Hi Gurus! I urgently need an ignition curve for my 78 GT4, my car goes great but it pulls max power about a 1000 rpm too soon (190bhp at 6080 rpm). I am guessing that is an ignition problem. I am running a Black Stallion ECU and dizzy. Someone on this forum suspected that I was running a QV curve some time ago. 0 0 800 17 1600 23 2400 27 3200 32 4000 36 4800 36 5600 36
The curve in my 1976 Euro carbed dry sump 308GTB handbook appears to plot distributor rpm against degrees of advance as follows: rpm deg 600 0 900 5 3000 16deg 30' linear interpolation between 600 and 900 and then 900 to 3000, i.e. 750rpm = 7deg 30', 2000rpm = 11deg etc Constant 16 30' above 3000. Tolerance is plus/minus 100 dizzy rpm. Engine rpm = double above dizzy rpm figures.
From the 155/78 OM (late carbed Euro 308) -- same as Paul's description. Don't know what the situation is now, but, 5~10 years ago, I was surprised at just how inflexible most aftermarket set-ups were for the advance curve. I.e., you couldn't match this curve well with the switches/knobs provided -- way too much mid-range advance better suited to a big pushrod V8 just like you show. Image Unavailable, Please Login Image Unavailable, Please Login
I didn't know much about it, thanks 91tr, but that was my understanding is it's pretty much full advance once revs go up to 3K......
Not quite sure what you're trying to say here Bubba? The 308 graph is for distributor RPM, not crankshaft RPM -- full advance is held off to 6K crankshaft RPM (very unlike what Nick T posted).
Thanks 91TR, assuming that at best the standard straight line graph was a compromise, and if Ferrari could have fitted an ECU based ignition on these carb'd motors, can you guess what the values would be for the rpm ranges above, 0 0 800 ? 1600 ? 2400 ? 3200 ? 4000 ? 4800 ? 5600 ? 6400 ? 7200 ? 8000 ? I know mine is wrong, but have no idea how to make it right! Peek power is supposed to be at 7000 mine is at 6000! You can see from the attached graph that at 6080 the power dies off, almost like the top bit of the graph is missing. I have set my rev limiter to 7200 Image Unavailable, Please Login
I don't think that the stock Euro curve was a "compromise", and you should shoot for that for a starting point -- i.e.: crankshaft RPM = total advance 1200 = 6 deg 1800 = 16 deg 6000 = 39 deg above 6000 = 39 deg If the values in your first post are for total advance vs crankshaft RPM, I think you have some other (fuel?) problem causing the torque to start dropping off prematurely at 5K crankshaft RPM. Or are the values in your first post just what the ignition electronics is doing and there is a large static advance value that would need to be added for calculating the total advance?
Nick the only way to get this spot on is to dyno or rolling road the car with an expert. I take my Caterham 7 to Track n' Road near Rainham in Essex, not too far from Iver. The two Steves that run the place will both adjust the ignition map, assuming it can be tweaked with a laptop, and get your carb jetting right. If you get the ignition advance wrong by guessing the values you could end up with very expensive pile of molten aluminium. Paul
No Steve, Those values include a 10 degree static advance. Reading the values above, would that be PLUS a static advance?, so at 1200 rpm 6 degs plus the static?
Hi Nick they charge about £300 - £400 for a full session for the '7 which includes mapping the whole ECU - fuelling and ignition. Best bet is to give Steve Greenald a call on 07774 773824 and see if he can do it for you. He'll need to know what ignition control unit you've got and whether you have any specific software needed to set it up. If you've never put your car on a rolling road before, be prepared to hear your baby scream! http://www.tracknroad.com/ At your own risk if you go ahead with it. Paul
Set-up the correct curve on a dyno is very easy. Simple doa pull, make a change and do another pull. repeat uintil you find the optimum point. The problem with your hp peak is that something is wrong with your engine. The timing seems about right and would not be the cause...unless it isn't what you think it is. Maybe confirm it with an adjustable timing light. You might be dropping a cylinder, maybe the mixture is buggered, but it's broken. Good luck!
Hi Mark, Not sure why you think there is something wrong with the engine? If it were a cylinder I would be down on power all the way, and not just at this one point, 190 bhp is quite reasonable for a 100k mile motor, and the fact its peaking 1000 rpm too early makes me suspect that my curve is out. As has been pointed out in this thread the stock curve goes to 39 degrees at 6000 rpm, mine max's at 4000 at 26 degrees. I have emailed Black Stallion in Australia to see if they have any ideas. My cams are spot on, carbs running a little rich, no oil from engine on acceleration or de-acceleration. The power curve looks spot on until you get to the sop bit, which looks like its been cut off!
Hi Paul I had mine on a hub dyno a few months back, quite used to it screaming! http://www.youtube.com/watch?v=R2fnauVAX3s Cheers Nick
.....like the ignition breaking down. It's very common to find problems like that on the dyno. Something is changing that causes the torque/hp to drop. It's not a lack of air because then the torque would drop, but the hp would flatline. You're losing what looks like exactly 1/8th of your power making me think you're dropping a cylinder, but you could be losing power in all cylinders which would most likely be the timing changing, like is the final rpm set point is set wrong. As to the 190hp, I have no idea what that means. Every brand dyno is different and some are most sensitive to operator input than others. also, you are on a hub dyno which gives you neither crank nor wheel hp, but something in between. What you are looking for on the dyno is the shape of the graph and the effects of the changes you make, the absolute number doesn't tell you much. For comparing hp numbers generally dynojet dynos are preferred because they are common and fairly consistent machine to machine.
Nick the rolling road at Tracknroad measures rear wheel torque/power and then, using a run-down test, measures the power lost in the transmission/tyres to calculate flywheel bhp and torque. Their machine has been used extensively and shown to be very repeatable over time and between cars of different types. They also claim good accuracy but that's another subject! They will give you a csv file at the end, as well as a printout, so you can spend hours afterwards mulling over what's happening. There are so many reasons why an engine will not make the claimed power anywhere, including at the top end, but maybe the valve springs are tired and the valves aren't closing, the contact breakers are bouncing or the coils/plugs/leads etc are breaking down. Could also be fuel starvation due to sluggish fuel pump or blocked fuel filter. I had a problem with my '7 when two of the injectors were off par and didn't deliver enough fuel at max revs. Probably worth checking out of few of these if you can before investing in a rolling road session again. Paul
As indicated elsewhere, the early cars should have 38-40 degrees crankshaft total ignition advance at 6000, with 34 @ 5000. Any of these dyno shops should be watching fuel mixture and ignition, or should be able to for a price. All the books indicate max power at 7000, so having it fall off at 6000 shows an engine problem that should be resolved before you hurt something, if you havnt already. Its very critical to carefully double and triple check fuel and ignition before running them hard. If your running on the ragged edge of lean or with possible ignition troubles (or both), and start running them out to max revs at wide open throttle, this could be where your headed. Image Unavailable, Please Login Image Unavailable, Please Login
Thanks for the info Paul, If anything my car is running a bit rich. I suspect that my problem is ignition, the problem with after market replacements is they are set up genericaly and not specificaly for one model. The curve I have been running for over a year only has 36 degrees (10 static and 16 electronic) at 4000 with no further advance through the rev range. I will reprogramme as suggested in this thread and see if it runs better. Do you have a view as to what the advance should be at 1600 rpm?
I still dont know how to extract a page from a pdf. file and post it, or I would post the page's from the 308 OWM that show the curves, as well as the curve shown in the owners manual (1977). However, as pointed out, the curve shown in the owners manual, as well as the curve shown in the emissions section of the OWM are identical. It the curve shown in the electrical section of the OWM that confuses things. Anyway, I found this image off a Jaguar site and thought I would post it. Its interesting because it shows the "range" (the grey area) of possible ignition timing advance curves over the rev band of various engine's. Things to notice are that this represents the distributor itself, not the engine. IOW, you can rotate your distributor advance or retard, yet you still have the same identical "curve". Its the OVERALL advance within the distributor vs your idle speed ignition setting point that alters your phisical engine timing. On the 308, our curves generally appear to start around 800-1000 (dist.) RPM, and top out at 3000-3400 (dist.) RPM. What I'm saying here, is that I dont know what YOUR ignition timing would be at 1600 rpm. That would be something you (or your "trusted" mechanic) would determine. The simplest way I could explain to get one of these cars running decent, is to carefully mark the flywheel in 5 degree intervals above and below the 34 degree timing mark. With a decent quality handheld tachometer, rev the engine to various speeds while watching a timing light, and note the rpm where the timing light flashes on the various flywheel marks. Ideally, you want the engine to hit 34 degrees at 5000, while matching the other points on the curve at the other speeds. Sticking weights will often times hold intitial static advance until the engine revs up to some higher speed, then the weights break free and timing "jumps". By watching your timing light "move" on the flywheel as you alter engine speed, you can determine if the distributor needs a "tune up". Because I dont like revving my engine above 5000 RPM without load any more than I have to, I bought a distributor machine. But a quick shot to 6000 RPM wont hurt a good engine while you check ignition timing. Image Unavailable, Please Login
FYI you don't need to mark the flywheel to do this . .. use a good timing light that you adjust to the "TDC" mark . .. I just bought upgraded recently to read DFI signals . . . had been using an old POS for years . .. the new one I got gives you engine rpm also. I'm gonna map what the stock US 2Vi digipliex box is actually doing on my car . .. well to 5k rpm There's another input on my data acq system for capturing real igntion timing events . . . shouldn't need to worry about what's going on over 5k anyway 'cause all advance should be in by that point . . . would be interesting to see if there's any fluctuations going on though. Sean
Russ, I show that same advance curve in both my owners manual, as well as the emissions section of the 308 GT4 Workshop Manual, page O8. What I am curious of, is the advance curve shown on page L15 of the electrical section. Not only is the curve on page L15 showing an entirely linear curve, it shows it to achieve maximum advance at 3400 distributor RPM, and only having 13 degrees total advance. Image Unavailable, Please Login
