Just curious if anyone is running a 4-spd 4T60 on a 4-cyl car. Is the Iron Duke making enough power to even pull the overdrive gear?

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1984 Indy Fiero

[This message has been edited by ag9123 (edited 06-21-2015).]

+1

I'm also interested if the top speed has changed with the transplant. I kind of feel the 3-speed just limits it by its gearing.

Just an opinion but I do not believe that any automatic transmission is really a good fit for the 90 HP Duke, The 4T65e weighs about twice as much as the 4 speed and RWHP and gas mileage numbers would probably plummet. I know an owner who put a 4T60 (4 speed non-electronic) behind his 2.8 L and he said that it was an improvement over the TH125H but that engine has 50 more horsepower.

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" THE BLACK PARALYZER" -87GT 3800SC Series III engine, custom ZZP /Frozen Boost Intercooler setup, 3.4" Pulley, Northstar TB, LS1 MAF, 3" Flotech Afterburner Exhaust, Autolite 104's, MSD wires, Custom CAI, 4T65eHD w. custom axles, HP Tuners VCM Suite.
"THE COLUSSUS"
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Transmission weight has little to do with the equation. What matters most is final drive gear ratio and overdrive gear ratio. And the question you need to ask is what overdrive and final drive gear ratio can the Duke 2.5 actually still make enough power to maintain highway speeds using? And that is going to be a question of engine torque production and not so much about how much HP it makes.

The overdrive ratio of a 440T4/4T60, 4T60-E, and 4T65-E is 0.705:1. The common final drive ratios of these transmissions are 2.84-2.86, 2.93-2.97, 3.05-3.06, 3.29-3.33, and 3.69-3.73 depending on what gear ratio diff and chain sprocket ratios you are using.

I think it might be possible for a Duke to work with one of these overdrive transmissions if you are using a 3.69-3.73 overall final drive ratio since that would give you an overall ratio of 2.60-2.63:1 in 4th/OD gear. The reason I say this is because the Duke was used with a Muncie 4-speed manual transmission in 1984 that had a 3.32 final drive and a 4th gear ratio of 0.73:1 = an overall ratio of 2.42:1 in 4th gear. Keep in mind the automatic will drain more power from the engine than a manual will (due to power used up by running the hydraulic pump in the automatic among other things), which is why I would recommend using an overdrive automatic that has a 3.69-3.73 final drive ratio.

I think it is doable. But if you wanted to use a 4T60-E or 4T65-E, you'd need a stand-alone module/computer to run the transmission. The 440T4/4T60 will work with the stock Duke ECM.

-ryan

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