What engine modifications makes a car use more fuel, in youre experience or other.

In my mind, I think that big port heads and big cam is the worst on the list to making a car guzzle gas. (not sure if it's right though)

Efi is obviously making a car use less gas....Only one making it use less perhaps?

Supercharging don't make it use more gas, so a mildish 300hp Na engine with 125+ hp from forged induction would use less gas than a 425 hp Na engine. Is this right?

What about valve size, does it matter more or less then port and cam size?

 

Yea, I agree (though I'm no expert, yet ). Big cam, big heads, and high compression. Also, very torque-friendly gears will drink the gas, probably more than other mods.

I think you'd get better mileage with forced induction than with an n/a engine making the same power.

An overdrive gear will help with maintaining mileage.

I'm not sure about valve size. I think having a valve too small for the application might restrict intake/exhaust which could have adverse effects of mileage.

Of course, I have no evidence whatsoever to back any of this up. This is coming from a guy who once believed that a 5.0HO would get better mileage than a 350

 

Well I too thought a 305 would get better milage than the 350. Wasn't that the purpose of the 305 to start with?

If not so, won't a 400 use anymore than the 305 with the same heads, carb, intake exhaust?

 

As far as I know, higher compression increases gas milage.

I'd assume that's part of the reason diesels manage better mpg.

But what the hell do I know?

Free flowing exhaust will help milage. Tornado fuel savers do not.

But gears are probably one of the bigger mpg droppers. Forced induction probably makes it worse if you drive the same way, but no matter kind of engine you have or how much power it makes, if you hammer it your gas milage WILL SUCK.

Laters,
Scott

 

Poor tuning would yield some nice drops in mileage. But that's not a mod At least, it SHOULDN'T be. I never thought higher compression would increase mileage. I understand how it would increase power. BUT, I know that once you get a better power/weight ratio, mileage would increase. I need to find out how to get there

 

For me...it was the huge cam, heads, converting to a 383, and Speed Demon 750.

Of course that stupid nitrous bottle doesnt help much either

 

mods that hurt fuel economy: smaller gears, higher stall torque converters, anything that deals with adding more fuel to each combustion stroke...

 

Which is why i think higher compression may improve mileage a tad. You are maximizing power output per combustion cycle. When you raise compression, you dont inject more fuel, youre just squishing it more so more power is created.

 

Yep, the thing about compression I think is right, been hearing that for years.

But what about shere boresize? a 305 vs 400 with the ame heads and averything else.

 

The bore size is why a 305 gets better mileage versus anything larger. As you increase the bore, you provide more volume that fuel/air has to occupy.

 

An increase in the CR is something that will improve fuel efficiency, that's something that's been proven.
Over the past two decades fuel efficency has been a primary factor in engine design, it's the law. An engine that isn't exceptionally fuel efficient can't be put into production. To find the most fuel efficient mods, look to the latest model/year designs. Carb gave way to TBI, that gave way to TPI, that gave way to LT1, and that to LS1. Each more efficient than it's predecessor, and more powerful.
I guess the point is that it's difficult to improve on the factory.
Since peak fuel efficiency takes place at 2000rpm or below, any mod that reduces the performance in that range will reduce fuel efficiency as well, though some mods might create a barely noticable change.
Valve size? I think that would depend on the chamber and port design, and valve timing. According to different theories, sometimes larger valves help and sometimes they hurt economy.
Just like performance tuning, economy tuning depends upon the combination of parts.
Supercharging? Yeah, a 425 hp supercharged engine will do better on gas than a 425 hp n/a engine.

It used to be possible to improve on the factorys MPG ratings, in the carb days, especially the mid 70s. I know because I've accomplished that. But any more, it's hard to better the factorys numbers without swapping in a smaller engine.

Disclaimer: Some fo the stuff I've mentioned, I haven't tested personally, just read some tests in books.

 

Okey, lots of good info here. Not looking to better the mpg on my current engine, but to chose the right combination for my future engine buildup. It has to deliver more power, and at the same time use the same or less fuel than my carbed engine does today.

As for efi being better than carb, that's a nobrainer. Was thinking of going with a Lt1 setup.

Dont' know what heads would be best, but the fastburn ones should perhaps be one of the better ones mpg-wise?

Dont know if lt1 efi can be mounted on those heads though. Maybe easier to just get some lt1 heads altogether... lol... or lt4 while I'm at it.


As I percieve it, it's the "high-port" design which makes the ls1 so much more efficient in design...correct? If so, which smallblock heads resemble those the most?

 

I can say that the fuel milage on a supercharger is yes and no
22mpg highway but only 7mpg city thats with aprox 550hp on a 305
don't know if I agree it a compression thing with the blower more a suck thing at 65 in 5th I am running about 1400 rpm and 12-15 In.Hg (no boost with throttle plates closed)

 

The more power the engine makes the more fuel it will require at WOT. At part throttle, if you have the right tune and keep the rpm.s low most engine will get similar mileage. It only takes between 15 and 20 hp to propell a car like ours at 60 on a straight road with no head wind. You are not going to be using a lot of fuel when your motor is running at around 20hp. This goes from stock motors to wicked combo motors. When it really boils down to it the more power you have the more fuel you have to use at maximum engine load. An engine is one of the few devices that converts chemical engergy into mechanical energy. It does it relatively efficient these days and your most advanced engines today won't make much more than 30hp at highway cruising low engine load situations. Thats where the advance tuning comes in.

 

I thought that was what you were trying to tell us in your original post but I wasn't sure.
I'm not an MPG guru, but it's been a major consideration in my build ups, so I've tried a few things.
As you mod a motor, the more radical the mods, or the more that combo leans toward producing top end power, the more fuel economy will suffer. Around town mileage will suffer the most.
In a 350, a cam of 220*@.050 can still give you pretty close to the same hwy mpg as stock, but in stop and go, it will be a lot worse. Cams with more duration than that will usually worsen the hwy mpg.
LT1s are a good design because the short intake runners shift the power curve toward the top end without using a big cam.
Two (of the many) things that can have a bad effect on fuel efficiency are, poor atomization or fuel particles falling out of suspension, and unburned fuel going out the exhaust. A small cam with little overlap is the solution to the problem of the unburned fuel in the exhaust. High velocity ports will help keep the fuel mist in suspension (along with other things).
In spite of the fact that the TPI is a low rpm torquey design, and good for fuel efficiency, it was replaced by the LT1 because it was considered overkill. By shortening the runners and shifting the torque to the upper end, there was no compromise in fuel economy, cause the cam stayed small.
The rule of thumb has always been, smaller/higher velocity ports to keep the fuel mist in suspension at low speed. That is something that originated with carbs, and I think it may apply less to multi port EFI.
I'm pretty sure the LT4 uses a larger intake port vol than the LT1, and I'm not sure but I don't believe there was any compromise in economy.
And right about at this point is where my knowledge falls away, so I should let someone else do the talking.
What I've said here could be covered in much greater detail, but I hope the basic picture has been presented.
David Vizard wrote a book called Performance With Economy. But basically it's what the factory is doing today.
There are some mpg compromises made by the factory for the sake of emissions. If you want to you can tune for economy and get a little better mpg, but it will throw off your tailpipe test a bit.
I'd like to hear what some of the other guys have to say about the LT4 compared to the LT1. I think the LT4 uses the fastburn heads, correct?
I'm trying to do a build like that myself. Right now 87 is $2.17/gal where I live.

 

Get ready to see 87 octane @ over $3.00 a gallon before the end of the year.

 

Well, here in Norway it's at a low $5,14

All time low last 12 years: $4.85
All time high last 12 years: $6,5
average of $ 6,1

with todays low exchange rate.

Efi is looking pretty good now :-)

 

What's the deal with that?
Did we lose the war, and they haven't told us about it yet
... or what ???

Time to start shopping for a moped

tilstad,
The LS1 is an even more fuel efficient design, but they're more than twice as expensive to build as a gen1 sbc.
@ $2.25/gal you'd be spending $20 to save $5, but @ $6/gal it might be worth your while to look into one of those.

I hope what I said in my earlier post made sense.
It made sense as I was writing it...
It's hard to explain the basic concepts in a short space.

 

 

Food for thought:
In the US, we're paying $2.25/gal for fuel that comes from the middle eastern desert, and it's upsetting to us.
Yet we're paying .89 for a pint of bottled water that we could be getting for less than a penny from our faucets,and no one seems to be complaining.

What is wrong with this picture?

And how much does a middle easterner pay for a pint of water?

It seems like with the way things are going, we ought to be able to strike up some sort of a better deal here.

 

 

So if all the TGO members pooled our $$, we could lease a supertanker and fill it with bottled water, take it to Kuwait, sell the water, buy oil, and all of us would have a lifetime supply of gas.

Why not?

Donald Trump... are you out there?

 

Should of brought some back with me lol
If youve ever been there you would understand they have nothin better to do than sit around and think about how to jack with everyone else!....They may have oil but the rest of that area sucks!

 

If I lived over there, I'd have a kickass dune buggy

 

If you lived there, you'd be lucky to own a camel...lol

 

I know LS1 probably is the most efficient and all over easy way of getting power reliably, fast and fuel efficient.

But the down side is, that I wont get experience with the smallblock gen 1 chevy, and I probably wouldn't ever afford to get the ls1 to insane power levels, which is a personal goal wich I WILL accomplish sooner or later.

So I was hoping to be able to build a Gen 1 smallblock with comparable technology to a ls1, and fuel economy at least approaching the same levels. Hope this could be done though, but I really dont know if say a LT1 is somewhat in the same ballpark when it comes to fuel efficiency.

My roughly planned combo so far consist of 383 or 406 (421) smallblock, forged bottom, LT1 efi, mildish to average heads and cam, and e good shot of NOS, say 250+. Maybe get a blower instead of the NOS, or both, overdrive transmission, no low gears, not much anyway.

Not so sure if going small on the heads really would help any on the fuel efficiency, but at least thats the reason I mention it.
More cubes to not need to rev high for everyday driving power.

What you said earlier made alot of sence! :-)

 

More HP = lower mpg

Thats because when you raise and engine's breathing ability with a better cam, higher flowing heads, bigger carb... it lets the engine take in more air. Because it can takes in more air, it will also take in more fuel, and thats what makes more HP, and thats what also lowers your MPG.

 

I haven't read much about the superiority of the LT4 over the LT1.
GMPP offers an LT1 to LT4 conversion kit that includes heads intake and hotcam + extras that claims 425hp.
It seems like an LT1 with a mild blower cam and a centrifugal supercharger would be a combo that's tried and proven and you could probably contact a company like Vortech or Powerdyne and they could give you specific info on a combo.
To me a supercharged LT1 350 with a smallish cam seems like it could be reasonably fuel efficient.

Owning a camel... that's depressing. No wonder they're blowing themselves up.
If they knew what it's like to go from 0-100 in 10sec, they'd have a different outlook.

 

If it is this easy, why do a 320 hp LS1 use less gas than a 170hp 305 lg4?

The thing is, it's more to it than this. The thing about a larger engine uses more gas is not always so.

In the same weighing car, with the same air restriction, keeping a steady pace at highway speeds, a large volume engine should not use any more gas than a smaller engine, because the car only requires the same amount of energy to produce that speed.

If an engine uses more gas anyway, that's because it's not using all of the gasolines power potential efficiently, and there lies the real question; what makes an engine fuel efficient or not.

I've have driven cars with engines with 60% moer displacement using 30% less gas on a long trip. The larger engine even produced 120% more hp. They where both bone stock by the way.

So dont come here with that "larger airpump, larger consumption" thing. It's just not so.
It's all about how the pump is managed, and with what parts. And that's what Im after, what parts is good, and what's not for power and efficiency.

 

Larger air pump, larger consumption is right! But you do have to factor in how its managed also(fuel control, chamber design...etc). It just shows you how much the newer motors have improved over the less efficiant older brothers. It also has to so with 6 speeds.....

 

You cannot make this argument because at highway cruising speeds and RPM's the LS1 and LG4 will be making roughly the same amount of power. So the motor with the better managnment system and head/chamber desgin will get the better mileage. At WOT and full load the LS1 will consume much more gas than the LG4 and be making 350hp vs 145hp. Does this make sense now.

 

Thats what I was talking about... the engine is only making full power at WOT. At WOT, the engine making more HP will suck back alot more fuel than an engine with less HP will.

As Shifty said, its a different ball game when you're cruising down the highway at a constant engine speed, because wether its a 400hp LS1 or a 200hp 305, they will be putting out the same amount of power, and will be using (all else being equal, like cruise rpm, aerodynamic drag, weight, etc) roughly the same amount of fuel to make enough HP to keep the car at speed.

Don't forget, the LS1 cars also have the very steep 6th gear, much steeper than 5th gear on a T5 behind a typical LG4, and that alone will improve gas mileage substantially. Just like the T5 did over the 4 speed saginaw and T10 trannys when it debuted in the '83 F-bodies.

 

Never denied that. It's just that 98% of the time, I'm not at WOT since this is my daily driver. So it's the "Off-wot" fuel consumption I want to lower. that means velocity, being able to run it lean etc.

Efi with it's "gas cut" when engine braking etc is key here. But other parts may aswell make a difference.It's the parts who can do this and more I'm interested in. I'm very curious about what kind of heads one should use...

 

A lot of it is about atomization, maintaining the fuel air mix in as fine a mist as possible at lower rpms.
Fuel droplets will fall out of suspension, given the opportunity. And that's where head design plays a critical role. Having good intake velocity, with the injector nozzles placed close to the intake valve and keeping the mixture stirred up once it enters the combustion chamber is key to all that.
Imagine a smoldering fire, then imagine that same smoldering fire if you take a poker and stir it all around. Suddenly the combustion process accelerates. It's all about exposing as many hydrocarbon molecules to as many oxygen molecules as possible, at precisely the right instant.
The head and port design is responsible for that. It has little to do with anything else.
LS1 heads are probably the best, for 2 valve heads. The thing about LS1s is that for a guy who can afford one, fuel consumption usually isn't an issue.
It seems like for you it should be between the LT1 and LT4.
Also I'm pretty sure you won't find a 4.125" bore LT1 block.

 

Another thing is, smaller engines like less cam duration. Or, a smaller engine will have a higher "redline" than a larger engine using the same cam.
With a smaller cam, there is less overlap, and less unburned fuel goes out the exhaust at lower rpms.
My 327 with a 206* intake duration, revs noticably higher (5800) than a 350 would. On the other hand a 383 with the same cam would
only rev to maybe 5000.
To get the same power range out of a 383 as a 327 might take 10* more duration, and that would add 10* of overlap if the lsa remained the same.

 

Several posts have hit different parts of the equation, but the answer to fuel economy is maximum efficiency at cruising rpm. Comparing an LO3 to an LS-1, you must realize the LS-1 is a much more efficient engine. Better chamber design, better engine management system to optimize fuel and spark timing for different loads and RPM's, more efficient intake and throttle body, smaller bearings with stronger block webbing, better ring seal with narrower rings with less drag. The list goes on and on. Another aspect of efficiency is the cam, and LS-1 cam, although higher lift, has shortish duration and wider lobe centers giving little overlap, thus a smooth idle and low end efficiency.

We know the LS-1 is capable of significantly more power when retuned with a different cam and head porting, but it would also be capable of greater MPG if recammed and tuned for that. A high horsepower engine is usually tuned for optimum efficency at a higher rpm, but the LS-1 is very clever engineering in that it has a very broad RPM range of efficiency. This didn't happen by accident.

The LT-1 is right in between the L03 and the LS1, and evolutionary step if you will. The LT-4 is just an LT-1 re-tuned for efficiency at a higher rpm (more power) The LS-6 is the same treatment to the LS-1. You will notice that they both put out less power down low than the original engines that they are based on, have more duration and overlap in their cams, slightly higher compression, and larger ports. Good old fashioned hot-rodding.

Large duration and overlap is only efficient at high RPMs. If you ever stand next to a fueler idling, the fumes are horrible. That is raw, unburnt Nitro Methane being blown into the air. A giant cam with lots of overlap (intake and exhaust open at the same time) out of it's efficiency range just spews raw fuel out the exhaust port, not exacly optimal for fuel mileage. Avoid Sewer pipe ports, too, they also demand high rpms to be efficient.

...blah blah blah

Troy
So Cal

 

Would be interesting to see if a LT4 vs LT1 had worse or the same cruise mpg.. Or with the LS1 vs LS6.

 

They are about the same. The engine managment units are still the same (tweaked for the added power) and doesn't really effect cruise conditions. I think a new Zo6 still claims 28 on the highway. That is what every LS1 sticker said as well.

 

tilstad,
Were you thinking of getting a set of LT1or LT4 heads & intake and modding them to fit a gen1 sbc? Or getting the entire LT1 engine?

 

I'm sure most of you know this, but I'll say it again. Probably the most important factor in fuel economy is the driver.

I've driven several v8's (neither one being a genII/genIII) that will easily get well over 20 mpg cruising. Stock, with auto's, (th350 and fwd equivalent of 4l60). Get on the gas even a few times and watch your mpg drop like a load of ****.

My "stock" '79 k5 (4wd, 350ci, th350, np203, probably weighs over 4500 lbs, horrible drag coefficient) gets about the same or better cruising gas mileage than my '91 firebird (mild 355, 700r, less than 3200 lbs w/o driver).

Your mpg will depend primarily on these things:

-Driver
-Vehicle weight (and enough low-end/mid torque)
-Rear gear ratio & Overdrive gear(s) (and tire height)

Next:

-Engine efficiency (compression, fuel atomization, velocity, cam choice, etc. as posted above)
-Keeping the rpm's within the engine's efficiency range
-As little exhaust restriction as possible
-Shaving as much reciprocating and rotational weight as you can
-Converter slippage? (Don't know much about that subject)
-Others

I'm sure there is more but I can't think of anything right now.

This is all assuming your engine is properly tuned and in the correct temperature range.

 

Larger displacement engines can usually turn at slower rpm's cruising, and you can use lower rpm's accelerating because of more low-end torque to carry you. But when you're idling at a light or any off-throttle moments you'll be using more gas to full up the cylinders than you would with a smaller displacement engine.

You spend a lot of time in stop-and-go traffic, or out on the open highway? A properly built and tuned carb'd 350 could probably get very good highway mileage but without displacement-on-demand or something similar you'll be wasting a lot of gas going nowhere in traffic.

Oh, and to add to the original question (and since I forgot to list it earlier) a double pumper would be a major gas sucking mod!

You should decide on a fuel mileage goal first, and then see how much power you can get out of it within your budget.

Laters,
Scott

 

I was only thinking of the injection setup.... for now. Some similar heads, but in aluminium, hard to decide on style and brand. I Know some of the best on the market is th AFR's, but If they hurt mpg much because of it's large ports, maybe it's not what im looking for. At the premium price they cost, I should at least get something that's fitting the project.

At the moment I get 15mpg, but then I floor it as often as I like, plus it's all kinds of driving, no long hauls max a couple of miles on the highway at a time.

Was hoping to get it up tp 20 mpg, with this kind of everyday driving, in the area I live, and with only the efi mod.

 

You can get AFR 180s you know.
I'm hoping for a set of those at some point. The guys who are aspiring to have 11sec cars are going with the larger runners, but I think the 180s will be a good choice for mine. Or the LT1 heads. There are guys here running in the 11s with 170cc vortecs and with LT1 heads (175cc?).
http://www.karl-ellwein.org/383y2001.htm

 

But will LT1 heads bolt right up to a gen 1 smallblock? I thought they didn't do that... If so why not go LT4 right away?

What powerlevel did the LT1 and LT4 produce?

 

LT4 won't either, They both would need to be modded.
I think the LT1 has a 170 or 175cc intake and the LT4 has 195cc. I don't have any charts comparing the two. But on that link on the last post there are some charts comparing iron LT1s to al LT4s.
Modding LT1 or LT4 heads to fit a gen1 is for guys who can't afford good aftermarket heads (like me). AFRs come in different intake bolt patterns, and it might be possible to get a set that would fit gen1 block and LT1 intake. Still the intake would need some mods.
Ever thought about AFRs + miniram?

 

Some other heads then..

 

Reread last post...just edited

 

http://www.tpis.com/
If you have the $$ these guys have everything you need.
And more info than you'll be able to get from me.

 

I'm not going the TPIS route, way too expensiv, That was the sole reason I considered LT1 intake instead of miniram, cost.

 

Same here.
So what's the plan at this point?