Broke 30 mpg in my GS400
09-26-12, 01:07 PM
#31
Instructor
Thread Starter
Sorta. It has the LT1, but not the same LT1 as the Vette/Trans AM/Z28. It has 2 bolt mains, iron heads, different exhaust manifolds (for the chassis differences) and smaller cam and of course a tune that matches that. Lost 40 hp over the Vette, picked up 5 lb/ft torque and torque is >300 lb/ft from 1600 rpm (stall speed) to over 5000 rpm. So torquey it is. Same engine, techincally no. Similar? Yes, most definately. Can you make it the same as the Vette, easily. Head swap, cam swap and you have 300 hp instead of 260 and you are lighter in the front end.
I am miffed because this was Cadillac's flagship and all it got a plane jane Chevy engine. Come on GM, get a clue. At least Lexus was better than that on everything save the ES. The Vette and Fleetwood should have shared engines, and the Buick Roadmaster should have got the iron headed engine and then the Caprice should have only got the 4.3L L99. If you wanted LT1 you had to upgrade to the Roadmaster or 5000 lb tow package car, and if you wanted 7000 lb tow package, you get what I have, the Fleetwood with option code V4P. But of course, 3 mpg less than a regular Fleetwood.... But it is fun. Hemi's hated me when I drove it....
I think 260 hp was underrated, my datalogger dyno showed 260 to the rear wheels at its peak.
I am miffed because this was Cadillac's flagship and all it got a plane jane Chevy engine. Come on GM, get a clue. At least Lexus was better than that on everything save the ES. The Vette and Fleetwood should have shared engines, and the Buick Roadmaster should have got the iron headed engine and then the Caprice should have only got the 4.3L L99. If you wanted LT1 you had to upgrade to the Roadmaster or 5000 lb tow package car, and if you wanted 7000 lb tow package, you get what I have, the Fleetwood with option code V4P. But of course, 3 mpg less than a regular Fleetwood.... But it is fun. Hemi's hated me when I drove it....
I think 260 hp was underrated, my datalogger dyno showed 260 to the rear wheels at its peak. 
09-26-12, 04:32 PM
#32
That is the recent mpg, not the 30 highway tank.
I was on target for 25ish till tonight, my daughter had a cheerleading practice accident and my wife and I made the mad dash to the school and then I led the ambulance hospital.... I love a v8......
She is okay, bad foot and ankle sprain. At least not obviously broken. She has to see surgeon to be sure all is okay and what to do for recovery.
I filled up the other day over 300 miles at just passed half tank. I forced in 12 gallons.
Now I was not too long far off, but now about 250 miles at half tank. Probably guessing 24ish now. Still better than I had been getting. Mpg is a fussy thing to measure accurately and consistently, too many environmental variables.
I was on target for 25ish till tonight, my daughter had a cheerleading practice accident and my wife and I made the mad dash to the school and then I led the ambulance hospital.... I love a v8......
She is okay, bad foot and ankle sprain. At least not obviously broken. She has to see surgeon to be sure all is okay and what to do for recovery.
I filled up the other day over 300 miles at just passed half tank. I forced in 12 gallons.
Now I was not too long far off, but now about 250 miles at half tank. Probably guessing 24ish now. Still better than I had been getting. Mpg is a fussy thing to measure accurately and consistently, too many environmental variables.
09-28-12, 12:50 PM
#34
Instructor
Thread Starter
11! Wow! My 454 in my Suburban gets 13.5 to 15 highway and 10 city, what are you doing with it?
Just checked this morning, even with my heavy throttle to get to the school and hospital with my daughter, I managed 26.9 in my daily commute, which is around 25-30% city and rest 55-65 mph. And usually plenty of passing if traffic is doggy.
I think the 5W20 had a nice improvement in mpg. Sole factor? No, temps are dropping and AC is off more often than before, but I never saw better than 24 in daily driving with AC off earlier in the year. 5W20 I think is an improvement factor at least.
Time till tell. I keep close tabs on mpg and what I have done/not done for mpg or to the car. Driving style is a lot too. I have done extensive things to test mpg on my Fleetwood. 5W30, 10W30, 15W40 (even year round in Chicago winters), belt fan, electric fan, AC on/AC off, 10% ethanol fuel vs 0% vs E85, oh I have tried a lot. 93 vs 87 octane, PCM tuning vs stock, Even did the Acetone in the gas thing. Yeah, didn't help at ALL, actually hurt a couple %. Save your $.... Ambient temps and driving style had the greatest effects on mpg.
Just checked this morning, even with my heavy throttle to get to the school and hospital with my daughter, I managed 26.9 in my daily commute, which is around 25-30% city and rest 55-65 mph. And usually plenty of passing if traffic is doggy.
I think the 5W20 had a nice improvement in mpg. Sole factor? No, temps are dropping and AC is off more often than before, but I never saw better than 24 in daily driving with AC off earlier in the year. 5W20 I think is an improvement factor at least.
Time till tell. I keep close tabs on mpg and what I have done/not done for mpg or to the car. Driving style is a lot too. I have done extensive things to test mpg on my Fleetwood. 5W30, 10W30, 15W40 (even year round in Chicago winters), belt fan, electric fan, AC on/AC off, 10% ethanol fuel vs 0% vs E85, oh I have tried a lot. 93 vs 87 octane, PCM tuning vs stock, Even did the Acetone in the gas thing. Yeah, didn't help at ALL, actually hurt a couple %. Save your $.... Ambient temps and driving style had the greatest effects on mpg.
09-28-12, 02:02 PM
#36
Instructor
Thread Starter
I have never got mine lower than 19 yet, no matter what I did. Do I hammer it daily? No, not at all. But I enjoy it too. Are all GS's equal? Dunno, but I would hope they are made to the same stds. I can say other brands I have/have had in my experience are not.
But I am not dissappointed in mpg at all. I would honestly like to see a GS300 or a GS300 Turbo and use the V8 gears and see what sort of mpg it gets....
But I am not dissappointed in mpg at all. I would honestly like to see a GS300 or a GS300 Turbo and use the V8 gears and see what sort of mpg it gets....
09-29-12, 12:20 AM
#38
Damn 30!!! That's awesome. I averaged 30-33mpg going 70-75 on my way to work today but I think there was a tailwind, plus I just bought my 430 so I've been doing my fair share of spirited driving, plus I never let it get below half a tank. I will try to see what the max mpg I can get next time I fill up until it's empty. I'll shoot for mid 20's since I do city/hwy
09-29-12, 08:20 AM
#40
I used to drive a silverado for a year before my 430 and I used to average 13mpg all hwy. It was an old truck with no ac in las Vegas 110+ weather so literally anything even 15mpg would've been a plus in comparison, but damn Neegroy why is your mpg so low? Laundry list of engine mods? Lol
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