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

[Dimis]

Originally Posted by Gaz64

Yes the 48 is too small, but you can buy 58 or 60 IDAs from Gene Berg.

Hey Gaz,

Is it not true that:
48s are suitably sized for street on an FE, even a big bore FE.
The limitation here however is that 48s will choke the engine starving it of air at high rpm. Therefore they are at their best in midrange power delivery, street flowing circuit type course use, as opposed to drag racing or oval track.
The 58s from Gene Berg that cost a motza (and are out of stock) shift the power to a higher rpm range, and intact could adversely affect street driving in the common low to middle band experienced in street driving, by reducing air velocity.

Or is my humble research ill informed?
Are you able to kindly clarify this?

On another note: I believe webers ARE workable for a street engine. EFI or otherwise. The only limitation is the the time energy money and inclination one has to invest it them. For a car that's driven as infrequently as most Cobras are, I've placed them in the who could be farked category, for now. As I'm unlikely to drive them often enough and far enough to resolve and sort the issues.
That said I still do find myself tempted. :

Thanks in advance.

[Gaz64]

Originally Posted by Dimis

Hey Gaz,

Is it not true that:
48s are suitably sized for street on an FE, even a big bore FE.
The limitation here however is that 48s will choke the engine starving it of air at high rpm. Therefore they are at their best in midrange power delivery, street flowing circuit type course use, as opposed to drag racing or oval track.
The 58s from Gene Berg that cost a motza (and are out of stock) shift the power to a higher rpm range, and intact could adversely affect street driving in the common low to middle band experienced in street driving, by reducing air velocity.

Or is my humble research ill informed?
Are you able to kindly clarify this?

On another note: I believe webers ARE workable for a street engine. EFI or otherwise. The only limitation is the the time energy money and inclination one has to invest it them. For a car that's driven as infrequently as most Cobras are, I've placed them in the who could be farked category, for now. As I'm unlikely to drive them often enough and far enough to resolve and sort the issues.
That said I still do find myself tempted. :

Thanks in advance.

Yes all true, up to a point.

I agree the 48s are good for mild to slight aggressive street manners, but on a big engine will limit top end.

Here is some beautiful 58s of a fellow member:

58 mm Berg IDA Carbs--Here They Are

Gary

[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 ?

[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

[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

[G-Pete]

Originally Posted by Gaz64

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.

------

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.

??? 330 cfm/barrel

[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.

[FUNFER2]

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.

"A wide lsa is required to limit reversion"
How much lobe seperation, was my question.

[moore_rb]

Originally Posted by FUNFER2

"A wide lsa is required to limit reversion"
How much lobe seperation, was my question.

there is no magic LSA number to make things all warm and fuzzy...

valve overlap is the real factor, and overlap is a function of LSA and duration taken together.

but like I posted earlier, 112 degrees LSA, or smaller, is typically where most aggressive street/strip cams begin messing with your MAP and your manifold vacuum

114 could be considered a safer, but again- it also depends on how much duration at .050 you are running- a super long duration cam (240+ at .050) is probably still going to introduce overlap instability, regardless of how wide the LSA is...

But when it comes to the question of how well your cam might (or might not) co-exist with EFI, just let your eyes and ears be your guide-

If your cam makes your idle sound like a Harley Davidson, and if your engine shakes the whole car while it's idling, then it's a fair bet that tuning a speed density EFI system to work smoothly with that cam is going to take time, effort, and money.

It will be a little easier if you have a MAFS , but again- no current 8-stack system uses MAF

[twobjshelbys]

Originally Posted by moore_rb

If your cam makes your idle sound like a Harley Davidson, and if your engine shakes the whole car while it's idling, then it's a fair bet that tuning an EFI system to work smoothly with that cam is going to take time, effort, and money.

I can vouch for this! The combination of the lopey cam and DFI 8-stack in the Roush 427IR are a really tough combination to get working at other than sea level. I hear they changed their controller from Accel to something else, but I struggled for almost a year to get a balanced tune that properly accounted for altitude.

[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)...