Lateral-g Forums - The 14 Car Performance Therapy Project Rushforths, Baers, Yokohamas, and more

Lateral-g Forums (https://www.lateral-g.net/forums/index.php)

- Project Updates (https://www.lateral-g.net/forums/forumdisplay.php?f=16)

- - The 14 Car Performance Therapy Project Rushforths, Baers, Yokohamas, and more (https://www.lateral-g.net/forums/showthread.php?t=34074)

With the rear of the car in final primer I spun the car around (Go-Jacks are awesome!) and turned my attention to lining up the doors and front end sheet metal. I'd loosely assembled everything to determine if I'd be able to use the 81 subframe, 70 steering, and 70 core support with the solid body mounts. There are differences in the subframe front horns that affect the position of the bumper brackets and steering but with various modifications it looks like I should be able to get everything to fit.

The door hinges were installed bare metal to bare metal at the factory on the 2nd gen F body cars I've worked on. If the area where the hinge mounts is covered in primers/paint it's a lot more difficult to line up the doors because the paint sticks together when the bolts are snugged or tightened. Then if you try to move a hinge just a little while aligning things it usually jumps farther than you want it to move once you get it to pop free.

So I sand down the area on the cowl and door as well as the hinge surfaces to make adjustments easier. Then because I'll be leaving the hinges on the cowl when the doors come off for the cut ins I sanded down the final primer that was already there to 320 for paint because it's easier to sand without the hinges in the way (they'll also get the Scotchbrite scuff before paint).

Once sanded, a little spray lithium grease gets shot inside where the plate slides around in the cowl and door and a thin film of grease where the hinge touches the cowl and door. This allows easier adjustment of the doors and a bit of corrosion protection. Careful attention to keep grease off areas that will be painted is a must and after the hinges are mounted wax and grease remover used all around hinges to remove any possible residue.

http://i240.photobucket.com/albums/f...pspg0mywq2.jpg

http://i240.photobucket.com/albums/f...psurzs3agw.jpg

I'm currently working on front end assembly/panel alignment and some fender vent aero mods I'll talk about in my next progress post. However I've been wanting to post about this problem unique to 70-73 bird's for years and today's the day!

Soapbox time! 70-73 Firebird front bumper and panel alignment.

I was a car guy teen when these cars were new and been researching/studying the bumper mounting , panel fitment, and the gaps for the past 25-30 years since my stepson got his first 70. Most of the 70-73 front ends on birds I see now have not been assembled/aligned correctly. THE FRONT BUMPER IS NOT SUPPOSED TO TOUCH THE FENDERS.

There is supposed to be a gap. It's wider than people want to see. Nobody likes it, not even the folks at Pontiac liked it when they were new. As you can see in the pics below the marketing people at Pontiac photoshopped (was that a thing then?) the gap between the fender and bumper right out of some of the pics in the 70 brochure because it looks "funny".

I see many beautiful cars where the owners have taken every step they can, buying NOS and correct original pieces for crazy prices just so they know they've got the right stamping's, date codes, etc. only to see the whole front end isn't panel aligned correctly. I feel bad for them because they just don't know. To me it's almost like hearing someone say they've got a "Big Block" Pontiac.

Soon after these cars were built they started getting in accidents etc.requiring bodywork and paint. IF the person took it back to the dealer the shop might have put the bumper back on correctly however many shops might just try to eliminate or reduce the gap if they even knew there was supposed to be a gap. It's been over 45 years since these cars were built and so even a body man who was in his 20's is probably retired even if he was a body man his whole life. So the folks who've been repainting these cars the past 30 years or so probably never even saw these cars new and don't realize the bumper isn't supposed to touch the fender. Most in the restoration/ body repair business now never saw these cars before they started being reassembled wrong so they try to split the differences and make the panel alignment/gaps look as good as they can with the bumper tight to the fender because they never even saw one with the correct gap. The misconception has gone on so long now that the majority of the cars I see now are assembled wrong and look kinda wonky but few realize why. The poor panel alignment is often attributed to the lower quality sheet metal stamping of yesteryear.

The subframe, bumper brackets, and bumper (as a solidly bolted structure) were isolated from the unibody,fenders, core support, splash pan, and core support/latch brackets (again solidly bolted structure) by 8 rubber bushings allowing the 2 sections to move slightly independent of each other. 4 rubber body mounts, 2 rubber core support mounts, and the 2 rubber upper bumper mounts. This allowed movement of the two structures individually and so a gap was needed between the fenders and bumper to prevent the bumper being deformed on uneven surfaces and when the car was jacked up. When the first urethane bumpers arrived on the 69's they put a rubber gasket between the bumper and body and people didn't like it so in 70 they reduced the gap and left it open.

The assembly manual says like up to 3/16" gap but from what I've seen the gap needs to be roughly 3/16" - 1/4" on most of the cars to get everything lined up as well as can be keeping in mind that factory stamping and tolerances of early 70's cars was nothing like today's cars.

In this first page from the brochure you can see that the marketing guys made the gap disappear on the passenger side of the upper image while it is clearly seen on the lower image.

http://i240.photobucket.com/albums/f...ps53db5f97.jpg

On the page below you can clearly see the gap, note the front of the hood lines up with the front of the fender.

http://i240.photobucket.com/albums/f...ps200f0ca5.jpg

Apparently the marketing folks figured the gap showed up waaay too much on a white car.

http://i240.photobucket.com/albums/f...psd6233dc1.jpg

Pic below is exaggerated to show how the body lines and fitment get screwed up. Think of it as taking a slice out of a cone and then trying to mate the remaining pieces. The gap needs to be roughly 3/16" - 1/4" on most of the cars to get everything lined up as well as can be keeping in mind that factory stamping and tolerances of early 70's cars was nothing like today's cars. When folks try to have the bumper touch the fender it causes problems aligning the front end sheet metal. Several problems arise and folks try to juggle all the pieces to minimize the affects but the pieces won't line up well so the common thought is "They just didn't make the cars very good back then"

These are the most noticeable effects of trying to have the bumper touch the fender.

1. The hood sticking too far back toward the windshield and sticking up even when the hinges are adjusted to the max trying to lower it.

2. The middle of the hood arches above the fender. Commonly attributed to the "Formy arch" or lousy hood springs. It's actually also caused by the hood being too far back and the arch of the hood not matching the arch of the fender.

3. When the bumper is tight to the fender people pull the fenders in toward the hood trying to get the points on the top of the bumper to line up with the top of the fender. this causes too small of a gap to the hood and often the car gets assembled without the side rubber hood bumpers because they push the hood up causing the mid hood arch to be off even more with the fender.

4. When the fenders are pulled in, the bottoms of the fender get pulled in afterward when trying to get the side of the fender to curve like the side of the bumper. Then the splash pan seems like it's too long.

5. The side body line will be off because when pulling the bumper tight to the fender it also gets raised to have the top of the bumper flush with the top of the fender. So the bumper body line ends up slightly higher than the fender body line. Sometimes this gets "fixed" during bodywork with filling/blocking if the bumper is on the car at the time.

http://i240.photobucket.com/albums/f...psqlvmwxjp.jpg

The crude sketches below show how the car is built. The main portion of the car is comprised of the unibody along with all the front sheet metal bolted solidly together (excluding hood because it's on hinges). It includes the fenders, inner fenders, inner fender extensions, core support, latch support, and splash pan. The smaller section includes the subframe, bumper brackets, and bumper (with lights and grills) bolted solidly together with the front suspension and steering attached. A third section is the engine/transmission bolted solidly together and "floating" on rubber mounts over the subframe.

The gap was necessary to allow the two main sections of the car to move a little independent of each other without damaging the sides of the bumper and paint on the leading edge of the fenders.. Even if you use solid body mounts the bumper still needs the gap to get the panel alignment correct because it was designed knowing the gap was necessary and the body lines needed to appear to flow over the gap.

http://i240.photobucket.com/albums/f...psd1uncyu6.jpg

Came across some pics on another forum that demonstrate how NOT to line up the bumper. This is a classic example of what happens when folks try to have the bumper touch the fender and don't know what they're doing is wrong. As an added bonus it also shows how the more flexible formy hood reacts. Don't worry, I'm not picking on someone's car that's being used like this. It's already apart for restoration.

The bumper below looks like it was installed while the car was on jack stands or a lift and they tried to have the bumper touch the fender. Then when they dropped the car on the ground the result was popping the paint on the drivers side of the bumper and a funny gap on the passengers. The hood was moved back so there would be a gap and the hood corners by the windshield probably got sanded off because they looked funny. The fenders were pulled in toward the hood in front trying to match the bumper causing the raised section of the Formy hood mid fender. Also notice the side body line of the bumper is now too high compared to the fender.

http://i240.photobucket.com/albums/f...ps2yhvzsnk.jpg

[URL=http://s240.photobucket.com/user/NOTATA/media/0321151817_zpsruxsxa1e.jpg.html]http://i240.photobucket.com/albums/f...psruxsxa1e.jpg

One of the aero changes I wanted to make involves the fender vents. I'm planning on a splitter and pan under the engine compartment. So I need to evacuate the under hood air that comes through the radiator and reduce high pressure air under the hood that causes lift. Many have experienced the effect called "float" at high speeds (over normal highway speed) in regular cars and some models are worse than others. The 2nd gen TA fender vents help reduce that and I want to maximize the benefit.

So I began by doing some tuft testing on the stock vent with the screen removed to see how it performed. Then I made cardboard modifications to the vents and tested again. I spent more than a day on this process testing various configurations and came up with a couple modified vents that should help keep the air pressure lower under the hood. For a more detailed version of the testing and how the modified vents were made see this thread which just covers my aero mods. http://transamcountry.com/community/...?topic=71522.0

The stock TA vent has a hole with surface area about 15 sq. in. The screen in the stock vent blocks off about 5 sq.in. reducing it to 10 sq. in. and creates turbulence as the air tries to exit through it. As I went through the testing process I changed the angle of the leading edge, added wicker bills of varying heights and expanded the opening. The modified vents now have openings about 3 times the sq. in. with steeper leading edge and the design of the housings seem to draw a lot more air from under hood. One set will be used for Land Speed racing type events (less drag) and the one with the wicker at the leading edge will be for road course use (more drag but also more evacuation).

As I mentioned it was a long process and lots of variations were tuft tested. Here's a few pics to show a couple of the differences.

Stock vent with screen removed.

http://i240.photobucket.com/albums/f...psth3q9sas.jpg

Modified vent below with steeper leading angle and stock opening.

http://i240.photobucket.com/albums/f...ps9hux3vb5.jpg

Modified vent with wicker and extra slot opening below.

http://i240.photobucket.com/albums/f...psviry1faw.jpg

This version seemed to get the best results for evacuation with reduced turbulence. But it wasn't enough "better" to warrant all the extra effort I'd have to put in to incorporate strakes into my design.

http://i240.photobucket.com/albums/f...ps4etgb5xy.jpg

Moving along with aerodynamic modifications this is the front end treatment.

The splitter/tray/air dam combination I've got in mind is a bit unusual from those I've seen on other cars.

A. Hinged to allow the splitter to be pushed up if I hit corner curbing or something. Splitter could rise till it hits the stock air dam. I've never whacked the stock air dam and I'll probably only loose maybe 1/2" ground clearance.

B. Two piece splitter/tray so I can have various splitters that stick out more or less with the biggest reaching out as far as the leading edge of the bumper and out as wide as the wickers on the wheel flares.

C. Height adjustable so I can use for street, LSR, Drag strip, road course, or open road with various height air dam extensions.

D. Various air dam extensions that will fold up if the splitter gets pushed up. Probably three versions, small for drag race & street , medium for road tracks, and a deep air dam extension with minimal ground clearance for LSR with no splitter but supported from behind by the tray section.

E. Breakaway provisions so if something bad happens, damage to the car would be minimal and hopefully confined to the splash pan and stock air dam/wheel flares.

F. Cheap/replaceable using as many pieces of scraps left from other projects and junk people gave me as I can. I gathered all the stuff I've been collecting and figured I could make something out of it even if just a prototype. It'll get the scraps out of my way and hopefully save me a few bucks.

While today lots of folks use CAD I still use DIG (Draw In Garage) for projects like this. Here's the basic concept drawing. The tray section the various splitters will be attached to has a smaller footprint than the stock air dam/wheel flare section.

http://i240.photobucket.com/albums/f...ps8uu4aohi.jpg

http://i240.photobucket.com/albums/f...psxpirxxyt.jpg

Based on my less than artistic freehand quick sketch of what I envisioned I got to making stuff. Below are pics of the splitter/air dam combinations I'll be testing. Not sure if there'll be any issues with using cable supports which might allow the splitter to oscillate or bounce. If there are issues I'll install solid splitter supports.

The contraption in it's current configuration adds about 27 lbs to the nose of the car. This includes a lot of hardware weight I'll eliminate if it works as planned. The splitter easily supports my full weight with just 2 of the cables in place. The hinging ability works and so in theory might save me from wrecking it. Front sections of various lengths can be slid into place in just a couple minutes. I started making plastic pieces to mate the original air dam and wheel flares with the splitter and will finish them when I determine the exact heights I'll try the splitter at once the car is assembled and on the ground with full weight. 3/8" plywood is being used for testing the front sections and I may use a different material later if everything functions as I'd like once road tested.

http://i240.photobucket.com/albums/f...psirxstnu6.jpg

http://i240.photobucket.com/albums/f...psgsc65mzj.jpg

http://i240.photobucket.com/albums/f...psksroqlgy.jpg

http://i240.photobucket.com/albums/f...ps91ms5mvr.jpg

http://i240.photobucket.com/albums/f...psxyfgvtln.jpg

http://i240.photobucket.com/albums/f...psnqctt6dr.jpg

Quote:

Originally Posted by NOT A TA (Post 645041)

Sounds like a cool car and I'm sure others like myself would love to see it. If you don't want to make a project thread then at least add it to the garage built thread with the description you wrote above copied and pasted. I had a very low miles 64 Biscane back in the 90's, not as cool as a bubble top though and was the last of the Chevy X frames.

Thanks. :) Ok, I'll make a quick build topic with some pictures and see if there is any interest.

Very cool.

I like the splitter idea, but I think you will get oscillation with the cable mounts if it doesn't simply get stuck in the up position after a bump gets air under it. From a weight angle, what if you made the final from aluminum, fiberglass or carbon fiber? I think aluminum would be the simplest. With fiberglass being reasonably light, strong, inexpensive and reasonably repairable. I've never worked carbon fiber because I can't make fiberglass pretty enough to show off the weave and never needed that type of weight reduction.

Quote:

Originally Posted by gofastwclass (Post 645066)

I like the splitter idea, but I think you will get oscillation with the cable mounts if it doesn't simply get stuck in the up position after a bump gets air under it. From a weight angle, what if you made the final from aluminum, fiberglass or carbon fiber? I think aluminum would be the simplest. With fiberglass being reasonably light, strong, inexpensive and reasonably repairable. I've never worked carbon fiber because I can't make fiberglass pretty enough to show off the weave and never needed that type of weight reduction.

I have a test in mind once the car is back on the road to see if the splitter would stay up at speed. After track testing various configurations of the splitter and deciding whether rigid supports are necessary on a size/design I'm happy with I'll make much lighter ones. Since the time I made the splitter I've had the opportunity to do some tuft testing on another car with the same body, ride height, tire sizes etc. I'll discuss more later on in the thread but here's a pic at highway speed, note all the tufts below the grill openings pointing straight down. Leads me to believe there will be enough pressure on the splitter to push it back down if it gets bumped up, but testing will be the best way to find out.

http://i240.photobucket.com/albums/f...psr3kuxkxn.jpg

I love the R&D you're doing, basically a poor man's wind tunnel. Aero is so important and most people don't even know it exists.

You seriously remind me a lot of how I approach things. You're also letting me know I'm not crazy - or at least I'm not alone in my crazy. Hahaha

Thanks for sharing.

Great work and a very nice write up!