3S gearing, I'm shocked!

[foreveralone]

Hey all,
While I have enjoyed an '88 Conquest TSi 5-speed, a '95 Probe GT 5-speed, and an '85 300ZX 5-speed, I'm mostly a Camaro / Firebird guy, except for a few Mustangs.
I did a carbureted 5.7L '78 Camaro that managed 25.1 MPG at 65 MPH with the ignition advance being way late. I used a 700R-4 automatic, and was geared for 1800 RPM. A year later, I drove a second-gen Eclipse 4-cylinder, which, to my extreme amazement, would also cruise along at 65 MPG doing just 1800 RPM! Great!
Just now, unable to sleep, I looked up all the gearing options ever used on any / every version of these cars. Very sad. The best possibility is the 6-speed, which is 1940 at 65! Can any of these cars even see 25 MPG? And my automatic, ( which is geared identically to '90s Cummins-powered Rams ), is 2300 at 65! Even then, it doesn't have enough first gear, even with the 3.958:1 final. We get a 10.1:1 first, when I know from experience that an 11.4:1 is great for a similar-weight, same-tire-diameter '88 IROC-Z 5.7L with a shorter-runner intake manifold.
I can see I'll need to do a 6-speed swap to like this car. Yet having done the whole Fiero thing, I'm thinking of the F40-MT2, ( not Ferrari ) which would require custom axles, flipping the engine around 180*( or outright swapping a GM V6, in my case ) and would give a cruise RPM of 1870. Plus the trans itself can be had new for under $1,000 delivered, and has proven strong enough for 500 HP V8 swaps. Ratios are 3.7692 / 2.0400 / 1.3208 / 0.9538 / 0.7547 / 0.6208 with a 3.5455:1 final.

[Alan92RTTT]

I get 27 on the highway with my TT and my SL while running 80 with no issue.

[deathsled]

My VR4 gets 25mpg easily on the highway.

[2fnloud]

I figged about 26MPG average driving. And that is just doing the math with one tank of gas, no average.

[EvanH]

I've gotten 25 on my TT. And a record of 32 with a tail wind going cross country. That's with 370hp at the wheels.

[niterydr]

My 700+hp 3/s build (last one) averaged over 30mpg on the highway, of course under load it was gallons per mile...but every highway trip was consistantly 30+mpg.

My E-85 stealth so far is getting 17mpg city/flogging on it. Ill see how the mileage actually is when I am done tuning. Anticipating 17 city/24 highway on E-85.

[Alan92RTTT]

Is 17/24 good for mileage on E85?

[niterydr]

Is 17/24 good for mileage on E85?

I would anticipate so as E-85 has less energy than pump fuel. Most vehicles average 5-30% less fuel economy on E-85 than pump. If I can achieve 17 city/24 highway it is cost effective for me as the price per gallon is 15-25% cheaper. Only problem is the car is currently on an E-70 blend and E-85 will be less fuel efficient due to the higher ethanol content.

Oh well, it is still cheap "race gas". Being able to run "all boost" on the 9b's is nice.

[Keyan]

I get 21.5MPG, but I have 2 dying cylinders, so that probably explains my perdicament.

[DocWalt]

28mpg through the hills of PA all day long. 17mpg around town haha.

[Intropy]

Anticipating 17 city/24 highway on E-85.

Exact numbers I get. There's more there if I would take the time to lean it out / drive like a sissy but I just don't care that much.

[Chris@Rvengeperformance]

If you had a manual FWD car there are some really nice extra overdriven 5th gears available. I went with a 12% taller 5th on my last car and achieved some very good mileage. It would get at least 27 and often 29. We cracked 30 one time on a long trip.

IIRC it was around 2000 RPM at 60.

It used to be atx and I usually got 24-25.

[ntcmpjg]

I got 29 hwy and 22 city in my 96 R/T with 291,000 miles on it. Hans must have work his magic on my 5th gear when he rebuilt it lol.


Sent from my iPhone using Tapatalk

[foreveralone]

You guys are all awesome! Thanks everyone. On every other forum I've joined, I wouldn't get that many responses that quickly, and normally there's be some bashing.
If I find any DOHC 6G72 at any local salvage yard, then I'll drive the F4A33 exactly as Mitsu intended it until spring of 2013, when I'll have a six speed.
The torque converter upgrade was appealing, based on past experience, until I found the price is so much higher than for a 700R-4.

[sublime_whatigo]

Also have seen 29 more than once in my car. MPG isn't always about low rpms, plenty of mazda's and nissan's run well over 3k rpms at 70 and still get great mileage.

[Hans@GZP]

A 6 speed non-turbo is going to be an absolute dog... good luck with that.

[Emilie@GZP]

I got 29 hwy and 22 city in my 96 R/T with 291,000 miles on it. Hans must have work his magic on my 5th gear when he rebuilt it lol.


Sent from my iPhone using Tapatalk

I continually got that kind of gas mileage before and after we rebuilt the 5th gear issue. That car is straight up magic I tell ya. :lol:

[stealthee]

A 6 speed non-turbo is going to be an absolute dog... good luck with that.

This is what I was going to say.

As for fuel mileage, I got 25-26 daily driving my Stealth. I've gotten over 28 on a trip before and I wasn't really trying to get good mileage. I ran 75-80 mph most of the way. This was with a factory geared NA 5 speed. Had I had the taller 5th I would have easily been into the low 30's.

[donniekak]

Just drove to San Diego and back from Phoenix last weekend. Averaged 25 mpg. This is with an average speed of about 85, and several high speed runs. Not to mention having fun going through the mountains.

To the op, I don't know what kind of Dsm you had, but my talon was at around 3600 at 80.

[DuTTch]

Hey all,
While I have enjoyed an '88 Conquest TSi 5-speed, a '95 Probe GT 5-speed, and an '85 300ZX 5-speed, I'm mostly a Camaro / Firebird guy, except for a few Mustangs.
I did a carbureted 5.7L '78 Camaro that managed 25.1 MPG at 65 MPH with the ignition advance being way late. I used a 700R-4 automatic, and was geared for 1800 RPM. A year later, I drove a second-gen Eclipse 4-cylinder, which, to my extreme amazement, would also cruise along at 65 MPG doing just 1800 RPM! Great!
Just now, unable to sleep, I looked up all the gearing options ever used on any / every version of these cars. Very sad. The best possibility is the 6-speed, which is 1940 at 65! Can any of these cars even see 25 MPG? And my automatic, ( which is geared identically to '90s Cummins-powered Rams ), is 2300 at 65! Even then, it doesn't have enough first gear, even with the 3.958:1 final. We get a 10.1:1 first, when I know from experience that an 11.4:1 is great for a similar-weight, same-tire-diameter '88 IROC-Z 5.7L with a shorter-runner intake manifold.
I can see I'll need to do a 6-speed swap to like this car. Yet having done the whole Fiero thing, I'm thinking of the F40-MT2, ( not Ferrari ) which would require custom axles, flipping the engine around 180*( or outright swapping a GM V6, in my case ) and would give a cruise RPM of 1870. Plus the trans itself can be had new for under $1,000 delivered, and has proven strong enough for 500 HP V8 swaps. Ratios are 3.7692 / 2.0400 / 1.3208 / 0.9538 / 0.7547 / 0.6208 with a 3.5455:1 final.

how about you just stay for ever alone and go back to your whatever

[foreveralone]

Okay there DuTTch, way to reveal your true character, attack a guy for thinking outside the box, asking questions. Maybe you could please consider trying to improve your thinking-and-asking? Or maybe you'd rather just offer me $1300 cash for my car, so I don't "molest" it? Bring a trailer.
30 MPG at 2300 RPM seems optimistic, but I'll give it a chance. Still can't help but expect it should be 35, in such a sleek 3-liter car, if only the revs were lots less. May need custom-reground cams to improve the low-RPM torque, but in the thin air at my elevation, that shouldn't cause detonation.

[stealthee]

Ignore DuTTch. He's an idiot who says stupid shit just to post whore.

As for your comments, you are overthinking this. RPM's are only one part of the equation. Like I said I was getting 26 mpg daily driving. Half of my commute it windy 2 lane roads and the other half is a bypass/highway. When on a trip I could easily get 28 mpg running 80mph. 80mph is around 3500 rpm.

You also dont want to drop the revs too low because you can actually hurt your mileage if you push it too low.

[donniekak]

Ignore DuTTch. He's an idiot who says stupid shit just to post whore.

As for your comments, you are overthinking this. RPM's are only one part of the equation. Like I said I was getting 26 mpg daily driving. Half of my commute it windy 2 lane roads and the other half is a bypass/highway. When on a trip I could easily get 28 mpg running 80mph. 80mph is around 3500 rpm.

You also dont want to drop the revs too low because you can actually hurt your mileage if you push it too low.
Yes, the engine is most efficient with the highest volumetric efficiency, with rpms low nough to keep internal losses at a minimum. My 600cc bike got 50 mpg at about 6000 rpms.

[ChargerX3]

I think its funny you are comparing a 3.0L car to 5.7 V8's. The gearing in our cars is actually ideal for their powerband. Our cars have little torque on the low end, so why do you think the rpms at cruising speed are so close to the mid 2k range? We dont have the torque. Keep in mind also that we are still lower on cc's, so those revs dont make that much of an impact on fuel mileage because of the lower fuel demand per cylinder. My TT before i sold it bested 32mpg at 65-70mph driving through Nevada.

[Diesel]

playing with the truck for mpg while towing its not always the rpm's that matter but what load % your operating at.

[EvanH]

All engines are efficient at a certain rpm. Trains can haul 2000 lbs for 456 miles a gallon. Yes, they are diesel electric, but the engine is 4-6000 HP turning at a near constant speed. Weight and aerodynamics are the biggest factors for mpg. There is a yugo getting 75 mpg and I read in a popular mechanics, a civic crx getting 60 mpg. He made a home made front air splitter that makes the front bumper a Sharp wedge.

[Boost4VR4]

If you keep RPMS and load down, you will get great mileage. 6 speeds aren't bad, but the efficiency of the 6 speed is when you are over 80mph because the amount of engine load it takes to maintain speed is higher because of the gearing. My 5 speed Stealth SOHC was averaging 30-35mpgs on the highway at 70 mph and I was pulling 3000 RPMS.

[BigTyla]

I believe the term you all are looking for is "brake specific fuel consumption."