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post #16 of 43 (permalink) Old Oct 22nd, 19, 11:29 AM
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Re: Gas Mileage Test 5 speed vs 6 speed

Thanks for the info, this is helpful. I've started looking into changing out my 4 speed for a 5 or 6 speed. A lot of people are steering me towards the 6 speed, did not realize it would make a 6 mpg difference. For me it's mainly the RPM's. My longest highway trips now are 20 minutes, just don't want to listen to the 427 @3200 rpms for longer than that.

Just wanted to add, one of my son's drives a car with a 5 speed and one drives a car with a 6 speed. I drive these cars regularly. When I drive the Chevelle and start going thru the gears, I always keep shifting as if I had at least a 5 speed. It seams natural, especially when your in 4th at 40 mph.
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post #17 of 43 (permalink) Old Oct 22nd, 19, 11:34 AM
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Re: Gas Mileage Test 5 speed vs 6 speed

Play around on this will make your choice easy
Wallace Racing - Automotive Calculators

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post #18 of 43 (permalink) Old Oct 22nd, 19, 11:44 AM
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Re: Gas Mileage Test 5 speed vs 6 speed

My 66 gets 12mpg (my setup is in my signature below). When I calculated it, there was no highway driving, just stoplight-to-stoplight driving around town. I hardly ever drive it on the highway, but with 3.42 gears and no OD I don't expect it would be any better on the highway.

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post #19 of 43 (permalink) Old Oct 22nd, 19, 12:01 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

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Originally Posted by 67 SuperSport View Post
Thanks for the info, this is helpful. I've started looking into changing out my 4 speed for a 5 or 6 speed. A lot of people are steering me towards the 6 speed, did not realize it would make a 6 mpg difference. For me it's mainly the RPM's. My longest highway trips now are 20 minutes, just don't want to listen to the 427 @3200 rpms for longer than that.

Just wanted to add, one of my son's drives a car with a 5 speed and one drives a car with a 6 speed. I drive these cars regularly. When I drive the Chevelle and start going thru the gears, I always keep shifting as if I had at least a 5 speed. It seams natural, especially when your in 4th at 40 mph.
Go with the 6 speed, it is too hard to choose between just one OD gear and I couldn't imagine just having one since both have their purpose.
I will say it feels natural to have a 5 or 6 speed in the car. You have just the right amount of gears.
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post #20 of 43 (permalink) Old Oct 22nd, 19, 12:04 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

BTW, that was a cool video.
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post #21 of 43 (permalink) Old Oct 22nd, 19, 12:25 PM Thread Starter
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Re: Gas Mileage Test 5 speed vs 6 speed

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Are those license plate gas doors lightened by drilling holds? Gosh.
haha yes.

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post #22 of 43 (permalink) Old Oct 22nd, 19, 5:58 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

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That's awesome. Now that I hit my goal... curiosity makes me think what I could do to hit 20 mpg.
good video, your results match exactly what I seen on race week and locally for the same speeds


My Beaumont at the same speed gets 18mpg steady with a 3.73 & 0.63OD . it is a 502 @ 4100lbs all in with driver. I run mine at 14.5-14.7 afr with about another 5 degrees of timing.


My old mans Camaro (3800lbs) with a LSA motor and TKO with 0.68OD overages 21mpg. 3.73 gearing. He runs the stock GM computer so its pretty well setup obviously.


Buddy Rich in red deer with the angry goat GTO gets 20-21mpg with a 517 Pontiac BB @ 4100lbs all in with driver, he has the 0.50OD gears in his t56.


my findings were as the speed went up, with the RPM, gas mileage dropped. When cruising at 85mph down south I was down to 12-13mpg, maybe even more. Ultimately gas mileage is driven by your RPMs, within reason or the confines of the motor. With the 3 examples above and yours included, HP is not the determining factor in MPG, efficiency and RPM is the driving factor. Obviously a full on race motor will not operate at 1800rpm and see the MPG.


I am toying with the idea of changing to a 0.50 OD gear in my T56 over the winter. Try and achieve +20mpg at highway speeds. my fear is that the motor will not cruise well at 1500rpm @ 70-75mph, well see how the new ZZ502 cam works... especially on boost!
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post #23 of 43 (permalink) Old Oct 22nd, 19, 10:06 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

Where is 69-CHVL Vince ?

I'd like to know what he gets out of his 502- T56 ?

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post #24 of 43 (permalink) Old Oct 22nd, 19, 10:50 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

depends how its cammed....last week I was going maybe 50ish? rpm in 4th was fine but seemed like I should upshift do I did, engine wasnt happy
Easy to get used to late model stuff loafing along.

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post #25 of 43 (permalink) Old Oct 22nd, 19, 11:16 PM
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Re: Gas Mileage Test 5 speed vs 6 speed

It was a cool video, but not a fair comparison. Five speed, six speed, it doesn't matter. It comes down to RPM and final drive ratio. I'm not surprised the 68 did worse. It had what, 800 RPM disadvantage with taller rear gears and barely any overdrive. I'd bet it would do a lot better mileage wise with a TKO600 with the .64 5th gear instead of .82. A good baseline would have been a road trip with both cars never going past 4th gear at 1:1, just to see how close they really are. Still cool as hell seeing you get out on the road and have fun though.


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post #26 of 43 (permalink) Old Oct 23rd, 19, 12:03 AM
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It was a cool video, but not a fair comparison. Five speed, six speed, it doesn't matter. It comes down to RPM and final drive ratio. I'm not surprised the 68 did worse. It had what, 800 RPM disadvantage with taller rear gears and barely any overdrive. I'd bet it would do a lot better mileage wise with a TKO600 with the .64 5th gear instead of .82. A good baseline would have been a road trip with both cars never going past 4th gear at 1:1, just to see how close they really are. Still cool as hell seeing you get out on the road and have fun though.
Thats what they were trying to show.
The 6 speed has the option to lower the rpm where the 5 speed doesn't.
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post #27 of 43 (permalink) Old Oct 23rd, 19, 12:47 AM
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Re: Gas Mileage Test 5 speed vs 6 speed

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Thats what they were trying to show.
The 6 speed has the option to lower the rpm where the 5 speed doesn't.

Not that 5 speed, but other 5 speeds would. The TKO-600 has two overdrive options, .82 and .64. It was an apples to oranges comparison, but the number of gears is irrelevant. If someone was trying to decide between a 5 and 6 speed for mileage, the video only shows that higher RPM in overdrive is worse for mileage. The 5 speed .64 TKO would be a closer match to the 6 speed in the video, and it would be capable of delivering the same mileage, everything else being the same. Now a 6 speed with a .5 OD would be another story. My point was the number of gears doesn't matter, final drive ratio does.


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post #28 of 43 (permalink) Old Oct 23rd, 19, 12:54 AM
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Thats what they were trying to show.
The 6 speed has the option to lower the rpm where the 5 speed doesn't.

Not that 5 speed, but other 5 speeds would. The TKO-600 has two overdrive options, .82 and .64. It was an apples to oranges comparison, but the number of gears is irrelevant. If someone was trying to decide between a 5 and 6 speed for mileage, the video only shows that higher RPM in overdrive is worse for mileage. The 5 speed .64 TKO would be a closer match to the 6 speed in the video, and it would be capable of delivering the same mileage, everything else being the same. Now a 6 speed with a .5 OD would be another story. My point was the number of gears doesn't matter, final drive ratio does.
Number of gears matter. Sometimes you can't use that 0.63 because it's too high where the the 0.82 would be just right.
That's why the 6 speed matters. You always have a hear you need to effectively increase mpg.
The tko is a compromise besause you can't have both and it depends on how you drive where you REALLY need to figure out which gear is what you need. In my case if I had the 0.63 I would hardly ever use it. With the 0.82 I would use it a bunch BUT give up mpg on the interstate. The t56 has both and can do anything you want it to, which is why I picked it instead. That's why it's important.
Now does it matter in these cars? Not really. But it's interesting to see.
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post #29 of 43 (permalink) Old Oct 23rd, 19, 1:26 AM
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Re: Gas Mileage Test 5 speed vs 6 speed

With a well chosen 1st, 5th, and rear gear ratio, I humbly disagree. I've had both and prefer the 5 speed. In fact the T5 had the best gear ratios of any manual I had. I preferred it over the T56. It's a matter of taste I guess. My plans for my 69 are for a tko-500, 3.36 gears.


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post #30 of 43 (permalink) Old Oct 27th, 19, 12:06 AM Thread Starter
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Re: Gas Mileage Test 5 speed vs 6 speed

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Originally Posted by GoFast Beaumont View Post
good video, your results match exactly what I seen on race week and locally for the same speeds


My Beaumont at the same speed gets 18mpg steady with a 3.73 & 0.63OD . it is a 502 @ 4100lbs all in with driver. I run mine at 14.5-14.7 afr with about another 5 degrees of timing.


My old mans Camaro (3800lbs) with a LSA motor and TKO with 0.68OD overages 21mpg. 3.73 gearing. He runs the stock GM computer so its pretty well setup obviously.


Buddy Rich in red deer with the angry goat GTO gets 20-21mpg with a 517 Pontiac BB @ 4100lbs all in with driver, he has the 0.50OD gears in his t56.


my findings were as the speed went up, with the RPM, gas mileage dropped. When cruising at 85mph down south I was down to 12-13mpg, maybe even more. Ultimately gas mileage is driven by your RPMs, within reason or the confines of the motor. With the 3 examples above and yours included, HP is not the determining factor in MPG, efficiency and RPM is the driving factor. Obviously a full on race motor will not operate at 1800rpm and see the MPG.


I am toying with the idea of changing to a 0.50 OD gear in my T56 over the winter. Try and achieve +20mpg at highway speeds. my fear is that the motor will not cruise well at 1500rpm @ 70-75mph, well see how the new ZZ502 cam works... especially on boost!
G force's 6 speed has a 0.54 6th gear, that'd be pretty sweet. I think in most applications, a 0.50 gear is too high, unless you run a ton of rear gear.

I find that 60-65 mph is the mpg sweet spot, at 75 mph my fuel efficiency reduces.

1971 Chevelle SS454, T56 Magnum 6 speed, 3.31 Posi

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