Need a starting point for revised BLM boundaries
 

I'd like to tune out the little bit of cam surge I have. The grind is 220I/226E/112+6/.544/.544(via 1.6 RR). The heads are 2.0/1.57 265/195 cfm w/185cc chambers. 355 w/longtubes. 6 PSI blower with Paxton bypass valve. If anyone has a similar combination ....what did you change the values to in the BLM matrix?

I hate to ask without searching but I have a miserable internet connection.

Re: Need a starting point for revised BLM boundaries
 

Are you sure its not blower surge?

Re: Need a starting point for revised BLM boundaries
 

Never had it before the cam and heads back when the blower was on a stock motor. It is only at light (very light) throttle when cruising in low gears (extrememly light load) which is very typical of cam surge from what I understand. Also, my blower is only 6 PSI and has a bypass valve.

Re: Need a starting point for revised BLM boundaries
 

Is this something people rarely try?

Re: Need a starting point for revised BLM boundaries
 

I'm wanting to think that most people get around cam surge with timing changes, rather than BLM boundry changes, but I'm not 100% sure on that since I don't have a cam.

Wish I could help more.

Re: Need a starting point for revised BLM boundaries
 

You really dont need to change the BLMs unless you are say bouncing between cells at idle or at least when you are seeing this cam surge. Otherwise Id say add a couple degrees of timing in the RPM/KPA range you are feeling the surge... and/or try adding a little fuel in that area via the MAF table.

Re: Need a starting point for revised BLM boundaries
 

OK, I'll see if it's bouncing between cells first. If not I guess I just need to add some fuel or timing. Thanks for the tip.

Re: Need a starting point for revised BLM boundaries
 

Changing the BLM boundries isnt a bad idea IMO, although i never have tuned a blower car.

I know on my 383 i was hitting like 3 or 4 cells in the 1000s of times, and some other cells werent getting used at all. I just kinda roughly guessed at where i could split it so that it evened itself out, making sure your idle has a decent map range to play with.

End result was better gas mileage, and better throttle response. Almost all the cells get used fairly evenly now.

Re: Need a starting point for revised BLM boundaries
 

Yup did the same, like some of the cells are only to be used with very low MAP readings which the stock cam gets but biggers cams never hang around there, so I just upped some of the cell boundries and now use many cells and yes also better gas milage.

Re: Need a starting point for revised BLM boundaries
 

How do you up the cell boundries? I have Tunercat and it just has full graphs and such, no cell ID for which is where.

Re: Need a starting point for revised BLM boundaries
 

BLM RPM boundaries, and BLM map boundaries. So you can adjust the rpms and map boundaries.

Example: Cell 12 in stock form is 0-900 rpms and 80-100 map.
Cell 5 in stock is 900-1200 rpm and 30-50 map

The boundary lines are like this
[CODE]
RPM..................900.....1200.....2000

.................12...|...13...|...14...|...15

MAP=80----------------|--------|--------|--------

.................08...|...09...|...10...|...11

MAP=50----------------|--------|--------|--------

.................04...|...05...|...06...|...07

MAP=30----------------|--------|--------|--------

.................00...|...01...|...02...|...03
[/CODE]
(via freds page)

Re: Need a starting point for revised BLM boundaries
 

Ahh It seems so simple now..lol . Thanks for the explanation.

Re: Need a starting point for revised BLM boundaries
 

No problem, pictures are worth 1001 words :)

Re: Need a starting point for revised BLM boundaries
 

In the RPM chart for the first feild, I changed it to 900 from 700 and the car immediatly responded with better idle. I was running short term BLMs of 118 to 108 and the LT was setting about 112, after flashing they hang around 120 and the LT is up to 115 Still a little work to be done but at least now they are in the right cell.

Re: Need a starting point for revised BLM boundaries
 

This is good information but I need a little more detail to understand how it works. Anyone have a suggestion as to where I should start? If I'm halfway understanding it right it seems like a bigger cam that has higher MAP while cruising/idling would need roughly the same RPM boundaries but slightly higher MAP boundaries (example: perhaps a cam like mine wouldn't bother looking in the bottom cells of a stock matrix due to never getting to a MAP reading of less than 30). Am I somewhat on par? Why did it help to change the first one from 900 to 700 ....so it would integrate fuel at a higher MAP relative to RPM? Also, what about the "Min MAP for BLM update" of 20 ..should that be altered? Thanks

The grind is 220I/226E/112+6/.544/.544(via 1.6 RR). The heads are 2.0/1.57 265/195 cfm w/185cc chambers. 355 w/longtubes. 6 PSI blower with Paxton bypass valve.