Carb. Engines vs. EFI Engines -hp per pound 3

[amorrison]

Can anyone compare Detroit RWD V6/V8 (250-300hp) engines using a Carb (usually - older pre 1985) vs EFI(post 2000) on a HP per pound comparison ? Any thoughts on the power/weight for the complete drivetrain?

 

[dgallup]

Well, if you take the 1981 (rather a low water mark for Detroit) Corvette it made 180 HP from the traditional 350 cubic inch small block Chevy. That was the last year for a carbureted 'vette. In 1982 it was a still pathetic 200 HP "cross fire" throttle body fuel injection system. In 1985 it went to port injection and 240 HP and by 2000 was up to 345 HP. These were all small block V8 so the weight probably did not vary much. I'm sure the aficionados can fill in a million details about aluminum heads, etc. The transmissions over that time went from 3 speed autos to 4 speed overdrive autos (does anybody buy a 'vette with a manual?).

I don't have weights but obviously the power to weight ratio improved a lot.

Now if you want to get into real power arguments you have to go back to the late 60's when the horsepower wars were raging and there were no emission or mileage regulations. Also the standard for measuring HP was different so you get all sorts of wild claims.

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[pontiacjack]

The term "power" isn't very specific. Peak power? Average power over a particular range of engine speeds?

Are you asking about a carefully-tuned example of each (carb vs. injection)? Or averages of random samples pulled from the production lines?

Real-world performance (large variety of temperatures, altitudes, air densities, fuel compositions, etc.) or controlled-conditions of a dynamometer lab?

I'm not merely nit-pickiing; the above clarifications bear directly on the answer to your question.

 

[patprimmer]

I think Jack is saying that advertised power is pretty useless for a comparison. You need to look at real as installed power measured under std conditions. Those figures will be hard to come by.

Real examples.

A typical mid 70s 5 litre (308CI) Holden V8 was advertised at 245hp and that was written in big letters on the air cleaner. They typically made about 145 corrected hp on the dyno. A "40hp" VW Beetle typically made 25hp.

A 1991 Honda D16A9 engine was advertised at 130hp. they typically made about 130 corrected hp or almost as much as the 5 litre Holden V8. I could just lift the complete with all ancillaries VW or the Honda off the ground with suitable straps and harness. I have loaded and unloaded both onto a Ute (pickup truck) on my own with no jacks or cranes. No way could I do that with a V8 that was anything more than a fully stripped bare block.

Regards
Pat
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[LionelHutz]

Many people haven't noticed, but there is a new HP war going on in North America and, almost without exception, the power and drivability of these new engines is better than anything ever previously produced. I can't see how weight would have significantly gone up in these new engines either, so I'd expect the power to weight ratio numbers to be some of the best ever seen as well. Many new 4-cylinder engines are making power levels that only V6 engines previously made and many new V6 engines are making what was previously only V8 power levels.

Tuning is certainly a problem with a carb. I've been to many cruise nights and I've only seen a couple of old cars with the big "HP war" era engines that have actually been impressive when pulling out. From observations, my personal opinion is that most of the older carb'ed engines are unimpressive out of tune dogs.

FYI, a 2000 Corvette @ 345hp has an all aluminum LS1 engine and is not the same basic Chevy 350 small block as pre '97 Corvettes had. Automatic? I would only buy 6-speed Corvette.

 

[NormPeterson]

Are we trying to compare OE advertised power or the power that's at least potentially available at some given level of modification?

Compared to the "pre-1985" range suggested, engine weights have dropped anywhere from about 50 to over 100 lbs. Think 430-ish for Ford's aluminum modular engines and GM's aluminum LS vs 500 - 575 for the older Windsors and SBCs. 460 - 475 for the 289/302 Fords.

Automatic transmissions have probably gotten slightly heavier over the same 1985 - 200? time span due at least in part to having 5 or 6 ratios instead of 3 or 4. I ran across a 25 lb weight difference claim for Ford's 5R55S vs the C4.

I guess if you buy a car to be seen in, the transmission type becomes irrelevant. Mine would be a manual too, just like every other car we've owned over the last 40 years.


Norm

 

[pwildfire]

I am going to assume a part of your question refers to the comparative fuel/induction system weight per power output. However, I think the deciding factor would the level of engine stress allowed for the application. In an instance where the engine can be run at close to cylinder pressure limits, the additional power provided by precise control using EFI will far outweigh the lighter weight. On the other hand, typical production engines are never run very close to these limits, so if reliability is of higher importance than ultimate performance, a precise tune may not be as critical, and a carburetor may prove advantageous simply because it does not require as much mass of overall equipment to implement. This is especially true on small displacement engines where the weight of the control unit, sensors/actuators, and high pressure pump could be quite significant.

In terms of ultimate performance on anything other than a steady state application, modern fuel injection will provide significantly more power at higher reliability, but there is always a trade-off somewhere, and system weight may be it depending on your application.

 

[Hotrodrobert]

I have done a lot of research on this topic. On the same engine, charge quality is the only thing that really matters, no matter how you get there.
Fuel particle size of about 3 microns seems to be the ultimate for power production, properly mixed with the charge air. Getting this size is more difficult with low pressure injectors or poor design carburetor venturies, boosters, air emulsion, etc.
Best fuel economy comes with thoroughly mixed gaseous fuel properly mixed and with a lot of turbulence in the combustion chamber. Gaseous fuel takes much more volume than mist, so the amount of energy in a given volume of mixture is much greater with 3 micron mist.
All that being said, a perfectly calibrated carburetor currently makes better power and economy. Problem is being perfectly calibrated is almost impossible. All the sensors and programability of electronic injection makes a more efficient fuel system.
Progress in injectors and using direct injection into the combustion chamber at very high pressures to better break up the droplets and more energetic combustion chambers is closing the gap.
Point if interest: Mercedes Benz used direct port injection on it's 3 liter six in the 1950's 300SL.

 

[mattsooty]

Generally speaking the minimum enrichment required for peak power is a lot leaner than that required for component protection.
Coupled with that the vast majority of SI engines are rather tolerant in terms of fuelling.
I'm sure that I don't need to teach grandma to suck eggs - I venture there is chuff all differences.

MS

 

[patprimmer]

I would suggest that EFI makes more power not because of accuracy of a:f, but because of better airflow as there is no need for the restrictions imposed by the venturi and discharge nozzles used in carbies and no need to restrict top end airflow by sizing the venturi to give enough low or mid range response.

Regards
Pat
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[mattsooty]

Hmmmm, that's a fair point Pat......

However, I would counter by saying that in some (not all) EFI applications the head/manifold geometries are actually compromised to allow the placement of injectors.

I'd say that, bottom line, there's not much in it!

MS

 

[patprimmer]

Having run some big Webbers in the past then converting to MFI (Bosch or Kuglefischer, not the garden hose variety) the main gain in the fuel injection was response and low rpm power rather than top end. Oh and the ability to run well at radical inclinations and when exposed to high G forces (off road racing in a buggy).

I would also say that carby placement mostly has as big if not more compromise on head and manifold than does injector placement, especially on V8s where a low bonnet line is also desirable.

Regards
Pat
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[CrankAngle]

You are correct Pat. I need to take into account the net force acting on the valve and the pressure differential across the valve is more appropriate.

With regards to the conditions conducive to valve float, it seems logical to take the cam profile, and translate the profile into translational displacement. Integrating the displacement twice yields the "required" acceleration of the valve.

For non-floating valve motion, the "actual" valve acceleration is equal to the "required" acceleration set fourth by the cam.

At an unknown elevated engine speed, the follower will leave contact with the cam, at which point the the required valve acceleration is greater than the actual acceleration.

Perhaps it is at this inequality, the equations of motion for valve float can be evaluated, thus yielding the engine speed at which float occurs?

 

[pontiacjack]

Crank- it looks as if you just replied to your other thread- "Quantifying valve float". And... you just said basically what I posted to that thread.

 

[PackardV8]

I've been a part of a few back-to-back dyno tests where carburetors and EFI were run on the same engine and spoken to and read the reports of several others.

For all-out-top-end maximum horsepower production, the carburetor usually wins. This is probably because the performance manifolds for carburetors have been much more thoroughly developed over many years than those for EFI.

Many aftermarket EFI manifolds for older design engines, such as the Gen I SBC, do not have optimum injector placement.

There is also some evidence the evaporative cooling effect of the fuel by the carburetor lowers the intake charge temperature versus the EFI where the fuel is sprayed low down the intake runner onto the top of a hot intake valve.

Having said that, this past year's Engine Masters Challenge was won by an EFI system on a Gen III Mopar hemi; an engine designed for EFI.

jack vines

 

[140Airpower]

As mentioned, carbs in street or road racing applications (not drag or track racing) have to be sized smaller than what would make maximum power. For that reason alone, FI tended to give about 10% more power. Now for a power-to-weight comparison, it depends if the FI system's weight is less than 10% of the engine's weight heavier than a carb (say 30 - 50 lb). However, the more pertenant weight comparison is the car's weight. So, the FI system's weight needs to be less than 10% of the car's weight heavier than a carb (say 250 - 400 lb). Historically in racing, the change from Webers to FI in 1,100 lb Formula 1 cars in the early '60s, was a decided advantage (but I think the FI systems may have been lighter than a set of Webers).
Another thing mentioned was atomization vs gassification of the fuel. It turns out that the displacement of air by gaseous gasoline is usually more than made up for by the increased density of the charge due to the temperature drop from vaporization. Hence, an ultra-low restriction drag racing carb on an optimized manifold may make more power than a port injection setup.

 

[patprimmer]

Another thing mentioned was atomization vs gassification of the fuel. It turns out that the displacement of air by gaseous gasoline is usually more than made up for by the increased density of the charge due to the temperature drop from vaporization. Hence, an ultra-low restriction drag racing carb on an optimized manifold may make more power than a port injection setup.

That is the exact opposite from what I have been lead to believe, hence the success of down nozzles where wet fuel is injected right above the inlet valve.

Regards
Pat
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[140Airpower]

Pat, I think the common wisdom is it is best to inject as close to the valve as possible. There can be several benefits including less problems with loss of fuel to reversion standoff and potentially less loss of fuel during overlap, if injection timing is quick and precise enough, and a reduction of wet flow, a factor in partial burning and HCs. It is the closest approximation to direct injection. However, air displacement by vaporized gasoline has to be balanced against the increased charge density from evaporative cooling.
The displacement of air by gasoline goes on a mole ratio basis. The mole ratio of air to gasoline for an 11:1 mass ratio is about 37:1. That is, 37 molecules of air(N2 + O2) for one gasoline. The reduction in air density can be made up for by a reduction in temperature of about 12 degrees. Since charge temperature reduces by more than 30 degrees from gasoline evaporation, it should make more power this way. Anyway, the Predator Carburetor experience implies that PORT FI has no advantage over a low restriction carburetor. IMVHO, this is only due to the advantage of charge cooling.
I also note that the history of Formula 1 FI setups saw them raising the injectors progressively from a low, below the throttles location until they eventually wound up with the injectors above the intake bell. Reversion is no problem since they use a plenum and fuel stealing by one cylinder from another can be compensated for by computer. I am not aware of benefits other than increased charge density, but there could be other considerations.

 

[dgallup]

We are completely off the OP question of Detroit RWD pre 85 carb vs post 2000 EFI. The late 70's and early 80's engines coming out of Detroit could barely keep running when you opened the throttle. They would bog and sometimes stall before they were warmed up because the primitive emission systems. Once warm they were still total dogs. Nothing remotely close to race setups.

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[IRstuff]

One thing that seems to have gotten little attention in this discussion is the fact that car mileage figures are substantially higher now than in the period specified. So, ignoring the power question, the cars today are generating their HP on much less fuel consumption. This makes modern engines more optimized overall

TTFN
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