Technical Need some help with my 31 drag / street truck

I drive my 31 ford truck on the street. Plus I go to some Nostalgia, Drag races also. And based on my 1/8 vs 1/4 mile ETs. I am about 2 to 3 tenths slow. In the 1/4 mile. I have been thinking about, cutting some holes, slots, louvers ETC. In my front and rear fenders. My fenders are fiberglass, and 30 years old. So no big deal if I cut them. They might even look better. Has anyone done this? And I hope it will pick me up a few tenths. And does it really help? Common since says it should. Would love to see some pictures of Old Coupes or Trucks with this mod. Any help and advice on this, would be appreciated.

Thanks BAD-A

 

Got a photo of the truck?

 

take off 100 lbs, go 1/10 quicker in the 1/4 mile.

You won't do much by cutting holes in thin fiberglass.

 

It is in the avatar.

I thought it would help get the air out, that the fenders hold in. And go faster, without the front end lifting at high speeds. And not sure if I have a 100lbs to lose. Truck is only 2500lbs now.

 

Aerodynamics don't do much until you're going pretty fast, and then it will affect top speed, more than ET.

 

I am down MPH in the 1/4 also. Based on the 1/8 mile.

 

Could test your theory and just pull the fenders for a week and run it

 

Lot of reasons it doesn't pull as well in the last half of a 1/4 ..... Mainly not enough motor.

What et's are we talking about here? How many mph? What motor? What trans? What gearing?

 

Do like they did back in the day, pull the fenders when you race.

 

There are guys here good with numbers. So give us a few.
1 The et's and mph from your runs. 60 ft times also.
2 Weight of the truck.
3 Approx HP of your truck. Real HP would be better if you have dyno sheet even better.
4 Carb size
5 Rear gearing and tire size.
6 What you are tach readings going over the line.
7 Are you getting into high gear in the 1/8th? If you are where on the track do you hit top gear? General rule of thumb is top gear at half track in the 1/4.

You give those numbers to some of the drag race guys they can often spot where your problem is.

 

9 second 1/4 mile truck. And I have been racing for about 50 + years. So It is falling off, after the 1/8 mile. Plus you can see the fenders catching air, lifting and the front end feels light. You can feel it in the steering wheel.

 

Going thru 1/4 at 6400RPM. And thanks for the input. I would love to see some pictures of the front fenders, that are cut.

 

Cutting holes in the fenders won't streamline that vertical windshield, radiator, and visor.

 

Cutting holes may actually make it go slower, because they make turbulence. This is how "dive brakes" work on airplanes. The easiest way to go faster is to get a "slicker brick".

 

So true. I was hoping it would help, some at least.

 

9 seconds in the quarter?...fast street truck! What do you think it should be running?

 

That really helps if you are running in the neighborhood or 130+ on the big end.

If your car is geared/setup to run the 1/8 as opposed to the 1/4 mile track it is not going to perform well in the 1/4. Cars that have to be going full tilt by half track are geared and or tuned differently. The whole deal that I ran and eighth in X time and I should run the quarter is smoke. You have to retune for the long track.

 

It is geared for the street. But the gearing worked out, perfect for the 1/4 mile. Most 6.40 car are usually 10.00s in the 1/4. If they are naturally aspirated. And around 25 mph form 1/8 to 1/4. I am about 5 to 8 MPH slow, in the 1/4. And about 2 to 2.5 tenths slow in the 1/4.

But now to get back to my question. Has anyone done a back to back test? To see if, Letting air thru the fenders. Will pick up ET & MPH. And pictures of how you did the fenders. I am not really trying to debate, gears, converters, tire sizes, tuning ETC. I don't want to get side tracked on power

Thanks BAD A

 

The rise you are thinking due to trapped air is probably normal tire growth, they get taller as you go down the track.
Under 10sec and 6400rpm is impressive. Don't know how you could improve that without a major rpm change.

 

Those fenders are huge scoops, and I agree that it is affecting the front end lift, and causing drag. Air dams/front spoilers came into racing to reduce air getting under the car, so why is it so hard to see that those A fenders would definitely cause lift & then also lower speed/ET?

In 1933 or 34, the Desoto Division hired race driver Harry Hartz to drive a sedan backwards coast to coast to help sell the new Airflow body design principle, that did not scoop air like conventional front fenders did.

Go for a ride and stick your hand out the window in the shape of those A fenders at even 40 MPH...

 

I probably should not point this out because it makes me sound argumentative which is not the point but if you are 2 seconds off (which I actually doubt) you gearing is not right for the quarter. I am guessing that you are driving that brick 130+ on the big end. Perhaps letting a little air out will help we never tried it on a car that would go faster than 120 or so though the lights and did not see any change. But what the hell its worth a try.

 

I think you feel the same as me. About the aero. Plus the rear fenders are wider that stock, and hang real low. I think. I am going to raise the rear fenders. And give it a bob tail look. That should help in the rear.

 

But if I am going thru the 1/4 in high. At about 200 to 300 RPMs higher, than my 6400 shift points. Would that not be about a perfect gear ratio? And I asked for info. So I am not thin skinned.

 

That's a fast truck. My Bonneville experience tells me that closing off the front area would be more effective. More streamlined effect. However, we do run louvers on the deck lid which is thought to remove air trapped in that area. Louvering the back side of the front fender might allow the same. That being said it might make things worse. Lose the fenders. Street roadsters run very small fenders on the slat flats for a reason. Probably not much help. Just my 2 cents.

 

I think I would pull the front fenders, running boards, aprons and stuff and see if it picks up like one would think. But then I realize it's a lot of work to pull Model A front fenders and stuff just for a test plus, I'm sure the truck looks the way you like it right now (looks great btw).
Many cars in the old NHRA street roadster classes had holes, slots and other cutouts in the fenders like you suggest. Some used small close-fitting cycle fenders to get around the front fender requirement. Check out what the Brogie style Super Gas roadsters did back in the '80s and '90s, there may be some ideas there.

 

Thanks. I looked at the roadsters. 95% had slotted, or round holes in the front fenders. Great info. I assume. They think like I do. That is letting air thru instead of holding it. Really helpful. THANKS

 

I started to post a picture from Google search but I thought it wasn't HAMB period appropriate and might get the thread closed.
I bought a '33 coupe years ago that was a lakes car at one time, it had two rows of 3" holes in the back of the front fenders and the trunk lid had as many louvers as could fit on it. Since I was building it for the street I thought the fenders were ruined so I tossed 'em! I sure wouldn't do that now. They'd be cool.

 

Send the pictures to my email. [email protected] Thanks

 

Picture of the truck at the track.