Hot Rods Anyone run sub 10s in the 1/8th mile with a flathead powered N/A coupe?

Im tearing my 34 5 window coupe back down in preperations for next year's vintage drag events. I'm a little discouraged. I weighed my car and its heavier than I thought. I'm currently putting it on a big diet but heres the thing. With all the online calculators (I know, I know) breaking 10 seconds in the 1/8th mile with a naturally aspirated flathead coupe is a tall order. Is anyone doing it here? Id love a little insight.

 

A N/A coupe that ran 12s in the 1/4" mile:

 

Just out of curiosity, what did your car end up weighing?

The Fly weighs 1880 with no driver....probably 2700 with driver, after yesterday.

 

I brought it to the CAT scale and with a tool box and extra battery it weighed 2340 lbs. I believe the extra stuff was about 50 lbs. Which I will weigh and confirm so lets call it 2290 lbs with 8 gallons of gas. This is a steel 1934 5 window. Alot of my car is already hole sawed/ drilled but theres alot of room for improvement. Shits about to get real haha.

 

I have an all aluminum floor pan, firewall and just one seat. No interior either and plexi windows.

 

Roothawg thankyou for the reply. My car has a steel floor which I havent even thought of with all the ideas I have so I really appreciate your input! I'll be replacing that with aluminum.

 

Pounds per horsepower has always been the name of the game.

 

Read the story in the above messages about the 41 Willys. Ed Bingnelli spent over 80 hours reworking the ports! Approximately 15 lbs was removed from the crank that accordingly”improved the acceleration tremendously.” This is quoted directly from a person who had a similar crank and ran at Bonneville. I have a pic in my flathead scrapbook that shows the crank counterweights as being knife edged/airfoil shapes and pretty thin;also notice the “rounding” of the areas next to the crank throws.A tremendous amount of grinding took place to remove this weight and a tremendous amount of skill is necessary to put it back “in balance”. Also note the 3:78 gear/probably ran 2-3 gear only. My 32 Henry cabriolet has run 80(et 9:50) in the 1/8 weighing 2210 on the scales b4glass was installed on the rollup windows running 2-3 only(gm5spd) and 3:89 Detroit Locker 9 in Ford(no slicks). Flatheads Forever.

 

To get close with calculations, you will have to weigh everything that will travel down the 1/8th. Car, appropriate amount of gas, you (in full race fancy dress, including helmet, etc), and anything else along for the ride.

My workings point at 31 wheel hp for every 500 pounds of mass to go sub-10 seconds in the 1/8th mile.
That works out to about 0.062 hp per pound, or 142 wheel hp for 2290 pounds (assuming 14% drivetrain loss).
In the real world it is probably going to need more. The real world almost always disappoints a little.

 

It creates it's own problem. Think about attaching the floor and how it will mate up with the walls. My floor is on the bottom side of the chassis. Basically its like stepping down into the floor. It freed up some leg room for the car since it was chopped 6" and channeled 3".

 

In a “light” car , a lightweight flywheel and clutch assembly can be utilized on the street. I run a 13 lb Weber flywheel with a brass or bronze insert. I run a 9.5 inch pressure plate and when my 32 cab ran 80’s in the 1/8 there was no glass in the roll up side windows,no door panel or kick panel upholstery,top bows were present, but no top(fabric) was fitted. Now, the car has near full upholstery and a full top and probably not as quick. 10 years ago, I had a similar engine in a 48 Prefect(4 dr Anglia) that had a Muncie 4 spd(could be power shifted all gears)behind the flattie, and a 3:91 gear 9 in spool and ran 14:90 at 93 mph in the quarter.

 

Thanks for all the great replies. I feel alot better about this whole thing. I bought a hanging digital scale and am weighing parts as I modify them to track progress. Car is already very bare bones but theres alot of trimming left to do.

 

There was a guy on "The Ford Barn" a few years a go that ran a full-fendered '32 coupe with an injected 260 ci flathead that ran consistent 12 second quarter miles and occasionally dipped into the 11's. He did a LOT of research on these engines. I haven't seen him around for a while though.

 

Adam, I would think twice before I cut my floor out.Speaking from experience,I think you will find that the weight differential between the two,when you add in all the extra bracing required, isn't worth what you are going to lose.Henry had his shit together with 34 floor integrity.

 

I think you're right. I get carried away in the planning stages of a project but usually level out before things get too out of hand

 

The guy who bought my Morris Minor that is my Avatar . Is installing a hot flathead with a Muncie 4 speed behind it. It weighed 2440 with me in it with a small block Ford.
So it should be a little lighter now. Aluminum case 4 speed , smaller headers , etc. He will be running a 5.29 gear. It will be an H/Gas SEGA car. It will be interesting to see what his 1/8 th mile times will be.

 

Interesting. I think gearing is gonna be a big part of my goal. Im building a new rear right now with 4.11 gears and am switching to a 7.00 tire. Currently I run a 3.78 and 7.50 tire. The car springs from a dead stop pretty well now for such a low hp car ill be curious to see if I can feel the difference.

 

grumpy65, would you be willing to walk through the math on this. I have wondered how to get it broken down to hp per pound. I use calculator's to get 1/4 times with hp but never broke it down on how much per pound.

Thanks Tony

 

Here's a useful fun fact:
Eighth mile times can be approximated from quarter mile times by multiplying the quarter mile time by 64%.

Example
12.00 sec quarter mile time x .64 = 7.68 e.t. eighth mile

Conversely
10 second eighth mile time / .64 = 15.62 e.t. quarter mile

Of course this assumes you've got the rev capability to do either 1/8 and 1/4 racing.

 

The lower gears will make a big difference.

 

As an example, the we ran the roadster pictured here in the 1/8 once. It weighed around 2150 with the driver, and had 292", Hi-Dome Navarro heads, 3-97's, Vertex mag, and a 425 Schneider cam. Backed by a wide ratio toploader 4 speed, and 4.11's in the quickchange. With 7.50 X 16 Firestones, as shown, it ran 8.90. Rule of thumb, you can add 1/10th of a second for every 100 lbs added.

 

It is all an approximation using the horsepower/elapsed time calculators.
If you run the calculators with different mass figures (eg. 1500 pounds, 2000 pounds, 2500 pounds, 3000 pounds), you will notice that for each increase of 500 pounds there is certain horsepower increase figure needed to attain the required elapsed time (in this case 10 seconds).

Using my prefered calculator - to go sub 10 seconds in the 1/8th mile:
1500 pounds needs 94 hp
2000 pounds needs 125 hp an increase of 31 hp
2500 pounds needs 156 hp an increase of 31 hp
3000 pounds needs 187 hp an increase of 31 hp

So, each extra 500 pounds needs an extra 31 hp to achieve just under 10 seconds in the 1/8th mile.
Simple math from here.
hp divided by pounds
31 diveded by 500
= 0.062 hp per pound to go sub 10 seconds in the 1/8th mile.

This will be a ballpark figure only. There are other factors (like gearing) that come into play, but this gives you a starting point.

 

This is true if you are up around 500 hp.
The lower the hp figure, the more time you need to add for each 100 lb increase in mass.
At 200 hp the extra time is around 0.13 seconds.
I know, it doesn't sound like a big difference, but it is an extra 1/10th of a second for every 308 lbs.
As we know, every little bit counts.

 

There were a lot of cars that went fast in the old days (mid 50's) that you never heard of because they came from far out in the sticks and got no magazine coverage.
This one did 116.58 at 11.34 in the quarter. 115/145 av gas.
!956 turned 120.40 at Arlington.

 

Damn that's impressive !

 

Adam not sure what you weigh and no disrepect meant but if you are a bigger kinda guy like many of us including me something to consider is the driver's weight. 'Back in the day' I used to hose my bigger friends on our bikes racing lights to lights because I had a significant weight adavantage being 100-150 lbs lighter than them at the time, not so much now . In some instances these guys were drilling out a aluminium brake brackets to save weight.....

Im not infering this is the case here as I dont know you, just I'll just never forget having the driver drop pounds is often over looked in the chase for weight reductions and depending on their initial weight could see 30-50 lbs, maybe more, lost from the total weight quite quickly. In a bare bones car its hard to find that weight anywhere else affordably. If they are bigger guys it also leads to better health outcomes too so its go faster and live longer.

Hope that came across the right way.

By the way LOVE your coupe. Pretty much my deam car! Actually came across this thread looking for a build thread for your car

 

So I can tell my wife I'm only a 10th of a second over weight? I like the way that sounds

 

Me too.

 

The easiest way to go faster is to turn the '34 into a street car and stuff that flathead into a nostalgia rail.