On a Mission Part 2

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POSTED ON October 30, 2017

Several years ago we featured a 355 Holden engine, built by A1 Hi Performance in Myaree, that produced 550hp and 468lbs/ft of torque. The engine idled like a stocker and eventually ran 10.25 at 132mph in a VH Commodore.

Well that was then and this is now, as they say. Recently, Leon from A1 had a request to build a similar engine but this time it was for drag and burnout duties and it was to be run on methanol. In the years that had passed since the previous engine was featured, technology and technical know-how had improved and Leon was keen to implement some of these updates in the new 355. Before this could happen, he had to make the best of the parts provided to him by his client. First up was the supplied block. After sonic testing this was rejected and another block was sourced. This block was also tested and deemed acceptable, so the project could begin. A trip to the machine shop was the next item on the list and it was here that the block was fitted with bronze lifter bores and four-bolt main caps. The cylinders were then bored to size and torque plate honed before the decks were zeroed true to the crankshaft tunnel (ensuring that all compression heights were equal from cylinder to cylinder). The Harrop crank, Scat H-beam rods, Mahle pistons and Total Seal rings were then sent off to be balanced. After much measuring and test fitting, all the parts came together and Leon finally assembled the short motor.

The client had also supplied a set of bare COME Racing cylinder heads, into which Leon cut custom six-angle valve seats (with matching angles on the valves). Multi-angle valve seats have a huge impact on air flow throughout the entire lift range and changes of even a few thousandths of an inch can show significant variations in port flow. A well-shaped port is one thing but if the valve seat angles are not right, plenty of potential power will go begging. By experimenting with different valve seat angles (a time consuming and costly exercise) it is possible to dramatically improve port flow, especially at low and mid valve lift, and increase the area under the flow curve. This results in greater cylinder filling and ultimately more torque and outright power. A Harrop single plane intake manifold was also provided, to suit the heads.

It goes without saying that the profiles and dimensions of the cylinder head ports and the intake manifold runners are critical when the goal is to achieve strong power figures with the widest possible spread of torque. A burnout engine uses almost all of the available rev range during competition as the tyres constantly grip and then break free. To prevent the engine from labouring hard under load, it must have the maximum amount of torque available at all engine speeds. This sounds great in theory but achieving it in reality takes an intimate understanding of airflow dynamics within the intake and exhaust tracts. To that end, a significant amount of port work was carried out in the manifold and the cylinder heads, focussing not just on flow but also on critical cross sectional areas that dictate the engine’s final characteristics.

When the heads and manifold were complete, a custom camshaft was designed and then ground to suit. Thanks to methanol’s love of compression, Leon set up this engine at 13:1. It was at this point that the build deviated from the previous 355 we featured. One of the main areas of attention in the new motor was oil return from the top end. The oil holes in the cylinder heads are blocked off, forcing all the oil that accumulates in the rocker covers to return to the sump via external -8 lines. Similarly, a baffle was fabricated and fitted into the centre of the valley, between the rows of lifters. This baffle prevents the oil that gathers in this area from flowing down the centre of the valley, past the camshaft and the crankshaft. Any oil that is allowed to follow this path immediately creates power-robbing drag (parasitic losses) on the rotating parts below.

A close look at the cylinder heads will reveal additional, external coolant lines, which rid the system of air and even out temperatures between cylinders – minimising the likelihood of head gasket failures. Furthering this effort are extra coolant holes drilled in strategic positions in the block’s deck, with corresponding holes in the heads themselves. Again, these holes eliminate known air and steam pockets within the Holden block.

When it came to headers, Leon opted for a tri-Y or interference design because of their ability to deliver a broader torque band. However, he did integrate a merge collector into the end, after removing the original collector pipe.

On Dyno.

Just how strong the new combination actually is can be clearly seen in this comparison graph. The bottom engine is a typical 355 with a Crane 288 cam and mild port work. Next is the engine we featured a few years ago. The new engine produces significantly more torque and power than both earlier combinations. Note that the engines were running on unleaded fuel for all three of these dyno runs.

With the long motor now complete, it was time to strap the engine to C&R Motorsports’ independent Superflow 902 engine dynamometer. As is always the case, Geoff from C&R ran in the engine to bed the rings and settle everything into position before any real power runs could be carried out. Although the engine was destined for an alcohol diet, it was actually run-in on VP 109 unleaded fuel, using a 950cfm Street HP carburettor. After run-in, the engine was given a final inspection and with the VP109 still in the dyno’s fuel tank the throttle was moved to wide open and the water brake strained to hold back a herd of Holden horses: 610 horses to be exact, with 475lbs/ft of torque. Now this is a Holden V8 were are talking about here, not a late model LS variant, so 600-plus horsepower straight off the bat was a remarkable achievement. Surprisingly, the engine still idled at 950rpm and maintained between 9 and 9.5-inches of vacuum while doing so.

While the petrol carby was still bolted aboard, Leon decided to try some ERC Sportsman DX fuel. After a little more tuning and tinkering the engine responded with 623.8hp and 486lbs/ft of torque.

Above and left: On the right is COME Racing’s intake port.
On the left is the new port developed by A1 Hi Performance
for their new cylinder head – on its way soon.
As this engine was designed for drag and burnout duties
it runs on methanol. Changes to air bleeds and jets were
carried out on dyno with a watchful eye


The external lines running from the front of each head allow air to escape which provides more even temperatures across all cylinders and results in less blown head gaskets.

The final change involved swapping out the 950 HP for a QFT methanol carburettor. More dyno runs were made to optimise air bleeds and jet sizes for the best possible fuel curve for the 355 with methanol coursing through its ports. All these efforts were rewarded with 624.6hp and 490lbs/ft of torque. Had the engine been solely built for street and drag racing duties, Leon and Geoff were both confident that they could have made a few more minor changes to the tune and achieved 650hp.

So, On a Mission 2 has brought the humble 355 Holden into the ranks of the LS, Smallblock Chev and Ford fraternities, delivering a huge, flat torque curve from only modest displacement by current standards and 620hp with more still left in reserve. But just like rust, Leon never sleeps. A brand new Holden cylinder head, which he has designed, is currently underway and will hopefully be available by the end of 2012. With over 300cfm of flow available at only .500-inch of valve lift, we can’t wait for On a Mission 3!

The smaller line at the top of the photo is also a coolant line to vent air in the system. The larger line at the bottom is the external oil return from the rocker cover directly to the sump.


The block was fitted with four-bolt caps and bronze lifter
The baffle fitted to the centre of the valley prevents oil from running down over the cam and crankshaft, causing power-robbing drag.


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