Tuning headache

[anotheridiot]

We didnt run into so many vacuum issues until we got over .300 duration at 107 lobe separation, but your idle would improve with 112-114 lobe separation.

Just sometimes we look past the obvious and did you verify the timing mark on the balancer or have a new balancer you verified after you degreed the cam. I know its too simple, but the stock balancers are two pieces with rubber between them and the mark can move. At this point a known good carburetor sounds like its a way I would go, after I sprayed the carb with carb cleaner when the car was running along the mating surfaces

[brotherGood]

Yes, when degreeing the cam I also verified the mark on the balancer. Specifically, verified the mark was incorrect on the balancer and subsequently scribed a new mark.

The previous carburetor that was on it only got 9", but it was more stable of a reading. Still quite low..but also that carburetor was way too rich. Im thinking (hoping) the bouncing of the gauge is due to the current carburetor still needing dialed in a bit. I know the gauge will move if the carb is out of adjustment.

[fatguyzinc]

verified the mark was incorrect on the balancer and subsequently scribed a new mark.

but does that tell you whether or not the outer ring walked? its not just is the mark correct,
but if its not WHY wasnt it correct-wrong balancer or outer ring walking is only things i can
think of, so if thats original balancer i would suspect the outer ring moved.

[Captain]

Just from experience......
Have you checked push rod length?
Deck the Block, True up the Heads, Bigger Bump Stick......all you need is a Valve not Tight in the seat..... compression/Vacuum Leaks. And as the engine warms, it will get worse.

Just my

[brotherGood]

but does that tell you whether or not the outer ring walked? its not just is the mark correct,
but if its not WHY wasnt it correct-wrong balancer or outer ring walking is only things i can
think of, so if thats original balancer i would suspect the outer ring moved.

The engine arrived from assembly with a "new zero" on the new balancer. This was verified, and reverified when the cam was being degreed.

[brotherGood]

Just from experience......
Have you checked push rod length?
Deck the Block, True up the Heads, Bigger Bump Stick......all you need is a Valve not Tight in the seat..... compression/Vacuum Leaks. And as the engine warms, it will get worse.

Just my

The push rod length I have not checked. The current idea is that when the block was cut at "zero deck", it was done so against different rods/pistons..and the new ones are shorter. This cam evidently requires at least 10:1, and if the pistons are down in the hole more than they're supposed to be..that could be the cause of the poor vacuum.

Saturday, before the bronchitis really hit I managed to go out and do another cold compression test. This shows the numbers after the cam was degreed. Some improvement, more concern however. (Recent test top, first test bottom)

[anotheridiot]

This is my favorite type of vacuum gauge to use
Amazon.com: Hromee Fuel Pump and Vacuum Tester Gauge, Carburetor Pressure Diagnostics Leakage Tool Kit : Automotive
We had this when we had a carburetor on the motor. Set it where it was supposed to be around 15 and had 7 pounds, advanced the timing and it jumped up.

Does your vacuum gage show increase in vacuum when you advance the distributor with no regard to where the pointer is?

[brotherGood]

This is my favorite type of vacuum gauge to use
Amazon.com: Hromee Fuel Pump and Vacuum Tester Gauge, Carburetor Pressure Diagnostics Leakage Tool Kit : Automotive
We had this when we had a carburetor on the motor. Set it where it was supposed to be around 15 and had 7 pounds, advanced the timing and it jumped up.

Does your vacuum gage show increase in vacuum when you advance the distributor with no regard to where the pointer is?

Yeah, vacuum increases as RPM increases (slowly & steadily). I had it hooked up the other day before it got off of the fast idle and it was rock solid at 9hg. Once it started to idle down, the needle started to drop and bounce.

[anotheridiot]

Yeah, vacuum increases as RPM increases (slowly & steadily). I had it hooked up the other day before it got off of the fast idle and it was rock solid at 9hg. Once it started to idle down, the needle started to drop and bounce.

I just meant to adjust the timing when it is idling and take it to the highest vacuum, just like you adjust the idle mixture screws to get to the highest vacuum.

[brotherGood]

Ah, following. I set the initial based on total minus mechanical at 18°. It would be okay until the car got warmed up. Then it would run hot and be a nightmare to restart. That's been a separate yet related issue this whole time. I don't beleive when the distributor was recurved it was done correctly, but I also don't think that's the issue.

[SuperBuickGuy]

I have not done a smoke test. I was advised to take the turkey tray out and instead put thinker gaskets in, but in hopes the thicker gasket would alleviate the gap rather than accentuate the problem.

The compression test was done after the car sat for a few days. Not saying that has something to do with the low numbers, but just for information sake. As mentioned, the block was milled when the original rods/cast pistons were to be used. The assembly shop (different shops-longer story) noticed that not only were some of the rods bent, but also the skirts on the cast pistons were hitting the counter weights. I then (with help from one of the top Olds builders-same guy who recommended this cam) found a set of forged pistons with longer rods. The math worked out, but I don't know if that in-turn put the top of the piston lower than where it was when the milling was done for the cast/factory rod combo.

When the cam was degreed, IIRC it worked out to putting on the "A2" notch on the gear, and it was still 1 degree off, but much closer than the 20 degrees off or whatever it was.

the A2 mark

which begs the question.... did you put the A2 mark as you see above or did you put it at the keyway?

Here is some good reading for you (and saves me a lot of typing ;) )

https://www.enginelabs.com/engine-tech/back-to-basics-understanding-a-cam-card-with-erson-cams/

[brotherGood]

the A2 mark

which begs the question.... did you put the A2 mark as you see above or did you put it at the keyway?

Here is some good reading for you (and saves me a lot of typing ;) )
https://www.enginelabs.com/engine-te...th-erson-cams/

Keyway was the A2. The outer "A2" is what got lined up with the dot in that case.

[brotherGood]

Got the wideband hooked up, and we took it up the block to get some numbers recorded for the carb builder. Hopefully we can get it squared away by the time the engine needs to come out.

https://youtu.be/_Q9Y6ldOkNo?si=pR55cUEEkeDDpkhX

[DanStokes]

Numbers are good!

[SuperBuickGuy]

Keyway was the A2. The outer "A2" is what got lined up with the dot in that case.

It is 2:30 am and I'm headed out the door to drive to SEMA (actually Ely). but in my time warped head, I think you're at least 6 degrees advanced (between cam grind of 108+2 and setting it at A2). It would explain the inability to start it at 18 degrees - reality you're at 24 degrees....

why would you want so much advance?

but as I'm driving today, I'll try to math this in my head....