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 intake system: In the motorcycle world the only type of intake arrangements used on high output motors are the individual throttle body type with a throttle body for each cylinder. I have a set of used Honda CBR954 units made by Kehin and a set of Suzuki GSXR600 units made by the same company. One of those two sets will adapted to the 5SFE to complete the hard parts list. All I am doing for the proof of concept stage of this to saw apart a stock manifold, lathe up some spigot adapters weld them onto the butchered stock manifold and add the motorcycle throttle body set with the velocity stacks going directly into the trunk...this lets me get the straightest possible shot at the inlet valves for high velocity and makes changing the length of the stacks to suit different mods easier. I also have plenty of room to make a proper high volume resonant airbox in the trunk area and then use a Tom's style air scoop with a little custom glass and metal work to feed the airbox cool mildly pressurized ram air from the roof area of the passenger cabin. I have access to lathes, mills, CNC machines, plasma cutters and plenty of welders...this is the stuff I do all day every day just for little motorcycles and other folks. I have not done a truly personal project in years and this one is a lot of fun...and probably a waste of a lot of cash but it will run hard and sound awesome.

I can not think of any real disadvantage to using individual throttle bodies other than the time spent dialing it in and the need for a TB synch at every other oil change....which might take 10 minutes to do...no real disadvantage at all.

The problem I am trying to overcome with the individual TB's is the fact that with a single TB you will never get really great throttle response and high flow characteristics since the plenum needs to have a lot of volume to make good high rpm power and the "goodness" of throttle response is directly effected by the volume of air and the distance between the throttle plate(s) and the inlet valves. By going to ITB's you get a very small volume of air between the throttle plates and the inlet valves (excellent throttle response) and you can still have a huge (think about 10 liters) "plenum" or airbox which will resonate at high rpm adding torque to the top end of the power band without a sacrifice at the lower end. Almost all real high performance small displacement motors use a variation on this theme and I just think it is the way to go to get a good amount of friendly useable power from the little 5SFE motor.

Engine management: The stock Toyota EMS is crude to say the least with a bank/batch fire system that really only looks at a couple of parameters to determine optimum fueling. Many aftermarket companies like Motech, Accel and Megasquirt offer stand alone EMS’s that completely replace the stock injection system. Since the mods I have planned will come close to doubling the stock power output of the 5SFE I will have to go to a radically different system for introducing fuel and spark to my motor. Which system will it be? I am not yet sure since they all have advantages and disadvantages compared to each other and the price definitely plays a role in my decision making. My goal with this project is to make in excess of 170 bhp at the back tires…we shall see if I even get close as the months roll bye…oh and I want to do it for less than $3000 which is what the car cost on the first place.