Distributor Recurve starting point

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72SwingerJosh

72SwingerJosh

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Im looking to recurve my distributor and have ordered the FBO plate and springs. I was looking for a good place to start at and was told 20* initial and use the 14 slot on disk to get a total of 35* and use springs to get it all in at 3400 rpm and also with vacuum from manifold for a constant 30* at idle and to set idle around 900rpm. Here are my specs for my build.

-340 stroked to 416
-Lunati Voodoo Cam 10200704 with advertised 276/284
duration at .050 is 234/242
Gross lift .513/.533
LSA/ICL 110/106 with rpm range 2200-6400
-compression 9.9-1
-750 street demon carburetor
- .039 quench
-RHS Indy LAX heads with 2.055 intake valves light bowl clean up
-rpm air gap intake manifold
-3.55 gears
-TCI street fighter 3000 stall torque converter
-340 HP exhaust manifolds
- 727 transmission with 2.45 first gear ratio
- HEI conversion with petronics flame thrower III module and flame thrower III coil .32
Ohms

My goal is to have a fun street car that runs good and isn't a chore to drive. I hope it is and will be putting the motor in it soon and figured I should recurve distributor and fine tune it after the break in. Any thoughts and suggestions will be appreciated. Thanks.
 
I'm quotting from another of my posts here. But this is the procedure I use to set initial and total timing.

Ideally you want to setup for initial timing first. The best way (to me) to do this. Is to get the distributor (not a dizzy) in and hookup a vacuum gauge (manifold vacuum). Make sure the vacuum advance is NOT connected for any of this. Set the idle where you want it, say 750 rpm. And MAKE SURE your carb is setup properly, t-port sync, no vac leaks and such. Or the carb can up the RPM on its own, causing confusion about whether the initial timing is increasing RPM or the carb is. Then start with something conservative. Say 10 degrees. Slowly bring the initial up. If the RPM and vac goes up. Keep going, making sure to reset the idle to your start idle with every adjustment. If you don't bring the idle back down. Then of course the vac gauge will read high. So resetting the idle is very important. You also want to make sure you aren't getting into the mechanical advance on the distributor. Some distributors can start their mechanical advance at 1000 RPM or less. If you are into the advance, it will screw up your initial timing. If you have to. Lock the mechanical advance out so you can get a proper reading. Once you hit max vac on the vac gauge. Back it down 1-2 degrees. Lock it down. Remember your initial timing.

Next step? Hot start. By now the engine should be very hot. Shut the engine off. Leave it for five minutes. Start it again. If it fires right up. You should be ok. Let it run for a few minutes again. Then shut it off again. Leave it for ten minutes. Start it again. If it fires right up. You should be ok. What you are testing here is the "hot start". That is, how well the engine cranks with a lot of initial timing and a starter that's heat soaked from the exhaust running right past it. This test is very important if you have headers. They can cause MAJOR heat soak into the starter. And if you run too much initial timing. The starter won't work proper. OR it might even kick back. Never a good thing. If there is hot start problems. You will need to back the initial down. I suggest 1-2 degrees at a time. You don't wanna lose too much initial timing.

Once you find your good initial. Then you know what to time for your total. MOST small blocks like 34-36. It's uncommon for them to fall out of this area. And it's usually the result of better combustion chamber heads (ie more efficient) or power adder. Or whatever else. So once you know your initial, say 20 degrees. Set your distributor advance for 14-16 degrees, usually all in by 3000 rpm. This is another most common thing. Although some guys run shorter or longer distributor timing. The best way to test total timing, is a track. Set it for 34 degrees. Record MPH/ET. Up it to 35 degrees. Record MPH/ET. Set it for 36 degrees. Record MPH/ET. Whichever one you get best MPH/ET on, is better. If it's best at 34, you could even try going down to 33/32 and see if it picks up. If it's best at 36, you could try 37 or 38 and see if it picks up.

As always. LISTEN for pining/detonation. Not something you should run into on your build. But always something to listen for when setting timing. Usually after I do a tune up like this (carb adjustments, new timing, etc) I also like to get a fresh set of plugs. The constant dicking around with stuff can foul the old plugs. And for a whopping 2 bucks each. It's an easy thing to change to help keep the car running as best as possible.

IDEALLY you want the MOST timing possible at the crank itself (initial) possible. The less mechanical advance you have. The better. The most initial possible will give you the best low end power. When I adjusted my setup and went up to 22 initial. The car was a whole different beast. It ran like a scalded dog. Way better idle. Way better throttle response on the low end. Just a much better tune.
Click to expand...
 
That's how to time it but I'm looking for a base to set the distributor up at with my set up should be able to get it close and tune it in from there.
 
I'm running a 408 (5.9 magnum based) in my '89 W150 with a NP435 4-speed, 3.55 gears, 31 tires. My engine specs are pretty close to yours...

284/284, 224/224 @ 0.50 (hyd roller), 114 LSA, 110 CL
9.5 compression
RHS-MAX heads but with smaller intake valves than yours (1.94")...I didn't pick 'em, just got a deal on the engine!
0.040" quench
Airgap intake
735cfm Quickfuel SS carb

Anything under 18* initial and it seems like it has to turn over a little more. 20-21 initial and it fires RIGHT up without any drag on the starter when it's hot. Initially I had it set to come all in (32* total) by 2,600 and it was too fast. Granted my truck is probably a LOT heavier than your car but, I've since moved to 34* all in by 3,400 and it's happy. Makes great power from 2,400 to around 5,800-6000 but, I know the small valves are hurting me.

You have a touch more compression...but, with a lighter vehicle I'd say you're fine starting at 20* and all in by 3,200 or 3,400.

Lastly, I'm also using a Crane Hi-6 CD ignition box and it reeeeally smoothed out the idle and helped with throttle response. My idle is set at 800 rpms and I'm pulling 19-20" of vacuum at idle.
 
Last edited:
1966DDart said:
I'm running a 408 (5.9 magnum based) in my '89 W150 with a NP435 4-speed, 3.55 gears, 31 tires. My engine specs are pretty close to yours...

284/284, 224/224 @ 0.50 (hyd roller), 114 LSA, 110 CL
9.5 compression
RHS-MAX heads but with smaller intake valves than yours (1.94")...I didn't pick 'em, just got a deal on the engine!
0.040" quench
Airgap intake
735cfm Quickfuel SS carb

Anything under 18* initial and it seems like it has to turn over a little more. 20-21 initial and it fires RIGHT up without any drag on the starter when it's hot. Initially I had it set to come all in (32* total) by 2,600 and it was too fast. Granted my truck is probably a LOT heavier than your car but, I've since moved to 34* all in by 3,400 and it's happy. Makes great power from 2,400 to around 5,800-6000 but, I know the small valves are hurting me.

You have a touch more compression...but, with a lighter vehicle I'd say you're fine starting at 20* and all in by 3,200 or 3,400.

Lastly, I'm also using a Crane Hi-6 CD ignition box and it reeeeally smoothed out the idle and helped with throttle response. My idle is set at 800 rpms and I'm pulling 19-20" of vacuum at idle.
Click to expand...
Thanks I'm hoping for good vacuum I heard mixed reviews on my cam choice with how much vacuum I will make. Guess I will see.
 
72SwingerJosh said:
Thanks I'm hoping for good vacuum I heard mixed reviews on my cam choice with how much vacuum I will make. Guess I will see.
Click to expand...

I'm at 56* overlap on my cam and yours works out to 60*...you should be fine! I'm guessing you'll pull around 16-18" at idle which is plenty for power brakes. Given that I'm at 800 rpms at idle...the 900 you mentioned should be about right for your set up. Having a good capacity discharge ignition box really help smooth things out...but, you give up a little of that rough idle sound.
 
That's good to know thanks. I want to have power brakes. Also I was thinking about the carbs vacuum secondaries and not sure if I should go with mechanical secondaries. I want to use my stock 340 air cleaner and not sure what carbs will work with it that use mechanical secondaries
 
Last edited:
72SwingerJosh said:
That's how to time it but I'm looking for a base to set the distributor up at with my set up should be able to get it close and tune it in from there.
Click to expand...

The first half of my post addresses the best possible way to set up initial timing for best power and vacuum. So I'm not sure what you were missing there. But if you'd rather skip the work that makes it run best. Go for it.
 

I didn't miss anything I asked for the best way to set a distributor up from my specs to save time when I start the process of actually getting it tuned and 100% timed. I don't want to take a stock spec distributor put it in and take it out a dozen times when from looking at my set up somebody with a little experience and knowledge can give me a head start on it. Which makes the whole process easier and less work.
 
72SwingerJosh said:
I didn't miss anything I asked for the best way to set a distributor up from my specs to save time when I start the process of actually getting it tuned and 100% timed. I don't want to take a stock spec distributor put it in and take it out a dozen times when from looking at my set up somebody with a little experience and knowledge can give me a head start on it. Which makes the whole process easier and less work.
Click to expand...

The best way to set a distributor up for your specs is exactly how I told you. And you don't take it out and put it in a dozen times. You just keep upping the timing while resetting the carb until you get best vacuum then back it down a degree or two. That will give you best initial timing possible. That is what you are after isn't it?
 
Which I also mentioned in my post.

If you want to throw a random number at the initial you can. You'll probably even end up close. But you'll still have to go back and reset initial timing for best power later. Or you might even have to back it down if you have hot start problems. And once you do that. You have to recurve for total timing. Again. Which means pulling the distributor. Again. Why do it twice?

Set the initial properly. For best vacuum/power, from the start. Then you know approximately what you need for total and you can tune that. Then it's all done once.
 
If it's not in yet I figured get it where it's close or maybe get lucky and it's right on. There is a way to get there from the cam specs and other set up info. I don't know how to and was looking for a answer from those who do. You can send a distributor to be curved from a build and they can get it so you can put it in and set the timing and your done. Just not to many around that know how to anymore I guess.
 
Anybody can use cut and paste. There are hundreds if not thousands of ways to get what I'm looking for. i was hoping that maybe someone that knew how to figure this out from the specs would see the post and chime in or someone that had same specs would say hey this is what I have which another member has done already.
 
72SwingerJosh said:
If it's not in yet I figured get it where it's close or maybe get lucky and it's right on. There is a way to get there from the cam specs and other set up info. I don't know how to and was looking for a answer from those who do. You can send a distributor to be curved from a build and they can get it so you can put it in and set the timing and your done. Just not to many around that know how to anymore I guess.
Click to expand...

If all you're looking for is close. Then yes. You can throw 20 initial at it. Drop the 14 or 16 plate in for 34 or 36 total and call it good.

But no. There is no way to get the perfect initial from cam specs and other info. You MIGHT get close. Or far. And you will always give up power doing it that way. The amount of things that go into determining best timing is FAR too large to make it that easy. There's no "magic" number. Things as small as elevation (which you don't mention) or brand of gas used can have an affect. Hell even ramp rates have an affect. Every engine, no matter how similar to yours, is different. The best way to tune for initial is by best vacuum, which usually indicates best power. And the best way to tune for best total is either on a dyno or the drag strip.

So it's kind of a matter of. Do you just want to get it running? Then sure. 20 initial with 34 or 36 total, all in by 3000 rpm. But if you want best power you WILL have to go back and do it ALL over again. Remember, every time you change initial you also have to change total. I don't like doing things twice. So I figure it's best to just tune it from the start. It's really not a difficult process.

And I cut and paste my own post. But hey. If you don't wanna take tuning advice from a guy who's tuned drag cars and sprint cars. That's up to you. You asked for expert advice. I tried to give it.
 
Don't take it personal I just want it close I have a session set up just found a place and it's not cheap so want to hopefully get things set up in 4 hours so I figured less time if I got a good base. Im not going to a drag strip so dyno is my best choice thanks for your response it was appreciated.
 
The dyno doesn't care about anything but finding the power timing, and they only pull the hammer after 3000 usually.So it cares not one little bit about anything but all-in.
Then you go home and after the first tank is burned up, you find out that maybe 38* was too much for the street. Or 36* was too much, or even 34* was too much. Or maybe 36 was ok after 4000rpm but it only wants 28*@2800, and maybe you can't get that with 20 initial. So, maybe there is no perfect curve for your engine. But you can get pretty close.
Then you take it on a cruise and the 12* in the can is hardly doing anything. So you get yourself at 18* can, and think you are happy, all the while the engine wants 30 from the can and you don't even know it.
What I'm saying is,if you want perfection, prepare to spend two summers screwing around with it. If you just wanna drop it in then drop it in.
There is an unbelievable amount of science that goes into that mundane little timing controller, and it just takes hours and hours of dicking around to get it pretty darn close. There is no perfect. There is only pretty darn close.
Put on your coveralls and get used to popping the cap.....
 
I hope I can get it close just need it to start when it's warm and for it to idle good. Im Not drag racing just want a reliable cruiser and I'm using dyno to do break in so no surprises. Not trying to set it up for all out maxed horsepower or I would get a better set up than stock. Thats why I asked for base set up suggestions to save some time. And get ideas where to start at.
 
IMG_0766.jpg
Found this chart helps get a idea where to start at.
 
Josh, give Don at FBO a call. He'll be happy to help with a starting point. I just put in his limiting disc and we emailed back and forth a number of times. I love the way my car behaves now. Its just a stock 273 Commando but throttle response is better now.
 
The initial depends what you want your total to be so I want 34 so initial is 20. I talked to Don and this is his chart. Just figured I would post it so if anyone was looking they can find it.
 
72SwingerJosh said:
The initial depends what you want your total to be so I want 34 so initial is 20. I talked to Don and this is his chart. Just figured I would post it so if anyone was looking they can find it.
Click to expand...

Backwards thinking there.

Your initial and total timing are two events that are determined independently. One should have no determination on the other.
 
I was just going from what that Don told me. He said I want to be conservative with total and 34 was a good place to start then his disk would have to be on 14 so it would be 20 initial. He said the chart shows where to start with the cam duration. I just wanted to know how to get the idea where to start at and the chart helps me visualize better I guess. I know the way to get the timing just didn't know how they came up with a starting point to try from. Didn't want to just throw the distributor in there set at a random starting point. He said the initial and total work together for the total curve. I guess there are a million views on this topic lol. Just like where to get the advance vacuum at. But now thanks to everybody I have a fairly good idea of it all and am sure I will get it all figured out I will be playing with it in a couple days and that's where the fun part stars and it's nice having theory down before I just start moving stuff or start in random spots which could get me way out of the ball park and make it all a lot harder. Thanks to everyone for all the replies and help.
 
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