hoov100

actually the flapper is there to increase back pressure for easier starting..

Z33Driver

Sorry, I'm not familar with the flapper. I thought you were referring to some kind of exhaust valve.

hoov100

it is, its just a huge butterfly valve at the collector.

snwbrderphat540

basically im saying you need backpressure. its just a minimal amount. you dont want to inproperly design an exhaust to eliminate all backpressur cause it wont happen. so until your a nasa scientis in aerodynamics and fluid dynamics and design the perfect exhaust, there certain basics you stick by and just deal with teh back pressure you have. basically around 6 psi about. because when you do try to eliminate it its done in the wrong fashion and thats where teh torque is lost in the lower RPM's.

Z33Driver

If it's an exhaust valve then my previous statement would still apply. Exhaust valve are ang attempt to get past sacrificing low or top end power.

hoov100

i hate to re-open this can of worms, but F1 cars have been effectively adjusting their powerbands by increasing or decreasing the amount of back pressure.

and the valve is there strictly for starting purposes, i tried to start the bike with it open and it wouldnt start.

Z33Driver

I agree that you don't want to completely emliminate it. I just disagree with the statement that increasing backpressure improves low end power. The faster the exhaust velocity the more power. Smaller piping makes a faster exhaust velocity in the lower RPMs, therefore more low end power. It's not the backpressure.

I also agree that it's practially impossible to creat the perfect exhaust. Theoretically it would have to be a pipe that expanded proportionally to engine speed (RPM). For example, at idle the pipe starts out 2 inches in diameter and stretches out to 3 inches by the time the car reaches redline.

Z33Driver

I'm not saying you are wrong. I guess we are both talking about exhaust valves but one's with different purposes. I'm am just saying that there are some exhaust systems that use valves to alter the exhaust speed. The valve is closed at low engine speeds to maintain high exhaust velocity. As the engine speed increases it reaches a point where there is enough speed to open the valve, which will allow for more exhaust velocity to match the higher engine speed.

Niku-Sama

flappers?

why are people from the 1920's in my exhaust?

teenbmxer

so wh cant we come up with larger primary tubed header with electric valves that adjust with your rpm's then run like 4" exhaust and have basically tuned backpressure. make it so that you have more in low rpms and more in high rpms. sounds like so ferrari stuff. just like the electric valce train the have now...now more cam and stuff....and 100x better than vtech

snwbrderphat540

price, emissions, and sound compliences is why. but BMW already uses something similare to this setup.

teenbmxer

oh ya haha. kool.

DriftZ83

actually popping in the exhaust on deceleration is over fueling... it's raw fuel in the exhaust igniting... tune back some fuel and it will go away!

Niku-Sama

tune back fuel how, the AFM?

DriftZ83

what kind of car/setup are u running?

DriftZ83

it does also have to do with back pressure with how much of it you hear... but the root of it is fueling. the engine isn't leaned out enough in deceleration so it's putting too much fuel in for not enough air and therefore have raw fuel into the exhaust. it's for the most part a pretty common thing as you open up the exhaust. i'm running wide open off my 2.5" down pipe from my turbo right now and do not have any popping but then again it's all going through the turbo and doesn't really have any pipe to resonate off of. the muffler/cat help hide this.

snwbrderphat540

when engine braking ALL engines will "pop".

Niku-Sama

hrmm well part of it is my variable timing mod that un intentionally happened, well some one suoer glued the screw head on the distributer adjustment so it fell off when i tried to adjust it, it was too far advanced and it was poppin alot from that.

i keep thinking i am going to get it out but i never do, mabe i should super glue it so it atleast stays in place

snwbrderphat540

remove the dizzy and get the rest of the bolt out and then get a new one and replace!

Niku-Sama

yea it just never seems to happen, its still poppy though

DriftZ83

i've never had an engine pop when power braking and i do it all the time at work when diagnosing misfire conditions... also when burning my tires with line lock on my caballero before i race it.... so throw that out.

snwbrderphat540

power braking? you mean engine breaking? like allowing the car to slow itself down by leaving it in gear and letting off the throttle? every car will do it. its not pop its more of a gurgle and it can pop. its like this, you let off the throttle so the TPS and AFM and what not arent reading anything but idle readings but the motor is still up in the revs so the mixture is off but its still rotating and getting spark so it will fire in wierd random spots sometimes louder than other times. it happens to EVERY car.