02-01-2002, 10:14 PM
what is the diff between these exhaust options?
Tazz R/C owner
02-01-2002, 10:34 PM
It is the shape, and location of the exhaust port...
The TRX engines use a standard side exhaust which is truely the worst one...
then there are side round exhaust engines that have a round exhaust port... the round port makes it less turbulant...
a rear exhaust engine has the exhaust port on the rear of the engine (above where the pull start is). This is the best type, because it is round, making the air less turbulant, and it is at the rear of the engine making the air flow more natural in a straight line from the carb, to the cylinder, to the exhaust port.
02-01-2002, 10:53 PM
usually round exhaust is rear. these are the best and have the most power most of the time. :D
02-01-2002, 10:54 PM
man tazz, you really know your exaust ports!
Tazz R/C owner
02-01-2002, 11:03 PM
The 3 exhaust types...
02-01-2002, 11:18 PM
this is from the march 2002 issue of r/c car magazine. i hoe this helps out a little, it doesn't really explain the differance, but the advantages of the two types (side exaust and rear exaust"
"7 Myths Exposed
Since Mugan brought the Novarossi-made MT-12 .12 size engine to market, all the buzz in the 1:10 scale nitro world has been about rear-exaust engines. But of course, big block .15 and .21 engines with rear exaust configurations have been around for many years. But do these "new" engines have an advantage over the tried and true side prots? We talked to Steve O'Donnell, one of the most respected engine gurus in R/C motorsports, and Michigan resident Dennis Richey, who is master motor builder in both scale and full size engines, to help blast (and validate) some of the myths concering these new engines.
Myth #1: Rear-exaust engines produce more power than side-port engines.
Sometimes. Many factors affect how an engine performs, including amient tmperature, humidity, break-in, glow plug condition, etc. But even given optimal conditions, the experts agree that both types of engines ahve such close performance that it really is just a matter of preference. Or marketing.
Winner: No clear winner on this one.
Myth #2: Rear-exaust engines "breath" more efficiently.
Both types of engines have benefits and detriments to their flow characteristics. On side-exaust engines, the intake port is partially blocked by the crankshaft and the transfer ports are partially blocked by the rear cover. While not optimized, their open area is pretty much equal, so the flow of fuel and gasses is pretty smooth. Now on the rear-exaust motors, the rotation of the crankshaft biases the fuel to the front transfer port. However, the intake port is still shrouded by the crankshaft, and the fuel and exaust have an extra-long route to get to the rear of the transfer port. So in essence, the rear exaust motor has one high flow front transfer port, one low flow intake port, and an even lower flow rear transfer port.
Winner: Side-exaust, but with only a minor advantage. Both have trade-off's in the breathing department, but we subscribe to the "smoother is better" ideal.
Myth #3: Rear-exaust motors are more expensive because they are "tuned for performance."
The only reason we can see for the premium price of the rear-exaust motors is that racers are willing to pay more for what is being marketed as a premium engine. When comparing a side exaust Novarossi with a rear exaust Novarossi (with similar characteristics--non-pullstart, non-turbo, long rod), most of the parts are actually the same. The crankshaft, rod, piston, wrist pin, wrist pin clip, bearings, and carbeuretor are all identical between lines. The sleeve is even the same, but the key notch is in a differnt location between the two types. And then there is the case, which only differs in the location and shape of the exaust port.
Winner: Side-exaust. We'll vote for the lower cost.
Myth #4: Rear-exaust headers are more efficient than side exaust headers.
Here is the other factor in the "breathing" issue--the joint between the exaust port and the header. On a side-exaust engine, the port opens up to a wide rectangl, kind of like a mail slot. If you look at most commonly available headers, the opening on it is usually kind of rectangular shaped, but no where near the same size as the exit from the crankcase. This restriction causes turbulance at the joint and makes more back presure to the engine, and is a variable most racers don't account for when choosing an exaust system. The experienced racer shapes his header to get as close a match as possible to the exaust port so that his pipe choice is more of an educated guess rather than a shot in the dark. The shape of the exaust port on a rear exaust engine is round. The header that mates to it is round. The exaust gasses exit the combustion chamber into the most efficient shape possible. Plus, we feel that the spring retainers on rear-exausts are easier to work with than the screws on a side-exaust. Okay, so this one isn't a myth.
Myth #5: Differnt pipes must be used for rear and side exaust engines.
The kind of pipe to use depends on many differnt factors, including car weight, avaliable gearing options, track layout and size, etc. Granted 1:10-scale sedan applications, the rear exaust motor uses a much shorter header than a side exaust motor, so this may play a bit of a role in your pipe selection process. But overall, there are many more things to consider when choosing a tuned pipe for your car other than the exaust configuration.
Myth #6: A motor tuner can get more power out of a rear-exaust motor than a side exuast.
Our sources tell us that they actully can make side-exaust motors scream just as hard, if not harder than rear-exausts. In fact, Dennis loves to talk about his modified Japanese engines, which are traditionally skewed towards bottom end torque, that can easily go head-to-head with his best modified Italian powerplants. Motor tuners have differnt tricks that work with both types of engines, and of course they are time consuming, hence expensive. But once you've seen a race-preped nitro mill run, you'll never look at a stock engine the same way again.
Winner: None, or both, depending on how you look at it. Either style can be made to deliver more power than most people can handle.
Myth #7: Rear-exaust motors are easier to fit into a car.
One of the reasons rear-exaust engines were developed for use in the first place was "packaging." When an engine is mounted perpendicular to the chasis, as in most belt driven sedans, road cars, and off road trucks, routing the exaust 180 degrees from the right side of the engine to the left side of the car involves lots of pipe--and lots of space. And then there's the issue of finding the right header that will properly clear any chasis bracing attached around the engine. With rear-exaust it's easy. Just route the exaust 90 degrees, usually a single bend to the left, and you're done. Okay, maybe it might have to deflect down a bit to line up with a pipe, but it still isn't anywhere near as severe as the side-exaust contortions.
Winner: Rear-exaust. Smalle footprint and easier pipe routing gets teh nod.
So, is there a winner? Well, the numbers tell us that it is pretty even, as is the performance of these engines. Even at the top levels, once they have been ported, polished, optimized, balanced and what not, they are still pretty much dead even (but much faster). So which one should you buy? The one that makes you feel better. Okay, that sounds like cop-out, but it really is a flip of the coin. Ah, but at least you now know a little bit more about those amazing little power plants we put in our model cars. And you can feel happy about any purchase you already made."
02-03-2002, 06:08 PM
I was gunna post that but fanman beat me to it. Basically if you didnt read all that it says once they are modded out or not they are pretty much even in performance. Just buy the one your prefer.
Powered by vBulletin® Version 4.2.2 Copyright © 2013 vBulletin Solutions, Inc. All rights reserved.