increasing torque without any big modifications 2

[Deividas]

Hello. I wanna ask, how increase engine torque without increasing displacement, compression ratio, and fuel consumption? Or how new engines increase fuel efficiency and power, when compared to older egines? I know, that new engines have higher CR, ecu controlled fuel injection and ignition timming, better designed combustion chambers, variable cams and intake manifold, but that is enough or there is something i missed?

 

[Lou Scannon]

Three basic factors for increasing BMEP:
[ol 1]
[li]increase the mass of the stoichiometric trapped charge (excess air, excess fuel, charge diluents & internal coolants do not count, though they might be useful for #2)[/li]
[li]burn it more efficiently (increase the effective expansion ratio) - this is in terms of IMEP, not BSFC!![/li]
[li]reduce parasitic losses (piston & ring to cylinder friction, bearings, valvetrain, ancilliaries e.g. oil pump, water pump, etc.)[/li]
[/ol]

"Schiefgehen will, was schiefgehen kann" - das Murphygesetz

 

[BrianPetersen]

If you compare those "new engines" to "old engines", you'll probably find that there HAVE been rather big modifications.

 

[Deividas]

I compared new engines vs. old, like old 5.0 V8 camaro, and newer civic 1.8 vti, camaro have 108kw at 3800rpm and 333Nm at 2400rpm and 121.4psi BMEP, civic 125kw at 7600rpm and 166Nm at 6300rpm and 168.4psi BMEP. So my second question: is BMEP always proportional to torque and is it calculated from only power stroke (180deg.) or from all strokes (720 deg. in 4 stroke engine)? Sorry for dumb questions, but i'm novice in these things

 

[BrianPetersen]

http://hpwizard.com/bmep.html

Your thread title includes "... without any big modifications", but going from an old carbureted points-ignition pushrod Chevrolet small block that was designed in the 1950s to a modern fuel-injected twin-cam pentroof 4-valve-per-cylinder with variable valve timing and with intake and exhaust systems that were designed with the aid of computer software that no one even imagined when the Chevy small block was designed ... is a rather big modification.

 

[Tmoose]

BMEP page 13 here -

http://www.amrca.com/tech/tuners.pdf

" number of power strokes/minute "

 

[Deividas]

BrianPetersen, yes, my thread title is wrong, sorry maybe it should be, "how increae bmep without increasing air/fuel mixture"

 

[Deividas]

*increase

 

[SomptingGuy]

Well, if you cannot change anything physical about the engine or how much air and fuel pass through it, you only really have snake oil and magnets left.

- Steve

 

[Deividas]

Maybe my question due to my not perfect english knowledge isn't very accurate, but i wanna find out, how much torque possible to increase only "changing software" in ecu, if all engine internals are the same. If i have engine, lets say that 5.0 V8 which i mentioned before, how much torque (or bmep) increasment i can expect, if i change carburetor to multi-point injection with ecu controlled ignition, (or if it already has ecu, if i remap it) and other inlet and exhaust headers, but not increasing my fuel consumption?

Thank You for answers

 

[BrianPetersen]

If the ONLY thing you want to change is software (e.g. mapping - e.g. "chip-tuning") then the only scope for improvement involves "losing less". It's really easy to LOSE power by changing settings. Sometimes the factory calibration leaves a little bit on the table for whatever reason. Maybe it's calibrated a little rich at full load in the interest of hopefully having fewer warranty claims, maybe the ignition timing is a little on the safe side in case someone puts too-low octane fuel in it. But typically the factory calibration engineers have some clue what they are doing, and there is usually very little to be found.

Exhaust systems were often restrictive in the bad old days. Nowadays, they are usually pretty well chosen.

Changing carb to fuel injection is a "big modification". It generally involves replacing the intake manifold with one of a completely different design. A manifold for multi-point fuel injection need not be designed for eliminating "puddling" or optimizing cylinder-to-cylinder fuel distribution. Manifolds for V8 engines nowadays look nothing like the traditional intake manifold of the (carbureted) past.

There is no magic involved here. If you get a certain amount of air into the engine, that calls for a certain amount of fuel, and the engine will want a certain ignition timing to run best. If you want to make more torque at a certain engine speed, you have to get more air in. Nothing you tinker with on your computer can do that. It's determined by hard parts ... piston displacement, ports, valves, camshafts, etc.

 

[tbuelna]

How much of a reduction in engine life/reliability are you willing to accept?

 

[Deividas]

tbuelna - how much ecu remap can reduce engine reliabilty, if ignition timing isn't too much advanced?

 

[GregLocock]

tbuelna, yay nitrous.

Cheers

Greg Locock


New here? Try reading these, they might help FAQ731-376

http://eng-tips.com/market.cfm?

 

[BrianPetersen]

If you are starting from an "optimum" setup then there is no way but down. ("Optimum" in quotation marks because the "optimum" for emissions may slightly differ from the "optimmum" for fuel consumption which may slightly differ from the "optimum" for power output, etc. But on a well-designed engine, these "optimums" won't actually be very far apart.)

Improper engine tuning can make an engine go kaboom in a big hurry under the right/wrong conditions.

 

[hydroman247]

Change gear.

 

[Deividas]

I wanna ask one question about intake and exhaust headers: i know, that longer and smaller diameter headers are better for lower rpm torque, and shorter and bigger diameter headers are better for hgher rpm torque. I know that in smaller diameter header air is moving faster at lower rpm and having more inertia and in this way increasing volumetric effiency at lower rpm, but at high rpm smaller diameter header becomes restrictive, so at higer rpm bigger diameter is better, but in bigger diameter header at lower rpm air is moving relatively slow and having less inertia (if this info is wrong, maybe someone can correct it). So i know (i think i know) how header diameter affects air flow and torque at certain rpm, but i didn't know how header length affect air flow and torque at certain rpm. Maybe someone can explain, why at higher rpm shorter header is better, and at lower rpm longer header is better?

 

[yoshimitsuspeed]

That is sort of an abbreviated and somewhat accurate summary. It's really not a simple subject and hard to accurately summarize.
This would get you started in the right direction.

http://www.amazon.com/Scientific-Ex...ientific+design+of+exhaust+and+intake+systems

 

[JackAction]

Maybe someone can explain, why at higher rpm shorter header is better, and at lower rpm longer header is better?

When the exhaust valve opens, a huge pressure wave is sent throughout the pipe. That pressure wave travels at the speed of sound. When it reaches the atmosphere (or an area increase large enough to simulate one), this pressure wave is reflected as a lower pressure wave (think vacuum). This lower pressure wave travel also at the speed of sound towards the cylinder (yes, against gas flow). When it reaches the valve, it then reflects again as a high pressure wave, but lower than the first one. And this process keeps going on until the pressure stabilizes through the pipe. Of course - in an engine - the pressure never quite stabilize because of the engine cycle.

Because we know the speed at which the waves travel, the trick is to tune the length of the exhaust pipe such that the low pressure wave arrives at the cylinder at a moment where the exhaust valve is open to facilitate the scavenging process. The wave can return in a following cycle or even at another cylinder valve (when there is exhaust collector).

You can see this as the molecules' way to communicate between each other. When the exhaust valve opens, the gas molecules are saying: «We're getting out, make space for us!». Of course, the molecules on the other side of the valve can't really move so they just pass the message along the pipe until it reaches an open end. At this point, the molecules are saying: «We found free space, keep coming!» But that message has to go back to the cylinder where the high pressure is.

The same process is used to tune the intake length, except that a low pressure wave is sent when the intake valve opens («We found free space, send more molecules») and it is reflected as a high pressure wave going toward the cylinder («We found a bunch of molecules; they're coming!»).

Search for «pressure wave» and «fluid dynamics». This article is a good start.

 

[JackAction]

I just realize that in my previous post, I might not have made clear the relation between length and rpm.

If we want the pressure wave to arrive at a certain crank angle after the valve opening (Δθ) and we know the rpm (ω), then the time that is available is Δθ/ω. The pressure wave will travel at the speed of sound (v) through a length of pipe (L). The time taken to do that is L/v. Both these times must be equal, so:

L = (Δθ * v) / ω

So we can see how when the rpm at which we want to tune the exhaust increases, the length of the pipe must decrease (and vice-versa).

This is extremely simplified as the speed of sound will vary throughout the pipe and with many other complex factors, but the principle remains.