I am considering swapping the 727 in the Cuda for a 518. I have 3.91s now and was just wondering what RPMs the different rear ratios give at hiway speeds. Say 70ish MPH.

I know there are other variables, but I was just looking for some ball parks from those that are already running the 518s.

With the tall tires and loose converter, the engine spins about 3,000 RPM at about 55MPH now.

Thanks!

The OD ratio is .69, so multiply whatever RPM you are getting now by .69 and that will be your new RPM, give or take a few for slippage.

So 3000@55 would be 2070@55.

you'll also get a significant reduction in RPM if you're working the lockup converter into the equation

I've always liked the idea of a loose converter, w/ lockup

Yeah, I assume his current converter is not a lockup so there is probably a couple hundred rpm gain there on top of the OD ratio.

You could play with this goodie from the tech archives. http://vexer.com/automotive-tools/speed-rpm-calculator

I was considering the lock-up version thinking along the same lines as you. But PTC said that the lock-up would limit the converter choice, so I picked up a non lock up 518 core tranny. I have a 4,000 stall in the car now, but I doubt that I will want that loose a converter with this next build especially given the higher OD tranny ratio.

The overall combo I am thinking about is something like a converter flash between maybe 3,000 and 3,500 RPM and a rear gear that will let the engine stay 3,000 RPM or less in OD at about 70 MPH. Nothing set in stone here, just beginning targets.

Of course, I have to wait to install the 518 until the bells are available again. Anyone have any news on that front?

Which bell? JW Performance ultra bell BB to 727?

I am open to a recommendation.

Which bell were you refering to that was out of stock?
Summit shows the JW ultra available for shipping tomorrow, $413.10

http://www.summitracing.com/parts/jpt-92457/overview/

I have read several times that they were out of stock everywhere. I dunno, maybe Summit doesnt have them. Jegs also shows them available to ship by 1/28/15

Thanks for the heads up on the JW. I will check with them tomorrow. Everyone has said for quite some time now that they were on B/O. Obviously, I didn't check myself.

I drove the car this afternoon and it tached about 3,800RPM @ 70 MPH. So multiplying by .69, that gets me to about 2,600 with the OD. That will work.

Thanks for all the help.

I am interested in your conversion as I am considering it also In a Cuda. Just wondering about the tunnel mods.

It seems that the 518 will fit in my E body with a little trimming on the tranny. I also have the engine and tranny dropped 1/2" or so for hood clearance, so that will help.

Have you read this thread?
http://www.cuda-challenger.com/cc/index.php?topic=84774.0

No problem. I never bothered to check either, I dont need another one.
Please post back with the availability, yea or nay.

The only real exterior difference 727 vs. 518 is in the tail housing, where the OD unit is.
Lots of good info on the swap, Id'ing the trans, etc. in the tech archives here on moparts.

Talked to Summit this morning and they verified that the bells were in stock and ready to ship. I do need a few other small items, but I think that I will go ahead with some other stuff that this swap involves and wait to see if a discount coupon pops up.