SAAC Forum

The Cars => 1966 Shelby GT350/GT350H => Topic started by: davez on June 18, 2018, 09:07:17 PM

Title: What gear to run
Post by: davez on June 18, 2018, 09:07:17 PM
So it's time to go through the rear in my 4 speed car. Currently has a locker with 3.89's. At 65 mph the tach shows 3400 rpm. Higher than I prefer. Going to be used for driving until a restoration years away. Was going to build a center section with a limited slip trac lok and what ratio? Was either going with 3.25 or 3.50's. Any suggestions or experiences with what you are happiest with? Is 3.00 too far the other way?
Thanks dz
Title: Re: What gear to run
Post by: deathsled on June 18, 2018, 10:18:23 PM
I have a 3.50 in big red.  It revs enough.  Would not want it higher.  If you're doing a lot of highway driving go to a taller gear.
Title: Re: What gear to run
Post by: JD on June 18, 2018, 10:20:34 PM
I had put a 3.50:1 limited-slip in the car I had for the same reason, to keep-up with highway traffic and not run the engine so high especially on 1-2 hour trips.  If I did it again I'd do the 3.25:1.  (One opinion, also kept the original 3.89:1 open and that went with the car)
Title: Re: What gear to run
Post by: J_Speegle on June 18, 2018, 10:28:08 PM
Guess we should ask, rather than assume, what transmission your running just to establish a base line to work from
Title: Re: What gear to run
Post by: davez on June 18, 2018, 10:34:30 PM
Close ratio t10
Thanks
Title: Re: What gear to run
Post by: GT350Lad on June 19, 2018, 02:50:56 AM
I have actually stuck with the 3.89. Had the diff rebuilt in 2014 and thought about changing the ratio but didn’t. Car hasn’t moved much since, did rev damm hard on highway but good fun between stop lights  ;D

Title: Re: What gear to run
Post by: SFM6S087 on June 19, 2018, 05:49:48 AM
What size tires are you running?
What rpm would you prefer at 65mph?

Steve
Title: Re: What gear to run
Post by: davez on June 19, 2018, 07:33:10 AM
205 65 15 tires
I used a tire size calculator that came up with 25.5 inches height but when I measured them they are actually 24.5 inches tall.
Motor seems happiest at 2800 to 3000 rpm.
Title: Re: What gear to run
Post by: gt350hr on June 19, 2018, 01:45:46 PM
  The 3.50 will drop about 400 rpm at cruise. "Some" change in letting the clutch out in 1st , but not bad.
        Randy
Title: Re: What gear to run
Post by: mygt350 on June 19, 2018, 06:41:17 PM
I had the original 3:89 locker installed in the car and I now find at my age, keeping up with traffic spins the engine more than I wish. So I located a date correct 3:50 posi from Jim Cowles at Shelby Parts and Restoration. It still makes engine spin up bit more than I would like, but it is definitely better ratio for me at this point in life. Have the locker with its original markings bagged and tagged. T10M with Sebring gears, again, from Jim years ago.
Had I to do again, I could have my arm twisted to go to 3:25. But its a real rush to run thru the gears and let it stretch its legs. Get nasty looks from Prius drivers though.
Title: Re: What gear to run
Post by: Side-Oilers on June 19, 2018, 06:55:58 PM
Not for the concours guys, but a Gear Vendors overdrive (0.80:1 ratio) drops the revs significantly when you want it to, yet gives you all the feel & acceleration of the original setup when you switch it off.

Have had it in my KR (3.50 rear, Top Loader) for about two years so far, and really like it.   


(http://www.saacforum.com/gallery/542-190618185506.jpeg)

(http://www.saacforum.com/gallery/542-190618185228.jpeg)
Title: Re: What gear to run
Post by: Bigfoot on June 19, 2018, 11:19:37 PM
3.89 Detroit is a dream
Title: Re: What gear to run
Post by: GT350Lad on June 19, 2018, 11:55:05 PM
3.89 Detroit is a dream

Sweet sweet dream
Title: Re: What gear to run
Post by: SFM6S087 on June 20, 2018, 04:10:24 AM
205 65 15 tires
I used a tire size calculator that came up with 25.5 inches height but when I measured them they are actually 24.5 inches tall.
Motor seems happiest at 2800 to 3000 rpm.

If your tires are 24.5 inches tall that should make their circumference around 76.9 inches. Starting with that, then a rear gear of 3.25 should net you around 2900rpm at 65mph. A rear gear of 3.50 should give around 3125 rpm at 65mph.

If your tires are really 25.5 inches tall that would make each of those tach readings a little over 100rpm lower.

Well, that's what the math says. Someone with real world experience might chime in with something different.

Steve
Title: Re: What gear to run
Post by: shelbydoug on June 20, 2018, 07:18:32 AM
It all depends on what you want out of driving the car.

Theoretically you could run a 2.50:1 9" rear but as far as acceleration, forget about it.

The best combination of having your cake and eating it too would be to run something like a Richmond 5 speed with a 3.26 first gear and use a 3.25 rear ratio.

That would give you a reasonable cruising rpm, a first gear acceleration ratio of what you would put in a GM with a 2.20 first and a 4.88 rear for acceleration with the close spaced gearing of a T10.

If you want lower rpm cruising then that, then you need the 6 speed where 6th is in overdrive by about .7:1


These considerations were never possible back in the day and along with electronic fuel injection are the largest changes to the original packaging of a "current real high-performance vehicle" for the street.
Title: Re: What gear to run
Post by: Bigfoot on June 20, 2018, 09:29:14 AM
3.89 Detroit is a dream

Sweet sweet dream

I also like my 3.91’s.....
Title: Re: What gear to run
Post by: shelbydoug on June 20, 2018, 10:31:06 AM
I'm running 3.50's in my '68 with a Richmond (Doug Nash) 5 speed. 5th is 1:1. First gear multiplication is like running a 5.00:1 rear.

I'm going to drop that to a 3.25 rear. That will be like 4.88's with a 2.20 (GM) first gear. That's still plenty for the street.

Personally I think a lot of the reason GT350's are only 14.5 second 1/4 mile cars is that they don't have enough first gear multiplication with a 2.32 first gear and only a 3.89/3.91 rear. You won't even start to get serious until you get to a 4.33 like in the factory drag pack but who wants to cruise with that set up?
Title: Re: What gear to run
Post by: kjspeed on June 20, 2018, 11:03:54 AM
It all depends on what you want out of driving the car.

Theoretically you could run a 2.50:1 9" rear but as far as acceleration, forget about it.

The best combination of having your cake and eating it too would be to run something like a Richmond 5 speed with a 3.26 first gear and use a 3.25 rear ratio.

That would give you a reasonable cruising rpm, a first gear acceleration ratio of what you would put in a GM with a 2.20 first and a 4.88 rear for acceleration with the close spaced gearing of a T10.

If you want lower rpm cruising then that, then you need the 6 speed where 6th is in overdrive by about .7:1


These considerations were never possible back in the day and along with electronic fuel injection are the largest changes to the original packaging of a "current real high-performance vehicle" for the street.


I've got a Richmond 5 speed in mine with a 3.50 rear gear. It's similar to running a 4 speed with a 4.56 gear but with a 5th gear 3.5 final to bring down highway RPM. The gearing in my trans is; 3.27, 2.13, 1.57, 1.23, 1.00. In your application you could run a 3.00 final and the first four gears would be about what you have now. Of course this setup would require; a new rear gear, a $2900 transmission (https://www.jegs.com/i/Richmond-Gear/836/54110A01/10002/-1), fabricate a rear transmission mount, cut the driveshaft and get a new shifter. Plus my Richmond doesn't have a reverse switch so I have a toggle switch for that.
Title: Re: What gear to run
Post by: Bigfoot on June 20, 2018, 12:06:22 PM
Have a good Friend with a 5 speed in his 67.
Saw the car Monday. He said first gear is like 4.88’s!
Title: Re: What gear to run
Post by: shelbydoug on June 20, 2018, 01:04:08 PM
Have a good Friend with a 5 speed in his 67.
Saw the car Monday. He said first gear is like 4.88’s!

Yes...and then some!

A DN 5 speed with a 2.80 rear is about equal to a TL (2.32) and a 3.89.

I got my Richmond when it was called a Doug Nash and it cost $800. Now I did snap off the friction welded gear selectors and went to the billet versions. After that was fixed, I broke the shift handle off. I suppose it became the weak link.

Lots of folks have been running used T-5s out of the wrecking yards. There's even a turbo T-bird version of it with a 4.11 first gear. You don't have to go the high roller route. Then you could save some money and maybe use it to get a hair cut? I've been getting hair cuts lately.

It has mixed results. Lots  of people stare?  ;)
Title: Re: What gear to run
Post by: GT350Lad on June 20, 2018, 04:05:32 PM
Have a good Friend with a 5 speed in his 67.
Saw the car Monday. He said first gear is like 4.88’s!

4.88! Feels nice under foot when racing the 18 year old in the rice racer!
Title: Re: What gear to run
Post by: shlby66 on June 20, 2018, 04:20:45 PM
 Just thought, I would add my 2 cents worth, to what has been mentioned. First, I'm more
 of the "old school" type and have used, what is referred to, as the "poor mans" 5- speed.

 For 30 years, or so, I've used the combination of: A wide ratio ( 2.78 first ) and a 3:25
 rear gear.

 The result is: You lose nothing in acceleration, because, the wide ratio transmission's gears,
 times, the 3:25 rear gear, is mathematically, the same, as a close ratio ( 2.36 first ) and a
 3:89 rear gear.

 The wide ratio x 3:25's will give you right at 2900 RPM @ 70 mph in 4th gear ( 1:1).

 The RPM may vary somewhat, depending on tire diameter. I've always used at least 26"
 diameter ( tall ) tires, all of the time.

 So, I end up with good acceleration, coming up thru the gears and decent RPM's, for
 cruising on the InterState.  Works for me.

 That's my story and I'm sticking to it. :)

 Doug C.   


 
Title: Re: What gear to run
Post by: zray on July 02, 2018, 04:41:26 PM

"........Motor seems happiest at 2800 to 3000 rpm.


My my we are getting soft in our old age.  A HiPo 289 will run very happily at 4,000 to 4,500 rpm all day long, and get up the next day and do it again. Over and over. These cars were driven coast to coast like that without wearing out anything, without hurting anything, and lasting decades before needing any internal motor attention.

YOU may not be used to driving at these rpm levels hour after hour because modern cars have lulled today's drivers into thinking a motor should barely turn over at highway speeds (thanks to emmision / pollution constraints). And nothing wrong with that, I like to breathe as much as anyone. But don't think the motor in the Shelby's can't take a little exercise. The cars haven't gotten soft. You can drive it to the limit for the rest of your life and it will still be ready for more long after you are 6 feet under.

Z

PS. If you add a vintage Paxton, a 3.00:1 rear gearing , and a 2.90 1st gear works fine. But at stock horsepower levels, I would not go any higher than 3.25:1 , with  the 3.50:1 being a good all-round choice, and the same std. gear found in the stock 289 K code cars.
Title: Re: What gear to run
Post by: gt350hr on July 02, 2018, 05:21:50 PM
+1
     4,000 was "cruise" rpm on the highway with 3.89s and a 26" tall tire on my first GT350 ( 4 speed ) . Hiway 50 west out of Wichita was a blur at 4,500 but that was 43 years ago. LOL Oh the good old days when gas was cheap and full of lead.
   Randy
Title: Re: What gear to run
Post by: GT350Lad on July 02, 2018, 06:32:23 PM
Right on Randy, there is nothing like pulling up next to a electric car and knowing that what there car has done to help the environment you have just undone in 5 min of driving! Love it

Ps. Even though the environmental impact of mining the lithium and making the batteries is far more then people realise
Title: Re: What gear to run
Post by: 427heaven on July 02, 2018, 09:25:09 PM
Hundreds of thousands of batteries litter the Nevada desert HAZ MAT site. This is waste that cant be undone for thousands of years. What impact it has on society wont be known for years... So much for progress. :-[
Title: Re: What gear to run
Post by: 98SVT - was 06GT on July 03, 2018, 12:21:48 AM
I built a 65 Fastback one time and all I had laying around was a 2.80 from an automatic. Ended up being a great highway gear. 28mpg @ 75mph.
I'd go the gear vendor or 5 speed route. That extra gear will not affect the "fun" factor but will drop the revs to acceptable levels at highway speeds.
Title: Re: What gear to run
Post by: GT350Lad on July 03, 2018, 01:26:53 AM
Hundreds of thousands of batteries litter the Nevada desert HAZ MAT site. This is waste that cant be undone for thousands of years. What impact it has on society wont be known for years... So much for progress. :-[


So true mate
Title: Re: What gear to run
Post by: shelbydoug on July 03, 2018, 07:43:38 AM

"........Motor seems happiest at 2800 to 3000 rpm.


My my we are getting soft in our old age.  A HiPo 289 will run very happily at 4,000 to 4,500 rpm all day long, and get up the next day and do it again. Over and over. These cars were driven coast to coast like that without wearing out anything, without hurting anything, and lasting decades before needing any internal motor attention.

YOU may not be used to driving at these rpm levels hour after hour because modern cars have lulled today's drivers i Tom thinking a motor should barely turn over at highway speeds (thanks to emmision / pollution constraints). And nothing wrong with that, I like to breathe as much as anyone. But don't think the motor in the Shelby's can't take a little exercise. The cars haven't gotten soft. You can drive it to the limit for the rest of your life and it will still be ready for more long after you are 6 feet under.

Z

PS. If you add a vintage Paxton, a 3.00:1 rear gearing , and a 2.90 1st gear works fine. But at stock horsepower levels, I would not go any higher than 3.25:1 , with  the 3.50:1 being a good all-round choice, and the same std. gear found in the stock 289 K code cars.

Yup! All the noise too! And the bumps in the road? How can I stop it?

What was it that attracted people to these cars to begin with? They are "performance cars". Granted the definition has changed just a bit BUT if you look at the current Mustang GT packages, they are still based upon the original concept with some updates.

We are giving the formula for putting a 60's something criteria into a '18 data.

Next everyone is just going to complain that all the '60s did was make the Nauga extinct because we killed them for their skins?

I think those folks should all stay home and play their video games that show they are F1 champions of the Rec Room? Those thumbs should just be put in the Hall of Fame?

Title: Re: What gear to run
Post by: Jimbc123 on July 03, 2018, 10:55:57 AM
When I bought my 4-speed GT350 I was surprised to find 3.00 gears in the rear. The date code on the axle tag was consistent with the build date, so I left it alone. I spent a lot of time on the highway so the 3.00 wasn’t bad. I was always a little unhappy with the performance on the street. After retirement I went ahead and installed 3.89 gears. I couldn’t be happier. It is a completely different driving experience and just what I needed after having the car as a driver 14 years.i would never go back to the 3.00, but I did save them. If I really needed to do more highway driving I’d try something in the 3.50 range, but not the 3.00.

Good luck,

Jim
Title: Re: What gear to run
Post by: deathsled on July 03, 2018, 03:41:36 PM

"........Motor seems happiest at 2800 to 3000 rpm.


My my we are getting soft in our old age.  A HiPo 289 will run very happily at 4,000 to 4,500 rpm all day long, and get up the next day and do it again. Over and over. These cars were driven coast to coast like that without wearing out anything, without hurting anything, and lasting decades before needing any internal motor attention.

YOU may not be used to driving at these rpm levels hour after hour because modern cars have lulled today's drivers i Tom thinking a motor should barely turn over at highway speeds (thanks to emmision / pollution constraints). And nothing wrong with that, I like to breathe as much as anyone. But don't think the motor in the Shelby's can't take a little exercise. The cars haven't gotten soft. You can drive it to the limit for the rest of your life and it will still be ready for more long after you are 6 feet under.

Z

PS. If you add a vintage Paxton, a 3.00:1 rear gearing , and a 2.90 1st gear works fine. But at stock horsepower levels, I would not go any higher than 3.25:1 , with  the 3.50:1 being a good all-round choice, and the same std. gear found in the stock 289 K code cars.

What about a 302 roller rocker out of an 89 Mustang? I get concerned the engine will blow up at 4,000 rpm for extended periods at 70 mph.  But I like the sound and fury and can live with it just fine so long as it holds together. 3.50 rear incidentally.  I really don't want to go to a five speed otherwise when I have a Toploader four with Richmond gears out of Klutt's race car. Don't care about gas mileage. Just means I buy more gas and eat less food.  Win win.

Happy motoring,

Richard E.
Title: Re: What gear to run
Post by: shelbydoug on July 03, 2018, 06:22:31 PM

"........Motor seems happiest at 2800 to 3000 rpm.


My my we are getting soft in our old age.  A HiPo 289 will run very happily at 4,000 to 4,500 rpm all day long, and get up the next day and do it again. Over and over. These cars were driven coast to coast like that without wearing out anything, without hurting anything, and lasting decades before needing any internal motor attention.

YOU may not be used to driving at these rpm levels hour after hour because modern cars have lulled today's drivers i Tom thinking a motor should barely turn over at highway speeds (thanks to emmision / pollution constraints). And nothing wrong with that, I like to breathe as much as anyone. But don't think the motor in the Shelby's can't take a little exercise. The cars haven't gotten soft. You can drive it to the limit for the rest of your life and it will still be ready for more long after you are 6 feet under.

Z

PS. If you add a vintage Paxton, a 3.00:1 rear gearing , and a 2.90 1st gear works fine. But at stock horsepower levels, I would not go any higher than 3.25:1 , with  the 3.50:1 being a good all-round choice, and the same std. gear found in the stock 289 K code cars.

What about a 302 roller rocker out of an 89 Mustang? I get concerned the engine will blow up at 4,000 rpm for extended periods at 70 mph.  But I like the sound and fury and can live with it just fine so long as it holds together. 3.50 rear incidentally.  I really don't want to go to a five speed otherwise when I have a Toploader four with Richmond gears out of Klutt's race car. Don't care about gas mileage. Just means I buy more gas and eat less food.  Win win.

Happy motoring,

Richard E.

Those roller rocker arms are bolted down with 5/16" bolts. These days I would say that 7/16" studs are preferred but 3/8" studs are acceptable.

l'd consider the 5/16" have a red line at 6,000 rpm. Where they fail depends on what valve spring pressures you are running.

I do not think that roller rocker arms were permitted by the rules back in the day. Valve train failures were mostly the valve keepers or the valve springs letting go and the valve getting sucked into the cylinder.

Valve spring technology of the day limited rpms pretty much to a strict 7,000 rpm limit.


In all these years I've only had one valve train failure and that was the pushrods in my Pantera. They were Crane "Ultra" push rods and the tips on about 6 of them all failed at once. The tips are welded on with a little pinch weld and they had been so hardened by Crane that the tubes cracked and shattered, letting the tips come off.

It's better to have them bend. That way you get no shrapnel in the top of the engine to clean out.


Regardless of what anyone tells you, all rocker rollers do is eliminate (or close to it) the scuffing on the bottom of a standard rocker arm, the valve tip, and the oblonging of the valve guide because of the pushing the rocker arm is doing sideways.

Picking up HP is really BS. Reducing oil temp is from reducing the said friction.
Title: Re: What gear to run
Post by: red66 on July 04, 2018, 11:06:56 PM
My T-10 4-speed with 14" BFG radials and a 3.50 rear axle ratio runs 3,000 rpm at 55 mph, 3,250 at 60, 3,500 at 65 and 4,000 at 70.   Although the car is just driven to weekly local cruise-ins and shows with minimal highway use, I believe a 3.25 would be a better fit for me.
Title: Re: What gear to run
Post by: Bob Gaines on July 05, 2018, 12:45:44 AM
My T-10 4-speed with 14" BFG radials and a 3.25 rear axle ratio runs 3,000 rpm at 55 mph, 3,250 at 60, 3,500 at 65 and 4,000 at 70.   Although the car is just driven to weekly local cruise-ins and shows with minimal highway use, I believe a 3.25 would be a better fit for me.
Did you mean 3.89 here?
Title: Re: What gear to run
Post by: shelbydoug on July 05, 2018, 07:58:46 AM
I don't know if this helps anyone on this decision but it may give a novice help in understanding in general.

http://www.5speedtransmissions.com/5sp_comparison.html


It all comes down to the intended use but I would suggest that anyone who purchased one of these cars wanted a real performance car.

You can have 900hp, but if you don't gear it right, it won't do what you want.
Title: Re: What gear to run
Post by: gt350hr on July 05, 2018, 11:15:16 AM
  Bolt down rockers are not an issue. The Crane manufactured ,"Cobra" bolt downs had to pass a 100,000 mile durability test to become an OEM part. Bolt down IS different than stud mount because it bolts down and doesn't move like a "loose" rocker on a stud does. I always try to use 7/16ths like Doug recommends. 3/8ths is for restorations only . NOT performance. IMHO anyway.
     Randy
Title: Re: What gear to run
Post by: zray on July 05, 2018, 11:38:02 AM
  Bolt down rockers are not an issue. The Crane manufactured ,"Cobra" bolt downs had to pass a 100,000 mile durability test to become an OEM part. Bolt down IS different than stud mount because it bolts down and doesn't move like a "loose" rocker on a stud does. I always try to use 7/16ths like Doug recommends. 3/8ths is for restorations only . NOT performance. IMHO anyway.
     Randy

^^^^^^^^. +1000

That extra 1/16" stud diameter adds considerably to the strength of the screw in stud.  ANYONE going to aftermarket rocker arms would do well to consider buying studs and rocker arms in the 7/16" size.

Note:  the only difference is in the top of the stud. The screw in part is already 7/16" on the studs labeled 3/8". So the threads in the head remain the same when switching to the 7/16" size studs and rockers arms.

I had a stock original 3/8" stud snap on my '66 GT350 and was fortunate the valve was not wedged open.

Z
Title: Re: What gear to run
Post by: shelbydoug on July 05, 2018, 01:25:34 PM
  Bolt down rockers are not an issue. The Crane manufactured ,"Cobra" bolt downs had to pass a 100,000 mile durability test to become an OEM part. Bolt down IS different than stud mount because it bolts down and doesn't move like a "loose" rocker on a stud does. I always try to use 7/16ths like Doug recommends. 3/8ths is for restorations only . NOT performance. IMHO anyway.
     Randy

^^^^^^^^. +1000

Z

If you go with the ARP's be aware you need to use their matching nuts also. They have an interference fit to lock the nuts.

7/16 is cheap insurance but make sure that you know the tensile strength of the studs. The ARPs are 190,000. Some of the "unmarked brands" are only 160,000.

There actually is trade off in hardened steels though. a 160,000 would bend more before it snaps then the 190,000 does. On the other hand I don't know how you possibly can snap a 7/16" stud.

YEARS ago (late '60s) Chevy was having issues with some of their racing parts developing stress risers just sitting on the shelf waiting to get sold. They were playing with parts in their race program much like Ford did but the issue for both of them was they didn't tell anyone.

They were super hardened which turned out to be over hardened. Hardened steel can get brittle.




I still don't feel comfortable with anything just 5/16" in the valve train. I've broken too many things that "NEVER" break.
Title: Re: What gear to run
Post by: davez on July 05, 2018, 08:09:28 PM
Circling back to intent. Going to stay with the close ratio t10. I've spoken to a number of people who said 3.25 gears can be hard on the clutch. My intent is to knock off some of the rpms at highway speed. More than likely I will be going with a limited slip with 3.50s instead of the 3.89's. Probably will get to it in the next month or so. Little improvements  for more enjoyment
dz
Title: Re: What gear to run
Post by: gt350hr on July 06, 2018, 10:42:02 AM
    Dave ,
        I am joking a bit but it is the "driver" that is hard on the clutch not the gears. MANY people slide clutches needlessly and murder clutches yet some are polite and they seem to last forever. If you are driving in a particularly hilly area I could see a potential wear issue . Flat ground not so much.
    Just This Old Man's Opinion.
       Randy
Title: Re: What gear to run
Post by: shelbydoug on July 06, 2018, 10:53:36 AM
    Dave ,
        I am joking a bit but it is the "driver" that is hard on the clutch not the gears. MANY people slide clutches needlessly and murder clutches yet some are polite and they seem to last forever. If you are driving in a particularly hilly area I could see a potential wear issue . Flat ground not so much.
    Just This Old Man's Opinion.
       Randy

Umm. First "slide". New clutch. First run. GOODBYE CLUTCH!

Hills. Don't downshift to slow the car. Brakes are cheaper then clutches or transmissions and certainly easier to do.

So far, that's what I remember. I wasn't smart enough to write it all down. Sometimes it's just all a blur, like the bumpy ride you take running off the road, down the hill towards the river...but don't ask about that. It was the squirrel in the road. Yup. That's what it was? Oye!  :o
Title: Re: What gear to run
Post by: red66 on July 16, 2018, 04:52:34 PM
Correction to the typo in my post dated 7/4/18:  My car allegedly has a 3.50 rear axle ratio, not a 3.25 as I originally posted.  It feels like a 3:89 though.  Wish I had a 3:25.

 
Title: Re: What gear to run
Post by: SFM6S087 on July 17, 2018, 05:00:39 AM
Correction to the typo in my post dated 7/4/18:  My car allegedly has a 3.50 rear axle ratio, not a 3.25 as I originally posted.  It feels like a 3:89 though.  Wish I had a 3:25.

The numbers you posted for tire size, gear ratio, rpm and speed don’t seem to match up. I suspect that either your tach is off, your speedo is off, or your rear gear is something higher than 3.50. Maybe it really is the 3.89 that it feels like.

As a reference, with 14” wheels & tires you should probably be turning 3000rpm (plus or minus a little) at 60mph.

I don’t know about checking/calibrating a tach. But there are free apps that will give you an accurate speed readout from your phone that you can use to check your speedometer. You wrote that your car “allegedly has a 3.50 rear axle ratio.” You may want to manually confirm that by jacking up the rear tires and counting how many drive shaft revolutions occur during one wheel rotation.

Just things to consider if you want to change your cruising rpm some day. It’s always a good idea to know exactly what you’re starting with before making any changes.

Steve
Title: Re: What gear to run
Post by: Tinface on July 18, 2018, 08:48:35 AM
Same exact concerns. I having a 5 speed installation now by Craig Conley in San Diego, Ca. With a 411, the 15” Cragers, and TA Radials, I hope this solves it: nice shot out of the hole and low revs at 80 plus on the highway.i’ll let You know when I get the car back next week.

Will you be at Sears Point in August?
Title: Re: What gear to run
Post by: kjspeed on July 18, 2018, 09:34:28 AM
This site has some nice calculators for tire size/gearing that might be helpful: https://tiresize.com/
Title: Re: What gear to run
Post by: pmustang on July 23, 2018, 10:15:55 PM
In 2170 is a 389 gear and WC T5

Couldn't wish for a nicer setup. In layman's terms plenty of off the line grunt and at a fair speed, 70? (speedo is useless) she is in the low 2k rev range. Other than the occasional blast that's as fast as I want to go and she performs lovely