Anyone ever try one of these throttle body spacers (advertised as a "billet aluminum spacer that increases intake air velocity and adds spin to that intake charge" to "enhance your mid-range power, torque, and fuel efficiency")? We have a Jeep with the little 2.5L 4cyl in it and just need a little more pep, especially at mid-range rpms. Are these things worth the $75 and do they make a noticeable difference?

 

Everything I've read, says save your money.

 

The only thing a spacer will do is make the fuel/air charge more uniform, and not much.

Thousands of people have bought the stupid "Cyclone" spacer or its varients and the only difference it made was psychological.

A hotter ignition might help, but a bigger engine is the only sure way to make it git up and hop...

In this day and age, I wouldn't be too quick to buff out the engine in your Jeep though. Smaller is better, and it is a Jeep. It's made to crawl through rough spots, not blaze down the autobahn at warp factor nine.

Think about the mileage it gets, and be thankful of it.

 

Well, the straight answer is it depends.....

Jeep used 3 different 2.5l motors of their own design, and the Pontiac Iron Duke 2.5l, in different years.

A throttle body spacer will make a bit of difference in carbed, or Throttle Body Injection systems. But later Multi-Port Injection systems the results will be negligable.

 

The concept behind it is uniformity of fuel-air mixing. In some carbueretted applications the density of fuel in some areas of the draw through the manifold results in droplets of fuel which cannot burn well - not having been adequately mixed with air so as to vaporise within it.

I have seen discussions regarding fuel "POOLING" in areas of manifolds and upper chambers which causes the fuel to be expelled unburnt into the exhaust system.

Needless to say, this is very inefficient use of fuel!

Upper chamber design, as well as manifold heating and other means, are intended to support "ATOMISATION" of fuel to more thoroughly mix fuel and air thus allowing it to be more completely burned during ignition.

To the best of my knowlege, this is a technology that is both still under developement and imperfect so far. To some degree, complete atomisation and mixing has yet to be achieved.

ALSO: The premise behind some of those "200MPG Carbuerettor" designs was to heat fuel in a sort of heat exchanger before introducing it to a carburettor, or even heat it enough so that it entered a gaseous state (I have seen the designs for them).

There are three states of matter:
Solid
Liquid
Gas

The problem with mixing air and fuel is that most fuels are liquids until heated enough. In addition - inflowing air charges are usually cold with respect to the vaporisation threshold of gasoline(petrol). In a nutshell - it may cause fuel condensation. Droplets do not burn well...

But the length of time in which charge flow in the manifold (intake) happens is very short. Effects are very fast, and thermo changes do not have a lot of time to happen.

I hope I have piqued your curiousity

Come to think of it - I hope this sparks off a whole new discussion!

 

Actually the ORIGINAL concept behind throttle body spacers was to add volume to the intake manifold and therefore increase power, just like how carb spacers are used. The power increases offered by throttle body spacers have always been minimal at best.

I'm not sure when this whole fuel atomization thing came around, but for the most part it's a bunch of garbage. You have to think about this: For one, you can't improve the atomization of fuel much over how the injector delivers it. And two, most vehicles out there today including our Fords have dry manifolds because they use multiport EFI. A throttle body spacer that "swirls" the air isn't gonna do jack on a multiport EFI car. The only type of engine it MIGHT help would be a throttle-body injected car, but even then it wouldn't help much. There's a chance it could be more beneficial on a carb, but still...I kinda doubt it.

 

Then why don't we polish the intake runners when we port heads? Why are there lines and ridges in the bottom of an intake manifold? Or is this just to prevent the fuel atomization from getting worse?

 

Either I am mis-reading this here, or you are looking at this backwards.

You would want atomization to be as complete as possible.

But polishing intake runners on a Multi-port Injection system won't accomplish that. The fuel and air don't mix until they enter the combustion chamber, so any atomization that is going to occur has to occur in there. Now the time between the injector opening and the piston arriving at TDC for ignition is simply too short for any more atomization to occur. So any atomization has to be a product of the injector nozzle design.

In a throttle body system or a carbed system atomization occurs at the point where fuel enters the system. Creating a larger volume of air in those systems can possibly increase the atomization of of the fuel/air mix.

 

The last sentence was sarcasm. Sorry.

The fuel and air does indeed enter before the intake runners/ports on the heads. Maybe I was confusing by not just saying "intake ports"? The roughness on the surface of the intake ports of the heads, does indeed help atomize the fuel. That is why we do NOT polish the intake ports when we port and polish. This is true of both carbed and EFI. I was simply arguing with this statement.....

 

I didn't notice any gains or MPG impovements with a spacer (2 different trucks). For an EFI application, there are more effective ways to spend your money.

 

On a fuel injected setup? No, the "rough" finish on the intake ports helps keep enough turbulence in the air that the fuel can't condense into larger droplets that don't burn as efficiently.

 

Then why do companies like AFR and Fox Lake offer CNC ported heads (intake and exhaust)?

 

Ported is ONE thing, polished is another.

 

True, but neither has factory casting marks.

 

Hey mjunk, you might want to consider installing a larger throttle body on your 4 banger, there are a few places you can get a resized t-body (60-62mm) for around 150 exchange and it will help out some on the midrange lag on the 2.5.