Has anybody ran an off road h-pipe on a Gen. 2 lightning?? just wondering if any HP gains?

 

There's not much you can gain with the exhaust as the stock system is pretty tuned. If you free up flow then your boost drops(pressure is a measurement of restriction) and when boost drops you will also have lower compression on your WOT runs. The biggest thing to watch is that you don't lose performance with exhaust mods. Switching to Flowmasters, Borlas, or any other for an improved sound doesn't seem to hurt any but messing with the cats will affect them. I'll probably catch some flames for this but a naturally aspirated and a forced induction are two different beasts. Freeing up flow on a N/A is no doubt a performance enhancer. On a forced induction to a certain point yes, after that I disagree.

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I need to ask this question since I am still new to this board. So do not view my questions in the wrong light. Why would freeing up a exhaust restriction be OK for a NA vehicle and maybe only so-so for a supercharged vehicle. What may I ask is that certain point. Also if we remove the catalyst will we actually lose performance.

 

Let's just say that I know someone who removed the back 2 cats and lost .2 of performance. It wasn't due to weather, temp, etc. This person had raced against an "L" on a previous occasion and both were fairly closely matched even though this one won the vast majority of the runs. Forward one month and the removal of the 2 cats. The same 2 "L"s are matched up again and again it is close although one wins the vast majority, this time it's the other "L" doing all the winning. That "L" had nothing changed on it. A good reference point in which to judge the change as the other "L" was unchanged then the weather factor can be removed and the only difference is the cat removal. BTW, the unchanged "L" ran almost identical times to the previous outting.

My opinion: A forced induction engine packs air and fuel into the cylinder on its downward intake stroke thus when it begins it's compression stroke some compression has already occured and when it reaches the top of the stroke(even though we have 8.4:1 compression pistons) the compression ratio is up around 10 or 12:1 compression(there is a formula for figuring it out but I wouldn't have a clue as to where to find it) therefore making more performance. If you drop backpressure(and it does show lower boost with the cats off, around 1-1 1/2 PSI less) you end up with less boost in the cylinder and lower compresion on the upstroke equaling less performance. Of course there is a point where you have to balance the flow so it's not too restrictive. I just feel the stock cats have already achieved that.

I don't know if that is why and someone more versed in engines can feel free to pick it apart, I won't take it personal, but it doesn't change the fact that performance was lost. That is an inescapable factor.

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Reducing backpressure "too much" decreases mid-range torque and increase top-end power - and moving your power-band around can result in a net decrease in performance... I'll buy that. This applies to N/A and S/C cars... doesn't it?!

And interesting comment about the boost level being lower w/o cats... this would only apply to Supercharged vehicles... in a turbo car, the wastegate would stay closed "longer" so you'd net end up with the same boost.

Sidenote: Some (many?) stock wastegates dont
flow well enough to handle boost being turned up and then removing too much intake/exhaust restriction... the wastegate cant dump enought boost, even fully open. So you get boost creep... boost increases linearly as long as you keep your foot on it. You make a ton of power, right up to the point your motor pops

 

I would think that a free(er) flowing exhaust would enhance performance. The pressure in the cylinder will be the same with or without the cats, because the valves are closed for the compression stroke. After the stroke, the valves open and allow the exhaust to escape. I know that you can lose some low end (TQ), but it is usually made up on the top end (HP), by having a less restrictive exhaust (engines like a little back pressure). An internal combustion engine is nothing more than an "air pump". The more air you put in and then allow out, the more power you should make (within reason!). So, I don't see how a less restrictive exhaust would hurt performance. But, I've been wrong before!

Later,
Roger

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The early bird gets the worm, but the 2nd mouse gets the cheese.

2001 Black Lightning
Stock, but not for long...

1996 White Mustang Cobra
Offroad H-Pipe, MAC Mufflers, and a K&N

,
This PIC provided so that Chevy
and Dodge owners can see what
the front of a Lightning looks like.

 

If you want to try something different, that costs almost nothing, take off your muffler. I put in straight pipes and went from a 13.89 to a 13.603 (.21 net after 60' differences). 14.0s to 13.8s consistently.

Those pesky dodge trucks quit bothering me since I went from the stock sounding escort to a monster with a hair up its a$$!

But since I went to the local dealer up here for the intercooler leak, I put the muffler back on, and I really detest the stock sound.

Or you can compare for yourself, the sound. All my movies from late last year were with Tundra Straight Pipes™, and the last movie at the bottom of the page I had the muffler on. You dont even hear the wind blowing my the microphone with the straight pipes!

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99 Black Lightning! Kills! More kills!
factory tonneau cover, 100k mile warrantee, Line-Xed

2.145 60' 8.789@82.71 (1/8) 13.603@101.05 1/4 track straight pipes, 'Major' rear lights, no chip

 

No, the pressure is different. Removing the cats showed a lower boost pressure because of the freed up flow. With a lower boost the cylinders precharge of boost(before valves close) is lower resulting in a lower compression of the cylinder at the time of ignition.
I agree it would be better on a N/A engine as the medium for moving the fuel and air into the cylinder is the lower pressure in the cylinder during the down/intake stroke. The more you flow out the exhaust the lower the pressure will be in the cylinder during the intake time resulting in more air/fuel delivery. But if you notice they also run higher compression ratios. You get the same results with forced induction because the air/fuel is already precompressed with the 'charger at the time the intake shuts resulting in a higher compression. Am I confused yet?

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[This message has been edited by 4D THNDR (edited 03-26-2001).]

 

I talked to a ford tech, dont know how much he knows, but he said the back pressure the cats provide is enough for our trucks. I told him I wanted to run straight pipes, and that was fine by him. He said there is nothing to worry about concerning the warranty. But I do see where you are coming from 4DTHNDR, it does change things, and for my truck, for the better.

 

BTW Tundra, the stock muff was put back on in order to regain lost backpressure which seemed to help. The next step will be to put the cats back and run straight pipes.
For those of you that were wondering taking off the cats at the very least doubles the volume maybe even triples with Flowmasters on. Only a little louder with the stock muffler.

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Are we talking about different setups?

Tundra Straight Pipes™ are installed after the cats.

 

Well
lets say if you put Long tube equal length headers n, 2 high flow cats, x pipe, and 2 mufflers of your choice. I belive you would deffently see a gain in hp,tq,and et. Its just my 2 cents, but like other i have been wrong before.

 

Burninout, I can't comment on that as I haven't messed with headers and know no one personally who has.

Tundra,yes, after the cats are put back on the straight pipes will be run from the stock muffler connection out like your setup.

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[This message has been edited by 4D THNDR (edited 03-26-2001).]

 

 

Well, compression is the name of the game here. I feel confident when I state these trucks are supercharged from the factory.

The fellow who supercharged his mustangs, did he adjust his compression ratio? As 4DTHNDR said, a free flowing exhaust on a supercharged vehicle will operate as an engine with a lower compression. I dont know what compression figures are for a stock mustang, but you can bet that its above 8.4.

Superchargers + high compression (9.5:1 +)= not much gain. Adding more than 6lbs to an engine with 11.0:1 compression would be not net much more hp.

Superchargers + lower compression (<8.5:1) = more power. We have 8lb superchargers, and 8.4:1 sompression. A fellow I race in a talon, has 7.6:1 compression I think. He is running 20 lbs of boost! Do you see where I am goind here?

Now, as 4DTHNDR states, a freer flowing exhaust with a supercharger on an engine with high compression will net in the engine performing like a lower compression engine under boost. Right? Or was it lower compression at ignition?

I think I have it right, just let us know if we have thoroughly confused anyone. We may be on slightly different pages here, kinda like our explanation of straight pipes.