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Introduction:
STS had create a new line of modified engine named “S” line. Starting with .12 onroad touring car, .21 buggy, .21 onroad to .28 truggy engine. These are top of the line race engine for racer looking for the edge over rival with budget in mind.

Feature:
STS had incorporate a lot of feature to make the S15X5 one of the fastest outlaw motor in the market. Features like black crankcase for better cooling and hardening. Low profit cooling heat for low CG. Separate turbo head button for better cooling and seal between head and sleeve. Which use turbo glow plug for maximum performance. 5 ports sleeve with revised timing and porting to maximize air flow. Special aluminum alloy piston machined from bullet alloy for less thermo expansion during long main’s. Lightened con rod with oil ring inside brass busing for best lubrication. Balanced and lightened crank shaft with red silicon to increase air flow and minimize vibration. Composite carburetor to prevent vapor lock. All these features make this engine able to run with the best Italian and Japanese manufactures.

Run-in:
With the special alloy piston’s low thermo expansion rate, the tolerance between the sleeve and piston is much tighter than normal engine. You will need a powerful starter box to start this engine. Or you can preheat the engine with a heat gun which will help on this issue. And as the alloy is very hard it do need some time to break-in this engine properly. Factory advises to change the crank shaft after break-in. But I had check the play at the con rod as there are no noticeable play after 20 runs I am still using the original crank shaft supply with the engine.

Performance:
Both low and high end power is very similar to the Japanese speed engine. One thing I notice is this engine is very sensitive to glow plug and tuned pipe selection. I had tried a few different combination and found it work best with the ATS or STS tune pipe with OS 7 plug running at 25% nitro and 0.4 head shims. And depend on the size of track you are running on you can select the correct exhaust tip size to fine tune the power band accordingly. The power is very impressive considering the price for this engine. I won’t say it is the fastest engine out there but sure can keep up with all modified engines on the market.

Conclusion:
This is a great engine with lot of power but will be easy on your wallet. It need a long run-in period but performance sure pay off. The only point need some attention is for such high performance engine it still come with normal steel bearing. It would be great if they can supply this engine with ceramic bearing and this is an outlaw engine. But if you need a race legal engine they still have the S12X3 3 ports modified engine which features the same high performance design but is IFMAR legal.

HITS:
High power
Low price

Miss:
Long run-in
No ceramic bearing