He's said it like twelveteen times.
Tuning with jets, Power valves and an O2 guage
- Thread starter Kern Dog
- Start date
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txstang84
Well-Known Member
I think he said its all in by 3100
I meant to map the curve today but got tied up in other matters.
Yeah, my advance starts just off the 1000 rpm idle. By 2200-2400 it appears to be all in. That seems way too soon to me. I have 2 MP electronic distributors. The one I have had for 11 years is the one that has the lightest springs and has been adjusted to a 13-14 degree advance. I took the advice of a FBBO member and emailed Don at FBO about getting the distributor recurved and phased. Instead of a simple "Sure, send it to me" response, Don asked a series of questions. I take this as a sign of good service. I had planned to send him my spare MP distributor. I'm going to call him on Monday.
Yeah, my advance starts just off the 1000 rpm idle. By 2200-2400 it appears to be all in. That seems way too soon to me. I have 2 MP electronic distributors. The one I have had for 11 years is the one that has the lightest springs and has been adjusted to a 13-14 degree advance. I took the advice of a FBBO member and emailed Don at FBO about getting the distributor recurved and phased. Instead of a simple "Sure, send it to me" response, Don asked a series of questions. I take this as a sign of good service. I had planned to send him my spare MP distributor. I'm going to call him on Monday.
Well see.....and I'm NOT bein a smartass here, but you JUST said on the last page that it was ALL IN by 3500, so it sounds like you really don't know. I bet that thing has more timing in it a lot sooner than you realize. It's a stroker. It ain't gonna need a GOB of timing down low for bottom end torque, so if you need to limit it by say 4K, it aint gonna hurt a thing. That's what makes up the curve. The WHEN and HOW MUCH. If it's too soon and too much, you're gonna rattle like a Waffle House waitress with six teeth, one and a half tits and three brain cells.
txstang84
Well-Known Member
Rob, I don't know whether to laugh at that comment, be confused, or be disgusted...somehow though, it seems pretty accurate lol
Maybe people MISinterpreted this?
I wrote that at 3500 the timing was all in and HAS been for several hundred rpms. NOT all in at exactly 3500.
My point in that sentence was to show that since the rpms were WAY past the ALL IN point, the actual CURVE probably isn't the issue. At this engine speed, (And several hundred rpms before it) the total timing is advanced as far as it is mechanically able to go.
I would think that is it took until 3500 to get all the timing in, it might be less likely to ping.
My rationale is that if the engine pings at any rpm point AFTER all the timing is fully advanced, how can the curve be the issue? I arbitrarily picked 3500 to demonstrate that it still knocks from there at WOT.
I am not trying to be arguementative. I am trying hard to understand.
Well crappomaggot, that's the problem. You got it comin in too early buckwheat. Too early and too much. That's what she said last night. Try having it all in BY 3500. Then if that doesn't work, 4K. There's no hard and fast rule that says it has to all be in by 2K. That's just a number you seen thrown around a lot.....and it's usually for lower compression engines. Because they need more advance sooner for more cylinder pressure and more bottom end torque. You got plenty of cylinder pressure. Try curving it so it has like 20 initial and then all in by say 3500 and see what she does.
Yes it IS the issue I believe now. More advance = more cylinder pressure. Less advance = less cylinder pressure. If it comes in too early or too much, it's gonna rattle. Get it now? Why do you think when you jack the timing up too high the engine yaks against the starter? Cause it has too much cylinder pressure for the starter to turn over.
Now I have to deal with being called names ?
I surely don't understand crappomaggot and I bear no resemblance to Buckwheat....
I surely don't understand crappomaggot and I bear no resemblance to Buckwheat....
txstang84
Well-Known Member
The more I see of Rob's post, the more I think they're terms of endearment...
crappomaggot was like a souped up version of "well crap!"
and buckwheat.........I mean really buckwheat. do I have to splain myself here? lol
This ^^^^^^^^
I figured it was in jest. I was just pretending to be offended. It is more effective when I do it in person!
As I wrote, I am trying to make sense of a few things, so bear with me on this:
The engine has an advance curve that starts at 17 degrees initial and reaches full advance at 31 degrees at around 2500 rpms. I am driving at 3500 rpms at light throttle in second gear. Suddenly I floor the pedal. The cylinders are suddenly packed with pressure and there is audible detonation.
THIS is where I am curious. How is a spark curve responsible for the detonation AFTER the advance quits advancing?
Wouldn't you think that the detonation is now a matter of too low fuel octane or too high cylinder pressure/compression? Wouldn't then the "fix" be either higher octane fuel or lowering compression?
The 100 & 91 octane mix wouldn't knock at 3/4 throttle, but did on full throttle.
The 110-100-91 mix ran without knock.
I think that I understand that by opening the throttle more, I am increasing cylinder pressure. This happens in every engine. I am not interested in driving the car and limiting myself to 75% of its potential. I want to be able to hammer it whenever I want without trouble.
The trouble I am having here in understanding RRRs logic is that if the car knocks at WOT from 1000 rpm, knocks at WOT from 2000 rpm, knocks from WOT from 3000 rpm, etc, how is the spark curve to blame? I can see that this perspective would make sense if it knocked at WOT at low rpms but NOT at any point past the "All-in" point.
If I am missing something, let me know.
As I wrote, I am trying to make sense of a few things, so bear with me on this:
The engine has an advance curve that starts at 17 degrees initial and reaches full advance at 31 degrees at around 2500 rpms. I am driving at 3500 rpms at light throttle in second gear. Suddenly I floor the pedal. The cylinders are suddenly packed with pressure and there is audible detonation.
THIS is where I am curious. How is a spark curve responsible for the detonation AFTER the advance quits advancing?
Wouldn't you think that the detonation is now a matter of too low fuel octane or too high cylinder pressure/compression? Wouldn't then the "fix" be either higher octane fuel or lowering compression?
The 100 & 91 octane mix wouldn't knock at 3/4 throttle, but did on full throttle.
The 110-100-91 mix ran without knock.
I think that I understand that by opening the throttle more, I am increasing cylinder pressure. This happens in every engine. I am not interested in driving the car and limiting myself to 75% of its potential. I want to be able to hammer it whenever I want without trouble.
The trouble I am having here in understanding RRRs logic is that if the car knocks at WOT from 1000 rpm, knocks at WOT from 2000 rpm, knocks from WOT from 3000 rpm, etc, how is the spark curve to blame? I can see that this perspective would make sense if it knocked at WOT at low rpms but NOT at any point past the "All-in" point.
If I am missing something, let me know.
The compression is the whole point of why I've been trying to tell you to curve the distributor. Which way would you rather fix it? Tearing the engine back apart or adjusting the timing curve? Take your pick. Christ almighty. Why is it so DAMNED hard to get you to simply TRY something. That distributor is the Mallory unit, right? It's so damned easy to adjust, you can try multiple timing curve within a few minutes. How do you know the advance had stopped? You've not even curved the distributor yet.
I just ordered the Mallory kit PN 29014. It has different advance springs to tailor the curve in several ways. Some guys have mentioned to try a two-stage curve. The first moment of advance is a bit fast but then at a point the advance rate slows. This is actually designed for the very thing that I am fighting.
IF....this makes the difference, you can be sure that I will admit my stubborness and apologize.
IF....this makes the difference, you can be sure that I will admit my stubborness and apologize.
805moparkid
Slant and AFX Guy
the reason you can sit at 2500 with no issues and then gun it and have it detonate is due to cylinder pressure. at cruise there is no or low load against the engine (lowest cylinder pressure) when you punch it or go up a hill or add timing your cylinder pressure increases and it rattles.
see on most builds the cylinder pressure isn't nearly as high, so they can run alot of timing early, even at max load and best timing it wont ping because the cylinder pressure isn't high enough compared to the octane (pump gas)...
your build is close to the edge so you have to dance with it to get it happy with pump gas.
Right. That's the kit. It has the sprAngs and the little red spacers in it too. Self explanatory. Has good deestruckhuns. I got my fingers crossed.
805moparkid
Slant and AFX Guy
spacers? is it to limit travel?
txstang84
Well-Known Member
Yes
Yes. They are kinda like plastic "keys" with a different size end on each one. They are marked according to advance degrees.
moper
Well-Known Member
That was the kit I have - I mentioned a couple pages ago that i'd mai lyou some iof you needed them and that you needed to slow down the curve - just as Rob has - over and over.
If it was in my garage I'd be dropping the initial to 12-14°, it would START coming in at about 2K, and FINISH about 4K for a total of 32°. Then I'd use the O2 to tune the carb.
I've had several big blocks with no quench - properly tuned - running great on local 89 octane with 10% ethanol that had 185psi and iron heads. It can be done - you just have to have the time, knowledge, and bits of parts to do it.
It's back in this thread - detonation and ping are self supporting. Once they start during an acceleration event they will stay unless the throttle is backed out of. So if it pings once at 2K - it's going to continue until you let off and change the air/fuel input and ignition input. That's why you have to alter the timing curve - not just one part of it. Then you'll probably have to reset the carb too - especially the accelerator pump circuit and power valving. There's a ton on quench online - if you don't get it - keep reading. If you don't want to accept it - keep reading. The short shortshort answer - less is more. Tighter is better - really tight is best, and after .045-.050 - there aint much good happening especially with a big bore and piston rock.
I'm sort of at odds here. I have tried the thicker head gasket trick to get out of the detonation zone but I keep hearing about tightening up the quench to achieve the same thing. I wish I had a Head gasket sponsor so I could try both!
The .027 Cometics still only get me to .044. for quench. I don't know of any other gaskets any thinner that work with aluminum heads. The .020 steel shim aren't supposed to be used with aluminum heads from what I have heard.
One thing's for sure. You could certainly be a test bed for quench. If you dropped your quench distance to say the recommended minimum of .035" and it stopped detonating, that would really hammer home how well quench works. But I really think you can stop the detonation easier than that. It's unfortunate that the block was not zero deck height milled because then it would be easy. The gasket thickness would also be the quench distance. I know Jim Laroy (IQ52) has run close to 12:1 on pump gas with aluminum heads. I think it was 11.8? Something like that. You're at 10.7 is it? Something just tells me you're RIGHT there on top of being able to run pump gas. I think the ignition curve will do it.
moper
Well-Known Member
When you run aluminum you should be running a composite gasket. There are some that have run the steel shim or the standard round wire fire ring head gaskets - the downside is they will eat into the head itself over time eventually leading to problems (called brinneling).
I don't think it will work at .044 with what you have. You'll have to retard the cam some too. Depending on the bore and compression height of the pistons I generally don't run any more than .035 and usually .028-032. The problem is your engine was designed without quench in mind - so you're kind of screwed unless you take it apart and address those bits, or find a way to tune it. I still think you can tune it out if you're patient enough.
I've read about guys using the .020 shim gasket even with aluminum heads. I'm still skeptical about it all though. The .020 gasket moves my CR to 11.22 to one. Quench or no quench, thats still a lot of squeeze. It seems impossible that I could add a half point of compression and eliminate the knocking in one move. I'm still worried that the high CR leaves me with too little wiggle room if I get a crappy tank of gas or if the weather is especially hot. I do not want to just barely be safe from pinging.
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