I just put an engine together, it's pretty mild and it's knocking. It runs well, makes good power, but.... I have a hunch. I have a 1976 maverick with a 302, it came with lots of emissions stuff from the factory. Since its a 76, I can get away with a non-smog rebuild. I built a 1970 style 302. No smog equipment,Autolite 4100 carb,351 heads, comp roller cam (.486 lift). The ignition is still the same as it was in 1976. It is the predescessor to the Duraspark system. It's all electronic with a "Hall effect" rotor and sensor and has a computer box on the fender wall that is labeled "Echlien". I thought it would be fine, but I have not been able to stop the knocking when I put my foot in it. I use 92 octane. I have no vacumn leaks. Timing has been set and reset. Is the advance curve factory set to run only with the smog equipped motor? Egr and all that stuff? I am thinking of using a pertronix setup distributor,set to say,1970 advance curve specs and trashing the factory computer module. Anyone with any ideas please help me come to a good descision. Thanks.
You have a Duraspark Setup. Echlin is a brand of replacement part. NAPA I think. What you have should be far superior to a Pertronix setup. You can use that distributor to trigger a Holley, Mallory, MSD, etc box if you like. But I think the advance is in the mechanical side of things. Are you running a vacuum advance? What is your compression, and did you (or your machine shop) actually measure the compression ratio or are you just going by what it 'should be' with the pistons you're running?
Two areas to look at the timing curve (including the curve for the vacuum advance (it may be coming on too soon) and the carb. If the timing is set at factory specs then you may have to retard it a bit. You might have to limit the vacuum advance and / or increase the spring rate to slow when it comes on. If the carb is running too lean it will knock with even modest timing. You should be able to go up to four jet sizes higher than the stock jets without any problem and I have seen the need to go up 6 sizes. This is the hard part of tuning - you have to make one small change at a time and look at the results. Keep good records because you will need to keep tuning one thing until it goes backward - then you need to change it back two steps. This goes for the carb jetting and the timing. Check the results on a road run starting at ten miles an hour in manual second gear then mash the throttle and click the stop-watch. Check how long it takes to get to "redline" on each run - allow the engine to cool down to "normal operating temperature" between checks. PaulS
Charlie makes some very very good points here. I would get informed as to what your compression ratio is. Then you have a baseline to start trouble shooting. The factory ignition was and still is good enough for anything running regulalry on the street, imho. Dan
Well I was ready to send the distributor out to be recurved, but the guy wants to change it the pertronix. 'Cuz that's what what he knows. I am worried that if I start trying to change it, I'll mess it up. Are springs and vacumn advance units still available? I'll check the local stores. They look at me like i'm crazy when I ask for stuff from 1976. How hard is it to change jets in the Autolite 4100? Do you need gaskets?... The compression ratio is just a guess, using a variety of info sources. It's a stock block(2002) with 1970 351 heads. These have 60cc chambers which should raise comp. slightly. 8:1 is the start point for a stock 2002 engine. So if it's now about 9:1or slightly higher I can't see where comp ratio could really be the problem. People have been using 351 heads and aftermarket heads with 60cc chambers for years and years on 5.0ltr blocks. Someone suggested I disconnect the vacumn hose from the dist. I'll try that too.
So it was a brand new crate engine? As far as I know there were no Fords with the 302 in 2002. 8:1 seems awfully low for a modern engine. Can you clarify where you got the thing? With 60cc heads, you are probably right, the CR is probably not that high. But I'm just curious about the engine.
From what I know mustang 5.0's 87-93 have 9.0 with 63-64 cc heads. I dont know about the explorer 5.0 but should be close. I have a stock 87 5.0 with 60 cc heads. I have figured my compression to be 9.43. With 57cc heads it is 9.7. My compression numbers are with desktop dyno 2000.
Yes Charlie the shortblock assembly is legit. I checked the part # with Ford. I got it on ebay. The guy says he has a virtually unlimited supply of them. I gave him 650 for it. He also has gt40 X heads. I didn't want that head. Anyway the block is an Explorer type. The cam had to go. Hypereutectic , flattop pistons, and 351 firing order.I don't remember where I got the 8:1 ratio from, but I'm stickin' to it. Also, I tried adjusting the vac advance tonight with a 3mm allen wrench. The thing was adjusted all the way out. I gave it one full turn. The knocking was signifigantly reduced. God that was easy! I wish I knew how to disassemble the distributor and adjust the springs. I also ordered the video from Pony Carburetors on how to install and adjust the Autolite 4100. They also sent a detailed instructions on how to set the timing. The problems I have had timing the thing are very common they said. Has anybody been able to set timing with a timing light???
A new set of advance springs, a timing light, patience, testing and record keeping will fix your problem. You have to much tip in advance. The only way is to recurve. The vacuum advance is to allow more advance under light load only. Disconnect the vacuum and start setting up the spring combo for a smoothe advance with a max of about 30* at around 2500 rpm with a limit of no more than 36 to 38 max. above 3500 rpm. Other things that enter into the mix is where you get the vacuum signal from. It has to come from above the throttle plates meaning never apply full time vacuum to the dis. or the only time the vac advance will retard is at near WOT when the vac goes low. As you see, the advance diaphram has a spring tension adjustment. That will also be involved in the final setup. There are few people anymore that knows about such things so don't depend on someone that has no knowledge of it.
Hmmmm... I thought that the vac source was the only possible connection. My carb has one vac source. It is the front passenger corner down low on the carb. Below the throttle plates. I guess I'll have to make a tool to remove the spring clip that holds the pickup on. Thats the only way to get to the springs. I should just buy a new dist. I would if I knew the right one to buy without major hassles.
