When you use the civilian distributor, with vacuum advance, on the 230 engines, where do you set the timing?
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When you use the civilian distributor, with vacuum advance, on the 230 engines, where do you set the timing?
6 degrees with the vacuum line un hooked.
5 degrees BTDC, just like the mil engine according to my Jeep tuneup manual.
You must unhook the vacuum line to get it right...then when you are done, hook the vacuum line up while you have the light on the timing scale and the timing should change quite a bit...that way you know the vacuum advance is working at least.
Rboltz, what carb are you running on ur 230? 1 or 2 barrel? Where are you hooking your vacuum advance line to?
I don't know if this matters, but my vacum advance is hooked up front on the ports next to the thermostat housing. I'm curious if someone has it in a different location.
yeah, thats what I've been trying to figure out. I've been told (and in my head it makes sense) that you can NOT hook it up to manifold vacuum, it must be hooked off the vacuum from the venturi of the carb, but I can't find any ports to go off of with my 2-barrel holley carb. Basically, it has to be a port "above" the venturi correct? The port that sucks air from the valve cover is the same as manifold vacuum, so that won't work.
I've been scratching my head with the thought. That's why I was hoping to get some feedback on the idea. My truck seems to run fine where it's hooked up. I am doing a complete tune-up this week, and I was going to investigate further. If something changes I'll definetly post up.
It will work on manifold vacuum but it will be "on" all the time. The preferred point to hook it to is ported vacuum...vacuum that is only there when the throttle plates open...not at idle but off idle.
The stock 1 barrel does not have a vacuum port to hook to at all, ported or not. I hooked mine to the vacuum tree a the front drivers side of the head behind the thermostat. Worked good, better than stock without the vacuum advance with improved power and gas mileage.
When I swapped in the 2 barrel, a stock for a 230 2 barrel, it has a ported vacuum port on it just for this purpose.
What 2 barrel are you using rpgdeity that doesnt have ported vacuum? This would be a port low on the carb, about at the level of the throttle plates.
I have been pondering and researching the issue of PORTED vs MANIFOLD vacuum since this tread started. Even did some hands-on testing, on my J10 (ported) and my M715 230 (civy dist - manifold), with a vacuum gauge and a timing light viewing both vacuum and centrifugal advances.
Having come to some conclusions, it was very difficult to find a reliable source that agreed with my thought that manifold is better than ported. There is so much conflicting information out there on the subject, that it is just amazing but I finally found what I was looking for. IMHO --Very good reading:
http://www.corvette-restoration.com/.../Timing101.pdf
“Ported Vacuum” was strictly an early pre-converter crude emissions strategy, and nothing more. Don’t believe any one who tells you that ported vacuum is a good thing for performance and driveability – it’s not. Anyone with a street-driven car without manifold-connected vacuum advance is sacrificing idle cooling, throttle response, engine efficiency, and fuel economy, probably because they don’t understand what vacuum advance is, how it works, and what it’s for. There are lots of long-time experienced mechanics who don’t understand the principles and operation of vacuum advance either, so they’re not alone.
The difference between ported and non-ported vacuum is at idle ONLY as noted by brute4c above. Once the throttle is opened they both theoretically (not quite) see the same manifold pressure (vacuum).
I say theoretically because of the venture effect -- Bernoulli theorem (When the speed of a fluid increases the pressure decreases). Ported at the throat of the carburetor is seeing the full velocity of all air being drawn in by all cylinders where some manifold locations will see much less air flow. I really can't find any source to support my theory on this (It may be negligible).
Conclusion:
I believe manifold vacuum located as far away from the carburetor as possible is best for the M715 230 engine with a civilian distributor.
I have no practical experience with both ways, like others do, so this is presented as theory that makes sense to me.
To stay on topic: My 230 is at five degrees advanced with manifold vac hooked up and slightly retarded without. Probably not optimum but it starts good, has plenty of power and does not overheat.
Since I need a port for the PCV I'll use the one as Jon shows, below the carb. The only other one is behind the thermostat so I'll connect the vacuum advance there. Currently, the wiper motors are there but I hope to reconnect those to the vacuum pump.
Just remember the vac pump needs manifold vac. too.
There are volumes that could be written into the theory behind vacuum advance and where to connect it. The standard is that it should go to ported vacuum, with base timing set while it is disconnected. Keep in mind that there is more to it than just how much advance and when. You start looking at valve timing, then you get into the engineering of the camshaft itself. But truly, what it all really comes down to, is than an in-line six cylinder with a carburetor and single runner intake and exhaust is never going to be efficient by today's modern standards, .. so do whatever makes it run best for you, in your climate, etc.
I guess I dont see how much advantage, or disadvantage, there is to having it "on" at idle as opposed to coming on at just off idle and beyond.
Keep in mind that you have to look at your performance across the board, ...The tuning process sets your base timing WITHOUT vacuum advance. If you set the timing with vacuum on you lose what you would gain with the vacuum advance, making it useless. Also keep in mind that at Wide Open Throttle, you have virtually no manifold vacuum, so at that point you are relying on mechanical advance.
Keep in mind that you have to look at your performance across the board, ...The tuning process sets your base timing WITHOUT vacuum advance. If you set the timing with vacuum on you lose what you would gain with the vacuum advance, making it useless. Also keep in mind that at Wide Open Throttle, you have virtually no manifold vacuum, so at that point you are relying on mechanical advance. Also, when you adjust the idle mixture, you want the throttle plates closed, to if your running manifold vacuum to the vacuum advance, it would throw off your mixture adjustment, what I have run across is that running manifold vacuum was that my power peaked at a lower RPM, and I also started getting detonation, however that was not on a 230, . . and your results may be different. FWIW
Agreed – I read volumes trying to understand why and when ported came into existence. There is a lot of misinformation published on the Internet. Some even believe ported increases vacuum and advance is in a linear fashion as the throttle opens from closed to full.Quote:
Originally Posted by moosejr
I'm not convinced it "should" go there but I do agree most use ported if available. The result is slightly retarded timing at idle making for an incomplete burn. This is a good thing if your engine uses an air-injection emission system because it aids the combustion of the hydrocarbons in the exhaust gas stream. Again this is at idle only.Quote:
Originally Posted by moosejr
Agreed – Go with whatever works for you because truly it is not a big deal either way.Quote:
But truly, what it all really comes down to, is than an in-line six cylinder with a carburetor and single runner intake and exhaust is never going to be efficient by today's modern standards, .. so do whatever makes it run best for you, in your climate, etc
Oh so trueQuote:
Originally Posted by brute4c
And yes moosejr – once you open the throttle significantly it is all over anyhow.
I have lots of old iron around here designed for leaded fuel. This stuff seldom, if ever, sees the road. I run premium gas and have the timing slightly retarded to minimize piston rock (pinging) under heavy load. This is true for my M715 with the 12v civilian distributor.