Best A/F ratio and timing for low rpm cruse with big cam and CI engines
#23
Here's my combo:
372ci small block
13.5:1 compression
268/274@.050 108 ls solid roller
AED 950 Holley
1,400rpm idle
7.5" vacuum
26 degrees initial timing with custom 10 degree advance stop bushing
14.4-14.7:1 idle afr
12.0-12.5:1 cruise afr might go to 13:1 under very light load)
11.5:1 WOT afr
That is with stock AED air bleed calibration and drives pretty nice for an 8,000rpm race engine. I'd like it to be a bit leaner under load.
372ci small block
13.5:1 compression
268/274@.050 108 ls solid roller
AED 950 Holley
1,400rpm idle
7.5" vacuum
26 degrees initial timing with custom 10 degree advance stop bushing
14.4-14.7:1 idle afr
12.0-12.5:1 cruise afr might go to 13:1 under very light load)
11.5:1 WOT afr
That is with stock AED air bleed calibration and drives pretty nice for an 8,000rpm race engine. I'd like it to be a bit leaner under load.
Last edited by Neil B; 04-07-2016 at 04:06 PM.
#24
Team Owner
If anything highly atomized fuel droplets like out of a 8 port injection system would require even less timing that it's carburated counterpart
#25
Race Director
Higher compression atomizes fuel better. atomized fuel burns faster. Combine that with modern fastburn heads like in Paul's case AFR 227 cc with small mid 60 cc chambers and being Heart shaped are not a good comparison to BBC large chambers.
If anything highly atomized fuel droplets like out of a 8 port injection system would require even less timing that it's carburated counterpart
If anything highly atomized fuel droplets like out of a 8 port injection system would require even less timing that it's carburated counterpart
#26
Team Owner
I had a laptop hooked up and the timing numbers are just a blur. So your 40 degrees might have been for only one cylinder and then ping and it dropped right back down. I have never seen a constant advance number on distributor less ignitions.
As for me I have rebuilt enough HP motors and looked at the bearings to know that stupidly fast advance curves just hammer the barrings.
I'm also not a fan of aftermarket FI systems. My friends find these super dynotune places and they cost about $600 for 4 hours of tune time to get their aftermarket systems running the best possible. They don't have 100's of millions of dollars to perfect them like the car manufacturers have.
Last edited by gkull; 04-08-2016 at 06:20 PM.
#27
Race Director
Also, pre-ignition is different from pinging and will destroy an engine in seconds.
OP wanted to know how to optimize low speed drivability. Lots of timing advance is the answer. Even if he goes too far, some pinging at low load isn't going to hurt anything.
#28
Tech Contributor
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I don't really feel like arguing, but I've never seen an OEM system intentionally running timing into ping. They have a timing table set for the octane the engine is speced for. If it senses pinging it does a pretty big retard, then slowly advances back to zero retard unless it senses more pinging.
Also, pre-ignition is different from pinging and will destroy an engine in seconds.
OP wanted to know how to optimize low speed drivability. Lots of timing advance is the answer. Even if he goes too far, some pinging at low load isn't going to hurt anything.
Also, pre-ignition is different from pinging and will destroy an engine in seconds.
OP wanted to know how to optimize low speed drivability. Lots of timing advance is the answer. Even if he goes too far, some pinging at low load isn't going to hurt anything.
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zwede (04-08-2016)