More NA POWER part 4: B6ZE cam specs and cam timing

See also the latest post in More NA POWER! Part 5: 100 bhp per liter in 1.7 liter B6ZE

It is hard to find documented data about the effect of cam timing in B6ZE. There are some general rules, though. Solo Miata's Randy Stocker has written in his site that 1.6 liter Miata engine with stock cams benefits from 6-8 deg retardation, if you are looking for max power. Advanced timing gives better torque to mid and lower revs. 

As a general rule increased overlap moves torque into higher revs and decreased overlap gives better torque in lower revs. Explanation is that overlap improves gas exchange in high revs but decreases vacuum in low, which results in lower intake velocity and poor mixing. 

For cams in general, a couple of rules apply. Increased lift increases flow across the power band, but extremely high lifts (1,5 times the original, maby) can make intake velocity to drop in low rpm. Increased duration moves power band higher up at the expense of lower revs.  

B6ZE WITH STOCK, 264/9 AND 272/9 CAMS

So what happens in real life with B6ZE? Here are two examples. Baseline is from Import Tuner Magazine's archives (intake, exhaust and JR cat). Real life examples are from two Finnish private engine builders, both measured at the same dyno. Graphs are in rear wheel figures.  Pay attention, don't concentrate on the numbers! Note how the torque curves look like and where the power starts to drop. 

Nro 1 specs: 79 mm high comp pistons (1.64 liter), 3-angle ground stock valves, mild street porting port matched intake manifold, 4-2-1 header (origin unknown), stock cat, sports exhaust, afm delete, stock 56 mm throttle body and 264deg/9mm Schrick cams (German street and racing cam manufacturer).

Nro 2 specs: 81 mm high comp pistons (1.7 liter), 3-angle ground stock valves, mild street porting, port matched intake manifold, Racing Beat 4-1 header, high flow cat, sports exhaust, afm delete, stock 56 mm throttle body and 272deg/9mm Toda Racing cams (Japanese). 

First I must note, that there is an odd dip in Nro 1’s torque curve. I think that could be sorted with some map and/or intake tuning.

Some observations:

- Schricks start to pull as low as the stock cams

- Torque stays up about 1000 rpm higher with Schricks (measured at a point where still 95% of max torque occurs)

- 95% of max power at 6800 rpm with stocks and and at 7300 rpm with Schricks

- Todas start to show some peakiness, as they start to pull hard from 4000 rpm

- Todas keep torque up until about 7300 rpm (95% rule)

- 95% of max power at 8000 rpm with Todas
- All three engines are running with stock intake manifolds and throttle bodies

- Torque/displacement-comparison shows no significant increase in max torque, but increased flow in high revs pumps power up

SAME CAMS – DIFFERENT TIMING

Here is a demo how timing affects the torque and power. Test was done with engine Nro 2. You can see that increased overlap (from 8 to 26 @ 1 mm) makes higher numbers from mid to high revs. But what really happens here? In theory bigger overlap should give better flow in higher revs. Max power gains are moderate, only about 5 rwhp. Torque gains are significant, but they are in mid revs. Retarded timing was also tested. It slightly dropped torque between 4k and 5,5k, but had no effect in high revs.

Obviously engine has reached its maximum torque, about 140 rwNm, in current setup and flow reaches its limit at 6750-7000 rpm. What happens when intake cam is advanced, in this case 9 degrees, is that dynamic compression increases. Advancing intake means that valves open earlier and also close earlier. Early closing means that there is more cylinder volume to be compressed, thus higher dynamic compression. More compression -> higher thermal efficiency -> more torque.

CAM TIMING CHARTS

Here is a collection of timing charts illustrating different cam timing options. It is easy to see overlap in degrees in circular timing charts. ‘Valve lift versus crank angle’ -charts demonstrates overlap in millimeters. If you find this information useful, please leave a comment!

CONCLUSION

More torque requires more flow. In reasonably tuned hot NA engines practical maximum torque per liter seems to be in 110Nm/l ballpark (in crank figures for 'hot street tune’). High torque in high revs means high power. To keep torque up above 7000rpm is a true test for engine’s, and B6ZE's, breathing abilities. For that, I would suggest, you need unrestricted (preferably tuned) intake and exhaust plus high flowing cylinder head with larger valves and 280 deg or bigger cams.

See also More NA power part 3!