Looking for some advice, Running a 302 with 9 psi of boost. (not intercooled) AFR is around 11 from 3500 rpm to 5000 rpm. I wanted to tune it safe by making sure I didn't run it lean under boost but I believe I just put fuel in my exhaust and set my cats on fire (they were smoking and stinking) ! I will be inspecting/replacing the cats this week but wanted to re-tune things to prevent this from happening again. How does an AFR from 12 to 12.5 sound from 3500 to 5000 rpm ? Car has a max rwhp of 448 at 5750 rpm and a max torque of 428 around
You indicate that you have no aftercooler so I'll assume your working with a turbo rather than something positive displacement.
I also see that you seem to have a good grasp on the effects of "walking too close to the line" as far as mixture is concerned.
Unless you're already there, go with the coldest plugs you can find.... if you are running a decent multistrike, high output ignition, don't get too shy with the gap. If you back the advance out a little (total or initial, you'll know best if you are sure of your curve), it will probably give you some margin for error. If you can, do a really hard pull with fresh plugs and do a "hot drop". Cut the ignition at the end of the pass, push in the clutch or put the trans in neutral and, at the same time, keep the throttle wide open to reduce the vacuum signal through the carb(s). Pull the plugs and inspect them with a good magnifier. You may have to repeat this process a few times, but it should ensure that you have little in the way of bad kharma. After you establish your mixture, start bumping you timing to find the ideal initial and all in numbers. I like using a G-Force accelerometer for this and you can work through different rpm ranges to fine tune the curve.
Unfortunately, you'll need to walk a tight rope. At your boost and power levels, with no after/inter cooling, I wouldn't go any higher than
12:1. Keep in mind that summer temperatures make things worse for detonation. If you want to add a nice safety factor and spend little money then look into water and/or alcohol injection. I use it on my KB blown Mustang and have run up to 16 psi without any detonation problems. It is very effective when used properly.
Thanks for the responses. I think I will keep the car tuned the way it is. Did some troubleshooting today .... realized if the cats were burning there should have been smoke out the tailpipe .... Duh ! Finally crawled underneath it and there is tranny fluid all over. I am going to post some questions on this group about the t5. An intercooler is the next investment. Thanks again.
The aftercooler (or intercooler if you like) is installed between the blower and the intake. As air is compressed, it heats up (increasing the space between the molecules) - cooling it serves to make the air denser.... several horsepower can be freed up with little in the way of pumping losses.
The multistrike ignition system helps keep colder plugs clean at low rpms and can also expose more working mixture to spark events. Bear in mind that the multistrike feature is active only at idle and slightly off idle..... as rpm climbs, there is insufficient time to saturate the coil. Also, most ignition controllers (such as the MSD) use capacitive discharge or similar circuitry to achieve a "hotter" spark.... combined with a suitable coil, these systems are very, very good.
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