One of the most fabulous things about having a dyno is being able to test every combination of parts imaginable. Having the partnership with Dan Pye and U2NDyno allowed development that most of us would just dream of.
Unfortunately there wasn’t the budget to go along with the awesome dyno – which would surely have sped up the development process, but I wanted to make a post to start from a STOCK non-revup 350z (VQ35DE) and show each and every step that we’ve taken to reach 372whp. Looking at some of the dyno charts below, you can really see how specific parts altered the powerband. You’ll also notice that beyond a certain point, peak torque will no longer increase (it will never go much above 280-290lb-ft).
Once you maximise the engine’s torque, the only way to make more horsepower is to make that torque at a higher speed. Infact, you’ll often see race engines lower peak torque in exchange for rpm, which makes more horsepower. The loss of torque is then made up with through gearing – in other words, horsepower is everything. Don’t let confused people convince you otherwise. The shape of the power curve is and always has been incredibly important, but horsepower, and horsepower alone is what makes the car go fast.
Before we start, let me show you all the most incredible dyno of all – STOCK versus NOW
I don’t think there are many words for this, other than to compare the horsepower gains – at 3900rpm there are almost no gains, 5200rpm ~70hp – but the peak to peak differences are 157whp! One thing that is awesome is how the torque peak is now almost the same as the factory rev limiter. Remember – these are FUNDAMENTALLY the same engines. Same displacement, same valves, same oiling system, same drive train. The differences are cams, heads, pistons, rods and external components. Incredible what a difference it makes, isn’t it?
So the first step was to free up the intake and add long-tube headers. This is what our race engine looked like with stock cams, longtube headers and an open intake:
The next step in the quest for making jam was of course cams. A quick primer on why cams make power – the faster the engine speed, the less TIME the valves are open during each combustion event. The gas (air and fuel mixture) entering and leaving the cylinders have a certain amount of momentum if you will – and the higher the rpm, the more cam duration is required to allow the gas mixture to fully enter and exit the cylinder. This is called volumetric efficiency – and at high rpm with a tuned engine we often see over 100% volumetric efficiency. In other words, a 3.5L engine is actually being fed more than 3.5 litres worth of fuel and air during each complete combustion cycle. Cam timing is the art of opening and closing the valves at the exact correct time to allow all of the air that wants to get in, IN, without leaving it open too long which would lower dynamic compression, and engine output (the point of closing the intake valve occurs while the piston is going UP, so you can imagine that you want to close it the moment air stops flowing through that valve!)
This is the power we were making after adding the larger Jim Wolf Technology GA cams, which have 300 degrees of duration, versus the stock cams which have only 238 degrees of duration:
At this point we’re starting to jam, but I hit a wall here and wasn’t able to make much more power than this for some time. I did lots of little work to try and make more power, but the main thing that was a big help was the addition of a 90mm throttle body and opened up intake plenum:
At this point we built the block with high compression pistons, switched to race fuel and installed eagle rods. Surprisingly the compression difference did not affect the engine output at all, but at least now I would safely be able to rev the engine above 8000rpm. The next step to make more power, and to rev higher, was to swap out to the revup lower intake manifold. This manifold lost torque at lower rpm, but gained horsepower higher up. Remember what we said about horsepower being everything? As long as the RPM was kept above 6500 it made sense to keep the revup intake manifold.
At this point Clark from Jim Wolf had some new cams for me to try – more or less with the same duration, but with much more lift. Since heads flow more air the more the valve is open (usually anyways), the more lift a cam has not only helps when the cam is fully open, but larger lift typically also goes hand in hand with a more aggressive ramp profile, so the cam will have more lift during the majority of its duration, so the amount of airflow is substantially increased.
All this time we’ve more or less known that airflow was the issue. If you look at the graph above you can see how at 6750rpm the torque signs off – and that is what we’re looking to eliminate. Keeping the torque up, and then building a bottom end that can handle the extra rpm to make power. So I sent my heads out to get ported by Gord Bush Performance, and after re-installing them we only gained something like 4whp. I knew this could not be right, since Gord flowed the heads and proved the airflow gains. The only answer was that there must be a larger restriction somewhere else. We “popped the top” and sure enough without an upper intake plenum the engine made a ton more power:
And then it was time for the ITBs. Tuned intake lengths, totally open and properly shaped trumpets meant that the gains we saw from popping the top were only a portion of the actual gains we would realize:
Now for some reason with the ITBs the power was not very smooth. That is something I am not sure of and will be looking more into in the future. But regardless the power gains are extremely noticeable and you can really see how the torque does not fall off nearly as much as it did with the factory intake manifold. Shorter trumpets, shorter headers and more tuning will hopefully yield even more power.
I hope you enjoyed this step-by-step story about how Kels has evolved and made more and more jam for the last 4 years!