Hi all nice place you have here. I just picked up a 91 RS tonight and would like to pick your brains on a few issues. My ultimate goal here is gas miliage. besides the basics like keeping up on the tune ups what else can be done to these cars to make them good smooth runners that get good miliage. the car owner told me the car is a 305 with 700r4 transmision. tommrow i plan on going over the car more closely i suspect the tach is off i think its a v6 tach becuase when i rev the engine it seems to go very high very easy and that doesnt seem right to me. im not sure what gears are in the rear end and the car has gone threw a few owners so im not sure what is all original so any tips on identifyingthe diferent drive train parts would be a huge help so i can be sure what im working with. Im willing to upgrade what ever i have to to make this a reliable long lasting car that gets the best miliage possible. once i go over the car more i may have more questions so please be patient with me. i will also upload a pic asap.

 

Good tranny health with possibly a shift kit (less lag between gears is less wasted power/gas), good cold air intake and high flow exhaust, computer tuning and possibly a slightly larger cam like a comp xr258hr. Also check out the stickies at the top of the forums they have a lot of things on mileage.

 

When my LO3 was stock, with 3.08 gears and T5, would get 31 mpg all day long on highway runs. These cars/motors get great mileage (small cam, fast burn SP heads, FI) when properly maintained.


The only way to truly know what gears you have it to pull the differential cover and count the teeth (or look for the teeth ratio stamped on the ring gear). Chances are the fluid needs to be changed anyways.

 

Spid label usually has the code for your gear ratio, that is if they're the factory gears in there.

 

probably 2.73 rear w/auto trans.

 

what or where is the spid please? well tommrow i will go over the car more i really think the tach is wrong it seems to rev up to high to fast and run to high at 55 60 mph in overdrive.

 

Service Parts Identification Label. according to my shop manual it's supposed to be 'attached to the inside of the console door'. (there wasn't anything on my console door)anyway it has a bunch of 3 character alphanumeric codes.
axle ratios:
GU2 2.73 GU4 3.08 GU5 3.23 GU6 3.42
under Transmission Usage in the book the tbi 305 with 700r4/4L60 used the GU2 2.73, and the M39 manual used the GU4 3.08

 

Its probably not a "V6 tach". So many tachs from 91-92 have that problem you would think they were off from the factory, mine does it too. Mine reads a 600 RPM idle at like 1300, and on the highway when i'm cruising 1800 RPMs the tach is close to 5 grand. Once the engine starts turning 3000 RPM + my tach is pegged.

For fuel mileage stick with the stock gears, and i'm not sure about a shift kit. It may save a little fuel but sounds to me like just an excuse to have a harder shifting tranny I'm not sure how cost-effective that would be just for the purposes of saving fuel.

The tune though is another story. For optimum fuel efficiency make sure all the typical stuff is working good like plugs, cap, rotor, wires, coil, filters, etc etc etc. Do some searching here on how to do a proper tune up, I know its here somewhere. I will put some emphasis on the fuel filter however. I took mine out at 170,000 and it looked factory. I couldnt blow through it at all. This could put extra strain on your fuel pump. I noticed a difference in my engine with the new filter. Make sure you put in in right though, I was an idiot and put it in backwards the first time.

Look at the "Tech Articles" on the home page of this site. There are some ultimate TBI mods on there you might want to look into.

If you have some coin to drop and some time to learn you should look into the EBL system. I just got mine and am currently tuning my car to run better. There are lots of people on here with countless good things to say about it and supposedly it GREATLY improves fuel mileage and makes the car runs better than it ever could on the factory ECM no matter how good the tune. Just something to look into.

DynamicEFI

Others will chip in...

 

Check the inside of the glovebox lid (under the rear hatch). GM moved the label in the later years.

RBob.

 

thanks every one. Hey dark shot what is a ebl and how much is it? also if its not a v6 tach and its a known issue what can i do to fix it besides mounting a after market tach?

 

EBL is advanced ecm to use on tbi vehicles. Here is a link to the website. I just purchased an ebl in hopes of both better mpg and performance. Prices range from 225 to 265 based on shipping and install. EBL has much better code and much faster datalogging.

 

For mileage the most imporant things you can do are make sure the ignition is working perfectly (or better than perfectly- an aftermarket ignition box, for example), make sure the timing is set to factory spec or a little advanced (0* is spec, 4* advance is no problem in most motors), make sure the injectors are clean, spraying a good pattern and flowing what they should (checking fuel pressure wouldn't be a bad idea) and that the O2 sensor is fresh and reading sanely.

 

sounds very nice, does any one know how to fix the fact the tach is way off? some one said above that 91 92 had this problem so any way to fix it? besides fabricating a spot for a after market tach.

 

There is a resistor that starts to fry and changes values. Check the Electronics board here on TGO. There is a really decent thread on this exact issue. It was last updated within the last 2 months.

RBob.

 

One of the first things I did to both of the RS's that I have owned is install headers and a full 3" exhaust system. This change gained gas milage on both.


(Not to mention "mo" power )

 

I second this fact. My van gained over 25 RWHP going from the stock exhaust to a full exhaust system with headers, it had a stock 305 at the time. Low-speed torque dramatically improved and fuel mileage improved slightly when I could keep my foot out of the added power (mostly open highway with the cruise set). I could pull most on-highway hills in OD with the TCC locked and 3.08 gears with 255/70/R15s!

 

do you have a web link for such a system? that sounds like somthing i would like to do. and in the future the exhaust could still be used on any new engine i might install.

 

Sorry to have missed this Justin. I replied to your pm with the links but I will post it here for others.

Edelbrock TES Tubular Exhaust System Headers with Ti-Tech Coating: EDL-68723 - summitracing.com

Flowmaster Force II Cat-Back Exhaust Systems: FLO-17152 - summitracing.com


Others opinion's will vary but this has worked well for myself.

I would also look at the Hooker headers that others here are running with good results. Someone else might remember the part number for them.

Edit.......Kevin came up with it on the exh. thread.........Hooker 2055's

 

yeah i saw but i dont think those hookers have the smog pump hook ups/
thanks for the links i think i would rather a dual tip exit with polished 3 inch tips by flow master.

 

You just have to shop for the prices and styles that you want. Just make sure that the system is 3" from the header Y to the muffler inlet. In other words do not order parts for the LO3. Order systems for an L98 camaro with a single cat.