Joined: Tue Mar 12 2013, 11:31AM
Location: Germany
Posts: 70
I ordered mr. gasket springs for my distributor and paln to buy a FBO limiter plate (maybe also with springs?). my engine is a 74 400 cui. questions are: what initial timing should I set? what total timing should it have? how do I identify the springs (heavy or light) and which should I change (I know it's a bit trial and error) does somebody already use the FBO limiter plate?
I want some acceleration from idle on. now full advance is at 3000 rpm? and it should be around 2400? I want to use the plate because (aso you might now) I plan to buy new heads and a new cam later. so I can change the degree easier when I do that.
Joined: Wed Mar 23 2011, 08:03PM
Location: 60048
Posts: 33
A stock 74 400cid would have low compression, so a fast advance curve would be beneficial, on my 74 440 I use 16 initial with 18 advance, so a total of 34 degrees.
Joined: Tue Mar 12 2013, 11:31AM
Location: Germany
Posts: 70
@gregcon I was told that the mr. gasket springs are really "too" light. but that's what I would want with my low compression engine. @eberg I'll try that as a starting point. did you change your springs?
and when I later use edelbrock 5090 heads (which would cause around 9.2:1 compression) should I change the timings?
Here is a great article on modifying a mopar dist. The plates have different degrees with the numbers stamped right on the plate and you may have to braze a bit and then file it smooth. I've done this plenty of times. Also the vacuum advance canisters were stamped with a number on the arm and you may want to look into this also. Check your bushings in the dist. for wear as a worn dist bushing is bad news.
You also could try one of the lighter springs in the kit and try it with the lighter of the two stock springs. Some were the same but some dist. had a light and heavy one.
Joined: Tue Mar 12 2013, 11:31AM
Location: Germany
Posts: 70
that is a very good article. interesting to read. so I get 34-38 degrees of total. now the inital is a bit of iritating to me. everybody says something different. the article says 5, eberg says 16 (with a different engine) and somebody else said I should use a vacuum gauge and set the inital to maximum vacuum at the manifold. what should I do?
Joined: Sun Mar 28 2010, 10:07PM
Location: DFW, TX
Posts: 39
For what your 400 might need, use what the middle 60s 383 2bbls used. 12.5 degrees initial and what mechanical that was in the distributor usually made it about 36-38 degrees total. This was with the closed chamber factory heads on the 2bbl 383s. On that engine and those heads, you could adjust the idle speed with the distributor timing, but with the 906s on my '70 Monaco 383 4bbl "N" motor, adding additional idle timing made no real difference in the idle speed.
When idle emissions became important, the initial timing spec went down to about 5 degrees BTDC, but the rest of the 36+ degrees total was made up for in the distributor. Look at the '70 383 4bbl "N" motor's distributor specs for that.
The Mr. Gasket springs might be for "race only", but that's all. The old Direct Connection Race Manual said to just remove the heavy spring and let the light spring control the advance weights.
NOW, unless you've now got a deeper than 3.23 rear axle ratio, you might desire to delay total advance until about 3500 rpm, even with race gas, regardless of compression ratio, too. Getting it in too soon could cause it to clatter, which is not good, at WOT and lower rpms. It'd be better to get your driving techniques finessed than to have a "full race advance curve" in the distributor on a street car. Keep the vacuum advance in the distributor, too.
You'll learn to respect E-berg's advice and knowledge. HE is one of the ONEs to listen to.