gas prices

i have hade my 89 735i and my 95 740il bmws for five years,and i have always used the higher grade gasoline,however with higher gas prices i would like to reduce the grade.... will this harm the performance,if so is
there something on the market that i can add to my fuel to make up for the difference..
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

The 735 will run quite well on regular - it's not a high compression engine and should have no problem on 87 octane. I doubt that you will see any performance or mileage differences - you were wasting money on 92 for the M30 engine.
The 740 is a bit more problematical, but should run ok - I would try mid-grade/89. It will probably run on 87 but the knock sensors and engine controls back then weren't quite as good as more recently built engines. If it knocks, go back up a grade. You will probably lose a little performance, and a little (1mpg?) mileage.
Floyd
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
BMW M30 The "big six" BMW M30 is an inline-6 cylinder engnine built by BMW and used in many of its cars, such as the BMW 535i. BMW's 3.5L straight six cylinder motors had the longest production run of any BMW engine, dating back to the 1970s. The 3.5L engine is 'bulletproof' and a true workhorse. Instead of the more common timing belt, the M30 had a timing chain designed to last the life of the engine. With regular oil changes and maintenance they have routinely lasted 250,000 miles or more.
a.. 3.5 liter (3430cc) SOHC inline-6 cylinder b.. 9.0:1 compression ratio c.. 208 hp. @ 5700rpm d.. 225 lb./ft. torque @ 4000rpm e.. 89 Octane fuel or better recommended
wrote

Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
Actually, I too have the M30 "Big Six" engine in my 1990 E34 535i, 5 spd, 102K miles, and at least for the E34, there is "one weakness" that isn't found in earlier versions like the E28 and E24. That is the E34 535i are known for its blown headgaskets. Earlier this year, my car blew its headgasket at 97K, and I was religious about changing my coolant with only BMW blue stuff every 2 years. If you go to the various E34 forums, you will see this is pretty common.
In fact Bruno's excellent E34 website has a complete write up on repairing blown headgaskets:
http://www.bmwe34.net/e34main/maintenance/engine/headgasket_M30.htm
Nevertheless, the repair cost me $1100 and the car now runs good. Its strong and I expect it to easily last 250K or more.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

If the car (owner's manual) doesn't call for premium gas, it's a waste of money to put it in, you gain zero benefit, unless you have installed an aftermarket performance chip that requires premium.
If it your manual does specify premium, you will reduce performance and/or fuel economy with the lower grade as the motor is forced to compensate to avoid detonation.
Any additive you buy will cost more than the difference between the grades of gas, per tank.
-Russ.
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload
"mw3" wrote

Not sure about the older 735i, but in your newer 740i, the computer will pull back timing with lower grade gas, which will result in worse performance as well as increased fuel consumption. So, it's most likely not worth using lower grade.

What's the price difference betw. regular and premium? 20 cents? You'll save $3 on a whole tank. I'm pretty sure you'd have to put more than $3 worth of toluene to increase the octane rating back up to 93.
Cheers,
Pete
Add pictures here
<% if( /^image/.test(type) ){ %>
<% } %>
<%-name%>
Add image file
Upload

Motorsforum.com is a website by car enthusiasts for car enthusiasts. It is not affiliated with any of the car or spare part manufacturers or car dealers discussed here. All logos and trade names are the property of their respective owners.