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Old 12-30-2017, 10:13 PM   #1 (permalink)
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Lightbulb How to build a muscle car for better fuel economy?


In the not too distant future, I plan on modifying my car's second-generation LT1 motor to make it a better daily driver with emphasis on shifting it's stock torque curve down to lower RPM range, where the car spends most of it's time in city traffic. Now, I don't race this car and I have no plans on taking it to a track, I even drive this car in the heart of the winter in decently deep snow! So, this is where I have to balance power production with fuel economy, which I would prefer to maintain with the given EPA estimates. The automotive performance forums are only so helpful since those guys specialize in building race cars and not the opposite side of the spectrum where I am at.

So, as a starting point for my build goals with my LT1 motor, I am very set on modifying a Tuned Port Injection intake manifold to fit on my LT1 heads, to use AS&M big runners and to have the plenum, runners, and manifold bottom port matched, gasket matched, and extrude honed. I plan on using 180cc DART heads since they emphasize port velocity, which is great for low end torque production and in my mind, helps in overall fuel economy. I also plan to use long tube headers designed to emphasize low end torque which are customized to work with my emissions devices and will use catalytic converters. Also, for the sake of better efficiency, using Iso-butanol fuel to allow for a higher compression ratio of up to 12, equipping my motor with smaller low friction bearings, piston skirt/bearing/valve stem/valve spring/crankshaft low friction coating, low friction crankshaft seals, and a true roller timing chain.

The last modification deals with the camshaft. After some research I found that the widest lobe separation is the most optimal for fuel economy, and such a lobe separation at 117 is what I have for my stock camshaft. I am left wondering if there is anything I can possibly do to improve upon the stock camshaft profile, increasing the lift for any marginal performance gain without sacrificing fuel economy. I do think the stock camshaft should be advanced to help improve the lower end torque that my car really needs, but again, I only have so much help using other forums that don't specialize in what I wish to achieve with my muscle car and daily driver.

So, what do you any of you think about these ideas to modify my second-generation LT1 motor for better fuel economy and a good enough increase in the "seat of the pants" performance.


Last edited by Phoenix'97; 12-30-2017 at 10:23 PM..
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Old 12-30-2017, 10:45 PM   #2 (permalink)
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Easy, spend lots of money.
More on the rest of the car than the engine it's self. You will need a 6 speed to get good fuel economy and get up and go performance.
Add an oil to coolant heat exchanger to get the oil up to temperature.
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Old 12-30-2017, 11:25 PM   #3 (permalink)
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I have owned a 1972 Chevelle, a 1972 Nova and a 1969 Camaro a very long time ago. Most of those cars got around 15 MPG and all of mine were bone stock except the 1972 Nova had a lower rear end gear swap at some point before I bought it. Someone was trying to make that Nova faster off the line and it was. The 1969 Camaro had a 327 with an automatic trans and tall rear end axle gearing. I remember running 130 MPH and it was turning 4,000 RPM at that speed with plenty more to go. None of these cars got fantastic gas milage, but the Camaro got the best with it's tall rear end axle gearing.

When you tell me you want to modify your LT1 motor I am going to guess any dealer non stock parts available for that engine are mostly performance mods.

To me to save gas with that car is going to require getting the RPM's of the engine down while you are driving it. You are not wanting super low gearing in the rear end axle if you want better gas milage. Lower gears cause higher engine rpm at any road speed. Your car might be fine as is depending on what gearing is in it already.

You can change rear end axle gearing and rebuild transmissions to achieve whatever you want with a Chevy/Pontiac. Lots of things you can do with a Chevy product because there are tons of parts made for Chevy cars to change whatever you want about the car.

To make my post FUN I am going to suggest you check out a car built by a guy who goes by the name of Speedycop who races in the 24 Hours of LeMons races. They race $500.00 cars in that race. Check out the Speedycop Bonneville Donk description why the build got better gas milage and then scroll to the bottom of the page to see some of the other cars he built. Speedycop has built incredible cars for that race. Here is the link:

The Greatest 24 Hours of LeMons Cars of All Time - Roadkill
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Old 12-30-2017, 11:55 PM   #4 (permalink)
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What would be the advantage of using iso-butanol? Is ethanol out of question?
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Old 12-31-2017, 12:42 AM   #5 (permalink)
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You could possibly increase the compression significantly more (e.g. 16:1) and run an Atkinson-cycle; to do this, you'd give the intake valve longer duration, and advance it to the point that it stays open partway into the compression stroke. It's easier to do this on engines with variable cam timing, because the fuel economy improvements come at the expense of power, and variable timing would allow you to switch it on or off at will. This is one of the tricks Toyota and Hyundai's hybrids use to get near 60mpg, and the loss in power is made up for by adding an electric motor to add torque down low.

On that note, I wonder if you could retrofit a servo or somesuch that would allow you to modify the cam advance on the fly, so you could get the best of both worlds - Atkinson while cruising, and OTTO while accelerating. You wouldn't be able to run astronomical compression, but you'd still see gains.

Other than that, you could play with the heads and see if you can get a stratified charge, to allow for leaner operation. My Insight is able to lean out to over 24:1 AFR on the highway, giving it diesel-like efficiency.

Other than that, taller gearing will probably make more difference than anything else.
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Old 12-31-2017, 09:57 AM   #6 (permalink)
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Are you in NYC or some other city in NY? Is a bicycle or bus out of the question?

F-bodies usually came from the factory with 3.20-ish gears I think: light weight, good aero, and good power enabled GM to run tall-ish gears to squeeze out a little better highway mpg. For city driving a rear ratio change won't help much. Plenty of heat under the hood, make up an adjustable WAI and monitor temps on a scangauge. Most exhaust manifolds sucked before 1990 but I'm not sure if the LT1 manifolds perform like other SBC manifolds of the past or if they were a shorty design like the LS1 manifolds, so gains could possibly be made by switching to headers. For Stop and go driving, weight reduction can help so you need less power to take off.

Best way to save gas is by not burning any but EOC and the 4l60e are probably not going to play well together.
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Old 12-31-2017, 11:38 AM   #7 (permalink)
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Quote:
Originally Posted by oil pan 4 View Post
Easy, spend lots of money.
More on the rest of the car than the engine it's self. You will need a 6 speed to get good fuel economy and get up and go performance.
Add an oil to coolant heat exchanger to get the oil up to temperature.
My Trans Am is already a 6-speed. I could not possibly imagine trying to drive this car with an automatic in the heart of blizzard conditions, you would spin out into a guard rail/cement block or act as a crooked thrown bowling ball headed for "pins" in the opposing lane of traffic. Not good!

The only issue with an oil-to-coolant heat exchanger is that in below freezing weather the engine oil will likely warm up faster than the coolant, which takes a good amount time to get up to temperature while letting the car idle for 15 minutes.
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Old 12-31-2017, 11:52 AM   #8 (permalink)
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Quote:
Originally Posted by Titanium View Post
...None of these cars got fantastic gas milage, but the Camaro got the best with it's tall rear end axle gearing.

When you tell me you want to modify your LT1 motor I am going to guess any dealer non stock parts available for that engine are mostly performance mods.

To me to save gas with that car is going to require getting the RPM's of the engine down while you are driving it. You are not wanting super low gearing in the rear end axle if you want better gas milage. Lower gears cause higher engine rpm at any road speed. Your car might be fine as is depending on what gearing is in it already.

You can change rear end axle gearing and rebuild transmissions to achieve whatever you want with a Chevy/Pontiac. Lots of things you can do with a Chevy product because there are tons of parts made for Chevy cars to change whatever you want about the car.
Well this is where my logic comes in with regards to using a small block chevy TPI intake, optimized for low to mid-range torque production for daily driving performance, from the 1980's, on my 90's LT1 with the TPIS miniram intake copy from GM, which is designed to optimize high end RPM torque, for racing! I can't tell you how many guys suggested I use lower gear ratio 4.11 to get my motor operating at a higher RPM level. This is great for acceleration and it solves my torque problem but it will kill my city mileage. Furthermore I don't have the opportunities to safely drive my car at RPM ranges above 5000 to "enjoy it". So, I have consigned myself to enjoying the cruise at lower RPM and hearing the exhaust tone from the V8 with Magnaflow cat-back exhaust!

For safety, my stock 3.42 gear ratio from GM is optimal for daily driving, bumper-to-bumper, stop-and-go acceleration speed. For fuel economy, my 3.42 gear ratio is optimal enough! I could probably go higher with a 3.23 gear ratio but the 3.42 seems good enough. So, instead of trying to make my car operate at higher RPM, I am looking to the L98 and the TPI intake to help me make my LT1 behave like it's predecessor, having lower end and good mid-range torque, BUT the car starts to starve for air beyond 4500 RPM due to the long runner intake manifold. However, this would work for the sake of fuel economy at higher RPM so this system is perfect for my daily driving needs, which is why GM developed it in 1985, for fuel economy/emissions standards of the time and for optimal daily driving!
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Old 12-31-2017, 12:02 PM   #9 (permalink)
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Quote:
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What would be the advantage of using iso-butanol? Is ethanol out of question?
Ethanol is out of the question! Butanol has a higher burning power than Ethanol. Butanol has 105,000 BTU, Ethanol has 84,000 BTU, and straight gasoline has 114,000 BTU, per gallon. Right off the bat, you are burning less Butanol than Ethanol to achieve the same power of gasoline in the same motor.

Second, Butanol mixed in gasoline does not undergo phase-separation, unlike ethanol. Butanol can be used up to 100% in a gasoline motor without the need to modify the engine. Ethanol is very corrosive and can only be mixed with gasoline up to 85%. Any motor using 100% Ethanol will have required extensive modification and will still not have the power production or fuel economy of it's gasoline equivalent and compared to the same car using 100% n-butanol or iso-butanol.

Iso-butanol is the 102 octane version of normal "n-butanol" with an octane rating of 87. So, I am forced to use Iso-butanol for my V8 motor!
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Old 12-31-2017, 12:13 PM   #10 (permalink)
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Quote:
Originally Posted by Ecky View Post
You could possibly increase the compression significantly more (e.g. 16:1) and run an Atkinson-cycle; to do this, you'd give the intake valve longer duration, and advance it to the point that it stays open partway into the compression stroke. It's easier to do this on engines with variable cam timing, because the fuel economy improvements come at the expense of power, and variable timing would allow you to switch it on or off at will. This is one of the tricks Toyota and Hyundai's hybrids use to get near 60mpg, and the loss in power is made up for by adding an electric motor to add torque down low.

On that note, I wonder if you could retrofit a servo or somesuch that would allow you to modify the cam advance on the fly, so you could get the best of both worlds - Atkinson while cruising, and OTTO while accelerating. You wouldn't be able to run astronomical compression, but you'd still see gains.

Other than that, you could play with the heads and see if you can get a stratified charge, to allow for leaner operation. My Insight is able to lean out to over 24:1 AFR on the highway, giving it diesel-like efficiency.

Other than that, taller gearing will probably make more difference than anything else.
Unfortunately, I don't have the budget of General Motors to conduct the Real McCoy research and development to really turn this "obsolete" motor into a truly fuel efficient and superior version of it's former self. Besides, with all the newer technology out there from variable-timing to direct-injection and direct-ignition, and cylinder deactivation (!), for the money I would spend to go nuts on an engine design over twenty years old, I would be better off swapping a 2014 LT1 into my Trans Am. However, with all the work required to make such an engine work with my factory gauge cluster, the computer required by this engine, and all the wiring from my existing 1990's equipment to work with the 2014 computer for this motor, it is more cost effective to salvage my existing motor and improve upon it with existing parts and coating.

The biggest problem is reducing internal friction, that is easily solved with the new anti-friction engine coatings that are now sprayed on the motors. I can have this same coating sprayed on the motor parts. I already use full-synthetic motor oil so this is one step in marginally increasing power output and increasing fuel efficiency! The other steps involve lower end torque production which, if the car can start moving from a dead stop easier thanks to lots of torque on tap, this helps in overall fuel economy. If I can drive the car mostly under 2000 to 2500 RPM, with full manifold vacuum, this all ties in to better fuel economy.


Last edited by Phoenix'97; 12-31-2017 at 12:21 PM..
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