Swapped to a smaller cam - one question
Thread Starter
Joined: Aug 2004
Posts: 11,258
Likes: 146
From: Pace, FL
Swapped to a smaller cam - one question I went from a 234/242 111 cam to a 227/244 115... so smaller in terms of overlap. I used my base tune from the larger cam and used stock 02 Z06 VE table to start tuning from (and idle spark from 28 to 20). I also lowered the RPM from 950 to 800.
It thumps like the bigger cam, but it's running rich. I can smell it. And reading the narrowbands they are pegged at 900mV. I leaned out the big cam to get the narrowband down as close to 0 as I could. Is that the same strategy with the smaller cam or try to get it around stoich and switching? I'm hoping it idles at stoich much better than the bigger cam making CL possibly without dips or slight hiccups. But I just was wondering what I should be aiming for? Smaller cam seems to be much less fickle...
One other thing; it is reading 80kPa at 800rpm (rich with low timing) vs the 68kPa in the bigger cam at 950 with a lot of spark and very lean. I'll set to 950 and it should be around 50-55kPa there... So not concerned as I'm using pretty much stock values for air and spark. But it thumps harder because of that kPa reading which I thought was interesting.
It thumps like the bigger cam, but it's running rich. I can smell it. And reading the narrowbands they are pegged at 900mV. I leaned out the big cam to get the narrowband down as close to 0 as I could. Is that the same strategy with the smaller cam or try to get it around stoich and switching? I'm hoping it idles at stoich much better than the bigger cam making CL possibly without dips or slight hiccups. But I just was wondering what I should be aiming for? Smaller cam seems to be much less fickle...
One other thing; it is reading 80kPa at 800rpm (rich with low timing) vs the 68kPa in the bigger cam at 950 with a lot of spark and very lean. I'll set to 950 and it should be around 50-55kPa there... So not concerned as I'm using pretty much stock values for air and spark. But it thumps harder because of that kPa reading which I thought was interesting.
My gut feeling is that the new cam will want to idle around 300mV. You might want to just pick a switch point like that and put it in closed loop. Then after it trims itself, just multiply the entire 800 and 1200 column by whatever the fuel trim tells you. Rinse and repeat a few times.
Honestly, your bigger cam might be a closer starting point. I think the 900mV readings are telling you the strategy for the new cam will
Mirror the older cam.
I would think it would idle around 55 to 60 kpa when you get it dialed in. It might still like 25 degrees idle timing.
Honestly, your bigger cam might be a closer starting point. I think the 900mV readings are telling you the strategy for the new cam will
Mirror the older cam.
I would think it would idle around 55 to 60 kpa when you get it dialed in. It might still like 25 degrees idle timing.
Thread Starter
Joined: Aug 2004
Posts: 11,258
Likes: 146
From: Pace, FL
That's what I'm going to play with. I will lean it out and add timing.
I need to get the air bubbles out of the coolant first. Still had a bit yesterday which limited how much time I could spend on it since the temp creeped up to 220. Hopefully today I can go out and work on the idle and **** off the HoA.
I need to get the air bubbles out of the coolant first. Still had a bit yesterday which limited how much time I could spend on it since the temp creeped up to 220. Hopefully today I can go out and work on the idle and **** off the HoA.
I agree with Darth...I think your tune for the big cam would be a better starting point then the stock zo6 tune. You still have 5-6 degrees of overlap so it will still want to run leaner at idle and I bet 23-25 degrees of timing. At least mind does and I have 5 degrees overlap. Mine also idles best at 850, any lower and it overshoots idle and hunts a little.
Thread Starter
Joined: Aug 2004
Posts: 11,258
Likes: 146
From: Pace, FL
It sounds just as good as the bigger cam at idle even running rich with low timing... But I'll definitely lean it out. Hope to drive it tomorrow and dial in the cruising A/F. But that will tell me a lot about the idle on how it returns to idle coming to a stop and low speed parking lot driving.
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