I'm fairly new to tuning, having played around for the last 2 or 3 months burning chips and trying to learn some of the inter-relationships different changes make. I'd like to start with a fresh ARAP bin (6E, '165) now that I'm more comfortable with what I'm doing; but I'd like to resolve a MAF question before I start getting into it.

Am I right in assuming stock calibration points are optimized for a 350 CID motor but would need tweaking for larger cubic inches because of the increased airflow? And if so, does the difference more or less follow a linear pattern to some degree? The motor I'm dealing with is substantially larger (421 CID) and I'd like to start this new tune on some fairly solid ground.

Thanks!

 

You will max out the read range on the MAF somewhere in the mid 4000 rpm range depending on how hot that 421 will be. Based on that, I'd only change MAF table 1 to dial in your IDLE air fuel mixture, and leave the rest alone. Well, take that back. Use table 2 and maybe some of table 3 to dial in part throttle air fuel mixture.

Change the maximum airflow vs rpm table as well. For certain rpms the ecm is limited to the MAF flow it can read. From around 3600 rpms on up, make them all 255 grams/sec. For rpms below 3600, add 15% or so.

Other than that, really not much else to really do. To tune WOT you just really need PE % enrichment vs RPM

For my 383 I only changed table 1 and 2 alittle, and then left everything else the same from AUJL. Ran great. WOT i realllly needed to adjust PE mode enrichment vs rpm.

really need a wideband o2 sensor to properly tune this.

 

Thanks very much for the info, this gives me a fighting chance at working out a decent tune! FYI, the motor isn't very wild at all, but more of a smog legal torque build (SR, LPE 219 & old style CnC AFR 195s). On my only previous dyno session it maxed torque at 3150 RPMs and ran out of HP at about 4900 +/- so it's definately tractorish.

I think it would be prudent to keep an eye on my knock counts as I move forward because of the ARAP timing curves, right?

Thanks again!

 

You will be moving ALOT of air at peak torque with that motor. May have a chance to max out the MAF sooner. No problem tho, still have source for fueling WOT.

Thats a good torquey combination. ARAP is a good place to start, but definately back off on the timing for now. Being an older style AFR head, it may need more timing to make max power as compared to the eliminators but that is something you will need to work out. Same applies for cruise, it may beable to take more timing at cruise compared to the efficient Eliminator heads but the old AFR 195's are not a bad head at all. I've seen them work very well, and they respond well to port work.

Definately watch spark retard while driving it. If the air fuel is drastically off, you may see timing being pulled. I'd work air fuel ratio back to ideal and check to see if the timing is still being pulled, then change timing if needed.


Problem you may have and I'm not 100% sure on this is knock sensor's ability to read correctly on a large 400 bore. I have noticed on my turbo motor that during cruise, it wil pull timing at only 35-36 deg of part throttle timing. I did not think thats alot of timing for low loads and such a low compression motor at low rpms.

305's have small bore and a knock sensor for that bore. 350's have a knock sensor specific for that 4" bore. I run a 350 knock sensor on a 4.125" bore and my timing seems conservative compared to what other guys have run, even in boost. There are different harmonics and such in a motor with different bore sizes so its possible its picking up false knock. I'd be curious to see what others have been seeing.

 

Thanks Orr, it's amazing to see you and all the other guys like you help so much..........what a great site this is! I agree about the dangers of detonation, even though I'm pretty new to tuning I've been looking at plugs since the 60s. It's curious I get very few knock counts though, and the plugs have looked good since the motor has been together.........my current bin has some pretty conservative timing & I'm sure that's why. Very conservative timing actually.

I'm excited now.......I can't wait to get some time to myself this weekend & see what happens!

Thanks again, this gives me a great basis to work from!

 

Well then your set This will be more of a help than any of the datalog parameters. YOu can watch the narrow band o2 sensor milivolts for WOT but check the plugs if you can. Usually I see around 900 milivolts as around optimal 12.5-13.0 air fuel. Just make a WOT pass and then shut off to check the plugs. Compare what you see to what the NB was showing and that will give you an idea where your at.