3.27 mileage

[jharkin]

since my conversion, i seem to be getting less mileage now. gone from 16.7 avg with the 3.75 to 14.4 avg with the 3.27
i do about 50/50 short local driving and highway.
my mechanic thinks it's because i'm shifting more than before.
anybody else experience this after a 3.27 conversion?

[Naj ✝︎]

Have you converted your speedo or do you make allowances for the lower mileage actually clocked?

naj

[waqas]

Naj is spot on. A reduction of 12.8% in the rear ratio leads to a similar reduction in perceived mileage if you haven't had the speedo adjusted. The odometer will now read 12.8% fewer miles than reality. Your perceived gas mileage will now be 12.8% less (0.872*16.7mpg = 14.56mpg).

So you see, you need to stop shifting so much! 

[waltklatt]

Actually Waqas, You'd add ontop of the previous mileage.
Best to have a gps device or something to measure in realtime mileage and run 10 gallons or 5 gallons from a start till an empty tank in a controlled test.
And see how much the mileage has increased.
My 220SL is getting me about 28-34 miles per gallon average.
The previous diesel conversion on a 1968 280SEL with 1982 300CD and auto gave me a range of 25-30 miles per gallon.  Had a full tank to the orange fuel light coming on a range of 715 miles.
See you at PUB.
Walter
1967 220SL-diesel

[jharkin]

if i understand all this higher math, if i multiply my current odometer reading by 1.128 i will get the 'true' mileage (until i can get the speedo recalibrated) and then i can calculate a reasonably correct mpg, yes? if that's the case then my correct avg mpg is 16.4 since the conversion, about the same as before the conversion. i thought it would have improved some, but maybe the higher revving and more shifting has evened it out. she had a C service 2100 miles ago so she should be in decent tune. well, she's in the shop to have the trans mount replaced and steering bushings replaced, and to have the throbbing sensation investigated. if she needs the tuning freshened i'm sure he will take care of it. thanks for the helpful info. 

[waqas]

John,

If you want your true mileage, then multiply your odometer reading by 3.75/3.27 =1.147.

From my understanding, in the old setup, 3.75 revolutions of the driveshaft cause a single revolution of the wheel. Now with the new axle, only 3.27 revolutions of the driveshaft create a single revolution of the wheel.

[Raymond]

Good work.  If the original ratio was 3.75.  If it was a 4-speed manual, the original would be 3.92 wouldn't it?

[jharkin]

It's a euro 230sl, and the 3.75 was visually verified.