cam selection and total timing advance
Thread Starter
Melting Slicks
Joined: Oct 2002
Posts: 3,193
Likes: 1
From: Cincinnati Oh
cam selection and total timing advance
How much can / does a camshaft effect *total* timing under WOT conditions?
This is probably a pretty stupid question, but I've always had the understanding that (on a SBC at least) you pretty much always shoot for around 30 - 32 degrees maximum spark advace under WOT.
I've always assumed that the 32* max timing comes into play at redline, or around 5500 RPM's, and this mimics what the stock L98 curves look like - but my particular combination doesn't want more than 20* or so!
My spark curve is 32* at lower RPMs and load conditions, but the most I can get without knock is ~20* from 4K on up. What's the deal? Can it be camshaft (LOTS of torque compared to HP) or does it just need way more fuel? O2 sensor is ~920mv and other factors like plug gap, base timing, etc are correct. The plugs are even 1 range cooler than stock. this is a superrammed 383ci with a ~224* I/E cam.
Any suggestions?
This is probably a pretty stupid question, but I've always had the understanding that (on a SBC at least) you pretty much always shoot for around 30 - 32 degrees maximum spark advace under WOT.
I've always assumed that the 32* max timing comes into play at redline, or around 5500 RPM's, and this mimics what the stock L98 curves look like - but my particular combination doesn't want more than 20* or so!
My spark curve is 32* at lower RPMs and load conditions, but the most I can get without knock is ~20* from 4K on up. What's the deal? Can it be camshaft (LOTS of torque compared to HP) or does it just need way more fuel? O2 sensor is ~920mv and other factors like plug gap, base timing, etc are correct. The plugs are even 1 range cooler than stock. this is a superrammed 383ci with a ~224* I/E cam.
Any suggestions?
Race Director
Joined: May 2001
Posts: 14,165
Likes: 9
It could need more fuel, who knows. Without a wide band O2 reading you're really just guessing. That 920 mv could mean 13:1, it could mean 11:1, they are not at all accurate for tuning and they don't need to be. They are only acurate at 14.7:1 where they should put out 500 mv. Other than that absolutely all bets are off.
Get the car on a dyno with a wide band O2 sensor and data log the run, then you can start playing with stuff and making educated changes.
I wouldn't worry about total timing too much. As long as the engine makes good power it doesn't really matter does it?
Get the car on a dyno with a wide band O2 sensor and data log the run, then you can start playing with stuff and making educated changes.
I wouldn't worry about total timing too much. As long as the engine makes good power it doesn't really matter does it?
