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Fuel Consumption
Driven my recently finished DRB Cobra for 300 miles.
It has a stroked 351W - Now 427 Dynoed at 520hp / 540ftlbs Torque The motor runs beautifully but boy is it thirsty. It has a Speed Demon 750CFM.Mechanical second stage actuation. Average consumption to date 3.5MPG (USgallons). The intended use for the car is 70% street -30% track day. Just wanted some feedback from the club on the fuel usage similar motors (like the ROUSH 427's). I dont have the car to compete in Economy runs but it would be nice to enjoy cafes and wineries insread of fuel stations. |
What trans. and rear gears do you have ????
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I average maybe 12 to 14 and that's with the air off. 209
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Need more info like jet sizes pri and sec. Timing, a/f ratio. Either the mpg calc is in error or the motor is way off tune. I have a 418W 550 hp and get 8-10 in town and 18-20 on freeway at a steady 70 mph. Sounds like you need a day at the chassis dyno.
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Thanks for the response
Zomm this - Primary 76 Secondary 86 - At 3500RPM AF left 11.94 AF Right 12.32 Rusty Bob Tremec TKO 600 - 0.86 Final Drive jag 3.31 Dif 209 Those figures would be ideal for me |
Sounds rich, might be washing the cylinders........get it leaned out. Look at your plugs.
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I have averaged 13 mpg and have a range from 12 to 15 mpg. Roush 427 SRTW, 512HP, 17" wheels, 3.46 rear ratio and 0.82 OD. At 70 MPH I'm turning 2,550 RPM. I just found out my ignition timing total advance is 32 degrees at 4,200 RPM. 16 Deg at 900 RPM.
209 - what kind of cruise control do you have? |
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Also, check your timing curve. Retarded timing costs you in fuel and power. |
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WardL,
I'm running a Rostra unit my installer adapted to the car. Unit was for Honda and Mazda. Model or reference # 250-1483 Cliff |
Could it be that your speedometer is not correct and recording more miles than you are actually driving?
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bobcowan is right. You are rich. Next time you're on a dyno look at your a/f ratio at 2000-2500 rpm under light load, 4th gear. Should be up around 13.5-14.5:1. I think your jetting is too rich on primaries and way too rich on secondaries. I'm going to guess that your jetting should be closer to 72-74 pri. and 76-78 secondaries to get a good a/f ratio. Get the primaries dialed in first under light load lower rpm, then fuss with secondaries under full throttle high rpm to get your overall a/f ratio right. I have an MSD 6AL ignition that is set for 20 initial advance and 32 total all in by 2200 rpm. Car runs like a top. 10.83:1 compression, cam is .565 lift and 232 duration on intake with 110 lobe separation.
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Hi Zoom This
Have ordered new jets - Start with 74 Primary and 78 Secondary. I have an MSD 6AL and MSD Distributer and will confirm which timing curve is being used - I think it is 32 degress at 4200 but will check with timing light - as opposed to yours all in at 2200.Will post the results - Thanks once again to all for your contributions |
I have seen allmost 13 MPG coming home from RENO. My milage is best when cruising in 4th gear.That doesn't happen around town often. I'd hope it's better than 3.5 MPG.
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Another reason to get a small block.
I get 24 mpg on the highway with my 0.63 overdrive T-5. I can pass almost anything on the road without shifting down to 4th gear. What I can't, I certainly can by downshifting. Those who say they will burn rubber if they floor it in 4th at 65 can just eat my dust as I walk away from them. I've always said, too much torque=too much tire smoke (and, apparently, too little fuel efficiency). Cheers from Dugly :cool: |
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To the OP, Demon carbs. are junk on the street. If you want better throttle response, performance and gas milage, get a Holley Street Avenger. |
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