: running car with NO exhaust...?

05-03-2005, 05:27 PM
hey guys..i was out bashing my car down at the local soccer
fields and i done a jump rolled after it and the exhaust popped
off...it was really noisy and sounded mad but i was curious...is it
bad for running the car with out the exhaust? It has a bit less
power but other than that can it wreck your engine? Thanks. https://www.ausrc.com/forum/smileys/smiley1.gif

EDIT: I still had the manifold/coupler or whatever it is called still
on Edited by: lil_timmy_88

05-03-2005, 05:37 PM
No it is BAD. Your engine will run leanhttps://www.ausrc.com/forum/smileys/smiley1.gif

05-03-2005, 05:39 PM
how does it make it run lean?? https://www.ausrc.com/forum/smileys/smiley5.gif

05-03-2005, 05:52 PM
it was still blowing a fair amount of smoke...but im not sure if it
was enough...but it looked like the same amount as usual...
anyone else agree its bad?Edited by: lil_timmy_88

05-03-2005, 06:03 PM
No exhaust = No preasure line. No preasure line = Less fuel. Less fuel = Bad.

05-03-2005, 06:07 PM
is that what my brother was talking about when he said there
was no 'back-pressure'? Thanks.Edited by: lil_timmy_88

05-03-2005, 06:09 PM
Yup thats it. https://www.ausrc.com/forum/smileys/smiley4.gif

05-03-2005, 06:15 PM
i see... very good...even though i dont understand all that back-
pressure crap and stuff to do with that its good to know my
brother knows what hes going on about... https://www.ausrc.com/forum/smileys/smiley20.gif

05-03-2005, 08:11 PM
Correct me if i am wrong but :

Basically the fuel line running from your exhaust and into your fueltank is what keeps the fuel flowing to the engine. Because these engines don't have fuel pumps like conventional motors, this sort of acts like it.

05-03-2005, 08:42 PM
Jected, you're spot on. The exhaust pressurises the tank to act like a fuel pump.

Tim, you're brother was basically right, but he wasn't talking about the pressure line going to the fuel tank.

A 2 stroke is an inefficient design, as fuel & air gets sucked into the combustion chamber, it also gets blown out the exaust. A tuned exhaust sends a pressure pulse back down the exhaust to stop that fuel from escaping, leaving more fuel to be burnt and less to pass through the engine. This is the closest thing to 'back pressure' and it makes a HUGE difference to a 2-stroke engine. It is why you noticed less power.

It could damage your engine - as already mentioned, there is less fuel pressure so the fuel mixture would be a bit lean, but without the tuned exhaust pulse to keep the fuel in the right place, it will run even more lean again.

Lean mixtures lead to high temperatures which then lead to a broken engine, so it's not a good idea. https://www.ausrc.com/forum/smileys/smiley1.gif

Cheers, Oggy.

05-03-2005, 08:46 PM
the other problem, is 2 strokes rely heavily on their muffler for proper performance.. this is why some mufflers give better performance than others.

a short fat pipe gives loads of top end, and a long pipe gives bottom end.

Basically your muffler has a Divergent cone (where it starts to taper outward) and a convergent cone (the taper inward at the very end)

the cones reflect the pressure waves from the exhaust, and it helps to pressurise the exhaust port to hold more charge in the cylinder while also helping to extract gases from the next charge..

both intake and exhaust ports are breifly open at the same time, and a proper exhaust helps to hold more of the fresh charge in the cylinder.

its extremely bad for your engine to run without an exhaust, or with those dodgy dual copper pipe jobs ppl make in their garage then sell on ebay.

edit: darn, ogier beat me to itEdited by: Oblivion

06-03-2005, 04:28 AM
Correct me if i am wrong but https://www.ausrc.com/forum/smileys/smiley24.gif/P]

Basically the fuel line running from your exhaust and into
your fuel*tank is what keeps the fuel flowing to the engine.
Because these engines don't have fuel pumps like conventional
motors, this sort of acts like it.


ok thanks for all the input guys. But i dont have a fuel line
running from my exhaust back into the tank. Am i suppose to?
The fuel still gets pumped to the engine without it.... https://www.ausrc.com/forum/smileys/smiley5.gif

06-03-2005, 05:12 AM
What type of r/c r u running?

06-03-2005, 05:14 AM
Has the tank got a nipple near the cap and has the exaust pipe got a nipple on it? (nipple=the thing u push fuel line onto)

06-03-2005, 05:25 AM
It should look something like this....


06-03-2005, 06:33 AM
huh no pressure fuel line/ nipple damn what have i been missing out on lol luky i was thinkin bout running no pipe thx for this thread thoughhttps://www.ausrc.com/forum/smileys/smiley1.gif

06-03-2005, 03:11 PM
im running a HPI RST MT with an O.S MAX .18CV-RX. The fuel
tank has a little nipple thing where the fuel tube can go but the
exhaust doesnt. Im not sure what exhaust it is thought because
my friend gave it to me but he did say it cost him $160 so it
must be alright..all i know is that its ribbed...

06-03-2005, 03:36 PM
Have u gotDigi Cam?

06-03-2005, 03:41 PM
yeah do you want a photo? I looked at the exhaust just then
and i noticed it has a screw where it looks like a little nipple
used to be in the exhaust....im just taking it for a run now and i
will be back soon ok.

06-03-2005, 03:42 PM
some mufflers have a hole instead of the pressure nipple andyou just poke about 10mm of fuel hose into the hole..

06-03-2005, 03:46 PM
well can u unscrew the screw to get to the nipple

06-03-2005, 04:35 PM
i'll give it a go tonight for yous(unscrew the screw).... cant do it
at the moment, shes a bit hot https://www.ausrc.com/forum/smileys/smiley36.gif ... i went to take the photos
and the damn batteries are flat for the camera so i will charge
them up over night and get back to yous in the morning...

07-03-2005, 04:26 AM
i got sum pics but they arent good quality sorry.... the exhuast
pic isnt good either... i will take a better one when ive got more
time but this is the best i could do for now... As for me un-doing
that screw i didnt even get round to doing that...



07-03-2005, 07:19 AM
That pressure screw in the exhaust is to block the hole off. It could be replaced by screwing in a nipple, not by simply poking the fuel tubing through, not sure that would be a good thing.

However, you appear to already have the pressure line fitted - the fuel tubing on the top of your fuel tank's lid, where does that go to?

Normally there's 2 lines, one from tank to carby, the other from exhaust to tank as a pressure line to act like a fuel pump.

Even if it didn't exist, as long as your engine was tuned for it and your temperatures were OK, then it might not matter. I would think tuning would be much more difficult though.

Cheers, Oggy.

07-03-2005, 07:41 AM
As the pressure line isn't present in photo two, I'd wager that it is
just hanging there almost as an 'overflow' line. I'm guessing a
clearer photo of the pipe might reveal the 'nipple' is actually closer
to the front of the pipe.

Just compare it to the other pipe... laying on the bag in the background.

Edited by: Skidd

07-03-2005, 11:52 AM
the car runs fine, it gets hot like they all do but not EXTREMELY
hot... I could try un-do that screw and see if i can get the nipple
onto it from the other exhaust if its the same diameter hole. And
yes the pressure fuel line is just sitting there doing nothing
really. There isnt a nipple closer to the end of the pipe the only
other thing there is that bit to link the pipe to the chassis so it
stays on right. (Sorry for the wording in this passage, i had a
brain fart and couldnt think of the words https://www.ausrc.com/forum/smileys/smiley36.gif )

07-03-2005, 04:51 PM
i think u just have to screw a nipple on there then it should be all goodhttps://www.ausrc.com/forum/smileys/smiley20.gif

07-03-2005, 04:55 PM
yeah i will probably do it some time, i will just take the nipple
from the other exhaust and see if it fits into this one. It still runs
good though. I will try take a video over the weekend and
shows yous how it goes...

07-03-2005, 06:44 PM
Don't forget to adjust the tuning if you connect a nipple and the pressure line to the exhaust.

It will probably just run very rich any way, but you might find much better throttle response and high end speed out of it.


08-03-2005, 04:40 AM
Don't forget to adjust the tuning if you connect
a nipple and the pressure line to the exhaust.

It will probably just run very rich any way, but you might find
much better throttle response and high end speed out of it.

Better throttle response!! High end speed!! I better make sure i
get around to doing this if i can get that out of a stupid little
pressure line https://www.ausrc.com/forum/smileys/smiley36.gif. Thanks for that GrahamEdited by: lil_timmy_88

08-03-2005, 11:43 AM
Ogier, good point i forgot to mention thathttps://www.ausrc.com/forum/smileys/smiley1.gif

08-03-2005, 12:44 PM
i took the nipple of my other exhaust to put on this one but the
screw needed is like nearly twice as big on this exhaust so i will
have to go down to the LHS and see if they have got some
nipples with a bigger diameter screw on the end.

08-03-2005, 01:59 PM
just poke the fuel tube into the hole, it works just as good as a pressure nipple coz the fuel tube is a firm fit, creating a seal around the hose..

as i mentioned before, some mufflers dont use a pressure nipple at all.