A bit over a year ago I fitted individual throttlebodies on my V8 to improve the throttle response and pick up some more power. With the ITB's fitted my car was pulling about 170rwkw with Rush extractors, 2.25” dual exhaust, a MAP-ECU to look after fuel and a “Harry special” ECU which had been modded to increase the rev limit, remove speed cut and a couple of other tweaks. It felt pretty good but the power was all over by 6000rpm.

My goal was to get 200rwkw by changing the cams and fitting standalone engine management. With an Adaptronic ECU and lightly ported heads with 265 degree intake and exhaust cams I got very close – 194rwkw at the Toymods dyno day in January, but the car actually felt like it didn’t accelerate as quickly.

Here’s the dyno sheet from that day just for bragging rights :-)

For comparison between stock and 265 degree cams I’ll use the dyno sheets from the tuning sessions as they’re overlaid and they show torque. And that’s the important bit – even though I picked up substantially more power, the peak torque had dropped (lower blue line compared to lower red line).

With the 265 degree cams it’s only better above 5000rpm and it’s substantially worse below. Looking at the torque curve and you can see that it falls short of the peak attained with the stock cams.

At Phillip Island in February it definitely felt slower – like the gearing was all too tall. I only had 15 minutes on the track before my power steering let go (long story) but I could feel straight away that it wasn’t as punchy and took longer to get up to speed. However I could go faster in each gear as it revved out to 7500rpm.

In a lighter car with the right gearing it'd be great fun but in a heavy car like the Soarer it just didn't work out. Peak power looks good on a dyno chart but torque is what accelerates the car. My Thrust Curve article covers this but, in a nutshell taking F=ma you get a=F/m. Force is measured in Newtons and Torque is measured in Newton-Meters so if we work out the torque at the tyre and divide by the radius in meters we're left with the Force accelerating the car.

So, I was chasing the wrong thing – since I don’t want to run an even shorter diff ratio I should have been looking at how to increase torque, not just peak power. For whatever reason, the change to 265 degree cams decreased torque so I had to work out how to get it back where I need it.

I bought a book on exhaust and intake tuning which was written in the 60’s (Scientific Design of Exhaust & Intake Systems - Philip H, Smith, John C. Morrison) and it had some great descriptions of what happens at the opening and closing events for exhaust and intake cams. The intake cam seems to have the biggest effect on the torque curve and largely from the timing of when the valve closes.

When the intake charge is being sucked into the cylinder it has some momentum behind it and as the revs increase you want the intake valves to close later to "catch" the air which is still rushing in. Even though the piston has already started to move up the air will continue to rush into the cylinder due to its inertia. With something like 265 degree cams the intake valves won't close until about 60 degrees ABDC - so 1/3 of the way up.

At lower RPM, the intake charge isn't moving in as fast plus there's more time between when the piston starts to rise and when the intake valves close. The intake charge slows and as the piston rises the air/fuel starts to get pushed back out the intake. So for low end you want the valves to close earlier. This is where VVTi kicks arse as it can make the valves close at the ideal point across the whole rev range - earlier for low end, later for high end and everything in between.

Since I really need decent torque from 3000rpm and up for the track (based on the standard gearing that’s about 50km/h in 2nd) it seemed the stock intake cams would be more suitable. On the exhaust side, the exhaust ports don’t flow all that well in the early 1UZ so the 265 degree exhaust cams might be best left in place to give it more time to exhale.

Back to the workshop to have the stock intake cams reinstalled then back to the Dyno to have it tuned. So now it’s got stock intake cams and 265 degree exhaust cams and the ported heads. Peter Scott fitted longer duration exhaust cams a couple of years back and he didn’t get much improvement so I wasn’t expecting to be blown away.

This shows stock cams vs stock intake cams with 265 exhaust. Identical peak power, slight drop in peak torque but it extends further up the rev range to get some more speed out of each gear... Seems a good compromise.

This is the setup I used at Eastern Creek on Anzac Day and it feels the best of the lot. Good acceleration and it continues to pull well to 7000rpm but gear changes are best made by 6500rpm.

I'll be heading back down to Phillip Island in June so it'll be interesting to see how it goes compared with the stock cams when I got a best of 1:59.5.

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