Timing and Octane

Well the past few days have been interesting.
I managed to fill up with 100 octane in Germany where its cheaper than 95 octane in the UK.
This allowed timing to be increased 3 deg with what seemed like a small increase in power.

I had been wondering why, if lower timing was better, why not just run lower octane and lower timing. Well after some reading and investigations the answer appears that if you run too low with timing the combustion will still be happening when the piston has past its best position for combustion pressure. (Around 15deg ATDC) So the ideal octane and timing is the one which puts the most pressure around 15 adtc and is all spent before the exhaust valve opens.

From others comments and feedback this optimal timing appears to be around 24-28 deg, now there will be variables such as combustion chamber design of aftermarket heads etc which could move this a little one way or the other.

My timing with 95 octane was around 18 deg. With 98 Im back to around 20 deg. Im hoping with the changes detailed here to be able to creep towards 24 deg with no observed knock.

So Im now officially running 98 octane and am embarking down a track to optimise compression and timing settings. My compression with Dart heads is right on the line, so extra margin for error will be good and hopefully allow more power from optimised timing.

A quick read of this excellent FAQ will reveal more for those interested. Particularly section 7.

So in order to see how this goes I have just ordered a set of 8 x NGK BKR6E-11 plugs which are a gasketed equivalent to the TR6 plugs. They are standard copper. But if they work well Ill change to Iridium.

Anyway my quest for reliable compression and timing will be as follows;

• Fit OTRCAI cold air intake to reduce IAT temps (on its way, hopefully here in the next week or two)
• Fit lower temperature Thermostat 170*? (currently researching this, David Vizard has a nice article covering all this here)
• Fit colder spark plugs as mentioned above

Other changes such as combustion surface polishing etc are out of scope for the time being, as the engine is already assembled. I could also retard the cam and flycut the pistons (dual benefit of allowing more lift and dropping compression) but wont for the time being.

The maximum benefit looks like it will be realised by the use of a lower temperature thermostat. Here the idea is to reduce heat soak to the intake air and closely related to this, the combustion chamber pre ignition temperatures. Thus inhibiting the spontaneous combustion that goes with knock. See the chart below from the David Vizard Popular Hotrod link above. My DCR is 8.3 or close to, according to this calcuator here. (Use 3.91 for gasket diameter, 3.9 for bore, 3.62 for stroke, 6.1 for rod length, 0.055 for stock mls gasket on stock ls1)

So based on 98 octane (98 + 87)/2 = 92.5 I need to be looking at a 170* thermostat and regulate engine temps around there. Users of the popular 160* thermostats report general operating temps in the mid 170's so. I think a 160 might be the go. I can regulate things somewhat with fan operation. Just need to order the thermostat now...

Other than that, I spent a good few days logging and one lap of the Nurbergring. Which is situated in the nice little town of Nurgerg in SW Deutchland. I logged the lap, but sadly cronic understeer from shoddy worn cheap chinese tyres prevented to much speed. I will rearm with better tyres and schedule another visit. It was great fun. Next time Im going to book a lap in the BMW M5 Taxi that takes people around. Apparently the drivers are excellent and will do a very very fast lap including some good sideways action.

I also attended the F-Body meet in Meerbusch, a good crowd from throughout Northern Europe were in attendance. Mainly older 3rd gen's but a few LSx vehicles were around. I took the organiser for a blast with a few of his friends. He said power was very smooth and fast. Which reminds me, its soon time to redo my 0-60 times.

Clarity and chaos

Well, day 2 saw the horrific discovery that the reason why the WB02 wasnt working was that it wasnt plugged in!

Starting had been a problem so I swiped a cranking VE table from a modified tune on www.holdencrazy.com. Starting is now fairly good, a couple of turns and its away rather than protracted cranking and throttle use being required to get it started.

Once started things got real messy, the idle was hunting up and down pretty badly. I recalled some comments regarding idle spark control and an investigation of tables B5934 -> B5936 showed that up to 25 deg was being pulled on startup. This showed me where the 9 deg total timing was coming from. Once warm it settled down and spark was running what I had set it to in the base spark table. So some big chops to these tables were made, basically 50% off each overspeed table. Underspeed was left as is. This seemed to make a good difference as well as generally reducing the cracker values overall. I had dialed my desired airflow in fairly well on day 1 so just a small amount of extra air was required.

I should mention that my baseline tune was a 2004 HSV GTS converted to efilive custom OS3.

Low level VE cells needed to be reduced a little, nothing more than 5-10%. Some higher end cells have gone up by around 7%. Im going to compare with a tuned VE table shortly to see where the gains, if any are.

I still have some low speed coming to a stop issues and when fan and power steer load goes on it can stall. I will add some more air for the fans and look at cracker and follower for idle transition stalling at low speed. All in all its come a fair way so far.

Spark is fairly close to stock a little less in parts. Compression is a full point up and spark at idle needs to be around 8 deg more than stock cam. A few more weeks of tweaking and it will be off to the dyno.

I wish I could have got a larger cam, but this one has a very wide powerband, I seem not to have lost any low down power except the car will surge in 1st gear crawling along the road with no throttle, so I guess no surprise there. Basically exactly my requirements. I have to meet emissions standards so it was 224 or less sized cam. I chose 220 for a safety margin. The car pulls well into the 6000rpm range. Im guessing Ive added power over around 3500 rpm to redline. Not sure how much yet. Its not like night and day which is what I was expecting.

Mr Dyno will tell all.

Stage one... again

Cam bearings were just within spec. So cam is now in.
Strangely piston to valve clearance was not sufficient to use the higher ratio rockers. It cleared, but not by enough to allow for heat and wear. Others have been able to get larger 23x duration cams in without fly cutting the pistons however I did note that my 0.006 spec's are very close to the larger cam specs at that lift. Perhaps due to high and fast lift. I just checked against the F13 cam and the crane has a later IVC and more 0.006 duration. So I guess that answers that. It must have slow ramps.

Anyway, car would not idle initially, I gave it 20% more RAF (Desired Airflow), still not good, so 20% more and once slightly warm it idled ok. I did a half baked log to check for idle air, but had to keep the throttle open to get it to run without stalling. Once warm it was fine, so Ill have to relog when cold. Its likely even more air is required.

Inital idle spark was 9 deg for some reason. It should have been over 20, so I will need to log some more and see where it got the 9 from. I overrode the spark with the bidirectional controls and got an idle map of 38kpa with around 34 deg spark. The engine runs crap with 9 deg spark, no wonder it was stalling.

I think the shop must have pushed the WB02 recall button, you know, the one with the red LED that nobody should touch, while wondering what it does. So anyway no chance to do any VE tuning as you cant recal the WB02 until the car has sat for 8 hours or you unscrew the unit from the exhaust and recal in open air. Suffice to say Im waiting 8 hours as its windy and rainy at the moment.

I drove off with my idle kind of ok except for coming to a stop when if I turn in on the power steering the car cuts out. Might need some cracker action or possibly even more air as mentioned above.

Next issue is due to no view of AFR I logged NB02 voltage as a kind of rough view on things. It turned out I was running over 1V constanly at low MAP (ie) very rich. Miles to go was falling like seconds on a clock. I pulled over and made some adjustments until the voltage was visably moving around. I drove like this for a few miles to check that the O2's were still working ok then turned on semi open loop fueling in custom os3. Basically if you command 14.63:1 the O2 sensors will trim the fuel to stoich. If you command any other values O2 feedback is not used.

This worked much better allowing the car to run pretty well. The STFT values showed that the VE table was out as at idle they were -15% and at some points +10%. This will be sorted out when the wideband is working again.

I swapped in my old spark map as the GTS table was showing up too much KR. Maybe due to the increased compression ratio or 95 Octane fuel. Lots more experiementing needed with spark and fuel.

In fact VE is fairly easy to dial in when you have a working wideband. Idle will take me a bit longer and spark will take the longest. Ill have fine tune it in on the dyno.

Af far as how the beast goes now. Im not sure. It feels at least as good as it was before and slightly beefier in parts. Nothing major. But Ive kept out of enrichment so far and its in a pretty basic state of tune. Idle is quite sedate, nothing too hairy. If it wasnt for emissions compliance I think Id go for the popular 224/228 comp cams grind.

More info once fueling and spark is dialed in further.

Under the knife

Well the doc has my R8 under the knife. We discovered the cam bearings are showing signs of wear which seems to be quite common. So the bearings are being measured out to check for signs of uneven wear etc. Ive got my fingers crossed that they will be fine otherwise its an engine removal and extra ££ to sort them out.

Worse still Im booked on a ferry to Europe late may!

Hopefully all is well, we will see in a few days.