mboe794

I am just about ready to button everything up from my JE 11.5:1 piston install. Lightened the flywheel at this time as well. In the past I have been running the Factory Pro +4 ignition advance rotor and have been satisfied with the results. I had planned on putting it back in. But I have come across a few mentions of this potentially not working well with the new pistons.

Is there any consensus on this issue? I have found mixed thoughts.

I spent the money on it so I am hoping to be able to put it to use.

If I run it and get detonation it wouldn't be the end of the world. Just go back to stock. But if there is strong factual opposition it would just be nice to avoid a new gasket and oil over such a simple procedure.

gboezio

By raising compression, you are increasing flame speed,the combustion happens more quickly, this is good since it allows you to ignite later and still have your maximum cylinder pressure around 10 to 14° ATDC where it belongs, igniting later decrease pressure BTDC and helps engine efficiency as well as the smaller volume of combustion chamber pushing a little harder on the piston (smaller volume = higher cyl pressure). The main goal of higher compression is to burn the charge faster to allow higher RPM (less time to burn), so it will do some good, specially at higher RPM.

Now the advance, Honda had a big safety margin, the 4° advance takes it, by using High octane fuel, there is even more, by increasing compressionm there is less margin.
I would at least use the highest octane fuel available in your aera, and I would definitely put the stock pulse gen. If you run the 4°, monitor the plugs for sign of detonnation, flakes of aluminium stuck to the plugs (yes the Al of your pistons), but be aware that a single WOT pull is enough to destroy an engine in case of severe detonnation, don't expect to hear it on a bike unless you have stock exhaust and do 2 or 3 rd gear pulls holding the rear brakes by a mall wall.

Maximum cyl pressure at 14° ATDC is pretty much Mean Best Torque, so it can be found on a dyno, in short, the less ignition for best torque is what you want, but there is very little adjustment (binary in your case). With a fresh gasket, stuck on the cover only with permatex, you can swap easily wheels, an hour of dyno time will tell you wich one to use.

The combustion chamber on a VTR is quite bad, I wanted to weld some squish pads, but it will distort the head severly, will need stress relief, re-machine valve seats, deck ground flat. I need a few heads to experiment on this, mine is low compression but squish is good for forced induction and high comp NA as well.

Sorry for the long post, I had too much coffee

cliby

i thought it was risky and never did it. I use my bike for a wide range of riding and often come upon less than the ideal octane of gas in this area - sometimes lucky to find 91. If you were going to do it I'd take all the precautions mentioned in Gboezio post to define if you are creating a problem. Lean running is not just an annoyance but could have real safety implications if riding hard

mboe794

Thanks for the info!

I think I'll go back to stock one to be safe. I kinda figured that would probably happen eventually anyway. Could always tinker with it in the future. I do have a dyno day coming up but I don't think the circumstances are going to allow for rotor swapping between runs.

I am still interested in hearing thoughts or opinions from anyone else who has them to offer.

mboe794

I just remembered something...I'm pretty sure I read somewhere that the later SH's with the updated gauges and whatnot had a slightly different ignition curve. There is supposedly little or no benefit to be gained from the FP advance rotor on those models.

Any truth to this?

If so, would the later SH's have trouble with detonation when running high compression? Or maybe not because the whole curve is different as opposed to the entire range being shifted forward with the advance rotor.

mboe794

I have seen many of your posts around here but never noticed that you from MN. Where abouts? If you don't mind me asking.

By the way, there is 110 at the pump at a handfull of stations here in the metro. But I know what you mean about certain areas. I do a lot of my riding in BFE. Usually SE MN and western WI. Not much goin on out there.

cliby

I'm in southeast, rochester. we ride a lot from here to the river and over. the best I can find around here is maybe 93 sometimes. if lucky. I have some buddies in the TC that I ride with and sometimes come up for first thursday if I can get my planning down right.