Engine Questions

[robriguez]

After lurking through tons of threads in the last month or so I've notice alot of engine talk. Whats fastest? Whats best for this setup? Whats cheapest?

Well my question is...Whats the difference???

In real life (not this alternate nitro universe I've been living in lately) I live by the motto.....There is no replacement for displacement. If I were to apply this theory to RC it would tell me that the XTM .247 or the Ofna Picco Outlaw .26 are the baddest things on the market today.

But then I see .12s kicking the hell outta .15s at my lhs and I have to wonder....is it displacement or rpms what you need to go fast in RC?? Maybe its both??

If anyone can provide info or guidance it would be appreciated.
And what is a "port" anyway and why is 8 better than 7??


Tower messed up my MBX order so I'm looking for something else now. Maybe an Ofna 9.5, XTM X-Terminator or Kyosho 7.5 Kanai and I want the biggest baddest engine they make. I dont want "Anyone" to be able to keep up with me.

 

[mjime714]

OK, let me give this one a shot.

not all engines are created equal. you get some that are made really well and some that are made with junk on the inside. I have opened up my RB X12 and then opened up the HPI SS. There is a huge difference in the quality and craftsmanship between the 2. Lets start with the sleeve. The RB has a chrome liner inside the sleeve where the SS is all bronze. the ports are smoothe on the RB where the ports are choppy on the SS. The piston rod is knife edged on the RB to allow the rod to flow smoother in the engine when the mixture is happening. The SS is like a square wooden block. there are a lot more, but as you can see, the craftsmenship will make a huge difference.

Displacement is related to how fast an engine is, but again, how it is made and the internal parts and design has a lot to do with it. Also what has a lot to do with how fast an engine is depends on how well the car the engine is in puts that power to the wheels and how much weight the engine needs to move. Heavier monster trucks will not be as fast as say an onroad with the same .21 engine because the engine does not have to turn huge wheels and pull the weight.

More ports does not necessarily mean better or faster, the design allows fuel to get into the combustion part of the engine directing the fuel away from the exhaust port in the most efficent way possible. By directing the fuel away from the exhaust port, you get a more complete combustion and less unburned fuel. More ports is a way of channeling the fuel to the right place more efficiently. I have seen 3 port .12's run just as fast or faster than a lot of 5 port .12's

If I am wrong please correct me.

I hope this helps

Mike

 

[backspur]

A port in an R/C engine is any opening for the passage of fuel or air. They can be found in the sleeve, case, piston, or crank. The ports that most engine manufacturers advertise are the sleeve ports. These allow fuel and air to pass in and out of the combustion chamber. The more intake ports an engine has the more combustion mix can pass through. This in turn
produces more power. Generally speaking, a 5 port engine will produce more power than a 3 port engine. Another thing to note, engine manufacturers never count the exhaust port. A five port engine really has 6 ports. BONUS!

I think a better assumption in the R/C world is "There is no replacement for quality." A high quality .21, such as an RB, will outpower a lower quality higher displacement motor. This is the reason you will see an OS .12 CVR-X spank a Traxxas Pro .15.

If you want the baddest thing out there I would suggest looking at the high end race inspired .21's, such as RB, Picco, etc. It will cost you. If you can tune them correctly no overbored sport motor will touch you.

 

[Akina'sMtx-2]

robriguez, your doing the right thing, giving a lot of quality time to research for your project. There are a lot of things going on out there in the world. Every thing has an up and down, no matter how everyone put it. People got their own way of doing things. Some work, some don't, you gotta go figure. More ports don't necessarily mean faster. It can be faster at some point, but Moded 3 ports will be able to hang or blow the 5 ports, and moded 5 ports will blow the moded 3 ports. Just the matter of theory. You will also need to pay more attention to your gearings, the engine will only take you so far, the rest will depends on gear ratios, set ups, etc. Mjime and backspur did a great job explaining everything. Displacement mean "Compress air-fuel from BDC-TDC". The larger the displacement, the more air-fuel you can compress, which = to more power(Torque and Hp). Most likely, you will get more torque in a larger displacement engine than a smaller displacement engine. Thats why a .70 will be able to out pull a .247. You won't get as much speed because of lower rev(rpm). If you want to be fast, then I recommend you getting a high quality .21, perferbably moded. Someone correct me if I'm wrong.

:sleeping:

 

[AoD]

Ok, let me give a shot at this as well.

Now as for engines, they are all similar. Let's put this in perspective because it may give you a better "idea" on what is going on.

Like Akina said, the engine will only get you so far, the gearing and tire size also will make a difference.

Now, let's take two real life cars. A Chevelle with a 350 and a Chevelle with a 454. NOW, here's the major difference. If they are exactly the same except for the engine; here is what will go on.

First, the 454 will have the brute horsepower and be able to jump the line before the 350 model would even decide to accelerate. That is because of the horsepower behind the 454. Second, the 350 will be able to achieve a higher speed, not much, but a bit because of the RPMs. (Revolutions Per Minute). The average 454 will hit 4500 RPM and the average 350 will hit 5500 RPM. So, with the same gearing, the 454 will beat the 350 in acceleration, and the 350 will beat it in top speed.

Now let's hit another variable. Carberatours. Let's say you set a 2 barrel on the 454 and a 4 barrel on the 350. We won't get too technical, just enough to show the point. As for the 350, the horsepower will be greatened highly compared to a 2 barrel, with the 4 barrel. This means you can push more fuel and air into the motor, and that can increase the horsepower on the motor. Now, that 350 may be able to keep up with the 454 that's only running the 2 barrel off the line. But it will still be able to ditch it in top speed. Understand?

Now, let's get into the gearing. Take those same two cars, both with the 2 barrels and stuff. Now, let's take this into perspective. Higher gearing means higher speed and less torque, and acceleration. So let's put low gearing into the 350 model and high gearing in the 454. Chances will lean towards the 350 beating the 454 off the line because of the gearing. Lower gearing increases the acceleration, but there is a downside to this. The top speed will be decreased, because the RPM's haven't changed, the gearing has. And once that engine hits top speed, it won't go any faster. As for the 454, it will most definetly waste the 350 in top speed. The higher gearing took away from it's brute acceleration and torque and put it into top speed. I'm not going to say it still won't get up and move, but the gearing will decrease from it's acceleration, and give that back in it's top speed.

Two more things, but we'll mutate them into one paragraph. Air filters and exausts. Let's take two of the same chevelles, both with a 350 this time. Let's put some inky dinky exaust system on one, and a huge awesome exaust on the other. Let's also put a small low flowing air filter on the one with the miniture exaust. And let's put a Maxi-Flow on the one with the large exaust.

First the one with the "maxi-flow" can get more air hence allowing it to mix more fuel and get more horsepower. Now as for the exausts, it's got more flow through the exaust so it's going to be able to run easier, without backpressure. Don't take that serious for these engines though..

Now ideas to look for. First, quality in the engine. See what engine looks hot, has the best porting system out there to allow you to press the most fuel in the cylinder. That will give you the start for the horsepower. Now let's look at carbs. Get the best carb out there. Get something able to mix and add fuel PERFECT to the motor you chose. Get a GOOD quality air filter. The more air you can pull the better, specially when you're wanting to suck down as much fuel for horsepower as you can. And last, I may have confused you earlier, but here is another important factor. The exaust. A 350 doesn't run a "tuned" exaust like these motors do. So what you need is a well tuned exaust for the motor you chose. Get one that gives a broad powerband, or one that makes the engine give some excellent torque. That's up to you. Just remember the torque will give you acceleration, and the broad powerbands will give you more power when your on the throttle hard.

Hope this helps you understand a little better. If you have any questions, just ask.

 

[Akina'sMtx-2]

GJ AoDaLiZeD, clear comparasion. Incase you don't know what is a 350 or a 454, it's just a measurement of Cubic inches, which can also be converted into liters. If a engine you buy has a weak low end, but high in the high ends, then you will need to set up a combination that will give the car a all around performance, your set up. Since the engine is good at top end, then you will need to set up a gear ratio that will help the engine out with the car during the low end. YOu will also need to get a pipe that will be able to even out the combo. :beer:

 

[SilentHunterKellen]

Well said both of you. If you are in the market for just and engine and buying a kit. Here is a good engine site .
[move]-Kellen[/move]

 

[robriguez]

Thanks for all the replies guys. I appreciate all the quick feedback.

I've been working on "Real Cars" my whole life so I understand all the theories you have presented. The question was more, "Whats typically better for RC? High RPM or high torque?" But I think somewhere in there I got my answer.

Thanks,
Rob

 

[xXRyCeCaKeXx]

higher rpm i guess is accel, torque is more of top speed, torque is more required for trucks or larger scaled cars, while higher rpms are the small cars who can use the extra hauling

 

[AoD]

Originally posted by robriguez
High RPM or high torque?

It's all in what you want. RPM's gives out the top speed. Torque gets you up to speed quicker. Personally I love a mix of them both. It's almost an art finding what's right. I personally will say, a motor that's built strictly for top end RPM's, would be excellent. And one built just for torque would be just as awesome in it's own respect. Like I said, I recommend a good mix with them both. Sacrifice maximum acceleration an maximum speed for good acceleration and good speed.

It's really up to you, and what application you're running into. I say more top end RPM's would be better for onroad, and more torque would be best for the rigors of the off-road vehicles. But I'll say this again. It's up to you for what you want and need.