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EFI big hp mileage

Anybody care to share how an EFI conversion with all the goodies (400 plus hp) has effected mileage. Are you down to something crazy like 15MPG or still in the twenty's.

I'd like to know mileage at legal highway speed. If your car can be held back to legal limit!

Thanks
Old 03-19-2010, 10:18 AM
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My 930 already has EFI (+425 rwhp) when I bought it so I can't really compare before and after. I get around 15-19 mpg (depending on type of driving but always get on the boost at least once no matter how short the drive). From my observations it appears that and EFI may be slightly more effecient (i.e. 1-2 mpg) when staying away from boosting on both type cars. It probably don't matter when you're on the boost a lot in either type of cars. It's the state of tune that mostly affects mpg in either cars. That's my opinion.
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Old 03-19-2010, 11:21 AM
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Quote:
Originally Posted by EmptyGarage View Post
I'd like to know mileage at legal highway speed.
Thanks

Uhhhhhh, what's that?
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Old 03-19-2010, 12:27 PM
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EFI on the track has to be more efficient than my CIS car with 400 RWHP. I'm getting about 3 MPG with 100 octane...
Old 03-19-2010, 01:04 PM
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A properly tuned 400WHP CIS 930 can achieve 21mpg @ 70mph and 15mpg in town. 350WHP CIS can achieve 23mpg.
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Old 03-19-2010, 01:30 PM
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Quote:
Originally Posted by RarlyL8 View Post
A properly tuned 400WHP CIS 930 can achieve 21mpg @ 70mph and 15mpg in town. 350WHP CIS can achieve 23mpg.
+1
I am seeing at least these figures with my perfectly tuned cis 400whp motor
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Old 03-19-2010, 01:40 PM
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My EFI fuel economy is in the $hittter at 500 to wheels, but probably little on rich side. However, i get more smiles per gallon than anything else i've ever owned
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Old 03-19-2010, 02:36 PM
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+1
I am seeing at least these figures with my perfectly tuned cis 400whp motor
Stu, nice you see you got your car sorted out.

I should hope you do get better mileage. Oddly enough, mine was much better in the UK as well. UK gallons are bigger...

They still use the Jacobean system for fluid measurement in the US, so a US Gallon is 3.78L, which is 83% of a UK Imperial gallon (4.54L).
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Old 03-19-2010, 05:42 PM
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I should point out my 3 MPG is at the track. No idea what the street mpg is.
Old 03-19-2010, 07:01 PM
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18 city, 28 hwy (65 - 75mph)
Old 03-19-2010, 07:31 PM
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Quote:
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18 city, 28 hwy (65 - 75mph)
I get around 15-19 mpg

Big difference between these two numbers ...who's right?
Old 03-19-2010, 07:48 PM
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Quote:
Originally Posted by EmptyGarage View Post
I get around 15-19 mpg

Big difference between these two numbers ...who's right?
What do you mean who is right? Why can't we both be right??? Have you read my frankenstein-like signature? Maybe your motor tune sucks...
Old 03-19-2010, 07:59 PM
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Quote:
Originally Posted by EmptyGarage View Post
I get around 15-19 mpg

Big difference between these two numbers ...who's right?
If you are referring to my quote and DonE's you need to keep in mind that there are lots of other variables such as type of driving (in my case it's mostly city driving so it's close to DonE's). It's been awhile since I've been on long interstate drives plus my 4sp is geared much lower than stock (2nd thru 4th) so its mpg would be worst than a stock geared equivalent.
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Old 03-19-2010, 08:01 PM
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Quote:
Originally Posted by DonE View Post
What do you mean who is right? Why can't we both be right??? Have you read my frankenstein-like signature? Maybe your motor tune sucks...
LOL...I don't think he has a 930 yet. Hope he will soon though!
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Old 03-19-2010, 08:03 PM
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Sorry for the strong response, but if you tune for an AFR of high 14's and timing around 36 degrees at 3000 rpm (and no boost), you can make these 3.4L motors go a long way on a tank of gas. Another reason (albeit a small one) I like EFI.
Old 03-19-2010, 08:04 PM
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LOL...I don't think he has a 930 yet. Hope he will soon though!
Yah, my bad - sorry.
Old 03-19-2010, 08:09 PM
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Quote:
Originally Posted by RarlyL8 View Post
A properly tuned 400WHP CIS 930 can achieve 21mpg @ 70mph and 15mpg in town. 350WHP CIS can achieve 23mpg.
I'm wondering what properly tuned includes. What needs to be adjusted?

I would assume that the stock adjustments are not enough and you need an adjustable WUR as well?

Thanks.
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Old 03-19-2010, 10:52 PM
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My EFI conversion was done back in '04 (Pat Williams Racing) and at my last dyno run (back in '07 I had 480 ponies to the ground.. I've gotten as high as 21 mpg cruising 75-80, and maybe 8-10 on more spirited drives...
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Old 03-19-2010, 11:21 PM
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Thanks for the responses. It sounds like the best thing for me to do would be contact the motors builder and see if he can shed some light on the specifics of the car I'm looking at. It's been interesting to see the different mileage recorded by similar Hp cars. Never intended to insult anyone. The passion overflow ith!

Last edited by EmptyGarage; 03-20-2010 at 03:14 PM..
Old 03-20-2010, 03:12 PM
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28mpg is the highest confirmed figure I've heard, cangrats Don! No doubt that tool a lot of work.
The highest confirmed CIS 930 I know of gets 24mpg. When you are off boost things even out a bit for engines of varying levels of boosted HP. All should be capable of mid-20mpg on the highway.
Obviously tuning the fuel curve is paramount, but as Don stated tuning the ignition plays in as well. With CIS you definitely need an adjustable or digital WUR to optimise city mileage as the stock WUR's are fixed.
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Old 03-20-2010, 05:12 PM
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