Thread: Would running a V8 with no exhaust cause this? (apart from hearing loss)

Yes to all of the above.

JC

I doubt very much re the lack of back pressure despite what others say. But the lack of exhaust will probably be reponsible for the flames and popping etc.

Originally Posted by justinc

Yes to all of the above.

JC

^^^^^

How does restricting exhaust produce torque gains?

i love children, keep reving it and watching the flames,
must sound awesome.
the down on torque feeling is directly related to the noise 'ain't a problem, its just that you aren't used to bagging it up without an exhaust system.
the flames and popping back are quite normal for such a short exhaust system, doesn't it sound good?
i have a couple of aircraft i look after with very short stubs, and if you close the throttle too fast, the pops and bangs are really loud.

Originally Posted by Slunnie

How does restricting exhaust produce torque gains?

It just does OK.....................

Its' to do with air speeds/velocity and lots of other black magic, also resticting inlet sizes (i.e. going from 600cfm to 450cfm, reducing throttle body size), but its all a compromise as you loose horsepower

Could be just a bad design of extractor. Does it idle? Idle smoothly?

the loss of back pressure means that your not getting the scavanging effect as much as you would with it...

the nuts and bolts of your exhaust cycle...and this is mainly applicable to low (say sub 2500) rpm

(all speed terms are relevent here a piston moving slowly aint really moving slowly but its moving slower than when its moving at its max speed in a stroke)

1. exhasut valve opens, piston is moving up slowly the gasses begin to exit from their own pressure, as this happens the exhaust port(the head and very first part of your exhaust manifold before it joins to another exhaust) gets a bit of pressure in it.

2. The piston begins speed up and to push up and force the gasses out, exhaust port pressure rises and the gasses begin to get serious about flowing. (now is the point when your back pressure begins to become important)

3. The piston passes the mid point of its upstroke and is now going flat out both exhuast pressure and flow are at their peak.

4. as the piston slows down past the mid point of the stroke the pressure begins to fall but the flow rate remains about the same due to the inertia of the gasses.

5. the valves begin to rock, exhaust pressure can be at less than atmosperic pressure in a well tuned system and the exiting gasses suck the last of the burnt gasses out of the combustion chamber leaving it clear for the fresh duel/air to come in...

Now with no back pressure you cant get the scavanging to effect properly. This will leave burnt gasses in the combustion chamber wich robs you of fuel/air mix...

This of course all goes out the window when you get the revs right up there as the relative inertia and motion of the gasses just cant keep up with the mechanically flung parts....

so the really really short version..

back pressure in a well designed exhaust at lower rpms is a good thing but bad if you want to rev the nipples off it as it slows down the gasses movement.