peppin

I herd from some people that not having any exhaust on my car(1986 non turbo) would make it have no compression, is this true, and if it isn't somebody better be selling an engine lol thanks

.........chad

peppin

come on guys I need an answer??????>>

Dougie_fresh_007

BULLSHIT... well i dont run exhaust but i have a turbo.. i dotn see how it would be any different... but perhaps im wrong... someone help this guy out

wwilliam54

they are thinking of backpressure
which is important on boingers

Diavolo

piston engine goes *boing boing boing boing boing* but the mazda goes VROOOOOOOOM!

what exactly do you mean by not having any exhaust?

I think having the proper amount of backpressure is important on any internal combustion engine however because of the rotary's design and the rate of its burn cycles; if youre refering to running a staight pipe you shouldnt feel any negative side effects with compression, youre more likely gonna need a set of ear plugs first.

It has been my experience that in general an exhaust that flows too freely may result in loss of low end torque, however at high RPMs you may benefit from a small amount of added power.

jeremy

iTrader: (1)

bawahahahahahha, ok sorry.

compression happens only on the compression part of the combustion process on the other side of the engine from the exhaust. backpressure on the other hand is probably what they were talking about. on your car the exhaust backpressure is used to open your 6th ports. so its good for you unless you go to an airpump control like the s5 or fully electrical as explained in the second gen section. exhaust backpressure is NOT a good thing. exhaust velocity is what is good as it will aid in sucking out undurnt hydrocarbons giving the next cycle a fresher mixture/bigger bang. this is a compromise as in keeping the pipe small enough to keep exhaust velocity up at lower rpms will become restrictive at upper rpms. anyone who has studied fluid dynamics knows the relationship between flow and velocity of a fluid. so unless an exhaust is dynamicly changing it will have a certain rpm where it is sized perfectly. however, this has nothing to do with compression.

the only difference in this and piston engines is the fact that it exits though the housing giving a direct hot charge, unlike a piston engine that has to pass through the valves. it is also the valves that help muffle it. thus diavolo's point about an unmuffled rotary being very loud. this will slightly change with the renesis as it is getting side exhaust ports.

hope i answered your question and 12 others you didn't care to know about.

Diavolo

thats very good info jeremy but it makes me wonder....

i dont quite understand that it seems to contradict itself?!?!

I think im confused by not understanding the relationship between backpressure and velocity.

could too little an exhaust pipe cause a high exhaust velocity thus not giving enough backpressure and causing the 6th ports to not open?

whats makes a good exhaust system on a rotary? (p(particulariy an s4)
would you mind elaborating?


thanx
-Diavolo

specRX7_22

the manifold is the biggest restrictor. after that it doesnt matter much. you should always have an exhaust that ends.... at the FURTHEST front, a few inches from the rear. anything from that point back is safe.

jeremy

iTrader: (1)

the gain is in your 6th ports actuating. they are closed to increase intake velocity so the charge of air at low rpms is greater. then they open er, 3-4k rpm to allow more air now that the rpms are higher and pulling more air in. for some stupid reason, mazda designed this system on the s4's to work with exhaust backpressure. so if you lose that backpressure it will not open the sixth ports, not opening the intake more and reducing the amount of air ingested. this of course offsets any gains in the exhaust since the motor can't breath as well at those higher rpms. so the only bad thing is the system mazda designed. the s5's moved to one that is operated by the airpump so a nice free flowing exhaust won't affect the system. thus you have gain from the factory system and gain from the exhaust.

back pressure happens when there is too much exhaust to make it down the pipeso it starts to back up. think of a pipe that is .5" in diameter and trying to shove 40 gallons down it. now a 1' pipe and 40 gallons. the trick here is to keep exhaust velocity as quick as possible. in doing so, the initial charge released will pull any lingering exhaust out of the port through a vacuum. so the trick is to keep exhaust flow as fast as you can without creating backpressure which slows it back down. its also thought that the swirling caused by backpressure will also scavenge exhaust.

the manifold is the biggest restrictor, but mainly due to causing the exhaust to make an immediate 90* turn coming out of the ports. not sure what furthest front means.

specRX7_22

i meant..... cuz he said "no exhaust". when i meant is you want the end of the exhaust pipe to be behind the cabin on the car.

jeremy

iTrader: (1)

gotcha. "hey, why's my firewall smoking"

specRX7_22

exactly!! lol

peppin

hey guys, listen I have no exhaust at all exsept for the manifold, but if having no exhaust makes no difference then does anybody know where I can find cheap rotary engine in canada thanks for all the help

..........chad

specRX7_22

backpressure-wise you'll be fine with the stock manifold, but as i said, you "need" a straight pipe or whatever so the exhaust can exit BEHIND the cabin of the car. even a downpipe before the axle would be ok. but you definately dont want to leave it open after the manifold.