whoa wait a minute here. We've been down this road before too. You're still using the stock lower pulley, right? Think about it.... that stock lower pulley is what--8" diameter? The alternator pulley is 2" right? That's a 4:1 overdrive which means at 5500 RPM the alternator is turning 22,000 RPM. Combine that with a hard shifting C4 and good traction...when the alternator is turning that fast with that much weight it doesn't take much to throw it off. Just a little bit of a belt slip is usually all it takes, the belt will start to "slap" and its over with. Also when the trans is shifted, the engine RPM will drop--sometimes drastically (depending on the trans and/or converter). The rotor in the alternator is heavy and its still trying to spin at 22,000 RPM where the crank has slowed down a bunch. That will cause the belt to start to "whip" and sometimes come off. My Mustang was doing the same exact thing. It would be fine around the pits and at lower speed (under 5000 RPM) but during a race it would come off every time. I rigged up a smaller crank pulley and it has not come off yet. Went from a 10" lower pulley to a 4". The alternator still charges fine. You could also change the alternator pulley to a larger one which would do the same thing. Just something to think about---it may not be your problem but it's a start.
Sure cheap fix: By installing a narrower belt ( in width) it sits down further in the groves. Always worked for me as I used to have the same problem 30+ years ago. Bruce
Had the same issue on my 460 drag truck,i used a MOROSO alt pulley i think it was like 4'' or something,it was for a chevy but gm and ford alt pulleys are interchangeable.But on the Comet i used a serpintine style belt and pulley system off of a 5.0 mustang and it works perfect. Derek.
Ford made a set deep v-groove pulleys for their performance engines in the '60s. The belt sat deeper in the groove and the rotating force did bring the belts above the pulley. If you look at a stock pulley, you see that a new belt is flush with the top of the pulley. On the deep groove pulleys, the belt sits well below the top of the pulley. However, mavman probably has the best solution.
I had good luck with the Moroso alt pulley myself. It is very deep groove and slows the alt at the same time. If you don't find any problems with any parts or alignment, I would go that route. It is cheap and easy. The only problem could be under charging if you run alot of electrical stuff. I had an issue with that when running a 60A alt and my battery in the trunk. A higher amp alt cleared it right up though. Edit: The alt I was running may not have even been 60A, don't remember, it was a long time ago. The alt I replaced it with was only marginally higher amp and it was never an issue again. I want to say it was a 60A alt and I replaced it with a 78A.
this may seem weird.. but are you using the correct belt.. there are deep groove belts and not deep groove belts.. maybe the belt you are using is the wrong v groove for the pulley you are using.. i wouls take your belt that you are using to the shop and find one that sits down in the groove better.
Thanks for all the help. Sorry i have been gone for so long. I have been out of town and busy with school. I just put on the deep groove 4" Pulley on the alternator and we will see how it runs tomorrow at the track. I have been meaning to take some pictures, but havent got around to it. I look forward to tomorrow as we are approaching the 12's. Once again thanks all. I will make another post after the race tomorrow to let everyone know how it went. I also believe we got a smaller crankshaft pulley that we can install after tomorrow. thanks kevin
I'll admit I didn't read the entire thread but Horepower TV just did a segment on this very thing and said the best solution is deep groove pulleys. In fact that showed a comparison side by side and said that the deep groove pulleys was one of the ways you coule tell the original Hi-Po engines in some cars. If it were me I'd try the deeper groove pulleys
I wish i had good news, but i am sad to say things have got worse. Yesterday at the track during my first run, my fastest yet at 13.35 @ 99.8mph, i threw the alternator belt once again, but this time it got tangled up with the fan and the fan belt. the fan shredded both belts. along with shredding the belts the transmission coolant line got yanked around and now is in a tangled mess and pinched shut. ill be able to fix the transmission cooling line easily but i have to figure out this belt situation. I plan to take off all pulleys an really work hard aligning them while maybe replacing some of them. I have already replaced the alternator pulley with the larger deep groove pulley that i had put on before the race, but now i also have the smaller deep groove pulley for the crankshaft. I hope that ill be able to solve our problems after i realign everything, but if not im open to all and any suggestions. I am trying to keep this as cheap as possible because ive dipped to much into my dad's wallets and need to come up with most the money on my own. Ill let you know how everything goes. Im open to suggestions???? Thanks Kevin
well you could always put a belt on the engine.. put a video camera on a stand and point it down into the engine bay , concentrating on the belts... run the engine to 5500 rpms for a second or two and see if it throws the belt. unless you know whats causing it, we really cant help you any more than the suggestions we have told you.. something is obviously wrong with it.. just need to find out what.. but you know that already good luck oh.. and you say you run 13.35 at 99 mph... shouldnt you be at like 105 mph or more? reason i ask.. i run 14.2 at 96.. just curious
i cant answer that one but thats what mt time slips are saying and they dont lie so im so close to that 100mph barrier it is a little more than .1mph, but that is what it is running
