Should I recurve my DSII or leave it stock? Why?

W

WhitePony

Well-known member
Ok, I keep hearing about people recurving their DSII dizy's. I've read the write-ups on how to do it, but I'm not sure if it's something that I need to worry about during my prep work for the new engine.

I understand basically what recurving does, but I'm not sure if it's appropriate with my configuration. Here's what I'm putting in:

-79 200 Block decked to zero
-FSPP 264 *112 cam
-FSPP (JP Products) dual roller timing set
-ARP fasteners all around
-79 DSII distributer out of a Fairmont with GM module (MSD to come later)
-100amp alternator (Chrome)
-79 D8 head milled to 53cc chambers.
-Holley-Webber 5200 carb on Clifford adapter (I'd love to do a direct mount, but can't find a machine shop locally to mill the intake down)
-Dual out headers (Haven't decided on brand yet) and a clifford port divider.
-T5 (when I find one at a decent price)

So, would it be a waste of time to bother with recurving the dizy for this combo? Or should I wait until everything is back together? I want this install to be as problem free as possible, so I'd like to get all the preliminary stuff done before I'm ready to yank the old engine and drop the new one in.

Thanks,
Kris
 
Kris..I had mine recurved last week. The car idles better and has better response. My understanding is that the Duraspark II were set up for emission system cars and when they are recurved properly the difference is quite noticable. I used Scott at http://www.reincarnation-automotive.com/index.html ...Hope this helps..Michael
 
Kris, you better believe you need to get your distributor curved. Especially since you are using a camshaft which requires more low advance compared to an engine with a stock camshaft.
Also use full vacuum advance at idle on your engine, for it will also perk up your part throttle response.
If you don't feel you can do it yourself, talk to scott @ the wesite Michael refered to. William
 
Howdy Kris and All:

The stock DS II curve will get you bye, but it will not optimize your combination. You can compensate somewhat by adding more initial advance, but that will likely give you too much total at high engine vacuum driving. For example, you're cruising down the freeway at say 3,000 rpm= all mechanical advance is in, your engine is sucking high vacuum= high vacuum advance, and you have the initial set at 16 degrees BTC. You will likely have around 50 degrees of total advance, which may be too much. Not to worry too much though. When you step on the gas to pass that line of trucks, the vacuum will drop and you will be left with only initial and mechanical advance for acceleration/high load.

The recurve should include-
*increasing the rate at which mechanical (centrifugal) advance occurs so that all is in by 2,500 to 3,000 rpms. That involves changing and coordinating the springs and weights under the stator plate in the bottom of the distributor.
*reducing the total amount of vacuum advance, which allows for
*more initial advance.

This process is best done on a Sun Distributor machine and experience helps too. Both are getting more scarce. I pay to have it done and you should too. It will be an investment in getting all you paid for with your new engine.

Adios, David
 
any benefit to doing it for a relatively stock engine?
worked over head (including dual 2bbls), pacemakers and dual exhaust with a T5?

or should i wait till a cam is done?
 
When the emission era distributors started, they went to ported vacuum sources and also ran less initial timing. The effect was a hotter engine that burned cleaner at idle, but NOX emissions increased as a result of the higher combustion temperatures. So EGR became a means to cool the combustion. Some of the “inertâ€￾ exhaust gases were recycled to cool down the combustion temps. But this diluted the intake charge. In order to increase the burn, the timing was advanced again via the vacuum advance. Compared to the distributors of the 60's, the newer distributors had less centrifugal advance and more vacuum advance dialed into the curve.

The engine of the 60's typically ran more initial advance. So when you put on an emissions distributor on a 60’s engine and connect it to a manifold vacuum source, there is too much advance because many emissions era distributors ran on ported source and may have had a larger portion of the total timing devoted to vacuum advance.

Your engine will have a bit lumpier cam. Engines with bigger cams do not expel the exhaust well at lower rpm’s. More ignition advance is needed in these diluted mixtures because the flame front progresses at slower speeds. But your engine also will likely have higher compression ratios than what the emissions era car had, so odds are that an emissions era timing curve will result in some pinging problems that may be hard to overcome without the performance suffering drastically. I had such a problem on an old Pontiac that was a mix of parts. I finally scrapped the HEI distributor and put in a points distributor. I probably just should have had someone recurve the HEI.
Doug
 
Well, that was easy. Scott at Reincarnation-Automotive seems really easy to work with. My recurved dizy will be here next week.

I was supprised at all the questions that he asked to get the right curve.

-Car weight
-Final drive gearing
-Cam profile
-Carb type and rated CFM
 
Kris, you will be very satisfied with the performance increase from the distributor modifications.
I have 12 degrees distributor advance X 2 = 24 total centrifugal all in by 2800 rpm's + 14 initial = 38 total advance at full throttle, plus my vacuum advance for idle & light load or part throttle. I have the same cam as you but with 1.65 rocker arms & with a direct mount 500 holley. The throttle response is very crisp & total drivability is great. You will be amazed when you get it all together over the stock carb & old head. William
 
I am about to have my Duraspark distributor spun in a Sun machine. It's being run in a drag race 200 engine in a '72 Maverick. I bought the car in its current state and have no idea what the curve is. Step 1; establish the baseline. Step 2; re-curve if necessary. Does anyone have any experience with this application? This is an automatic car, 4000 stall converter, 4.62 gear and 26" tire. The Maverick weighs 2600 lb.
 
what's done to the engine?

and does anyone have any comments on the stock cam engine?

Me":k9nc0qxb said:
any benefit to doing it for a relatively stock engine?
worked over head (including dual 2bbls), pacemakers and dual exhaust with a T5?

or should i wait till a cam is done?
Click to expand...
 
ok
addo":4q0l921n said:
Yes, the car would probably benefit a little.

You'll be shifting more with the 5 speeds. Depends on the overall health of the motor, though.

Gee, I'd better get onto my assignment. It hasn't done itself... :lol:
Click to expand...

so, here's another question, would it need to be recurved once it was built up more?
i'm assuming so...
 
Well, I finished the assignment and gave a photocopy to one of the less mathematically inclined guys there... He compared my answers to his, then gave the photocopy to the worst student in our class! Not good, as that fellow will just plagiarise it. :roll:

Onto the dizzy: Yes, you'll have to re-recurve. No big deal; nothing gets broken.
 
You must log in or register to reply here.

Similar threads

W
Parts are accumulating! The build is near!
2
Replies
22
Views
5K
WhitePony
W
W
MSD: Does it really make a noticeable difference?
Replies
12
Views
3K
66Sprint6
66Sprint6
Back
Top