Tail pipe restrictor test

[ZugyNA]

Originally Posted by Powerstroke IN

Seeing as how I lost my scientific calculator years ago, how much exhaust diamter do i need for 650hp at the wheels?

What exactly do you do with that beast? Go around scaring the bejeezus out of people driving small hybrids?

[kitcar]

Originally Posted by 8307c4

I'll make it simple:

An Ice requires three things:
Air
Fuel
Spark

Increasing Air and / or spark should increase mpg so long you do NOT 'test' your new found power. Increasing fuel otoh will not increase your mpg.
As for the air, it really doesn't matter whether you increase the in or the out flow, for best results enhance both.

Exactly. Until gas prices got so high and I started going to the shack every couple of weeks, I was a high horsepower guy. Higher horsepower (and torque) allows you to use less air/fuel mixture at a given speed thus allowing for higher mileage. Remember, it's not the ponies but the torque. Increasing the torque of the engine is key. The HP just kind of shows up. My first experiment with this was with my first Dakota with a 3.9L V6, based on the LA block (318 cu. in). With a lot of work in the increased air flow = HP world and tricking the computer into richening the mixture (and leaning it out), I could beat my kids 5.0 Mustang (no joke, he's still pissed about it) and get 25-28 mpg when needed. Of course in the winter that leaning out deal caused a lot of "check engine" conditions.

[trautotuning]

Do this,

A flap closes and created backpressure when accelerating (more torque, can shift earlyer).

For idling and cruising have the flap open so there is less backpressure = less torque = less strain on the engine and better mpg.

Thats the best for mpg gains, not just A LOT or VERY LITTLE backpressure.
-------------------
Like others have experimented, reduction in backpressure HURTS in the city but HELPS in the hwy (steady cruising). So if you can make a flap that does both, add and reduce backpressure, this will give you the gains of more backpressure in the city and the gains of less backpressure in the hwy.

[dkjones96]

Originally Posted by trautotuning

Like others have experimented, reduction in backpressure HURTS in the city but HELPS in the hwy (steady cruising). So if you can make a flap that does both, add and reduce backpressure, this will give you the gains of more backpressure in the city and the gains of less backpressure in the hwy.

Can you link me to those experiments? I'd like to see that because I fail to see how removing something like a cat in favor of a test pipe to reduce back pressure can have any negative effect on mileage.

With a stock cam(like almost everyone here runs) the exhaust valve closes early enough that back-pressure does nothing but harm. In an engine with a radical cam, your exhaust scavenging can suck good intake charge out the exhaust port during overlap without at least a little back-pressure. By that time though you've built an engine up and cammed it out so gross that the last thing on your mind building the thing was fuel economy anyways so it doesn't matter. ONLY in this case would a restriction that would make you lose power would make you gain fuel economy.

[trautotuning]

It gives it less fe because it removes torque in the low rpms and so you have to add more throttle input in order to compensate thus injecting more fuel and ultimatley reducing fe.

There has been many members here that drive in the city a lot, got a huge exhaust, and lost mpg. Now if they were all driving in the hwy more then yes they would have gained more mpg.

Get what I am saying?

[dkjones96]

Originally Posted by trautotuning

There has been many members here that drive in the city a lot, got a huge exhaust, and lost mpg. Now if they were all driving in the hwy more then yes they would have gained more mpg.

I get what you are saying but they didn't lose FE because of no back-pressure. They lost torque/FE because of no scavenging effect caused by low EGV(exhaust gas velocity) because of excessively huge exhaust pipes. Without that, the engine can't get as much of the gases out of the chamber and it dilutes the incoming mixture causing a reduction in flame front propagation and decreased efficiency.

On the freeway they probably lost mileage too.

[trautotuning]

^ That to!