MPG & HP

[vdogamr]

I know that MPG is to HP like delicious is to healthy, computational memory is to computational speed, and pretty is to smart... but in each of those situations you can occasionaly find the best of both worlds.

What can be done to a C4 to get you both? (By HP I mean horsepower and/or torque)
Are there known additions, or replacements that will do this?:confused

Two specific questions I have:
#1) Does a turbocharger reduce MPG?
#2) If my engine is most efficient at righer RPMs, wouldn't the larger rear gear ratio help me be more efficient?

Now of course I care more about improving my stick-shift 88 than other models, but I am interested in hearing anything.

And one more thing... just because I have the 4+3 doesn't mean I have a Torque Converter right? From what I understand they replace the clutch, and since I have a clutch, I would not expect to have one. And although I understand they are a brilliant piece of engineering, apparently they are less fuel efficient.

 

[G Winter]

The 4+3 is a standard 4 speed transmission with an automatic overdrive attached to the rear. It has a standard clutch and flywheel. No experience with that set up but with my six speed overdrive, the overdrive does improve MPG.
The L98 is set up to operate efficiently at relatively low rpm,so any gear change should be small.

Glenn

 

[Schrade]

The best of both worlds STARTS with a PERFECT TUNE.

Air, fuel, fire.

Air flow has to be clear. Fuel pressure HAS TO be spec. If too low, you get less atomization in the fuel spray. This means less power, AND less mileage. Injectors also have to have a good 'close' when pintle pulsewidth stops the spray. Leaking injectors won't hurt power, but WILL reduce mileage. And fire... Good plugs - especially good wires are important. As is PROPERLY routed (in the wire looms) and connected wires, which is VERY important...

 

[Tuna]

As I recall, the EPA mileage ratings for the late C4 were 17/27 and with 300 HP.

The C5 jumped to 350 HP and still had ratings of 17/27. The C6 shows similar mileage figures with 400+ HP.

Engine efficiency, cruise RPM, rolling resistance, air drag and driving style affect MPG.

Turbocharging should increase HP without killing MPG since the turbo doesn't require engine HP to turn it. But extra HP usually kills driving style and therefore, MPG.

 

[vdogamr]

As I recall, the EPA mileage ratings for the late C4 were 17/27 and with 300 HP.

Turbocharging should increase HP without killing MPG since the turbo doesn't require engine HP to turn it. But extra HP usually kills driving style and therefore, MPG.

The mileage sounds about right for my 88, and I think it's a fine MPG, but I believe my HP is supposed to be around 245. Is it an "easy" swap to swap the L98 with an LT4 or even an LSx?

Turbocharging increases backpressure right? That doesn't "require HP":confused?

I know tuning is important, and ever since I got my car I have been trying to put it in the best shape I can. I was just wondering if there were any well known modifications that got you a bonus without a negative.

And yes I know the phrase about too good to be true, but what about the parts and kits sold through the parts stores that claim to increase HP.

 

[Tuna]

Every thing is a compromise when it comes to horsepower increase.

Turbochargers use the exhaust gas pressure and flow to turn the impeller, so that definitely more back pressure but it's not directly taking away HP from the engine to turn the turbocharger - unlike a supercharger that requires the engine to turn the supercharger. The extra power created by the turbocharger more than makes up for any issues with exhaust backpressure.

However, turbochargers have a certain amount of 'lag' between pressing the throttle and getting the extra horwepower especially at low RPM. At low RPM, there not enough exhaust flow to spool up the turbo to provide 'instant' HP. This means you drive it differently when max performance is required. It also means that the turbo isn't making unnecessary HP when you don't need it and therefore you do waste gas. You need a twin turbo system with a 350 V8 to minimize the lag.

There's also the issue with heat. If the turbochargers are under the hood, they get real hot and that means you need a way to get the excess heat out from under the hood. That also means that the intake charge coming from the turbos to the engine is hotter. That means you need an intercooler to take advantage of all that extra air and that's more weight. Take a look at some of the Callaway twin turbo cars of the C4 era and note the scoops on the hood and other places to all cooling air to the intercoolers and under the hood.

There's at least one company that makes twin turbo installations at the rear of the car replacing the mufflers with turbos. This removed the heat from under the hood and mostly eliminates the intercooler need but I think that company focuses on C5 and C6 installations.

Then there's the boost level to consider - how much boost can your engine use without needing to be rebuilt for higher levels of boost. And, don't forget the computer reprogramming that needed.

I don't even want to get into superchargers and nitrous.

Corvette Fever did and LSx installation into a C4 and has articles on that in their magazine. That's a lot of work but doable. If you use an LSx from a Vette, it lighter and that requires a suspension change to rebalance the car. Way beyond my knowledge.

Dropping an LT4 into an early C4 would be less work but putting a Gen II in a Gen I car has its own problems.

 

[ZumZum]

In simple form (which is appropriate for me), your V8 engine is an air pump. The way to increase HP is to allow more air to flow through it. Intake mods, heads, cam, exhaust, supercharging, they're all designed to flow more combustible material (air) into the combustion chambers. Unless you're going to run the motor in an extremely lean condition, it will take more fuel to burn that air efficiently and create more HP.Simply put, that is.

One way to go faster and get better mileage has nothing to do with increasing power. It's the power to weight ratio. Put your car on an extreme diet. Get rid of the spare tire, carpeting/sound deadening, put in light weight seats, lightweight alloy rims, remove the AC and pollution controls, etc.

 

[Schrade]

As I recall, the EPA mileage ratings for the late C4 were 17/27 and with 300 HP.

The C5 jumped to 350 HP and still had ratings of 17/27. The C6 shows similar mileage figures with 400+ HP.

Engine efficiency, cruise RPM, rolling resistance, air drag and driving style affect MPG.

Turbocharging should increase HP without killing MPG since the turbo doesn't require engine HP to turn it. But extra HP usually kills driving style and therefore, MPG.

Uh-oh... Your recollectin' is like a politician's

I guess his '88 has L98 (245 hp).
I think C5 LS1 had 345 hp...







(just kiddin' about the politician part - no one deserves that disrespect, except politicians!)

 

[vdogamr]

In simple form (which is appropriate for me), your V8 engine is an air pump. The way to increase HP is to allow more air to flow through it. Intake mods, heads, cam, exhaust, supercharging, they're all designed to flow more combustible material (air) into the combustion chambers. Unless you're going to run the motor in an extremely lean condition, it will take more fuel to burn that air efficiently and create more HP.Simply put, that is.

One way to go faster and get better mileage has nothing to do with increasing power. It's the power to weight ratio. Put your car on an extreme diet. Get rid of the spare tire, carpeting/sound deadening, put in light weight seats, lightweight alloy rims, remove the AC and pollution controls, etc.

Well, I guess this is what I expected to hear. I was hoping someone had a miracle product though.:L

I don't think I would ever entirly remove the carpet. Maybe lighter weight material or something, but looks are important too. I like that I have pollution controls, and I think I already have the allow wheels. I could probably remove the AC, it doesn't work anyway. But I think it would be more enjoyabe to fix the AC than to remove it. (seems like the easy way out )

I am intersted in the "light weight seats". Is there actually an aftermarket seat modification kit? I personally think my seats are a little low in the back. Not only do I not have airbags in my 88, but I am pretty sure the top of the seat is in the perfect position to break my neck too. If I could get taller, lighter seats that would be great. But that is probably a contradiction too.

I guess if improving one area requires compromising another, I am just not willing to do it yet. I do have 2 cars, so maybe I will let the MPG side slide a little someday.

 

[Smmmokin']

I know how you can pick up some HP pretty quick, go to your local Chevy dealer and make a deal on a new or fairly new Z06!! otfl But, maybe not so funny, it just might work!!

 

[Schrade]

Well, I guess this is what I expected to hear. I was hoping someone had a miracle product though.:L

There is a miracle 'design', and it's worth millions to whoever wants to perfect it. The oil companies and the car makers know about it too yup... Works the same way the EVAP cannister system works, and propane-fueled cars.

Open up a vapor line from the tank, to the intake. It would have to be sized close to the size of the TB bore. The fuel will vaporize plenty fast all by itself to sufficiently supply a motor. Some 'honeycomb' material in the tank will assist vaporization, for pedal down types .

I did it with my lawnmower. I did a trial configuration in my '02 1-ton, while doing delivery work several years ago. I had a gas can in the back of the van, with a 3/4" line clamped to the can, going all the way just behind air filter intake opening, sealed tight. The gas can vent wasn't big enough, but it whistled all night long, telling me it was pullin' the air and fuel vapors.

My route was 430 miles each night. My 1-ton got always got just under 16mpg. I got over 19mpg's that night. That was with a little gas can and little vent hole. A bigger hole would make mileage much better.

I don't know how the PCM would react to a drastic DECREASE in injector pulsewidth. Mine for the test was only a slight decrease, with no problems.

Safety is the only concern. Electronic timing would prevent firing the way cars used to do with a carb. That would be 'The END'. Check valves, in redundancy, would be necessary. Even then, a crash could be a problem. So that solution would be to get liquid fuel up front, but then you have the problem that I had - too little of a pool for the fuel to evaporate by itself.

Your power increase won't be substantial. Your mileage will increase substantially.

Any ideas?

 

[joelgjoel]

Tune

Dynotune the car. Look into it. You may have to travel to find the nearest one but it's worth it.

 

[vdogamr]

Dynotune the car. Look into it. You may have to travel to find the nearest one but it's worth it.

This may be showing my ignorance, but... I thought dynotuning was when someone with a lot of mechanical knowhow (not me) used a dynomometer to test their tweaks. I assumed it was for either mechanics with one in their shop, or the rich who are willing to pay a mechanic with one in their shop. Why do I think it would be expensive? Because I imagine it being a lot of tweak-then-test, which equates to hours of labor.

How close am I?

And actually... I have decided that, on the interstate, my car gets excellent gas mileage and it has extra power I will probably rarely use. So I shouldn't worry about it too much. And if my engine ever blows, I will look into installing a newer model. All Corvettes seem to get about the same MPG, and the latest engines get more than double my HP. I do wonder what the best engine would be that would be reasonable to install. (My current thoughts are on LS6 and LT5 )

In the past 2 months (last major shop trip) I have driven probably 500-1000 miles with an average MPG of 20.1 (so says the dash) and I have gotten it to coast on a flat road for a couple minutes at a little over 70mph at 27MPG.

 

[joelgjoel]

dynotune

The cars rear wheels sit on rollers in the floor so the engine can be adjusted under load at high speed. Around here it's about $400. I had it done a long time ago on a car and it made a worthwhile difference. They told me not to bother if I was only running regular gas.

 

[vdogamr]

The cars rear wheels sit on rollers in the floor so the engine can be adjusted under load at high speed. Around here it's about $400. I had it done a long time ago on a car and it made a worthwhile difference. They told me not to bother if I was only running regular gas.

That sounds like a reasonable price. My car has been running well since it last went to the shop, but here lately I have started to feel something off. If this tuning is involved enough to find a problem if one exists, then I would gladly pay $400 to put my car in top shape.