A busy time for us the last month or so. Project engine had to wait for a while while we completed regular work tasks. It was worth the wait however. Fitted with a new camshaft, lifters and matching valve springs the engine was bolted back on the dyno, started, camshaft run in and power runs were made after fine tuning the software tune in our GMH computer program to optimise fuelling, spark idle and other parameters. We bolted the same Pacemaker 1 3/4" primary header size Tri-Y pipes back onto the engine. Our test day was considerably worse weather wise which can significantly effect in the room results. Applying a valid and correctly calculated correction factor is important so that results from different days with differing weather conditions can be compared accurately.
Bottom line...the best average run with stock camshaft produced 299 bhp @ 5250 rpm and 336 ft lbs. torque @ 3750 rpm. This is in the dyno room with density altitude conditions of around 450 ft. What this means is the air conditions were equivalent to being only 450 ft. above sea level. An experienced Drag Racer will tell you those conditions are approaching excellent in terms of the percentage of oxygen in a given volume of air. We all know oxygen combines with fuel to burn and make the explosion above the piston. This "combustion" process forces the piston down the bore and turns the crankshaft via the connecting rod. The crank turns the transmission which in turn rotates the driveshaft, differential and the rear wheels in the case of a rear wheel drive car.
OK, so now we know how the engine propels our car. If the same engine is tested on a day when the density altitude is equivalent to 1400 feet above sea level it is logical to assume correctly that there will be a lower percentage of oxygen in the same given volume of air. By definition then, a normally aspirated engine will make less power and torque as a result. Less oxygen means a smaller combustion flame front and therefore less pressure created above the piston to push it down the bore. Hopefully this explains why a correction factor must be applied to the dyno results from the better 450 foot day compared to the 1400 foot day. Comparing the two days in terms of raw power numbers achieved is not valid. The correction factor is designed to standardise the results so the comparisons can be looked at as though both tests were done on a day with equal weather and atmospheric conditions.
Logically then we need to look at both results in "corrected" form this time since their tests ocurred on days with differing conditions. The enclosed photo is simply a quick snap of the test with stock engine and cam next to the cam change engine. Well worth looking over these numbers in detail if you want to learn something. I will come back and add my own conclusions with cam details and reasoning behind what we tried here. First we are going to have a break up lunch. We will close from today the 23rd December until January the 19th. You can still reach us on either of our email addresses. We will respond to the emails daily.
Back to project engine...we decided to change the goal posts a little. Developed a pair of new camshaft lobes specifically for the Holden V8. The part # is CSBH-524. For project engine the cam was ground on 108 degree lobe separation angle, a spec usually associated with carburettored strong performance engines. The rationale behind this hair brained scheme was simple. Our stock engine has an actual compression ratio of barely over 8.0:1 Yes, we know GMH literature boasts 8.4:1 for these engines but the truth is that was factored without the thickness of the production .050" thick head gasket. Add the gasket and you will have no more than 8.0:1 Not exactly a compression level ideal for performance applications or for the addition of large increases in camshaft duration. Add large duration without a consistent proportional increase in static compression ratio and you can end up with losses in torque low down and often also in many other areas of the power curve. By narrowing lobe centres we are effectively increasing overlap which is not great for fuel efficiency, produces a much rougher idle but on the positive side it opens and then closes the intake valves earlier in the timing cycle. This effectively builds compression pressures artificially. This was evidenced by us doing a compression test on the dead stock engine yeilding a maximum of 135 psi. With the new cam the cranking pressure rose consistently to just under 145 psi If however the new cam was ground on 110 or 112 degree lobe centres the cranking pressures and hence torque output would drop accordingly. Logically then cam duration needs to match the compression pressures the engine has or the heads need to be milled to raise compression to ensure cranking pressures will be greater than the stock starting point.
Our cam has 223 degrees @.050" intake and 227 degrees @.050" exhaust. Lifts using the stock 1.6:1 ratio pressed steel rockers are .490" for both lobes. Yes, the stock factory ratio is not 1.65:1 as everyone has been shoving down everyones throat for many years. It's actually 1.6:1
As you can see from the corrected dyno sheets, our little foray into the cam change has not only yielded a peak power gain but low end and mid range torque gains when in fact a cam this size should not really achieve this if we had not cheated a little with the lobe separation angle. By the way we don't recommend this cam with the 108 lobe centres in a stock compression engine because of the other reasons mentioned...rough idle (difficult to tune), excessive fuel consumption and large increase in exhaust emissions levels.
On the other hand this fast acting cam will work wonders in a well designed 5 litre or stroker combination and we will put it to the test in a daily drive 383ci stroker most likely.
Power figures corrected for best air conditions...Stock 309bhp @ 5250 rpm and 346 ft.lbs torque @3750 rpm
Power figures corrected for best air conditions...Cam 320 bhp @ 5500 rpm and 360 ft.lbs torque @4500 rpm
If you look at the sheets carefully you will see the cammed engine still has more torque at all rpm, even as low as 2750 rpm than the stock cam engine. You should be learning something from all this. Cylinder pressures optimised produce the strongest torque right through the rpm range. The opening and closing values of the cam, it's design parameters and it's mechanical efficiency in controlling valve motion precisely will yeild best results.