Mercury Cougar Owners banner

1 - 8 of 8 Posts

·
Registered
Joined
·
628 Posts
Discussion Starter #1
As some of you know who read my previous thread I had my rear end replaced and changed the gear ratio to 3:55. I never got a chance to post the rpm's at different speeds because we had a snowstorm and a 2 week long cold spell and I couldn't drive the car. Well here they are for everyone who asked. I'm still running the break-in fluid and will replace it in another 100 miles or so but I don't think that will have any effect on the results.

I got the car nice and warmed up then hit the highway for some fun. I'm listing the rpm's in 10 mph increments. Here goes, 40 mph @ 2800, 50 mph @ 3200, 60 mph @ 3800, 70 mph @ 4400, 80 mph @ 5000, and finally 90 mph @ 5600 rpm's. My car has the 351 windsor engine and I'm running a Holley carburetor with a 750 cfm jet.

I'll have to confirm the mileage (because I don't believe it) but it appears that with the carb and engine tune my miles per gallon jumped from 13 to about 22. I'll be able to confirm the exact numbers when I fill up again. But if those numbers prove to be true the Cougar will get better gas mileage than my 03 Maxima which gives me a consistent 19mpg's at the moment. And when I drive any of my cars I don't baby them.
 

·
Premium Member
Joined
·
6,980 Posts
How accurate is that speedo now that you changed ring and pinion gears? Did you change the speedo gears?

If you have a GPS, you can verify the mph.
 

·
Registered
Joined
·
7,552 Posts
Some mileage gain isn't a big surprise, as you are getting better bang for the squeze. That's a pretty big jump though...
 

·
Registered
Joined
·
11,950 Posts
Yeah, I think your calculators a bit optimistic! :>) 3800 at 70 doesn't sound right - same gears as me (but I have an AOD too) and still turnin' over the 14" tires. You may need to bump up a tooth on the speedo. If you gander through the old sticky notes I think Royce posted some good info on that.
 

·
Registered
Joined
·
628 Posts
Discussion Starter #6 (Edited)
Bad69 I was running 4400 rpm's at 70 mph not 3800. I didn't have my gps in the car this time (I left it in the Maxima) and yes I did change the speedo gear to a 21 tooth one and I'm currently running 15in tires. I'll take it out again tomorrow with the gps and post those results here as well. But now that I think about it the speedo with the new gears was about 2 or 3 mph slower than normal.
 

·
Premium Member
Joined
·
2,142 Posts

·
Registered
Joined
·
628 Posts
Discussion Starter #8
Something is wrong with your speedo. You should be seeing much less RPM at each speed.

Take a look here: http://www.ringpinion.com/Calc_RPM.aspx
I changed out the trans gear but my speedometer reads 2 mph faster than indicated, (I can live with that) I'm also running 15in tires and the car came with 14's. This time I used my gps for the actual speed and the results are still close. This time 40mph @2800 rpm's, 50mph @3400 rpm's, 60mph @4000rpm's, 70mph @4500rpm's, 80mph @5000rpm's, 90mph @5600 and 100mph @5800rpm's.

Bear in mind that I have a 3 speed with no overdrive, I plan on taking the cat on a 2 hr drive in a few weeks and really get a feel for how it drives then. Lastly, at fill up I calculated that I'm getting about 15 mpg's not 22 as I hoped. Oh well you can't have everything, I'm still satisified with the overall performance.
 
1 - 8 of 8 Posts
Top