DCR and octane with 243 heads
11-22-2014, 09:43 PM
#1
Staging Lane
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DCR and octane with 243 heads Heads are AI 232cc 243 heads on a stock LQ9 shortblock (flat tops).
Head cc is a measured 64.7, gasket is .041 compressed, and assuming pistons .006" out of the hole, that puts me at 11.35:1 SCR.
DCR from Wallace Racing's calculator says that puts me at 8.98 DCR at sea level, and 8.78 DCR at 1000 ft where I live.
As an old-school car guy, these numbers are way over what I would use with pump gas, but I'm not used to modern chambers and their efficiency.
What DCR would you think is OK with 243 chambers?
Car weight is about 3000, trans is T56 with 2.66/.50 gears, rear is 4.11:1. It will be using a tuned stock computer with knock sensors, not an aftermarket setup or carb.
Head cc is a measured 64.7, gasket is .041 compressed, and assuming pistons .006" out of the hole, that puts me at 11.35:1 SCR.
DCR from Wallace Racing's calculator says that puts me at 8.98 DCR at sea level, and 8.78 DCR at 1000 ft where I live.
As an old-school car guy, these numbers are way over what I would use with pump gas, but I'm not used to modern chambers and their efficiency.
What DCR would you think is OK with 243 chambers?
Car weight is about 3000, trans is T56 with 2.66/.50 gears, rear is 4.11:1. It will be using a tuned stock computer with knock sensors, not an aftermarket setup or carb.
11-23-2014, 04:43 PM
#2
What cam are you using?
I'll be at 11.25:1 on my LQ9 with the same heads at 63cc and a .051 MLS gasket. Using a Tick SNS Stg 2, my DCR will be 8.9 which Martin told me will be fine as that is where this cam works best.
Kerry
I'll be at 11.25:1 on my LQ9 with the same heads at 63cc and a .051 MLS gasket. Using a Tick SNS Stg 2, my DCR will be 8.9 which Martin told me will be fine as that is where this cam works best.
Kerry
11-24-2014, 05:58 AM
#4
Heads are AI 232cc 243 heads on a stock LQ9 shortblock (flat tops).
DCR from Wallace Racing's calculator says that puts me at 8.98 DCR at sea level, and 8.78 DCR at 1000 ft where I live. It will be using a tuned stock computer with knock sensors, not an aftermarket setup or carb.
DCR from Wallace Racing's calculator says that puts me at 8.98 DCR at sea level, and 8.78 DCR at 1000 ft where I live. It will be using a tuned stock computer with knock sensors, not an aftermarket setup or carb.
93 Octane & then pay close attention to timing chart(s) tune in PCM. Knock usually occurs @ max tq RPM & during last 1000 RPM up top. Additionally, stay away from 5th 6th gear hard pulls from low RPM. In other words log the engine knock & adjust timing tables accordingly.
Stock computer has mountains of timing settings based on several operating conditions. It's far more sophisticated than an MSD timing curve. So, it's capable of pinpointing optimum timing as needed whether it be higher or lower.
11-24-2014, 10:32 AM
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Staging Lane
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93 Octane & then pay close attention to timing chart(s) tune in PCM. Knock usually occurs @ max tq RPM & during last 1000 RPM up top. Additionally, stay away from 5th 6th gear hard pulls from low RPM. In other words log the engine knock & adjust timing tables accordingly.
Stock computer has mountains of timing settings based on several operating conditions. It's far more sophisticated than an MSD timing curve. So, it's capable of pinpointing optimum timing as needed whether it be higher or lower.
Stock computer has mountains of timing settings based on several operating conditions. It's far more sophisticated than an MSD timing curve. So, it's capable of pinpointing optimum timing as needed whether it be higher or lower.
11-24-2014, 11:34 AM
#6
Good info, thanks. I'm trying to determine if I should drop SCR instead of "crutching" with less-than-optimum timing. On the one hand, I can keep it at 11.35:1, drop timing where I need, and have the teeny benefits of 11.35:1 everywhere else in the curve. On the other hand, if I drop it with a thicker head gasket, I don't have to worry as much and its really not going to make much difference.
Don't. Your SCR is fine. It's the DCR that may need timing adjustments. Regardless of either, timing settings vary NORMALLY within the tune based on engine load.
I don't want to say that for sure the DCR will cause a need for some reduced timing because w/ new cams/heads, it's not always the case. However, with our cam we had to retard the cam 4 degrees to get the DCR down to 8.6. Above 8.6 we had engine knock @ high RPM & near max torque. SCR is 12:1. Anyway, we can only generally predict what may happen w/ yours for the reasons noted. Just be sure to pay attention to knock sensors while tuning. For sure, run on 93 Octane, though.
