whats your top speed in a 46, 47, 48 plymouth with a flat head

[michael.warshaw]

well mine gets to about 45-48 and when i push on the gas from their she has nothing and the motor just starts to shake is this normall or does something need to be adjusted? at this speed its hard to take the parkway?

[Plymouthy Adams]

you sure need to check something out here...last tune up, plugs set right, timing etc etc...brakes dragging...if no e-barake, did you remeber to put the SBC anchor in the trunk..as Johnny 5 says,,need input...

[Reg Evans]

Vacuum advance on the frits maybe ?

[Plymouthy Adams]

the car would still obtain max speed without vacuum advance..it would however suffer on economy...

it would be extremely hard to guess at this without any input at to the condition of car...when and what was done and how long ago..compression reading, tune up condition, fuel deliverly, exhaust pipe condition..oh yeah..restricted pipe kill top end..is the choke all the way off..are the brakes dragging..if on the rear would be hard to tell by driving..unless you burnt your hand touching them..

as for shaking..does he have a two piece balancer..bent drive shaft, chunk thrown/broken off the clutch....it seems rotating mass is the culprit by his description..

[BobT-47P15]

I've had the convert up to 70 - several years ago when it had radial tires. That

was going down hill. Seemed awfully fast in that old car.

Usual cruising speed is 50 to 60 mph. Should be pretty smooth there....no real

extra effort needed.

Sounds as if the things mentioned above need to be checked.

Easy fixes are new plugs, wires, points, condensor, distrib cap, timing.

If changing wires, need to be sure and get new ones back in the correct

sequence. Only remove and replace one wire at a time.

At least, that's how I would do it. Need to determine the firing order and

where wires go. They could even be off as is.

[55 Fargo]

I've had the convert up to 70 - several years ago when it had radial tires. That

was going down hill. Seemed awfully fast in that old car.

Usual cruising speed is 50 to 60 mph. Should be pretty smooth there....no real

extra effort needed.

Sounds as if the things mentioned above need to be checked.

Easy fixes are new plugs, wires, points, condensor, distrib cap, timing.

If changing wires, need to be sure and get new ones back in the correct

sequence. Only remove and replace one wire at a time.

At least, that's how I would do it. Need to determine the firing order and

where wires go. They could even be off as is.

I have to agree with you Bob, I have had mine up to about 65 to 70 mph with a 3 spd trans and 3.73 rear end, that seemed very fast in my 47 Chrysler Coupe.

I like to cruise at 50 to 60 mph like you do Bob, lucky I can get away with it around here for the most part, would hate to have to drive on the freeways, like say LA.

If I had an OD trans, completely rebuilt front end, and disc brakes, I would consider cruising at 75 mph, till then 50 to 60 mph will do for me.

I salute those that drive there P15s with a 3.9 or a 4.1 rear end at 65 mph, I would be nervous driving my car at those speeds..........Fred

[claybill]

I CAN GO 60....tops would be 70 just to see.

however...in my 3 plymouth flatheads...they are like wome...oops! people. they each have a mind of their own and starting peculiarities and different top speeds. the rebuilt motor is fresh and has pull and pep at any speed. the more tired '41 goes 55+ easy but doesnt have much of a spurt after that.

bill

[james curl]

I run my 48 at 70/75 on the interstate three or more times a week for the 12 miles up to the next town for coffee in the mornings with friends who live there. When I travel as I will this comming Saturday, I drive the posted speed limit. I will be going on a one way trip of 145 miles to an inliners chapter meeting then back home 145 miles afterwards all at or above the posted speed limits which will be from 55 to 70 mph. So you surly have a lot wrong with your car if it will only go 45/48 mph wide open.

Edited August 17, 2009 by james curl
additional info.

[55 Fargo]

Wow James, you really give her pepper in your P15.

Here are some specs on running high speeds and RPM.

Tire Size P215 75 15 =27.7 inches

Speeds 70 MPH and 75 MPH

3 speed trans, no OD

3.73 Diff=3393 rpm @75 mph, 3167 rpm@ 70 mph

3.90 Diff =3548 rpm@75 mph, 3311 rpm@70 mph

4.10 Diff=3729 rpm @75 mph, 3481 rpm@70 mph

So this is getting up there RPM wise, gotta have an engine in great shpe, as this is getting close to max HP rpm of 3600, and OD tans would redcue these values significantly, allowing the car to drive much faster........Fred

[james curl]

I have a 90's Dakota 3.55:1 rear end in the car and Old Daddy's disc brakes on the front and a slightly modified 218 flat head I 6. I drove it 4600 miler on a round trip to Reno, Grass Valley, Calif. and on to Bonneville in 2007.

[TodFitch]

Somethings wrong. I cruise at speeds between 50 and 60 in my 190 cu.in. 1933 with its 4.375:1 rear end. With your larger engine with higher compression ratio and taller rear end your car should be faster than mine.

[55 Fargo]

I have a 90's Dakota 3.55:1 rear end in the car and Old Daddy's disc brakes on the front and a slightly modified 218 flat head I 6. I drove it 4600 miler on a round trip to Reno, Grass Valley, Calif. and on to Bonneville in 2007.

Hi James, yah I am thinking of going to a different rear end too, maybe even higher than a 355. I have a 3.73 now, but if I go with higher gear rtiao, afarid of not having enough oomph of the line.I live in flat country, so hills are not a porblem for me.

Sounds like you have a nice set-up there, happy motoring....

[55 Fargo]

Somethings wrong. I cruise at speeds between 50 and 60 in my 190 cu.in. 1933 with its 4.375:1 rear end. With your larger engine with higher compression ratio and taller rear end your car should be faster than mine.

I am not sure if you are referring to my car or not.

47 Chrysler Coupe 3600 lbs, 218 25 inch Canadian engine 98 hp, 3 spd trans,dry clutch, 3.73 rear end, P205 75 15 tires 27.2 inches.

I drive my car at 50 60 mph, my engine has miles on her, the front end could use a little attention, maybe I am chicken, but don't want to drive her faster than this for sustained miles, I admire those that do, I don't,wish I could...........Fred

[james curl]

I live in gentel rolling country and the 3.55:1 rear takes a little more rpms to launch. I think 3.30:1 would be about as low as you could go and still be comfortable around town from stop light to stop light unless you had a S 10 T 5 5 speed transmission or a S 10 T-4 4 speed transmission with their 3.9 or 4.01 low gears.

[Plymouthy Adams]

where Tod is on the low end of the model year, I am a bit above it, 54 Plymouth..I do enjoy the fact that you can obtain 52 MPH before shifting out of low gear...this car seeks cruise at 70mph as a confort spot per say...

[55 Fargo]

where Tod is on the low end of the model year, I am a bit above it, 54 Plymouth..I do enjoy the fact that you can obtain 52 MPH before shifting out of low gear...this car seeks cruise at 70mph as a confort spot per say...

Tim, what gear ratio is the diff in your car, it sounds like a nice highway cruiser......Fred

[Plymouthy Adams]

3.73

[55 Fargo]

3.73

The for sure I am chicken, as I have a 3.73, maybe a little less HP, and my car is probably heavier, I only drive at about 55mph, it does have a lot of get up again go at this speed though as it would surely run up to 70 mph no problem, but may blow up after that.....Yeeeeeehaaaaaaa

[Jim Yergin]

Have you verified that it is a "true" 40-45 mph. Had a Mustang once where I thought it was a poor performer because it just didn't seem to be able to get up to speed. Then I discovered I had the wrong speedometer drive gear and the only thing wrong was the speedometer, it read too slow. Strange how "perception can become truth."

Jim Yergin

[greg g]

Well I had mie up to an indicated 85, for a touch, felt like it was still pulling. I drive it at an indicated 70 which on the gps is 68.

Could be as simple as a improperly set float in the carb or a restriction in the fuel delivery system. A clogged fuel filter will aloow a car to runn around all day at 35 or 40 but shut it down over 45.

Again there are basic tests you can do to check fuel flow and fuel pressure.

Could be as simple as misadjusted points. or a loose coil wire.

I hate to see you not enjoying your ew purchase, but some basic reading and studying of automotive systems would be greatly beneficial to your ownership experience.

[Captain Neon]

I usu. drive at 50 mph, but, when I was a teenager and was "burning out the cobwebs" in the spring, I had her up to 90 mph. To only be able to get 45 mph. max., there is a big problem, and time to find a better mechanic! I'd look for a graduate of Universal Technical Institute to work on your car. UTI still trains their students in the basics, and not just how to change parts as read from a computer.

[Phil Martin]

My 50 Dodge with gyro cruises good at 60. I did kick it up to 85 one time and had more to go. Running radial tires stock rearend not sure what ratio is.

[hkestes41]

Was running 72 per the GPS this afternoon (just over 60 indicated) on the 121 Tollway, speed limit is 70 and I was still getting in some people's way. OD makes all the difference.

However, I just installed a stock rear that I got from James and I now have a vibration start between 60 and 65. Will try to figure that out before heading to Missouri on Thursday for the HAMB Drags.

[james curl]

I never had any vibration when it was installed in my car but it sat from June 2007 until you picked it up. How bad a vibration is it? Will you try to re-orientate the U joints to the rear end? I can not think of anything else that would cause the vibration.

[55 Fargo]

Okay, what is wrong with "Me", I am a little afraid to bring my car over 55 to 60 mph, hasa 3.73 rear end, 27.2 inch tires(P205 75 15s).

I realize my car is a bit noisy as I have no headliner or door panels yet, but yet am paranoid about the big pop of blowiong an opld engine by driving over 60 mph.

Hope I can get over this.......Fred ps or is this a slower driving part of Canada thinking