it is DOHC, SOHC, or pushrod.

But once again, to point out the positives of a pushrod engine:

"The pushrod design was invented to do primarily two things – make the V-type engine more compact and make it lighter. By throwing out the tall and bulky SOHC or (especially) DOHC heads, and actuating the valves from a single in-block cam you save three camshafts, lots of head height, lots of head width, lots of parts and yes lots of weight. You also make the cam drive much simpler, more compact and lighter."

engineermike

With the same rwhp and properly geared and stalled for the needed rpm range, they will run the same. Or maybe the smaller motor will run better since the car will be lighter.

Mike

engineermike

Remember it's only 1.3 liters. Even with a 6.80 gear, cruise rpm will be about 4000 rpm. That's not bad for a small motor. My ZX-10R cruises at 6500 rpm on the interstate and gets 45 mpg.

The real debit here is reliability. A 1.3 liter motor making 350 rwhp will not last long. Whereas, a 5.7 liter motor making 350 rwhp will last a very long time.

Mike

germeezy1

I would rather an engine to be understressed than pushing the edge

Stang's Bane

iTrader: (22)

How much does your bike weigh though?? Comparatively very,very little

I agree with every statement. But you left out one that Germeezy hit on. The relativve load on the engine.

Back a few years ago when gm still made the 305 in the trucks, you could compare 2 trucks side by side, one with a 4.3 v6 and one with a 5.0 v8. Exact same trucks, the v8 would get better gas mileage everytime and last longer.

We had a 1 ton cc worktruck with a 350. It averaged around 10-11 mpg. We traded it in on a newer 1 ton with a 8.1 and got 12-13 mpg. In my train of thought, the reason was less stress on the engine at cruise rpm.

Like I said earlier, small displacement and very high rpm can be fast, but is not the best solution in the everyday automotive world.

Let's look at it this way. Almost every engine has been developed for a reason. Most of the I4 engines in cars are there because of space constraints. The very design of an inline engine almost makes whether it is a pushrod or ohc design irrelevant. When you switch to a v configuration, the relevance becomes paramount. Each design is a solution to a different problem.

B T

>>>

Wouldn't you think the 1300 would have a hard time turning a 4l60-E gearbox, a drive shaft and such a power robbing rearend compared to what it has to turn on a bike drive train?

Parasitic losses seem high to me, would rob allot from the 1300's ability to move 3400 Lbs.even if the 1300 is lighter.

That's allot of mass to turn even with proper gearing, stall, and torque converter size and weight...your thoughts on this Mike?

germeezy1

I think its a moot point, you won't be seeing 1300 cc engines in full weight cars anyway. I still stand by the fact that light weight is truly the only thing that can make up for no torque. Gearing can help mask it but not without tradeoffs.

engineermike

350 rwhp is 350 rwhp. Parasitic losses don't affect it more just because it's less cid producing it.

engineermike

Longer lasting: yes. Better gas mileage: no. Whatever anecdotal evidence you have is flawed. It is well-established that smaller engines get better gas mileage than large ones, all other things being equal. This is because, the more lightly loaded a gasoline engine is, the more intake manifold vacuum the piston is working against on the intake stroke. For this reason, gasoline engines become directionally more efficient with increasing load - that is, the BSFC (lb/hr of fuel flow required to make 1 hp) goes down, but total fuel consumption (lb/hr) goes up.

Mike

Stang's Bane

iTrader: (22)

Not being a smartass here, but according to that we would get better mileage on a vehicle if we made it drag the brakes and made them less aerodynamic. Like I said, I am not being a smartass, I am just trying to understand what you are saying. I probably missed the target with my examples but basically that is what I got out of it.

EDIT: After thinking on this a little more I can understand what you are saying. This would be the case in a controlled enviroment. However in the real world of rolling hills and stiff winds, the engine with a higher torque rating at cruise rpms (GENERALLY larger displacement) would require less fuel at a given speed.
I have some more to add, but at this time I need a few facts to back up my train of thought. I will return

B T

>>>
Mike said:
For example. Let's take a your typical turbocharged Hayabusa 1300 motor. A hot one will make in the neighborhood of 350 rwhp and 180 ft-lb of torque.
>>>
If it was making 350 rwhp through a bike drive train and then you add 4l60-E gearbox, large dia. torque convertor, huge drive shaft and huge rear end...I would seriously doubt that the same engine would dyno 350 " RWHP ". with the changed driveline setup and added rotational mass.


180 lbs. feet of torque is at the rear tire on the " bike drive train ", with less mass to turn.

Maybe I'm wrong here, but something ain't jiven.

engineermike

I said that engines become directionally more efficient as load is increased, NOT that they use less fuel as load is increased.

For instace, at 25% load, and engine may make 100 hp and be 25% efficient.
At 50% load, the same engine will make 200 hp and be 28% efficient.

At 200 hp, it will make twice the power, but only use 1.78 times the fuel. As I said, the BSFC (lb/hr of fuel used to make 1 hp) goes down, but the total fuel consumption will go up.

Now, look at the LS1 350 cid example. At cruise, you're only using, say, 60 hp. The engine is running at only 17% load, so it's relatively inefficinent. Replace the LS1 with a smaller 60 cid engine that has to run at 80% load to make 60 hp. At 80% load, the small engine is much more efficient than the large engine at 17%. Again, this goes back to intake manifold vacuum that the engine has to work against at part throttle.

Mike

engineermike

Stop nit-picking. You're not seeing the forest for the trees.

Okay let's try this. Take all the rwhp numbers and call them fwhp instead. Now, re-read everything. My whole point was that a small engine making the same power as a bigger one, but at a higher rpm, can be geared to run just as good.

Mike

engineermike

Gearing can totally overcome any lack of torque. Let me give an example from my work:

I deal with large industrial machinery. When you purchase a large compressor, you spin it whatever speed is require to efficiently do whatever job it is you need to do. What you wind up with is a drive requirement of, say, 10,000 hp at 8,000 rpm. Next you choose a driver based on hp required, fuel available, maintenance, etc. . . NOT torque or rpm. You may wind up with a recip engine that makes 10,000 hp at 200 rpm (263,000 ft-lb), an electric motor that makes 10,000 hp at 1,800 rpm (29,000 ft-lb), or a gas turbine that makes 10,000 at 5,350 rpm (9,800 ft-lb). Then, you put a gearbox in to get the output speed to 8,000 rpm. Guess what. . . the gearbox output torque will be identical in all cases even though the driver torque output is vastly different!

Mike

engineermike

Holy crap! How could I have forgotten about my favorite hp + gear vs. torque analogy.

The Abrams M1A1 tank. This thing weighs nearly 140,000 lb. It has a 1,500 hp turbine engine. This beast produces a whopping 395 ft-lb of torque.

However. . . mounted immediately to the turbine is 10:1 gear reducer, which multiplies it to 3,950 ft-lb.

Mike

gun5l1ng3r

Mike, you have some GREAT posts. I absolutley LOVE the Abrams tank! Nothing is more sexy than a jet turbine hooked to a hydraulic (torque converter style, lots of slip?) drive system

B T

>>>

trying not too nit-pick.

Just reading what you typed.

Why are we going from rwhp to fwhp?

Don't turn on the M1's AC.

germeezy1

We are talking about cars here not tanks, case in point the S2000 has no torque but great gearing to mask it, its tradeoff is worse fuel economy than an LS1 with 100 more hp and way more torque.

black_knight

iTrader: (1)

Mike, I get what you're saying. But then it comes down to longevity, I think. All those RPM's. And you're also missing that the larger engine, geared correctly, isn't using 17% load. The gearing would reduce the TQ and you'd use more throttle.

If you want nitpicking, how's this: An LS1 is 346 cu in, not 350. Come on, man.