Highest vacuum/ top gear/ slowest speed survey.

[enkeivette]

I'm starting this thread to collect results. Drove the SRT4 last night, and I was surprised to find that it pulls highest vacuum at the lowest speed of 65mph in 5th gear, on flat road. Thought it would have been closer to 55 mph seeing as how it's a 4 cylinder. It pulled 10" at 60mph, 12" at 65mph, and 12" at 70mph. Meaning, 65mph would be the most economical speed to cruise at... if my theory about pumping loss is correct, and assuming the engine has enough power to develop highest cruising vacuum in the top gear.

List (To be edited):

Year / Vehicle / Slowest speed at highest vacuum in OD

2003 / SRT4 / 65mph

2006 / Mod Evo (E85) / 65mph

1996 / Mod Cobra (C SC) / 60mph

Feel free to add info and I'll add it to the list. Mods feel free to edit the list. Going to try this in my friends car that has a vacuum guage when we get a chance. His motor/trans setup was NA from the factory and has much higher gearing than the SRT, so I suspect his best will be around 50 - 55mph.

[Vettezuki]

I'm starting this thread to collect results. Drove the SRT4 last night, and I was surprised to find that it pulls highest vacuum at the lowest speed of 65mph in 5th gear, on flat road. Thought it would have been closer to 55 mph seeing as how it's a 4 cylinder. It pulled 10" at 60mph, 12" at 65mph, and 12" at 70mph. Meaning, 65mph would be the most economical speed to cruise at... if my theory about pumping loss is correct, and assuming the engine has enough power to develop highest cruising vacuum in the top gear.

List (To be edited):

Year / Vehicle / Slowest speed at highest vacuum in OD

2003 / SRT4 / 65mph

Feel free to add info and I'll add it to the list. Mods feel free to edit the list. Going to try this in my friends car that has a vacuum guage when we get a chance. His motor/trans setup was NA from the factory and has much higher gearing than the SRT, so I suspect his best will be around 50 - 55mph.

I love empirical observation. But, uh, don't we need mpgs at the theoretically most effecient speed and compare to some other base point, like 55mph? This also means you need a fixed moderate length test loop and vaguely similar conditions (temprature, humidity). Take it up to this level and I'll participate with my 5 very different cars.

[SeanPlunk]

According to this post from the other thread, the highest vacuum is not the only thing you take into effect when figuring out the best mileage:

"Way back at the top of the post, someone made the statement about the highest vacuum producing the best mileage- that may be how you are advised to drive to get the best mileage, but you are loosing volumetric efficiency on the engine- working too hard just to suck air-

The best mileage comes from having your throttle open very far, usually in a high gear at low RPM's- of course, our vehicles are typically so powerful, that, when you open the throttle, even at 1500 RPM's in high gear, they begin to accelerat- think of like a 1 liter Opel or something similar, running along at 50-60 mph, in overdrive, and you will get the most efficiency holding the throttle open-

Wind resistance, which is the primary thing you are burning fuel to overcome at highway speeds, is logarithmic- if speed doubles, resitance quadruples- things like rolling resistance and the drag of the axles and gearbox pretty much remain constant at a wide range of speeds- This is why small aero mods can make large percent differences in mpg's"

Here is an example from someone in that thread with a C5 Vette (an aerodynamically efficient vehicle).

"My Corvette definitely does not get better gas mileage at 90mph! You can clearly see it on the instant MPG readout. Mine seems to get it's best mileage somewhere around 50-55mph. At that point the instant MPG will read around 34-35MPG if you're on perfectly flat road."

[SeanPlunk]

I think the highest vacuum thing is where the problem is coming in for you. It appears that is not the only thing to take into account when figuring out best MPG. I believe the basic premise of what you're saying isn't entirely correct and a lot of factors come into play.

[SeanPlunk]

That Vette is an A4 with 3.15 gears for the record.

[Vettezuki]

Your points on theory are understood. I think enkei's goal for this thread is observation and attempting to control for one variable across a range of vehicles. I think if it's done properly it could be very interesting.

[enkeivette]

Sean, yes there will be less pumping loss at WOT. But you're confusing volumetric efficiency with fuel consumption. Obviously gunning the motor is not the best way to save money at the pump. If your Cobra made 30hp, then this would work... or if it were a diesel. :D With a motor that makes enough power, with more throttle the computer will increase pulse width to prevent the motor from going crazy lean, right?

And what you said about wind resistance is true, yes. The power required to propel the vehicle increases at the cube of the speed while aerodynamic resistance increases at the square. Which is why I specified that this is assuming the engine produces enough power to pull the highest vacuum in OD. And once again, vacuum readings will take this into account.

Not trying to argue with you Sean, I know you're right. Most vehicles will do best at 55mph. This is why I avoided the words best mpg and added so many conditions. Just trying to observe the highest vacuum pulled at the lowest speeds in top gear for different vehicles, assuming my theory is correct (which can neither be confirmed nor denied). ;)

[enkeivette]

And for the record, I don't think that there is any C5 or C6 anywhere, that will get the best mileage at 90 mph in OD on a flat road.

As you said, my car is atypical. And the high rpm carbed motor is not smart enough to cruise at a low rpm.

[SeanPlunk]

Sean, yes there will be less pumping loss at WOT. But you're confusing volumetric efficiency with fuel consumption. Obviously gunning the motor is not the best way to save money at the pump. If your Cobra made 30hp, then this would work... or if it were a diesel. :D With a motor that makes enough power, the computer will increase pulse width to prevent the motor from going crazy lean, right?

And what you said about wind resistance is true, yes. The power required to propel the vehicle increases at the cube of the speed while aerodynamic resistance increases at the square. Which is why I specified that this is assuming the engine produces enough power to pull the highest vacuum in OD. And once again, vacuum readings will take this into account.

Not trying to argue with you Sean, I know you're right. Most vehicles will do best at 55mph. This is why I avoided the words best mpg and added so many conditions. Just trying to observe the highest vacuum pulled at the lowest speeds in top gear for different vehicles, assuming my theory is correct (which can neither be confirmed nor denied). ;)

Fair enough, and right on.

[SeanPlunk]

And for the record, I don't think that there is any C5 or C6 anywhere, that will get the best mileage at 90 mph in OD on a flat road.

As you said, my car is atypical. And the high rpm carbed motor is not smart enough to cruise at a low rpm.

Your car is one of a kind, I can't wait to see the new paint.

[enkeivette]

I love empirical observation. But, uh, don't we need mpgs at the theoretically most effecient speed and compare to some other base point, like 55mph? This also means you need a fixed moderate length test loop and vaguely similar conditions (temprature, humidity). Take it up to this level and I'll participate with my 5 very different cars.

Should I control head winds too? :surrender:

[Vettezuki]

Should I control head winds too? :surrender:


You should control what you can control.

[enkeivette]

We'd have to empty the entire tank at a specific speed to get accurate results.

Besides, I'm not trying to convince anyone that pulling the most vacuum (gas engine) will provide the best economy, I'm already convinced of that. I'm just trying to find an average for the speed at which these cars pull the highest vacuum.

[Vettezuki]

We'd have to empty the entire tank at a specific speed to get accurate results. . .

Nope. Fill the tank SLOWLY with the nozzle fully inserted. Stop after the first kick off. Run a loop (e.g., 50 - 100 miles). Fill up the SAME WAY AT THE SAME PUMP. The difference between this method and fully draining the tank would be nominal, maybe even better because a motor can run out of fuel while there's still fuel in the tank depending on the shape of the tank and location of the pump.

[BRUTAL64]

We'd have to empty the entire tank at a specific speed to get accurate results.

Besides, I'm not trying to convince anyone that pulling the most vacuum (gas engine) will provide the best economy, I'm already convinced of that. I'm just trying to find an average for the speed at which these cars pull the highest vacuum.

That's highest vacuum at lowest possible RPM. Just in case you forgot.:D

[enkeivette]

Ben, true true.

Glenn, true true.

[st-evo-9*corn fed-8urvet*]

when u say highest vacuum what do u mean because say in an NA car the vacuum number would increase say giving u 15 vacuum...which in that case woudl be the highest. and in my case the highest vacuum number would be 1-0 seeing as how turbos force air in illiminating vacuum and creating BOOST!!

ill just toss in my results for my "highest vacuum runs"

the vacuum where i start to feel power and can maintain speed on a flat road is
10-9 vacuum and the air/fuel ratio on my car reads 18.1-17.6:1 at that vacuum the speed will usually get me to 65 on a flat road.

the highiest vacuum for me which is 1-0 vacuum can excellerate me on a flat road to 103mph at 16.1:1 air/fuel ratio.


so ya now define higher vacuum so i can be on ur page!

[enkeivette]

...the vacuum where i start to feel power and can maintain speed on a flat road is
10-9 vacuum and the air/fuel ratio on my car reads 18.1-17.6:1 at that vacuum the speed will usually get me to 65 on a flat road.

<- This is what I'm talking about, the highest numerical vacuum. Are you sure you get the highest vacuum at the lowest speed of 65? Not 60 or 70? If so, I'll add it to the list.

My motor is boosted too, I see the best vacuum (or highest) around 10 or 12" off the top of my head.

[enkeivette]

Wanted to post another clarifying thought about the vacuum theory.

As Sean mentioned, a throttle blade is a restriction. When it comes to efficiency it would be best to be at WOT, this is one of the reasons diesel engines get such good mileage. But, for a gas engine, more throttle equals higher cylinder pressure (due to more air flow) which causes a higher demand for fuel... So although the engine is less efficient with the throttle closed, there is less fuel consumption, and that's primarily what we're concerned with here.

So how do we measure fuel consumption without doing it directly? We look at the vacuum guage, the higher the vacuum reading, the less the throttle is open and therefore the less fuel is being metered with the air. Because the vacuum guage is actually reading the restriction, the negative pressure which relates consequently to lower cylinder pressures and once again, less fuel consumption necessary to match the air being sucked in.

So, if the vacuum guage does not read the highest number possible while cruising, this means that the throttle is open more feeding the engine more air, and yes more fuel, to maintain speed. There is a greater need at lower rpms, (where the engine is making less power) for increased cylinder pressures to maintain speed. :judge:

Was that good, did that all make sense? I think I've said most of this before, just trying to be more clear.

[st-evo-9*corn fed-8urvet*]

oh ya crystal ass clear!!!

so ya after my tune my highest vacuum is 10-9 in numerical value which yields me about 65mph at on cold nights or cold weather in general

but this is only because of my tuning. a stock evo would probably hit 50-60mph

and if u look at just about every stock tune out there

there fuel areas read at 14.7 in the idle and cruising cells in relation to engine load and rpm.

this is because 14.7 is the air/fuel ratio that is perfect for best emissions....all cars i have seen that have installed a wideband o2 air/fuel ratio monitoring system will read at 14.7 no matter where u are in the cruising area of ur stock tuned factory map

so in essence u arent really gonna yield to much better gas milage by letting off the throttle because the car is always gonna compensate the afr and make it 14.7:1 which most cars to get the best fuel efficiency there afr needs to be at 15.8:1 to 16.1:1 on petrol based fuels.

[enkeivette]

oh ya crystal ass clear!!!

so ya after my tune my highest vacuum is 10-9 in numerical value which yields me about 65mph at on cold nights or cold weather in general

but this is only because of my tuning. a stock evo would probably hit 50-60mph

and if u look at just about every stock tune out there

there fuel areas read at 14.7 in the idle and cruising cells in relation to engine load and rpm.

this is because 14.7 is the air/fuel ratio that is perfect for best emissions....all cars i have seen that have installed a wideband o2 air/fuel ratio monitoring system will read at 14.7 no matter where u are in the cruising area of ur stock tuned factory map

so in essence u arent really gonna yield to much better gas milage by letting off the throttle because the car is always gonna compensate the afr and make it 14.7:1 which most cars to get the best fuel efficiency there afr needs to be at 15.8:1 to 16.1:1 on petrol based fuels.

That's interesting, pretty damn lean, does it run any hotter like that?

And the AF ratio in a normal engine can also be 14.7:1 at WOT, with more fuel/ air consumption. Trying to see here where there is the least fuel consumption, because 14.7 is just a ratio.

[st-evo-9*corn fed-8urvet*]

That's interesting, pretty damn lean, does it run any hotter like that?

And the AF ratio in a normal engine can also be 14.7:1 at WOT, with more fuel/ air consumption. Trying to see here where there is the least fuel consumption, because 14.7 is just a ratio.

normally what ull find is on well built and cooled motors have these general afr's

rememer this is for petrolium based fuels IE. 91, 100, C16 octane's etc....

16.1:1 = best fuel consumption for running the engine at its leanest

14.7:1 = best fuel emissions reason y all cars read this almost everywhere

12.5:1 = most power potential.

as for my afr of 18.1-17.8 its because im running ethonal E85 and it cools the combustion temps which in turn cools the egt's my egts are around 800F while cruising when they used to be at 1400F on my gas tune at 14.7afr. also e85 is highly oxygenated so its gonna raise that air part of ur afr.

so what might be a 14.7 afr on gasoline, would in turn be a 16.4:1 on e85

really if u guys couldnt tell im enjoying everyday im running this hippy corn shit :sm_laughing:

also when u get into the most efficient power, and best fuel consumption afr for e85 things kinda get mixed up.

im not even sure of what the best afr for e85 is because of its high oxygenation which in the tests ive done in my car have seemed to end up being the 18.1:1 range and the engine actually starts starving for fuel but doesnt over heat. u just get split random nano seconds of random cylinder misfire.

and in theory the best power ratio for e85 is around 9.4:1 i believe but if u run it that rich it bogs ur engine down alot!!!

but in reality ive found that 12.5:1-12.8:1 seem to do just dandy for the best power ive made out of e85.

im sure with a direct injection motor such as the one found in the solstice u could get more power out of a richer fuel ratio for gasoline and e85.

[94cobra69ss396]

I ran the Cobra today and recorded the vacuum at 55, 60, 65 and 70. At 60, 65 and 70 I had 12 in. HG and at 55 I had 10 in. HG. This got me thinking, as long as you have enough power to cruise at the given mph without loading the engine you should have higher vacuum the higher the rpms are. To test this I dropped the car at 65 from 6th gear to 4th gear and the vacuum increased to 15 in. HG while still cruising at 65. Not sure what this means because I'm not an engineer.

[SeanPlunk]

Interesting stuff - I'm actually glad you started this thread Enkei :laugh:

[BRUTAL64]

I ran the Cobra today and recorded the vacuum at 55, 60, 65 and 70. At 60, 65 and 70 I had 12 in. HG and at 55 I had 10 in. HG. This got me thinking, as long as you have enough power to cruise at the given mph without loading the engine you should have higher vacuum the higher the rpms are. To test this I dropped the car at 65 from 6th gear to 4th gear and the vacuum increased to 15 in. HG while still cruising at 65. Not sure what this means because I'm not an engineer.


The main thing to look for is highest Vac in inches and the lowest possible RPM. As your speed increases the greater the resitance from air itself. :bang:

[94cobra69ss396]

The main thing to look for is highest Vac in inches and the lowest possible RPM. As your speed increases the greater the resitance from air itself. :bang:

So theoretically since I had 12 inches HG at 60, 65 and 70 I should get the best gas millage at 60?

[enkeivette]

The main thing to look for is highest Vac in inches and the lowest possible RPM. As your speed increases the greater the resitance from air itself. :bang:

:iagree:

So theoretically since I had 12 inches HG at 60, 65 and 70 I should get the best gas millage at 60?

And ya, theoretically.

[94cobra69ss396]

Well, I have to drive out to Phoenix in September for business so I'll do some testing and let you guys know what I find.

[enkeivette]

Well, I have to drive out to Phoenix in September for business so I'll do some testing and let you guys know what I find.

Sweet.

If you have the patience, do 55 one way and 60 going the other. This would be the tell all about the vacuum theory.

[94cobra69ss396]

I'd did some testing today because I had to drive out to L.A. to visit a customer. I filled up at a gas station right before I got on the freeway and set the cruise control for 60. After visiting my customer I stopped and filled up the tank before getting on the freeway to head home. I had gone 67 miles and pulled 27.202 mpg. On the way home I set the cruise control at 55 and filled up when I got off the freeway. At 55 I only pulled 22.218 mpg. This was in my Cobra which has 3.55 gears, 245/45/17 and a T56 with a .72 overdrive.

[BADDASSC6]

Let's not get bogged down too far over vaccum. It's effects are insignificant compared to the larger forces acting on the vehicle. If you want to save gas put the car in the highest gear available and run it at the lowest speed that it will operate (preferably smoothly) in that gear.

[94cobra69ss396]

Let's not get bogged down too far over vaccum. It's effects are insignificant compared to the larger forces acting on the vehicle. If you want to save gas put the car in the highest gear available and run it at the lowest speed that it will operate (preferably smoothly) in that gear.

That didn't work for me. I got 27 mpg driving at 60 mph and only 22 mpg driving at 55.

[BADDASSC6]

I'd like to preface what I'm writing with a statement. I'm drunk as shit right now.

O.k. If ou got a five mile per gallon difference by increasing you speed by 5 miles per hour then there is something unique at play with your car. Vaccum is a measure of headloss cause by the butterfly valve as a flow resitriction. In an ideal situation to maximize efficiency wyou would design a system were it would hit peak efficieny at wide open throttle. That's why they sell the barrell valve type throttle bodies. because at WOT they are more efficient. You have a blower on your car. it's possible that it can mask some of the losses at low RPMs. the difference between 55 mph to 60 mph is negligable when you compare 85 mph to 90 mph based on the fact that air resistance is an exponential force.

I'm still super loaded by the way.:beer:

[Vettezuki]

I'd like to preface what I'm writing with a statement. I'm drunk as shit right now.

O.k. If ou got a five mile per gallon difference by increasing you speed by 5 miles per hour then there is something unique at play with your car. Vaccum is a measure of headloss cause by the butterfly valve as a flow resitriction. In an ideal situation to maximize efficiency wyou would design a system were it would hit peak efficieny at wide open throttle. That's why they sell the barrell valve type throttle bodies. because at WOT they are more efficient. You have a blower on your car. it's possible that it can mask some of the losses at low RPMs. the difference between 55 mph to 60 mph is negligable when you compare 85 mph to 90 mph based on the fact that air resistance is an exponential force.

I'm still super loaded by the way.:beer:

I'd like to preface my response with I'm drunker than most, not as drunk as some (you). Which really doesn't seem to have been such a swell idea considering I'll be on the bike in six hours. :barf: Oh well, I digress.

What are you referring to when you say "peak efficiency" in this case?

[BADDASSC6]

I'm no longer drunk, but I am hungover.

If I were going to try to design a vehicle that got maximum fuel effiency. I would pick a resonable speed and I would design the motor to operate at a low constant RPM where it made enough torque to maintain that speed at wide open throttle.

[enkeivette]

I'd did some testing today because I had to drive out to L.A. to visit a customer. I filled up at a gas station right before I got on the freeway and set the cruise control for 60. After visiting my customer I stopped and filled up the tank before getting on the freeway to head home. I had gone 67 miles and pulled 27.202 mpg. On the way home I set the cruise control at 55 and filled up when I got off the freeway. At 55 I only pulled 22.218 mpg. This was in my Cobra which has 3.55 gears, 245/45/17 and a T56 with a .72 overdrive.

:judge::judge::judge: :D

Let's not get bogged down too far over vaccum. It's effects are insignificant compared to the larger forces acting on the vehicle. If you want to save gas put the car in the highest gear available and run it at the lowest speed that it will operate (preferably smoothly) in that gear.

Define smoothly. That's what I'm trying to do.

I'd like to preface what I'm writing with a statement. I'm drunk as shit right now.

O.k. If ou got a five mile per gallon difference by increasing you speed by 5 miles per hour then there is something unique at play with your car. Vaccum is a measure of headloss cause by the butterfly valve as a flow resitriction. In an ideal situation to maximize efficiency wyou would design a system were it would hit peak efficieny at wide open throttle. That's why they sell the barrell valve type throttle bodies. because at WOT they are more efficient. You have a blower on your car. it's possible that it can mask some of the losses at low RPMs. the difference between 55 mph to 60 mph is negligable when you compare 85 mph to 90 mph based on the fact that air resistance is an exponential force.

I'm still super loaded by the way.:beer:

Very true, but you need to read the first few pages. Went over this already.

[enkeivette]

See:

Sean, yes there will be less pumping loss at WOT. But you're confusing volumetric efficiency with fuel consumption. Obviously gunning the motor is not the best way to save money at the pump. If your Cobra made 30hp, then this would work... or if it were a diesel. :D With a motor that makes enough power, with more throttle the computer will increase pulse width to prevent the motor from going crazy lean, right?

And what you said about wind resistance is true, yes. The power required to propel the vehicle increases at the cube of the speed while aerodynamic resistance increases at the square. Which is why I specified that this is assuming the engine produces enough power to pull the highest vacuum in OD. And once again, vacuum readings will take this into account.

Not trying to argue with you Sean, I know you're right. Most vehicles will do best at 55mph. This is why I avoided the words best mpg and added so many conditions. Just trying to observe the highest vacuum pulled at the lowest speeds in top gear for different vehicles, assuming my theory is correct (which can neither be confirmed nor denied). ;)

Wanted to post another clarifying thought about the vacuum theory.

As Sean mentioned, a throttle blade is a restriction. When it comes to efficiency it would be best to be at WOT, this is one of the reasons diesel engines get such good mileage. But, for a gas engine, more throttle equals higher cylinder pressure (due to more air flow) which causes a higher demand for fuel... So although the engine is less efficient with the throttle closed, there is less fuel consumption, and that's primarily what we're concerned with here.

So how do we measure fuel consumption without doing it directly? We look at the vacuum guage, the higher the vacuum reading, the less the throttle is open and therefore the less fuel is being metered with the air. Because the vacuum guage is actually reading the restriction, the negative pressure which relates consequently to lower cylinder pressures and once again, less fuel consumption necessary to match the air being sucked in.

So, if the vacuum guage does not read the highest number possible while cruising, this means that the throttle is open more feeding the engine more air, and yes more fuel, to maintain speed. There is a greater need at lower rpms, (where the engine is making less power) for increased cylinder pressures to maintain speed. :judge:

Was that good, did that all make sense? I think I've said most of this before, just trying to be more clear.

[94cobra69ss396]

Sorry, my 6th gear is .62, not .72. Also, I have to go out to the same customer this Thursday so I'm going to do the same test again only I will drive 55 there and 60 back.

[enkeivette]

Sorry, my 6th gear is .62, not .72. Also, I have to go out to the same customer this Thursday so I'm going to do the same test again only I will drive 55 there and 60 back.

I'm willing to bet that it will be even worse this time at 55mph. Approaching LA the 5 and the 101 start to incline. I'll bet that 55 going up hill with a cammed motor will bog the piss out of it.

[94cobra69ss396]

Actually, I think it will do better at 55mph next time. The route I drove at 60mph was the 15 South to the 210 West to the 605 South to the 105 West. On the way home at 55mph I went the 105 East to the 605 North to the 210 East to the 15 North.

On Thrusday I will drive to my customer at 55mph and home at 60mph and see what the difference is.

[94cobra69ss396]

So I finished testing the second half today. Today at 55mph I pulled 25.844mpg and at 60mph I got 28.333mpg. So my car definitely gets better gas millage at 60 then it does at 55.

Next time I go out to the same customer I will drive both directions at 65 and report the numbers.

[enkeivette]

:D:judge:

Awesome, thanks man!

[94cobra69ss396]

No problem. Now I just hope that I can get better millage at 65mph then 60mph because I don't think I have the patience to drive a really long distance at 60mph.

[Vettezuki]

No problem. Now I just hope that I can get better millage at 65mph then 60mph because I don't think I have the patience to drive a really long distance at 60mph.

Even if it costs more gas, think of the time savings. Time = $. Therefore, it's at least a wash, and possibly a gain depending on how you leverage your time. :thumbs_up:

[BRUTAL64]

No problem. Now I just hope that I can get better millage at 65mph then 60mph because I don't think I have the patience to drive a really long distance at 60mph.

You've done a lot so far. If you are in the mood, would it be possible to do a MPG at 80. Yea, really.:D


I can't, no speedo or odometer.:bang:

[enkeivette]

No problem. Now I just hope that I can get better millage at 65mph then 60mph because I don't think I have the patience to drive a really long distance at 60mph.

For your sake, I hope you do. For the sake of my theory, I hope you don't. My guess would be that your mileage at 65 would be similar to your mileage at 55, but for a different reason. Being wind resistance over lugging.

[94cobra69ss396]

So I drove out to Scottsdale, AZ today and I drove at 65mph to the border, filled up and then drove 75mph the rest of the way into Scottsdale. At 65mph I got 25.083mpg and at 75mph I got 22.043mpg. So it looks like I do get the best mpg at the highest vacuum in my car.

[enkeivette]

So I drove out to Scottsdale, AZ today and I drove at 65mph to the border, filled up and then drove 75mph the rest of the way into Scottsdale. At 65mph I got 25.083mpg and at 75mph I got 22.043mpg. So it looks like I do get the best mpg at the highest vacuum in my car.

:judge::judge::judge::judge::judge::judge: :judge::judge::judge::judge::judge::judge:

[94cobra69ss396]

You've done a lot so far. If you are in the mood, would it be possible to do a MPG at 80. Yea, really.:D


I can't, no speedo or odometer.:bang:

Ok, this was my last test. I ran from Scottsdale to the border (192.2 miles) at 80mph and got 20.055mpg. In my Cobra the rpms at 80 were 2400.

[enkeivette]

20 mpg at 80 mph aint bad with that much hp. :bigthumbsup:

[94cobra69ss396]

20 mpg at 80 mph aint bad with that much hp. :bigthumbsup:

It's not all that bad but my buddy has a LS1 GTO that has twin turbos and makes around 550rwhp that does better. I've only been in the car once when we went to Magic Mountain and he pulled a little over 28mpg driving at 85mph.