I have a 1973 Ford Ranchero 500. It has a 351 Cleveland 4 bolt mains and 4 barrel closed chamber heads. Also has Performer Intake, 600 carburator, headers, mallory unilite distributor, and has been bored .030. I have a ping problem at 75 mph, when I goose the throttle a little it pings. I have tried 104 octane boost with no luck at all. I have retarded the timing enough to stop the ping, but have no power. I have been told that I need a carburator with around 850 cfm because the 600 cfm I am now using is causing it to lean out causing the ping. Is this true or am I possibably living with to much compression.
Thanks for any help I can get,
RCR

 

My guess is it's a little of both -- too lean will ping, and 10.7+ :1 compression can be tough. Usually the octane boost should fix the compression end, so you might try a different (bigger) carb.

 

ok here is what you need

http://www.racegas.com/gt100locals/default.asp

100 octane at the pump

 

If it's true that the carb being too small causes the Ranchero to run llean, what's wrong with putting one step richer jets in it and increasing the accelerator pump shot so more gets in there when the pedal hits the floor? Maybe running a bit richer will help with the pinging.

 

73Galaxie makes a good point. Airflow capacity is not related to fuel/air mixture. A bigger carb will allow you to pull in more air, but that's not your complaint.

Mid-range lean out is a common carb tuning problem. You need to find a way to enrich the fuel mixture at the engine speed where this problem occurs. I'd suggest you find a good carb tuner before you melt the pistons.

 

wow! Not only was my post actually relevant, but someone said I had a point!!! (jumping up and down). Um, I don't know which carburetor you have, you just said a 600, but on a Performer, the mid range cruise can be kept at the same mixture while enrichening the power by a different metering rod or a different jet or stronger springs at the primaries, also you might try putting a .101 or .098 jet or whatever is richer in the secondary jet bowl fitting - it sounds to me like your secondaries are too lean. Buy a set of plugs in the cooler heat range, plus a few extra plugs. Gap them so they're exactly the same. Buy some richer jets and metering rods. Read the tuning section in your carb manual. Then you figure out which piston you want to use to read your plug for richness/leaness/detonation - after all, you don't want to pull 8 plugs at a time over & over. Set the timing to where it just barely begins to detonate, back off a degree or two with the timing light and tighten down the distributor. Drive the car for a few miles, getting on the gas once or twice, then pull the plug. Compare the condition of the plug to a chart and adjust your carb accordingly. Then replace the plug with a fresh one and repeat until your plugs are that nice lightly toasted marshmallow color. It'll cost some bux, but since a mech charges $40 an hour, you'll save money and time, too. You might also want to recurve your distributor advance, but I'll leave that discussion to more knowledgeable minds than mine.

 

From listening to a friend of mine, DEFINITELY change the carb. He feels that the 351w (I know, you've got a Cleveland) should come factory with a 750. I'd say get a bigger carb. I know Predators (up to 930 cfm) will never overcarburate your motor, as it only give as much as you need. Fuel mileage will suffer a bit, but how good the 351c do anyhow? And you'll feel a monster return when pedal = floorboard. Get one with the idle circuit for street use.

 

600 CFM is plenty for that engine. It makes no sense to put a carb with more airflow on an engine that is getting too much air and not enough fuel as it is! (A 'lean condition' by definition is too much air and not enough fuel.) Now assuming that your problem is caused by the engine leaning out, the good news is that Holley carbs are very 'tunable'. You can get larger main jets, different springs for the secondaries, different cams for the accelerator pump, larger 'squirters', etc.

I'd also look seriously at tuning the distributor advance curve along with messing around with the F/A ratio issue.

 

You need a dizzy with vacuum advance if you don't already have one. if you do make sure it retards when vacuum drops.

 

I am running an Edelbrock 600 cfm and have already jetted to the .101 & .098, still pings. Also the distributor has vacuum advance hooked up to a ported vacuum source. Timming is set to 10* BTDC. I have not tried a colder spark plug yet. Could be a good change. I'm trying not tear this engine down and go to dished piston's but, may be only option.
Thanks for the ideas that I'm getting from you guys,
RCR

 

What's your compression ratio? What kind of pistons? If they're flattops, then the CR is probably like a 1970 4 valve cleveland with closed chamber heads which is 11:1, if it's a 1973, then the pistons are already dished, the CR is 8.6:1. I don't see why you'd be pinging, my 400's CR is 8.75 after factoring in a factory ratio of 8.4 plus a increase because of my 030 bore and another increase b/c of the heads being milled and leveled. Your CR with dished pistons and a rebore should be around 9:1.

What octane fuel are you using? 104 octane booster doesn't raise your octane to 104, it might go up 3 or 4 points, but not a lot. Pouring a bottle of 104 into a large gas tanks mean less improvement than a smaller tank. Try using a different brand of gas or a higher grade, you'd be amazed at the variations in actual octane when the pump sticker says 89 or 91. One gas station in town sells racing gas at the pump for $2.99, see if someone in your area does that. If it still pings on race gas, your distributor's advancing too much!

 

It has flat top pistons and I'm running Exxon Premium 94 octane, so I'm realistically only getting around 97 or 98 octane. I haven't tried a colder spark plug yet, but will this weekend. I'm not sure what the compression ratio is and I will check the compression this weekend also. Maybe that will give us some insight. Also I believe this is a 1971 Boss motor.

 

RCR,

I have Aussie CC 2V heads and my chambers are 3cc's smaller than yours. I haven't had pinging problems with mine running on 92 octane, but haven't run it hard since the temps have been above 80 deg. One thing the folks over on the 335 series forum talk extensively about zero decking the block when using closed chamber heads. With a .042" thick Felpro head gasket and zero deck, you don't have much more distance before you lose the quench effect (I think .053"). Mix 3 gal. of avgas (110 octane) in a full tank of gas and see what happens.

With that said, I also agree you may have timing curve issues, possibly a broken spring in the distributor. Another thing that hasn't been suggested yet is that your damper may have slipped and is way off.

Steve

 

Thanks Steve,
I haven't thought about the dampner. I have also been reading about backing off on total advance to a total of 24 instead of 32 degrees. I will be trying anything I can to stop this pinging problem. I have also read to try turning the screw on the vacuum advance all the way in, could possibably help. I even read of going to an NGK 6 spark plug (colder plug).
Anyway Thanks,
RCR