Rescaling RPM points in timing tables - SRT Forums

phubarr · 03-20-2009, 01:40 AM

I'm starting to get my hands dirty with my PRP using the 05 S2 850AA code, and I'm looking at the timing tables and seeing some questionable things. I'm seriously considering rescaling the RPM points instead of working with the factory ones. I mean the factory gave us just 17 points on the table, so does it really seem appropriate that 7 of them (40%) are below 2080 RPM? Unless I'm missing something, I think we can do a lot better with a little rescaling.

Has anyone else done this and had good results? Or at least tried it and learned something? I'm just looking for any input before I start taking blind stabs at making my own tables...

julius717 · 03-20-2009, 11:05 AM

im not a master or nothing but its probably because most of your driving is usually below that stop and go and starting up. up top your usually at WOT so the points can be farther appart. since most people usually dont shift above 3000 for normal driving. just my opinion

SRT-What? · 03-20-2009, 12:15 PM

^^^^
he's probably talking about WOT spark... it make some sense... never actually tought about it, I was more concerned about the pressure values.

**SkullingAxe** · 03-20-2009, 11:48 PM

I never really thought about it as well.

I could see it being beneficial to rescale the rpm band as well. You could get a more stable timing curve throughout your wot rpms... however... your probably going to loose some drivability down low.

Rescaling the rpms along with the pressure readings would be something that will take a long time to get right but i could see if being very beneficial in spark control. I say give it a shot and post up results. I might do it as well once i get some more free time.

Bryan

phubarr · 03-22-2009, 10:40 PM

Quote: Originally Posted by SRT-What?

^^^^
he's probably talking about WOT spark... it make some sense... never actually tought about it, I was more concerned about the pressure values.

I was actually referring to both tables, mostly WOT but part throttle too... I mean I don't really spend much time below 2000 rpm, I probably engage my clutch at 1500-1750 rpm and work my way up. I can see having one interval point at idle, and putting another one every additional 400 rpm to give you even scaling up to 7200 rpm. It's just that having 7 below ~2000 seems like a waste, and I was looking for other opinions.

phubarr · 03-22-2009, 10:48 PM

Quote: Originally Posted by SkullingAxe

I never really thought about it as well.
Rescaling the rpms along with the pressure readings would be something that will take a long time to get right but i could see if being very beneficial in spark control. I say give it a shot and post up results. I might do it as well once i get some more free time.

Bryan

I'm interested in your statement... but I don't fully understand why rescaling along with the pressure readings would be that beneficial? I figure it doesn't matter too much if there's a slight error in the sensor's reading of the actual pressure, because as long as the spark timing is appropriate for the vacuum/pressure conditions, it doesn't matter if the label of the reading is slightly inaccurate.

**SkullingAxe** · 03-26-2009, 09:54 PM

Quote: Originally Posted by phubarr

I'm interested in your statement... but I don't fully understand why rescaling along with the pressure readings would be that beneficial? I figure it doesn't matter too much if there's a slight error in the sensor's reading of the actual pressure, because as long as the spark timing is appropriate for the vacuum/pressure conditions, it doesn't matter if the label of the reading is slightly inaccurate.

Well, its all about spark control IMO.

Having a more refined scaling of rpms and pressure during the points your motor is normally in when at WOT will allow you to control your spark a lot better. Right now the PCM Essentially models everything as RPMs increase between the points on the Spark table. By having more refined points the PCM doesn't have to model as much during the points.

Example:

You building your car for ALL OUT DRAG, you engine RPMs are usually within 4k and redline(assuming stock to stage 2 or 3 redline) You rescale your RPMS section for greater control in that area. AKA if you want to see less timing at this RPM point you pull it out rather than adjusting 2 points and hope the PCM models it for you. However, rescaling for greater control on the top end will probably affect your daily driving ability, when your more in the low to mid range.

Rescaling for pressure will allow you more spark control for the boost pressure you run. On the stage two graph the scaling jumps from 225kpa IIRC to 300 kpa That means for any pressure point in between those two points the PCM has to model. If you rescale it for greater clarity between those two points you take a lot of guess work out and could maximize your timing with less chance of knock during a certain RPM point.

The steadier your timing curve the better your ability to build power.

Now keep in mind this is my opinion and logic which is open for debate. I haven't fully tested it yet myself as I'm working on my VE table right now and not really tuning for wot yet. It will be A LOT of work but I could see some benefits of doing it. If anything to help prevent KR from the PCM over modeling between points.

Bryan