Engine Management/EFI- Vs- Carbies

[Ross Nicol]

I can't believe that carbies are still being fitted in preference to fuel injection and only today I received an email from a forum member who has been recommended to use carbies for simplicity and power.Now I don't have a problem with simplicity and maybe you could match top end power but with fuel injection you have the ability to feed in the absolute precise amount of fuel for best combustion and power for all throttle points/load.Now this is not rocket science as computers are used in all things these days.
Basically the computer has a few inputs and a few outputs and based on what is happening at the inputs, the outputs will control injectors, coils, fuel pump, fan etc.Most of the timing is taken from a sensor on the crank and camshafts,so it is vital to have these working correctly as they are important inputs.Other inputs are TPS or throttle position sensor (basically a potentiometer or volume control in amplifier)which is mechanically connected to the throttle shaft, MAP sensor, senses inlet manifold pressure, water temp sensor, air temp sensor and any others I have forgotten to mention.
Now on my car I have the 8 throttle body inlet manifold so the throttle position sensor is used on it's own for the computer to work out how much air is flowing.The MAP sensor can only be used on a single throttle body type inlet.So on my car the MAP sensor is monitoring Barometric air pressure.This is not a bad thing as when I drive up into the mountains where the air density changes this sensor tells the computer to modify the air/fuel ratio.So how do carbies acheive this, well you pull over and change the jets in the carbies of course or swear at the car for running so rough.Ok you get in the car on a cold morning and pull the choke out and 20 minutes down the road you realize you forgot to push the choke in.Now most of us know thats bad for engine wear not to mention cost of wasted fuel.With EFI this can't happen cause there is no choke.The computer has checked the water temp sensor which says I'm cold and richens the mixture by holding the injectors open longer until the car warms up, all automatic.
Now I have a friend who is a gun at tuning webers he whips the top off them between races, tweeks float levels,balance etc and he can hear when they are off song with his expert ear listening to the exhaust.This he does while I clean the windscreen on my car.I know that he will never match the tune that I achieved on the dyno with my engine management because for every 250 rev increment right up to my max revs and for every position of my foot on the accelerator the computer has calculated the precise fuel required.Now this translates to best possible torque out of slow corners and no bogging down or coughing which (carby) accelerator pumps are notorious for.So I'll go along with IDA's for originality but I won't be joining you.End of sermon
Regards Ross

 

[Tim Kay]

Amen Ross /ubbthreads/images/graemlins/laugh.gif

In addition, a dear friend of mine told me wilst I was agueing the right to maintain originality with Weber 48 IDA. He simply said, "but Tim, it's not an original car" /ubbthreads/images/graemlins/smirk.gif

Needless to say, then and there I switched to 8 body EFI for all the reasons stated above /ubbthreads/images/graemlins/cool.gif

 

[Mike Dozier]

I'm using same Holley 4bbl/Edelbrock RPM intake used on my Cobra....total cost about $ 450 with air cleaner.
With electric choke it starts just fine in cold weather...never had a backfire, never even opened the carb.
Set the idle and drive away...plenty of torque and power.

If I had the budget some others did maybe I'd consider EFI...but maybe not. If someone tossed $ 5,000 my way
I'd probably upgrade my tires/wheels/brakes or maybe spring
for a nice 347 shortblock. Sorry...to each his own.

MikeD

 

[ QUOTE ]
I can't believe that carbies are still being fitted in preference to fuel injection...

[/ QUOTE ]

Carbs are chosen because you can have the performance of FI for 10% of the cost. A properly set up carb does not need constant tuning. I am not talking about a set of Webbers, I am talking about a basic Holley. It does not need 10 different sensors connected to a computer. It does not have 12 different things that can fail and leave you stranded.

Do these facts make it more believable?

 

[Paul Thompson 'Hooligan']

Each to their own!

However, Efi will work well with just 3 sensors (possibly even just one) and a trigger! (air temp/water temp/throttle posn + TDC) and if one of those sensors fails, the ECU may well inform you which one is failing and may even have a 'get you home' strategy programmed in.

Also - you can connect a map sensor to individual throttle bodies, Roys Kinsler system had a small pipe from each to a common block that combined the vacuums to give a signal for a map sensor and whilst some cams create a rather erratic signal at low revs, even this can be filtered by many ECUs.

Correctly tuned, an ECU will at least equal and generally out perform a carb system in terms of both power and reliability. Many major developments in engine technology have only been possible since the advent of fast high performance, reliable electronics, that allow an engine to be tuned to within a whisker of destroying itself in terms of mixture and timing. I wonder what the current F1/Indy series engines would be producing if they were all told to switch to carbs and simple ignition (other than increased profits for the fuel companies and a heap of scrap metal!).

Nope, for me EFI is best - I love 'the look' of Webers and accept that a carb can give good power, but nothing beats EFI....

Now off to bed! /ubbthreads/images/graemlins/smile.gif

 

[Ron Earp]

I can agree with all of you fellows and I can definitely do both - I've pulled ECU systems apart and adapted them to other engines, craked Lotus code to tune the GM ECU, done lots of stuff to Ford's EEC-IV, and tuned a few other systems. I also can tune carbs well, and understand ECU system just fine. But, I'm going to use carbs. Why?

I like the simplicity of them and the clean look on the engine. I think that when I redo my engine I am even going to fit it with an old style cover and mechanical fuel pump (I can hear it how, The Horrors!). I'm not going for that original factor since it is a replica, I'm going for the "I like a clean motor look and one fuel line plus one distributor wire is cool" look.

I'm sure I'll covert it to fuel injection at some point, I like to mess with stuff. Bart and Mike have good points on cost though, a well setup Holley/Demon/Carter on a good manifold is dang simple, makes great power, and is really, really, cheap. Used it could be done for $200 easy.

 

[Mike Dozier]

If EFI is so "modern", how come NASCAR still runs carbs?
It can't be due to simplicity or cost since all teams
have huge budgets filled with the best engineers money can buy.

I'll guess it's because carbs are a throwback to
simpler days (Nostalgia if you like), when an "average"
person could work on their engine. Today...DAMNED few of us
can tune new engines since they become computer controlled. Don't get me wrong...I LOVE my modern
daily drivers...but I love my simple carbureted toys
when I'm playing on the weekend. Off soapbox now...

MikeD

 

[ QUOTE ]
...Roys Kinsler system had a small pipe from each to a common block that combined the vacuums to give a signal for a map sensor and whilst some cams create a rather erratic signal at low revs, even this can be filtered by many ECUs...

[/ QUOTE ]

I got a quote from Kinsler for my Cobra. $8500 with a relatively simple FI. And then I had to install and tune it. I passed for a Holley.

Don't get me wrong. I built my first FI in 1989 using DFI and a custom made manifold setup on a 302 Ford in a 65 XKE. Still have the car. I love FI. But there is nothing wrong with a carb.

 

[Hershal Byrd]

WoW ! IS THIS A GOOD THREAD OR WHAT??. It's kinda like the big block VS the small block thing.. /ubbthreads/images/graemlins/grin.gif
I have been through the gamout with Holley's, Webers and EFI. I Luv EFI. It's the best for me and the most dependable so far. I had Webers on my Cobra and 34 Ford for 15yrs. Loved the look and hated the tuning when I went up to a higher altitude. That wasn't to often but enough to be a pain when I did.
All fuel injection systems are not $5K or $8K. There are several units available that replace the carb with a throttle body injection unit for under 1K. Very cheap and they work great . They do the same thing as a carb but with more precision. I personally like the Edelbrock Pro Flo EFI system as it gives you a computer and all things needed to hook it up for $2500. Holley also makes one and it's more expensive.
The eight barrel unit does have the WOW factor but it also has a few draw backs. The biggest of which is the lack of a low cost, good looking, air filtration system. Nothing works without sacrificing the view out back or performance.
Everybody I know that has these run those sox or nothing. I run nothing. Another problem is this unit is a b!tch to clean and the trumpets bend easily. Those trumpets ain't cheap either.
Alot is still to be said for a good carb. They are a simple economical delivery system and many new designs have made it much better than the old Holley of yesteryear.. /ubbthreads/images/graemlins/grin.gif
All my daily drivers are EFI including the Dodge diesel. I can honestly say I have had no failures on any of these vehicles. I used to have a Toyota Paseo with 142,000 miles on it and it still ran nice up until the day it was stolen.
I guess it all adds up to your personal needs and perceptions of what works for you.

Hersh /ubbthreads/images/graemlins/smile.gif

 

[Ross Nicol]

As a side issue CAMS the Australian motorsport controlling body are forcing all carbied cars with electric fuel pumps to fit a (zero crank speed) fuel pump cut off.A dangerous situation after an accident is when the ruptured fuel line continues to feed fuel.Now most EFI computers turn off the fuel pump within seconds of zero crankshaft rotation.A very comforting thought when you stop to think about it.
Ross

 

[Tim Kay]

A nice comparable Weber setup is $4,500+ (manifold, carbs, linkage and selection of jets). So cost can be expensive either way /ubbthreads/images/graemlins/smirk.gif

 

[Paul Thompson 'Hooligan']

Hi again -

I suspect that Nascar regulations don't allow injection for the purpose of making the sport more equal, as 'clever' engine management can add all sorts of things that would be difficult to police effectively. They still run restricter plates on the inlets don't they?

Yes - Kinsler can be very expensive, but the magnesium setup that Roy purchased, was second hand off a v8 powered german touring car, so somewhat discounted. It also came with Accel batch fired management, which worked very well and was easily tuned. I just like tinkering about with engine management systems so the 8-coil Motec sequential setup was a challenge and lot of fun to fit (fired-up 1st press of the button too!)

The Edelbrock Pro-Flo system that Hersh mentions is very good too and whilst being based on a batch-fired Weber Marelli ECU (like Ford Cosworth over here, F40 and Lancia Integrale - to name a few others) has a clever little module added to allow the seetings to be 'tweeked' from the supplied setup, to allow for individual engine installations. Edelbrock will also supply custom chips based on the details you give them re your engine spec. Not perhaps as tuneable (easily) as other systems but works very well. Also, the throttle body supplied will flow up to 1000cfm, with 2+2 throttle butterflies and an active idle control valve.

For Daves R42 we kept the throttle body and but have now fitted 8 coils + 59lb injectors + Motec M48 (sequential). Starts easy too! but the 100-150BHP of Nos has yet to be tested.... /ubbthreads/images/graemlins/grin.gif

Anyone got a cheap supply of driveshafts??.. /ubbthreads/images/graemlins/wink.gif