trying to figure a realistic cruising speed limit so I can pre-plan for other options if needed. standard 225, a230 3spd, 2.76 gears .... and with 3.23 gears


thoughts?

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1970 Barracuda 225 /6, 3spd on the floor, Blue/Blue

If you are looking for a steady state engine rpm, where the vehicle is achieving a good level of fuel efficiency, that really depends upon the engines torque curve. Which is mainly dependent upon the camshaft profile.

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Your local driving conditions are probably the primary concern. If I was to be stuck in stop-and-go traffic more than once in a blue moon I wouldn't ever consider 2.76 gears. I had 2.76s in my '67 Valiant for a while as it had a bad rear end and I tossed in a rear end from an automatic trans Duster. That Valiant is lighter than your E body and it was miserable when starting off on hills at sea level. I feared for the clutch. Later I installed a 3.21 geared 8.25 rear axle and life was much better! 2.94 is the lowest numerical ratio I would try. As you live at high altitude I would use the 3.23 unless highway fuel economy was the primary concern and if it really was I would use a different car.

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Joshua

fuel economy won't be a concern, just some freeway speed for some daily driving. there is an e-body 8 3/4 on CL I was going to pick up, it has 2.76, but it's easier to find 3.23 for it than the 7.25 I have now. the engine isn't built yet, but I'm concerned for the slant with a 3spd/a230 being able to do 65-75 with half decent RPMs. don't think I have many other options though, a 5/6 spd would be interesting if douable, lol.

my B'cuda came from Spokane area dad drove it from '73-around '87

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1970 Barracuda 225 /6, 3spd on the floor, Blue/Blue

I drove my Valiant with the 3.21 gears and 25" tall tires 70 MPH no problem. Yes, it sounds like it's spinning fast, but it's not that fast. Overdrive is certainly nice, but it's expensive.

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Joshua

FYI- my 76 D100 is equipped with a 225/727 drivetrain and a 9 1/4 rear axle with 3.91 gears. It will cruise the highway at 70- 80 MPH, but that little slant is screaming around 3500 RPM. Fuel economy isn't the greatest, either.

My brother has an 83 Dodge shorty van with a 225/904 and 3.2 rear gears. It cruises at 70 doing about 2500-2600 RPM.

My 2¢ about rear axle gear ratios for a 3 speed trans is that 3.2 or 3.5 gears are about as good as it gets. If you have an overdrive then 3.9 gears are pretty good. If I lived in a high altitude hilly place like Denver and was driving a big E body, I think I would go for 3.5 gears, if possibe, but 3.2s would be OK.

I am slowly collecting parts to swap an overdrive automatic into my truck. If I can find an A500 at the local pick and pull, I can get it for under $100 on one of their sale days.

3.2 rear gears with a 25-26" tall tire would be a nice combo. If you are commuting and not driving for hours at 70+, the RPMs will be fine for your ears and no problem for the engine.

Lou

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Home of Slant6-powered fun machines

good advice, thanks everyone! I got lucky and scored an 8.75 e-body rear end today. it has 2.76 in a 489 case, but I'll just rebuild it and do 3.23 or 3.55, maybe try 3.55 first to see how the RPMs are at freeway speed and get the little extra off the line boost too

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1970 Barracuda 225 /6, 3spd on the floor, Blue/Blue

I have an A 904 automatic and was running 3.23's, but even then at 75-80mph, my normal highway speed, it felt like I was pushing it down the road. I put in 2.76's and I really like it better. Sure, it will never be a drag car or have off the line performance, but then again my main mode is highway driving. I had 3.55's in it when I first installed the 8.75 rear, and it would really scream off the line, but terrible on the highway.

My dream is to put the 3.55's back in and switch to a 6 speed Tremec....oh yeah....

Brian

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