'74 C20 w 292ci inline 6, manual 4, no idea of miles on the engine.
When I got it ~2 months ago it was getting approximately 5MPG City. I removed the addon rack (original listed weight was 4600, now probably 4300), replaced points with pertronix, new plugs, wires, cap, rotor, coil, battery, and retimed the engine. City mileage is now just shy of 11.
How does this compare to others with a similar engine? I'm presuming best case you don't get much above this. I'm thinking maybe rebuild the carb and possibly change the gearing in the back axle, but those are both low priority for now.
I timed it per the sticker on the air intake. 8 BTDC @600RPM. Are you suggesting to try to advance furthur?
That was a big pain. I went to Autozone without a plug in hand and just trusted their system to give me the right thing. What I got had 1/2 the thread depth I needed. Except for 1, which apparently was a screw up by the manufacturer. So went back and pulled one of the old ones and of course that crossed to something they don't stock. I can't remember the exact numbers, but they are Bosch Platinums. The too short ones were 4806 maybe, the one that matched the old plugs was 4835, and the ones I put in were
4805. It appeared to have the same temp range from visually inspection but I need to pull one to check how it is wearing. I gapped the plugs at .044 (spec says .035), since I have the pertronix Ignitor and coil, and it seems to be working fine so far.
Timing lights are almost useless on high mileage vehicles because of slack in the timing chain and other components. Bump it up 2 or 3 degrees, and see if it pings. If it starts to be hard to start (firing too soon makes it drag), it's too much.
Repeat after me: I will never, never, EVER use bosch platinum's in my Chevy. They are crap. The correct plug is the Delco R44T. They stock them, at least around here they do. Very common plug. Buy a set of those. Enjoy. I wouldn't go much over the stock gap even with the high perf coil. Try .038 to .040 for starters.
292 straight six is gear to gear drive, no chain, no belt, no slack. things to check, vaccum signal to advance unit on distrib. The port sometimes gunks up on the carb, the base of the carbs underside does the same blocking vaccum passages. Find an electronic igniton distrib from a later model and ditch the points. Make sure the carb screws are tight, the screws that hold the base to the center part of the carb get loose with age as the gasket shrinks. Quick check grab carb firmly and GENTLY try to twist back and forth. If there is movement, they need tightening.
I will agree here, Bocsh, NGK, Nipsendenso have no place in GMs, some fords (only some because so many are more Mazda then ford these days) and even fewer chryslers.
Now then if you want to have some real fun, first make sure compression is good, as its a good indicater of the general engine health. The intake is a bolt on unit. Clifford has a real nice four barrel intake for this engine and even nicer exhaust headers.. If you really want to go, there is tri power set up..They also have a far superior two barrel manifold for use with
350, 500 cfm holly 2 barrles, or 370cfm weber. for really sweet there is a dual two barrel set up using webers. Clifford also has some nice cam shafts. Isky makes numerous cams for it.. Only thing better than a 292 is an OVC Pontiac straight six.
Someone wrote: "Repeat after me: I will never, never, EVER use bosch platinum's in my Chevy. They are crap."
I agree 100% that Bosch is crap. I had one blow the electrode clean out the metal threads. The electrode was still attached to the wire so the plug did not go flying through the hood. It destroy some other wiring under the hood causing 435 dollars worth of damages and towing. Photos were taken of the damages and the plug. Removed the rest of the plugs and found spots where compression was leaking through the and they were about to blow out. Sent a bill for damages to Bosch and long with the plugs, a receipt for new Delco plugs and all eight of their crappy plugs.
I received a letter from them three months latter stating that they did not believe that the plugs were defective that I installed them wrong. They were either over torqued or under torqued and that is what cause the damage. I had an attorney friend write back along with a sworn affidavit form the friend that put them in that they were installed correctly. A month latter they offered to pay for the plugs only. My attorney friend reply back "SEE YOU IN COURT". Their reply was a check for the plugs and damages.
Judging only by the picture at Delco's website this plug won't fit. It looks exactly like the one autozone crossed to for the engine, but the threads are not long enough. On a vehicle this old who knows what happened in the 30 years between manufacture and me getting it, but perhaps the head has been replaced with a different unit. I will try to make that determination once I clean things enough to get numbers off of them.
I bought an '82 Chevy 4x4 350 and am working on it to put on the road this spring. The previous owner put plugs from a Ford in it and the reach was unreal. I knew right away that the plugs were wrong when I saw how much thread there is and some time on GOOGLE told me where the plugs really belong. Exposed thread, glowing red, can make for a lot of pre-ignition. Always use what is recommended. The Platinum's,
4-gaps, etc. are just marketing successes to make money from you and me. They don't and cannot work any better and sure as hell are not worth the extra green.
you didn't mention a new air-cleaner.You did check/replace that I hope.Also check that the vacuum advance diaphragm isn't broken.This happens and will wreck your mileage.Disconnect the hose at the carb and apply vacuum(suck on it).You shouldn't get a mouth full of air. Even if it's good I would invest in an adjustable vac.advance which will allow you to set it for max possible advance.They are about $25 and come with 3 sets of springs to set the centrifugal advance as well.It really helps your mileage to get the timing dialed in as close to knock as possible. Best ...Brian O.
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