66 MERCURY COMET

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wyatthead
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Joined: Mon Mar 02, 2020 12:08 pm

66 MERCURY COMET

Post by wyatthead »

Is 4,600 rpm too high while driving at 60mph? The tranny is an original 3 speed automatic, and the rear axle has a 2.8 gear ratio. Old engine was replaced w/ a Ford 302 from an 88 mustang, topped with a 4 bbl edelbrock. Idle rpm ranges from 1100 to 1600, but at 50mph it’s already at 4000 rpm. Is this irregular to be running that high of rpms at high speed? What could be causing high rpms at high speed? Any advice is helpful, thanks

SASSY
Posts: 4023
Joined: Fri Jan 06, 2006 11:32 pm
Location: Wynndel, BC CANADA

Re: 66 MERCURY COMET

Post by SASSY »

I think so, 2g-2500 would be better.
Are you sure it gets into drive? 2.8 rear gear, sure?
I think it should idle under a 1000.
Fred
I'd rather do it myself if it's done right or not,,,isn't that what hotrodding is all about?
Mission bc 09/12 (I think)
Roy, Brian n me
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Jims65cyclone
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Joined: Sun Nov 23, 2014 9:29 pm
Location: Lexington, SC

Re: 66 MERCURY COMET

Post by Jims65cyclone »

I'm not too familiar with ATs, but assuming your third gear ratio is 1.0, you're running a 25.5" diameter tire, and your rear axle is 2.8:1, at 4600 rpm you should be running 125 mph. :shock: My guess is that you're stuck in second gear (or less). If you change the trans ratio to 2:1 it drops to 62 mph, which is about where you say you are. I think the tranny is your problem.
https://spicerparts.com/calculators/tra ... calculator

Jim
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