i picked this up from another forum but would like to know if anyone would agree or no.

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote &raquo;</TD></TR><TR><TD CLASS="quote">[user]lasthope05[/user] wrote:

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<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by lasthope05 &raquo;</TD></TR><TR><TD CLASS="quote">I guess you dont understand how car operates. The level of modification has little impact on your gas mileage. A vehicle from the factory has its preset limitations of fuel consumption A finer tune by pulling a bit more fuel out of the entire LTFT range will net you better fuel mileage. The amount of fuel a vehicle consumes remains constant. When modifying a car you are essentially giving the motor more oxygen to product more power. Now this is where fuel mileage comes into play. Say that a stock supra gets 20mpg. Now lets modify the car, add a larger turbo, cams, bigger injectors, fuel pump...etc etc. So now the supra is now magically a 1000hp vehicle. Since the turbo is much larger doesnt spool as fast as the stockers the car does not get into boost as fast or as much. If the car is not seeing boost the ECU will know not to inject more fuel. The same car will get the better gas mileage from the lag alone. Now even tho the car is 1000hp, it is 1000hp at WOT. So that particular fuel consumption remains constant. It uses the same amount of fuel to move the vehicles weight.

That brings us into another topic. Weight plays a large factor in fuel consumption as well as over all performance. Less weight means less power and fuel is needed to move the vehicle.

So short as sweet. A 1000hp car is only 1000hp at WOT. It still uses the same amount of fuel to move, with the exception to turbo size(larger turbo spooling later and giver you a much broader range in driving and cruising), a much finer tune from factory and weight all playing a specific role in reducing fuel consumption and increasing fuel economy.</TD></TR></TABLE>

 

So let me get this strait. Did I just read a thread where this guy states that a 1000Hp car will consume the same fuel as a 200Hp car????? That may be true at idle as long as the bore, stroke, compression, intake, and exhaust hasn't been changed.

If a 1000hp car requires 1600cc per hour injectors and the 200 hp only requires 240cc per hour injectors. How can they both consume the same fuel? The difference in the injector flow rates gives that away????

Engine Modifications have everything to do with fuel consumption. the more air you add you have to add fuel. that is why it's called a ratio. 14.7 parts air to 1 part fuel (or whatever AFR you choose) If you add more air the AFR will lean out (raise 15-17:1) In order to bring it back down you need to add more fuel. So how can adding more fuel not effect your fuel consumption?????

Or am I missing what he is trying to say and I'm all F'd up????????

 

I am the one that wrote that.

If you read closely I stated that a 1000hp car is only 1000hp at WOT. Do you not agree? So at WOT it consumes more fuel. Thats a given but daily driven and responsibly driven it receives the same amount airflow and fuel it normally uses to move.

Fuel consumption remains constant and idle cruise and normal driving. Do you understand that it takes the same amount of fuel to move the same car at the same speed same, at the same acceleration as it would if the car was modified or not. Drivers dictate the amount of mileage they receive.

I guess you dont understand that injector size plays no role in fuel consumption. I understand seeing more airflow means need more fuel. But in my example of a turbo car with a larger turbo where lag plays a role. Before boost even builds you will not even be seeing that extra airflow. Power rises in increments its thats why larger injectors are needed. As it rises higher and higher thats where the larger injectors come into play to give that needed fuel. You can put 1000cc injectors into a 4 cylinder and only have 200hp but it will have the same fuel mileage. Injectors are seen as limitations on how much power you can make not, bigger injectors means worse fuel mileage. That is the common misconception that larger injectors means a more fuel consumption while daily driving.

 

Your theory would only apply to a turbo car with the same bore and stroke as stock right? (just larger turbo and larger injectors) in which case i might agree(also assuming gear ratios are kept the same) However, i refuse to believe that while maintaining the same gear ratios, that a larger displacement, or at least a longer stroke will still get the same mpg as stock, at cruising speed.

 

No I did not imply that changes in stroke or displacement will net you the same MPG as it is a known fact that increasing stroke or displacement increases your intake airflow as a constant rate through out the entire power band. It is mostly applied to turbo cars but can be applied to NA's as well, but NA guys approach their power gains in a different way.

 

well then i guess i can agree with you. i was actually having this discussion with my pops yesterday, if u stock a big turbo on a little motor, considering you drove conservatively, that big turbo wont spool up and your not pulling all that air in and your not needing all that fuel. kinda coincidental you post this two days after i was talking about it haha

 

I fully understand what injector size and duty cycle is all about. I don't need to be schooled, thank you very much.

Yes I agree that two cars that idle and cruise at the same RPM and Manifold pressure no matter what size the injector will use the same amount of fuel. I'm not contesting that. I'm still a wee bit lost on your only 1000hp @ WOT. A boosted car doesn't just go from 200 hp strait to 1000hp or does it? Isn't there a power curve and therefore an increase of fuel needed to feed that curve in increasing amounts. Or is a turbo only all or nothing?

I don't profess to be a turbo guru nor do I care to be one. That aside, isn't there going to be different amounts of boost even when cruising between these two Supras? Doesn't the velocity of the exhaust gas and the tubo impeller size determine the amount of boost supplied to the engine? So say these two cars are both cruising at 60Mph @ 3500 RPM. What your saying is that Your stock 200hp turbo Supra and the 1000hp larger turbo Supra are going to have the same boost levels? That is where you loose me, I always thought that the larger turbo would always create more boost at any given RPM therefore use more fuel even at a cruising RPM. Once she's spooled your getting boost right? So does this larger turbo not spool until after 3500 RPM is that what your saying? If that is the case I agree with you also.

 

We'll its kinda hard for me to break it down so I'll try to explain it as best I can. Say the stock turbos of the supra gets full boost at 3000rpm(18psi) and the larger turbo gets full boost at 4000rpm(18psi). Boost pressure isnt the factor here it is the actual airflow in cfm. So both cars are crusing as you said at 3500rpm, Since you are not at wot you are not seeing boost so your cruising fuel mileage is the same as stock. Now where your shifting and accelerating is here the most of the gas saving takes place as when you are accelerating, since the smaller turbo spools faster in the rpm range you are hitting boost much more often. In the larger turbo you wouldnt be seeing boost as often as the larger turbo would take longer to spool and make power. I guess its best seen as the larger turbos moves your power band higher so since your power band is higher in the rpm range the lower portion consumes less fuel than before with the stock turbos that spool faster and see more boost and cfm at the lower range. So the increase in cfm from the larger turbo is still seen but its seen but is much higher in the rpm range. So since the smaller turbo makes its power in the lower to mid range thats where it consumes more fuel.

 

The theory sounds convincing I'm pretty sure I understand what your saying now. Do we have any one out there that wants to put up some datalog/graph info on boost levels (cfm) for different size turbo applications. If what your saying is the case and the smaller turbo sees more time in boost (higher cfm's) than wouldn't the smaller turbo burn more fuel on a daily basis.

Just to take this to a realistic level..... It's not like your going to daily drive a 1000hp car to work every day. How about a 300hp turbo vs a 500hp turbo. This would be like a realistic turbo upgrade for a Daily driver wouldn't it? I'm pretty sure you will see a decrease in fuel economy with this type of upgrade. It would be along the lines of a N/A setup adding higher CFM cams, intake and exhaust. I know that there is no comparison in fuel economy there. I've seen it a few times myself.