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#1
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15 mpg city & 21 mpg hi-way mileage with a 400!
I know mileage considerations usually take a back seat with our cars, but I have been tuning for gas mileage and performance and got some good results:
The stuff: (see sig for more) TA with 400 engine has 0.7 overdrive + lockup converter. Final ratio is 2.39:1 so engine rpm is about 2K at 70 mph. Holley #7054 4165 body 650 cfm spreadbore double pumper. #59 jets primary jets + 2 stage PV (10.5"&2.5"), #582 secondary jets + 6.5"PV Engine timing : 16 dgrees BTDC + 20 degrees mechanical advance by 2800rpm, 12 degrees(mechanically limited) vacuum advance @10" manifold vacuum Fuel : 93 octane pump gas. Idle - 15:1 A/F, 15" vacuum at 700 rpm Cruise - 15.7:1 (>10.5" vacuum) 5mph to 45 mph Cruise - 15.5:1 (>10.5" vacuum) 45mph to 80 mph (maybe squeak out another 1/2 percent getting it to 15.7:1 A/F by dropping to #58 jets) Part throttle - 14.5 to 14.8 (<10.5" vacuum) on 1st stage of 2-stage power valve Part throttle - 12.5 (<3" vacuum) on stage 2 WOT - 12:1 (or any time the secondaries are opened, PVCRs are bit too big) The test: Fill ups are at same station, same pump, same time of day (morning) each time. Fill until pump stops. City driving is to-from work following same route and time of day (time selected to avoid stop-n-go traffic for best case) hi-way driving is 80 mile round trip loop following same route and time of day. Driving style for best case is "Grandma" keeping engine vacuum > 10" as much as possible, light accelerations and coasting to stops. NO AC Best city mileage : 15.27 mpg (averaging 40 mph over 20 minute commutes, no AC) Worst city mileage : 12.24 mpg (stop-n-go traffic with AC, or with aggressive/spirited driving) Hi-way mileage : 21.56 mpg (averaging 65 to 70 mph, no AC) While it is possible to see some improvements in city mileage I think its hugely dependent on traffic conditions and driving style. Most of the benefits of my carb tuning efforts improved throttle response and performance. Response is much crisper and I use less throttle most of the time. YMMV
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1977 TA 400 9.5:1 CR 351hp 414LbFt, #13 Heads + 1.52 Roller rockers, 1968 Pontiac 400 intake, Holley 4165 650 DP #7054 Howards Hyd .447/.467 IN:288 EX:298 214/224@.050, MSD6A + MSD timing control + H2o/Meth 1-5/8" headers, Magnaflow 200CPI Cats + 2.5" Pypes X, Dynomax STs, TH-700R4 2200 stall, 3.42 Eaton 10-bolt, PS/PB/PW/PL/AC/Cruise 13.84@100.14mph 2.18 60' on P255-60-R15 radials, pump gas, mpg : 21.5 hwy 15.2 city |
#2
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This and getting high 13's? not bad...
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#3
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Good job on your choice of parts and your tuning here !
Like Scarebird says, all this and you run 13 something in the quarter mile, that's damned good I say as well. On the streets and highways, it takes some serious will power to stay out of the secondaries. Ask me I know
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Knock Knock Knockin' on 11's Door '70 Judge, Palladium Silver w/Red Interior Powered by SD Performance, Ported 6X Heads 501 HP, 554 ft lbs TQ 12.14 ET @ 114 MPH , Supercase Muncie M22, 3:55 Suspension: HO Racing, BMR< Sykorat, and Bilsteins Narrowed 12 bolt , 16x8 VintageWheel Works, Comp T/As on street, MT Drag Radials @ Strip http://www.sdperformance.com/custome...1.php?carID=42 |
#4
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I think this shows what a well thought out combo can do. Congrats.
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‘63 LeMans- ‘69 400 w/ original transaxle. 2.69 gears. ‘55 Catalina ‘62 Mercury Meteor-all original, bought new by my grandfather 71' GTO -original 400/4-speed/3.23 posi 13.95 @ 102.1 on street tires @ 4055lbs.-now my sons ride |
#5
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Congrats indeed. A orthy goal for some of us doing the OD upgrade.
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#6
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Nice going, I'd bet a well-tuned Q-jet would bump it up by 1 MPG or so.
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#7
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Thanks, its been a lot of trial and error (mostly error) before finally sitting down and doing the research. I tried for years using a 3.08 axle behind the OD tranny and running super lean mixtures. Ended up with a car that cruised below its torque range, was slower, ran hot, had detonation problems, and had smelly exhaust. I finally started to listen to you guys and went back to basics.
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1977 TA 400 9.5:1 CR 351hp 414LbFt, #13 Heads + 1.52 Roller rockers, 1968 Pontiac 400 intake, Holley 4165 650 DP #7054 Howards Hyd .447/.467 IN:288 EX:298 214/224@.050, MSD6A + MSD timing control + H2o/Meth 1-5/8" headers, Magnaflow 200CPI Cats + 2.5" Pypes X, Dynomax STs, TH-700R4 2200 stall, 3.42 Eaton 10-bolt, PS/PB/PW/PL/AC/Cruise 13.84@100.14mph 2.18 60' on P255-60-R15 radials, pump gas, mpg : 21.5 hwy 15.2 city |
#8
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'Nice going, I'd bet a well-tuned Q-jet would bump it up by 1 MPG or so.'
I've had customers report 17-20mpg's from 455's installed in later T/A's with the mid 2's gear ratios and no overdrive. One very competent tuner maxed out his Holley carb using an 02 meter, and did some back to back testing against a Q-jet we set up for him. Right at 2mpg's better with the q-jet. He ran the same course, filled up and the same station, etc......Cliff
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If you can read this, thank a teacher. If you can read this in English, thank a Veteran! https://cliffshighperformance.com/ 73 Ventura, SOLD 455, 3740lbs, 11.30's at 120mph, 1977 Pontiac Q-jet, HO intake, HEI, 10" converter, 3.42 gears, DOT's, 7.20's at 96mph and still WAY under the roll bar rule. Best ET to date 7.18 at 97MPH (1/8th mile), |
#9
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What size tires you running?
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#10
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Not bad, I hope mine is that good
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www.fquick.com/Captainofiron 68 Firebird 400, YC 400, Hbeam rods, ported 670 heads (2.11i, 1.77e valves), 1.65 RRs, Torker 2 intake, Nodular Crank, Eaton Limited Slip, Richmond 3.55 gears, M-20 M4 97 Trans Am WS6, LT1, M6, FLP LTs, Cutouts, Flowmaster catback, Jet Airfoil, K&N air filter, MSD Opti and Coil 14 Fiat 500e 83kW motor, 24kWh lithium ion battery, +2 sized summer tires |
#11
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Very ecouraging results, thanks for posting it up.
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#12
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Quote:
eric: what kind of $$$ did that overdrive cost ?
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Two 1975 455 Grandvilles & '79 455 Trans Am ‘69 Camaro SS 396/375 (owned since ‘88) ‘22 Toyota Sequoia V8 ‘23 Lexus LS500 awd ‘95 Ford F-super duty 4wd 7.3 p-stroke & countless Jeeps & off road vehicles. |
#13
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That's impressive, and encouraging. I've been slowly improving my 350 stroker and this proves I still have a good bit of room for improvement. You're about 4mpg better in all cases. If you think about it, you're better than at least 1/2 of the newer cars/trucks on the road today.
I am very interested to know more about what equipment and how you've used the A/F meter to aid your tuning. I think that might be my next learning experience. |
#14
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Nice!
You're making more HP than I'm sure my old '69 Firebird was but I had great mpg's with my old '69 Firebird. It had a very docile 400 (compression/cam unknown), tuned up and adjusted the Q-jet, points distributor, installed a 700r4 with lockup. 2.73 rear gears. Regular 87 octane fuel it would get 18mpg around town and 25+mpg highway. This was over a period of two years of daily driving it to college and around. It was great for college! Looked good and got great mileage. It pulled 17inHg at a 700rpm free idle, 15inHg 600rpm in gear idle, some times more if the weather was right. Cruised down the highway pulling around 12-14inHg.
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__________________________________________ "How I learned to stop worrying and love the OHC Pontiac L6" The Silver Buick- '77 Skylark coupe w/455, SPX, MegaSquirt 3 & TKO-600 (Drag Week 2011, 2012 & 2015!) 1969 Firebird with a turbo'd Pontiac L6 controlled by a MegaSquirt 3 and backed with a microsquirt controlled 4L60e and 4.56 gears! (Drag Week 2018!) |
#15
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Very nice.
FWIW I got 16mpg highway once (normally 15) in my GTO when it was restored to stock. 400 with TH400 trans. Drafting other cars really helps
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1968 GTO - 400/400 - Currently being rebuilt - 455/T56 1996 WS6 - LTI M6 - Sold 5/11 1979 Trans Am - 403/Auto - Sold 12/18 |
#16
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P255 60 R15 (27" diameter) Firestone Indy Firehawks
Quote:
I was more interested in the deeper 1st gear for better acceleration at the time! Quote:
Its a great tuning tool. It replaced an old narrow band O2 gauge which I learned is useless for tuning. The wideband showed the it was dumping excess fuel through the carb at all times. The AEM even revealed during braking fuel was sloshing up through the secondary vent tube due to a high float setting. The AEM gauge reaction time is lighting fast, it easily registers the accelerator pump shot when blipping the throttle and any other transient changes. Quote:
Quote:
Funny thing about doing this was it improved seat of the pants performance which makes it more enjoyable to drive. I wasn't even thinking about that and assumed improving mpg would make it run crappy. Completely the opposite. Before tuning my car was only working well at WOT, and even then it was too rich (still is). I have some more tuning to do for WOT (leaner) and the primary pump shot needs refinement (it shoots ALOT of fuel every time the throttle moves)
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1977 TA 400 9.5:1 CR 351hp 414LbFt, #13 Heads + 1.52 Roller rockers, 1968 Pontiac 400 intake, Holley 4165 650 DP #7054 Howards Hyd .447/.467 IN:288 EX:298 214/224@.050, MSD6A + MSD timing control + H2o/Meth 1-5/8" headers, Magnaflow 200CPI Cats + 2.5" Pypes X, Dynomax STs, TH-700R4 2200 stall, 3.42 Eaton 10-bolt, PS/PB/PW/PL/AC/Cruise 13.84@100.14mph 2.18 60' on P255-60-R15 radials, pump gas, mpg : 21.5 hwy 15.2 city Last edited by ericwy; 05-24-2012 at 05:45 PM. |
#17
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I consistently get a bit over 20mpg@ 75 mph with the 400 in my '67 with a TH400 and a 2.56 rear gear. No overdrive. It has 87cc small valve heads (#15's) and stock exhaust. It sure won't touch 13 seconds in the quarter, though!!!
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Jeff |
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