Ahvenisto lap comparison – 3 times NA Mazda MX-5

THE TRACK

I’ve spent most of my track time in Ahvenisto Racing Circuit. It is by far the most demanding race circuit in Finland. It’s technical, it’s beautiful and it’s legendary. And perhaps it’s world famous already since Captain Slow visited it with Mika Häkkinen – a Formula1 double world champion. http://www.youtube.com/watch?v=2bmqdnx5R1U

Ahvenisto Racing Circuit is built in late 1960’s and that makes it a bit different. It’s like Norschleife’s little brother. Most of the time it’s either uphill or downhill and there are no real runoff areas. Difference between the lowest and highest point is 30 meters (100 feet). It’s pretty much for a track that is roughly 3 km long. No picture can communicate track’s true profile. Incar videos give a hint but this track is something one must experience personally.

Enough with the praise. Here is some data extracted from this video  http://www.youtube.com/watch?v=Ft3Cx6fHrhI&feature=youtu.be. Here is some basic steering, throttle and brake input data to tell its own story about track’s profile.

Lap time (dry weather): 1´38 s

Steering wheel straight forward: 22% of the time

Wide open throttle: 43%

Foot on brake: 17%

Throttle partially open: 40%

Longest time throttle is continuously 100% open (including gear changes): 17 s

THREE CARS, THREE LAPS

Next follows a brief analysis of three laps done by three different MX-5s. They are in many ways similar but at the same time totally different. I will call them Silver, Red and Green. They all are from early -90’s with B6ZE engine.

Red’s specs:

- About 120 crank hp, completely stock engine with silenced decat pipe, 7200 rpm rev limiter

- 4.1 final drive with torsen type-2 differential

- BC Racing BR coilover suspension, Energy Suspension poly urethane bushing, stock stabilizers

- Track spec wheel alignment

- Yokohama Advan AD08 tyres, 205/50/15

- No roll cage or roll bar, P5 frame rails
- Lap time 1:39.5

Silver’s specs:

- About 130 crank hp with intake and exhaust mods, 7200 rpm rev limiter

- 4.3 final drive with Kaaz 1.5way L.S.D

- Tein SuperStreet coilover suspension, full set of poly urethane bushing, stiffer front stabilizer (22 mm diam.)

- Track spec wheel alignment

- Toyo Proxes R888 tyres, 195/50/15

- Full roll cage, interior strip down to compensate cage’s extra weight, plus no air-con and power steering.
- Lap time 1:38.5

Green’s specs:

- About 160 crank hp, 8300 rpm rev limiter.

- 4.3 final drive with Kaaz 1.5way L.S.D

- Koni Sportskit suspension, stock bushing, H&R stabilizers front and rear

- Track spec wheel alignment

- Yokohama Advan AD08 tyres, 205/50/15

- 6 point roll bar
- Lap time 1:37.5

Colors painted on the track illustrate gears: light green is 2^nd, yellow is 3^rd and orange is 4^th. Numbers in the boxes are “gear”/”revs” and speed below (in kph).

Okay, what does this tell then? First take a look at the gear changes. Red changes gear 6 times per lap because of the wider total gear ratio (4.1:1 differential and large tyres). Silver must change gear 10 times per lap (shorter overall gear ratio). Compared to Silver, Green’s total gear ratio is similar but Green benefits from higher rev limiter set to 8300 rpm - hence 6 changes per lap for Green. Silver’s extra two up and down changes both come in bad places. The first is before turn 3 where all the concentration should be aimed on upcoming left turn heading uphill. The second is between 8 and 9, on an uphill, not the best place to shift up either.

Next take a look at the table with cornering speeds. It’s interesting to notice that all three have almost identical cornering speeds in 5 turns out of 11. Track is very technical from turn 6 to 10 and the trick is to keep up the momentum. It’s basically one big complex of turns where clean driving and good handling is rewarded.  In paper Silver should have highest apex speeds as it is equipped with a set of R888’s.

After turn 10 it’s flat out for a while. Keep the throttle floored through turn 11 and get your top speed measured before going on brake and diving into turn 1! This half of the track from turn 10 to turn 6 holds all the straights - or not so curvy parts. High powered cars gain some ground here but are usually caught between turns 3 and 5 if drivers aren’t familiar with the track. Turn 11’s apex speeds show Silver’s more favorable gear ratio and power over Red’s.

Technicality of the track, the effect of gearing and apex speeds were three most important things I wanted to highlight here. Power isn’t everything in Ahvenisto and skillful driving is a key to success. Please continue checking the graphs by yourself – there is plenty of more to be found!

Practice, practice, test and practice…

This season’s first handling modification was a set of H&R adjustable anti roll bars. There is two possible settings in front and three in the rear. I decided to try something in the middle. Well, I couldn’t do that because while lying on the garage floor (car was jacked about 30 cm of the floor) all my muscle seemed to have disappeared somewhere and the front was set “stiffer”.

Testing took place at Ahvenisto Race Circuit. With stiffer anti roll bars corner turn in felt immediately more responsive and weight transfer was noticeably quicker. This is what these parts are for and they were doing their job nicely. However mid corner- and corner exit oversteer was kicking in. One had to be very careful with gas. Let’s see how milder rear setting affect…

Wednesday is the day for free practice session for everyone. There was a couple of modern formulas (F3 class?) and older ones also. Bikes had their fun for the first half of the day and left the track for cars when it started to rain.

I managed to drive both on dry and wet track. I really enjoyed driving in the rain because limits could be found at lower speeds. The other agenda was to shoot some film and test new Hero 2 –camera. In car pictures shown here are from testing different helmet mounts. “Chin” is a bit too low and I believe that “fore head” makes a better angle.

Just can’t wait for the next visit! http://www.youtube.com/watch?v=1VB9yoYNxrg

More NA POWER part 2!

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

The efficiency of an engine can be divided into three main factors: Volumetric efficiency (Ve), Thermal efficiency (Te) and Mechanical efficiency (Me). Te and Me stay more or less constant when basic bolt-on engine modifications are made. (For more info check: http://www.fordscorpio.co.uk/efficiency.htm)

Te tells how well engine makes use of the energy that is produced when fuel is burned in the cylinder. Compression ratio and combustion chamber design affect this factor. Higher compression ratio -> higher Te.

Me tells how well engine transfers energy from burned fuel into rotational force that turns the crankshaft. Higher inner and outer mechanical losses means lower Me. For example lowering the masses of rotating engine parts lowers internal inertia. Instead of using power to accelerate engine internals more power is fed through the crankshaft to the transmission to propel the car. Lower internal inertia and other internal losses -> higher Me.

Volumetric efficiency is what one is improving when basic bolt-ons are installed. Ideally, during the intake stroke, cylinder would “suck” in as much air as the mechanical volume of the cylinder is. In B6ZE’s case this would be 399.25 cc. If the volume of the air “taken in” is under that, the Ve is under 100%.

Naturally aspirating engine works optimally (= Ve is close to or even over 100%) in a narrow rpm range. Variable valve timing, valve lift and variable geometry intake designs are used to widen the optimal rpm range.

Ve tells how well the gases flow through the engine. First air flows through the entire intake tract to make its way into the cylinder. After work stroke exhaust gases flow out of the engine through the entire exhaust system. If there are flow restrictions either in the intake or exhaust side of this “gas pump”, Ve is decreased. It’s that simple! Take out restrictors and Ve is increased. Higher Ve -> higher torque. The trick is to know which restrictor should be eliminated first. Throwing in a race cam to an otherwise unmodified engine does not improve Ve at all because flow is heavily held back by other parts of the engine.

That was basic introduction to combustion engine’s efficiency. Now back to business.

Graphs shown here are from two different sources: Import Tuner Magazine and my own engine build. Both are lacking a baseline graph from a completely stock engine. Import Tuner’s stock engine’s torque curve is an estimation done by me (some discussion about it in my previous post) and “Einspritzer motor” is a copy of some kind of a manufacturer’s graph from some German site. All figures are presented (and converted, if needed) in crank torque and hp. To make comparison easier all curves are presented in similarly scaled graphs.

When I compare Import Tuner’s (IT) findings to my own many similarities and some differences can be found.

First similarities:

- Stock intake and exhaust (together) form a flow restriction worth for 10-20 Nm and 10-15 max hp. That is 10-15 % power loss across the entire rpm range.

- Stock intake makes about half of that. High quality cone filter is a must compared to stock airbox. Snorkel’s diameter is small and in stock airbox there are too many tight bends. Just make sure intake air is as cold as possible, at least not hotter than with the stock airbox.

- Stock engine benefits from a better flowing and better tuned exhaust manifold and gains worth for 5-7 Nm can be found. A little torque is lost below 3500 rpm.

- Both engines start losing torque above 5500-5750 rpm. Reason for that is cam specs (duration and timing).

Then differences:

- IT’s engine made its max hp at 6500 rpm and after that power dropped quickly. Exhaust manifold improved flow but torque curve’s form stayed more or less the same.

- My engine showed no signs of choking above 6500. Reason for that is a bigger AFM that outflows the stock unit. Stock AFM limits air flow to previously mentioned 165CFM, which is about 130-135 crank hp. Exhaust manifold’s true potential can be seen above 6500 rpm because stock AFM isn’t there to limit the flow.

- IT’s engine made about 10 Nm more low- and midrange torque. I have no real explanation for that. Maybe high flowing cat does its job there or drive train losses were less than 20% that was used for calculations. If losses were 18% instead of 20%, max figures would have been 153Nm and 128hp.

Enough with the speculations! My point here is not to stare at the numbers but the shapes of the curves. They will guide you to think of the right things.

More NA POWER for 1st gen Miata, Part 1

What interests a gearhead the most? Getting more juice out of the motor, of course. So lets drill deeper into B6ZE's potential of producing more than 136Nm/116hp - in naturally aspirating form.

Q1: Why only 136Nm and 116hp?
- In 1600cc engine that makes 85Nm and 72,5hp per liter. That is not the poorest result if you see the big picture. Late 80's engine management tuned for "what ever gasoline", low compression ratio (9.4:1), super silent stock intake and exhaust, mild cams and relatively standard valves. Clearly a healthy dose of performance potential is hidden somewhere there.

Q2: Why so small torque?
- Displacement is only 1600cc, so it will never be a torque monster of any kind. Compressio ratio (CR) is only 9.4:1 and stock ignition timing is far from wild. Adding 4deg ignition timing can produce 5-8Nm extra torgue below 5500rpm (with basic intake and exhaus upgrades). Check dyno graph: http://www.mymazdamx-5.blogspot.com/2007/05/tehomittaus-dynamometriss.html

Q3: Why torque peak is in relatively high rpm, 5500?
- Mazda wanted to make a revhappy motor. That was basicly the only way to make such a small motor enjoyable and at the same time produce decent performance, with the right gearing of course. Stock intake manifold and cam specs are the main reasons for torque peak to occur at 5500rpm. Intake manifold's runner lengths are tuned so that the resonation takes place at around 5500rpm. Stock cams make the airflow (edit: not airflow, but volumetric efficiency, Ve) reach it's peak between 5500 and 6000rpm. It is intetersting that this can also been seen in boosted motors with original intake manifold and stock cams.

Q4: What restricts the top end power, essentially the air/exhaust gas flow?
- Through the whole rpm range there are two basic restrictions: intake (air box and filter) and exhaust (original cat back exhaust pipe). Torque curve come's up about 5% from bottom to top with each of the basic mods: high flow cone filter and high flow cat back exhaust. Import Tuner magazine has done excellent dyno testing that can be found here: http://www.importtuner.com/powerpages/impp_0808_1993_mazda_mx5_miata/
NOTE that baseline is not showing true stock motor rear wheel performance because catalysator was busted. Guys put a new one in but did not bother to make a new dyno run. So, I would say that estimated stock crank hp in that particular motor was about 112 hp or so (89-90 rwhp with 20% drive train loss).
- Flapper door style air flow meter (AFM) is small and can flow about 165CFM (cubic feet per minute) in atmospheric pressure = naturally aspirating motor. Randy Stocker has done some flow testing (http://www.solomiata.com/airflowmtr.html) and with 90% volumetric efficiency at 6500rpm the peak intake flow rate becomes 165CFM (http://www.mk5cortinaestate.co.uk/calculator3.php). This is enough evidence for me to come in the conclusion that stock AFM restricts power to about 105rwhp (about 130 crank hp) as seen in Import Tuner's dyno testing: http://www.importtuner.com/powerpages/impp_0808_1993_mazda_mx5_miata/total_cost.html.
- Stock header get's small above 6500rpm if all the other basic bolt on mods are made, including larger AFM. Graph shows significant gains from 6500 to redline (pictures are really poor, sorry...): http://www.mymazdamx-5.blogspot.com/2008/05/tehopenkitys-nro-2.html
- Unbroken stock cat can support at least 155 crank hp. It's highly recommended to get rid of it, but I would do that last.
- And last there is The Flow: the cylinder head, valves, cams, throttle body and intake header. More about these later.

No pictures at the moment, only hard core text. Links should give you something to watch for a while. Better quality graphs, torque curve comparison and further analysis coming up in Part 2!

Yes, it's still active!

I finally reactivated my account and noticed that it has been almost two years since last update. First, thanks for all of you who have been following this blog! I discovered that this new version can tell some stats about visits and dispite my lack of time there has been some readers' activity.

So, what's new? About year and a half ago I had a spun conrod bearing. That was no biggie and hardly did any damage. Oil starvation during hard driving on the track caused that more or less. Remedy: racing oil pan baffle that keeps oil under the snorkle at all times. Having the engine opened it was also a convenient time to finish all the other stuff that was left half way the year before.

2011 upgrades:
- 160000 km driven short nose cranck -> factory new long nose cranck (balanced)
- Stock rods -> Carrillo A-beam rods
- ACL Raceline bearings (main and conrod)
- 3-angle valve job and valve train rejuvenation
- Toda adjustable cam gears
- DIY CAI with pressure box: inlet pipe from the "mouth", pipe diameter 100 mm -> 76 mm -> 60 mm -> stock TB
Result: Fully maintaned, reliable, in tune B6ZE. More of these will find their way here soon.

Thus summer 2011 was filled with carefree and revarding moments on and outside the track:

Another nice video for you. White gen 1 Miata emits very nice exhaust note (3:00 on, and 4:30)!