David Gersic wrote:
> On Thursday 10 August 2006 08:19 pm, Terrible Tom wrote:
>
>>As some of you may know, my Ram has no muffler. Sounds frickin
>>awesome... probably was the exhaust note and volume that made me buy it
>>in the first place.... but I've been recently wondering with the high
>>gas prices, if its hurting my fuel economy.
>
>
> It could be. It's probably hurting your performance, at least a little bit.
> The engine's designed to have some backpressure, and does like to have the
> scavenging going on. Plus, most places make it illegal to run with no
> muffler. Having the right exhaust setup is probably worth a few horsepower
> and lb. ft. of torque. I can't think of any studies of it relating to fuel
> economy, but it seems reasonable to expect the increased efficiency could
> result in slightly improved fuel economy. Of course, the biggest fuel economy
> gains may be found in your right foot's operation.
Right foot operations do play some factor in my fuel economy :) I'll
admit I'm a little hard on the gas most times. "Home in bed asleep or
foot in the water pump"
>
>>So not knowing volumes on exhust dynamics and flow, I started
>>researching. I read that the exhaust flow actually does create a
>>negative pressure, as in a suction effect... helping to pull exhaust gas
>>from the cylinder and decreasing the amount of effort the engine has to
>>used to pump the exhaust out on the exhaust stroke. (thus increasing
>>power by actually decreasing parasitic power loss through higher efficency)
>
>
> Right. Adding a X or H pipe to true dual exhaust helps with this as well.
> Running a cat-back dual exhaust is not quite as good as dual with an H pipe,
> but it's better than a single all the way back.
I do have a single exhaust. Basically what was done was the exhaust
from the factory muffler back was removed, and while I don't actually
know the diameter of the pipe that was welded in (I'll look tomarrow) it
ends with something like a 4 inch tip. (again I'll measure because it
erks me to realize I don't know the exhaust pipe diameter on my own truck)
>
>
>>Have I grasped this concept correctly? If this is the case, I can
>>clearly see the effect that increasing exhust pipe diameter too large,
>>or reducing backpressure drastically, can have on this scavenging
>>effect. It basically takes the suction effect away, forcing the engine
>>to have to pump the exhaust out vs. having a helping hand pulling it
>>out... that sound logical?
>
>
> Yep. Sounds like you've got it. Depending on the cam, it also helps pull the
> fuel / air charge in to the cylinders for the next stroke as well.
I've got the stock cam. Fuel economy isn't really my main concern with
this truck, considering where I want to go with it in the future, but I
still want to make it as mechanically efficent as possible... while
boosting the overall performance. Making the driver more efficent is a
completely seperate issue...
-- ------------------------------------------------------------- Rocks are for skipping... I'm all about the mud 75 Honda CL360, 89 Dakota, 89 Dakota 4x4, 95 Dakota 4x4, 96 Neon, 01 Ram 4x4 http://members.aol.com/silvereightynine/ AIM & Yahoo: SilverEightynine
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