How to build up your 5SFE, Taken from the mr2 forum Options

[hioctane]

NOTE: THIS IS FOR THE 5SFE MR2 MOTOR. I HAVE BEEN HANGING AROUND THE MR2 FORUMS FOR A WHILE AND THOUGHT THIS MIGHT BE HELPFUL.

source: http://www.mr2oc.com/showthread.php?s=&thr...30&pagenumber=1

The 5SFE motor in the Toyota MR2 makes about 100 bhp at the rear tires as delivered from the factory…plenty for a commuter car but lacking for horsepower junkies. Very few people in the USA have even seriously attempted to get more power from this engine which is surprising considering how many millions of Toyota Camrys, Celicas, Corollas, and MR2s there are out there on the roads here in the states.

The stock Toyota 5SFE motor has a bore of 87mm and a stroke of 91mm which means it can safely be revved to about 7,000 rpm before linear piston speed becomes critical even though the stock redline is about 6,400rpm. The stock motor’s cam timing and lift make the power peak around 5,000 rpm with peak torque in the 4,500 rpm range. Once again fine for a commuter car but lacking the real grunt I am looking for. The stock Compression ratio is about 9.5:1….low enough to run without complaint on 85 octane fuel. My car is a California model which mean in addition to the Exhaust Gas Recirculation (EGR) and Evaporative Emissions systems I have two catalysts on the exhaust system with the first being less than 12 direct inches from the exhaust valves….very poor for power production, very good for tight emissions standards. The Engine/Electronic Control Unit for the fuel injection is also specific to a California model car. All 5SFE motors also ventilate the crankcase through the inlet manifold which is far from ideal since most of the gas the being ventilated is previously burned blow bye that got past the stack of compression rings on each piston. Just like EGR, PCV gases will not add to the power production of the engine since they contain next to no oxygen or beneficially combustible hydrocarbons. The stock single throttle body has a 50-55mm throttle plate to feed all four cylinders through ridiculously long intake runners designed to benefit torque off the very bottom of the rev range. Most if not all Toyota 4 valve cylinder heads are either produced by Yamaha or at least partially engineered by Yamaha, a motorcycle company with an excellent history of producing very high specific outputs from very small displacement motors. My goal with this project is to make my Toyota commuter car motor into an automotive version of a Yamaha Sport bike power plant with no less bottom end than the stock car and way more power everywhere else.

With a goal like this all I am really doing is a backwards engineering project on the 5SFE. A typical Yamaha 4 cylinder sporting motorcycle has around 12:1 compression, 4 individual throttle bodies with bores of approximately 40mm each, a stainless steel header of either a 4:2:1 or 4:1 design, cams designed for the greatest benefit in the mid to upper third of the rpm range, next to no emission control equipment, ram air induction, a generous airbox with lots of volume to perform well across a broad range of conditions and a maximum linear piston speed of about 4,500 feet per minute.



This post has been edited by hioctane: Oct 5, 2004 - 1:16 AM