1971viking

My buddy picked up a 1974 olds 455. It has some head work, performer intake and edelbrock 750. It also has a lopey cam that we have yet to identify. It also has a crank girdle. The previous owner claims 500hp.

The problem we are having is setting the timing. The car is running fine at 1000rpm with the timing advance set at way past the indicator. The indicator ends at 24 I think so that is the correct one for HEI. The vacuum is disconnected at HEI distributor and pulling about 14 at idle and 10 in gear.

I am thinking there is something wrong with the distributor. Other than the timing being high everything else seems in order. Oil pressure and temp are good. The engine runs good. The car starts without much effort.

We have the timing set now at the highest vacuum. Not sure how else to do it.

Thoughts?


Thoughts?

oldcutlass

Set your total mechanical timing with a dial back timing light to 34 deg BTDC with the vacuum advance disconnected. Then see where the initial winds up at idle. You want to try to keep your idle around 7-750 rpm. Then you can subtract you initial from your total and thats how much mechanical advance you have.

You may still have some more room to advance a bit more but this will get you in the ball park. Be mindful of detonation.

cutlassefi

Disregard where the timing marks are, you need to verify that the outer ring on the damper hasn't slipped and/or it has the right pointer on it by installing a TDC stop in the #1 plug hole.

Do that first, then if your timing is still off, which I doubt it will be, then adjust the total timing to 34 or so to start with. Make sure you spin the engine high enough to make sure it's reached full advance, then go from there.
Total advance is actually more important than what it wants at idle and low speeds.

And sorry to inform you but unless it has really really good heads on it, with 14" of vacuum, a Performer and 750, it ain't making anywhere near 500hp.

1971viking

Sounds like a plan. We will check the ring on the damper.

Like I said this is not my car so not concerned at the horsepower rating.

I think the guy before had a demon 800 carb as the original setup. Not sure if that make much of a diffence.

Yes his vacuum @ idle is 14 at 1200rpm and 10 in gear with the timing advance where it is at. (very high) Not sure why the original owner has a girdle on it and a 7QT pan.

What is your thoughts on setting timing based on vacuum? That is really what we did. As long as it does not ping we will not back it off.

oldcutlass

I prefer to use the right tool for the right job, timing light is the most accurate. Caburator settings will effect vacuum.

1971viking

OK Checked TDC and the timing indicator is correct. Timing is now @14. Still runs a bit ruff. Idle at 1000RPM. Going to see where timing is at when @3000 RPM.

Here are the specs he gave me for his motor.
Performer intake 455
A heads Fresh valves and valve job. 2.07 1.71
New springs with 105 lbs. on the seat.
Harlan sharp full roller rockers
Heads decked flat,milled .030 80cc
Arias custom pistons for 425 7 inch rods. .020 in the hole with a 6cc valve reliefs
425 rods polish and shot peened and balanced with the pistons
N crank
f block J&S 4 main girdle
ARP rod bolts
ARP main Studs
Accel High Performance Billet Distributor
50K Volt Coil
Rotating assembly balanced with stock damper and flywheel.
Comp Cams .532/236 @.050
Comp Cams pushrods.
Headman A body 1-3/4 headers
High Flow water pump
High Flow fuel pump
Moroso 7qt pan
HV oil pump with deep pickup

oldcutlass

You need to try this.

ziff396

x2

Octania

I would add that you may want the vacuum advance hooked up and canned properly. And Mech Adv set properly.

I went thru a similar thing last year with a lot of cam in a 403. The motor is not stock so you CANNOT use stock timing specs for optimizing.

Consult the thread at realoldspower.com for all the details
Oh yeah, that vaporized. Bummer.

Well, basically, at retarded initial timing and ported dist'r vacuum, the engine would NOT idle well, vacuum dropped off, which opened the power piston and made it richer which made it worse. Overheating. Low power. No upper RPM. Meh.

Bumping initial timing raised the idle to 1000 and then detonation at part throttle under load.

I went thru the above 34 degrees max routine and adjusted MA and VA until I ended up with this:

Lots of static, not sure where it ended up, but around 20-24 degrees.
Vacuum hooked to manifold, so that at idle, it had even MORE advance, and it loved that. Improved throttle response, and that VA part backs off under load [low vacuum conditions] thus alleviating the part throttle pinging. This required an adjustable VA can and limiting the VA travel to about 11 degrees. There is a can 1973511 that does not actuate until a higher level of vacuum, like 10-11 in. Hg. Search Amazon, epay, etc. for one perhaps. It is not adjustable for travel, but you can modify to suit, right? Limiting washer on the screw for instance.

I also fiddled with various pcs of MA kit and got the MA down to about oh I think 10 degrees. This was done on the bench with a pointer wire on the rotor mount, tape on the dist'r OD, and some mathematical gymnastics to translate distance on the dist'r housing OD into *crank* degrees of motion. Trivial math of triangles.

The result was well worth the effort. Plus I learned a lot.

You may try a Google search on the matter, for many other brands also have done the same thing, and you can find vac can part numbers, picture stories of how to limit your vac can travel, and whatnot.