More NA POWER part 3!

PREVIOUSLY ON "MORE NA POWER..."

Let’s drill deeper into tuning a naturally aspirating B6ZE for more power. Until now we have done all the basic bolt-on upgrades in part 2. Better flowing intake and exhaust are in. Ecu has been left stock with only mild adjustments to AFR and ignition timing. These modifications gave us about 85 crank hp/liter from 1597 cc engine.

See also 'cam specs and timing' in More NA POWER part 4.

ECU UPGRADE

Next there is the programmable aftermarket ecu. Nowadays many have opted for Megasquirt which is an affordable choice with good online support. Aside the make of ecu, what matters is that with fully programmable ecu it is possible to fine tune ignition and fuel tables for every setup. A chance to get rid of possibly restricting AFM or MAF is also an added bonus. Here is a dyno comparison which shows nicely how some 10 extra hp can be found by getting rid of stock AFM and tuning the ecu. I must mention that ARC intake was also installed, but I have no idea what kind of an effect it would have alone. 90 crank hp/liter is pretty nice for B6ZE with stock internals.

INTERNALS

Most of high power B6ZEs are equipped with 80,5 mm (or so) diameter pistons. Larger bore increases displacement to about 1700 cc and high compression pistons also rise compression ratio from stock 9,4:1 to 10,5 or even 12:1 –depending on the piston design. Both serve the same purpose: pumping torque up from bottom to top. And then there is The Flow. In order to make high power in high revs the head must flow properly. In addition either exhaust or intake must not form a bottleneck for the gas flow. Bigger cams, larger valves and head porting all serve the same goal: better exchange of gases in the cylinder. And don’t forget high quality, light and balanced internals like valve train parts, conrods, crankshaft and flywheel, if you also want your engine to last long in high revs. Here were the starters.

SAME GOAL, TWO PATHS...AND TWO RESULTS

At last we come to main course. Here are torque and power figures from two different engines. They are plotted into same graph and presented in wheel Nm and hp to make comparison easier. Original data for both is taken from chassis dyno graphs presented in wheel torque and power. So the only “manipulation” that I have made is torque conversion from lbft to Nm for the Engine nro 2. Power was calculated from torque in both cases. Still some consideration is required! I don’t know in which conditions Engine nro 2 was originally tested, what type of dyno was used and what was car’s actual drivetrain setup. So the figures presented here are not 100% comparable. “Are not 100% comparable”, what does that mean? It means that I, or anybody else, can’t state that engine nro 2 is “exactly” 10-20 Nm stronger than engine nro 1. But yes, nro 2 outflows nro 1 above 7000 rpm. That is “sure”.

Engine nro 1’s specs:
• Toda 81 mm bore pistons (1720 cc)
• Carrillo A-beam rods
• Balanced stock crank
• Street ported head, stock size valves, 3-angle valve job
• 272 degree cams, 9 mm lift
• Stock intake manifold fitted to throttle body and head
• Stock 1.6L throttle body
• 4-1 Racing Beat header, 2” pipe after collector

Engine nro 2’s specs:
• Maruha (Mahle) 80.5mm bore pistons (1700 cc)
• ETD Rods
• Knife-edge Crank
• Race head with oversized valves (ported and polished)
• 284 degree race cams (possibly 10-12 mm lift)
• Maruha ITB
• Racing header, 2,5” pipe after collector
• (This data is from winkyl’s engine taken from clubroadster.net and youtube.com.)

CONCLUSION

As was mentioned before, the aim of the comparison is not to stare at the numbers. The shapes of the torque curves are the most interesting part. Power band for both engines starts from 3500 to 4000 rpm. It doesn’t mean that nothing happens below that. There is more torque at 2500 rpm than in stock engine at 5500 rpm. The biggest differences between these two power plants are above 7000 rpm. Nro 1’s torque starts to drop from 6750 rpm and power reaches its peak at about 7000 rpm. Winkyls’s engine keeps torque up until 7000 rpm. And more importantly, the angle of descent is gentle enough to keep power rising until redline at 8000 rpm. I wonder what figures would be with higher redline!

This comparison isn’t the best demonstration of camshafts’ effect on torque and power since the other engine is equipped with stock intake manifold while the other runs on ITBs. Stock manifold possibly forms a bottleneck for airflow. However, the reason for broad power band up to 8000 rpm+ in engine nro 2's case is evident: High flowing head, larger valves, 284 deg. high lift cams and ITBs are the main factors.

See also:
More NA POWER part 1! and
More NA POWER part 2!