Lots of people have predators now. Some people have wideband AFR gauges. A handful of people actually know how to tune an engine. Most of us have an idea of what the common terms are like AFR, timing, knock/detonation, knock retard but really don't know how they interact. Some people are tweaking things without a clue, some are tweaking things with only half a clue. Some people opt to have someone else completely do it for them. I think most would like some basic understanding of the fundamentals specific to our engines (that would be me). I think EVERYBODY could benefit from what I have in mind here. The clueless will be less likely to disappoint themselves and the people in the know will spend a lot less effort in the long run explaining things (I think a lot of times they would/want to help but don't get involved 'cause it would be painful starting from scratch). Even the people who have someone else do it for them would like/benefit from some understanding of how and what. First the disclaimer: If you want SAFE, stay stock. You CAN use a Predator to break your engine. It's always best not to change things "just to see what happens". Now frame of context: I'm hoping it won't turn into strictly a bunch of specifics like "I want you to tell me exactly what to do for MY motor, tell me exactly how and what to log/try and tell me exactly what to change to what to tune it." (except for me since I think I have the perfect generic case. haha). I'm assuming you guys with the major mods and n2o know what you're doing. So maybe it should be focused on the masses with CAI and cat back. Nice topics could be something like what's the general relationship with afr and timing (I'll start the first post with that one). Do you want the afr flat across the whole rpm range? How about timing? etc. Thoughts?
A/F ratio should be flat across the power band. The timing should be adjusted accordingly to what the Dyno graph shows (best way to tune any engine). There should be NO dips, hills, valleys, loops, whatever in your powercurve. These can be corrected by fine tuning the timing and A/F and other stuff I am not familiar with. lol Great topic, just not sure why you have it in the Supercharger forum?
AFR and Timing? What's the general procedure? Seems that you want to shoot for an AFR between 12 and 13 at WOT. I guess the idea is to get as lean as possible with as much spark advance as possible while still avoiding detonation? For our motors some say afr at the bottom around 12.0 and others say towards the top at 12.8. Surely timing is closely related. In general, would you first fix the afr at some value and then adjust timing? Then maybe check for power and repeat at a different afr? What spark advance would you think typical for a particular afr? Say 12.2:1 and 12.8:1 for examples?
How the hell did this end up in the supercharger forum? Must be a bug in Main's transition to V2.0... I thought it was in the SRT-8 LX Discussion forum. You can move it right? (haha, guess it got your attention right away)
The best tools to tune with are only part of the CMR. For example, adjusting your VE (volumetric) tables will correct your closed loop long-term fuel trims so they're almost 0. Setting VE table also also influences open loop AFR (indirectly by influencing closed loop operation). So its one of the best ways to flatten out your fuel curves. Here are some basics about tuning, its not specific to Diablo or HEMIs but the concepts and terms are the same: http://www.lt1howto.com/articles/pcmtuning.htm
Excellent. That will clear it up for those who aren't familiar with the terms or basic relationships. He's saying 12.8:1 to 13.1:1 is ideal for WOT (shoot for 12.8:1 on a dyno because real world loads at the track will tend to lean it out just a bit). Can we assume this number applies to our Hemis like it does to the LS1s? or close enough? Let's get just a bit more specific. I'm currently fooling with my car (on the road, without a dyno). I figured I wanted to tune towards optimum but stay on the conservative side. I started with the CAI 91oct r20 Predator tune and made fuel adjustments until I got a flat 12.7:1 AFR through all 3 rpm ranges. Oddly, I was seeing a 0.5 to 0.7 spike in AFR in the transition range between the first and second rpm ranges -- about 3800 to just over 4000. Diablo fixed that for me by smoothing the VE table there since the handheld won't let you adjust there. It was 12.7:1 until it crossed that range where it would climb to maybe 13.5:1 or so and back down again. Just over 4000 it was a flat 12.7:1 again. I'm assuming that was done with adjustments to the PE table? I was seeing a pretty constant knock retard of up to 5.5* or so. Usually below that averaging about 2.5* to 3*. I figured it was time to add fuel or pull timing to see if I could get rid of that. I know the stock tune will give spikes of around 4.5* KnR right around shift points or lugging the engine and zero the rest of the time. I was looking to get to something similar. So I took that tune and adjusted for 12.2:1 AFR through the rpm ranges. The KnR was less but only slightly so and pretty much always there instead of spikes only around the shifts. I figured it was time to start pulling timing. By the way, it seemed it wanted to be around 20* or 21* but was being pulled down to around 15*? Generally speaking, with a WOT AFR of 12.7:1 what would you expect the typical spark advance to be? I started pulling 1* or 2* until I was at -5*, -5*, -7* in the three rpm ranges respectively. This got me to only a couple of "bumps" of KnR (not at the shift points but I'll get to that). Is that a HUGE amount of timing to pull? Or does it just depend on the power produced? Seems that without the KnR, spark advance is still around 15* to 18*... So now I still have a couple of "bumps" of KnR up to 2* and 1.5*. Happens at about 4600 to maybe 4900 rpm and then again at 5250 to maybe 5350. It spikes and then trails off to zero both times. Slightly shifted each run but 2 distinct spikes. This only happens in 3rd gear. 1st and 2nd are zero all the way through.
It's not a CMR tune. You wanted to compare the handheld to the B&G right? I can set it to stock if you want. Still run you. Your car sits too low. Probably wastes a lot of power being pulled down onto the road where I'll be floating like a butterfly and stinging like a bee.
A/F affects the timing the engine will take before knock starts. Timing will affect your A/F. VE affects both. easy right. LOL a/f, ve, timing are inter related to power out put. Duh,, right? I'll ramble for a bit and hopefullly it makes sence to everyone These modern Hemi's tend to like 12.2-12.6 for best power. Old school engines, hemi's included make there best n/a power from 12.7-13.2. With every change in VE, (cai,cam,p heads) the perfect A/F will change slightly. For example Say you start a dyno pull with 12.0 a/f across the board. Then you advance the timing 1* for a test. Your a/f will lean out because of the timing change. If you did the opposite and retarded your timing the engine would run richer. Depending on your specific combination, you may make or lose power because of the change. If you get NO change. You have complete burn of the charge. So,,, add more fuel. Test again. When you go to the dyno, look at the AVERAGE #'s across the board first. Worry about peak latter. Bring the average up and the peak will take care of itself. Fuel demand will be highest at peak tq(peak ve) timing will also be at it's lowest of the wot table. you will be able to bring in more timing after peak tq. that will give you peak hp. How well the tq curve carries up in rpm will depend on your heads and cam. If tq carries, hp will follow. hp is tq x rpm/5252 Another thing to note. Knock retard needs to be logged in the lower gears first. To avoid heavy knock in higher load 4th. For you high mph guys. Best to dyno on a load bearing dyno. Mustang dyno's dont give bragging #'s but your tune will be spot on.
So I had 12.2 a/f across the board. With Knock. I gradually pulled 5* to 7* of timing. Most all the knock is gone and I'm still running 12.2 a/f across the board. That would indicate that maybe I should add fuel (to where I can increase timing)? If our hemis typically like 12.2-12.6, what is the typical timing seen at that a/f?
What's the earliest version that allows you to log your runs....18? What is the procedure to log a run? SDCarguy and I did it starting in second at low rpms and went WOT through second. Great thread BTW Dave!
N/A you should be able to get 20-24 at peak tq. 24-26 peak hp. Your mods will affect this of course. (I don't know what you have).
i am pretty sure 17 will data log...... although i have not really ever tried, i would love to know the EXACT process to get info from the pred...... anyone????
Wanted to sort of keep the thread where the huge majority of us are. Stock motor with CAI and cat back only. Adding cams and heads in the mix is going to be way too many variables for now. Just curious. What advance gets you close to TDC?
It's something like plug it into the car, start the motor, diagnostics -> watch and log -> select pids -> watch and log... something like that. Then you see them on the hand held. Then you hit escape to stop, then you can replay (pause, back, forward with arrow keys), then you can hook it up to the PC later to download and see in a graph with the DataViewer. I'd like to keep these kind of operational details for another thread maybe? to maintain the signal to noise ratio.
Not sure what you mean "close to tdc" affective WORK is over by 30* ATDC. So the window is small. These hemi engines have a very efficient chamber.
(CAI, cat back, engine temp about 187*) First off. I adjusted fuel to get WOT 12.2 AFR across the rpm range. Then pulled 5* low/mid rpm and 7* high rpm to get rid of most of it. Is that a huge amount of timing to pull? generally speaking. With the knock retard I was seeing mostly 15* to 18* advance on up to 21* (kind of followed the rpm curve). After pulling 5*-7* I'm not seeing hardly any knock (basically zero except for 2 bumps in the middle of 3rd gear) but I'm still seeing 15* to 18* advance. Maybe that's why I didn't see any change in AFR? Basically the spark is the same? It looks like this. First graph is with the knock. Second graph is with 5* and 7* pulled.
