Need advice on ignition advance The stock Microplex ignition advance at WOT is about 32.5 @ 5K. I know the 2v motors carry a bit more, especially the early carb's cars. The Forza Carobu article says that adding advance to the 308 engine (38 degrees) helps power output. Would be interested in folk's experience and knowledge with the effect of adding more advance, and if any unique precautions apply to a 4 valve engine. Many thanks Russ
Adding ignition advance can add or subtract power depending upon where the advance is currently set. If it is set anywhere close to optimal, more advance is likely to reduce performance. A dyno is the only real way to tell.
I must agree that the best way to set it up is on "the Rollers". Past experiences in dialing in Electromotives, found that in some cases there was not enough available to dial it in on the unit itself. So Resetting the trigger wheel to the trailing edge of the 12th tooth, instead of the 11th, "fooled" the unit, allowing the dialing in to go a bit more. At the 11th tooth setting, the adjustments were maxed, and still no detonation. HTH, Kermit
Thanks Kermit and Mitch So Kermit, understanding that every situation is different, just how much advance have you been able to use on a 308 without detonation? Anyone? many thanks rt
Kermit I understand you didn't experience detonation but did max advance correspond to max power on the 2V cars? I am curious if anyone has data on this. Intuitively, I'd have thought adding in more timing in the 3000 - 5000 range using modern technology would lift the lower end of the torque curve, but I'd be surprized if the top end wasn't timed for max performance already (acknowledging the bottom end was compromised for emissions). Philip
Dyno is the only real way to find out. In addition, the dyno can be used to find the best advance curve not just the static advance. Perhaps you can add a few degrees just above idle, then subtract a degree between 2000 and 2500, stay the same from 2500 to 3500 and then add 2 degrees from 3500 on up. But the only way to know is to use a dyno.
Ignition timing is a very complicated subject! The factory spec should be best for normal road use, but with the help of a dyno you can tweak the HP and torque curves with more (or less) advance. Computerized ignitions are fun but I doubt most people know what they're doing with it. Again, only a dyno can really tell you what you've done. On my little carb Lotus, I just advance to detonation and back off a few degrees. This is 12 degrees static and 6-8 at idle but of course this is irrelevent to anyone else's car. Ken
The 2-valve injected cars have way too LITTLE advance below 3000 RPM. This was done for entirely for emissions purposes. One conversion I worked on went from the stock setting of a few degrees ATDC to 10-12 BTDC at idle, then worked its way up to about 37-38 BTDC at full song. The car idled 1000% better and off idle response was drastically improved. The maps were optimized for stock compression, but with EFI fuel delivery. IMHO, the biggest gains are where the car needs it most: down low.
I added timing to QV below 4000, so it's 32 degrees from about 3000-redline (0-5psi boost). More timing on top didn't help, but more down low improved responce.
Peak advance on the Microplex MED806A for 3.2 engines is at 4K, where it ranges from 25 to just shy of 45 degrees, in nine curves, depending on manifold pressure. The test figure for 5K with the vac line disconnected is 28 deg. The Microplex's map is severely complex, for emissions purposes, compared to aftermarket sparklers.
Are timing settings independent of the fuel delivery system? In other words, assuming the same cams, will optimized timing specs for the 2v injected 308s be the as those for carb cars? That said, did the later 308 carb cars (78-79) have the same cams as the 2v injected cars? --Mike
Yes, totally agree, and thanks for the data. My interest primarily lies with the engine under load (curve #1, as I best recall) at high throttle openings (low delta P). As with most vacuum advanced ignitions, most advance is placed while the engine is not under load to provide more efficient combustion and prevent detonation at open throttle settings. Setting emissions concerns aside for a moment (or two) I'm trying to get an idea of how much advance is optimal for power and torque at different rpms. Mark - it's interesting that advance over 32 degrees did not make any more power. Ric's 2v car went up to 38 at high end. I wonder if it is a 4v thing? His experience with better response from more advance down low seems to match yours.
With the carb and Kjet cars, advance is independent of fuel delivery. The ignition maps of the injected cars are a bit more sophisticated and emissions optimized than the mechanical advance distributor. Not near my spec sheet, but don't think the timing on the carb and kjet cars are the same - will check. more to follow
"it's interesting that advance over 32 degrees did not make any more power. Ric's 2v car went up to 38 at high end. I wonder if it is a 4v thing?" I think it's a combustion chamber thing. The shape, size, turbulence and plug placement all effect the optimal timing. The better the design, the less total timing is required. Ive seen engines that use as little as 22 (bike) and as much as 50 (side valve). I think it makes sence that the newer engines need less.
Thats really an open ended one to answer Russ, as Fuel mixture, combustion chanber design, et al play such a part. IMO 38 degrees , providing you "stepped on the fuel" ( a shot of straight Tolulene is my favorite,wouldn't be a problem. Ive tested carbed 308's that Ive ported, that ran best with 30 degreees with it backed down at 8000 by 2 degrees. The burn characteristics have a bunch to do with the advance needs, and the 2 vave definately flows different upon entry into the cylinder. As these motors depend more on the "tumble and swirl" to propegate the flame front, it really opens a can of worms on definite numbers. A porter with experience can easily encourage the tumbling, and therefore the power, and yet have ports a bit smaller than one would think necessary (providing they will flow up to the capacity of the valve open area) One thing I would note here, is all testing is done with the head bolted to an old liner, so theat it is a realistic of a test as possible. An odd tidbit learned by my years on the Bench has shown time and time again thatthe 4valve flow in stock form flattens out @.350 lift, another .050 lift gives up a wild 2CFM! The 2 valve on the other hand, still comparing stock, will keep climbing the flow meter until the retainer hits. Iv'e even removed the seal to see, and yes there was more after I could move it another .050. go Figure. HTH Kermit
