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Old 01-10-2007, 09:20 PM   #1
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getting better mileage out of a 450hp car :)

Well a 25 cent part is broke in my metro trans. Going to have to take it out and split the case to get at it though Meanwhile I get to drive my drag car to work. 2002 Camaro Z28, ls6 block, GM ASA racing cam, 3000 stall converter, wide open exhaust, and lots of other stuff that doesn't do much other than run real good 1/4 mile at a time.

So the car stock would run a 13.08 1/4 mile and get 25 city 31 highway. Currently it can run anywhere from 11.6 to 12.3 depending on traction and I typically get just under 10mpg driving to the track racing all day and driving home. I drove it to work today trying to be easy on it and managed 14mpg. But it is a lot different than a metro doing a lot of stuff. It does not require any extra throttle to hold speed going up any hill is the first thing. Taking all curves at full speed with no braking is another helpful advantage. Before I left for work today I reset the L-trim tables and set the torque converter lockup to 45mph, 35mph in 3rd gear. I also am thinking of setting the target voltage on the O2 sensor to .3 or so to lean it out a bit but I am not sure if the 110 degree lobe separation cam even lets the O2 sensor properly work. The cam has a big overlap and lets plenty of intake air out the exhaust. It is impossible to stand near the back of the car with it idling due to the fumes. 226/236 int/exh @ 0.05" duration 0.525" / 0.525" int/exh lift 110 LSA are the cam specs. Also I wonder how much extra drag I get from driving with drag radials on the road.

So anyone got any ideas for experiments I can try on my 100 mile round trip to work the rest of this week? I am not thinking there is much to be tested but it could be interesting seeing what I can try in it.
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Old 01-10-2007, 10:02 PM   #2
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I would say that for how much you are going to spend on gas in a week, you could almost replace the cam with something more reasonable, and that alone should help a great deal.
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Old 01-10-2007, 10:23 PM   #3
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I'll probably have the metro back on the road friday after work so I don't think there is much point in trying to swap cams or the torque converter just for a few days of driving. I might do a few simple tests if it is warm enough friday like seeing how much difference there is with the windows down and tops out compared to the car being closed up. I figure I don't really have much time to do any major tests but I'm just trying to have some fun with what I have without having to get any more speeding tickets fixed. I am thinking tomorrow to run the car with 45psi in the tires to see if it is different than todays tire pressure of 40psi front, 28psi rear I normally run.
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Old 01-10-2007, 10:39 PM   #4
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Try testing tire pressure. My theory is that the rolling resistance of typical drag radials isn't that different from standard street tires once they're pumped up hard.
Edit: doh! you beat me to it!

I'd like to see if higher rpms yields better FE since you have a big cam in it. There may be a point of diminishing returns as rpms go lower. For example, does 1000 rpm give worse FE than 1500 rpm?

How many miles can you cover before you give in to the lure of big HP and floor it? Can you restrain yourself and drive a full day at Metro speeds/accelleration in your drag monster? See what that does to your FE?
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Old 01-11-2007, 04:13 AM   #5
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Coyote X: So anyone got any ideas for experiments I can try on my 100 mile round trip to work the rest of this week? I am not thinking there is much to be tested but it could be interesting seeing what I can try in it.



If you have a means to change your centrifugal advance, do this. I have removed the springs from the centrifugal advance weights in the distributor. This allows full advance constantly. Using lighter springs or only one spring does the same to a lesser degree. Under light throttle, low load conditions this will cause no ill effects. You retain the total advance as before.

With a big camshaft and low vacuum, your cylinders are just loaded with too much fuel. More low RPM advance will alleviate some of this and make the engine smoother, more responsive and burn cleaner. Let us know if this helps.
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Old 01-11-2007, 06:18 AM   #6
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Replace the high rpm cam with a low rpm (torque) grind, and take out that automatic transmission with its ridiculous 3000 rpm stall torque converter, and in its place install a manual tranny.............
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Old 01-11-2007, 07:31 AM   #7
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This will probably just reveal my ignorance about exhaust theory: but would constricting the flow / increasing back pressure help to get more fuel burned at low RPM? That would be an easy mod (sticking something on the end of the pipes).
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Old 01-11-2007, 07:47 AM   #8
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From what I've read of your post and background, just do the basic setup (inflate tires, keep it light, keep it aero, etc.) and stick to FE driving techniques so you can spend the time getting your XFi fixed ASAP. If you can afford a few extra minutes on your commute, you can make some big gains by spending them in the right places.

One example is if you come up behind a truck that's only a bit slower than your normal cruising speed, draft it for a while. Also, when you come up behind somebody, instead of passing them right away, you could shift into neutral and coast into and then out of their draft, accelerate into their draft, then coast down in neutral from your passing speed to cruising.

WOT and pussyfooting are both bad for FE; keep it somewhere in between and use the brakes as little as is practical.

The best info on techniques:

http://www.cleanmpg.com/forums/artic...mile-1510.html
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Old 01-11-2007, 08:44 AM   #9
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I didn't think about sticking something in the exhaust but that might help control some of the overlap in the cam. I might give it a shot tomorrow. I set the tire pressure to 45 front and 40 rear. The rear tires have a max rated pressure of 32psi so I didn't want to go much over it, they are pretty expensive tires so I don't really want to blow one of them out. One thing that does suprise me is how much better the mileage is than I would expect. I drove 70mph cruise control with the old tire pressure and managed 19mpg. I will find out what the higher pressure gets me then I might try plugging the exhaust pipes partially and maybe try driving with the rpms below 2000. I pretty much will only drive the car tomorrow then I will be back to the metro but it was kind of interesting that I can still manage 20mpg in a car that can run 11 second quarter miles It might be kind of fun doing some more experiments later with this car so I might drive it some here and there but, it would be a pretty expensive car to do tests on. 300$ per tire that gets about 5000 miles of life, starter motor and IAC stepper motor don't live long due to it not being able to idle well, not to mention the land sickness you get from driving a car for long periods that shakes as bad as this one does.

As far as the ignition timing when I dyno tuned the car I advanced the cam timing a huge amount on the bottom end to make the car even able to idle under 1000rpm. I know the car has practially no power under 2000rpm and yesterday when I was driving it I tried keeping the torque converter locked up as much as possible and always shifted down to keep the engine around 2000 and downshifted to avoid running under 1500rpms if possible.
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Old 01-11-2007, 09:28 AM   #10
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Do you have another set of tires you can put on the car?
I run Toyo T1R set at 50 psi for daily driving.
You also might want to see if you can do any aero improvements, such as an under tray.

I know several people that dumped the N/A LS1 and went turbo. This can make a huge difference in highway MPG and HP level.

I should be low 11s to high 10s this year (V6 Turbo w/ automatic). I am shouting for 40 mpg at 65 mpg on the interstate. I am concentrating on tuning and aero mods.
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