5.7 swap for 72 Road Runner Transmission suggestions\questions

[mopardog]

Ok, after much debate and weighing options and nagging from my friends to go resto mod crazy on my 72 Runner, I have decided to go with a 5.7 swap. After reading through this forum, youtube, and other sources....it doesn't really scare me too bad to put a newer drivetrain in car "she's not numbers matching anyway so might as well have fun" so says wife and my buddies.

My biggest question is transmission suggestions and clearance with the tunnel. my bird was originally a big block car, so anyone know how much cutting and how much I am gonna need to expand the tunnel? Thinking of going the '05 route on drivetrain. Which would be the better setup overall and which would involve the least amount of expansion if possible.....car setup or pickup setup (engine-trans)?

While I am at it, rear gear ratios. I currently have factory 8.75 3.23:1 suregrip. Would 3.91 or 4.11ish gears be better for new drivetrain?

One more I swear....Will oem power steering box clear engine or will I need aftermarket?

ANY information would be greatly appreciated. I am trying to cover all bases before

 

[Dreamcatcher]

The transmission is an issue. I am just starting on my 5.7 conversion. But I have followed a lot of builds. The tunnel isn't the real issue. It is the torsion bar cross member in the tunnel. But follow keepat and sixpactogo and a few other threads and you will be on the right track. Some people go with the small block 727 as it will bolt to the 5.7 and then use with a gear venders over drive and no cutting is needed. As far as the power steering It has been done here several different ways. Just read the build threads of these guys. They are top notch builds. 5.7 is another great source on this site. Like I said I am just starting my build as well and so learning as I go. But the threads here really help get the big picture. Good luck.

 

[mopardog]

Thanks Dreamcatcher, yeah I've been reading through the articles a lot of good info. I called gear venders, I don't have quite that big of a budget for a bolt on overdrive for my 727. Might just have to move some sheetmetal around for now at least. Of course, if something changes then it's nice to have the contact.

One thing that has just occurred to me, who makes retro style gauges to work with computer? I would like factory looking setup or can I make what I got work?

 

[Dreamcatcher]

Thanks Dreamcatcher, yeah I've been reading through the articles a lot of good info. I called gear venders, I don't have quite that big of a budget for a bolt on overdrive for my 727. Might just have to move some sheetmetal around for now at least. Of course, if something changes then it's nice to have the contact.

One thing that has just occurred to me, who makes retro style gauges to work with computer? I would like factory looking setup or can I make what I got work?

Mine will be a budget build as well. But at a minimum with computer re-flash wiring harness oil pan , pickup tube , dipstick , engine mounts , oil filter adapter and not even to mention headers to fit past the power steering and driveline , a budget of at least 3000.00 to 3500.00 after you buy the engine and transmission. Is about as cheap as you will get.

 

[mopardog]

good information, you read my mind because I was going to ask about a "grocery list" of stuff to look at. After speaking with gear vendor, I've been thinking, I wonder if a production overdrive trans would work or aftermarket version say a A518 overdrive transmission from Monster? Has anyone looked at this option? Would I be able to get the 5.7 computer to "talk and agree" with this transmission? Just trying to explore all my options. Thanks again for your patience......

 

[Dreamcatcher]

From all my digging around and questions I do not think there is another transmission that will fit except the 727 with out modification. How ever I have heard that there is a GM (hack gag) that will fit and it is adaptable. Now if you will excuse me I must go wash my mouth out with gasoline. And yes do explore all options. I am not really any sort of authority on this swap but there are many who are. I am pretty sure they will jump in on your thread. If not PM 5.7 hemi or sixpacktogo and several others on this site that are up on about every aspect of this swap.

 

[joe12459]

I got away with no tunnel modifications, using the NAG1 trans in my 5.7 Hemi Mirada build, by mounting the engine four inches forward of where it would be normally located, but that was using an RMS AlterKtion suspension. This might not be possible on a stock B Body k frame. In my big block 72 roadrunner, I run a 4L60 based tranny, which also requires no modifications, and the overdrive is great. Mine is an older Keisler (out of business) A41 setup, but Silver Sport Transmission bought their assets and now makes the same setup. It is available for Gen III Hemi/B Body as a bolt in kit, but I'm not sure of the price.

 

[5.7 hemi]

The truck trans (2wd) 545rfe will fit, but you will have to cut the tb crossmember and raise the tunnel. You can use whatever gauges you like, gps, or electronic to get vehicle speed. Also with 4th and 5th being overdrive gears, you can run a pretty steep rear gear such as 3.91 or 4.11's. The low first gear on the 545rfe is 3.00 and coupled with 3.91's you will launch outta the hole really well and in 5th, with a 28 inch tall tire you will turn 2500 isn rpm's at 70mph. Not bad!!! If I were to to it all again, I would run the 545rfe again without hesitation. But I would consider using an aftermarket K frame to get rid of the tb's so I wouldn't have to set the car up as level as I can get it before cutting the tb crossmember out and gabbing a new section to clear the trans.

 

[kb67mopar]

5.7 is right...If I had the budget I'd go back and put in an aftermarket suspension and ditch the t-bars. I find that with my stock setup I would like to add sway bars, stiffer bars and in the end the steering box is still in my way from making nice headers. (I didn't buy the conversion parts so my build is a little out of the box).

I can't speak to automatics for what fits under the tunnel. But what I can say is if you want to use a different transmission and keep the stock computer, just have the ECM flashed with a manual transmission tune. As long as the transmission is hydraulically controlled or stand alone there won't be any issues in running anything you want.

Gauges, I recommend Speed Hut and just put in your own sensors. The only one I didn't have an easy install option for was temp. I plan to drill and tap the water outlet housing the next time I have a reason to drain the coolant. If you want to set your own resistance values you could piggy back of the stock ECM sensor and still run your gauge. Or you could throw all this out and run CAN gauges off the ECM can signal pins...but you may need to read some more on that.

Shopping list...well I would debunk your need for a dipstick. I run the Milodon 31000 pan and related pickup with the stock dipstick. Reads an appropriate level and doesn't interfere with the pan. Fuel system, I run a 99 Dodge Durango fuel pump and sending unit...it contains a built in regulator and filter, houses the level sender and only costs about $100 on rock auto. You just have to modify your tank if your up to the task. Russell makes fittings to convert AN line to the pushlock fuel rail connectors, for $20 you can get two of them and run the OEM style pump out back and the stock fuel rails. Overall you can do the swap for cheap if you want or cost $$ if you want fancy. I was too broke for fancy so I made my own mounts, used off the shelf parts and even kept the truck exhaust manifolds. So far 9000+ miles and its still reliable and fun.

Happy Hemi-ing

 

[mopardog]

Great information everyone. It sure helps being able to talk to folks who have already "been there, done that" so to speak. I have plenty of time to worry about dropping in the drivetrain. I have focused my efforts for the time being on getting what body work needs the car has addressed. Then she will be ready for the motor. Thank you again for all the support.