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#1
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440/ Purple Cam/ Timing
I have a 440 in my 69 Roadrunner with a purple cam ( 292/509)/ new 670 CFM Holley Avenger/Original Hurst 4-speed/ 3:91 Posi rear end/electronic Orange Box Ignitiondistributor. The car runs good but I am always playing with the timing. I have had the car for four years and am taking it in to a Dyno shop on Monday to see if I can get anymore out of this setup. My question is regarding the cam timning/spark plug gap. First can anyone tell me what the stated timing should be with this Purple Cam? And secondly, should my spark plug gap be .35" ( Champion J12YC) as described in my manual or something else? Thanks, Dean.
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#2
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You could go up to 40 on the gap with stock ign. box. 34* would be a good starting point. You prob is the carb. It's wayyyyy to small. Stock was an 850 cfm Thermoquad. And with that cam you could use it. I ran one in a RoadRunner Years ago and that's a pretty hefty cam to be using with too small a carb like yours. Your just wasting hp by using it.
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#3
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Thanks for the quick response. I had a 750 Eddy for the past 3 years and constantly had problems with low end torque. The car is running much better with the 670 Avenger. I have a two other cars with Holley 670's and they run great. I will put in a new set of plugs and check the timing again. Again, I'm just trying to get the best combination for the what I have on the car for weekend cruising, no racing. Thanks again, Dean.
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#4
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Any spread bore carb will get you more vaccum due to the smaller primaries and with the old tried and true bumpstick you have in it you need all you can get for street use.Those newer holleys are supposed to be a good carb,read your plugs and open the gap to 40 for electronic ignition.The more advance you can dial in to it the better for street use as long as it starts good and doesnt rattle.Might also try lighter springs on the counterweights.
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#5
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A spread bore, or a small carb will not give more vacuum, but especially at part throttle the gases flow quicker which gices teh boosters a better signal and makes the carb more accurate & responsive (all else remaining comaprable). A 670 in a 440 is on the small side with a cam like the 292/.509, propably somewhere after about 4500 rpm you would gain power from bigger cfm carb. You can make the vacuum holleys work great, and they are not very sensitive if the carb is even a little "too big". Have you done any playing with the secondary springs yet?
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#6
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What compression and cylinder head are you running? That cam should have no issues with bottom end. I've run it with anything from 3.23's to 4.86's and that was with an auto. The carb is waaay too small. A 750 would be at the lower end of what I'd pick. Start at 34 degrees total. Limit the full advance in the distributor so you can run more initial to keep the low/mid strong and engine running.
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#7
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even if you set total timing at 34* total, most of the time there is to much advance built into the mopar distributer. the new ones, i believe are adjustable but the old one needs the slot welded up. i think you would need in the neighborhood of 17*-20* initial and a total of 34*-36* total. if you set your total at 34* and your initial is 10*, that is why your bottom end felt so soggy with the 750 eddy carb. with a very similiar cam in my motor, my car would hardly run with 10* initial and if i put it up to 17*, it would have a total of 40something.
i agree with everyone on the carb being too small. get a double pumper holley. unless your into fuel milelage. i would go for an 850 too. |
#8
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I haven't changed the secondary springs yet. I will take a look at that today. I did put in a new set of plugs yesterday and it is running better. Thanks to all replies.
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#9
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Your orange box is retarding the timing...watch it as you load it on the Dyno it'll fall off like a brick and the output will drop right along with it.
MP Cam, Orange box, Holley with a 40 year old design and new paint Avenger....ever think about trying something that didn't come out of a magazine article? You'll always have trouble with that ignition, call Don at FBO he's got a special right now on his stuff...works great dozens of cars around here run it and it flawless. |
#10
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I am just zeroing in on your statement about "...but I am always playing with the timing...."
Make sure the timing chain is in tip-top condition and is not stretched. Even with the MP setup usually you just set the total at between 34 and 36 degrees and forget about it. That puts the initial at anywhere from 8 to 12, and with a stick shift and the 3.91 gears that should work out great. Automatics like more initial which is hard to get with the stock MP setup. Any more initial than 10-12 and the total goes past the detonation range of 38 plus degrees. I have taken some older junkyard engines out and readied them for a new application and always upgraded the timing chain. That fixes a lot of problems right there, even a couple of engines that were fouling plugs real bad, and is not that hard to do even with the engine in the car. Then, if you want to optimize, go with the tuned distributor and controller from FBO. Just keep in mind that even a new perfectly tuned distributor will not work well if the timing chain is sloppy. PS: I have a car with that exact .509/292 cam (the cam is about 15 years old and has been in 3 engines now!). It is also a 440 4 speed with 3.91 gears and headers, completely stock valve train in re-conditioned 906 heads. I just run a stock MoPar type reman electronic distributor with the MP chrome box. Total is at about 36, all in before 2000 rpm. I do run a stock thermoquad intake with a thermoquad carb "smiled-on" by demonsizzler. This thing Idles at 950rpm, the car can move out with no throttle on flat ground, has nearly instant throttle response in any gear, can be a tire-fryin SOB at times. It has low-end GRUNT, midrange GRUNT, starts pulling even harder at 4000 rpm. It pulls the same thru 5500 all the way to 6000 where it flattens out a little bit. The timing is set as far as I am concerned. The next thing for this engine is an FBO special.....then a street dominator intake....then.......!!! |
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