Side exhaust vs rear exhaust

[Omega]

Well, I guess this should be an old topic. But I just couldn't find a straight answer after the search. :stupid:
As far as I know, the major difference between them are the manifold/header location Obivously, one is from rear and the other connect the engine from the side.
Can someone tell me the advantages and disadvantages? I see many "serious" cars are using rear exhaust, is it mean better performance???
Right now, I've side exhaust ntc3 w/ OS .15 pull-start. Just wonder is it any good to upgrade it to rear exhaust.

So far, I'm really enjoy this nitro car experience (1 month), especially the tuning engine part. And of course, this friendly discussion forum keep me positive :thumbsup: on this hobby.


:n00bie:

 

[petal2thametal]

hello

the major difference is that only rear exhaust are legal in most races. most 12 engines have rear exhaust. it seems that rear exhaust produce more hp and 12 engines with rear exhaust dont have a pullstarter. so extra weight is gone for extra performance.

so the difference's are

performance
most cases no pullstart
legal for racing.
no extra weight.

and if its good for you to upgrade your engine?

dont know. depends what you are planning to do.
if ya plan to enter at race's. then yes.you should get a 12 engine then. mostly good for around 1.3/ 1.5 hp.

if you are just bashing around then stick with the one you got. or if ya just want a new engine check out the sirio 15's with 1.7 hp or 18 engines.
should work fine also

 

[Arrow]

umm.. I've never heard of side being illegal..

the reason rear exhaust is different is becuse the exhausr coming out of the engine is going to same direction it was going in when it came in(free'r exhaust flow) where the side exhaust has to change.... form what I've read side exhausts are smoother. where rear i geuss are not as smooth? you can also have a side exhaust motor with no pullstart... so thats not really a big deal

 

[petal2thametal]

yes you can have one with rear and pullstart. but they are not race worthy. waste of money if ya want a 12 with much hp. like a said most cases they dont have one and most rear exhaust pullstart engines are bigger then 12. i got a 25 rear exhaust pullstart, but thats for a savage.
and its legal or ilegal depending on the organization you are racing with.

i would always choose a rear exhaust over a side exhaust.
rear seems better then side.

 

[Omega]

Thanks guys. I'll stick with my OS pull-start now until I master the tuning technic.

 

[Lessen]

Bump for this thread. I'm thinking of hinting for a new TC3 kit around the holidays but not sure if it would be better for me to have a side or rear exhaust. Any other opinions out there????

FYI. Completely new to on-road. Probably be learnin in parking lots. Would like to get into racing eventually

I just couldn't find a straight answer after the search.

I still feel this way... hense the bump

 

[AC48]

I don't really have an answer as to which is better but Lessen, I think it's this simple for you: If you race pick up a .12 rear exhaust, and if you're aren't reacing then get a .15 side for a little more torque. Just my .02

Also, remmember that if you get a rear it will more than likely be a non-pullstart which means you're gunna need a starter box.

 

[olds97_lss]

Someone already explained the point of it up above. It has to do with flow through the engine.

The air comes in through the carb and obviously exits the exhaust. In a side exhaust engine, it has to make a 90 degree turn, on a rear exhaust engine, it goes directly out. This makes for higher RPM's and quicker throttle response, this in turn gives you a better torque/horsepower curve.

 

[G8RMaxx]

Someone already explained the point of it up above. It has to do with flow through the engine.

The air comes in through the carb and obviously exits the exhaust. In a side exhaust engine, it has to make a 90 degree turn, on a rear exhaust engine, it goes directly out. This makes for higher RPM's and quicker throttle response, this in turn gives you a better torque/horsepower curve.

I have to disagree with the flow theory, as the incoming charge has to also go thru the crankcase and ports, into the cylinder, get compressed, then fire. Not to mention the crank and conrod moving at an incredible speed inside the crankcase. It has more to do with port placement for the case ports, and also the rear exh. has a smooth round exit, where side is rectangle, and most side headers are not even close to matching the exh. opening. OS-type engines that are side exh. actually are about 120 deg. from the centerline, where as other side exh. are 90 deg. That puts the transfer ports over the backplate and rear engine bearing, which inhibit flow, but with a rear exh., the exh. port is over the backplate(which doesn't affect it at all), the boost port is over the rear bearing, and the transfer ports are on either side where ther is no interference. The transfer ports are the most responsible for the incoming charge.
Not that all side exh. are bad, some are bad-ass. Sorry such a long post, but that is pretty much the reason for the difference.

 

[olds97_lss]

It was just what I remembered reading somwhere is all. What you said does sound accurate though...

 

[Lessen]

Those are some really great points Gr8Maxx, thanks. Thanks everybody, I feel I have a better understanding now.

 

[parris001]

I've found that rear exhaust engines are less prone to a leak between the engine and the header. I had a .21 Picco and while the silicone boot around the exhaust flange and the spring that held the header on looked pretty cheesy, it all worked great. And you can't argue that the massive round exhaust port is not going to flow more than the little rectangle port. But I wouldn't rule out the possibility of the port placement enhancing performance. :shrug: I hear what G8RMaxx is saying but there may be some swirl action going on inside the combustion chamber and the placement of the port in the rear allows the gas to escape easier.

 

[Lessen]

it just seems to me that a round exhaust port going to a round exhaust header would be a much smoother flow rather than a rectangular port into a round header but.... I was thinking that the actual exhaust flow out of one rpm would happen a nitch quicker in a side exhaust because of it's horizontal position. I guess I'm sayin that maybe the side exhaust (horizontal rectangular exhaust port) would become completely open quicker than a rear exhaust (round exhaust port) because of it's height relative to the vertical motion of the piston. Does that make sense?

But aside from engine performance I didn't realize that pullstarts were so much more rare in rear exhaust engines. I don't need to have a starter box while I'm just learnin in local parking lots.