Turbo timing questions...

[acarlson]

I currently have my '66 Corsa turbo initial timing set to 18 degrees at an idle of about 900 rpm. That is because I have Clarks retard/advance canister installed on the distributor and 18 degrees is what they recommend. I have a question about the stock timing table below:

The stock initial timing is supposed to be set at 24 degrees. That doesn't change based on manifold vacuum. It does change based on turbo pressure and engine RPM with the centrifugal advance in the distributor. According to the table, the max centrifugal timing change is 18 degrees. Is that advance timing or retard timing ? Is that added or subtracted to the initial 24 degrees or does it supercede the initial timing ? The stock retard canister maxes out at 8 degrees. I assume that is subtracted from the 24 degree initial timing giving me 16 degrees BTDC when the turbo exceeds 3.7 psi if I am below 4K RPM's.

OK, now here's my real issue... I am considering removing my Clarks retard/advance canister, not replacing it and leaving my initial timing set to 18 degrees. I am ignoring the distributor centrifugal advance since 4K RPM's would put me over 80 MPH and I'm not planning to drive that fast. I don't think my car has even been over 60 MPH. The stock retard canister would adjust the timing to 16 degrees BTDC (max) at 4 psi. One additional point to make here - I have Snow's Stage 2 Methanol Injection system installed on my turbo. So, my last question is: have I got this all figured out correctly and can I just remove the retard canister and run 18 degrees timing all the time ?

Alec

[thewolfe]

The 18 degree mechanical advance is added to the initial. It would not be wise to run your engine without some sort of boost retard, meth injection or not.

[miniman82]

Nothing wrong with reduced initial timing and no retard, in the VW world we call it "locked out" timing when this is done.

It's not harmful to the engine when done correctly, but there are side effects:

1. you will likely have to add idle throttle with the adjustment screw to raise idle RPM, since the lower timing will tend to bring down RPM.

2. the engine will feel less 'snappy' off boost, due to there not being enough timing to properly ignite the full mixture

3. MPG will suffer, as a result of #2

4. there's a practical limit to how much headroom you get with this method for on boost timing. generally speaking if you don't intend to go past a certain limit, say 7-10 lbs, you'll be fine pulling 8 or so degrees and leaving it. Problem is if you go past that, you must retime it or detonation will likely result. Also the farther you go into boosted land with locked timing, the worse your idle quality will be. It's the land of diminishing returns in other words, since headroom up top gives up advance down low.

This is why it's best to have idle timing set for lean best, and address boost timing in some other way. Either with limited mechanical advance by recurving the distributor, or by using some form of electronic timing control like MSD 6BTM for example. I like crank triggered ignitions, because I can program and timing I want at any point in the engine's operation boost or not. But it's not for everyone.

[joelsplace]

If he isn't running past 4000 RPM he doesn't need to worry about boost. Might as well put in a NA engine. It will work a lot better at lower RPM.

[acarlson]

I get boost well below 4000 RPM and it works quite well. The 4000 RPM is only an issue because thats when the mechanical timing adjustment in the distributor kicks in. It is expecting the stock timing to be set at 24 degrees, not the 18 that I am running.

[miniman82]

To answer your question since I missed it last time, I don’t think you can just remove the retard canister since it’s connected to the plate inside the distributor. I believe you still need something to keep it from flopping around, so the correct solution would be to leave the can but remove the hose and plug it.

[acarlson]

Ahh, good point. I did remove it. The diaphragm inside was ruptured so it was just leaking vacuum air and turbo boost. I sent it back to Clark’s so they could check it out but I have a standard vacuum advance canister I can put on as you suggest and plug the manifold port. That’ll keep the timing plate from moving around on it’s own.

[miniman82]

I don’t trust those things any farther than I can throw them, just too damn inconsistent for my liking. Do megajolt, you’ll thank me later.

[toytron]

I don’t trust those things any farther than I can throw them, just too damn inconsistent for my liking. Do megajolt, you’ll thank me later.

Hey Nick, which megajolt do you use/recommend?

Ed Stevenson

[miniman82]

There only one, so what do you mean?

[toytron]

There only one, so what do you mean?

Megajolt jr. Or megajolt/E MK2

Ed Stevenson

[miniman82]

Ah, there’s a new version. I used the old v3 lite jr model, apparently the latest/greatest version has native USB support and some other features. I tend to go the cheap route, but the choice is yours. There’s not much price difference anymore, might as well get the best one I suppose?

https://www.autosportlabs.com/product/m ... _ignition/

[toytron]

Ah, there’s a new version. I used the old v3 lite jr model, apparently the latest/greatest version has native USB support and some other features. I tend to go the cheap route, but the choice is yours. There’s not much price difference anymore, might as well get the best one I suppose?

https://www.autosportlabs.com/product/m ... _ignition/

[emoji106]

Ed Stevenson

[Mrzapatos]

Nick- Are you still rebuilding turbos for others? I'm interested - My PM disabled?? another way to contact you?
I like your tutorials, but with 2 babies in the house, i get no time with my car- outsourcing work that i can?
Sorry -OT

[toytron]

Nick- Are you still rebuilding turbos for others? I'm interested - My PM disabled?? another way to contact you?
I like your tutorials, but with 2 babies in the house, i get no time with my car- outsourcing work that i can?
Sorry -OT

I am afraid Nick has rebuilt his last corvair turbo. He will be retiring from the Military and might take up other hobbies. Sad :(

Ed Stevenson

[bbodie52]

I did this once in 1971, enjoying the feeling of my turbocharged Corvair pushing my Corsa coupe up the length of the Conejo grade, driving on a hot summer day from Camarillo to Thousand Oaks, with the windows down, and not a care in the world. Just as I reached the crest, BANG!

A sure sign that you've pushed your turbo Corvair too hard...




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