Check this out! A 1.6 litre four-cylinder cranking out 180kW (241hp) at the flywheel without the aid of a turbocharger or nitrous; we’re talking about a performance-built Honda VTEC that spins to 10,000 rpm!
This particular engine - built by Shane Wilson Competition Engine Developments - is configured to meet Australian Class 2 off-road racing regulations. Class 2 buggies require a naturally aspirated engine not exceeding 1.6 litres capacity; adding forced induction puts you in a field of buggies with engines up to 6.0 litres... This means it’s wise to grab the most sophisticated and powerful naturally aspirated 1.6 litre you can get your hands on. And that’s where the Honda B16A VTEC stands out from the crowd.
"The owner of this engine previously ran a Toyota 4A-GE 20 valve. I did some light modification on the Toyota and it went well - but when we wanted more, the Honda VTEC was the obvious choice," says Shane.
So what’s been done to the engine, you ask?
Well, pretty well everything...
Shane started off with a late-generation Honda B16A, which has a slightly higher compression ratio, larger throttle body, different cams and some other minor differences compared to early versions. Despite its reputation, Shane tells us it’s a nice engine – but it's not a standout above its rivals.
"It has a full-length windage tray, a pretty good cylinder head and, of course, VTEC - but when you look at most other parts it could easily be a Nissan or Toyota," he says.
The original aluminium block has been bored, honed and fitted with a deck plate that effectively makes it a closed-deck block. Inside the bores you’ll find CP forged pistons from the US. These increase the compression ratio from 10.4:1 (stock) to 11.0:1 – still mild enough to let the engine run on 98 RON unleaded without detonation. Conrods are from Carillo while the crankshaft is the standard Honda steel item. Everything is balanced and the bottom-end is assembled with genuine Honda bearings.
Interestingly, the stock oil pump is fitted with billet steel gears to provide greater reliability at high rpm. Shane also modified the original sump, increasing its capacity to 6 litres, installing baffles and fabricating a custom oil-pick up. A high-torque starer motor is also fitted to cope with the engine’s extra compression.
In the hunt for maximum power it was decided that the standard DOHC, 16 valve cylinder head would receive the die-grinder treatment. Cylinder head guru Bill Hanson says he spent considerable time working on the Honda head and his trusty flow bench revealed an 11 percent potential power increase. A set of US-sourced titanium valves is also installed. The cylinder head is attached to the block using an ARP stud kit (which replaces the factory head bolts) and a TODA multi-layer steel head gasket provides effective sealing.
With the expectation that the engine would run at high revs, Shane installed Crower high-tension valve springs, retainers and collets. And the cams? Well, they’re Crower shafts that retain a near-standard lobe profile for low rpm operation - this gives almost standard levels of drivability and bottom-end torque. However, the new lobe profile for high rpm operation delivers considerably greater valve lift and duration as well as altered lobe separation – and this is where much of the engine’s top-end power comes from. The cams are driven via a TODA competition belt and cam timing is manually altered using Edelbrock adjustable gears.
Induction and Exhaust System
Shane researched aftermarket parts to suit the B16A and decided a US-sourced TWM induction system was too good to pass up - there’s simply no way you could fabricate a similar set-up for anywhere near the cost of this off-the-shelf kit. Purchased from Quantum Racing Industries in Queensland, this particular TWM induction kit comprises quad 50mm throttle bodies, a relatively long runner intake manifold (with two injector bosses per cylinder), bell-mouth entries and a composite airbox. Note that the engine was dyno’d without the airbox attached.
This photo shows the underside of the intake manifold and throttle bodies. Note the elaborate, fully adjustable linkage arrangement and throttle position sensor mounted on the third throttle body. It’s a very nice kit...
The exhaust system is uniquely built to suit the off-road buggy chassis. The 4>2>1 headers employ 1 5/8 inch primaries (which step up to 1 ¾ inch a short distance along their length), 1 7/8 inch secondaries and a 2 ½ inch tailpipe. Exhaust backpressure at full power is minimal.
Fuel and Engine Management
Fuel is squirted into the Honda motor as far away from the combustion chambers as possible - Shane uses the injector bosses that are furthest away from the engine. This helps improve the fuel/air mix and provides a small cooling advantage.
Interestingly, the fuel injectors, rail and pressure regulator were purchased as part of a kit along with the TWM quad throttle manifold. The injectors are 400cc units which operate at a rail pressure of 55 psi. A Bosch Motorsport fuel pump was employed in the dyno cell.
Shane tells us he was reluctant to retain the factory distributor-type ignition system given the engine’s off-road application – dust and water always seems to end up inside the distributor cap... His solution is a switch to direct-fire ignition using a pair of M&W double-ended coils and Bosch 008 modules.
Fuel and ignition are controlled by an Autronic SMC programmable management system. Shane has added a crank angle sensor to the flywheel and a cam angle sensor in the position of the original distributor. This photo shows the new cam angle sensor with a detonation sensor also seen near the foreground (the detonation sensor was used for dyno tuning only). Note that mapping is based on throttle position and rpm – there is no engine load input to the ECU.
On the Dyno
Installed on Bill Hanson’s SuperFlow water brake engine dyno, this heavily worked Honda 1.6 is surprisingly docile. It idles smoothly, happily accepts full load from 1000 rpm and runs to 10,000 rpm without hiccup. But at 10,000 revs Shane admits it sounds "busy"...
Tuning began with a lot of experimentation using different cam timing (with optimised fuel and ignition timing to suit each configuration). Shane settled on cam timing settings that give the best average power – he says he could have achieved slightly more top-end by sacrificing mid-range torque, but it wasn’t worth it.
The optimal VTEC change-over rpm was found by running the engine at wide-open throttle with the VTEC system locked in each of the two configurations. Optimal change-over rpm is where the torque curves intersect. However, due to an inevitable delay to actuate the secondary VTEC lobe, Shane says the switch-over point is programmed into the Autronic ECU approximately 100 rpm earlier than this point.
Once the cam timing and VTEC switch-over were set, a Lambda sensor was installed in each header pipe to measure cylinder-specific air-fuel mixtures. As it turns out, one cylinder was running slightly lean and another slightly rich. Shane says injector duty was individually tailored to give consistent mixtures and an extra 4kW (around 5hp) was found.
The final tune uses 26 degrees of ignition timing at wide-open throttle all the way from 4500 rpm to 10,000 rpm – and note that the detonation meter shows no sign of detonation when running on 98 RON pump fuel. A full load mixture of 0.91 Lambda (13.3:1 AFR) gives maximum power.
And exactly how much power are we talking?
Well, this graph shows a peak of 180kW (241hp) at 9500 rpm without any steep rises or falls. We should point out that 180kW from a 1.6 litre engine equates a specific power output of 112.5kW per litre – we can’t think of another naturally aspirated production-based piston engine that comes close! The torque curve (shown in pink) shows there’s just over 150Nm from 4000 to 5250 rpm, at which point the second stage of VTEC is engaged. Torque then swells to a maximum of around 200Nm. Note that engine output data below 4000 rpm was not available.
And, in case you’re wondering, what’s a highly-tuned 1.6 litre beast like this worth?
Shane says approximately AUD$15,000 - $20,000 - depending how you source an engine, the exchange rate and a few other variables.
It’s not cheap - but, then again, achieving 112.5kW per litre without a turbocharger is no small achievement...
Shane Wilson Competition Engine Developments 0409 550 351/+61 8 8724 8000
Bill Hanson Engine Developments +61 8 8362 8545
Quantum Racing Industries +61 7 3290 5911