Throttle body spacer?

[DIABLOBLANCO8658]

Thanks for the info. Looks like maybe the manufacturer hyped up what it can do for you by about 100%.

 

[BBeach]

Yes, good point. And you answered that quite well. The engineers at Jeep wanted at least 190 hp out of the 4.0 and put on an exhaust that would allow that for the least amount of money along with other acceptable qualities like you mentioned. But I and many others know that a 4.0 is capable of much more than 190 hp. But as always there is no free lunch as horsepower costs money.

I know a little bit about multi criterion decision analysis. I'm in civil engineering so I have experience with project management with big stuff like dams and such. I could write an Excel program (with custom VBA code and what not) all about it if I wanted to, but that would cut deeply into my leisure time which is already very limited as an engineering student.

I really shouldn't be on this forum as much as I am to be quite honest. But I like to talk Jeep.

Congrats?:yelclap:
Its crunch time, finals next week, but freedom right around the corner.

 

[j99xj]

My finals are a week after yours then. But yea, its almost summer vacation.

But I'm still taking a summer class to get caught up...differential equations, (that I've been putting off for about 2 years).

 

[xjh3]

I have to take differential equations next semester for the Mechanical Engineering program I am in... NOT looking forward to it.

 

[BBeach]

I have to take differential equations next semester for the Mechanical Engineering program I am in... NOT looking forward to it.

I heard its a bunch of fun, I was supposed to take it last semester but I didnt feel like waking up early so i'll just take it next semester.

 

[1985xjlaredo]

A spacer wont do much unless you have a carb or a TBI setup. All that they do is allow the fuel and air to mix better before hitting the intake manifold, and the setup on an XJ doesnt have fuel running thru the throttle body. They do let the air moving thru them stablize a little before it enters in to the intake.

 

[bfred]

j99xj-[
If you had a perfectly tuned carburetted engine, and changed to a free flowing exhaust, you would have a power loss. But that power loss is not from "loss of backpressure" or any other nonsense like that, its because its running lean and can't adjust the air/fuel mixture without new adjustments and/or jets.

.[/quote] You are correct in saying a carburated engine would be lean with less backpreassure. This can be corrected but is not the point I was trying to make. Please explain to me the purpose of a balance pipe in a dual exhaust system,why a try-y header will make more power than a standard one, or why its been proven time and time again on a dyno that often a short extension or a race muffler bolted to the end of a header will make more power than open headers. The exhaust flow from the other cylinders help draw the gases out of the cylinder.If there is not enough backpreassure this will not occur. It also helps draw the intake charge into the cylinder due to the overlap in the valves. Kind of like how you can start a siphon in a hose by inserting a blow gun aimed down stream. It creates a low preassure in the tube upstream strong enough to draw a fluid up the tube. If you still doubt me, try unbolting your exhaust and see if you see any drop in manifold vacuum. this will tell all.

 

[j99xj]

You are correct in saying a carburated engine would be lean with less backpreassure. This can be corrected but is not the point I was trying to make. Please explain to me the purpose of a balance pipe in a dual exhaust system,why a try-y header will make more power than a standard one, or why its been proven time and time again on a dyno that often a short extension or a race muffler bolted to the end of a header will make more power than open headers. The exhaust flow from the other cylinders help draw the gases out of the cylinder.If there is not enough backpreassure this will not occur. It also helps draw the intake charge into the cylinder due to the overlap in the valves. Kind of like how you can start a siphon in a hose by inserting a blow gun aimed down stream. It creates a low preassure in the tube upstream strong enough to draw a fluid up the tube. If you still doubt me, try unbolting your exhaust and see if you see any drop in manifold vacuum. this will tell all.

A crossover pipe in a dual exhaust system allows one side of an engine to breathe through 2 mufflers instead of 1. This reduces backpressure and increases performance. (assuming we are talking about a v6, v8 or any 'v' engine) It also transfers exhaust pressure waves from one side of the system to the other.

Tri-y headers do not make as much peak horsepower as a good equal length header. Although they are better a making a wider power spread.

Serious race cars do not use mufflers. Mufflers serve no function whatsoever besides noise control. Mufflers increase backpressure, all of them. (some are better/worse than others)

Backpressure does negative work on the power stroke. It makes the engine work harder, and that costs horsepower.

If you increase backpressure on an engine, and the horsepower goes up, then obviously the engine wasn't "in tune" before the backpressure was increased.

 

[jbmoose]

the best way to NOT know if a particular modification helped is to make several changes at once. Who's to say which ones helped and which didn't?

I never said I did 'em all at once. I did my mods one at a time, which is how I noticed the difference. Sure I have to pay for everything and do all the work, but the boss (i.e. wifey) says when and where

 

[MaXJohnson]

I never said I did 'em all at once. I did my mods one at a time, which is how I noticed the difference. Sure I have to pay for everything and do all the work, but the boss (i.e. wifey) says when and where

Oh,

so even though throttle response is inversely proportional to intake volume, by carefully installing your mods one at a time and closely adhering to scientific method, you overcame a large body of engineering knowledge, with the end result being "a huge difference in throttle response" which was directly attributed to the throttle body.

cool

 

[bfred]

j99xj, here is an article that can explain this better than me. ( www.circletrack.com/techarticles/exhaust_header_exhaust_gas_tech/index1.html ) Yes, this article refers to a race engine but the theory is still the same with any engine. Probably more apparent on a stock engine that isn't nearly as effiecent. As for 1st hand expierence with this, our "serious race car" we actually remove header extensions for certain track conditions to make the car less responsive at lower RPM's so it's easier for the driver to control. At WOT when the engine is operating at it's max volume, back preassure WILL hurt performance, but will help at low RPM's and increase throttle response. Unless you're operating your jeep at WOT most of the time,too large of an exhaust will reduce low RPM performance.

 

[j99xj]

Engines make power by burning fuel.

The more fuel burned, the higher the power.

The net power produced by an engine is the power produced by combustion minus the power lost by friction.

That's why you get rotten gas mileage if you use the engines full potential on a daily basis.

That being said, if and exhaust modification allows a power increase (at any rpm or throttle position) there MUST have been more fuel burned and/or friction reduced.

With this in mind, backpressure can't increase power because backpressure is a friction loss. Ever plugged a cat up? A plugged cat kills power across the rpm range. So if a smaller pipe is installed and a power increase at low speed is reported, then the engine was running lean to begin with and the smaller pipe richens it up a bit.

Same thing with an intake mod.

 

[jbmoose]

Oh,

so even though throttle response is inversely proportional to intake volume, by carefully installing your mods one at a time and closely adhering to scientific method, you overcame a large body of engineering knowledge, with the end result being "a huge difference in throttle response" which was directly attributed to the throttle body.

cool

OK smartas.s Glad to see it makes people feel superior by demeaning others on a Jeep forum. Way to go.

 

[bfred]

Engines make power by burning fuel.

The more fuel burned, the higher the power.

The net power produced by an engine is the power produced by combustion minus the power lost by friction.

That's why you get rotten gas mileage if you use the engines full potential on a daily basis.

That being said, if and exhaust modification allows a power increase (at any rpm or throttle position) there MUST have been more fuel burned and/or friction reduced.

With this in mind, backpressure can't increase power because backpressure is a friction loss. Ever plugged a cat up? A plugged cat kills power across the rpm range. So if a smaller pipe is installed and a power increase at low speed is reported, then the engine was running lean to begin with and the smaller pipe richens it up a bit.

Same thing with an intake mod.

Please take time to read the article I posted, so that you can understand the theory of torque output related to a properly designed exhaust system. If not, maybe you should approach some of the companies such as Borla, Flowmaster, Dyonmax, etc. about becoming they're head engineer. Think about the countless hours and millions of dollars they've spent on research and developement. They won't know how to thank you! You can just tell them to put the biggest pipe that will fit on a vehicle, and all will be good! You'll make millions!...Mechanical theory and real world application can be two different things...there are many variables that come into play. As for others reading this, select performance components for your vehicle with the intended use in mind. Nothing that enhances power usually increases power across the entire power band of the motor. If a manufacterer claims a 10-15 HP increase, question at what RPM this occurs? Is it even relavent to the way you intend to use the vehicle? As an example, the race car I speak of puts out tremondous amounts of horsepower, approx. 860@9800 RPM. Sounds impresive right? This same motor pretty much has nothing under 3500 RPM. This would be useless in a trail rig. It's designed for one purpose, and so should the vehicle your building. make desisions wisely and ask questions, and you can end up with a very potent package. Hope this is helpful...

 

[j99xj]

I understand and agree with you point of view about the "performance package" concept, that is, an engine must be tuned to its specific application. Ie, no race engines in Jeeps, and no Jeep engines in race cars. That would be foolish.

But I want to talk a little while about basic theory of horsepower and torque. Because there is a lot of confusion on the topic.

For many years I used to think that horsepower and torque were vastly different and unrelated to each other. I also used to think that horsepower sold cars, and torque won races.

But as I progressed in my higher education it occured to me that the performance of any vehicle had everything to do with power, in this case, horsepower. I know some of you are going to call me out on this and say I'm wrong. But let me explain this further.

Lets compare a Jeep 4.0 engine (190 hp @ 4600 rpm, and 225 lb-ft @ 3000 rpm) and a Honda Civic Si engine (197 hp @ 7800 rpm, and 139 lb-ft @ 6100 rpm).

Lets install each engine into identical (and I mean idential everything) go karts EXCEPT final gearing. We'll give the Jeep a 3:1 final, and the Honda a 5:1 final. Since the Honda engine is much lighter we will add weight to the Honda go kart to make it fair with the Jeep powered go kart.

If we lined these go karts up at a 1/4 mile dragstrip who would win?

I'm almost certain the race would be about even.

I can read your responses now: "j99xj you are full of crap, the Jeep has to win because it has more torque!!!"

Yes it does. But ONLY at the flywheel. You forgot the effects of the final drive ratio.

Take a look at the math:

Jeep: 225*3=675 lb-ft
Honda: 139*5=695 lb-ft

In this case the Honda actually out torques the Jeep, not because the engine makes more torque, but because it has a lot of leverage the Jeep doesn't.

Some will say "lets make them identically geared". Ok, lets do that. Let's race again but this time both go karts have 5:1 ratios. Now who would win? I would have my money on the Honda, because it has the overrev the Jeep doesn't. The Jeep would beat the Honda off the line but the Honda would ultimately win the 1/4.

Now lets reverse our thinking and give both karts a 3:1 ratio. In this case, the Jeep would win hands down because it developes lots of power at low rpms (which the 'high' final drive allows). The Honda would take forever to get into its powerband and once it did the Jeep would be long gone.

The main point of all this is that torque developed at the flywheel is meaningless when you can have unlimited options for gearing. Your 900 some odd horsepower engine could be geared down to be of use in a Jeep, but it would undoubtably break down (race engines are very unreliable), overheat, and generally not want to idle. But it COULD work. The Jeep engine shines for off roading because it idles great, and doesn't have to rev to get the torque you want. This makes the Jeep engine worlds more reliable and easier to control in tight spots off road.

You are 100% correct that the engine must fit the designed purpose of the vehicle.

Back to our discussion on exhaust design, even if you didn't want to re tune your engine to lower backpressure (and thus take a torque loss), you can easily get that torque back by installing lower (numerically higher) gears. This is why race cars with very high powerband are still very quick to accelerate (because they are geared ideally to suit their power bands).

 

[MaXJohnson]

OK, so you didn't believe my b.s. post. Glad to see it makes people feel superior by catching others spewing ignorant crap on a Jeep forum. I bow to you O' Mighty Max.

 

[Stumpalump]

The throttle plate hangs way down into the intake plenum. By raising the throttle body you raise the butterfly valve out of the air stream of the intake. This is how they help. You can open the throttle and see the dumb plate hangs right in the way of the intake air.

 

[BBeach]

The throttle plate hangs way down into the intake plenum. By raising the throttle body you raise the butterfly valve out of the air stream of the intake. This is how they help. You can open the throttle and see the dumb plate hangs right in the way of the intake air.

Its only hanging down there maybe less than a half centimeter...its not much.