thottle body spacers

[Dr. Dyno]

I don't doubt your mileage claim, but I'm curious as to how you would explain a mileage increase from a change that ordinarily would not effect fuel consumption. A 5% increase in plenum volume that may contribute to a slight increase in power in a narrow part of the upper RPM band which is a very minor part of your drive cycle. It doesn't add up. Increasing power does not automatically result in an increase in mileage. In fact, more often just the opposite.

My first reaction is that you've made so many changes to your rig that it would be difficult to attribute a change in mileage to a specific modification.

The 62mm bored TB spacer does more than just increase the plenum volume by 76cc. It also increases effective intake tract length by 1" and raises the TB further away from the plenum floor. This allows the intake air to reach a higher velocity before entering the plenum, particularly at low/medium rpm, thus producing a small torque gain. The mpg gain is due to the slightly leaner air/fuel mixture that results from the higher airflow velocity. Think of the spacer as a mini tunnel ram and you'll get the idea about how it works. The helix bore is merely a marketing gimmick.
As for the Tornado, that's completely useless. It has been tested by independent testers and the result was zero HP and mpg gain. The only thing you gain from it is a lighter wallet.

 

[Bloose]

The 62mm bored TB spacer does more than just increase the plenum volume by 76cc. It also increases effective intake tract length by 1" and raises the TB further away from the plenum floor. This allows the intake air to reach a higher velocity before entering the plenum, particularly at low/medium rpm, thus producing a small torque gain. The mpg gain is due to the slightly leaner air/fuel mixture that results from the higher airflow velocity. Think of the spacer as a mini tunnel ram and you'll get the idea about how it works. The helix bore is merely a marketing gimmick.
As for the Tornado, that's completely useless. It has been tested by independent testers and the result was zero HP and mpg gain. The only thing you gain from it is a lighter wallet.

Isn't that what I said??

I could see the leaned out mixure being true because our Cherokee's use a speed density type FI with no mass air flow sensor. I still think though engine speed, cruise speed, and driving style could vary results greatly. You guys are both making good arguments!

B-loose

 

[Bloose]

Oh, another thing I was thinking. I am always a bit skeptical of HP and mileage increases with ANY bolt on item. I read a really good article about plug wires that verified many of manufacturer’s way over blown claims. They even had people who should know better claiming increased HP with a certain wire type. But when dynoed there were either no increases or even decreases in HP in some cases. There is actual and perceived and perceived is impossible to measure. I would love to see some before and after dyno reading from real XJ owners with TB and spacer changes, and then with exhaust changes. Then there would be quantifiable proof of what these mods can provide at the rear wheels. From there people could make their own conclusions about the value of these mods.

The Dyno doesn't lie. (That was a pun you know)

B-loose

 

[MaXJohnson]

The 62mm bored TB spacer does more than just increase the plenum volume by 76cc. It also increases effective intake tract length by 1" and raises the TB further away from the plenum floor. This allows the intake air to reach a higher velocity before entering the plenum, particularly at low/medium rpm, thus producing a small torque gain. The mpg gain is due to the slightly leaner air/fuel mixture that results from the higher airflow velocity. Think of the spacer as a mini tunnel ram and you'll get the idea about how it works. The helix bore is merely a marketing gimmick.
As for the Tornado, that's completely useless. It has been tested by independent testers and the result was zero HP and mpg gain. The only thing you gain from it is a lighter wallet.

At partial throttle, the intake tract is generally considered to be from the throttle plate to the attachment at the air box. At wide-open throttle, it could be considered as part of the intake tract length. In either case, the intake tract length effects air flow in a specific RPM band with the outcome modifiying power output(in that narrow RPM band only) rather than fuel efficiency. On your own website, you calculate that the manifold is tuned for maximum cyliner fill at around 4900 RPM. How much of your drive cycle is at redline?

Raising the throttle body further away from the plenum floor would not impact charge velocity which is a function of demand (piston speed) and cross-section area at any given point. You can change the cross section area at the throttle body to change air velocity at that point, but velocities at other areas of the intake remain unaffected as they are dictated by local cross-section area. Furthermore, there is no reason to believe that a higher air flow velocity would result in a leaner air/fuel mixture. If more air enters the combustion chamber as a result of higher velocities, the computer will alter injector pulse-width to maintain the air/fuel ratio dictated by its fuel maps and algorithms.

Knowing how things work, I would not think of the spacer as a mini tunnel ram. What I don't know is where that .8 MPG increase came from.

 

[xray]

I think that you would not notice much difference unless your tb is bored out, you would also have to have an upgraded exaust to accomadate more air flow. I think you would get as much airflow improvement if you removed the venturi inside the intake tube, which would cost you nothing but a little time( 5 min.) and if it would, by any chance, have an adverse affect you could replace it in no time at all. Also dont forget about a less restrictive air filter.

 

[jdraylob2002]

ok.. so in the end, what are we talking about here?

To get reasonably mild power increases to a stock setup, should it ideally go like this?

K/N style high flow intake setup
62mm bored TB
TB spacer

High Flow cat
performance cat back exhaust system


Are we now in a more reasonable field of increased performance?
Or is this worth it? time/cost/trouble

 

[bigwhitey]

ok.. so in the end, what are we talking about here?

To get reasonably mild power increases to a stock setup, should it ideally go like this?

K/N style high flow intake setup
62mm bored TB
TB spacer

High Flow cat
performance cat back exhaust system


Are we now in a more reasonable field of increased performance?
Or is this worth it? time/cost/trouble

Just a heads up the K&N FIPK will not work with the TB spacer unless you raise your hood 1". The K&N intake rubs the hood already .