what engine to fit in my RS4
 

I have the .15 enging fitted in my HPI RS4 and want to go faster. Is it worth buying the HPI nitro star 3.0 engine thats comes in the rs4 now. Will that engine make much difference to the speed or is there something better i can buy. I dont want to spend a fortune.

RE: what engine to fit in my RS4
 

Speed is not a direct function of displacement. Torque usually is though. However, not a lot of torque is needed to propel a 1/10th nitro.

Why bother explaining this...because the displacement of racing engines is .12. The advantage of this is that all makers make at least one .12 sized engine, and they are usually the fastest engines. For example, the top racing OS .12 is much faster than the top OS .18, despite having smaller displacement, this is because it is aggressively ported and built to small tolerances for racing.

The bigger engines (.15ci and 3.0cc (.18ci)) are called 'outlaws', as they are above the size for racing. An outlaw .18 will indeed usually be a significant power upgrade to a .15, and offer more low down torque than even a racing .12, but nothing will match the top speed of a racing .12.

There is one particularly famous .18 which many use in that car, it's the OS .18tz. In case a racing .12 is outside budget, the OS .18tz is a great choice. The HPI 3.0 is not a good engine, I have experience with one in a Bullet MT.

There are a couple of good Thunder Tiger engines at modelsport.co.uk for a reasonable price, the .18bx springs to mind, but the exhaust is right side exit, which might be a problem. what side of the car is your exhaust pipe on?

RE: what engine to fit in my RS4
 

I've been through 3 Os18tz in the past 5 years and have to say they are worth every penny. Always stay in tune as with HPI always fell out if a tune. But buy getting a tz you will have to change the header and motor mounts and depending which shaft you get you may have to get a new flywheel and clutch along with shims and spacers.

RE: what engine to fit in my RS4
 

All that information has been a great help and makes a lot of sense. I took out a .25 kit engine from my kyosho inferno neo st truggy and replaced it with a smaller novarossi px5 .21 engine. The difference was unbelievable.

RE: what engine to fit in my RS4
 

Exactly, well observed, .21s are the most evolved 1/8th engines, just as the .12s are the most evolved 1/10th engines.

Having said that, the OS 18tz is a pretty special engine. It is almost as good as a racing .12 and because its an .18 it has a lot of torque. You can gear higher to get the same top speed as a .12 with no real compromise. Here are some tips from someone who has fitted the OS 18tz to the RS4...

http://www.rcuniverse.com/forum/m_45.../printable.htm

RE: what engine to fit in my RS4
 

If you want speed on a low budget, I'd say go with what Foxy suggested and get that 18TZ. Im a very strong believer of that motor, specially in smaller, lighter cars. I ran a fully modded Novarossi 12 in a Racer2 which is an upgraded RS4 and achieved 82mph which is really good for a 12. Then later gave the 18TZ a shot with the same gearing and got a screaming 85. Geared up and managed a best of 92 but locally. This is the same ISC car that went 90 at the event. So in short, the OS is the best and easiest to tune small motor I've ever dealt with.

RE: what engine to fit in my RS4
 

I suggest  you the OS .18. Quite powerful and easy to break in and tune.