Is it possible for an exhaust system to be too free-flowing? I have heard some people say that there needs to be at least some back pressure on the exhaust system for it to work right. Here's why I ask: I"m adding a Calmini header to my 8v Tracker engine and emissions isn't a concern due to the woods-only nature of it's use. I was planning on just running straight 2.5" pipe from the header to a turbo muffler, then out the back like the stock setup, but I don't want to do this if it wont be of any benefit and especially if it hurts performance any. So what's the deal on back pressure?

2" is a better size for a non force
fed engine, 2-1/2 would probably
be OK, but it's not emission that
would be hurt, it could be performance

An engine needs some back pressure
to keep too much fuel from flowing out
the exhaust valves, the more radical the
cam shaft, the worse or more critical the
backpressure is.

The idea is with the overlap of the intake
and exhaust lobes on the cam, the intake is
opening and the exhaust is closing at the
same time, the more they overlap, the worse
the idle quality is, but the better high RPM
power is too. Most cams are designed for
smooth idle, and quality power band in the
2000-6000 RPM range

The back pressure is a needed thing to prevent
unburned gas from going out the exhaust and
through the Cat, besides it doesn't make power
when it's going out the tailpipe

Wild

I have the Calmini header with 2" pipe no cat and a flomaster muffler and it works great.  ;DI think Zig has a 2.5" kit on his.


kevin

"Is it possible for an exhaust system to be too free-flowing?"  -- Yes.  I can tell you for certain that a 350cid Chevy engine with just stock manifolds and 2" pipes, 9" long, provides too little backpressure.  The car moved like a 20' boat with a 3 hp engine.

That said, I would guess that with the header and the muffler, and the 2-1/2" pipes you'll be fine, but, unless you plan on making a lot more horsepower than the 8v has stock, you'd probably be fine with 2" pipes.

i was thinkin of doin 2" pipe from the manifold, no cat and a flow master and then route the pipe out the side, how would that work?

It looks as if the reducer that was included with the header goes down to 2", so I guess I'll use that and run 2" pipe.

As for routing the pipe out the side, I don't see how you plan on doing it without either cutting a hole through the frame for the pipe to go through or losing at least the diameter of the pipe's worth of ground clearance by taking it under the frame...If you have a 3" body lift, you could probably run the pipe OVER the frame and out the side though...

There is no really good way to have
the exhaust exit the side on the trucklet.

I have been working on this new exhaust
system for a while now, and the best I can
come up with is to run a 3" (for turbos only!!)
system thru a 3" cat and straight out the back
and thru a custom bumper (the stock bumper
is in the way)

No muffler needed, the turbo muffles the
exhaust note to a nice "Flowmaster" style
tone, and the whistle of the turbo from
the tailpipe sounds really cool    

Wild

I have tried (thought about, rather) making my exhaust exit out to the side, as it ends at about the end of the door, but found that it would be much too complicated, so I opted for a downturn instead.

i was thinking of routing it over the frame, under the body, 2" pipe dunno if it will work

i was thinking of routing it over the frame, under the body, 2" pipe dunno if it will work

It shouldn't be too hard if you've got a header... but I figured it would be too hard to do when I was doing my exhaust with a stock manifold :-/