Buick 455 idle
I have a rebuilt Buick 462 (+30 over 455) with a high duration Stage 2 cam that I'm struggling to get a good idle in gear. I recently upgraded to the T198i software and it seems a little better than the T195o that I was originally working with. My vacuum is terrible, but I can't find any leaks with the starting fluid, and I've been told that's what to expect with a high duration cam. Trying to idle it at 850-900 rpm, seems to be happier at 1000rpm. Startup hot and cold seem to be fine now, I'm running the fuel command center with a setting of 40, its vented back to the tank with the factory vent lines (car is an 85 Buick Regal). I have noticed the tank builds pressure.
Here are the cam specs:
225 intake, 253 exhaust @ .050", 340/360 adv duration
.453" intake, .480" exhaust
Lobe Center 108 intake, 122 exhaust
I'm using HEI timing with a distributor that was recurved by TA Performance (Buick specialists), initial timing is about 13 degrees at idle. Throttle response feels pretty good and the motor feels very strong. I'm wondering if my cam is just too much to get a decent idle for street use. Cam profile selected was #3, #4 may have been a little better but it seemed like it was trying to throw a lot more fuel at it to hold AFR at idle than #3 was. Here are the logs, first one is a #3 profile, they are idle with a throttle blip. Any tuning suggestions?
https://www.dropbox.com/s/poek5lqz9yow0k5/Cam%233_setting.csv?dl=0
https://www.dropbox.com/s/dk90kahircfpj7l/Cam%234%20setting.csv?dl=0
The 2nd log looks a lot better. What did you change there?
My suggestion is cam 4 and raise your idle AFR to 14.5. Low vacuum idle will load the engine up. Need to lean out the mixture. I know guys with cam 4 running 15.5 afr at idle.
Idle AFR is just like setting idle mixture screws on carbs. Lean out to best vacuum and idle quality. Pull plugs and read.
I tried raising the AFR to 14 and the idle speed tonight, may have helped a little but it still not great in gear (still in cam #3 profile). Also adjusted the IAC screw to try to get it to 5-6 range when it settled in. Interesting it thinks the timing needs to go to -25 when its doing this. Should I be suspect of noise coming through the tach wire?
https://www.dropbox.com/s/jvy7h2m4pc0z4vz/DashBoard3.csv?dl=0
Go to cam 4 and AFR to 14.5. Don't worry about IAC until you get the idle surge cleared up. It is loading up. It is trying to pull all the fuel it can. Cam 3 is not correct for this application.
Should I do a reset learn when going to Cam 4?
Here are some logs from this morning, I just tried the reset all and restarted it. Cam setting #4, I varied the idle AFR and idle speed a little in each. Seems a little more stable, should I try bringing the IAC in?
https://www.dropbox.com/s/eynedrsmpqp9hyl/DashBoard4.csv?dl=0
https://www.dropbox.com/s/omipe7e0vq1e0xe/DashBoard5.csv?dl=0
https://www.dropbox.com/s/7lytv5mm4ezsrke/DashBoard6.csv?dl=0
These logs are looking a lot better. Looks like idle RPM set around 1000 is going to be about as low as it will be with this build. When this radical, IAC steps will work better between 15-25. I would want to see a more stable idle. Work with your AFR, check your plugs.
Making progress!!!!!
I haven't had a chance to mess with it since last weekend, but I had the idle AFR up to 14.9 and it might be a little better. Should I consider letting the FiTech control timing to help smooth the idle out? I keep seeing the suggestion to throw more timing at it to smooth out the idle on a big cam, but that leads to other issues. Wasn't sure if the FiTech could do a better job of timing control than the recurved distributor, where it could throw more timing at idle and correct as the motor revs. Looks like I would need a MSD 6AL box as well for my HEI.
On the flip side, my friend said its impressive I was able to get any kind of decent idle quality with this Stage 2 cam. Still trying to figure out what guys were getting for vacuum and timing when these motors were popular, long before EFI!
I have a meanstreet 800 on my punched out 454 small block with monster cam 268/284 duration @ .05 and valve lift of 0.766/0.792 and it likes 30 deg initial timing with my HEI distributor that I'm not using timing control on, but I don't need it, nor is it provided on the meanstreet. Once I found the exhaust leak around my O2 sensor, it likes 14.5 AFR at idle -- plugs look great. I have just 10:1 compression and run cam 4. It likes to idle at 1050. Oh, and it has just 5 in Hg vacuum at idle.
Idling pretty nice now that I know to keep the battery charged. Fitech EFI can be a little picky on that, but once you dope it out it runs pretty good. 😀
Posted by Brandt Hulderman on Friday, April 19, 2019