Topping out at about 90mph

[Orange71SE]

I have a 1971 charger that is topping out at about 90mph (monitored with gps app that is fairly accurate +/- 5mph) mild 440/727 with a cheetah full manual valve body forward pattern. Has a hughes 2k stall converter. Rear end is a dana 44 with 3.54 gear (46 splines on ring gear and 13 on pinion). Rear tires are 275/50/15, measure about 25in when car is on the ground. I know my rear tires are too small but i cant even get on the freeway at 60mph because this thing is cruising at 4k rpms. Any ideas?

 

[Lefty71]

Camshaft is completely worn out??

 

[Hemirunner]

Are you missing high gear?

 

[Orange71SE]

Are you missing high gear?

I can feel the trans going into all 3 gears

 

[Orange71SE]

Camshaft is completely worn out??

Engine has about 1000 miles on it, and pulls real hard with no misfires. Plugs are all same color

 

[davek]

I would check the tranny,low on fluid? Not going into 3rd.

 

[Orange71SE]

I would check the tranny,low on fluid? Not going into 3rd.

Trans fluid is at level, i can feel all 3 gears going in when shifting

 

[davek]

with 3:54 gears and small tire I would not think you would be at 4 grand at 60mph. Are you positive on the rearend gears? Just asking.

 

[Hemirunner]

What’s the rpm at 90mph?

 

[Orange71SE]

with 3:54 gears and small tire I would not think you would be at 4 grand at 60mph. Are you positive on the rearend gears? Just asking.

Just pull the diff cover off yesterday and counted like 5 times lol. Ring gear also had 46-13 stamped in ring gear.

 

[Orange71SE]

What’s the rpm at 90mph?

6500rpm

 

[davek]

yep check this out

6500rpm

http://www.businesspath.com/business_paths/auto/rpm-calc.html

 

[davek]

get a taller tire or change to 3:23 to lower rpm

 

[Orange71SE]

get a taller tire or change to 3:23 to lower rpm

Im definitely going to get a 28in tall tire but i still feel that with the tire swap im leaving something on the table?

 

[Cranky]

Either your tach is wrong or your speedometer is if it's showing 4000 at 60

 

[66 Sat]

You're losing about 1,000 rpm somewhere. According to the calculator you should be at about 3,000rpm at 60 mph. I don't know if the calculator takes into account converter slippage (3-5% on average from what I've read) but it can't be slipping that much surely? Maybe try holding it 1st and 2nd and recording the speed at 4,000 rpm to see if you get the same results for those gears relative to the ratio they have.

I've been doing a lot of the same checks on my car recently - for reference 3.23 rear, 727 stock converter, 25.6" tire diameter and at about 2,900 rpm I'm at 60 mph.

 

[Orange71SE]

Either your tach is wrong or your speedometer is if it's showing 4000 at 60

Using gps for reference, but i will double check tach. But just listening by ear the engine is spinning in higher rpms

 

[Cranky]

Using gps for reference, but i will double check tach. But just listening by ear the engine is spinning in higher rpms

I'm pretty decent listening to engine rpm but I ain't THAT good lol

 

[dadsbee]

Stuck in 2nd or your converter is f'd..

 

[davek]

Did you buy the converter brand new? How old is the tranny?