Just thought I'd let you guys know that I'm still running my L98/LT4 hotcammed motor with somewhat of a 305 chip in it. It still has the 19# injector constant. I'm also running a T56 and 3.42 rear. Its doesn't do that great in town for MPG, but on the interstate I'm getting 25MPG or more. I think once its tuned it will get some more MPG!! What do you guys think. Anyone else with this cam having similar results?? Later I"m pretty satisfied so far....

 

Matt87GTA is running a somewhat wild combo its a 355 with an LT4 hotcam with some cleaned up TW 23* heads. He is getting around 30mpg on the highway. Now in the city that is another story. He has a 6 speed with 3.42 gears IIRC, 4 gen rear.

 

The LT4 hot cam isn't all that radical. I used to regularly get 26mpg in my old 85 with a computer controlled carb and a 355 w/ a similar cam. And it was an A4 too.
Still not a bad number, especially considering that TPI isn't that great for gas mileage to begin with due to the overall inefficient design of the intake. With tuning and highway mode there is more potential though.

 

Not bad!!

My Formula averaged 19mpg on the Bowling Green trip. This was with three crappy plugs and two burnt plug wires.

 

Just a question, But how are you measuring your Milage ?

You have the appropriate Correction for the gears and T56 ?

But yeah, thats totally feasible.

 

I'm getting similar results, 16 MPG city and 24 MPG highway.

 

Well, I think its really good MPG for now just because of the fact that the chip isn't even close to where it needs to be at. I hope I can get about 30 MPG when I'm done.



Bort, as for my calculations, YES i have a dakota digital interface box to convert the signal to the proper one for my factory speedo. I've checked it with multiple other cars, not to mention a highway patrol man's radar.


Kevin, yeah about 15 city and 25 highway. I'm missing the old 305 in town now. I'd get about 20MPG in town no matter how I drove it. Later!!


BTW- wonder what kinda highway mileage a cc306 would get??

 

As Drkhrse89 stated, I was seeing about 28mpg highway (not quite 30, but close ) but that was with my 355 TPI/TH700R4/3.42 gear setup. My average with that setup was down around 16-17 with city driving and all of the "messing around" I tend to do .

I have since swapped to a T56, have 3.73s sitting on the bench, and swapped to Speed Density. I haven't gotten my base tune with the new setup to where I am comfortable engaging Highway Mode again..... And now winter is setting in so I won't be playing with the PROM again until spring.....

But you can really wring out the mileage with the Highway Mode routine (hint: Get into tuning your own PROM today and it will pay for itself in mileage!! )

 

Matt, that sounds pretty good. Nice GTA BTW!!! As for highway mode engagement... my tune is pretty much stick. Should I not be running highway mode right now? What exactly will it do or not do with it on or off. I'm almost ready to start doing my own proms and am always looking for good advice. Thanks!

 

Well if the PROM is mostly stock on your engine than you can count on the AFRs commanded in HW mode to be off. That being said, it is up to you if you want to have it coming on or not.... Got forged pistons??? ..... Basically the HW mode routine works in conjunction with a HW spark adder routine to up the spark advance and lean the AFR out when a few criteria are met. Like a minimum speed attained, a maximum MAP signal not being attained (or MAF when applicable), a maximum TPS not attained, minimum CTS attained, etc.. Basically it can tell when you are cruising byt sensor readings. I myself am not comfortable having it come on until I know my PROM base tune is set since the HW mode routine uses your base tables and a modifier to calculate AFR.