Octane Rating

[Pablo]

I'm not an expert at burning methanol so don't take the following examples as the limit of what can be done with it.

First engine: 10.45 to one CR. Insufficient fueling. Blew at 31 psi.
Second engine: 11.27 to one CR, mixture read 11.4 on the O2 (calibrated to read out gas numbers) This mixture gave best power. Not necessarily best safe power. Blew at 28 psi.

Can you figure out what the dynamic CR was for the second engine?

Third engine: 9.27 to one CR. Target mixture 13.4 at idle, 11.7 to 12.2 before boost, 11.0 to 11.3 under boost. Target max boost 28 to 30 psi. Preliminary fueling requirements of this engine are down 9% on the injector pulse width from the last engine. This is in the non-boosted regions of the fuel map. This goes to show you that methanol likes compression.

That doesnt sound too off of what gasoline would do. Isn't the rule of thumb for gasoline 4% more power across the board per point in compression? Since power has a close relationship to the amount of fuel used (BSFC), I would think that 9% would actually be pretty close to the same effect as that change on a gasoline engine. You basically went 2 full points lower in CR which by rule of thumb is 8% difference in power. Or am I missing something here?

 

[Pablo]

Another thing to remember about boost is that boost pressure is a measurement of RESTRICTION. If you were to hook your turbo at WOT to, say a hot air baloon, it wouldn't make ANY boost (at least not for a week or two ) If you have a good set of heads and a matched camshaft, then the car will make more power at a lower boost setting. There is sooooo much that determines how much boost your combination can handle on your tune-up. 25 psi boost on a NHRA prostock engine would KILL it even on straight methanol. We have a set of heads (8445 castings) that really do work well with some talented porting, but they are 40+ year old technology. Combustion chamber mods, good valve seat prep, correct valve to guide clearance, NO oil in the combustion chamber, (i.e good rings and valve seals) ALL plays a role in what an engine can handle as far as boost is concerned. I know this is old info, but I think that everyone needs to keep the whole package in mind when they start to wring out as much power as they can from these little V6's. Just because "John Doe" has the same parts on his car, doesn't mean your car will run the same! It takes many, many, hours and TONS of thought to safely persue your horsepower goals. Go slow, or you might just drive over the crankshaft

Yeah, exactly why it seems like stock long block cars (with stock cam and all) can seem to get away with so much boost and not blow apart. Ill bet the amount of psi to get the dynamic CR up where a heads and cam car is at is a whole lot

 

[Alky V6]

Yeah, exactly why it seems like stock long block cars (with stock cam and all) can seem to get away with so much boost and not blow apart. Ill bet the amount of psi to get the dynamic CR up where a heads and cam car is at is a whole lot

An interesting note about engine #2. I had noted earlier that it blew at 28 psi. That was do to an initial boost spike off the line. Earlier runs were done with boost spikes to 26, 27 with no problem. The impressive deal is that after the short initial spike, the rest of the run was accomplished with only 22 psi boost. So I think in my case, the large cam I am using actually allowed me to run less boost to get the performance target I was shooting for.