Lowering a formula
 

Hi! Sooo i am thinking of lowering my 1970 formula. As of now it consists of 50 year old oem springs, and spiral shocks. The ride is not bad at all, but i do want to lower it. Any feedback on what everyone is using?
So far i have came down to Hotchkis 1909f big block coils, And 2408c rear leaf springs. Or the pro touring f body gt comp kit. Also thinking of the rear windowed forward leaf spring mounts from ptfb. Bilstein shocks will be absorbing the bumps
In the end i am looking to lower the car about 1.5 inches. Looking for a ground to fender height of about 26-26.5 inches. Its about 28 right now.
Thank you. Have a great day!

i vote for the PTFB GT kit. hard to beat performance & stance for the price. i have that kit on a 72 firebird & it sits great & exactly as advertised. ~1.5" drop in the rear & ~1.5-2" in the front. handles great with their supplied steel adjustable shocks but im sure there are better shock options.

i also have their subframe connectors that fit great & install to the rear ends of the subframe, not under the bushing like some of the cheaper ones & the front of the rear frame rails. also have their G-braces but havent installed them yet. IMO, PTFB is the best price/performance kits out there.

Thanks for your opinion. I have many good things about the ptfb kits

heres a couple pics to give you an idea of how it sits with the PTFB GT kit, this is with 225/70/15 tires. & the rear shackles are set on the lower of the 2 options, can raise it a little on the higher setting.

76 Trans Am. Two years ago, I installed UMI tubular uppers and lowers, and their A225-550R coil overs (Viking). On the rear I used Hotchkis leaf springs (2409C) and their matched at the time Fox shocks (I believe they used to match up with Bilstein shocks). Also used the Hotchkis frame connectors (4013), a huge upgrade from my old Lakewoods. From PTFB I used their heavy duty leaf spring plates which are super – no bending and take the larger diameter U Bolts. Night and day difference and I am very happy with the outcome, both handling and the stance. Be forewarned the ride will be harsher. I expected it so it was not a concern or disappointment. I also had to rework the exhaust system due to the reduced clearance. To do that I went to the flatter Borla Pro XS Series (40352) mufflers and swapped my long tubes (Hedman 4-Tube) to Hedman shorty headers (26164). I didn’t really notice a loss of power, although I don’t track it so have no idea if it made a difference. The Borlas droned (my Welded Dynomax didn’t) but that was resolved by adding Vibrant resonators immediately after the headers. There are a ton of combos out there and you can’t go wrong with most. For me, this combo worked. As added info, I was able to easily get 285 40 18s in the back using a 10-inch wheel with 5.75-inch b.s.

Pro touring GT in back, saggy stock in front.

what spring rate did you use in the front . I have the same system in the front of my 70 TA with a 550 sprig . I'm thinking 550 may be to stiff Thanks

I went with the 550 lb springs after a discussion with UMI technical, based on the 455 block. Its stiff but not too stiff, and the handling and cornering are awesome now. Maybe the 450 would soften things up, but based on what I experienced maybe the lighter springs would have created issues simply due to the fact the car is lowered and there is less room for movement. I had to spend some time tweaking both the compression and rebound adjustments to dial it in, remove bottoming and not go too stiff. I'm no pro on this stuff but it works for me.

I also started by using their recommended settings, but had to do some trial and error to really dial it in. Pretty easy to do with the spanners and didn't take that long.

the 450 were for small block camaro the 550 they say BB chevy . I do have alum. heads, waterpump ,A/C .

just hope I can lower car to fender . I bought Detroit Speed rear leaf spring with 3 inch drop

Thanks for comments

If it helps, for reference I also have aluminum heads, intake, timing cover, water pump etc. This side shot might give some idea of fender height. UMI claims you can drop 3 inches with this coil over. I could have lowered more but I was targeting a level height through length of car.

yes thanks just what i want.

I'm going to use trans mount muffler from Pypes so some room on bottom ??

Thanks for posting pics. I almost wonder if i want the more than 1.5 inch drop. I run 26" tall tires currently (275/40/17 on year one 17x9 wheels) and i am sure my suspension is saggy from being so old. I wonder if an advertised 1.5 drop could actually keep the car about where it is, as i am sure its gotta be 1 lower than factory from time alone.. I guess i am on a google hunt for other cars with that same size tire and see if i can find suspension specs.
78w72, i see your car runs a 15" tire that is about a 2" increase in diameter, or 1" taller on the fender side than my tire. I like your cars stance, but may desire more due to the shorter tire i run.

yeah thats a short tire, have you considered a little taller tire to fill the wheel wells better? my info shows a 275/40 is actually 25.7 but that can vary a little with the brand of tire.

https://tiresize.com/height-chart/

each car & personal preference is different so all depends on your combo & how you get to the final stance you want. for example on my 72 i have big 2" tube 3.5" collector hooker super comp headers that hang down very low so im at the lowest i can go safely for street driving. with the 27.5" tall 15" tires, i plan to get some 17 or 18" wheels but will stick with a 27-27.5" tire so it fills the wheel wells & keeps the overall height of the car for header clearance.

but all in all im really happy with the PTFB GT kit's stance. i also have their tubular uppers but that doesnt really change the stance.

I ran 275 40 17 on 9.5 on the front and 315 35 17 on 11" rears (pic below). As mentioned, short tires don't fill the wheel well for the pro touring "look" many are after. If you lower it enough to "tuck" the short tires you end up with very little suspension travel and have to use a high spring rate to keep from bottoming. Pic below is with those wheels/tires and 1/2 tank of gas on Hotchkis suspension with Bilsteins. Car was lightened a bit but 200lbs of roll cage tubing took that back. The PT guys don't like the "gap" between the top of tire and fender lip but I'm more about performance than looks and wanted the suspension travel. When I installed the suspension in the early 2000's I was still using the car a lot on the street, like taking vacation trips 2000-4000 miles.

My new tires are even shorter 285/295 30 18's on 10" rims. New suspension is all PTFB with higher spring rates than their packages since it's more for track use. My car is now primarily being built for road course use so 900 lb front springs this time around. Most would not want to drive much on the street set up like that.

Full disclosure: My car is sponsored by PTFB however I'd started buying and switching to the PTFB products prior to the sponsorship so it's not like I'm recommending them just because of the sponsorship. Also, I make products for use with PTFB products so there's also that sort of weird connection. Dave's been moving all of his equipment into a different larger shop in the same complex and even though it's a short distance it's still a lot of time consuming work to move a business (BTDT several times). So ordering PTFB products currently might require a bit of patience.

https://hosting.photobucket.com/albu.../14less008.jpg


EDIT: Because I'm sure some would wonder why switch to 18's when I had 17's already? You can't fit the really big brake kits in the 17" wheels. My new Baer brakes are 14" rotors front & rear. Because my car started life as a lowly Esprit the original wheels on my car were 14" !!!! hahaha

https://hosting.photobucket.com/albu...hres/011-2.jpg

Hello, and thank you not a t/a. I have pretty much came to the conclusion that i am going to reach out to Dave at ptfb, and get one of his suspension kits ordered tomorrow.
On a side note, after the update to the suspension, i may buy a larger wheel. I will handle one thing at at time. Btw, Not a t/a, 17x11 wheel? Bother you for wheel specs? May i ask for a picture from the rear and is that mini tubbed? Are you running Oe location leaf springs, not a 4 link? Have you run tailpipes ever or just side exit exhaust? I have a 17x9 in the rear, looks like i could go wider. i have 3" pypes tailpipes and 3" oem appearing hockey stick tips. I have plenty of room there. Thanks.

No mini tubs, no modifications to the wheel wells or fender lips at that time (lips now rolled while I had the body to bare metal). OE leaf spring location, no 4 link. I don't think I had stock exhaust with the wide wheels, but memory faded after 20 years. Rears were 5.75" backspacing IIRC and I had 3 different rears at the time I used to swap out based on what I was doing. 8.2" Pontiac 10 bolt 2.72 ratio, 8.2" Chevy 10 bolt with 3.73 ratio, and a 8.5" "corporate" with 2.41 ratio. The 12 bolt your Formy should have in it may be a slightly different width than the 10 bolts, the experts here could tell you. So, MEASURE MEASURE MEASURE before ordering custom backspacing. Every car is different and what worked on mine might not on someone else's due to weight, ride height, suspension, tires, payloads, etc.

I would get a slight rub in the rear on the inside of the wheel well above the shock if I hit the angled corner curbing on certain corners of certain road courses too hard at high speed. Considered a Watts link but decided it wasn't worth the expense and weight. Did not have rub issues in street driving. The front tires would slightly rub the 1 3/8" hollow sway bar at full lock which only occurs a low speed in paring lots and what not. Daves high clearance solid 1 1/4" front bars allow more tire space there.

Bottom pic because I was often asked how much a 275/315 combo sticks out, they didn't.

https://hosting.photobucket.com/albu...nterior454.jpg

https://hosting.photobucket.com/albu...ps935dda21.jpg

Great car NOT A TA. Actually, when doing my research I referenced your car a lot. It shows up in a lot of places. In addition to checking out lots of lowered second gen F Body cars I also liked the “1976 Pontiac Trans Am - Shaken, Not Stirred” articled in Hot Rod magazine 2010 for wheel etc. sizes. I upped my wheels from 15 to 18 inch only because of a brake upgrade. Prefer the “old school” look of the 15s and fat rubber, but you can’t have it all. Big Matt, for added reference (although not 17 inch) my 18s are 10 inch in the back with 5.75 bs and 8-inch front with 4.75 bs. 285 40s on the back with no rubbing (except flattened seat belt bump – cut it out and welded a flat piece in its place with no adverse effects to seat belt retractor). Lots of measuring in advance before purchases were made because it seems each car is always slightly different (great 1970s QA QC). Front 245 45s fit well, just needed to grind down the upper inner fender body bolts and “massage” the driver inner fender way down and behind the battery where its invisible except to me. I chose 18 inches for tire height options. Really wanted the 275 60 15 height, but still came up shy.

I am thinking that after i get the suspension where i want it, i may go to an 18" wheel.. i see the bandit 2 wheel is a USA made(Yay!), 2 piece billet i think, is made is 17x11 and 18x11. I like the bandit 2 wheel, as my car already has wilwood brakes, to be honest i can hardly see the rotor, or caliper. i prefer the larger window openings of the bandit 2. i will post back after i get some suspension on and maybe a few pics. Thanks

Matt, 76TA462 mentioned something else I forgot to mention. Another reason to go up to 18" wheels is tire selection in 17" sizes is getting smaller. A lot of tires that were available in 16"-17" sizes have been discontinued. Check to see what tires will be available for the wheel sizes you consider before ordering wheels.