the saga of a truck

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well i'm not getting my old truck back anymore.... don't that blow.


however i've got my eyes on a 1990 - ram 250 with 318/5.2L EFI V8 and 4 speed stick shift... interior is like mint... engine is in fantastic condition... truck needs a paint job -- its not rusty (its got a few spots here and there, but nothin bad.... but its fkin yellow... when its all 'done' i'll do it up in twilight blue pearl coat with some harley davidson pearl white accents... but the body is straight as hell).

i like it a lot... dude is sellin really cheap. i even started making a "parts wish list" of afermarket **** -- all i can't find is stainless steel / aluminum / high temp painted / ceramic coated / or some other sort of "we're not gonna rust righrt away" headers for the 318 motor (1990 ram 250 318v8).

gonna do my own exhaust -- headers to reducers to pipe to separate catalytic converters to separate outlet pipes with no mufflers.... sound good? yup -- it will.

if all goes well im puttin cash down on it tomorrow night.

nadams

I must've missed something somewhere....

sntnsupermen131

you should just have exhaust pipes coming out of the hood
you dont need a muffler or catalytic converter
-Cody

MTXMAN

just run dual stacks, it'll look pimp as hell, one of my friends has his truck run like that. looks sweet ;D

PoweredByDodge

if you run open headers for long enough you can fk up an engine due to lack of back pressure... not sure 'how' or 'why', but its just not healthy...

a 10 foot long dual 2 1/2 inch exhaust is plenty for most any car that's not a big block -- anything over dual 3's for a big block and shorter than 10 feet is also nto exactly healthy.

the above being said for no cat, and no mufflers, and nice beafy headers.

.... gonna add some goodies to teh current truck instead for a while

valve covers, headers, new cam, yet another air filter system, better TB, some 8 mil shielded wires, and some other ****.

Jstas

Eh, that is not entirely true.

Open headers will not kill an engine per se unless specific criteria are met.

When open headers DO kill an engine it is because the primary tube length is not long enough to move the hot exhaust gasses away from the engine. You end up baking things like gaskets and valve seals or even the valves themselves. When they bake, the dry out and/or warp and do not seal properly. Cause exhaust leaks and drops in compression which can lead to a whole host of things like running way too rich, detonation, misfires and even blow-by. All of which will kill and engine in no time.

The major benefit behind headers is thier ability to scavenge the combustion chamber of exhaust gases. They do this by timing the exhaust gas pulses so that the low-pressure area just behind the exhaust gas pulse causes a vacuum in the primary tubes when it hits the collector. This vacuum sucks the hot exhaust gases out of the other primary tubes. This happens on every exhaust cycle of the engine. Because the exhaust gases are basically being sucked out of the engine, the engine has to do less work to push the gases out. The less work the engine has to do to operate, the more power is freed up to push the vehicle down the road. That is why simple, metal tube headers make a difference in power.

Now, given that idea, backpressure is a bad thing but also a good thing. Too much backpressure impedes flow, too little and you are basically blowing into the atmosphere and that is like hitting infinite backpressure. The reason why is hot exhaust gases are compressed in the combustion chamber. When the valve opens, the exhaust gases escape and expand into the exhaust system. That expansion is driven by the heat contained in the gases from the combustion process. That expansion also gives the gases velocity because expansion happens in the direction of least resistance. In an exhaust system, the direction of least resistance is out the exhaust pipe. If you are venting open headers into the atmosphere and you do not have sufficient primary tube length, due to the atmosphere, the direction of least resistance can be back into the combustion chamber. That makes the engine work harder tha before and you will actually lose power.

The reason the atmosphere is less efficient at extracting hot gases is simple really. It's too big. There is too much mass in the atmosphere for a piddly little internal combustion engine to generate enough heat to make the atmosphere pull the gases out of the engine. It cools the hot gases too quickly and they have no velocity to move away from the chamber. Think of it as a hose. The exhaust port on the engine with a header of sufficient length will squirt that water out 20-30 feet away from you. It has velocity because it is compressed and wants to expand. As soon as you pop that valve, it shoots out as fast as it can. Now, take that nozzle off and leave the open end on. What happens? Water just gurgles out in a fat and sloppy flow that gets your shoes all wet. The hose with no nozzle is like the exhaust port with no header/manifold. There is nothing there to force the water to move away from the end of the hose. Same thing happens with exhaust gases.

So open headers can be a good thing or they can be a bad thing.

PoweredByDodge

... is there anything you don't know?

hey at least now i can explain this to anybody who asks me "how come this or that?"

thanks for the explaination... one less automotive 'mystery' for me.

so a tube header is actually going to be better than the stock manifold not because of any size difference, but rather because separate primary tubes cause vaccuum in the other tubes and suck the exhaust out ?

if that's the case then that's the first damn thing i'm getting come warm weather.

Jstas

Well, yes, fundamentally. Take a single side of a V8. You have 4 primary tubes going into one collector. If the tubes are equal length for each exhaust port then the pulses of the exhaust travel down the tubes in sequence with the firing order, 180 degrees out of phase of the ignition spark. So if the one side was numbered 1234 and the firing order was 2143 then the pulses would travel down the tubes in that order too.

So the pulse from 2 would draw the exhaust out of cylinder 1 which would then have its own pulse traveling down the primary tube. That pulse would then draw the exhaust out of 4 which would then create a pulse in 4 that draws the gases out of 3. By now, cylinder 2 is ready to eject exhaust gases again so the pulse in 3 draws the gases out of 2 and it goes down the firing order again.

So when you hear the term "equal length headers" they mean equal length primary tubes. Equal length headers make more power than non-equal length headers. The reason for that is the equal length headers are, in a sense, tuned where as the non-equal length headers may have a primary tube that is shorter than the other 3 and that can cause a hiccup in the chain reaction detailed above. That causes a decrease in efficiency. However, equal length headers are expensive and often a **** and a half to install. So a cost effective solution is un-equal length headers which are still much more preferable to manifolds.

The other two differences between headers are shorty headers and full-length headers. Full length headers usually have the collectors exiting down below the floor of teh passenger compartment. Shorty headers are relativly the size of a manifold and exit in the same position. You can get equal length headers in both the shorty and full-length versions. The full-length headers will be more efficient than the shorty headers for two reasons. One, they hold more heat and heat is essential to exhaust gas velocity. Two, full-length headers keep the gas velocity up for a longer period of time which increases scavenging. If you get the proper sized primary tubes on your header, the exhaust gases can actuall accelerate in the primary tube and cause a vacuum in the combustion chamber which will also help cylinder filling after the exhaust valve is closed. So headers can even make power on the intake side.

So how do you know what size header to choose? If you have, say a 1.68 inch exhaust valve, you want your primary tube to be maybe 15-20% larger than the exhaust port at the most. So, given a 1.68 inch exhaust valve you would not want a primary tube larger than 1 7/8ths of an inch. 1 7/8ths = 15/8ths = 1.875 which is .195 inches larger than a 1.68 inch exhaust valve. That is if my math is correct. I'm an hour away from the end of a 12 hour shift and I got maybe 3-4 hours of sleep last night.

Jstas

One more thing Vinnie, put an X-pipe or H-pipe in your exhaust system after the catalytic converters. It smooths out the xhaust flow and balances each bank or cylinders. Otherwise you get uneven backpressure per side of the V8 and it can cause not only some really violent vibrations and shaking but it can also cause resonances that drone and vibrate things apart...like your senses.

geolemon

So did you buy this truck then?

Sounds pretty cool, with a manual tranny... surprised at the 4 speed though!
I'd think a truck, particularly one built more for stump-pulling and boat-towing, would have more gears, not less... like a semi-truck.

Jstas is right, if not a little wordy (not that I'm not known for that myself )...
In short form, you can design a header so that the exhaust pulses exiting the cylinder head line up, one after another, in the exhaust pipe after the collector...

If they line up like that, you don't have exhaust pulses (pressurized hot air) colliding into each other as they try to merge into the main pipe at the same time...

And also, if they are lining up properly, the first pulse (naturally higher pressure node of air) will be followed by essentially a node of vacuum (relatively speaking), that will help pull the next pulse out of whichever header tube is next...

If they all line up this way, the header itself creates a natural vacuum, that helps draw the exhaust more efficiently out of the combustion chamber, meaning the next squirt of air/fuel that's pulled into the combustion chamber is much purer, and can burn more completely, more power.
This is known as the "scavenging" effect.

Also, they can be RPM-dependent...
With my little 4-banger, they sell 4-1 headers, and they sell 4-2-1 headers...
The 4-1 headers provide more HP in the higher RPM range, at a sacrifice of HP in the lower RPM range... more of a pure-racing header.
The 4-2-1 headers (like the one I have) provides more power in the midrange RPM range, but doesn't provide as much peak horsepower, which is considered a bit more streetable (since you aren't redlining each shift on the street).

And again, to put jstas words in a little more concise form...
If the header and/or exhaust diameter is TOO large, you won't get that "scavanging" effect, because the exhaust pulse of pressurized air will simply dissipate into what is relatively just a giant chamber... you won't get that vacuum effect, and in fact the motor will be purely on it's own to just pump out what exhaust it can, very similarly to how it operates with a poorly shaped exhaust manifold.

Definitely an interesting part of the motor. :cool:

Jstas

This post was redundantly brought to you by the redundant department of redundancy!

MTXMAN

Jstas has been perticularly witty today ;p