I forgot to mention but I put an HEI distributor on it with vacuum advance. But yes I'm talking about cam timing. I'll check it with a timing light, set it at 10 and see how it does. I swear when I get the BEST throttle response and tremendous power, under normal driving conditions it starts spark knocking under light-medium acceleration. I can't have my foot heavy on the pedal with this monster all the time...haha but thanks for the tips everyone I'll give it a shot and keep messing with it!

 

Is your vacuum advance adjustable?
​​​​​​​How does the truck drive with it disconnected?
Does your hei vendor offer a spring kit?

Sounds to me like you have knock in cruise, and this is what egr is meant to address.

 

I would think any speed shop would have a spring kit for an HEI.
If he doesn't have adjustable vacuum advance they would have that too and both might even be in stock as it is a Chevy part.
Dave ----

 

As a test, unplug the vacuum line and put a screw in it. I bet your problem goes away. If it does, you know you have a little too much vacuum advance.

I saw an idea somewhere the other day where a guy put a tee in the advance vacuum line. He made it up and drilled different orifices as vacuum bleeds to try and adjust the advance. I think he may have actually used carb jets for the orifices. The other end of this probably should be plugged into the aircleaner somewhere to suck clean air into the bleed-off.

Best would be a adjustable advance from the store.

 

This is not correct. Total timing is base + centrifugal. Total advance does not figure in vacuum advance. Vacuum advance is added on top of the total. With the vacuum advance added on top, you can have up to 50 degrees total, which is fine for the engine when it's not under load.

 

This is kind of similar to how my stock DSII advance is set up, except there is only an orifice inline. (VREST, vacuum restriction)

 

And how often is a motor NOT under load?


Also how can base + centrifugal be total and then add vacuum on top?
In my book total is EVERYTHING, base + centrifugal + vacuum = total.

I buy a car for $200 then add taxes of $30 for a total of $230
Then add plates & other fees of $30 would this not be the total of $260?
You show up with the $230 total and see if you are driving off.



You do it your way I do it mine.
Dave ----

 

But you are quoting above the common figures for static plus centrifugal which is the correct way "total advance" is calculated. You can do it your way, but your numbers will be a lot higher. If you limited your static + centrifugal + vacuum to a total of 34 to 38, the engine would be a dog.

Think about it this way; The engine runs on static plus centrfugal, and makes its peak power with this figure, since there is no vacuum at wide open throttle. So the vacuum doesn't figure in on tuning a engine for max power. That's why racers don't use the vacuum advance units, there is no point when they are wide open most of the time with no vacuum anyway.

Vacuum advance is for a street vehicle only, and is just icing on the cake, over and above the regular total timing. And it's usage is just during part throttle when the engine is just loafing along without any appreciable load on it.

 

I didn't know about the adjustable vacuum advance! Maybe once I hit a sweet spot in my timing degrees where I have it advanced just far enough before I get spark knock then I assume I can adjust the vacuum advance to advance the timing more under acceleration. I've been driving around with a ratchet, extension and 1/2 swivel tweeking it every where I drive. I got it set already at the spot where it doesn't spark knock but if I do advance it more it does so I'm at an okay spot now. And I have no EGR or vacuum pump hooked up. It's all deleted which I know isn't the best. Sound like an okay plan Dave F? And I'll hit it with a timing light at work tomorrow see where it's at. Maybe I'm close to 10. I'm just wingin it at the moment

 

Have a look at this, and then check Jegs or Crane for the 99600-1 instruction sheet.
This spells it out step by step (it's important to do A before B, ect)

Crane Cams 99600-1: Adjustable Vacuum Advance GM HEI (V8) JEGS

This kit appears to include springs, adjusting wrench and cam limit plate.



A distributor wrench is always a nice addition to the tool box and isn't very expensive.

 

Sweet, thanks! I've got four or five distributor wrenches in my Macsimizer box but I was closing up my shop and had my tool cart near by so it was just laziness on my part. Thanks for all the help everyone

 

That's ok, and check where you are at with the timing light and make a record of it. Then do it all over again, but with the vacuum advance unit disconnected. Keep adjusting it up till you get some pinging and then back it off, all the while the vacuum advance is disconnected continually. See how it drives and take another reading with the light to see where you are at.

I have found usually if you can run the timing up as high as you can get it, it gets real responsive and is fun to drive at lower rpms. The only thing you have to be careful about is pinging(you already know that) and hard starting when hot. If you start advancing the timing up to around 12-14 btdc, after a long run where the engine is nice and hot, shut it off, wait 5 minutes and then try to restart it. If it suddenly struggles like the battery is dead, go out and twist the dist back ever so slightly till it cranks over easier. If it struggles to start when hot you went just a little too far, even though it may not be pinging yet.

If you see an improvement in performance by doing it with the vacuum advance disconnected, I would check the timing to see where you are at and make a record of it. If you are significantly higher than your first method, and you want to keep it where it's at, you will have to buy the adjustable vacuum advance unit and install that. Check the timing to make sure you are starting off in the same place with the vacuum line off, and then start doing road tests again, slowly bringing in more and more vacuum advance till it pings and then backing it off.

This is the only way to really set your engine timing up to maximize a non-stock engine setup.

 

Got it! 👍 I'll give it a shot tomorrow at work when I get time...IF I get time and try it. I'll let y'all know how it went. Thanks again for all the info it helped a lot!

 

Ok so I got the distributor straightened out...putting on a bigger carb too. 600cfm isn't enough for my beast I'm going with an edelbrock 1411 750CFM.

SO I still have problems getting in gear and figured t out. I have a thicker than stock spacer plate between my tranny and motor resulting in the throat bearings "throw" not as far as I need it. So I'm going on a rampage attacking this truck this weekend. The tranny makes a little noise in neutral and my bench guy is gonna look at it for me. So I'm going to yank that, fix my leaking rear main. I know the oil pan needs removed to do it and it's not needed to yank the tranny but I think since t will be out, I can pull the pan easier and leave the motor in the truck and hoist it up a little. So here my question for this!

I'm getting a felpro Viton two piece seal to replace the rope seal. A sneaky Pete install tool cannot be used with it. I gotta drop my crank a little. So....do I need to take my timing cover off or if I pull my front crank seal and balancer will that give me enough clearance to drop the crank to install the rear Viton seal? Any thoughts? It'll only drop the distance of the bottom of the crank to the edge of the timing cover where the outside or the seal seats if I leave the timing cover on. Or am I completely wrong here?

 

On dropping the crank for the seal.
I want to say guys, I have not had the pleasure to do this, is leave every thing on the front of the motor and only drop the rear of the crank so you can R&R the seal.


Yes it can put stress on the front seal so if you there working might want to pull the balancer & seal, do the rear seal then install a new front seal.


You know that sounds like a better way to go but you don't need to remove the timing cover.


Un-less.........how many miles on the motor? How much play is in the chain if it uses one? See where I am going? Drop the cover and install a new timing chain.
Dave ----