I hate acronyms. I have heard that as well along with minimum base timing. Just wanted to make sure. At least I assumed correctly what you were referring too after looking at my timing maps.

 

Base timing is different - this is the amount of "timing offset" that the ecu uses when it starts counting (ring gear) teeth. So, the pins on the flywheel dictate this offset and trigger a starting point for calculating engine position. If memory serves, the factory offset is around -47 degrees BTDC (before top dead center). This also marks the maximum amount of timing advance you can apply to your timing map.

 

I kind of like this one:

Minimum (advance) for Best Torque

Is it true that that you will achieve the best or peak torque if you adjust your timing advance so you create peak cylinder pressures at approximately 15 degrees ATDC(After Top Dead Center)?

 

If anybody else is interested, found this thread and the information is quite good:


http://www.eng-tips.com/viewthread.cfm?qid=251159

It is a bit lengthy and in depth though.

 

MBT is one of those TLA's that seems to have a few different definitions. Like you said, I prefer Minimum (advance) for Best Torque aka the lowest timing that produces the best power. If a tuner adds more timing on top of MBT the stress level goes way up while power starts to drop. Since I'm running E85 I might not get any knock until timing is advanced way beyond MBT, so I have to tune on a dyno and do timing sweeps to find MBT. I started doing a timing sweep at 14psi on the dyno last Sunday, I added 1.4 degrees per run on 3 back to back runs and it gained around 10HP each time. Then I ran out of time.

Yes I realize my timing is very safe right now. I wasn't exactly sure if the new engine would like more or less timing. I'll keep it there until the next oil change. Right now I have cheap 10W-40 in the engine for break-in. Once I have enough miles and some good 20W-50 I'll start ramping up the timing to find the limit.

 

Dave, are you logging knock off the stock sensor, or do you have a real time display? I tuned my car myself and and ready now to do a final timing sweep as mine is extremely conservative, but I want a real time view of knock while I do it. I dont know if it was stated earlier in this thread, but what sort of timing do you run at peak torque? I'm at 22* but I don't know how far I can push it, or what a reasonable value after MBT is.

 

Interesting, had read MBT as max brake torque in textbooks and thought it to be generally 30 degrees BTDC. What are you guys seeing your max brake torque timing to be? And you are saying you actually retard your timing from this MBT timing?? So for example if MBT timing is 35 degrees BTDC you are setting your timing to 5 degrees BTDC (30 degrees after MBT timing like you say?)

 

I have a Curtis knock counter, but it's never picked up a single blip since I converted to E85. I typically run conservative timing anyway. Right now I'm at 12* at torque peak @3k rpm and 14 psi. Looking at the previous posts is killing me, I figure I can add another 5 degrees easily and pick up some decent power with no other changes. I'm hoping things go well this weekend so I can change the oil and schedule another dyno session.

 

Yeah, You will pick up a lot of power!! Like I said, I picked up 10 mph in the quarter going from conservative timing to what I have now. I bet I'd pick up at least 2 MPH bumping my current setup with the bigger bore.

You're right, you won't register any real counts I'm betting. I would just ramp up the top end quite a bit and then come back to the mid range and try to figure out where the tq drops off. I imagine you'll be around 37 degrees on the top end and 22 at 4k. Not sure where you'll be in the spool area.

I'm sure you know this, but generally you can be very rich w/o losing much power on E85. For example on a few runs tonight I was running in the 11.0:1 AFR range and still laid down some good mph.

The reason I say this, is that it would be less time spent on the dyno by adding a bit (alot) of fuel initially and bringing the timing in and then fine tuning it after you figure out where you come in on the timing.

For example I'd drive it and get the AFRs around 10.9-11.0 and then go play with the timing on the dyno.

My 02

 

Good advice, thanks. I was trying to keep the AFR's around 12.0 more or less. You're right, I have more to gain by finding the best timing curve and ramping up the boost. We'll see what happens this weekend.

 

This question is aimed more at sid, im really surprised that ramping up the timing that much after peak tq is ok. Right now with a k27 that peaks at about 4k, im at 22* at peak tq @ 22 psi and 23.5 at 6.5k. Do I stand to gain a lot by adding in a lot past 4k? To me, the car still pulls hard to 6500 but maybe im missing something? Im on e85. I try to keep my afr around 12:1 on boost as that is where the car seems to pull the hardest.

 

You are probably missing some power with that low of timing. However, one thing to note is that the k27 will fall off if you are over around 18-19 psi in the upper rpms anyway. So you may not gain due to the hot air. That is where you'll need to pay attn to AIT's.

When talking about using aggressive timing, I'm talking about with a turbo that is still efficient throughout the rpm and boost range. Getting too agressive with hot air is asking for trouble..

 

It surprises me too, but even pushing thd little turbo as hars as I am, my IAT on boost never get over 110. I have a comically huge FMIC, what kind of temps do you see with the hx40? I cant remember if you're running a front mount or a modified stock unit. It hardly matters re: the k27, im about to buy a bunch of pipe and convert to an hx35/.64 vband in/out setup. It should have no problem holding 23-24 psi to redline because yes, im only seeing 17ish psi by 6.5k with the k27.

 

I have the biggest FMIC you can install without MAJOR redesign. it's 4" core 31x18 IIRC. My AIT's are never much above ambient.

 

im guessing you have to be careful over speedbumps with an 18" IC...what a beast