[MoreGAS]

Bob
You need to actually calculate compression by getting volume numbers for your new piston and heads. We have returned likely 20% of the custom pistons we order because the manufacturer totally missed on some critical detail, either way too much compression, or way to little. Hard to explain why but they mess up too, like all of us.

If head folks report you are going to gain 30 HP, they think they have achieved a ton more air flow(I suspect way to rosey a prediction unless you old heads were absolute junk- totally possible w someone who has no idea what they are doing ported them however) and logically that means in keeping with a 12:1-x A/F ratio, you are going to need a corresponding bunch more fuel in those areas. On a dyno monitoring lambda(A/F) you would have seen this and adjusted accordingly.

Setting an arbitrary number like 28 degrees is a tiny step in the correct direction I believe, but these lumps are expensive, and to not dyno it and set it up properly, tune it for fuel and ignition, is very risky(as demonstrated) . You don't want any more ign advance than what makes peak power and Tqe, and really want to build some safety margin in above that by taking out a wee bit more advance in some areas for when things get really warm etc. We have that ability w Motec (any decent EFI system actually but shameless plug for me being a Motec dealer in North America for 12 yrs or so) and when head temps creep up we pull timing. You don't have that luxury w MFI. If you cannot dyno it at bare minimum get a high quality Lambda meter always displaying in the car (I can link you to one and you can thereby check fueling is in the "ball park" , dual lambda one on each side would be better not sure if avail. in a meter display) , set timing at 25 , and hopefully you get lucky. Realize, we NEVER do this and dyno , and tune every engine we build, customer's and our own, but trying to give you a chance here. These are way more fun to enjoy on track at RPM than work on, so hope I have convinced you .

Last thought, also verify w a timing light (easy to do on a dyno or briefly free revving to say 5500 RPM -oil warmed up already!) that at rpm and load at Peak Tqe , that ign advance is where you believe it is.

beST

Kevin
GAS Motorsport