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Ported vacuum advance or manifold. Let's debate!

Photon440 said:
If your country is still measuring octane in RON, that would make a difference in numbers compared to the USA, Canada or Mexico. We use the RON/MON combination, listed as R+M/2, which is about 4 to 6 numbers lower than a RON rating. So if I go to a Chevron and buy our 94 octane, it would be rated a few numbers higher in Europe.

Most octane boosters that use "points" are showing little value, it take ten points to make 1%.
Click to expand...

BSB67 said:
US 93 octane (R+M)/2 = 98 RON.
Click to expand...

Never knew it was numbered like that in the US.
I checked once more but it says E10 is 95 octane and E5 is 98 octane, looks like in Europe we do not use the RON identification anymore. (years ago it was though)
In Germany you could even get 100 and 103 fuel, not sure they still have it though.
 
What's that beside the duster
 
New video is really interesting:


I´ve always run ported as my engine idles like crap with MV.
Though when it gets hot again outside I would like to try a full MV tune like in the video.
 
I've ran ported in everything but may experiment with manifold vacuum just to see if there is any improvements to see.
 
Jonas Nordstrom said:
New video is really interesting:


I´ve always run ported as my engine idles like crap with MV.
Though when it gets hot again outside I would like to try a full MV tune like in the video.
Click to expand...

This must be due to the carburetor needing tuning to MV. It should idle better. Now I'm running MV I have 25° BTDC at idle and it's so smooth and feels so powerful, idling in Drive, held on the brake. When it's cold though, it doesn't idle as well (no choke, just nursing it on the throttle). I think this is also carb tuning related as the idle speed screw is backed off a lot now I'm on MV.
I've done no tuning other the idle speed, just switched ports. The reason I haven't is because I'm only just learning all this and don't want to stuff it up.
If I hadn't limited by vacuum advance travel I'd have even more timing at idle, but I have no pinging now so it seems to be working.
I really need to buy a vacuum gauge and learn all this stuff - or spend a few days with someone who knows what they doing and watch and learn. Youtube, forums etc are helpful but aren't close to actually being there and talking to a real person about it and seeing what they are doing.
 
66 Sat said:
This must be due to the carburetor needing tuning to MV. It should idle better. Now I'm running MV I have 25° BTDC at idle and it's so smooth and feels so powerful, idling in Drive, held on the brake. When it's cold though, it doesn't idle as well (no choke, just nursing it on the throttle). I think this is also carb tuning related as the idle speed screw is backed off a lot now I'm on MV.
I've done no tuning other the idle speed, just switched ports. The reason I haven't is because I'm only just learning all this and don't want to stuff it up.
If I hadn't limited by vacuum advance travel I'd have even more timing at idle, but I have no pinging now so it seems to be working.
I really need to buy a vacuum gauge and learn all this stuff - or spend a few days with someone who knows what they doing and watch and learn. Youtube, forums etc are helpful but aren't close to actually being there and talking to a real person about it and seeing what they are doing.
Click to expand...

Yes for sure, I only switched ports and tuned the idle screws when trying MV.
But my base timing was at 14 and I had not thought about upping the timing to over 26 at idle.

So it would be to start over with everything, carb/jets/needles/timing/mec adv/vac pod adv.
This is actually a ton of work to change path and try MV.
 
No, I'm at 12° base timing, but it now idles at 25° with the vacuum advance connected. Sorry for the confusion.
I just watched the whole 32 minute video. I'm still a bit confused with the inches of vacuum etc. I limited my vac advance unit in the same way he was talking about in the video (but I've done mine with metal blocks glued in rather than a piece of wire) and by coincidence have the same 13° in the vac advance unit he has (25° at idle less the 12° base). But he's starting at 22° base and going to 35°.
How does his timing light show the timing digitally? How does it know?
Honestly my car runs great on MV. It was running good before on ported but there is almost zero exhaust smell on my clothes now after driving it, and my garage is hospitable immediately after parking instead of having to wait half hour for the fumes to clear.
So I have done some tuning, but only to the distributor, nothing to the carb.
I wish the distributor was on the front of the engine like a big block, it a pain in the *** with it at the back of the engine when I'm fiddling with the timing.
 
66 Sat said:
No, I'm at 12° base timing, but it now idles at 25° with the vacuum advance connected. Sorry for the confusion.
I just watched the whole 32 minute video. I'm still a bit confused with the inches of vacuum etc. I limited my vac advance unit in the same way he was talking about in the video (but I've done mine with metal blocks glued in rather than a piece of wire) and by coincidence have the same 13° in the vac advance unit he has (25° at idle less the 12° base). But he's starting at 22° base and going to 35°.
How does his timing light show the timing digitally? How does it know?
Honestly my car runs great on MV. It was running good before on ported but there is almost zero exhaust smell on my clothes now after driving it, and my garage is hospitable immediately after parking instead of having to wait half hour for the fumes to clear.
So I have done some tuning, but only to the distributor, nothing to the carb.
I wish the distributor was on the front of the engine like a big block, it a pain in the *** with it at the back of the engine when I'm fiddling with the timing.
Click to expand...
Ok, good info.
The thing I remember when playing with MV is that my engine is worn so the vacuum is not steady, this made the timing jump around as the vacuum pod did not get a smooth vacuum signal.
Im a bit allergic against choppy idle so that really ticked me off against MV.

Though if I understand correctly from the video, this could be adjusted with the vac pod screw? (More tension = less sensitive)

Yeah, what timing light is that? I have to flash the balancer manually.
(Ah wait, he just set it to where it was and showed it to the cam, adjustable.)

For sure, having a big block has its perks. Dist at back sounds no fun.
 
Photon440 said:
Post #24. :)
Click to expand...
Perhaps the correct answer is in responses from #1 thru #214.......its obvious that there us no REAL CORRECT answer only speculation as to why the respond's comment is the correct (?) RESPONSE. We're in serious danger of having the FBBO server explode due to overload......just a casual observation.....??
BOB RENTON
 
There will be instances where MVA will NOT be a benefit....or most commonly......it is set up wrong.......which leads to comments like.......MVA didn't work for me. Post #206 would be an example.
An analogy would be: I replaced the factory cam with one with 40* more duration & now the engine idles really rough, therefore the cam is bad.
If you just move the VA hose from a ported to man vac port.....& do nothing else.....chances are you will have problems.
If the engine is a candidate for MVA, it will work EVERY time. The carb idle cct will also very likely need adjusting.
Here are a few examples where MVA will give problems...& get the blame for 'not working':
- using a non-adj VA unit
- using a VA unit that adds 25+* with an engine that already has 30* of init timing. The 55+* will be too much for the majority of engines & cause rough, erratic idle.
- the VA unit cannot work with the engine's low vacuum; result is varying, erratic timing.
 
Geoff 2 said:
There will be instances where MVA will NOT be a benefit....or most commonly......it is set up wrong.......which leads to comments like.......MVA didn't work for me. Post #206 would be an example.
An analogy would be: I replaced the factory cam with one with 40* more duration & now the engine idles really rough, therefore the cam is bad.
If you just move the VA hose from a ported to man vac port.....& do nothing else.....chances are you will have problems.
If the engine is a candidate for MVA, it will work EVERY time. The carb idle cct will also very likely need adjusting.
Here are a few examples where MVA will give problems...& get the blame for 'not working':
- using a non-adj VA unit
- using a VA unit that adds 25+* with an engine that already has 30* of init timing. The 55+* will be too much for the majority of engines & cause rough, erratic idle.
- the VA unit cannot work with the engine's low vacuum; result is varying, erratic timing.
Click to expand...
Sure, I didnt go full MV. But my engine has 23hg at idle so vacuum is not a problem.
A worn engine is.
 
Jonas,
Your engine is an example of one that will probably get little benefit setting up MVA because with 23" of vac at idle, it must be stock or near stock in configuration [ very mild cam ]. That means the timing for best idle will be MUCH less than an engine that has a longer duration cam/lower idle vac. Still, GM got it right & used MVA with smooth idling production engines, & had 24-26* at idle.
 
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