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]

a V8 Crankshaft weighs 50-80 lbs, usually has a pretty big radius, and spins 5,500 RPM. One thing we do to test engine parasitics on an electric dyno is to spin the engine over by using the electric dyno and measuring how much power it actually took to spin the engine.

There is no doubt that a larger radius journal bearing will consume more torque to spin at a given rpm, than a smaller radius journal bearing. But that is not what you claimed in your original statement:

Your crank shaft requires a lot of torque to spin it. If you can reduce weight there, you reduce a big parasitic.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[Lou Scannon]

4 Barrel Carburetor's claim - "I will deliver more horsepower than EFI if we are both running the same AFR"

,
While I agree that there were some very elegantly optimized carburetor setups back in the day, I don't subscribe to that generalization. For the simple reason that, a carburetor that is accurate from part to full load of necessity imposes an appreciable air flow restriction at WOT, in order to have a sufficiently accurate pressure drop vs flow to be used as a signal for fuel metering. Of course, some fuel injection air metering systems impose their own pressure drop (e.g. vane meter, MAF), but these can typically be of lower order than a state of the art accurate carburetor.
Furthermore, when considering PFI vs single point carburetor, air manifold design imposes its own restriction to airflow, in order to mitigate inherent maldistribution issues of air and fuel of a single point system. I hasten to add, PFI systems are not perfect, just inherently better than single point carburetors, in this regard.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[Panther140]

hemi- I am having trouble viewing the maldistribution of air being inherent only to carburetors. PFI also has a single point of induction for air in their manifolds just like most carb setups. In fact, I am using an EFI intake manifold with my carburetor. Does my carburetor make it distribute air less evenly than the EFI throttle body allowed it to? If not. then why would it not be distributing fuel/air as evenly as it did with EFI? Is it not true that all of the air coming through my carburetor is uniformly mixed with fuel and air? Unless certain parts of the intake manifold are getting air from some other point of entry than the carburetor, I don't see how the AFR would be different in any cylinder. All of the cylinders are pulling air from the same point, which meters every cubic foot of air equally. Slightly off this exact topic - You can have 1 carburetor per cylinder! It works well.

Carburetors meter all of the air coming into the manifold. If there is air in the manifold, it theoretically already has the correct amount of fuel metered into it.

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[JackAction]

Maldistribution is not inherent to carburetors, it is inherent to single point fuel mixing. Yes, the AFR might be OK right after the mixing point (carburetor or TBI), but due to the inertia forces, the fuel can leave one point of the air stream to go to another, sometimes accumulating on intake walls. This is how cylinders can end up with different AFR if one receive the «lean» portion of the airstream and another one the «rich» portion.

 

[Lou Scannon]

Panther140, I take it you have not heard of fuel puddling and wall wetting. While not unknown to PFI, the problem is much more pronounced with single point metering. To counteract this issue, single point manifold geometries are "gerry-mandered" to coax the liquid fuel on the walls to distribute itself roughly equally. This tends to undermine efforts to achieve absolutely equal air distribution, not to mention minimize flow restriction.
Regarding 1 carb/cyl., I agree, it works well (assuming proficient application & calibration), but is OT relative to your original claim regarding 4BBL carburetors.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[tbuelna]

....a V8 Crankshaft weighs 50-80 lbs, usually has a pretty big radius, and spins 5,500 RPM. One thing we do to test engine parasitics on an electric dyno is to spin the engine over by using the electric dyno and measuring how much power it actually took to spin the engine. This huge moment of inertia in crossplane counterweighted V8s is one reason flat plane cranks are preferred for a lot of racing applications....

The rotating mass of the crankshaft is dynamically balanced by the counterweights and produces very little mechanical losses at the main bearings. Most of the mechanical friction losses in a recip engine are due to the dynamic forces produced by the reciprocating conrod and piston masses, and the high sliding frictions at the ring and piston skirt contacts from high combustion gas pressures.

 

[BrianPetersen]

High performance motorcycle engines have been one carb per cylinder historically. In all forms of top-level motorcycle roadracing, carbs are gone and will not be coming back. If it were really possible to make more power with a carb, they would have stuck with them, particularly in the MotoGP classes which are not subject to being built from a road bike that has to meet emission standards.

The high-performance bike EFI systems usually use two injectors per cylinder nowadays - one near the port downstream of the throttle, and one in the airbox pointing straight down the intake runner.

 

[Tmoose]

Panther said - "..snipped..... Is it not true that all of the air coming through my carburetor is uniformly mixed with fuel and air? Unless certain parts of the intake manifold are getting air from some other point of entry than the carburetor, I don't see how the AFR would be different in any cylinder. All of the cylinders are pulling air from the same point, which meters every cubic foot of air equally. .........
Carburetors meter all of the air coming into the manifold. If there is air in the manifold, it theoretically already has the correct amount of fuel metered into it."

=========
I think most sources would say the fuel provided by a carburetor is far from evenly distributed and thoroughly and uniformly mixed. Testing on the dyno may not simulate what acceleration does to the fuel in the carb, or the multi-phase mixture flowing into the engine.

https://www.youtube.com/watch?v=s-q1eJu1Wz8

=================

AMC Rambler's best effort to create equal AF ratio back in 1957 or so.

http://worldpowersystems.com/AMC/Ra...Engine (SAE Paper details)_files/v8-fig12.jpg

===================

" At this point, it hadn't yet become evident to dyno users that the use of in-car pieces (headers, ignition systems, cooling systems, etc.) on the test stand would be a logical step toward the need for linking engine testing with on-track performance. The importance of this fact was brought solidly home to me in the mid-'70s when sorting out some cylinder-to-cylinder mixture distribution fixes in a now bygone "Smokey Ram" intake manifold. Distribution fixes Smokey had determined on the dyno barely resembled what were required on the track."

Read more:

http://www.hotrod.com/how-to/engine/ctrp-0808-power-evaluation/#ixzz3cQFBxfMs

Follow us: @HotRodMagazine on Twitter | HotRodMag on Facebook

================
From the Hilborn INJECTION SITE -

http://www.hilborninjection.com/tech_elect_manifold_tech_paper.asp

"First it is important to keep in mind that the air and fuel have not mixed into a homogenous mixture in the venturi of the carburetor or in the runner of the intake manifold. A homogenous mixture is defined as a mixture whose physical properties are uniform throughout. Fuel in the manifold is not uniformly mixed as this only happens under the extreme heat and pressure contained in the combustion chamber. In reality, fuel in the intake tract uses air as a carrier; therefore, it is relatively easy for fuel to fall out of suspension, causing mixture distribution concerns."
And lots more.

==============

Here is a thread on a bulletin board showing some of the stunts that sometime have to be used to get carbs on "high performance" V8 manifolds to get the right amount of fuel to flow to the dry sections of the manifold.

http://racingfuelsystems.myfunforum.org/viewtopic.php?f=28&t=230

============
Post 10 here shows some of the carb assymetry applied by Chevrolet to improve the fuel distribution on the legendary L88 engine.

http://racingfuelsystems.myfunforum.org/viewtopic.php?f=28&t=230

 

[Panther140]

Tmoose - Those are all good points. I hadnt completely considered the potential for maldistribution of fuel from carburetors. I am going to look into getting another carburetor and a better intake manifold now if I find that my car is indeed not running like it should. That should farther improve my peak power over stock.

Tbuelna - I wasn't really talking about friction as much I was talking about the actual rotating mass of the crankshaft and how it affects acceleration through the RPM range. Crankshafts have mass, which rotates. It takes torque to spin a mass in a circle. It takes more torque to spin that same mass in a circle if the mass is farther away from the center (higher moment of inertia).

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[Deividas]

The high-performance bike EFI systems usually use two injectors per cylinder nowadays - one near the port downstream of the throttle, and one in the airbox pointing straight down the intake runner.

I also saw two injectors per cylinder in sports cars, but i don't understand purpose of second row of injectors. Is it for better fuel evaporation at high rpm's or for what?

 

[Panther140]

You can meter fuel more precisely at low RPM with 2 smaller sized injectors than with one large one. Injecting fuel earlier with the air also cools the intake charge, atomizes the fuel better, and makes the air more dense

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[BrianPetersen]

With the motorcycle systems, the lower injectors (downstream of the throttles) are active all the time for driveability and emissions, and the upper injectors are only active beyond a certain engine load (near full throttle) generally in the upper half of the RPM range. Both sets of injectors act together when the engine is near full load and high revs.

 

[Lou Scannon]

Your crank shaft requires a lot of torque to spin it. If you can reduce weight there, you reduce a big parasitic.

Tbuelna - I wasn't really talking about friction as much I was talking about the actual rotating mass of the crankshaft and how it affects acceleration through the RPM range. Crankshafts have mass, which rotates. It takes torque to spin a mass in a circle increase the rotational speed of an object with non-zero rotational inertia [edit by hemi]. It takes more torque to spin that same mass in a circle increase the rotational speed of an object with the same mass if the mass distribution is farther away from the rotational center (higher moment of inertia)[edits by hemi].

If my edits for clarity are accepted, that is all true, but I don't consider rotational inertia as a source of parasitic loss. Of course you have to invest energy accelerating the rotating masses (everything from the crankshaft to the wheels, not to mention the reciprocating parts of the cranktrain, i.e. pistons & rods), so we all understand the value of reducing their moments of inertia as much as practicable (respectively, masses of the rod small end and piston), but at least for everything forward of the gearbox, that energy can be harvested to some extent when shifting. I don't know, and I haven't bothered to do the analysis, but some straight line racers I know assert that a heavy flywheel, when spun up to redline or so prior to the start of a race, can produce faster net acceleration times than a light flywheel.

"Schiefgehen wird, was schiefgehen kann" - das Murphygesetz

 

[BrianPetersen]

You could get a 48 hp VW Rabbit diesel to lay rubber off the line by spinning up the engine to 4000 rpm and dumping the clutch. That engine needed a heavy flywheel due to the 22:1 compression.

The momentary hard acceleration you got from doing that, was the only hard acceleration you got ...

 

[Panther140]

Right, a heavier flywheel and crankshaft would get you better launches based on simple conservation of momentum. The heavier flywheel also improves tractability for engines that would otherwise have abrupt powerbands

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[dgallup]

A friend picked me up to go skiing in his Tercel Diesel. There was about a foot of snow on the ground, a real rarity in SC. He was dumping the clutch and driving like a mad man, when I suggested he take it a little easier he said "When you drive a Toyota diesel and you have an opportunity to spin the tires you have to take it".

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The Help for this program was created in Windows Help format, which depends on a feature that isn't included in this version of Windows.

 

[Deividas]

You can meter fuel more precisely at low RPM with 2 smaller sized injectors than with one large one. Injecting fuel earlier with the air also cools the intake charge, atomizes the fuel better, and makes the air more dense

I think, that nowadays ECU can easily control 1000cc or bigger injectors at idle or low load, so why not to use one big injector further from intake port? With one injector per cylinder it's also easier to adjust ECU. Maybe there is more advantages to use one injector near intake port and one near throttles than one big?

 

[Panther140]

Deividas - I think size of the injector could affect fuel droplet size and the duration that it can be injected for. Id imagine that a longer "cutoff ratio" relative to the time that air flowing in would have an advantage. Also, if you have multiple intake ports per cylinder it would make sense that you would want 1 per port or have one upstream to have more time to mix with the air, but one downstream so that there isn't as much puddling effect on the walls of the runner. 2 injectors per cylinder probably makes more sense for some engines than others

"Formal education is a weapon, whose effect depends on who holds it in his hands and at whom it is aimed." ~ Joseph Stalin

 

[BrianPetersen]

The injector downstream of the throttle and near the intake valve is necessary for driveability and emissions at light engine load (shut throttle). Fuel injected at this injector either goes straight into the cylinder, or lands on either the backside of the intake valve or the inside of the intake port which is hot when the engine is warmed up, and on top of that, it is downstream of the throttle and under light load, this throttle is nearly shut and has a big pressure drop across it so the air that is getting through is very turbulent (which is better for fuel mixing). Cannot do that if the injector is far upstream.

But on the other hand ... when the throttle is nearly open and the engine is spinning fast, fuel injected further upstream has more time to mix with the air and partially evaporate, cooling the intake charge. The throttle is open or nearly so when these injectors are in use, so there is no issue with the fuel droplets landing on the throttle blade and accumulating and then being fed to the engine in (relatively) huge drops, which is what would happen if you tried to use the upstream injectors at light engine load.

 

[RFburn]

Hi all,
Just read this thread so I may be a bit late, but just my observations.

I have a GMC motorhome, the one GMC designed and built back in the 70's using the Oldsmobile Tornado front wheel drive train. It came with a 455ci engine with a quadrajet carb. (

http://www.gmcers.org)

When I bought it in 2008, the original card had been changed to an aftermarket Rochester 4 barrel carb. It had the usual carburetor issues (hard starting, hesitation, wont come off high idle, dieseling) all that good stuff. There is TBI kit for these machines from Howell EFI (

http://www.howellefi.com),

so I went with the EFI kit. It took me a bit to get all the bugs out of the system, but now it starts and runs like a modern engine.

I also added a more up to date engine control computer system (

http://www.dynamicefi.com)

and electronic spark control.

I had to learn about and deal with things like fuel condensing on the runner walls when the engine was cold, and clearing out the rich mixture from puddling (but that only happens from stone cold start-up in my case).

As far as torque and fuel mileage goes it does have more pep, although the electronic spark control seemed to make more difference there than the EFI. GMCer's say with a well tuned carb engine you will get 8 to 10mpg depending on whether you tow a car with you. I never had a good carb on it, but with highway lean cruise and deceleration fuel cut-off I have no problems getting over 10mpg even with my jackrabbit starts.

Just my experience