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1971 olds 455 v8.
Stock pistons and bottom end.
Comp 268H cam.
1968 C heads.
2.5 inch dual exhaust.
Edelbrock Performer intake.
Holley 750 cfm carb.
Mechanical advance only:
I set my total at 34 degrees because I read 34-36 total at 3000 rpm. but my initial went to 22 degrees and that caused me to have 1300 rpm idle but drops to 800 when my AC comes on. Never tried it in drive.
Less timing at idle will drop my rpm at idle (idle screw is completly off) but it will drop my total timing.
If my advance is at 16 mechanical at 1k ish rpm, then I plug in vacuum advance, it will idle okay but be a bit weak for drive sometimes I have to tap the gas very lightly while stopped.
Driving locally with 16 mechanical advance at idle then connecting vacuum advance and it has some kick but feels like its lacking in power.
I am not sure what I should have the spark set to.
This distributor was like this when I got the engine.
I did the top swap stuff and cam.
Is there an HEI distributor I can buy from summit racing that is a drop in ready to go option that I can advance to 34-36 total and be right?
I can get a 10 dollar weights kit but I don't know if its compatible with my current HEI distributor.
I have been trying to find charts or guides online but no success.
Last edited by GHOSTOWLGRID; June 9th, 2017 at 12:19 PM.
Reason: Spelling errors
Most GM HEI distributors have ~14º mechanical advance, so the initial is ~20º. Set the total and let the initial be whatever it will be.
My points distributor had 24º mechanical advance, so the initial was ~12º. After installing the HEI the engine idles a lot better with ~20º initial, has higher vacuum, and the vacuum is smooth instead of bouncy.
Leave the timing where it is and try reducing your idle speed to 600-700 and see how the engine runs.
Do you have full battery voltage connected to your distributor? Are the plugs gapped at .045? HEI's have somewhere between 18-21 degrees of mechanical advance built in. Set you total without vacuum hooked up to your 34 (the number you selected) at what ever rpm the distributor stops advancing (you stated 3000). Lower the rpm back down with the carb idle adjustment screw to its lowest rpm where you see no advance note that timing setting. Subtract that number from your 34 will tell you how much mechanical advance is actually built into your distributor and can be used to formulate future adjustments. Then adjust your curb idle, I like 750 in gear with a lopey cam, while making sure your timing is staying fixed at the number you just wrote down. If its advancing at idle you need stiffer springs. Next connect your vacuum advance to manifold vacuum, readjust your engine idle speed back to where it was, and see how much timing it adds at idle. If its more than 10-15 it needs to be limited with a stop plate that you can purchase or fabricate. So the math is such The timing number you wrote down at idle + the mechanical advance will = 34. Add the vacuum advance of 10-15 degrees and your total timing with vacuum will be 44-49. You may find that you can increase it 2-4 more degrees at idle which will move your total up by the same amount.
Now the A/C issue loading everything down. Buy a stock idle stop solenoid that is activated to pop out and stop your throttle before the normal idle setting and raises your idle speed when the A/C is on.
There's another thing that was improved on my engine with the initial set to ~20º - the RPM doesn't drop much from neutral to drive, or when switching the AC on.
I read the posts you guys made to help me to try and figure this out, but its still seeming a little weak at idle and not all of its umph is there when accelerating.
I have about 16 advance at idle, goes to about 26 total.
I found out my vacuum advance is not advancing or retarding anything at all on my distributor, I believe it needs replaced, I will look into fixing it.
Idle still seems weak, drops from 1100 to about 650 in drive or reverse and isn't seeming like its as strong as it should be at idle.
Driving it, it runs strong, but I feel like it isn't 100% there, seems like only 60% of its overall power is there.
I will keep trying, however I will also look into places who can properly tune spark and fuel on this engine, I feel like I am just guessing at this point.
I looked up the idle stop solenoids as suggested, I like that idea for when the AC pump comes on, but I feel like the car should be doing better than it is when I move the lever from P to D. about 400-500 rpm drop seems like a lot.
Last edited by GHOSTOWLGRID; June 10th, 2017 at 07:17 PM.
Reason: added
... its still seeming a little weak at idle and not all of its umph is there when accelerating.
Idle still seems weak, drops from 1100 to about 650 in drive or reverse and isn't seeming like its as strong as it should be at idle.
Driving it, it runs strong, but I feel like it isn't 100% there, seems like only 60% of its overall power is there.
I have about 16 advance at idle, goes to about 26 total.
So your mechanical advance is not set to about 36° BTDC, maxed out at about 2,500 RPM, i.e.: you're running 10° retarded?
Why not follow Eric's instructions? He's gone over this so many times with so many people that he's quite good at it by now.
Originally Posted by GHOSTOWLGRID
I found out my vacuum advance is not advancing or retarding anything at all on my distributor, I believe it needs replaced, I will look into fixing it.
The system does work better when its component parts are functional.
You answered your own question on your issue, its the 26 total. However the math does not add up with you having 16 at idle. Are you sure thats what you have, please double check? The vacuum advance has nothing to do with full throttle power output as at wot vacuum drops to 0, its there for fuel efficiency at part throttle cruising.
I got help from my dad and we were checking vacuum and stuff.
It turns out our spark was fine, turns out I was turning my spark up to much to compensate for not having enough fuel.
I need a bigger carb and one that can supply more fuel at idle and when driving.
My current carb is maxed out at idle and just keeping up under load.
I got help from my dad and we were checking vacuum and stuff.
It turns out our spark was fine, turns out I was turning my spark up to much to compensate for not having enough fuel.
I need a bigger carb and one that can supply more fuel at idle and when driving.
My current carb is maxed out at idle and just keeping up under load.
What does maxed out mean to your dad? What is your timing set to now?
Listen to Eric, Eric and Kenneth
They all worked me thru this same issue on my 69 and it now starts Great, Idles great and runs like a scoulded a$$ rabbit. If you follow the steps EXACTLY as Eric suggested you will get there. Personally, I highly recommend a HEI distributor
Good Luck
We figured it out after taking the time to test the engine, the intake manifold gaskets were not seated correctly and leaking vacuum from under the intake.
I meant the carb was set to full rich and the engine was running lean, I am still new to this engine and I assumed the carb wasn't able to supply enough fuel.
I didn't realize this and I was turning up my timing too far to try and keep it running.
I will follow what Eric and Kenneth said for setting the timing, now that we found the issue it is running much better, just needs fine tuned.
I have a new HEI distributor with mechanical and vacuum advance capabilities on order.
Last edited by GHOSTOWLGRID; June 12th, 2017 at 08:15 PM.
Reason: added
Note 2 things with the HEI, 1 - it needs full voltage to operate correctly (run a 12ga wire from the IGN terminal at the fuse box to the HEI bat terminal) and 2 - your stock timing specs will not work (set your total mechanical timing to 34-38* at whatever RPM it stops advancing with the vacuum advance line plugged). You will need to probably limit your vacuum advance to only ad 10-12* with the part below to keep your total with vacuum at around 50*. Running off manifold vacuum is recommended.
June 9th, 2017, 12:17 PM
