After spending almost a year reinventing the wheel and trying to sort out our custom coilovers from Koni and Ground Control, we finally have the time to make some additional power. In the case of our big-port, low-compression (9.4:1) 4AGE engine, lifted from a first-generation MR2, additional power is strictly a relative term. But the game plan goes like this. While there are plenty of variants of robust Toyota 4AGE motors that make respectable and healthy power, they require stupid amounts of money and maintenance, as well as parts that take half a year to arrive. That pretty much loses the point of having a track beater.
So we'll settle on reliability necessitated out of budget and time, and shoot for a track car with superb handling and just enough power to make things interesting. This rules out aftermarket turbocharging, ITBs, carburetion, retuning (since these old ECUs require replacing a chip) or tearing into the engine, all of which might add up to expensive return trips from the track aboard the back of a tow truck before everything is idiot-proof.The already idiot-proof options are the usual bolt-ons: cams, header and intake. We left the intake side alone as it still has the restrictive stock flapper-door airflow meter that probably functions better as a mousetrap. In order to remove the intake restriction, we would have to change to a Japanese MAP-based ECU and wiring harness, or install a modern hot-wire MAF meter and recalibrate the existing ECU. We'd rather not dig in to 20-year-old wiring, thanks.
So it boils down to cams and headers. Several options of intake and exhaust cams are available from companies like HKS, BC, PDM Racing and Toda, but since the 4AGE is now so old, most manufactures have discontinued much of the selection, leaving only one grind available for a given duration. We went with Toda Racing's recommendation for a direct bolt-on application of 272-degree, 7.9mm lift intake and 264-degree, 7.9mm lift exhaust cams, along with a set of adjustable cam gears, lightweight valve springs (with a 20-percent increase in spring rate) and a Kevlar-reinforced timing belt.
Toda offers an assortment of 4AGE cams with yet higher lift and longer duration, but more aggressive cams have steeper ramp-up angles (or a more oblong lobe) that could potentially flick out the stock shims (on top of the valve buckets) at high revs. According to Toda, any cam with over 9mm of lift would risk this and should be converted to a shim-under-bucket design, as well as a retune to increase the rev limits in order to make full use of the larger cam. Toda makes a shim-under-bucket conversion kit, but it can also be done on the cheap with OEM Toyota parts. For the exhaust headers, TRD supplied a US-made, ceramic-coated four-into-one manifold (since most Japanese headers will not clear the US-spec left-hand-drive steering column).
Cams: theory, design and realityInstalling the Toda cams is a straightforward process, since the 4AGE uses a direct cam lobe-on-bucket design. Each lobe sits on top of the valve assembly it actuates and is spaced by a shim situated above the bucket. There are no timing chains, VTEC solenoids, rocker arms or secondary lobes. Just a matter of pulling the valve covers, loosening the timing belt, removing the cam gears and caps, and yanking the bumpstick.
Project Corolla's rat-nest engine gets the Toda treatment with new cams, gears, valve springs and a reinforced timing belt.
For the valve springs, we once again enlisted the help of our project car mechanic, Mark Dibella at MD Automotive, since he had the trick tools needed to change out the valve springs without pulling the head. Installation is the same procedure in reverse, making sure each cap came from the same spot, each lobe and shim bucket has the correct clearance, and the cam and crank are indexed correctly.
We could have just tested the cams before and after, and made life easier, but we had to take the geek route instead. While the original cams were still in, we took a dial indicator and measured (as accurately as we could) the bucket or valve height for cylinder one, for every 10 degrees of crank rotation. This would provide a rough profile of intake and exhaust valve opening and not just the cam lobe profile, which doesn't account for slop or expansion in the valvetrain. If we were working on an engine with rockers, getting the valve profile would be even more important on account of the motion ratio and all the variables of thermal expansion. We repeated the same process for the Toda cams.
Now we have lift profiles of the Toda and stock cams, which allows us to plot a graph and see the differences. This is the most important part of cam design. Opening and closing profiles are absolutely critical in affecting performance and valvetrain harmonics. Lift and duration are only the basic requirements, as they put the cam into the ballpark of airflow. But how a valve opens and closes (as stipulated by the profile) will affect whether or not a cam allows a head to optimize its flow.