mpg on my 340
my compression is 175 -180 psi on all cylinders. AFR while cruising is around 14.1-14,4
The cam ?? Don´t know... and yes..my Ignition is probably...the weak point...because I can´t use the VC If I use her... the engine is pinging... The CR is probably way to high
...I have a Carter Trick KIt... also jets from 95 -to 105
Rods..... so I can lean out the carb..
So the Carb is not the problem... the VC is the Issue...
Today I checked my timing.. ( after I changed the set up in the Distributor)
12 deg @ idle... 17 deg @ 1500 rpm 24 deg @ 2000
29 deg @ 2500 and 33 deg. @ 3000 rpm.. ( without the VC ! )
With VC... the timing goes up to 46 deg. @ 3000
But if I use the VC,,,I always have this klicking /pinging sound when I drive steady in the 50 to 60 mph range...
60 mph ...in my case equals 2650 rpm... more or less close to the peak of the timingcurve...with /or without VC... The engine accepts 33 deg... of timing...but the 13 deg from the VC... are too much...
The VC is connected to the Ported vacuum btw.
so perhaps I need to reduce the VC a bit more.. but then will end up with 42 deg.. all in..incl VC.Greetings Juergen
-This post is, for me, very hard to read; are you saying that with the Vcan disconnected, you are having NO detonation issues while cruising?
-So I'm gonna reduce all this to one line: 12/33@3000 plus 13ported, no detonation on the mechanical curve. Is that right?
Well then it seems obvious to me;
-Detonation is caused mostly by too high a temperature
in the chamber.
It might be due to; excessive timing,or too high a cooling system temperature, or a restrictive exhaust, or the carb sucking hot underhood air. I leave the timing for last, cuz you can lose a fair amount of driveability when sacrificing timing.And you can gain power with fresh cold air and a free-flowing exhaust.I also try not to sacrifice the minimum running temp.
-Someone mentioned running a lower temperature. This is an option; just remember that the thermostat sets the minimum running temp. If you are running 200*F at highway speed with a 180*stat, you will be running the same with a 160*. If you want to run a cooler highway speed, you will have to figure out how to shed heat faster.
But if you are now down to timing;
-Here's what you need to do; map your mechanical advance against rpm, on a graph paper, and you will instantly see the issue. Run advance up the left vertical axis and rpm along the horizontal.In your case it is a straight line running up very steeply.This curve won't work with your cylinder pressure, and your available fuel. OK let me rephrase that; it didn't work on my combo which is very similar to yours. You have two choices;1) reduce your cylinder pressure, and 2) delay your timings
-Your curve is putting too much timings in for a 2650 rpm cruise.
All your mechanical advance is not allowing the Vcan to function as it is intended too.
- Your curve works out to be 1*/100rpm, beginning at about 1000rpm; so at 2650 your all-in mechanical might be 16.5 +12=
28.5 And you have 46 -33 =
13* in the can, so
TOTAL cruise timing @2650,should be 28.5 + 13=
41.5, and you say this is too much.You also say that the 28.5 by itself is ok. So, the solution is to find out exactly what she wants, between those two.And then redesign the curves to provide it. And the easiest way to find out,is to just rev the engine up to 2850 and set the total(with vacuum advance) to some arbitrary number between 28.5 and 41.5 and see what sticks.When you find it, deduct the 13 and you will be left with the mechanical target to hit.
-Example; let's say you found that 37* was accepted by the engine at 2650 while cruising. Then 37 less the 13 in the can, Equals 24* so you will have to build a curve that makes 24* at 2650 rpm.Bada-Boom!
-At this point you will be thinking that you are gonna have to make a choice between power and economy.I tell you what if you can tell the difference between 28.5 and 24 at 2650 at WOT, your but-dyno is a heck of a lot more sensitive than mine.You are only ever at WOT and 2650 when you are on your way to some higher rpm. And if you have something like a 2400TC, then you are talking maybe,one or two seconds in the zone from 2400 to 3300(depending on your power to weight ratio). At most non-WOT throttle settings you will probably be on the primaries, and the power difference will be un-noticed; so give the engine what it wants for cruising, and forget about any powerloss.
-You might be able satisfy the cruise timing requirement with a single stage curve, by delaying full mechanical timing to some higher rpm, than where it comes in now. I'll guess 3600 or perhaps even a little higher.When you build your own engine, you kindof have to throw out the timing book and let the engine tell you what it wants.But if not;
-I gotta warn you,a two-stage curve is not easy to build. The curve needs to have a kink in it. (At 180psi, my combo needed it's power-timing to be slowed down from 2800 and on.The max mine will accept at 2800 is 28*, but from 3400 on it will accept up to 36*).I suspect yours will want a similar curve. The dizzy will need two different kinds of springs. One of them has to have a long-loop that basically does nothing, for the longest time, and when it finally comes into play it slows down the other spring.The second spring will be doing all the work while the long-looper is on vacation. Since it is now doing the work of two springs, it needs to be twice as strong. I have only ever set up factory dizzys this way.I doubt you will find a spring-pair to work exactly as your engine needs. When I get close, I start lightening up the flyweights to dial it in.The positioning of the kink needs to be done by you, experimentally. I can't tell you where to put it, but;
-But putting the kink at 2800 worked for me.I run about .78*/100rpm(below 2800). So at my cruise rpm,(2200); I run 14idle plus 10centrifugal plus 22 in the can equals 46 total cruise-timing.. The engine is fine with 7/8 more from my dash-mounted dial-back timing gizmo.But it really makes not much difference, so I just leave it at 46*@2200. So my timing works out to 14/34@3400,plus 22ported
