EFI is more susceptable to the turbulence than a carb because EFI's intake charge doesn't carry any fuel.

On a racetrack torque isn't the prime need, it's horsepower. The turbulence isn't an issue at higher rpms, pure volume is the issue. Long runner intakes have more flow capacity on a carbed car. Short runner, large diameter intakes have more flow on an EFI car.

The upper intake on an EFI car is very messy. It's complex and it's since the intake charge has very little mass, it serves to reason the flow would be restricted and imperfect. Getting rid of the long runners in favor of big short runners and connecting them closely to the external air supply makes for more flow. It also makes the air charge more likely to be disrupted by turbulence (including the turbulence that would be created by the fuel injector itself), and it's large volume makes for poor velocity.

A carbed car doesn't have an upper. It's intake flow is more stable because of the additional mass of the fuel. Large, long intake runners hold a generous amount of air/fuel mixture, and at higher rpms, that's what you want.

Velocity must be obtained two different ways because of the place the fuel is added to the intake charge, and how it's added to the intake charge.

For a load of BS that I'm just thinking through my head it sounds pretty convincing doesn't it? LOL.

It sounds better than any other explanation I've received, but I'm still not convinced. The fuel added to the mixture has to be the key ingredient to the reasoning though, because the throttle placement on mechanical fuel injection works best as close to the heads as possible. On our Sprint, there are 8 throttle plates, and they are located within 2 inches of the heads, but we add 10 inch (some are longer) velocity stacks to increase the velocity. Since we have a throttle plate and velocity tube for each cylinder, we don't require a plenum.

So then I guess an EFI engine would benefit from velocity stacks, but hood clearance makes that difficult. Still, someone would have figured out something.

I'm still puzzled.

Take care,
-Chris

I have always wondered about putting 8 butterfly's on the EFI intakes between the upper and lower intake manifold, if that would increase throttle response?

The one thing I really dislike about EFI is the response. You hit a carbed car and it revs WAY faster.

efi feels more responsive too me

Kell-
That's an interesting idea, but is also partly why I'm puzzled. If the performance gain was there, why in Gods name are the stock EFI runners so long and cumbersome? Why not just put them there like you are suggesting. It would cost more in butterflies, but think of the money they'd save on the upper!

This is when I wish I was still enrolled in a class at the cc. They loved questions, and teaching you how to figure them out.

As far as which is more responsive, I can almost always get a carbed engine to respond faster than someone else can get an injected engine to respond, but there are other factors. The Sprint engine has unbelievably quick throttle response, but then again it has 8 butterflies within inches of the intake valves, AND it doesn't have a flywheel to spin.

Take care,
-Chris

Some thoughts on runner length.

The stock 5.0 runners are VERY long. This helps torque production on a very oversquare motor ie 4.0" borex3.0" stroke. If I am not mistaken a typical carb 302 be it a Ford or Chevy likes tons of RPMs and does not have tremendous torque at low RPM's

Obviously you could never run fuel through a EFI 5.0 manifold it would certianly puddle out.

Without any actual data handy ( nice huh) I would imagine that the shortest EFI manifold runners ( victor JR?) is still longer than anything short of a tunnel ram for a carb motor, based on the upper vs lower manifold question.

So for EFI, shorter runner length loose torque gain airflow and higher rpm peak power.

For carb, gain runner length and also runner volume, gain airflow and peak power. But loose low rpm vac signal to the carb due to plenum volume.

The 8 butterflys probably is about the best setup, man that looks trick.

Ok my brain hurts now , gotta go

you all made very good points. it all made sense. well let me give my idea on this. i may be wrong, or i may repeat what one of you said, so correct me:

the only thing i can come up with is, where the fuel is getting atomized, or the location. on carb, it on the very top of the intake. FI it is at the valve basically. try to put a carb on a FI 5.0 upper and lower. wouldnt that create too much fuel in the runners? the vacuum would pull to much in, correct? now put multiport style injectors on a carb manifold and it would work. why? well the only thing i can think of is that the fuel is regulated by a computer and you can make it compensate for the shorter runners. injectors have a duty cycle, a carb basically relys on air flow (venturi effect) to achieve proper fuel mixture. so the FI wont flood out the runner as would the carb hooked up to a FI intake would.

as for runner lengths, i assume carb would flood out with long runners with a mulitport FI intake would. also to bring into the scene is throttle body FI. uses a carb style intake, doesnt it? all the throttle bodies from foreign to domestic, dont have really long runners, do they? i havent seen any. is thier? bring it to my attention. to me, i think it is where the fuel is being atomized makes the difference of runner length. a carberator seems more suseptable to flooding due to how it regulates its fuel.

does any of this make sense? am i right? after reading your posts, this is what came to my mind. these arent facts, just me thinking of it mechanically in my mind. i am very interested to hear any other ideas. PKRWUD and UNIT made some good points.

Most import cars are utilizing variable length runners. A vacuum operated solenoid controls a set of butterflies that change the path of incoming air. When vacuum is high, they seal off the short runners in favor of long runners that build torque. When vacuum drops under hard throttle, it shifts to a short runner path for higher upper rpm hp.

I'm a little suprised there haven't been any of those type manifolds out for the 5.0.

I may be wrong but don't the DOHC Cobra engines run 8 butterfly valves inside the runners???

to me I've seen alot of new mustang owners try to make thier cars look nicer while their cleaning them and then go and use wheel cleaner, completely stripping the wheels.

Or adding new headers before buying an offroad H-pipe

I know and race against a lot of guys around here with horribly mismatched combos.

For them they start stock with:
H-pipe
2 ch Flows, dumped
underdrive pulley
K&N
3.73's
and usually a Cobra intake before too soon, and the cars seem to run fairly well. But then, oh dear Lord, here it comes and in IT goes! Usually a B or E 303 cam thru stock heads, TB, MasAir!

And to make things worse the morons not only mismatch their combos, they throw them together in back yard in an amazingly filthy manner! And then they wonder how I rebuilt my motor, made it a little faster, and last 55k miles (so far), and theirs wont last 15k!

And what REALLY get me is when the basicly 'first mod' (behing exhaust) is a CAM!!! I've seen SEVERAL sets of stock 302 (87-93) heads and I wouldn't dream of putting a cam in a stock headed engine!

Here lately they're starting to listen to me on engine combos and it shows. Guys are getting WAY faster and looking to heads before cam (sometimes). I want to build the next 5.0 that gets rebuilt around here to show everyone what Tolerances and Clenliness are!

But i'm still learning too!

later
graham

l personally think the worst things to mess with/waste money on are:

-low temp thermostats
-gutting mass air flow sensors
-removing/gutting cats (states that require strict emissions inspections)
-running expensive octane boosters
-large bore throttle bodies
-underdrive pulleys

these are all things that have very little performance gains, and some can greatly sacrifice drivability.

Wow, an old thread here,

I dont think the lower temp stat is a bad move, especially if you live here in tx, plus, its not like your out thousands of dollars if you dont like it:confused: pfft