I'm wanting to get the best mileage I can from my 1973 F100 longbed - new 390. How much better would the mileage be if I replaced my hood, fenders (front & back) and tailgate with fiberglass parts? Is it worth the money to save weight? Am I loosing strength and stiffness by doing this?


Thanks for any help,
Mike in Charleston

 

Welcome to FTE! Yo lots of good advice on this Forum from guys who know their stuff As for glass, I'm not an expert, but how much money are you going to spend? Is this your daily driver? What is your MPG now and what are you hoping for it to be? Finally, what do you have on your engine to make it breathe easier?

 

Maybe 2 mpgs. Not anything significant Keep in mind you have go make s support system to hold the fenders on

 

I predict that you would never recover the purchase price of the fiberglass panels in saved gas. Plus it won't fit properly or look as good.

It would be like saying that you want to replace your oem panels for Chinese panels to lighten up the truck by 30 lbs. because they are thinner steel.

There is so much time involved in aligning original parts and panels, to get it just right. I can't imagine trying to make aftermarket stuff work at all, it sounds like a nightmare.

Gaps have to be spot on or the doors rub the fender. Clearances have to be right for weatherstrip or the door won't close. Hoods have to fit perfectly with the contour of the cowl and have the provisions for bolting be spot on or the hood won't sit right. Fenders have to be shaped right at the top or it will rub the door. Fenders also are what ties in the inner fenders and core support and keep it all sturdy and sitting in the correct spot.

I also love the feel of fiberglass. It's amazing to rub it into your hands, arms and face. Mm mm.

 

Welcome to FTE, lots of good knowledgeable people here...and a couple of old grouches.
As for your question, I don't think it would be worth the expense. With these trucks, it not so much the weight, they are heavy, but its also the aerodynamics. Pushing one of these trucks down the road is like trying to push a barn down the road sideways.
Well made (and I stress, well made) fiberglass parts aren't going to be that much lighter than the steel they're replacing.
Plus the other thing you have working against you is the 390. FE's were never noted for good mileage. These were designed when fuel was in the 21¢-24¢ range. So great mileage wasn't a top priority. Don't get me wrong, I like the FE, I've got a 390 in my truck, you just can't expect good mileage from them.
You have to sit down and look at reality. Fiberglass parts are going to be expensive. Then there's the paint and bodywork to make them look good. None of this is cheap. How much are you willing to spend vs how much you will save? Even if you improve it 10%, it will take a lot of driving to make the swap pay for itself.
But, in the end, it's your truck. Do what you want. Make it your truck.