Low end power

[Wetpaper]

I'm trying to make a car that accelerates quickly, but most of the engines I make seem to have no power until about 6000 rpms and if I add turbos it takes even longer because they have to spool up.

I've also tried engines with longer stroke which helps but they still take forever.

Thanks

[Tycondero]

This is a bit too fague to comment upon properly. In short there are many ways to improve power output and torque. One of the best (and most straightforward) ways to fitting in a turbocharger. With the right specs it can cause a sudden boost in torque and power.

Overal though, as engine technology develops over the years. Using more modern fuel injection techniques will help to boost engine power output, torque and responsiveness a lot. Just try out some different technologies to get the hang on what to do. Also the timing of the engine can increase both fuel economy, power output and responsiveness, as does compression.

[WildKarrde]

It might be your transmission that's holding your cars back, as well. I made a car that goes 0-62 in under 6 seconds with this engine:
https://youtu.be/5eGss0bq6tU

As you can see, that thing has virtually no power until 8500 RPM.

[Wetpaper]

I wan't to make an engine that has a lot of low end power, not one that has a lot of power but only at high rpms.

[WildKarrde]

I'm not saying you should build an engine like that... it's quite impractical. Just saying that your transmission matters just as much with acceleration.

There's no way to know how to help you specifically without more information about how you're building engines already.

[Daffyflyer]

I'd also like to point out that our current turbo simulation is pretty crappy, they spool really slowly like a 1980s turbo, no matter what you do.

That'll improve when we go back to take another look at the turbo code!

[PlagueFerret]

In the real world in order to properly increase that low end torque you would want to change the intake runner lengths as well as the exhaust runner length, ontop of that of course your stroke is going to increase your torque output, but take away your top end horsepower. Turbo's are alright at producing power but they are based on volume of output from the engine itself in order to spool.

Although this is easily achieved with fuel injection, carburators are a bit more tricky, if you use a dual plane carburator your going to have a stronger idel and low end, but lose a bunch on top end, and you would go with a single plane long runner carburator (high boy).

Also you have to look at how things are built, using a pushrod engine with solid lifters than with hydraulic due to the hydraulic's tend to float at higher rpm's (unless of course you counter with springs, which is an entire other lecture)... the list goes on and on. For me in this program, and ive been playing with the program since mid last year about, ide like to see different supercharger setups (centerfugal, screw, etc.) Or be able to tinker with the deeper core pieces like oiling, balance, etc.

[Wetpaper]

I'm trying to make a car that can get from 0-60 in under 4.0. I finally made an I4 with 750hp and put it in a really light car and got 2.7 seconds.

I'd like to have twin turbos where one is really small and spools up really fast and when that one has lost it's effectiveness a big one takes over, or superchargers. I'd also like V4s, V6s, W8s, flat engines and rotory engines.

[Mike]

Can you give an example of a real world car that is similar to what you are trying to make? I'm eager to give it a go :D

Lots of low end power is quite tricky, what you need to achieve is lots of torque at a low rpm.

[PlagueFerret]

Here is what i do, just try to aim it around a real car, i made my rally car and set a limit of 40k (thats about the evo/sti average) and i came out at $39,938 with a 4.2 0-60, 380hp 4 banger and a top speed of 154mph.

[Wetpaper]

Basically I was trying to make a drag racer. But we don't have superchargers, so I was trying to do it with out turbos so it would have more low end power. Then I just ended up making a really light car with turbos and then gearing it really low so it had like a top speed of 96mph.

[PlagueFerret]

Try building a base vehicle first, then after you have it finished go back and create a seperate variant oriented towards drag, what suspension are you using? solid axle seems to be the best in my experience.

[Alf]

Keep in mind that cars that accelerate fast do not necessarily have good low end power. In fact, a lot of sports cars rely on the driver keeping the car high in the rev range and the gear ratios are set up to allow the driver to do that. Also, acceleration is all about grip and power to weight ratio, so make sure that the car isn't too heavy.

If you are simply trying to get low end power, you can try building a larger engine (bigger bore and stroke) with a less aggresive cam ratio, but this might not always be the best option since a really big engine will also be quite heavy.

[bill]

Bear in mind that power is directly related to engine speed and torque.

To make 'power' low in the rev range means masses of torque down there. This is what you might want in a street car - as much torque available from as low in the rev range as possible, while still trying to maintain enough torque in the higher rpm's to have good top-end power.

A naturally aspirated engine has a relatively linear power curve, because the torque curve is smooth. You gradually make more and more power as the revs increase. This can depend on lots of variables that affect the torque curve, but I'm keeping it simple here.

A turbo engine has a power curve that spikes at a certain amount of revs - when the turbo starts spooling (kicking in).
Until the turbo kicks in, the torque curve is like an NA car but perhaps lower due to lower compression ratios and other things. And because this off-boost low torque is low in the rev range, you make almost no power at this stage. Once the turbo kicks in though, the torque curve gets a massive boost and of course the power at the same time goes up too, since power is relative to torque and engine speed.

There is a balance between how quickly the turbo kicks in and how much power it makes in the higher rpm ranges. You can't have a turbo engine that has maximum torque at 2000rpm and maximum power at 10000rpm. At least, I can't build one.

You can make your turbo kick in lower in the rev range by decreasing the turbine size, compressor size, and AR ratio.
You can make your turbo make more power higher in the rev range by increasing the turbine size, compressor size, and AR ratio, as well as adjusting the camshafts and perhaps even the ignition timing.
:)
It's a fine balance.

Generally, I like to pretend I'm building a car that someone might actually drive, so I like the turbo to kick in as early as possible, but I also want to run the engine close to the rpm-limit of the materials and make max power at max rpm.
What I usually do is pick the 'Performance' pre-set turbo tune, then lower the turbine size and increase the AR ratio. Then fiddle with both of them as well as the compressor size and camshafts until the turbo kicks in as early as possible while still makes max power at max rpm (or very near to it).

In any sort of race car you almost never use the bottom end power, instead you are better off tuning the gear ratios to use the mid-high rev range torque and power. So don't worry if the car doesn't make much power below 3000rpm. If it revs to 7000rpm you'll almost never be below 3000rpm anyway.
In a low-power car, you might want 100km/h at the top of 3rd gear (out of 6).
In a more powerful car, you might want 100km/h at the top of 2nd gear (out of 6 or more).
In an extremely powerful car, you might want 100km/h at the top of 1st gear lol.

[PlagueFerret]

GrIfFiN님이 먼저 게시:

Besides of all the given advices, try to optimize your camshaft and don't forget about VVT. This might make a huge difference.

Absolutely, your cam is your #1 power maker in an engine good call.

[ihateshaman]

Timing and cams. don't think too much about it, pull up the graph and watch it as you tweak.