68GTconvert
Well-Known Member
I always hear about Distributor Recurving. I am not really sure what this does. Can someone explain what benefits you get from doing this? Should I get it done for my electronic igintion distributor?
Distributor Recurving?
- Thread starter 68GTconvert
- Start date
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jaimus
Old School ASE Gold
x2,...????
I believe these were posted some time ago by abodyjoe. It's an excellent read. You can save these images to a file on your computer for future reference.
Right click on them and "save as" to a file for future use.
Right click on them and "save as" to a file for future use.
Coronet 500
Well-Known Member
Mad Dart
Nothing to see Here!
Sent you a PM. I have one brand new set up Phased and Re-Curved for the 402.
68GTconvert
Well-Known Member
67Dart273
Well-Known Member
The simple things about distributor curve
You have initial timing, what you set with a light at idle
You have mechanical advance
You have vacuum advance
You add them all up for TOTAL timing, IE
10* + 23* = 34 initial and mechanical
plus
say 15* vacuum at highway cruise, light throttle = 49 total
Many talk of total and leave off the vacuum because they do not run vacuum, and the initial + mechanical is the "foot on the floor" figure, because vacuum is not "in" with heavy throttle
CURVE is this:
The springs --- how heavy as well as the "slack" (some springs) that allow some movement against the heavy spring, I.E. sometimes a light spring that allows lower RPM movement, up against the "slack" in the heavy spring, which requires a lot more RPM to move the heavy spring.
The above is illustrated better at the webpage posted below. Go towards the bottom of the page, the photo of the various springs. NOTE the slightly longer, heavier springs. These are what I was referring to, allow the weights to move "so far" in the "slack" of the longer heavier springs
http://users.erols.com/mathewg/Dist.html
(The above would be a typical stock application)
So "recurve" springs are lighter, and often one OR BOTH springs are left out. Back in the "points" days, some of us used to run with NO springs. The friction of the points drags the weights to retard for starting, and as soon as the engine starts, you have full mechanical advance.
Springs, then, affect the RATE of the mechanical advance Several race parts outfits, Summit, Jegs, Mopar Performance, etc, sell "spring kits" with a selection of springs. You just have to fiddle with them until you get what you want.
SLOTS. The LENGTH of the slot determines the AMOUNT OF DEGREES, which for a performance / street dist. is usually between 18-22* or so. Factory ones -- especially smoggers -- can be much much LONGER, so if you try to run a stock smog dist. at more INITIAL timing, you may end up OVER advancing at the top end, because there is simply too much advance in the distributor
So you have to braze up the ENDS of the slots and file them back to what you want (trial and error) to get the AMOUNT OF DEGREES you want. This is made much easier with the use of a distributor machine.
ALSO be aware that some people talk of DISTRIBUTOR degrees while others talk of CRANK degrees. Crank degrees are double dist. degrees. Here for example is a chart I found "at that other place" and this shows slot length versus DIST degrees. So for say, 20* at the crank you will want to use the 10* figure in the chart
Modifying advance slots
degrees / slot size
6.............. .340
7................355
8................375
9................390
10...............405
11.5 ...........420
12...............435
13...............445
14...............460
15...............475
16...............490
17...............505
18...............520
Here is a good example of a factory setup, 67 426 Hemi, right out of the factory manual. NOTE that these figures are in DISTRIBUTOR degrees
If you take the left column, go down towards the bottom, TIMING says 12.5BTC, so this is your INITIAL IDLE setting
Now up towards the top see "Advance--Centrifugal (Distributor) it says "7.5 to 9.5 @ 1400 RPM. THIS MEANS you get 19* AT THE CRANK (9.5 x 2).
(You can also see in this chart how RPM affects the mechanical advance, at different RPMs the SPRINGS are controlling this function)
Go down further and see Advance -- Vacuum (Distributor...shows a max. of 11*, this again is 11 X 2 for 22 CRANK degrees
So you add 12.5 and 19 (mechanical) so with your foot on the floor, the advance will be 31.5*, and I'm sure many of these could have used a little more initial back then
And then for cruise, you add the vacuum of 22* for 43.5* total.
see? easy.
You have initial timing, what you set with a light at idle
You have mechanical advance
You have vacuum advance
You add them all up for TOTAL timing, IE
10* + 23* = 34 initial and mechanical
plus
say 15* vacuum at highway cruise, light throttle = 49 total
Many talk of total and leave off the vacuum because they do not run vacuum, and the initial + mechanical is the "foot on the floor" figure, because vacuum is not "in" with heavy throttle
CURVE is this:
The springs --- how heavy as well as the "slack" (some springs) that allow some movement against the heavy spring, I.E. sometimes a light spring that allows lower RPM movement, up against the "slack" in the heavy spring, which requires a lot more RPM to move the heavy spring.
The above is illustrated better at the webpage posted below. Go towards the bottom of the page, the photo of the various springs. NOTE the slightly longer, heavier springs. These are what I was referring to, allow the weights to move "so far" in the "slack" of the longer heavier springs
http://users.erols.com/mathewg/Dist.html
(The above would be a typical stock application)
So "recurve" springs are lighter, and often one OR BOTH springs are left out. Back in the "points" days, some of us used to run with NO springs. The friction of the points drags the weights to retard for starting, and as soon as the engine starts, you have full mechanical advance.
Springs, then, affect the RATE of the mechanical advance Several race parts outfits, Summit, Jegs, Mopar Performance, etc, sell "spring kits" with a selection of springs. You just have to fiddle with them until you get what you want.
SLOTS. The LENGTH of the slot determines the AMOUNT OF DEGREES, which for a performance / street dist. is usually between 18-22* or so. Factory ones -- especially smoggers -- can be much much LONGER, so if you try to run a stock smog dist. at more INITIAL timing, you may end up OVER advancing at the top end, because there is simply too much advance in the distributor
So you have to braze up the ENDS of the slots and file them back to what you want (trial and error) to get the AMOUNT OF DEGREES you want. This is made much easier with the use of a distributor machine.
ALSO be aware that some people talk of DISTRIBUTOR degrees while others talk of CRANK degrees. Crank degrees are double dist. degrees. Here for example is a chart I found "at that other place" and this shows slot length versus DIST degrees. So for say, 20* at the crank you will want to use the 10* figure in the chart
Modifying advance slots
degrees / slot size
6.............. .340
7................355
8................375
9................390
10...............405
11.5 ...........420
12...............435
13...............445
14...............460
15...............475
16...............490
17...............505
18...............520
Here is a good example of a factory setup, 67 426 Hemi, right out of the factory manual. NOTE that these figures are in DISTRIBUTOR degrees
If you take the left column, go down towards the bottom, TIMING says 12.5BTC, so this is your INITIAL IDLE setting
Now up towards the top see "Advance--Centrifugal (Distributor) it says "7.5 to 9.5 @ 1400 RPM. THIS MEANS you get 19* AT THE CRANK (9.5 x 2).
(You can also see in this chart how RPM affects the mechanical advance, at different RPMs the SPRINGS are controlling this function)
Go down further and see Advance -- Vacuum (Distributor...shows a max. of 11*, this again is 11 X 2 for 22 CRANK degrees
So you add 12.5 and 19 (mechanical) so with your foot on the floor, the advance will be 31.5*, and I'm sure many of these could have used a little more initial back then
And then for cruise, you add the vacuum of 22* for 43.5* total.
see? easy.
67Dart273
Well-Known Member
The point is if you are RECURVING it having a dimension to work towards makes it a hell of a lot easier
Snake
Mopar Nut
I took my dizzy in to my engine builder and told him I want to get up to 20 at idle and 14 mechanical,total 34 no vacuum advance. He had to weld up the slots.Also I bought the Mr Gasket springs for a faster advance,my 360 screamsssssssssssssss,no pinging nothing.So yes there are big advantages to this mod.
SleeperScamp
Well-Known Member
Subscribed..
67Dart273
Well-Known Member
...Heh... I cheated. One of the guys on here sold me a "stock look alike" Accel which has ADJUSTABLE mechanical weights, actually an adaptation of the old Mallory Y? series. So it takes all factory parts, pickup, reluctor, but has adjustable mechanical with no welding.
For the life of me, I cannot remember who I bought it from, Rumble or Adam, one, I think
If you are going to weld up the advance plate you can do it either on the inside or outside of the slots. The inner fill puts more tension on the springs and may slow it down a bit on advancing. Outside it will come in quicker. Just food for thought.
Here is a guy that makes a spring selection for recurving Mopar distributors. I purchased a set from him a few years ago to solve an early mechanical advance problem on a tarted up slant six. His parts are first rate, and he includes a graph showing advance characteristics of each spring.
http://www.slantsix.org/forum/viewtopic.php?t=46266
http://www.slantsix.org/forum/viewtopic.php?t=46266
stroker402
1968 dart GTS convertible
I don't mean to hijack your post .... sorry !
I just got done recurving my single point distributor for my 273 .. put a 8* slotted plate in and it had already two light oem springs in it.. Got it all timed in 18* intial and between 34-36 total*and when I hook the vac line up to the dist it will won't stay running smooth and when you give it some gas it fights itself bucking up and down on the throttle.. the when I disconnect the vac line it runs fine.. must be a faulty vac. canister right ? it's a 9.5 diaphram .
I'm not going to run the vac. adv. anyway But...just like to know .
other wise... It maid a biggggg difference overall .
I have a pertronix III coming to install into it with built in rev limiter.
I just got done recurving my single point distributor for my 273 .. put a 8* slotted plate in and it had already two light oem springs in it.. Got it all timed in 18* intial and between 34-36 total*and when I hook the vac line up to the dist it will won't stay running smooth and when you give it some gas it fights itself bucking up and down on the throttle.. the when I disconnect the vac line it runs fine.. must be a faulty vac. canister right ? it's a 9.5 diaphram .
I'm not going to run the vac. adv. anyway But...just like to know .
other wise... It maid a biggggg difference overall .
I have a pertronix III coming to install into it with built in rev limiter.
stroker402
1968 dart GTS convertible
yep.......... hooked up to the carb .. front lower port on stock 273 charger afb 500
stroker402
1968 dart GTS convertible
My pertronix ignitor III and flame thrower II coil came today and installed it .. works Great!! .. this unit has a rev limiter built right into it.. worked like a charm!
I rebuilt the mopar single point dist with a 8* slotted plate and two oem light springs..
Boy.......... does this engine rev fast now and has waaaay more torque just cruising and I can go around a corner now in 4th gear without even a little buck..
What a difference !
I rebuilt the mopar single point dist with a 8* slotted plate and two oem light springs..
Boy.......... does this engine rev fast now and has waaaay more torque just cruising and I can go around a corner now in 4th gear without even a little buck..
What a difference !
stroker402
1968 dart GTS convertible
OK .........
update ...
installed another vacumn canister 9.5 and it works fine .. no more cutting out.
update ...
installed another vacumn canister 9.5 and it works fine .. no more cutting out.
Rice Nuker
Let the Coal Roll!
Interesting thread!
stroker402
1968 dart GTS convertible
update
after playing around with the curve in the 273 HP and setting the timing , I tried setting the total timing at 36* and appears this stock 273 hp does not like that much timing .luggish ! backed it back down to 34 total with a curved distributor at 18* inital and runs really strong there. haven't tried anything lower yet with timing. pertronix III ignitor in the dist.stock afb 500
loves to fry the tires at a roll.:happy2::burnout::burnout: and it pulls really hard in third gear too . big top end pull . (4 sp. dartcharger ). 3.55 gear.
Love this car !! sleeper !!
after playing around with the curve in the 273 HP and setting the timing , I tried setting the total timing at 36* and appears this stock 273 hp does not like that much timing .luggish ! backed it back down to 34 total with a curved distributor at 18* inital and runs really strong there. haven't tried anything lower yet with timing. pertronix III ignitor in the dist.stock afb 500
loves to fry the tires at a roll.:happy2::burnout::burnout: and it pulls really hard in third gear too . big top end pull . (4 sp. dartcharger ). 3.55 gear.
Love this car !! sleeper !!
discharger1332
Well-Known Member
interesting
Saetun,in Nor-Cal has a line on a guy,with a Sun dist recurve machine.PM him,takes all the guesswork out of it.
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