3.2SS Engine feedback - post break-in
 

It has been a few months since I finished my rebuild and I wanted to take some time to share my description of the motor and its current state of tune.

Background:
top-end build due to broken head-studs.
1978 930/03 SC bottom end - untouched with 88K miles
1978 large port SC heads - stock
Normal head machine work from G2 Racing (CGarr) - sealing surface, guides, cut seats, twin plug
Usual HI\igh performance valve spring set.
98mm Mahle PC set
CR measured 9.98:1
twin plug SC distributor using Aaron Burnham's (Burn-Bros.) rotor and OTS Jag cap.
DC40-108 cams
MegaSquirt EFI using Innovate LC-1 WBO2 for feedback
TWM 3003 46mm ITBs
Full DFL and ceramic coatings treatment on the top-end.

I started the initial drives slowly. I had to retune the EFI and this was a great time to perform the break-in process. My process for EFI tuning is to carefully drive while gross-adjusting the map such that the car runs. Next I slowly expand the range of throttle inputs while datalogging the motor and running the analysis software. The analysis consists of a comparison of the existing AFR for each cell on the map with a target AFR and then adjusting the fuel quantity up or down such that the AFRs match. Its a simple iterative process of driving, logging, analyzing, reflashing and then more driving. You hit a large range of engine loads from WOT through closed throttle decel (high vacuum) and hit every corner of the map. This took approximately 2 Hours to have the engine running at 92-95%.

Once the engine was running well it was time for an oil change and then a drive. I organized a Hill Country drive for a few locals. I told them I was breaking in the engine and to leave a gap behind. I beat on the motor hard once it was warm. I started with lots of throttle input and lots of high-vacuum decel. Usually 3rd gear from 2K to 6500 with full open to snap closed letting the engine brake effect slow the car. Within 100 miles or so the engine was noticeably stronger. Acceleration was better but the biggest improvement was on decel. The motor really has good compression and you can FEEL it. All I could do was try to contain the perma-grin as the car is a rocket ship.

Since then I have taken a few other drives and also been using the car on my daily commute. The motor is exactly what I wanted to build. I set a personal rev limit for design purposes of 7200 rpm. The motor pulls hard to this number and feels like its ready for more. However, its the area under the curve that counts.

The motor is completely docile around town. It feels like it has about the same torque as the stock 3.0 through 3500 rpm or so. Above 4K its a totally different animal, it just keeps pulling harder and harder the farther the tach needle swings clockwise. The car will effortlessly pull from 1500 in 5th with a smooth torque curve. Part of this is due to the lightweight and shorter gearset but it is unlike any other 911 I have driven.

Now let's discuss a few of the details. I performed my post-break-in oil change valve adjustment and head stud torque last week. 3 valves were slightly loose. One nut barely moved before the torque wrench clicked. All of my DFL treatments are still pristine on the cam lobes. All is good with the build.

After the break-in was done it was time to gain the last few percent output and lean out my cruise cells for better gas mileage. One thing I have noticed is how lean I can run the motor. On the stock SC I could not get much above 14.2:1 before it would hestitate, pop, stutter and generally run like crap. Look at all the CIS posts during the fall when the air density changes due to cooler temperatures and you will see an intolerance for lean running. However, this motor is happy with cruise AFRs nearing 16:1. I can't believe it. I really think that the ceramic coatings on the heads and piston crowns help with combustion efficiency.

I have experimented with the length of the air horn trumpets on the EFI. I started with the stock TWM 3003 openings. These are 2 1/4" tall with 85mm top diameter and a high radius edge. I have also tried a set of Weber IDF stacks that are 4" tall, 76 mm top diameter and a less pronounced lip. The short stacks have an annoying sonic reverberation at the rear deck at normal cruising speeds. They pick up resonance (tuned port) above 5K. The high-rpm sound is incredible. The longer trumpets have a much smoother sound and seem a bit quieter. The torque curve is noticeably smoother through 6K yet they seem to fall off slightly at 6K compared to the short ones. I will see if I can dyno these changes in a few weeks.

I have our annual Hill Country Rally this weekend. When I get back I plan to schedule some dyno time. I will update the thread with some final numbers.

Besides this I am trying to find time to go to the track. Work is taking too much of my "play time".

Great result! It is interesting that you can run that lean. I can't get mine close to an AFR of 15 without issues but I have a Carrera intake. Can you post your AFR, VE, and timing maps?

Steve, I am extremely surprised how lean the car will run. I am a believer in the engine coatings. I noticed that the engine runs cooler too. When it was 95 last week my front oil cooler thermostat never opened. How's that for an evening commute home in traffic? Yes, it is working properly, but the engine really has to be pushed to heat up.

I can get some scree shots of the maps later tonight.

No timing maps, I am running a mechanical distributor... For now. :)

timing is 8 BTDC at idle and 27 BTDC at full advance. Ramp kicks in at 1400 or so and finishes just over 3200. I don't know if this is optimal but the engine does not feel like it is lacking for timing.

I have most of the parts to convert to MS to control ignition with the exception of the knocksensor. I have it all figured out, just have not acquired the parts. The install will still go out through the twin plug dizzy for a vintage look.

No dyno sheet yet???

I would think not with twin plugs... that should be pleanty of timing. My 3.6 was running 24' advance when I started tuning, I have backed it down to 20' while I set my AFRs.

When you go to the dyno, establish a baseline full throttle pull at settings you are comfortable with, then BACK DOWN on your advance by two degrees and see what happens. If you pick up torque anywhere you were giving the engine more advance than it wanted. How much effort is it to make the Mega squirt run the ignition?? That would be ideal as you could tune for the least advance at best torque in each load cell. This allows the ramp up to fall wherever the engine wants it. Tuning until you get knock and backing down is not the path to finding a nice and safe torque curve.

Jamie,

Just reading your post to learn. A couple of questions:
1. what are "DFL" treatments?
2. It's really surprising that the engine will run that lean. I agree it must be the coatings...well, unless something is lying to you and your AFR is not what you are reading. Anyway, let's say it is the coatings doing the magic, would the case change once carbon builds on the pistons? And how quickly would you expect that to happen to where you have to remap?

Congrats on your new engine. The specs sound like a lot of fun.

DFL = Dry Film Lubricant