Upgrading the 410 Final Drive Ratio

David C · #1 (**permalink**) 04-10-23, 09:36 AM

Hello John.

I'm nearing the end of an overdrive installation, keeping the original back axle ratio. Happy to share details if that helps.

If you are happy to trade acceleration for slightly lower cruising RPM a differential swap could well be worth a try. It shouldn't be too hard to find a 2.8 and you can upgrade to limited slip diff while you are at it.

Another option you might consider is finding an A999 transmission. This is non overdrive with lock up torque converter so would fit without the modification to crossmember and tunnel required by overdrive. Removing the slip would probably give a similar drop in revs as the diff swap and it would save plenty of fuel as well. You could go for broke and do both.

Please can you post pictures of how your air conditioning compressor is mounted? I am considering a Vintage Air system. Original Mopar air compressors were fitted above the alternator and I don't think will fit under the 410 bonnet. Sam Frost has kindly offered to help with details of what I believe is his factory installed system with the compressor mounted above the power steering pump.
I would like to compare all options before committing.

John Keighley · #2 (**permalink**) 04-10-23, 11:42 AM

Thank you Andrew for your reply. This is the information I am looking for. sounds as if the 2.8 ratio may be what we need as the car generally will do longer runs. Fuel economy in the car's original state gave us 21-22 mpg but I hope we can improve on that, particularly as the tank is not that big!
Many thanks!
John K.

AndrewA · #3 (**permalink**) 04-10-23, 02:20 PM

Well if you think of anything you need - let me know. Re the attachment, Kevin who kindly looks after this forum will probably sort it out for you if you ask nicely!
I think - but could be wrong - that once you go into the 2's as it were on the ratios you need a different carrier to the 3's - worth checking.

David C · #4 (**permalink**) 04-10-23, 02:41 PM

I have just spotted that you say the fuel tank is not very big. Has your car had a smaller tank fitted? The standard tank seems huge when I'm paying to fill it!

David C · #5 (**permalink**) 06-10-23, 03:56 PM

Thank you for that. Loving the exhaust manifolds. Who made or supplied those?

I'm still keen to see some pictures of aircon compressor mounted on 410 engine as this is very different from the 411.

Thomas591 · #6 (**permalink**) 06-10-23, 04:07 PM

Uups, sorry that was a bit stupid from my side, of cause I am aware that your engine is different. Sorry for that.

The exhaust manifolds are from Spencer Lane Jones.

Regards

Thomas

AndrewA · #7 (**permalink**) 06-10-23, 04:21 PM

Updated figures (!) with GPS and a co pilot/scribe/second pair of eyes.
No o/d or lockup 72.1 mph 2400 rpm
O/d only 71.4 mph 1850 rpm
o/d and lockup 72.1mph 1650 rpm

John Keighley · #8 (**permalink**) 10-10-23, 11:16 AM

Quote:

Originally Posted by David C

I have just spotted that you say the fuel tank is not very big. Has your car had a smaller tank fitted? The standard tank seems huge when I'm paying to fill it!

David, it's a standard tank - 18 gal but given the distances we sometimes travel, the contents disappear rapidly.

AndrewA · #9 (**permalink**) 10-10-23, 01:31 PM

Sorry to fail you but it's been wired that you can't engage lockup unless overdrive also engaged - I did try.

David C · #10 (**permalink**) 10-10-23, 08:02 PM

No worries, Andrew. Having had a bit more time to think I'm not sure how much it would tell us. I was thinking of the torque converter purely as a fluid coupling but there's more to it than that. At lower speeds my understanding is that input RPM and output RPM can be quite different with attendant torque multiplication but I don't understand is how this relates to efficiency and therefore MPG.
Enough pontification, it's time for me to hurry up that gearbox installation and then report before and after EFI MPG figures.