Last updated 05Sep99.

JasonCuadra@fcmail.com

Excuse my terrible HTML'ing, I'm just starting in the world of HTML writing.

3 consecutive runs of Jenny's car:

'91 US version Miata (1.6) mods: 14 deg timing, JR CAI, headers, catback, cat-ectomied.

This was done with ambient air around 28 deg C and no correction, so if SAE correction is applied that would be around +3hp(?).

I was surprised by how consistent the 3 consecutive runs were. The method and software are consistent.

On various websites on the Internet, a '91 U.S. Miata with these same mods does about 103 hp peak. The above curve looks very much like them, but with consistently 4-5 ftlbs less. 3 of those hp are accounted for by the temperature correction, the remaining 2 could be slope in the road - it's confirmed to be slightly uphill, lowering the readings.

Here is Jenny's car again, before and after the above mods (before, had 14 deg timing). Dyno readings taken on the same road.

Here's Jenny's car against my car, which is a stock "90hp" 1.6, with K&N filter and 16 deg timing. Dyno readings taken on the same road.

Note how my torque drops above 4.5k rpm. The Euro/Asian >1994 1.6 is rated at 90hp, and uses the same cams as the US auto-tranny 1.6's. 15hp difference isn't too bad, considering I may gain 4hp from the muffler and 3hp from the CAI, closing the gap to 8hp.

Here is the effect of timing, with the stock airbox but snorkel removed. 16 degrees was found to be best, not 14. At 18 deg, the midrange starts to drop. Effect is huge! Note that effect is least at around 3-4.5k rpm, indicating this is where the factory timing curve is most advanced wrt the optimum curve. This was taken on a different road from the above tests.

That's 6hp improvement, free! Apparently the Euro 1.6 engine responds differently (i.e. more) to timing changes.

Here's the effect of the K&N filter, with 16 deg timing, against the stock airbox without the snorkel (2 runs shown). Torque curves:

And power curves:

Here are dyno runs showing the effect of a CAI. JoeyB's car;

Before: 14 deg timing, K&N cone, stock muffler

After: 14 deg timing, JR CAI, stock muffler

The surprise is the reshaping of the torque curve. It fills in the 2-3.5k region nicely, and adds quite a bit at 5k rpm. Seat of the pants clearly shows torque building up to 5k rpm instead of rolling off after 4k. I wonder what causes the loss of torque at 2.5k to 3k rpm.. the big resonator?

Next are some of the runs done in Subic last June.

The following are:

Keith: Sebring, exhaust, 6 deg timing

Streak: Sebring, water injection, 12 deg timing

Jenny: Above CAI'ed 1.6

Note: road where Jenny was dynoed is different from the other two so there may be a discrepancy.

Water injection affords more timing, which makes a huge difference. Streak (Hernan's car) really feels powerful. Jenny may have slightly more peak power than Keith, but Keith has more average power in the power band (4.5k-6.5k rpm), so overall Keith will win a drag race (given the same tire diameters) Keith happens to have huge tires (215x45x17) which will be a disadvantage in 1^st gear and the launch. The Sebrings also have huge torque, starting at 2k rpm.

This begs the question: Why are the Sebrings only doing around 100 rwhp? See next plot.

Here are the same 2 Sebringized Miatae, against Mig's engine, 90hp w/ unifilter and muffler.

Here you can see that the Sebring gives around +30% torque from 2.5k up. This jives with calculations assuming 6psi non-intercooled. However nobody has yet connected a boost gauge to his Sebringized engine.

There is a theory that a positive displacement blower will force-feed an engine whatever air it ingests, which is a function of blower displacement and speed. If the engine is restrictive, boost pressure will rise to compensate.

The pulleys we have are the same as standard 1.6, so in theory power output should be the same as the Sebringized pre-1994 Miatae (120-140 rwhp). When we get boost gauge readings, we can see if the theory is correct. (Unless something else comes into play, like exhaust cam duration)

Here are 2 of the stockers in the club:

Miao: My car, 14 deg timing, stock airbox with no snorkel.

Mig: Miguel's car, 14 deg timing, freeflow muff, Unifilter (mounts like a cone filter).

For some reason the data from Mig's car is "noisy" around 2.5k rpm. However, you can "visually smooth" the data.

Here is another stocker, "stocko" (Alfie's Miata), compared against Miao.

Stocko is bone stock, 14 deg timing:

The difference between these 2 Miatae may be the intake snorkel. Since timing is worth about 6hp, the resulting ~72hp at the wheels jives with the 90hp rating.

Timing 6hp

K&N cone 5hp

Muffler 4hp (?)

This is a total of 15hp, yielding ~105hp at the crank.

The mystery of why our engines are 90hp whereas the U.S. auto tranny engines, with the same cams, are 105hp is still.. a mystery. What restricts the power, aside from the cams, I want to know.