What gear to run

[deathsled]

"........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.

[shelbydoug]

"........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.

[red66]

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.

[Bob Gaines]

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?

[shelbydoug]

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.

[gt350hr]

  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

[zray]

  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

[shelbydoug]

  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.

[davez]

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

[gt350hr]

    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

[shelbydoug]

    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! 

[red66]

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.

[SFM6S087]

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

[Tinface]

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?

[kjspeed]

This site has some nice calculators for tire size/gearing that might be helpful: https://tiresize.com/