ImBatman

I didn't want to high jack 2th farmers thread but I wanted some clearification on distributor setup. Someone in 2th farmer's origional post suggested to go to the lightest advance spring and the largest bushing to allow all advance to come in almost imediately. Does this hold true across the board for non daily driven weekend hot rods like mine? Should I do this on a new motor break in or wait till I break in the cam then make the change?

There was also mention of gapping the plugs to .045 is this also a recommended practice?


IGNITION COMES IN TODAY!!!!!!

Thanks

luerja

I'm waiting on an answer for that too? mostly about plug gaps

OK I have read on the MSD site that Plug gaps are to be .10 to .15 more then the standard... I think my plugs are gapped at .35 and will tweak them up to .45 and see how it works.

MsVetteMan

Black rat.....I don't think I'm running the hp you are (I'm 400hp), but I had to go to the stiffest springs to get mine to run worth a crap. Tried all the lighter combo's, they would NOT work very well....no power. Did not change the stock bushing. For what it's worth......

Also gapped at .045.......

Fevre

There is a chart with graphs showing the dist curve with each combo of bushings and springs, been a while but I think I choose the 14 int and all in at 2800 rpm's curve and it works great

2th farmer

I gapped my plugs at .045 but unsure about the spring issue. Keep the info. coming.

gkull

The whole idea behind light springs and very fast advance curve comes from the days of smog motors. Do to low compression, EGR, and low initial timing hot rodder figured out how to get some performance back.

Modern real hot rods with compression and modern chamber designs require slow advance to keep them out of detonation. I run dist. with all in at 3000 or 3200 rpm. I limit my curve to say 16 degrees total mechanical advance with 16 initial to add up to 32 degrees which is what modern heads like.

I now have a MSD electronic dist my choices are 15 or 20 degrees advance and all in at 3000. So I can very the inititial to get the best idle and manifold vacuum.

enkeivette

I think my plugs are at .042 and with my MSD HEI I'm using the two blue springs with the black 18 degree bushing, 18 degrees initial in at about 2500 rpm for 36 total. There is actually a stumble below 3K at WOT that wasn't there before with the 21 degree bushing and 15 degrees initial. I'm going to richen up the squirter nozzles but if that doesn't help I'll go back to the 21 degree bushing and 15 initial.

Older Than Dirt

That's interesting....the stiffest springs are the heavy silver ones (the slowest curve). The MSD's come with the blue 21 degree bushing installed. If you were looking for 36 degrees total then your inital timing would be set at 15 degrees. The odd thing here is by using the heavy silver springs your total advance doesn't peak until about 4000 rpm. Not exactly recognized as a performance curve.

2th farmer

Not sure about any of that spring stuff but DAMN! My car is now STRONG!!! I'll be wearing my "FREE" MSD shirt tomorrow, they are the shiznit!

ImBatman

K switching gears here a little. Where is the #1 post supposed to be on an MSD cap? I have the motor set at 8 degrees btdc and am ready to set the distributor in. Is there a defined #1 tower location or can I drop the distributor in with the rotor pointing at the #1 cylinder? I know that I need to position it where I have clearence for the vac advance canister. So how should it be positioned?

Thanks

big_G

I installed my new MSD tach drive dist last week, and was able to point the rotor at # 1 plug general location, this gave good clearance for the vacuum can with 18 deg. initial advance.....

MsVetteMan

I'm not quite getting 36* in. Still easing into this motor............but, for some reason, with an initial 16*, she likes the heavy silver springs. I have to run thru the springs again, as I has a cluster yesterday while making some swaps......pinched the wire inside the distrib. on the cap........

I'm thinking one heavy, one blue........probably will put me right on the money.......

427Hotrod

I'm the one that started all this. It all depends....you've heard that one before right?

GKull is right..new stuff with fast burning chambers don't need lots of timing. But old stuff...like just about any bigblock...and stuff with pretty healthy cams are different. You end up in the 36-40* range usually. The new AFR big block heads seem happy around 32-34* total. Mine likes 39*.

BIG motors are different. I usually aim for as much initial as I can get by with to get good throttle response. My 427 was happy with 22-24* initial at idle (no vacuum, 40* total). That same dist in the 540 felt very lazy. I ended up re-doing it to allow 31* at idle and only have 8* centrifugal. I did that by welding up the slot and tuning the advance amount and by playing with springs to get it in where I wanted it. I also limited vacuum advance to only 6* more degrees.

I have the MSD in it now...and am just using the large bushing and light springs and no vacuum advance. The one that comes on it adds a ton and my motor won't take that much at light throttle.

The biggest bushing still doesn't allow me to get initial as high as I like....but I'm close.

You just have to try stuff, but large cams have lower cylinder pressure at low speeds and bigger bores have slower burning chambers..so a little more low speed advance helps a lot. Just don't forget to keep an eye on the total advance. As you add initial, you ahve to make sure total doesn't get out the window. What you add on one side, you have to take away on the other..all things being equal.


JIM

BDVT69

I went with one blue and one heavy silver spring on my 454.

ImBatman

Ok I am thoroughly confused now but getting better I amgoing to drop the distributor in today as is from MSD to establish a base line. Then after cam breakin I will start tinkering with it. I wil have to admit I am still a liittle confused by initial, centrifugal, total, vaccum etc etc advance.

I have the balancer at 8* btdc so it this 8* initial?

Once the car is running I want to advance the distributor as far as possible till just before ping and at highest engine vaccum?

This gives me my total advance?

Adjustments should be made with vaccum advance disconnected correct?

Then my total timimg at say 2800 would be what I advanced with vac disconnected + what comes in with VAC connected at the desired RPM of 2800?

Am I at leeast in the ball park of under standing????

Thanks

427Hotrod

Yes...whatever you are reading on the balancer is INITIAL. That is measured with no vacuum advance.

Then you rev motor (still no vacuum) and observe timing as it advances. You need a dial back timing light or a degreed balancer to know how much it's moving. You will rev motor and check timing at a point above where it stops advancing. So if you have the heaviest springs in there and they keep it from maxing out until 4000 rpm...you have to rev engine to 4000+ rpm and watch timing marks, BE CAREFUL here...watch that fan!! But it's the only way of knowing exactly what's going on in YOUR motor.

What you see at 4000 rpm is TOTAL advance. If you had it set at 8* INITIAL..and at 4000 rpm you saw 32* total...then that means it added 24* CENTRIFUGAL advance with the weights etc to the initial 8* setting.

If you wanted 36* TOTAL....then all you need to do is advance the INITIAL to 12* and recheck. You need to recheck to make sure..wrong timing can cause all sorts of issues from poor driveabilty...low power, overheating and engine damage.

When we change the bushings around inside, we usually install a LARGER one. This LIMITS the amount of CENTRIFUGAL that gets added to the INITIAL. You do this so you can run more initial, which usually adds throttle response and cooler temps.

So let's say we added a larger bushing that only allows 18* centrifugal instead of the one that was in it that allowed 24*. In that case, we could bump INITIAL timing all the way up to 18* and still have only 36* TOTAL.

Hopefully all of this makes sense.

Usually you want as much INITIAL as you can get by with while keeping the TOTAL in the area that doesn't ping under full throttle. But understand that real life best TOTAL timing will often be lower than it liked on say a chassis or engine dyno. It will usually be somewaht less. Old style BBC heads usually like 36-40* or so TOTAL. But that is all based on compression/cam/temps and gas available. You just have to try it and see.

Sometimes you need to add different springs to get the advance CURVE where you don't have any issues with pinging under light throttle. Gearing and HP and car weight play in here. The CURVE is how fast it ramps up. A heavy car without much gear and an auto can't stand as quick of a curve. A lighter car, or a stick shift with some gear can stand a lot more. It doesn't stay under load as much. So if you get some pinging while riding around you can change springs to heavier ones to keep timing lower until engine builds some RPM. But if it was able to pull in high gear with no pinging at say 36*..then you still want to keep that figure static. Don't back off TOTAL timing by backing the INITIAL down...remember...what you do with one...affects the other. The CENTRIFUGAL is still added to whatever INITIAL you set.

You can install a bushing that allows a little more CENTRIFUGAL advance. This allows you to back off INITIAL to say 10*...but still have 36* total.

When you're all done with this stuff....you start playing with VACUUM advance. This is a big help with light throttle and fuel economy driveability. It help keep engine cool at low speeds and cleans up idle. Usually best if you have it hooked to a full vacuum source. But you have to understand that there are LOTS of different vacuum cans out there. They all have different characteristics. The MSD one adds a lot of advance. I think some of them add 15* more! Hook it up and check how much it adds at idle.

The problem can be that after you set TOTAL advance...and let's say you use the lightest springs to get all advance in by 2800rpm or so. Then you are going down the road at 3000 rpm..the TOTAL is already at 36* because that's where you set it...now you throw some VACUUM advance on top of it. You now have 51* under light throttle cruise conditions. Many engines will take that..but some won't. If it's too high you will notice it feeling like it's "skipping" or missing while riding around.

They make adjustable vacuum advance cans (FORD used them from the factory..you use an Allen wrench up inside the nipple to limit it) where you can limit it all.

So in reality..you have INITIAL....and at idle you will add whatever vacuum to it. If you set it to 10*..and added 15*..then you would be idling at 25*. That could be fine probably. It will keep idle clean. BUT..remember...as soon as you open throttle and vacuum drops...the vacuum advance goes with it. If you rely on lots of vacuum advance at low speeds. your real throttle response will likely be much poorer.

So there you were idling at 25*...10* INITIAL plus 15* VACUUM.....then you stomp your foot in it and the VACUUM drops to zero and timing goes back to 10* for an instant..maybe no big deal because now the RPM's are climbing and the CENTRIFUGAL is beginning to add timing back in. RPM's climb and eventually you hit the RPM where springs have allowed all the CENTRIFUGAL to be added (based on that bushing)...and you end up with that 36* TOTAL that we set it all at. The VACUUM is NOT added anywhere here...because your foot is on the floor and there is only 1" or so vacuum in the intake..not enough to activate the VACUUM system.

When you let out of it..VACUUM will go real high, and the advance will be added back in....but it's no problem because you're coasting to pick up your time slip at the timing tower!!


Hopefully all of this helps a little. As you can see....it really does 'depend" on lots of stuff. You can see why there are specific timing curves from the factory for various engines and drivetrains as well as options. Things like A/C., automatics, gearing, etc change the load on the engine and they had to change the curve around to keep engine happy. Higher HP motors have larger cams usually that bleed off low rpm cylinder pressure, but they also have higher compression to try and make up for it. They juggle things around there to add some better low speed response to help with big cam, yet still limit it enough to keep it out of detonation at high rpms.

Race car stuff doesn't care about Vaccum advance..in fact the old 283/270 hp Vette's came without it too. They had a pretty basic Hot Rod style timing curve in them from the factory!

JIM

ImBatman

Thanks Jim that info is GREAT!! I appreciate you taking the time.

Wade

7t2vette

Set initial timing to 15 degrees, then use the 2 blue springs and the blue 21 degree bushing to bring in 36 degrees total timing at around 3000 rpm. This is a general rule of thumb for small blocks. Plug gap with an MSD ignition depends on your CR; I have 10.75:1 CR and use a 0.45 gap. All of this information is in the instructions that comes with the distributor and ignition box.

BrentDev

Jim / 427 Hot Rod -

Thanks! That is a very articulate, understandable explanation about the various timing types. I knew there were different types, but I never could have been able to explain it.

Now I understand it pretty well.

Great write-up. Right click, save as......