Author Topic: are 2.79 gears that boggy? (Read 1246 times)

67resto-coupe · « **on:** August, 26, 2010, 11:47:26 PM »

ok, so the roller 5.0 is running smoothly...got a new 2.5" x-pipe exhaust with spintechs....yet i'm not "feeling" that this is what 86-93 5.0 should feel like.
i had expected a bit more of a surge when i get on it, but can my stock gearing really be that slow?
i remember driving this car at 16yrs old....couldn't even get it to barely leave a stripe with the orig 289 and holding the brakes...
but with a new roller, E-303 cam, etc, etc, i can leave a little stripe on command, but i expected more.

i imagine i may be leaving a bit out from tuning, but overall, is the gearing really affecting it that much?

i also have a tci torq converter in the c4 and i can't go beyond 3.23s according to the box. would 3.00 or 3.23's make that much of a difference over the stock 2.79's?

p.s. i plan on running 17" wheels if that makes any difference....thanks.

daveSanborn · « **Reply #1 on:** August, 27, 2010, 04:13:25 AM »

Quote

are 2.79 gears that boggy?

Yes, they are. They're designed to improve fuel economy, not performance.

I'm not sure about your TqConv warning, but I'd have no problems stepping up to 3.25/3.50 gears to improve your acceleration. Understand that your top end speed will suffer as you improve acceleration. AOD's and T5's are geared better for 3.25/3.50 than your C4 is.

apollard · « **Reply #2 on:** August, 27, 2010, 05:07:21 AM »

In HS, I had a '67 with a straight six w/ auto. I blew the rear end out of it, and went to the junkyard and pulled one from a manual car. That took me from a 2.79 to a 3.25 gearing. The difference was incredible - I could keep up with my buddy's 289 2bbl car easily, and after decent exhaust and tune, out run him. So, I'd say moving to just a 3.25 would help quite a bit.

The gas mileage took a good sized hit, though.

blue65coupe · « **Reply #3 on:** August, 27, 2010, 05:09:49 AM »

Ditto. Step up the gear. If you're gonna be doing a fair amount of highway driving I'd go with the 3.25. I've got a 3.55 in mine with a c4 and it pushes over 3K at 70 mph. If I had it to do over I would've went with a 3.25 or ran a 3.55 with AOD.

Starfury · « **Reply #4 on:** August, 27, 2010, 05:31:39 AM »

I swapped from 2.79's to 3.25's a couple years back. The difference was huge. The gears made more difference in my butt-meter than my entire stroker rebuild, which added a good 100hp to the motor.

RustyRed · « **Reply #5 on:** August, 28, 2010, 09:44:34 AM »

Quote from: 67resto-coupe on August, 26, 2010, 11:47:26 PM

i imagine i may be leaving a bit out from tuning, but overall, is the gearing really affecting it that much?

In a word, yes. In two words, big yes.

I had built the motor on mine (302, ported GT40's, mild cam, holley 600, etc) and upgraded my transmission with higher stall, B&M shift kit and my car was still very sluggish off the line. You'd have thought I still had the worn out 289 with 2 barrel we had pulled out of the car.

Got po'd about it and ordered the Currie posi third member with 3.55's.

Night and day difference. When you punch it now you feel the wheels grab immediately and seems to have a lot more snap with less wasted energy.

Makes the car run at higher rpm's on the freeway but I don't drive on the freeway much so I don't really care. However, I am considering upgrading to a larger aluminum radiator due to the higher rpms when running say 45 - 50 mph.

camachinist · « **Reply #6 on:** August, 28, 2010, 02:46:09 PM »

Quote

i also have a tci torq converter in the c4 and i can't go beyond 3.23s according to the box. would 3.00 or 3.23's make that much of a difference over the stock 2.79's?

LOL, more likely *below* 3.23 numerically, due to the propensity for constant slip and subsequent heat/wear. You can run 5.67's with that converter; it could care less.

If you drive the car all the time, 3.25'ish would be my advice. Weekend cruises and blasts, 3.50's. I drove my '67 to college, work, street raced and drove to the track, all with 3.50's and an 11" converter, this back in the 1970's. It was perfectly fine on the freeway, but I was a kid and didn't care about 'driveability'.

Have fun!

70_Fastback · « **Reply #7 on:** August, 30, 2010, 01:35:19 PM »

I am running 3.80 gears with my C4 - and it's horrible for the highway. I need a 4th and 5th gear.

It boils down to your main intentions with the car though...

jonward786 · « **Reply #8 on:** August, 30, 2010, 02:31:24 PM »

Good lord, i bet those 3.8s are fun stop light to stop light tho

blue65coupe · « **Reply #9 on:** August, 30, 2010, 05:51:49 PM »

Quote from: jonward786 on August, 30, 2010, 02:31:24 PM

Good lord, i bet those 3.8s are fun stop light to stop light tho

He needs it to offset the effects of the scoop.

silverblueBP · « **Reply #10 on:** September, 07, 2010, 06:16:40 PM »

Quote from: 70_Fastback on August, 30, 2010, 01:35:19 PM

I am running 3.80 gears with my C4 - and it's horrible for the highway. I need a 4th and 5th gear.

It boils down to your main intentions with the car though...

Pansie, I run 4.11's and drove it to Topeka and back, 140 miles @ 8mpg and a 4 speed.

RustyRed · « **Reply #11 on:** September, 08, 2010, 06:03:59 AM »

My car runs decent at 55 - 60 mph with the 3.55's.

Granted, I am running close to 3,000 rpm but it hums right along. I have not tried to calculate my miles per gallon but I figure I probably don't want to know and since it's not a daily driver...who cares.

Starfury · « **Reply #12 on:** September, 08, 2010, 04:47:23 PM »

Close to 3k? lol. I cruise in my 331-powered '67 at 3300rpm @ 70mph with 3.25's. I'm considering 3.93's or 4.11's now that I have a short-ratio toploader installed. First gear is a dog...

RustyRed · « **Reply #13 on:** September, 09, 2010, 06:56:47 AM »

The changing out isn't the problem, getting the speedo to read the right speed is the problem I've had.

When I had my 2 point something stock rear end I was running an 18 tooth driven gear. Went up to a 20 tooth based on an online calculator and it was still way off. I changed out again to a 23 tooth that they advertise as being for a 4.10 rear...it's close now but still reads about 5 mph faster then I am actually going. I can't find a gear with more than 23 teeth so I guess I'll have to live with that.

silverblueBP · « **Reply #14 on:** September, 09, 2010, 10:31:02 AM »

might need to change the drive gear in the tranny.

RustyRed · « **Reply #15 on:** September, 09, 2010, 10:38:43 AM »

Quote from: silverblueBP on September, 09, 2010, 10:31:02 AM

might need to change the drive gear in the tranny.

That had occurred to me but at only 5 mph off...it's a lot easier to just adjust the speed in your head. :5

silverblueBP · « **Reply #16 on:** September, 09, 2010, 10:50:00 AM »

I agree! I have the other drive gear to install in my toploader, but I'm not taking it apart unless I have a better reason!

RustyRed · « **Reply #17 on:** September, 09, 2010, 11:28:35 AM »

I've seen a deal that screws onto the cable that will slow down the reading 15% or 28%...but they are a little under $100 before shipping which also made me think I can live with 5 mph, LOL!

70_Fastback · « **Reply #18 on:** September, 09, 2010, 12:59:13 PM »

Use a GPS to monitor speed.

blue65coupe · « **Reply #19 on:** September, 12, 2010, 06:35:16 PM »

It also screws up your odometer. For every mile I'm reading 1.2

kyle67 · « **Reply #20 on:** September, 23, 2010, 05:58:12 AM »

Does anyone make a c4 with a more agressive gear set? Maybe a more agressive first gear? I am going to swap to 3.25s and posi shortly but I have been told the car needs 3.80s.