Australian V8 Supercar Series Work
Larry Widmer's development work on the Australian V8 Supercar Series - Nissan entrant for advanced cylinder head design.
A little background: The Australian Supercar series has been the F1 of sedan racing for several years now. The racing is incredibly close with drivers running each lap like it’s the last lap of the race. Racing includes sprint and endurance competitions (with pit stops). The cars are front engine 4-door sedans with tubular chassis integrated. Independent suspension on the rear transaxle. They’re “trick”.
Engine rules require displacements of 5.0 liters or less. Fuel is (awful) E85, compression cannot exceed 10.0-1, there’s a 7500 rpm ignition cut-off, valve lift and duration are also fixed by the rules, as are component weights (pistons, cranks, rods). Induction was individual throttle bodies with long ram tubed enclosed in an air-plenum.
Four years ago, I was contacted by the owner of the four-car Nissan Australian V8 Supercar team. Their cars/engines just didn’t respond and accelerate competitively. The engine in-use is the V8 from the Nissan Titan truck, and to bring it’s displacement to 5-liters, they made the unfortunate decision to run the same large-bore/short stroke that the competitions’ 2-valve V8’s run. The rod length in their combination netted a rod to stroke ratio of 2.4-1….meaning the pistons are moving so slowly that there’s little “excitement” on the intake-side of the engine.
They sent me a head sample (NISMO-modified) head that they’ve been running. In examining the head, it was obvious that the ports and chambers were designed by someone who had absolutely no concept of how a normally-aspirated engine breathes and burns. The head’s huge, low velocity ports combined with an in-active, slow burning combustion chamber isn’t conducive to response.
I agreed to help them out by designing a new head, while supplying pallet-loads of the OE heads modified my way.
The differences between the NISMO head and our modified castings are very apparent. During this program, we made the ports as small as possible to increase intake velocity which enhances throttle response and acceleration rates. The trick was to make the port small enough for high velocities without having the engine run out of port (and air) before reaching 7500 rpm. Modifications began with welding the combustion chambers to create shapes around the valves that were more conducive to airflow and mixture stability. Our chamber also permitted a reduction in spark timing of eight degrees for a significant reduction in negative work, and since peak cylinder pressure moved further past TDC, we increased positive work. As for the ports, we kept things as small as possible and we reduced the valve sizes from what NISMO was using. These heads provided the team with their first win, as well as many pole positions. Note, that winning poles doesn’t necessarily translate into winning races because in traffic, one needs immediate response…which is still compromised by the short-stroke/long rod engine combination.
It now came time to design a proper cylinder head for the engine. NEMAK (in Monterrey Mexico) had an old set of tooling for the production heads which we were able to modify to give me a casting that was basically a blank slate (within reason). The new-design was supposed to run on a small-bore/long stroke engine combination (at last), so that’s how I designed the ports. My combustion chamber was “minimal”, with lots of quench area strategically placed to “condition” the mixture. The piston crown was a mirror-image of the combustion chamber. I moved the intake valve seat to the edge of the deck and placed the exhaust valve below the intake seat to help eliminate some flow-through at overlap, increasing the engines fuel efficiency. We moved the valve angles of inclination by .5° on the intake and 1.0° on the exhaust. The new guide angles also had to intersect the cam’s centerlines up-top.
The big gains on the ports were from the vertical length gains we achieved by moving the valve seats closer to the head’s deck. That greater “drop”, allowed us to negotiate the valve seat to chamber transition with lower losses. On the exhaust-side the higher port floor (relative to the valve seat) keeps the flow well-attached and with careful area management, we achieved higher flow with a smaller port.
With the V5, head done, we were informed at the last minute that the geniuses at NISMO decided the stay with the big-bore/short-stroke combination after all. A re-design of the intake port was required to reduce cross-sectional area, and after producing a number of new design heads, as well as a “homologation” piece for the rules people to keep on file, and that’s where we left the program