So, the majority of aftermarket performance focus (regarding engine power) has been for the 951/944Turbo, leaving out the 944NA. Gains with the 944NA are hard to come-by, and typically aren't as "impressive" as the 951.
After doing MAF conversion for the 951, and flow-benching many factory airflow meters, two things became evident: One, the 20+ year old electro-mechanical AFMs are dying, and losing their original calibration. Two, the AFM is a huge airflow restriction, and that by doing nothing besides removing that restriction we see airflow improvements.
So, I bought a 944NA to test with, and I am very pleased with the results. With our MAF kit, on an otherwise stock car, we saw an ~8% increase in HP, with that gain occuring at
every RPM! Here is the back-2-back (same car, same dyno, the pulls within minutes of eachother) dyno result:
FYI, the
only mod to my 85NA is the N-Tune, everything else is completely stock down to the cast-iron headers. The dyno really shows what I've felt all along - great gains at every RPM!
Since then, I've quantified other modifications for the 944NA. I removed the (supposedly) restrictive catalytic converter and stock muffler, replacing them with a straight-through 2.5" resonator, 2.5" exhaust and 951 muffler (also straight-through and 2.5"). Additionally, I picked-up an K&N air-filter, and an 4° offset camshaft key from
928Motorsports.
So, things learned:
K&N air filter made no power over a new paper filter. Again, it made
0hp &
0tq, over a standard parts retailer paper filter. So, if a K&N filter was on your list, I suggest to not bother. Furthermore, the K&N will get oil on the MAF sensor as it uses oil in the filter media - shouldn't be a real issue, but why even risk it.
The air filter is not a restriction period. We did a couple pulls with the air-filter completely removed, and again it made
0hp &
0tq difference. So, the short lesson here is just use a standard paper filter, and replace at recommended intervals.
Second thing, the improved exhaust and removing the catalytic converter, there isn't whole lot of power increase, and most of those gains are in the upper-RPMs. I would say it was worth 3-4rwhp. Though with the resonator & 951 muffler it does sound damn good!
Third, we installed the offset camshaft key, which gave a
-4° shift in cam-timing. This should shift power to the higher RPMs... Well it did help keep HP/TQ up in the higher-RPMs, but was improvement was extremely limited and that was at the expense of lower-RPM hp/tq. The
-4° shift only made better hp/tq after 5700rpm; everywhere else it gave up power.
So, we changed the cam timing to provide a
+4° shift. This was the ticket! Power everywhere below 5700rpm was vastly improved compared to the previous runs. The drivability improvement and overall acceleration was very noticeable. Even with the advanced cam timing, the upper RPM was improved compared to stock.
Here is the stock vs modified (NA-Tune, 4° advanced timing, "cat-back" exhaust):
peak power stock: 117.6rwhp, 122rwtq.
peak power mod: 132.8rwhp, 142rwtq.
The % gains are ~13% increase in power (+15rwhp), and ~16% increase in torque (+19rwtq).
These mods are easy to do, and can be done for less than $800-900 (NA-Tune $500, offset cam key ~$20 (one pack will do two 944s), exhaust ~$300).
And finally, the before/after dyno:
The next modification I am going to try will be a reground camshaft that is fairly aggressive. I will also put on a true adjustable cam-gear to dial in the new cam.
It won't be this weekend, but maybe next.
The goal for me is to show how to make some respectable gains with the 944NA, with the minimum amount of effort and keep the cost reasonable.