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Ok. So here is where im at. Been messing with may carb too long to not address my ignition timing and curve . I been fiddling with the advance springs and due to my my mechanical advance. I have 22 total I can only run a max of 14. So. Say at a lower RPM my timing is 14 but at the ideal idle RPM where it can sustain its self in gear im closer to 18 since im up on the mechanical already. Does this intersection of mechanical timing and initial in gear kill my total advance or is it still 36 degrees is it just coming in sooner now since im advancing 4 degrees at idle. I may get some bushing to limit some travel on the advance but because it's so minor would it be an issue ?. I plan in sending this distributor out once the season is over to be curved.
If you set your idle timing at 14 and have 22 degrees of mechanical built in, then your total timing will be 36* at whatever your springs allow it to stop. Since you have to raise your idle rpm to get the car to run and your advance is coming in early and going to 18, your timing is going to fluctuate, I would install 1 slightly heavier spring so that the advance starts coming in at a higher RPM. Yes, this will move your total curve a bit higher, but you will still have 36 total.
The fluctuation is helping me. Thats why at the moment im gonna live with it. This engine likes to idle at 900 and finding a curve that wont advance at idle but maintain steady is hard. Probably why lots of guys lock the timing. The other issue is it likes all the timing as soon as it can get it . 2 medium springs and the engine isnt happy going from idle to WOT. What i ended up with right now has been the best but thats probably because the extra 4 degrees at idle along with timing ramping up helps with the fuel combustion much sooner. I know whats going on just never had a situation where my idle was just enough into the advance to stay alive in gear. Usually the RPM drop kills the advance and slowly then the engine RPM degrades until it dies. But it seems to work well with the slight advance coming in. I was just curious if the intersecrion of the mechanical working during idle would affect my total timing which i assumed it would not and you confirmed what i had thought.
Last edited by coppercutlass; August 21st, 2019 at 07:49 PM.
This gives you the ability to lock out the timing, but also retard the timing during starting so you don't kick the starter off the block or require a super hot battery. You can use your distributor to trigger the system.
It even has a secondary retard that you can adjust and trigger for a nitrous system if you install one.
Trying to avoid an ignition box at the moment. I know with an ignition box you can Taylor it with the starter savers to pull 20 degrees out under 800 rpm. I could easily just hit the starter button and flip the ignition on since I have both the starter and ignition on separate switches. But my biggest obstacle is money at the moment. Got house projects so that takes priority.
I ran a 455 that liked a lot of initial timing. It transformed the engine power curve off-idle, eliminated bogs, and stabilized the idle speed and quality.
I ran 20° initial and fabricated a bushing that limited the advance to 15°.
Just another option for you. And it's very low cost.
I love reading about your projects. Good luck with everything.
I ran 20° initial and fabricated a bushing that limited the advance to 15°.
Just another option for you.
A potential issue with a limit bushing is some distributors, such as the GM HEI, don't use one. The points distributors, do, though.
The "advance stop" on the GM HEI is a function of the mating curves of the weights and center bar - once the weights move outward a certain amount, they bind against the center bar and further movement is prevented. I do not know if the aftermarket HEI clones are the same or not.
This may be overly simplistic, and I apologize in advance if is, as it is just a thought that I have.
In theory, Could you start with where the heads begin picking up the biggest increase in flow, if you have that info. Then try to match the curve from there as a base line?
I know there are a lot of variables to consider of the overall build; but where to start, other than trial and error. Once you adjust the curve, are you not going to re-jet the carb?
The curve is coming in before 3k RPM. The only time im seeing a spike im AFR is during the transition from idle to WOT. My AFR is 12.5 across the board besides that. The earlier timing at idle did lean up my AFR but that was adjusted with the fuel mixture screws. I think what was happening was the fuel shot was coming all in before the timing was all in . On the AFR it showed up as a lean deal. But then i got a big lean pop with a 6 foot ball of fire so I have enough fuel to puddle up in the intake but the spark timing in relation to the fuel shot timing was off. Too late in the cycle.
Keep in mind we have about 15 passes on this engine and about 500 street miles already.
This gives you the ability to lock out the timing, but also retard the timing during starting so you don't kick the starter off the block or require a super hot battery. You can use your distributor to trigger the system.
It even has a secondary retard that you can adjust and trigger for a nitrous system if you install one.
Why would he need a retard? You've rode in my shop truck with locked out timing, ever remember a starting problem?
Last edited by VORTECPRO; August 22nd, 2019 at 07:48 PM.
Vortec pro my only issue is im running 93 octane on 10.25 to 1 compression on iron heads. I still want a curve for those situation where cylinder pressures are hi and temps are high like around town and up hills and what not. That's my only fear. I feel if I have say 20 degrees initial with a fast ramp all in by 2600 I would still be good and better than tyring to pull from a light at 190 degrees on a 90 degree day from a light with the timing locked in at 36 . which light acceleration will be the only high pressure situation I would be under most of the time due to the fact I normally cruise above 3k rpm but around town im still under 3k. That's my thinking atleast.
Last edited by coppercutlass; August 22nd, 2019 at 08:23 PM.
Location: Colorado Springs Colorado/Thousand Oaks Ca
Posts: 1,719
My shop truck, NA 331 cu in @ 4200 pounds runs a open 3.07 gear with a 30 inch tire, iron heads, 11.1 compression 42 degrees locked timing, pulls 1 degree out for every 1000 RPM, 35 degrees @ 7000 RPM. Dailey driver in 95 degree heat. My truck NEVER runs over 158 degrees, this is the trick. BTW runs 13.80 @ 8000 feet DA.
Last edited by VORTECPRO; August 22nd, 2019 at 08:31 PM.
The best I have ever gotten my olds to run temp wise was 180 on hot days with the old engine but I run a moroso water pump drive so Water pump RPM is always the same. Knowing my obstacles and the cars characteristics I would prefer a timing curve. I wouldn't mind carrying a lock out plate and swapping at the track and resetting the timing. That's a 5 minute job.
With my 455 I use a Mr.Gasket recurve kit, it came with springs, center ramp, nylon wear pads, and bushings for the weights. To get the curve I wanted I ended up using 1 medium spring and 1 heavy spring for the street, starts at 1,500 rpm (helps with tire spin) and 2 medium for the track starts at 1,200 rpm. 18 degrees initial and 36 total, both cases all in by 3,000 rpm. I've also been using a seperate ignition switch for 30 years. I start cranking the motor, half pump and then throw the ignition switch on. Before this I went through 2 starters. No vacuum advance, also I get better idle with the power valves blocked off. I tried every power valve from 9 down to 3.5 but runs best with the power valves blocked off. One other thing we sometimes do for people is cut off the internal parts off the vacuum advance that are inside the distributor and use that to limit the total advance, beats welding/soldering/grinding the center ramp or drilling holes and using small nuts & bolts or screws in the center ramp because of balancing issues. Mind you if you use the OEM vacuum pod you can drill a hole in the mount and use a nut & bolt to hold the rod which will make it adjustable, sorry I don't have a pic of this setup.
I know how guys hold it back but i need a precise way to measure the total mechanical. And I came up with something. I will share later when I can confirm it and share what I did. I been trying to work around it but at the point I cant ignore it lol.
Last edited by coppercutlass; August 23rd, 2019 at 06:40 PM.
I know how guys hold it back but i need a precise way to measure the total mechanical. And I came up with something. I will share later when I can confirm it and share what I did. I been trying to work around it but at the point I cant ignore it lol.
I found a significant issue with my carb. I still plan on showing what I came up with to measure total mechanical .
I fixed the issue and now the bog is gone. But I will need to go back to square 1 as this really was significant enough to where most of my carb tuning has been to aid the fact the. Nozzles has 2 issues going on.
Made a vid for my youtube page detailing what i found
https://youtu.be/EDWTDBWqtRk
Last edited by coppercutlass; September 4th, 2019 at 01:27 PM.
The HEI I have has been curved so i only buy those kits for the springs. Once I do my set up i should be able to check full mechanical on a bench but havent gotten around to doing what i need to
If I recall adding HEI in place of points generally means more advance since they were preparing for emissions when HEI came into play.
With an HEI, do heavier springs make the advance curve slower? I’d love to run more advance at idle, but always wind up with pinging at WOT when I advance the initial.
I’ve got a spring kit and various HEI weights in my HEI box, would you suggest lighter weights and heavier springs to reduced WOT pinging?
I think I’m running 10-11 initial advance, but if I go much beyond that I get a bette idle, but high RPM and WOT pinging, so I’ve been running it a bit further back than I’d like probably because I don’t understand the weights and spring relationship to advance.
What do you all suggest for street cars to get best power and smooth idle?
With an HEI, do heavier springs make the advance curve slower?
Yes.
Originally Posted by cfair
I’d love to run more advance at idle, but always wind up with pinging at WOT when I advance the initial.
That's because when you advance the initial without doing anything else, the total advance is increased by the amount you increased the initial.
Originally Posted by cfair
I’ve got a spring kit and various HEI weights in my HEI box, would you suggest lighter weights and heavier springs to reduced WOT pinging?
I think I’m running 10-11 initial advance, but if I go much beyond that I get a bette idle, but high RPM and WOT pinging, so I’ve been running it a bit further back than I’d like probably because I don’t understand the weights and spring relationship to advance.
What do you all suggest for street cars to get best power and smooth idle?
I recall some posts by Dave Ray years ago and he said GM had something like 300 (or was it 3000?) different weight combinations for different advance curves. He gave the numbers for some popular weights and center bars and how much mechanical advance they gave, but I didn't save that info. Maybe it's still out on the web somewhere?
Let me backup and start with some basics. The GM HEI distributors do not use an advance stop bushing to limit the amount of mechanical advance as the points style distributors do. The contour of the mating surfaces of the HEI weights and center bar are what limits the amount of mechanical advance as well as the rate of advance (the advance curve). So with what Dave Ray had posted, you would need to experiment with a lot of different weights and center bars to get the "perfect curve" for your particular setup.
I experimented a lot with the GM HEI on my car over the years. I found that the weights and center bar in the Moroso HEI Advance Curve Kit gave 24º mechanical advance, which was the same as my original points distributor, so I set the initial at 10-12º to keep everything the same as my original factory setup. After installing a hotter camshaft, I began experimenting with ways to increase the initial to get more vacuum and smooth out the idle. I eventually discovered that the factory HEI weights and center bar gave just what I was looking for: 16º mechanical advance, so I could set the initial at 18º and get the same amount of total advance. My factory HEI weights are stamped 139 and teh center bar is stamped 446.
If I recall adding HEI in place of points generally means more advance since they were preparing for emissions when HEI came into play.
With an HEI, do heavier springs make the advance curve slower? I’d love to run more advance at idle, but always wind up with pinging at WOT when I advance the initial.
I’ve got a spring kit and various HEI weights in my HEI box, would you suggest lighter weights and heavier springs to reduced WOT pinging?
I think I’m running 10-11 initial advance, but if I go much beyond that I get a bette idle, but high RPM and WOT pinging, so I’ve been running it a bit further back than I’d like probably because I don’t understand the weights and spring relationship to advance.
What do you all suggest for street cars to get best power and smooth idle?
There is actually a lot more going on and to consider with engine knock. You also need to give more info on your setup. In the 40 some years of working on cars I've only ever heard ping once on a car and it sounds exactly like a loud ping and not knock, sparkplugs were too hot of heat range in a Ford 302. Knock is all the clearance in your bearings suddenly being taken up by the engine trying to turn backwards. Anyway, are you using a vacuum advance pod? Have you tried using cooler sparkplugs? What cam are you using? What carb are you using? Are you using ported or manifold vacuum? Is it ok if you don't stomp on the throttle but increase it with RPM to WOT?
Fun71 hit on a key problem with knock. Some cams are designed to artificially raise the compression ratio in the low to medium RPM range. With these cams when you suddenly go to WOT you get maximum cylinder pressure at high load which speeds up the burning process but, if you were to slowly increase the throttle to WOT you get no knock. Also a lean air/fuel mixture will create knock. To get around this there are 4 things that can be done, cool down the air/fuel charge some how, richer main jetting, use a higher octane fuel, or decrease the amount of ignition advance or even a combination of the 4. My first choice for cases of bottom end cams is to install an adjustable vacuum advance pod connected to the manifold, that way you get easier starting, better idle, and no knock. I usually leave the stock weights.ramps, and springs in until the cam is a mid to top end cam and on lighter cars As always you have to give the car/engine what it wants and this takes time, money, testing, and time.
After reading up, I think I need to limit mechanical advance at WOT. At WOT vacuum = ~ 0, so vacuum advance doesn't matter. Does that sound right?
If I understand it correctly '75 HEI distributors had more degrees of advance designed into them as compared to '66 points distributors to prepare for tightening of emissions standards. If I've got it right, that means that retrofitting an HEI to a '66 big block means I need to get some timing out of the HEI to make it run great on a '66 engine.
Goal I'm looking for a solution to provide max. power, staying stock to avoid getting stuck somewhere with a need for exotic ignition parts. So, I think I have to to modify HEI mechanical advance to make it work more like the points distributorsthat preceded it before emissions controls really kicked in.
Approach
I think I need to reduce the HEI mechanical advance between a 10-14 degree initial timing and keep it to 32-34 degrees at max advance. How do I do that? Is reducing mechanical my best option, or should I work on vacuum advance to?
I've got a small library of parts I think may help, but I'd like to do something other than a random search: What combination might reduce total advance to allow high initial advance & not knock at WOT?
Rotors
My hunch is Rotor 2 provides less advance based on the holes being farther retarded in the counterclockwise scale that Olds distributors use. Does that sound right? Based on the clock position of the holes, a I right in thinking rotor #1 will fire the plug earlier all other things being equal than rotor #2?
Weights
Moving onto weights, I've got 2 choices. The weights stamped #139 look heavier (meaning quicker & more total mechanical advance, right?). I've also got some lighter-looking aftermarket ones that I'd guess will hit max advance slower (but maybe not?). Just to complicate things, the aftermarket weights have 2 different bushings. My guess is the larger diameter bushings limit total advance which may help. Is that right? If I want less total timing and get there more slowly across the RPM range, am I aiming for lighter weights with heavier springs to restrain the mechanical advance?
Springs
I've got 5 sets of springs. I know I can mismatch them, but I'd like to confirm that I should stay on the heavy side to keep advance down. Is that theory correct until I know the motor won't knock from testing?
Vacuum Limiters
I've got 2 gadgets from MSD (left) and Crane (right) that limit vacuum advance. Given that vacuum advance at WOT = 0, can these help me at all? Or should I continue to rely on retarding the vacuum advance can by 10 turns (toward the extreme retard end of it's adjustability?)
This is kind of like carburetor tuning -- meaning it's good to have parts to test in combination. If any of you have sources for different HEI rotor, springs, & weights, I'm interested.
Thank you for any experience you can offer to help me figure out what will work best while searching something-less-than randomly...
Approach
I think I need to reduce the HEI mechanical advance between a 10-14 degree initial timing and keep it to 32-34 degrees at max advance. How do I do that?
What you are looking for sounds like the setup I posted about earlier.
Originally Posted by Fun71
I found that the weights and center bar in the Moroso HEI Advance Curve Kit gave 24º mechanical advance, which was the same as my original points distributor, so I set the initial at 10-12º to keep everything the same as my original factory setup.
Pretty all sure the Chinese cheap distributors have similar to above as well. Mine was well made, just upgraded the coil and module. Most aftermarket distributors seem to be set up out of box with sbc or Olds points advance curves, whichever you want to call it.
Make sure and watch out for carbon tracking and crossfire on the Chinese HEI cap.
We had some weird ignition/timing issues related to this on our Chinese HEI that we were using just to dyno our engine, and we later found melted terminals inside the cap after the 20+ Dyno pulls. With it sounding a little weird, with some misfire, we probably left 10-20hp the table on our last pull related to ignition issues.
Last edited by Battenrunner; November 1st, 2019 at 07:14 AM.
For once it was carb problems. I kept the curve the same way. Clicked off an. 11.86 and an 11.85 back to back. I fixed the carb no more issues. It was a minor carb issue but was overlooked on my part until i decided to go through it.
I know how guys hold it back but i need a precise way to measure the total mechanical. And I came up with something. I will share later when I can confirm it and share what I did. I been trying to work around it but at the point I cant ignore it lol.
Well. I left the tomimg curve where it was. And locking out the timing is not for this combo and a few things hinted to that. 1 being my 60 ft. At the track is about as good as it gets for my set up at 1.59. Albeit my timing is all im by 2500 and coming in after 1000 rpm. My problem was Indeed a lean carb issue but the problem was the discharge nozzle threads where damaged , the gaskets that where in it where obstructing flow too. So even at idle fuel would drip from the bottom of the nozzle. I went to an m6 thread 1 size up and clearanced the bolt for "high flow" and bam all lean spots gone. Now the car launches hown it should. The reason why locked timing would not work for me at this time is all that timing leans out the fuel mixture. And ideally I still want a timing curve for low RPM high load situations like coming off a light. The converter might slip but i still feel all that timing that soon for my set up would not be ideal. I just finally got everything working right. So who knows maybe we can fiddle with locking it out later. But in this situation is was a carb issue not timing.
Location: Colorado Springs Colorado/Thousand Oaks Ca
Posts: 1,719
Originally Posted by coppercutlass
I'm 111 @ 11.85
Thats the point, over 100 % efficiency with a less than a optimum drive line, not very often done, especially with a small inch engine. So the potential 60 for a high 11 sec car can be around 1.47 but that requires a different drive line. 111 MPH over 1320 shows 369 observed crankshaft HP @ 3500 pounds?
Last edited by VORTECPRO; November 2nd, 2019 at 07:29 AM.
About 3500 lbs but i dont know how the calculators factor that stuff because ln one it says in 415 and one 369. The calculators say my 60 ft. Is good for mid 11's. The e/t vs mph give 2 different numbers on up.
If you type in 3500 lbs and 415 HP the e/t calculator is bang on ., on giving you my exact e/t. Then HP for mph is 369 HP which im gonna guess has to be to the wheels not the crank because if you figure loss of up through the driveline and multiply by .15 it comes up with 424 HP. Those calculators are always a guessing game
Last edited by coppercutlass; November 2nd, 2019 at 08:30 AM.
August 21st, 2019, 03:49 PM
