Swapping in a 86 FWD 3.8L into a 81 Skylark

[wroberts]

Well, heres my car:

I'll be swapping this new FWD 3.8L into it:

But before you tell me it can't be done here it is in the same body (A Chevy Citation, AKA GM X-Body, same as mine:

I have pretty good details on this swap, but as you can see thats a 3800, not a 3.8. So I need details on what makes this swap different.

I'm planning on upgrading to the newer (82-96) Engine Cradle found on X, and A Body cars, and if you will remember they made the FWD 3.8 for the Century T-Type. Included in this a new cradle mounted rack, and I got all the details for the wire harness and the 86 ECM I'm using is A LOT easier to manage than one from a 3800. The only question I have relates to Flywheels. I'm planning on using the TH125 Trans that I have as I need a cable driven speedo and am not going to swap in a Century dash, as the Citation in the above picture did. What flywheel would I need to mate the 3.8 to the TH125? Will a stock 3.8 work (OE# 25515222; 142 Teeth; Pitch 12-14; 11.91" Outside Diameter) Or could I use a flywheel from a 3.0 (Which is derived from the 3.8) to mate the trans? (I used to own an 84 Ciera with the 3.0 and a 3 speed Trans)

So what do I need, please help (and yes I know I'm the Tech Advisor for 80-85 Skylarks, but as you should note this engine was not a stock option)

[Turbo Loyd]

I would use the flexplate from the engine you are installing as these engines are usually externally balanced. The torque converter should bolt right up to the flexplate. The bellhousing for the FWD engines all use the Chevy 60 degree pattern, with the smaller torque convertor.

Good luck that looks like a great project.

[NTX5467]

I presume you will be using all of the necessary later model electronics that came with and work with the newer engine? You'll probably need some sort of signal generator so the computer will know what speed the vehicle is running, but I seem to recall that your '81 should have a "speedometer buffer" on the backside of the speedometer head for this purpose, but the signals might not interface with your later model computer system. Seems like the later computer systems also had switches to tell the computer what gear had been selected by the driver, on the transmission linkage belcrank area of the transmission, and probably included the neutral safety switch in them.

Things might physically fit well, but it'll be the electronics interface that will make the "second part of the story", I suspect.

In a Pontiac enthusiast magazine several years ago, a guy in Louisiana took a Pontiac A6000 and put a 210 horsepower Chevy 5.L V-8 in it, using the T125 transaxle. The article noted that a drive axle shop built him some fwd drive axles with HD joints in them. It also noted that a certain transmission shop built the T125 transaxle and went in and enlarged all of the fluid feed lines in the valve body and gear train to increase the fluid flow volume and better handle the power that transaxle was not designed to really handle (when it was designed back when).

I'm not sure if there's any "racing off-road" stand-alone computer systems for your engine, which would allow you to not have to worry so much about the correct interface per se. Or possibly ElectroMotive could design something to do the ignition and fuel injection in the earlier chassis (similar to what it would be in a street rod/street machine application).

Just some thoughts . . .

NTX5467

[wroberts]

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> I would use the flexplate from the engine you are installing as these engines are usually externally balanced </div></div>

The engine I got doesn't currently have one, so I'm looking for which one I should go with. To mate the 3800 to a TH125 Trans most guys have to buy a special machined down one West Coast Fiero 3800 Flywheel but as I'm using a older 3.8 I'm unsure if the stock one will fit, if you're saying it does, then I'll just buy a new one. If I do get a new one should I have the motor rebalanced?

<div class="ubbcode-block"><div class="ubbcode-header">Quote:</div><div class="ubbcode-body"> I presume you will be using all of the necessary later model electronics that came with and work with the newer engine? </div></div>

The 86 ECM I'm using does need a speed signal from the Trans, but to quote the manual "The VSS sends a pulsating signal to the ECM, which the ECM converts to MPH. This sensor mainly controls the operation of the Torque Converter Clutch" The Diagnostic steps for the error code I would get from not having the signal only involve the speedometer and TCC operation, no mention is made to any performance differences. Besides I don't have a TCC on my 81 Trans anyway. I do rember reading about other guys that have done similar swaps and GM did offer an inline cable sensor as stock item on one of the 80's cars, I just need to find it. If I don't I may get a custom chip with the speed sensor disabled. The 86 ECM pretty much just talks to the Engine. The only other input it needs besides the speed signal is the Park/Neutral Switch. The electronics for this swap is a lot easier than the 3800.

So since I'm already in the modified class with the convertible Skylark, how much help would a 3.8 swap be in grading my modified car?