Garrett76Zt Posted August 23, 2005 Share Posted August 23, 2005 Just want some input on my cruising MPG. At 80 mph with KA tranny and open 3.9 R200 and 235/45/17's im at a whopping 2700 rpm. This is about where i cruise. Today from Chicago to Nashville i got 24 mpg . . . and i think i can tune it a bit better . . . you tell me. AFR's while cruising are in the low 14's typically. timing is between 30 and 32 depending on exactly what rpm im at. And EGTs are around 1350-1375ish. my off throttle goes rich for some reason before going lean . . . . just tuning i guess. Can I change anything to make it better? does advancing timing increase gas mileage but also raise EGT? Just curious. Input? Garrett Quote Link to comment Share on other sites More sharing options...
speeder Posted August 23, 2005 Share Posted August 23, 2005 I got around 29-30 mpg at 80mph with my old setup - 3:36 rear, stock L28 bottom end, Electromotive TECII w/550cc injectors. I tuned for low-mid 15s for cruise AFRs while wtching EGT, which stayed around 1400*. This did not bother my cast pistons one bit. I ran about 40* advance in the cruise regions of the maps. Advance helps mileage. More advance will lower EGT, as will richer mixture. Seeing your 3.9 gear, you are pretty well tuned for mileage, but probably can improve some. Quote Link to comment Share on other sites More sharing options...
Guest bastaad525 Posted August 23, 2005 Share Posted August 23, 2005 that's a hell of a lot better than I ever got on mine I'm lucky to get 19mpg's, with late nissan 280zx five speed and 3.5 diff, cruising at 80mph is about 3000rpm. My car runs rich all over the place with the stock EFI. I've tried leaning it out using the AFM but the motor makes it very clear that it doesn't like that one bit stumbling and backfiring thru the intake, and basically just running like crap. So yeah, I'd say that's fantastic gas mileage Quote Link to comment Share on other sites More sharing options...
Garrett76Zt Posted August 23, 2005 Author Share Posted August 23, 2005 I got around 29-30 mpg at 80mph with my old setup - 3:36 rear' date=' stock L28 bottom end, Electromotive TECII w/550cc injectors. I tuned for low-mid 15s for cruise AFRs while wtching EGT, which stayed around 1400*. This did not bother my cast pistons one bit. I ran about 40* advance in the cruise regions of the maps. Advance helps mileage. More advance will lower EGT, as will richer mixture. Seeing your 3.9 gear, you are pretty well tuned for mileage, but probably can improve some.[/quote'] Perfect info Rick! Thanks! You gonna gimmie a piece of that porker at SEZ? haha Quote Link to comment Share on other sites More sharing options...
speeder Posted August 23, 2005 Share Posted August 23, 2005 Bring it on! Quote Link to comment Share on other sites More sharing options...
Garrett76Zt Posted August 23, 2005 Author Share Posted August 23, 2005 Bring it on! I can just imagine your avatar sayin that too!! HAHA Quote Link to comment Share on other sites More sharing options...
AK-Z Posted August 23, 2005 Share Posted August 23, 2005 What type head are you guys running? Quote Link to comment Share on other sites More sharing options...
wigenOut-S30 Posted August 23, 2005 Share Posted August 23, 2005 Heh, Its on.. Battle of the blue beasts.. Sorry Garrett, my money is on the porker.. Quote Link to comment Share on other sites More sharing options...
Garrett76Zt Posted August 23, 2005 Author Share Posted August 23, 2005 Gabe! You traitor! Quote Link to comment Share on other sites More sharing options...
speeder Posted August 23, 2005 Share Posted August 23, 2005 Hey, my spastic driving is a great equalizer.... Quote Link to comment Share on other sites More sharing options...
wigenOut-S30 Posted August 23, 2005 Share Posted August 23, 2005 Hey, my spastic driving is a great equalizer.... let me try it out... :) :) Quote Link to comment Share on other sites More sharing options...
Garrett76Zt Posted August 24, 2005 Author Share Posted August 24, 2005 Well Rick i made the changes you recommended and it seems to be working great! Although i was in the mountains today and I wasnt exactly driving conservatively! HAHA. Tomorrow I hit I-75 to Fl so it'll be nice and flat, I'll get some new MPG numbers. The only time that i get EGT's above 1400 is when i go part throttle Accel above 80 mph. It gets to like 1500 when im at like 5 in vacuum or so. If I floor it, I get plenty of fuel and EGT's drop back below 1400. Quote Link to comment Share on other sites More sharing options...
Drax240z Posted August 24, 2005 Share Posted August 24, 2005 My rule of thumb: Cruise: Tune for 15.5:1 AFR Small Hill: Tune for 14.7-15.5:1 AFR Medium Hill: Tune for 14.0-14.7 AFR Large Hill: Tune for 13.0-13.5 AFR Full Throttle (boosted engine): Tune for 11.5-12.0:1 AFR Quote Link to comment Share on other sites More sharing options...
Guest tony78_280z Posted August 24, 2005 Share Posted August 24, 2005 What is in EGT and an AFR Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 24, 2005 Share Posted August 24, 2005 Exhaust Gas Temperature and Air Fuel Ratio Quote Link to comment Share on other sites More sharing options...
Guest tony78_280z Posted August 24, 2005 Share Posted August 24, 2005 What is used to read EGTs? Never heard of an EGT meter. I'm thinkin about setting up a digital-Multimeter to a O2 sensor to get my carb tuned right. What volt readings go along with those AFR numbers you quoted? Advance = Milage Retard = Power So setting up the vac advance properly is rather important for milage purposes. Any advice on this? Quote Link to comment Share on other sites More sharing options...
dragoontwo Posted August 24, 2005 Share Posted August 24, 2005 you use a thermocouple to read egt's. there are different types of these as well. for example a "K" type thermocouple is made of 2 different metals. Alumel and Chromel. the temp. is read by reading the resistance between the 2. Quote Link to comment Share on other sites More sharing options...
speeder Posted August 24, 2005 Share Posted August 24, 2005 Drax gave good rule of thumb numbers for tuning AFRs. The other (important) part is advance curve - I always use as much advance as I can, up to 40* in places, while avoiding detonation. This is for power and economy.I have heard of some NA tuning that involves retard at high rpm/high load - My own experimentation on my Haltech'ed NA daily driver has been inconclusive on this. I consider a wideband O2 meter an essential tool - The EGT meter is just supplemental rough, quick-look "health" info for me. I really do like all the input available ( Have been tuning the 22psi load areas on my maps this week on the new 3.0 w/T67, will ultimately go to 25-26.). There are some people who have become quite skilled at tuning with EGT alone, but that skill takes much study and practice. AK-Z: The old (30mpg) setup had a ported N42 on the stock L28ET bottom end, moderate Isky turbo cam. Made 367 rwhp @ 17psi with a T61. New setup has a lightly worked P90 on a forged piston stroked 3.0, Largish Elgin turbo cam, 1mm oversize exhaust valves. Should be somewhere in the 425+ rwhp range. The P90, in conjunction with pistons made with D- shaped dishes to mirror the combustion chamber shape, has proven to be very detonation resistant. Beyond these observations, I will not get into any arguments over what heads are better:twisted: . There is no means for comparison of head performance on these two very different motors. Tony78: The narrow band O2 sensor does not have the needed range to accurately measure that range of AFRs. It is only accurate within about 1 point AFR on either side of 14.7. The O2 voltage method has been used successfully to get some indication of "rich" or "lean conditions while tuning. My new motor has been somewhat difficult to tune, probably because of the 780cc injectors:shock: . But it's getting there. No reason to think that it shouldn't have similar economy to the old one. Quote Link to comment Share on other sites More sharing options...
JMortensen Posted August 24, 2005 Share Posted August 24, 2005 What is used to read EGTs? Never heard of an EGT meter. I'm thinkin about setting up a digital-Multimeter to a O2 sensor to get my carb tuned right. What volt readings go along with those AFR numbers you quoted? Advance = Milage Retard = Power So setting up the vac advance properly is rather important for milage purposes. Any advice on this? Digital multimeter and one wire O2 will work, but it is a rough tuning tool. If you're still running a carburetor you can't fine tune like these guys can, so IMO the wideband is a waste of $$$. If you have the programmable injection then narrowband is a waste of $$$. I did the O2 multimeter thing, shot for .8V under full throttle which is ~13.2:1 AFR. I wasn't trying to get mileage so I didn't pay attention to the cruse voltage. I think there is an old post here somewhere that says what voltage = what AFR. Advance = power & mileage Retard = resistance to pinging Not a big vacuum advance fan here. You're right, you can get better mileage with it, but it can also start advancing timing when you're at the end of a long WOT pull, pushing you past where you want the timing to be and into the pinging area at the worst possible time. That said there is probably a ton of advice elsewhere online about vacuum advance. These guys are controlling advance and fuel with a computer so your question doesn't really fit with what they're doing. Might want to start another thread. Quote Link to comment Share on other sites More sharing options...
Garrett76Zt Posted August 24, 2005 Author Share Posted August 24, 2005 Well we're taking our time getting out of Atlanta today, but I tried to get an estimate on yesterdays drive. Like I said I was driving somewhat aggresively through some twisties, up and down some hills and I'm still gonna get 400 miles to this tank. So I think yesterday was in the 26 mpg range. Like I said we'll see what today looks like for mileage. Nothing interesting on this trip so far . . . Yesterday a pair of g35's stradled me on the interstate . . . made a couple runs and it turns out they didnt want any of it! HAHA. I guess its not cool gettin smoked by an old Datsun. Quote Link to comment Share on other sites More sharing options...
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