back pressure,needed or not

MrSmog wrote: I love when engineers talk, you know, the ones that bury oil filters behind things so you remove all flesh on your hand gettin it out, require truck cab removal to work on a engine and all sorts of other glorious things. I recall a whole forum of engineers told me I couldn't swap a inboard jet drive to a bracketed outboard (I did it easily), another half dozen told me I couldn't swap a v10 in place of a 318 without massive frame damage/suspension failure ( I did it easily), and a few other things they said was impossible. Some people over think things. To the original poster, many people run cats with no mufflers, you'll be fine. As for the zoomies destroy engines, tell that to all the rat rod/street rod guys who run them and have run them for years with no ill effects.

I'd like to know what forum of engineers told you this and the circumstances of your question. Attitude can make a difference too. Maybe the information you got was about something other than your question?

If you want to blame engineers for putting 10 pounds in a five pound bag, feel free too. It's really ignorant but if you need someone to blame. . . .

I decided to leave the NHRA rules about top fuel cars and the time they get between races used to rebuild the engine out of my last response. What does anyone know about the effect of zoomies when the engine they are using has a quarter mile lifetime? The blocks? Maybe a 3 mile lifetime.

This is from Jim Thorton who the NHRA recognizes as the inventor of the funny car. Paraphrased, "Nitro burning cars are no different from any other car when evaluating exhaust. Power is forfeited with straight pipes but the cars run so rich headers become a pipe bomb halfway down the track. Choosing between the advantage of headers or nitro with straight pipes didn't take a lot of thought. There's also no doubt straight pipes are the better crowd pleaser." 

Mixing street cars and track cars about zoomies? OK I guess? The effect of zoomies on engine life and power I thought was pretty well understood since the 50's. Typically the same engine on a dyno with both zoomies and tuned headers creates more power with headers. It didn't take much searching of hot rod websites to verify this. The earliest versions of the Merlin engine in the P-51 Mustang engine is a good place to start to learn about the effect zoomies have on engine life. There's not much to compare between an engine designed to operate at ground level to 25,000+ feet but it is a good place to start. On the street, the effect zoomies have on engine life I thought was pretty much taken for granted.

On the street zoomies are about some combination of looks and sound and have little to do with performance. The few places where you might get away with running zoomies legally on the street usually at least require zoomie baffles. I don't know this for sure but I imagine true, straight pipe zoomies are pretty rare on the street. Legally anyways.

If anyone wants to limit back pressure to the purvue of exhaust then I agree, back pressure restricts exhaust potential. If anyone wants to consider the exhaust as part of the balance of the entire system then the answer begins to look a bit different.

I would like an explanation though of why of the two common header designs, restriction and velocity, velocity is the better performer? Restrictions increase back pressure in the exhaust system so why are designs aimed at restriction reduction the poorer performer?

Don V.