Flathead speed trials 1-10-10

So im getting ready to pull the flathead out of my pickup this winter and wanted to run a few tests to see what my gains are going to be in the spring. As of now i am running a bone stock "rebuilt" 53 truck flathead with the exception of headers and a stock flywheel just lightend a bit. Its in my 32 ford with a 39 ford box and a stock deuce rear with 3.73's and a 31 inch tall tire. This motor runs very well for a flathead so i am going to be conservitave with what i am willing to do to this motor. This winter i plan on instaling an original set of edelbrock heads, an edelbrock regular intake with 2 97's, bumping up the compression, doing some port work to the block and adding a hot ignition. So today was a clearish day not to much salt on the roads after a resent snow so i took to the roads. Took the pickup to a local high way along with my navigation with built in speedometer and ran some tests. I did 3 pulls in each gear and came up with the same numbers every time!!!

1st gear 30mph
2nd gear 56mph
3rd gear 85mph


So i guess the whole reason to this post is im wondering if anyone has any comments or has done any similar test with a flathead and 3 speed trans and would like to share there numbers {and not one of those new traditinal period correct s-10 5sp trans}

 

What's the gearing on the ****** and do you have any idea of your RPM at each gear?

 

i do not know the gearing of the trans but it is stock for a 1939 ford. as for the rpms i do not have a tach in the truck now but will be adding one while the motor is out. stcok rpms for this motor is 3800 so thats probably right where i was.

 

I'm not clear what you're measuring. Top speed in a given gear is going to be governed by whatever is limiting your RPM, primarily.

 

Neat truck, fella...

 

is the crank in your avatar one of those new full-floating rod journel cranks i've been hearing about?

 

That crank is the most expensive damn paper-weight I'll ever own, man....

 

85?! Wow, about the only way my truck could do 85 would maybe going down a very steep hill (with me ****ping my pants because the brakes failed). And my truck has a 3sp with OD too, but being a 3/4 ton, the rear is geared pretty low. But mine is a Studebaker I6 anyway, so not a good comparison to yours regardless. If my truck could do 85 and the motor ran nice as you say, I'd probably move that project down the list and be working on other things over the winter.

Nice looking truck though by the way.

 

I am measuring my top speed in each gear to have something to compare it to after i hop up my mill

 

Unless you measure how quickly you get to that top speed, what are you going to compare?

Speed in gear is strictly an RPM thing. For example an early Ford car with a 16/28 ge****t 3-spd, a 3.78 rear gear, and a 7.50x16 tire will "top out" at:

1st - 35 @ 4400RPM
2nd - 60 @ 4350RPM
3rd - 105 @ 4300RPM (***uming it can overcome drag, etc.)

You're limited by what RPM you can turn, so making more power only means you'll get there quicker - all else being equal.

So, if you had done timed runs to a specific RPM in each gear, you'd have something for a valid comparison. But increasing horsepower of an engine won't change how fast you can go in a given gear if you're RPM limited - again, all else being equal.

Now, most flathead speed improvements focus on increasing the breathing, so you should see some minor improvements in top speed in each gear, but it won't have much bearing on power output.

 

Well i giess this test was performed to find out my top speed in each gear (mostly top gear for that matter) and to see what my gains are: with a set of heads, 2x2 intake, added compression, port work, and a hotter ignition. I feel that i shoudl see an increas in mph as if this is what they used to do back in the day...... or am i wrong?

 

I doubt you'll see much. It's a function of RPM, not power.

All that said, RPM achieved is somewhat related to power. AND because the flathead breathes so poorly, you're somewhat self-limited by stock.

If you take your top speed from say 60 to 75, that's a 25% increase, yet you may not have a 25% increase in power....but if all you care about is going faster at the top end, that's fine.

This is why most folks use 1/4 mile times (or any other time/distance) - there are relatively simple calculations required to determine the minimum power to move a given weight a given distance at a given speed, so calculating power increase is reasonably achievable.

 

If the only change is the motor, then top speed accurately measured in a quarter mile or eighth mile from a standing start (drag strip) will give you the best estimate of a power increase. In that case mph is considered a better measure than ET. Top speed in the highest gear will probably tell you something as well. At high speeds, rolling resistance from friction and wind will play a more significant role than at lower speeds and it does take power to overcome that. Ask those land speed racing guys. However, I know of no way to tell how much power you have from just top speed. You can estimate power to the rear wheels from mph on a drag strip.

 

I think i may have confused some on how i worded my first post so i will try and clear that up for you. I am NOT trying to calculate my hp gains ex 1<SCRIPT type=text/javascript><!--vB_Editor['vB_Editor_QR'] = new vB_Text_Editor('vB_Editor_QR', 1, '5', '1');var QR_EditorID = 'vB_Editor_QR';//--></SCRIPT>00 to 115. but rather see my mph gains do to the modifications i plan on making while retaining my old trans and ring and pinon gear....

 

best hp increase for you would be to change your ring and pinion if that's how you want to measure it....

 

when calculating your HP gains this way be careful not to run over your crankshaft !

 

hey now u would want a chevy in there

 

Nope, I think both Jim and I get it. It just isn't a useful calculation by itself...

And with your stock trans and ring/pinion, little you do to the engine will make a big difference really.

 

Have a buddy ride with you and a stopwatch. Have him start the stopwatch as soon as you begin to move. Holler when you get to 85MPH and have him stop the watch. Do this about 3 times and average the times. Now you have something to compare to.

 

so ur telling me that after i do the modifications to my motor i will see no increase in mph?

 

Without a tach - you don't know what RPM you're spinning the motor. I have no idea as to if your speed is limited by the horsepower of the motor (it can't push the brick at a given speed) or the RPM that the motor can be safely run or will run.

When you build a high-performance flathead, typically you'll have more horsepower, and be able to turn a higher top-end RPM (the power-band has moved up). If you have the right combination of cam, ports, relief, valves, heads, ignition, exhaust, gearing, etc -- then you should be able to spin the motor higher than stock, with more horsepower available. Given this, you'll achieve a higher top-end speed. You also might be able to drive a taller gear and maintain RPM . . . giving you a faster speed.

Now - any one thing can limit you --> if the ignition ****s out at 4500, you're done. If it breathing is constricted such that power really drops off after 4500, you might run out of usable horsepower/torque and you just can't push the car any faster. (Ask the guys at Bonneville - you can change a gear to a higher one and NOT be able to drive it any faster as the motor lugs and can't make the torque/hp to push the car).

Hope I'm making sense . . .

B&S

 

Get this, the Bonneville record for XFMP (a modified cl***ic pickup with a naturally aspirated flathead) is only about 98mph! McCabe's "Old Bones", a '53 Ford truck, set it a few years ago. I haven't heard if it was broken last year or not. Sounds like an easy target, until you get to the Great White Dyno......

 

Correction: the XF/MP record was shattered last year, it's now 111mph:
http://www.scta-bni.org/Bonneville/BNIrecs_cat_d.htm

 

PS: sorry to hijack the thread. I agree with these other guys, your mods might increase your RPMs and therefore increase your top speed in each gear, but a better measurement of power would be to measure your acceleration.

 

I know that my test does not measure power. I just wanted to see a before and after in my MPH before I did my modifications

 

1946, 1933 ford cabriolet, no fenders, edelbrock, winfield super, edelbrock heads, zephyr ignition, headers, 3:54 rear end, 7.50x16 rear tires.
First gear , zephyr gears, 72 miles and hour, Second gear 95 mph, Top gear 101 .
All at ElMirage. Pump gas!

Too much gear, too much air resistance, not enough torque to pull the car in high gear. Estimated 170 horse power.

it takes power to overcome the air resistance of the bigger cars, which is why you see the channeled , sections, narrowed, and all that in the record cars.

until , of course, they found nitro!

TraderJack

 

Oh, by the way, 75 octane gas!

TraderJack

 

my half breed 29 model a / chevy caprice has a windbag 305ci and a 700r4 and a traditional 10 bolt rear with a chineese jegs chrome cover. she turned some consistant numbers when i went to autozone yesterday. she pulled 1st gear 40 2nd 60 and when i went to go into 3rd my lokar geenie shifter got hung up and w****d up in some fake spider webs i have hanging from the roof. who knows

 

Thanaks for the added info

 

Why not time your acceleration to a specific MPH, say 60 MPH. Do it several times and average it. There's a reason folks quote the 0-60 time for cars - it's a known standard.

I'm still not sure what you hope to achieve.

For the sake of argument, let's ***ume your top speed in 3rd gear was at your imaginary RPM redline of 5000. No changes you make to your engine with normal bolt-on parts are ever going to change that - it's a function of gear ratios and RPM.

The reality is, that your top speed may indeed be limited by power, but it could just as easily be limited by a bad ignition or carburetor.