hi everyone, i hope i’m posting this in the right spot i have a 1957 f600 with the original 272 stock motor (rebuilt) and i put an hei distributor on it a buddy had one new and he gave it to me. so i put it on set it to 10 deg my truck shop manual said attached the vacuum advance (to manifold has original holley 2300 on it and no ports on the base) and at idle it jumps to 30 deg advanced is this right? or even safe for that matter? common sense tells me no but i’m not sure how the vacuum advance should work it’s my first y block and the original distributor that was in it was original to the motor and it was mechanical only i don’t want to run it until i find out if this is right or not. it idles great so but it just didn’t seem right. oh also there is a port on the upper left (looking at the front of the carb) that has a 1/8” npt brass plug screwed into it is this a vacuum port by any chance? any help would be appreciated. thanks

If it is a mechanical and vacuum advance distributor and the vacuum portion it's hooked to manifold vacuum, then that is about right.  You will get full vacuum advance at idle and that will be added to the initial.  It should not be a problem. 
Many vacuum advance mechanisms are adjustable.  If you get detonation, first verify that it is the vacuum advance by driving with it disconnected and the port plugged, then pull some timing out of it.  If it is "hei" then it is aftermarket and probably is adjustable.
You should have also noticed the idle rpm increase.  Adjust that back to where you want it and make sure the mixture screws are still adjusted well.


Lawrenceville, GA

it is mechanical and vacuum and yep the idle speed did increase when it was attached. i will take it for a drive and see what it sounds like thank you so much for the info and quick response a huge help!!

Some people prefer to connect a distributor for full advance advance at idle. There's no load on the engine, and fuel mixtures are relatively lean. Lots of advance at idle helps the engine run efficiently and cooler. The only thing, a 2300 should have a "ported" distributor connection iirc. If you set the idle high, it will start to pull in vacuum though. No worries.

10° BTDC is about right for initial, but it's important to check where the mechanical only advance tops out at.

Disconnect and plug the vaccum advance port. Then (be careful, stay out of the plane of the fan!) rev up the motor to 2k to 3k+ and see where the timing pointer ends up with a timing light. Make sure it's done advancing all the way.

Y Blocks are like many V8, 36° BTDC or even a bit more is optimal. May need to mark the lines with chalk. Test drive with the vacuum advance still disconnected and plugged. Advance the distributor more if there is no rattle on hard acceleration, back it off slightly if there is.

Then re-connect vacuum advance and test drive again. Start with the vacuum can at full advance and back off 2 turns at a time. Check for part throttle ping or knock. Only adjust the vacuum advance, don't go back in and make adjustments at this point to the distributor. This will put the ignition curve right where it should be.

Gentlemen,

Below are my thoughts only as I do not wish to get into the ported/manifold vacuum debate/argument-

IMO

Jbrake57 POSTED-

" i have a 1957 f600 with the original 272 stock motor (rebuilt) and i put an hei distributor on it a buddy had one new and he gave it to me. so i put it on set it to 10 deg my truck shop manual said attached the vacuum advance (to manifold has original holley 2300 on it and no ports on the base) and at idle it jumps to 30 deg advanced is this right? or even safe for that matter? common sense tells me no but i’m not sure how the vacuum advance should work it’s my first y block and the original distributor that was in it was original to the motor and it was mechanical only i don’t want to run it until i find out if this is right or not. it idles great so but it just didn’t seem right. oh also there is a port on the upper left (looking at the front of the carb) that has a 1/8” npt brass plug screwed into it is this a vacuum port by any chance?"

Your 272 (if rebuilt to original specs), is either a 272 MD or HD and the mechanical only distributor was governed to not allow the engine to over speed. This engine is LOW TORQUE (1900-2400RPM) and is not designed/assembled for high RPM.

If this is a work truck, I would source the PASS CAR DIST to ported vacuum and watch my RPM's as it will want to over-rev without the governor feature. The threaded plug you see on the RS metering block (H2300) is the source for ported vacuum.

If you check your SHOP MANUAL, you will see where this is too much IGN lead for the engine.

PASS CAR H2300 shown-

____________________________

Yeah, I read the OP again, engine is actually connected direct to manifold and not to the port on the carburetor.

A (heavy) truck will certainly tolerate less lead than a lighter car or truck. Does anybody have the ignition specs from the manual? Then we don't have to guess.

The specs are one thing but we all know that the optimum tune is usually found by deviating by some degree from the factory specs.  The manual will also be in regard to the factory distributor, which is not being used here.  Mix and matched parts are being used.  This means that attention needs to be paid to how the engine runs and adjustments need to be made as necessary.  There will be no by the book spec since the engine and possibly even usage of the truck itself is not by the book.


Lawrenceville, GA

i thought that was a vacuum port the holley tech i emailed said it wouldnt be because it was threaded 🙄 i’m just comming here first from now on lol so first things first i check the total with vacuum disconnected, if all is good then reconnect and connect it to ported to try that. now i guess another question if it does fine with just mechanical can i just leave the vacuum canister unplugged?

You can leave it unplugged.  The vacuum advance on that distributor is an economy feature and is not critical to the operation of the engine,


Lawrenceville, GA

There are three advance "stages" to sort out.....
(1) Initial setting - stocker cams like about 10º
(2) Mechanical / Centrifugal - this summed with the initial should be on the order of 36º. This would be the upper limit the heads / compression ratio / octane mix will tolerate at wide open throttle. So you adjust the mechanical to stop advancing at 36º- 10º so you will need 26º at the crank. The distributor is running at 1/2 crank speed so the distributor will need to get 13º. Without directions for the distributor - you are going to have to try it out and see what you have by reading the crank degrees.
(3) Vacuum - The vacuum pot may or may not be adjustable..... but it sums onto the initial + mechanical based on manifold vacuum. This implies a mostly closed or partial throttle condition. On mine - a pretty stock set-up, I have the vacuum limited to 7º. So maximum at cruise is 10+26+7=43º

At idle - the type of vacuum source becomes important to your set-up. If the source is "ported" - no vacuum applied to the distributor pot - you would see the initial setting of 10º until the throttle is cracked. I can tell you - you won't see the best engine idle vacuum at this setting. So many go in and set the initial at a higher value to make the engine happy - but you must obey the upper limit of 36º to avoid detonation elsewhere in the rpm range. Lets say that testing shows best idle vacuum is at an initial 16º - you must then readjust the stops to only add 20º at full mechanical advance. The vacuum advance must then be set pretty "tight" or as the throttle opens, the engine is going to want to go pretty lean. As an alternative - I use this and several others do as well - I use the initial setting of 10º and hook the vacuum pot to live manifold vacuum. On my outfit, the pot is set to stop at 7º and at idle the timing light shows 17º at the crank. The 17º nets the best idle vacuum on my engine set-up and the 10º initial makes it start really nice.

I would suggest doing some experimenting with the "unknown" distributor to find out what its adjustment capabilities really are. You are going to want a timing tape on the damper and a timing light and a vacuum gauge and a tachometer. And in fairly short order - you will have the info to make a good judgement of what to do next.




 
 Steve Metzger       Tucson, Arizona