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

[hioctane]

The camshafts in the 5SFE do not allow for torque to continue to build after 4,500 rpm due to short duration and small lift of the inlet and exhaust valves. When the new motor arrives the first items to come out of it are the camshafts. The will be sent to either Web Cams or TED components for a weld up and regrind procedure followed by heat treating to insure they are hardened to a spec equal to that of the stock camshafts. ON the 5SFE only the intake cam is driven by the timing belt with a sub gear on the intake cam driving the exhaust camshaft in an opposite direction. These timing gears are a helical cut variety with a silencer gear added to the exhaust cam to make the cam run quieter. I am after a bit of gear whine so I will be making the exhaust cam gears bind together by installing a special service tool designed to lock the gears in place. This should give a nice sound while doing nothing to effect performance either good or bad. The new cams will have a grind spec to allow for peak torque to occur at least 1,000 rpm higher than in the stock motor and for peak power to occur about 1,500 rpm higher. The new cams will also lift the valves about 2mm more than the stock cams did for superior cylinder filling at all rpms. Both the inlet an exhaust valves will be allowed to stay open for about 20-30 degrees longer than the stock cams allow for. This improves cylinder filling and effective compression and BMEP at elevated rpm. In the case of the 5SFE more duration and lift on the cams will make more power at all rpms than the stock cams allow for.

Headwork: the stock inlet and exhaust ports in the 5SFE are about the right size for the rpm range I am working with. My motor is retaining small but re-shaped ports...actually smaller than stock in a place or two. People get the idea that big ports are better because a flow bench (the simple kind) will always show that a bigger hole flows more air...but, the physics in play inside a motor are way more complex than a flow bench alone will lead you believe. I cannot tell you how many custom ported heads I have dyno tested on motorcycles that made less power than stock heads...but looked way cooler and had way better flow bench numbers! I will go to oversize valves since the stockers are coming out anyway. My goal with the head work is more based on air velocity than absolute flow numbers. I am using longer duration cams but do not want to loose low end power since this is a daily driver street car, the solution is to have as much valve area as possible and as much intake velocity as possible since the a high intake velocity will keep the trapping efficiency of the head as high as possible even at low rpm. The trapping efficiency is how much air actually gets trapped in the cylinder at the close of the intake event. Since the piston is rising and the inlet valves are still open the intake charge tends to back flow out of the combustion chamber…but if it is moving fast enough more of it will get trapped at all but the highest rpms. I will gladly trade few ponies up top for a few more on the bottom. Tuning is compromise and there will always be ways to get around small problems. The final piece of headwork is the milling or decking of the head to set the compression value to the desired spec. 10.5-11.0:1 sounds about right to me for 91-93 octane pump fuel. Track days will be run on leaded VP Racing Fuels Ultimate 4 which is 92.2 octane and about 7% oxygen by volume. This is usually worth about 6% gains in total power at all rpms. The head can have about 1mm of material removed by the milling machine. With this headwork and these cams, a timing belt failure will be catastrophic to the motor…but this is normal for high output engines.

Bottom End: The stock pistons in the 5SFE are cast units as opposed to the stronger forged units used in most high output 4 stroke motors. I am looking for suitable replacements that are of the forged variety. I will only use a slightly larger bore than stock since the bore centers are pretty close to maxed out as the motor comes from the factory. In my opinion the stock connecting rods are plenty strong and will not need to be replaced. I will make sure to the big end bearing clearances are correct and will replace as many of the bearings as needed.