Time to tune up the crate

[73c20jim]

GM Goodwrench 195/260HP 350CID with HEI distributor. Stock exhaust manifolds into true dual exhaust. No "X". PB, PS, AC. TH350. 2 wheel drive. 14 bolt FF rear. 8200 lb capacity.

Eddy 1405 on adapter to stock quadrajet manifold.

Street use only. Just a delivery kinda truck with some rides in the country.

No clue as to correct spark plugs.

OR oil filter.

OR timing (4500 ft altitude.)

OR benefits of adjustable vacuum advance.

Anyone have any input on this???

 

[1987 GMC Jimmy]

Your distributor is new so no issues there. I use the AC Delco R43TS plugs if I’m not mistaken. It’s usually a good brand, and they’re a cheap, cuprous plug that have a service life of 30,000 miles which should last me around 3.5 years, give or take. You can get platinum or iridium plugs, and those will last longer, but personally I feel better with the shorter lifespan plugs so I can throw fresh ones on. A good running engine shouldn’t have nasty plugs, but combustion is a violent, hot, and nasty process, nevertheless. Gap spec is .045”, which you need more gap to compensate for the ‘hotter’ HEI spark. If you haven’t done wires, I’d go with the AC Delco wireset.

Oil filters are generally in the same league with one another with the exception of Fram. I don’t use that crap, but I’ve used Wix, NAPA Gold, STP, Bosch, and most of all, AC Delco. I prefer a filter with an anti-drainback valve so if any of them are described as/have suffixes in the part numbers of “classic”/CL or “racing”/L, I’d give them a pass. I think your filter would be the PF1218.

An altitude conscious, benchmark initial timing setting should be in the 4-5* BTDC neighborhood, but since you have a 350, and your compression isn’t insanely high, I’d try 10*. My way of thinking is the world is your oyster when it comes to timing with a 350 say versus a 305.

I can’t speak to adjustable advance canisters or more broadly the merits of modifying the timing curve on a mostly stock engine so I’ll leave that up for grabs.

Besides doing a once over for vacuum leaks and replacing your fuel filter, I think your questions here and your recent HEI conversion cover what a tuneup an older vehicle should consist of.

 

[73c20jim]

Exactly what I was asking for. Thank you. Great write up.

 

[1987 GMC Jimmy]

You’re welcome!

 

[73c20jim]

I think getting a new skip white dizzy is cheaper in the long run than buying a new cap and rotor.

 

[75gmck25]

I used to have a nearly stock 350 crate, and can tell you what worked for me.

I used Delco R45TS plugs, gapped at .045 because that what what the directions said that came with the crate engine. I had base timing at 12 degrees BTDC. My HEI was a GM performance unit that added about 18-20 degrees of mechanical by 2500 rpm. The vacuum canister added about 18-20 degrees. I ran it on manifold vacuum to give a little more timing at idle, which seemed to work better. I had MSD ignition wires, but I think that was just what was available at a good price when I bought the distributor.

For oil filters I usually used a Delco PF1218 filter, but sometimes used Purolator or STP if it was part of the special at the parts store. I always used Mobil 1 15W50, which has the high phosphorus and zinc needed for a flat tappet cam.

A 1405 is supposed to be richer than the 1406, but you still might need to tune it for your altitude. One very common change is to swap out the step-up springs to a set that brings in the power mode sooner. The stock springs usually shift from lean cruise to power mode when the engine drops to about 5" of vacuum, which may cause a bog as the fuel flow catches up. You usually cannot fix that bog by adjusting the accelerator pump; you have to change out the springs.
If you use a 7" or 8" spring it will move the rods sooner and transition to power mode (richer) sooner. You can buy Edelbrock step-up spring kits and install a different spring without even taking the carb off the manifold. Its about a 5-10 minute job, at most. You could also try new richer rods at the same time, if you have some to work with. Edelbrock has all the documentation online to explain how to do it.

Bruce

 

[82sbshortbed]

I think getting a new skip white dizzy is cheaper in the long run than buying a new cap and rotor.

I agree. Bought a skip white distributor for $57 And installed it about a month ago or so. Comes with a lifetime warranty too. I think a new cap and rotor would cost you more than that. So why not get a whole new one.

 

[73c20jim]

Great stuff guys. Thanks.

 

[73c20jim]

I'll use the recommended Delco PF 1218 oil filter. I like Delco stuff for GM vehicles.
I'll use Mobil1 15W-50. I use Mobil1 in all my cars.

Getting a new Skip White Dizzy. Specs are total timing all in at 32 degrees. Mechanical advance all in by 4500 RPM. I think I want the timing in earlier than that.
But I am new to adjustable vacuum advance. On my race cars I always took out the vacuum advance and ran with all mechanical. Total advance of 38 degrees. Maybe messing with the vacuum advance will get the advance in earlier. Vacuum will come from manifold setting. Does the vacuum advance help with better fuel mileage??? Should I go only mechanical???

Plugs we have R45TS and R43TS recommended. I'd think I'd rather go with the colder recommendation. Too cold ruins plugs (fouled), too hot ruins engines, has been my philosophy.

Going to run total timing a couple of degrees advanced more the recommended because of the altitude, I'll start with 38 degrees total timing. I don't use initial timing to set dizzy, always total timing. Then I can see what the initial timing is after total timing is set.

I know the Eddy 1405 is wrong for what I want. I would rather have the 1406. 1405 is what it came with so that's what i'm going to use. I'll try to lean it out to get better fuel mileage. Looking at the Eddy chart for the 1405, I'm going to set it for the leanest setting on the chart (lower left). If it makes no difference in fuel mileage, I'll leave it alone.

Please comment on flaws in my thinking.

 

[DoubleDingo]

R44T or R44TS is another plug that works. I think you're on the right track for the timing since you know what the dizzy is set for and appears to be adjustable. I run q-jets so I know nothing about edelbrock or holley. I like valvoline conventional with stp oil treatment for the zinc, but there are some good modern oils with zinc in them.

 

[73c20jim]

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[75gmck25]

The main reason you want vacuum advance to work is for better fuel mileage at cruise. It also makes the idle smoother if you run off manifold vacuum.

The Edelbrock tuning kit works well, but many folks try to tune an Edelbrock like you tune a Holley, and they get frustrated. For a Holley its common to play with accelerator pump shots and settings to eliminate a bog, but with an Edelbrock its better to first make sure you have the right step-up springs so that it transitions at the right time from cruise to power mode. Then play with the accelerator pump if you still want to see how it transitions.

The Edelbrock metering rods are tapered, and the specs list the two diameters of the rod. Since the rod sticks down into the jet and reduces its opening, the sizes work in reverse of what you expect. In other words, a smaller size rod gives you more fuel than a larger size rod. The large diameter is the cruise mode and the small diameter is the power mode.
Example: A rod that is .065 (cruise) x .047 (power) would have a leaner power mode than a rod with .065 (cruise) x .037 (power), but the same fuel flow in cruise. The overall flow is also determined by the jet size (.095, .098, etc.), so you can get different combinations of flow by changing both jets and rods.

As the engine starts up the vacuum pulls the rods down against the step-up springs and the large diameter of the rod partially "plugs" the jet opening to get the cruise mode. However, when vacuum drops during acceleration it can no longer overcome the springs and the rods start be pushed up by the springs. When they are fully up you will be at the power mode diameter of the rod and more fuel will flow. The strength of those step-up springs determines how low the vacuum has to be to let the rods start to pop up and go to power mode. If you use what Edelbrock calls an 8" spring, it means that it will pop up when vacuum drops to about 8". Stock springs are usually 4" or 5" rating, depending on the carburetor model.

Bruce

 

[73c20jim]

Better fuel mileage at cruse is what I am looking for. I realize I a pushing a box through a windstorm, so I don't expect miracles.

Thanks for the input.

 

[fussfeld]

1) Why not use a quadrajet? Especially considering it's a q-jet manifold?

2) (ties in with #1) Remember, we have plenty of room underhood to go with a hi-rise manifold...............

 

[73c20jim]

1) Why not use a quadrajet? Especially considering it's a q-jet manifold?

2) (ties in with #1) Remember, we have plenty of room underhood to go with a hi-rise manifold...............

Simply because I don't have a q-jet and the cost would not be covered by the mileage savings. UNLESS someone would trade a Q-jet for a 1406.

CORRECTION: 1405 not 1406. The manual choke version.