Thread:

reading plugs on blown bbc

Educate me on reading the plugs on my twin turbo blow thru 496setup. I want to know what why and where

reading plugs and understanding what is going on both with fuel control and timing is absolutely a great skill to have. I know I've said it many times, but with your setup, you need to buy a wideband O2 sensor/gauge/logger. That engine will melt faster than you could ever react to, get the right stuff to help prevent that from happening.

BTW: I still pull and read plugs when doing street or lake tuning, and I always run a wideband. I still like looking at them, especially for dialing in ignition timing AFTER I've got the AFR exactly where I want it on a WOT pass. And remember the main key to reading plugs is getting a brand new set to put in right before a WOT pass, then shutting it down as quickly as you SAFELY can. Then see what the plugs say about your timing...with a wideband the porcelain ring doesn't matter.



Andrew

Originally Posted by ap67et10

reading plugs and understanding what is going on both with fuel control and timing is absolutely a great skill to have. I know I've said it many times, but with your setup, you need to buy a wideband O2 sensor/gauge/logger. That engine will melt faster than you could ever react to, get the right stuff to help prevent that from happening.

BTW: I still pull and read plugs when doing street or lake tuning, and I always run a wideband. I still like looking at them, especially for dialing in ignition timing AFTER I've got the AFR exactly where I want it on a WOT pass. And remember the main key to reading plugs is getting a brand new set to put in right before a WOT pass, then shutting it down as quickly as you SAFELY can. Then see what the plugs say about your timing...with a wideband the porcelain ring doesn't matter.



Andrew

Thanks for the help... I'm going tto get a new set. I do run the lm-2 and datalog airfuel. It is 11.5/7 wot . Never seen 12's. I just worry bout detonation.

Originally Posted by stallion176

Thanks for the help... I'm going tto get a new set. I do run the lm-2 and datalog airfuel. It is 11.5/7 wot . Never seen 12's. I just worry bout detonation.

whats static compression ratio? how much boost? what kind of fuel? how much total timing?

9.5:1 straight 100ll avgas, 8lbs of boost in mandifold, timing at 26 but its lazy and I want to wake it up with some timing .496 CI twin turbo in a jet with intercoolers.

Originally Posted by stallion176

9.5:1 straight 100ll avgas, 8lbs of boost in mandifold, timing at 26 but its lazy and I want to wake it up with some timing .496 CI twin turbo in a jet with intercoolers.

that's a good setup, it'll probably like a little more timing, but that was a very smart and safe place to start. 11.5-7:1 is a good safe AFR, you are likely leaving some power on the table, but there is nothing wrong with those numbers, I do not like seeing anything in the 10's, but high 11's is great for safety, most of my stuff ends up in the low 12's. go get yourself a few sets of plugs, take your time and read the ground strap for heat strip location. Also, it is good to know and document the current top speed and rpm. As you advance the timing in 1-2 degrees increments watch and see if there are significant speed/rpm increase, as this will also help confirm you are making good changes. Validate these changes by reading the plugs, and as you are making these timing advance increases, once you see small or no increases in performance, stop....and maybe pull a degree or 2 out to keep it safe, then also confirm with plug ground strap reading. The biggest thing is patience! Go slow, make very small changes and you will have no problems getting that thing to run hard and consistent.


Andrew