Do 8 Stack EFI or Weber Carbs Run Good On The Street?

[redmt]

Originally Posted by Ron61

I have the Mega Squirt fuel injection on my Coupe and like it. I did have the power cut back on the engine when I quit racing it and it works very well on the street and in our mountain roads.

Ron

I don't mean to correct Ron but he has a TWM Borla setup with the Mega Squirt ECU. The engine was built by me and the M S system was setup and tuned by Brian Rebello of Rebello Racing. It's an easy system to check the tune if you have the correct and original program but you need to take it back to whomever tuned it, or have them rewrite a new program and send it to you if you want to do anything but run the fuel pressure up or down.

[Gary(SF)]

Originally Posted by twobjshelbys

Do you find the linkages to be stable? I've heard that many folks have to rebalance them frequently. A friend, not a tinkerer, eventually gave up trying to set them up but I think he was using a cheap vacuum cap.

Yup, no issues.

[Dimis]

Originally Posted by 66gtk

I'm just going to put this lil' photo here. Lot's left to do before this engine is where I want it, but for now it starts easy, idles at 6-700 RPM and is super easy off the line and put putting around town. Pretty much the opposite of what the article suggests. Hell, I don't even use 1st gear unless trying to go up a hill off idle. The article talks mostly about Weber carbs as opposed to EFI, though.

You B@stard!!! I'd just finished convincing myself that I wasn't going to spend the kids college fund!

Thanks for the porn... that's a nicely executed example. All parts well integrated.

Now where did I put my hammer... I need to crack open that piggy bank.

[Gary(SF)]

Originally Posted by Dimis

The limitation here however is that 48s will choke the engine starving it of air at high rpm.

I have heard that before, but my 521 with Weber 48 IDA's pulls strong to the redline. Go figure.

[FUNFER2]

Can a cam be too big, that you have little vacuum, meaning do we need vacuum to run the system properly ?

Are there any other specs of the engine that will screw up the working of this type of injection, thus the engine will not run well ?

Any special engine build needs for this injection ?

[Dimis]

Originally Posted by Gary(SF)

I have heard that before, but my 521 with Weber 48 IDA's pulls strong to the redline. Go figure.

Great to know! Its always perplexed me how 8 trumpets theoretically can't supply enough air for each cylinder when compared to a single carb

If you don't mind kindly sharing please:
What are your cam specs?
Hydraulic or solid rollers?
and Rpm red line?

Thx

Originally Posted by FUNFER2

Can a cam be too big, that you have little vacuum, meaning do we need vacuum to run the system properly ?

Are there any other specs of the engine that will screw up the working of this type of injection, thus the engine will not run well ?

Any special engine build needs for this injection ?

My understanding is a wide lsa is required to limit reversion, and the more vacuum the better the end result. I'm no expert. I defer to greater minds for info on this.

[FUNFER2]

Do you know apx how much ?

[Gaz64]

Originally Posted by Dimis

Great to know! Its always perplexed me how 8 trumpets theoretically can't supply enough air for each cylinder when compared to a single carb

Anthony,

That's because a single 4 barrel carb supplying 8 cylinders via a single plane intake, has only 3 inlet valves open at any time supplied by a carb of example 750 cfm.

The constant flow of air, and the manifold plenum volume allows the cylinders in turn to draw from.

In an IR carb application (48 IDA), each cylinder can only draw from the volume within it's own runner, through the carb to the trumpet.

An IDA flows about 330 cfm per barrel at best.

Gary

PS. Email reply soon

[Dimis]

Originally Posted by FUNFER2

Do you know apx how much ?

Sorry, I'm not certain I'm clear on how much of what?

- If Price (apx) $4-8K for webers. $9-12k for EFI webers
- If LSA (apx) 112-114 (110 is marginal)
- If vacuum (apx) 20mmgh +/-

Kevin - I'm NO expert on this topic. My slim research is mostly based on reading other peoples experiences and internet searches. As such I'm early in the learning curve with NO hands on experience with 8 stacks.
I would seek info from someone with more knowledge and experience than myself before drawing any conclusion.

Good luck with it

[Gaz64]

Anthony,

With carbs, the cam timing is way more critical.

With EFI you have more scope, IF it is sequential EFI.

Gary

[fordracing65]

Originally Posted by Gaz64

Anthony,

With carbs, the cam timing is way more critical.

With EFI you have more scope, IF it is sequential EFI.

Gary

Exactly. Key word sequential.

[Gary(SF)]

Mechanical roller cam, I use 6000 for red line, don't know the cam specs but it is the Ford Racing 521 crate motor if that helps.

Originally Posted by Dimis

Great to know! Its always perplexed me how 8 trumpets theoretically can't supply enough air for each cylinder when compared to a single carb

If you don't mind kindly sharing please:
What are your cam specs?
Hydraulic or solid rollers?
and Rpm red line?

Thx


My understanding is a wide lsa is required to limit reversion, and the more vacuum the better the end result. I'm no expert. I defer to greater minds for info on this.

[moore_rb]

Originally Posted by FUNFER2

Can a cam be too big, that you have little vacuum, meaning do we need vacuum to run the system properly ?

With Carbs (Webers) - Yes. With Throttle Body injection (TBI) - Yes.
With Multi-port injection (MPI) - It depends on the computer.

Speed density MPI (Also called "open loop") systems use manifold absolute pressure (MAP) as the primary air measuring device for calculating the injector pulse needed to achieve the correct A/F ratio for any particular throttle position; and cams with a lot of overlap will cause a lot of instability in the MAP, the same way they wreak havoc with vacuum. This makes the MAP sensor send erratic signals to the computer, making the computer think it has to make hundreds of adjustments per second. So tuning the idle and part throttle settings in a speed density controller can take lots of time, and lots of trial and error on the dyno, when you throw a big cam into the mix.

BTW- all the current crop of 8-stack style EFI systems out there today are speed density MPI designs, and so they will require this more sensitive tuning, (and probably more time on the dyno to accomplish it)

The other style of MPI is MAF/MAP "combination" (also called "dual circuit", "sequential" or "closed loop") systems. These systems use MAP for calibrating the WOT A/F ratio, and they use Mass Air Flow (MAF) to calibrate the idle and cruise throttle positions.

MAF systems are, hands down, the BEST EFI design for running with a large cam (especially in a street driven car); because the cam would have to be REALLY extreme to influence the air flow in front of the throttle valves.

The reason none of the 8-stack EFI systems use a closed loop controller is that there is no practical/feasible way to incorporate a mass airflow sensor into each air horn (yet), nor is there a controller out there that can aggregate 8 MAF Sensor signals into a single value that the computer can use. (This is what Olddog and I were talking about in the other thread you opened up about the Ebay manifold you had found)

Originally Posted by FUNFER2

Are there any other specs of the engine that will screw up the working of this type of injection, thus the engine will not run well ?

Any special engine build needs for this injection ?

Nah- the cam profile (overlap most specifically) is really about it. Tight lobe separation angles (below 112 degrees), and mega long durations (above about 230 at .050) are where you are going to start running into potential part-throttle hassles with a MAP sensor system (These values are just yardsticks, not hard values)...

[RodKnock]

Just from an aesthetics point of view, the system pictured above has those rails right through the middle of the manifold. Not a big fan.

[fordracing65]

Originally Posted by RodKnock

Just from an aesthetics point of view, the system pictured above has those rails right through the middle of the manifold. Not a big fan.

I don't mind the rails at all. The common guy would not even notice them. He would be starring at the stacks. I actually like the carb turkey pan look.

[RodKnock]

Originally Posted by fordracing65

I don't mind the rails at all. The common guy would not even notice them. He would be starring at the stacks. I actually like the carb turkey pan look.

I considered the 8-stack EFI or carb setup for my car, but there's something to be said for simplicity, which is the turkey pan and carb.

Ultimately, I love the look of the 8-stack setup, but the setup and maintenance steered me away. I thought I'd have to add a fuel delivery expert to my payroll and saving $10,000-$15,000 didn't hurt either.

[fordracing65]

I don't think any 427 Cobras came with the stacks from the factory. Another reason I like the carb turkey pan look. I like competition cobra cars.

[Luce]

I put one of those $1000 cheap chinese 8 stacks on the wife's 71 vette with a blueprint 383 long block advetised as 440 HP. I only have about 2 hrs messing with the tune and it runs great, with AC. I did some "work" to it. I'm running megasquirt and eliminated the distributor and put 2 Dodge Neon coil packs on it. Picks here are a bit difficult, but if you're interested and want to learn to tune yourself, PM me.

You guys can flame on, but I have less than $2000 in the whole thing and it runs well enough for me to put lovely bride behind the wheel with confidence.

[fordracing65]

Originally Posted by Luce

I put one of those $1000 cheap chinese 8 stacks on the wife's 71 vette with a blueprint 383 long block advetised as 440 HP. I only have about 2 hrs messing with the tune and it runs great, with AC. I did some "work" to it. I'm running megasquirt and eliminated the distributor and put 2 Dodge Neon coil packs on it. Picks here are a bit difficult, but if you're interested and want to learn to tune yourself, PM me.

You guys can flame on, but I have less than $2000 in the whole thing and it runs well enough for me to put lovely bride behind the wheel with confidence.

Small cam. Easily done. It's when you get an aggressive cam they get strange. Read the threads in here about them.

[Luce]

I'm going to say with the individual runners, the reversions of a happy cam doesn't spit the fuel from one cylinder to the others, so you get better fuel distribution than a single plane multi port injection, and WAY better than a carb (trying to work with no vacuum) in a single plane manifold.

The "work" I did was adding an idle air valve from a 5.4L triton, and 2 separate vacuum chambers under the manifold. One for idle air (and makes the syncing far less critical) and one for the MAP signal. Megasquirt uses SD metering for light throttle, then switches to Alpha-N metering when MAP drops below 10 kpa