Thread: BKR8EIX or BKR7EIX / 93 oct.

Hi!
What is the best spark for 250 psi + 93 oct gas, BKR8 or BKR7. I like heat 7 but i want test heat 8 in my high CR engine. Any experiences?

EDIT:

Damn notebook...

No experience with 8's here. I run 7's around 15psi of boost on 91 octane. I think that's around a 12.5:1 CR in boost. I did the equation once and it was around 12.5~12.7:1, based on an 8.5:1 CR DET.

I might be a bit silly right now since I just ran 5 miles but here are my thoughts on the CR matters:

For an 8.5:1 engine at 15 Psi:

P2 = P1*(r)^1.4

= (14.7 + 15)*(8.5)^1.4
= 594.21

If volumetric efficiency is 85%

294.1*0.85 = 505 Psi

And that is for a regular 8.5:1 at 15 Psi boost.

If you convert that back to a CR at atmospheric pressure:

(505/14.7)^(1/1.4) = 12.5

Good work Tekkie And with greater volumetric efficiency it would be better. Not sure what the SR20 is around.

Thanks for putting it up. It's possible to acheive greater than 100% VE on a turbocharged engine, but I just left it around an average, as it was somewhat unknown to me what the actual VE would be for my specific motor (as all motors aren't created equal, after all.)

More than 100% VE on a turbo motor would mean discounting the boost pressure in the equation or you would be counting it twice. I also got told that 15psi being twice atmo pressure would result in twice the amount of air being forced into the cylinder so 90% VE would be 180% VE and therefore 8.5:1 compression is equivalent to 17:1 compression as there is twice the air being squeezed into the same space as a na engine?

As for spark plugs, 7 heat range will be fine if your plug gap is sensible. 8 heat range might need gaps closed down to stop misfires but that reduces flame so 7's are probably a better idea maybe?

Compression ratio is the ratio of volumes, not pressures. About the VE, it is more like assuming that the cylinder is actually only takes in 85% of the airflow through the MAF, regardless of the pressure. At least I think that's how it works for the VE I can hardly remember since I've been doing so much other stuff since I last was doing that stuff.

Also OP not trying to jack the thread just wanted to verify that calc lol

Good point, it was late last night for me and I was on my way to bed VE of turbocharged motors can exceed 100% easily, but you wouldn't want to count that in your initial calculation. You'd need to do the formula based on N/A figures.

Ok! Maybe the best option is heat 7 . . .? Any gap number for this?

Thanks!

Unless you are using 110 oct race fuel and a microwave zapping MSD there is no need for the 8's. Even the 7's work best with an MSD, but still a little too cold for pump gas.

Mine are gapped at .0028", however I'm also boosted, so they're gapped low to help prevent blow out. Not sure what they should be in N/A. I would try around .0030" and work your way up to around .0035"?