Originally Posted by D-CEL (Post 941063)

RodKnock,
I'm all about air flow. The 58mm throttle bores are only 2.283 inches
the 3.000 are 76.2mm. roughly 25% more area
The engine is an all aluminum 565 ci
Its an A96 block with 351 main journals (2.750 vs. 3.000)
forged Ford/Sonny Bryant 4.250 stroke crank with 2.200 rod journals
6.800 rods
TB coated spherically dished 4.600 JE pistons, 11.8-1 @ "0" deck with a .040 gasket.
Charlie Evans ported SCJB heads 2.25 intakes, Isky springs, Titanium retainers, 400 cfm @.800 lift. TB coated combustion chambers and exhaust ports
Danny Bee belt drive
ATI damper
Ed Pink 5 stage dry sump pump with a oil-air separator
Billet Fab 2 piece pan with piston squirters
Meziere remote 55gpm water pump (reverse flow cooling system)
Roller cam bearings with oil squirters
Blue thunder Competition valve covers with valve spring oilers

The goal it see how much hp I can make on pump gas, naturally aspirated.
To me, detonation control it key. So I'm working to control the combustion process. Keeping the heat out of the head and the piston.

Anyway, with the 3" throttle bores should offer no intake restriction at whatever

Jason

Originally Posted by D-CEL (Post 939967)

In theory, a carb or an EFI system that have equal flow and are properly tuned will make the same power. Flow is flow at WOT (wide open throttle). What we are really talking about is low and mid range power and drive-ability.
The main advantages of an EFI system over a carb, comes from its ability to precisely control the mixture. The result is better drive-ability, enhanced fuel economy and usually a flatter, wider torque curve under the WOT threshold.
But with these "PROS" come with some big "CONS" (no pun intended to the EFI mfgs) primarily system complexity and much higher costs. On top of that, you have to re-learn how to tune. The good part is that tuning becomes more scientific in practice, taking away some of the Juju associated with adjusting a carb.
Conversely, carbs are cheap(er) and simple(er) and for the most part can be made to produce sufficient power and acceptable drive-ability. While cabs work, to me they are a “compromise” system. I run them, but I don’t like them!! LOL

We all search for BIG HP in our mostly STREET DRIVEN toys.
But we must all remember that carbs need Vacuum to function. The wilder the engine combination becomes, the less happy most will be with the street manners of a carburetor.
EFI doesn’t need or care about vacuum and because the fuel is forced into the engine and the high level of control, it can be used to tame an otherwise….grumpy motor, another advantage.

While it is interesting to see head to head comparisons of the power, I think the true measure is how they start and drive on a cold morning in the mountains. How crisply it accelerates after idling for half an hour on the freeway when it’s 110 Deg. How controllable is the power delivery when you’re rolling into the throttle while exiting a hard right hand turn.

All things I don’t like about my very expensive, well tuned, super trick carb.

I’m putting EFI on my new motor, because it has flow potential that no carb can match thereby making the most possible HP and torque and with the right ECM (BIG STUFF or ACCEL DFI) will offer the best possible drive-ability. No compromises.
To me that is worth the additional cost and extra effort.

As I have said many times, there is no right way or wrong way, just opinion.


Jason

http://www.clubcobra.com/photopost/d.../KINSLER_3.jpg

Originally Posted by D-CEL (Post 941113)

To say that the EFI system made less hp because the fuel was “occupying space” that should have been occupied by air… confuses me.
The mixture of air and fuel (a/f ratio) to achieve peak performance is fairly straightforward. Chemically correct is 14.7:1, slightly lower in practice. If the volume of fuel was so great that it displaced air, the a/f would be hugely rich (read to much fuel). Combustion performance would suffer or not work at all.

Originally Posted by D-CEL (Post 941113)

Are you saying that a carbs make more power because they rely on vacuum and therefore the fuel takes up less space in the combustion chamber?

I think the article was comparing the dual plane manifold and a Holley Carb the early Mercury Cast aluminum EFI manifold with a single throttle body and a small square flame arrestor. It successfully showed that the EFI system made less peak hp than the carb, because the intake tract was long and more restrictive.

Originally Posted by fkemmerer (Post 986797)

Some additional thoughts on the EFI vs carb question. In many cases, an EFI setup (when properly tuned) can be bolted onto an engine build for a carb and performance and drivability will improve. This is due to the EFI motor's ability to deliver an broader and more ideal range of fuel and timing in any give range of engine load and RPM (as well as responding better to transient conditions like mashing the throttle at low loads/RPMs). EFI is also very helpful in solving difficult tuning problems like big cams with short individual carbs or throttle bodies.

Something to consider is what happens when a motor is built with EFI in mind in the first place. Carbs need a strong vacumn signal to work. This is especially true at low RPMs and idle (this is why cam selection is critical with webers for example). This forces an engine builder to pick a cam that can provide some level of idle vacumn. EFI systems do not need this and therefore cam selection, intakes, etc. can be tuned for maximum power and torque without these compremise. This coupled with that fact that all restrictions required to create lower pressures to atomise fuel in a carb are eliminated give the EFI system a decided advantage in high performance applications.

- Fred

Originally Posted by Cobra #3170 (Post 986820)

We dynoed my engine back to back with a 1050 Dominator and a 1650 cfm Wilson throttle body (with spacer). The manifold was a highly modified Victor Jr. The Dominator made 819@7600 and the EFI made 806 @7600. The theory was that the additional cooling provided by the fuel vaporizing upstream with the carburetor may have been responsible for the improvement. Formula 1 engines (several years ago, I am not sure what they do now) had the injection nozzles above the intake trumpets in the plenum probably for the same reason. The location of the EFI nozzles in the intake track on my manifold were not optimum due to packaging which may also account for the difference. The EFI did have a fatter more consistent torque curve and does not crap out under high G stops and cornering. That is the main reason I went with EFI. It also starts much better because it doesn't flood the engine when you move the throttle like those twin 50cc accelerator pumps do.

Originally Posted by fkemmerer (Post 986822)

Any thoughts on the idea of power gains that a difference cam that was optimized for fuel injection might have allowed?

Originally Posted by Cobra #3170 (Post 986829)

The cam was optimized for EFI because that was what I was going to run. We just put a carb. on it to see how the two compared. We tried varying the injection timing in relation to cam timing with different sized injectors too. I think if the nozzles were further up stream in the intake runners it might have helped but packaging would have been an issue. One thing we found was that retarding the ignition above 7000 helped with the EFI. We did not try this with the carb. because the main effort was to get the EFI right. We made so many dyno runs the engine had to be freshened with new rings when we got done.
I was really surprised at the results because several years ago we tried the same experiment on a milder engine and it was 20 hp better with EFI. That engine was in the low 700's @ 6700.

Originally Posted by fkemmerer (Post 986834)

Interesting, what are your thoughts as to why retarding the ignition above 7000 RPM helped the power output with EFI? How much retard did you use?

Originally Posted by Cobra #3170 (Post 986820)

It also starts much better because it doesn't flood the engine when you move the throttle like those twin 50cc accelerator pumps do.

Originally Posted by TButtrick (Post 986958)

Doesn't your EFI ECM lengthen the injector pulse width to give the motor the same fuel shot on startup? A carbed car that doesn't start just as quick or "easily" as EFI has the carb setup incorrectly.

Originally Posted by Cobra #3170 (Post 986987)

The carb starts fine when it is cold however when the engine is hot it will not start if you look at the throttle, any movement of throttle linkage dumps enough raw fuel to make for a very slow and rich start, it is a single plane manifold so the fuel runs right down the ports.

Originally Posted by TButtrick (Post 987136)

My experience is the opposite. On a cold first start of the day, I give a half squeeze of the throttle and no choke. Starts first crank. Subsequent warm starts throughout the day, I don't touch the throttle and starts first crank.