1970 Pontiac Grand Prix, too HEAVY?

[TanMan]

About to dive into a fun project: transforming my 1970 Pontiac Grand Prix into a pro touring machine. Though I’m new to this, I do know that weight (and weight distribution) is a crucial factor in building a car for autocross/road course racing. So the big question is: how heavy is TOO HEAVY?



The ‘70 Grand Prix is a beast, 118” wheelbase and 4,000+ lbs. I’m concerned that I might be headed down the wrong path with such a heavy machine. It’s a great street cruiser so I don’t plan on “gutting” the car to remove weight. Just wondering if I ought to hold off and try to build a much lighter car. (I don’t have the funds to acquire a ‘69 or ‘70 firebird, but damn that would be fun!) Anyway, is 4,000+ lbs (without driver) just too much??

[c4racer2]

It’s heavy. But even more so is the aftermarket support for suspension setup is limited. Unless you keep it close to stock.
I would personally build a A body not a full size.

[alocker]

Im pretty sure this body style shares suspension with the A-body.

Weight is only relevant if you want to be competetive. Suspension, tires, and setup will make these pleny of fun but if your chasing lighter or newer cars then weight is a concern. Whats the typical front rear bias? I think these are pretty nose heavy which certainly doesnt help.

[TanMan]

From what I’ve learned, the suspension is 100% A-body, so luckily parts are everywhere. It’s essentially a ‘stretched A-body’ with 6 extra inches in the middle. Technically referred to as a G-body.

As for front/rear bias, I can’t seem to find that data anywhere. Nose-heavy might be fairly accurate though.

[c4racer2]

oh cool - in that case go for it. I was considering building a Monte Carlo at one point as a street cruiser - same idea, it's a stretched A body and suspension stuff is all compatible. But now I'm thinking if I do build a DD type of classic it will be a earlier A body 64-67 vintage - I just prefer the lines and the size of those. But this would make a great road trip car!!

[silvermonte]

I say run it and have fun with it. Who cares about being super competitive, you are not racing to make money so just do what you can and drive the crap out of it.

[68Formula]

Weight and distribution is very important. But if that's all that mattered this would be a Miata forum.

That thing is cool! Build it, be the only one at the track with one, and enjoy surprising the <censored> out of everyone.

Yes, A-body suspensions will swap on, and there's a ton of aftermarket support for that.

[TanMan]

Thanks for the feedback, guys. I’ve actually had many a road trip in this beast. It was my restored-daily-driver in the late 90’s and it hasn’t seen a lot of love in the past decade or so. Can’t part with it, so might as well pro-tour it!

Anybody else dealt with large, front-heavy cars? I don’t know how to pull weight out of it without going full-on racecar. I’m looking at ridetech coilovers, improved caster spindles, Wilwood on all 4 corners, and a 3.55 or so posi. Guess I won’t be road tripping without an overdrive mod to the TH400...

[68Formula]

Thanks for the feedback, guys. I’ve actually had many a road trip in this beast. It was my restored-daily-driver in the late 90’s and it hasn’t seen a lot of love in the past decade or so. Can’t part with it, so might as well pro-tour it!

Anybody else dealt with large, front-heavy cars? I don’t know how to pull weight out of it without going full-on racecar. I’m looking at ridetech coilovers, improved caster spindles, Wilwood on all 4 corners, and a 3.55 or so posi. Guess I won’t be road tripping without an overdrive mod to the TH400...

As far as moving more bias to the rear:
Aluminum radiator and electric fans.
Move the battery to the trunk.
Aluminum heads, intake, block, etc.
Tubular a-arms can weigh less than the factory stamped steel sometimes.
If it's the same radiator core as an A-body, there are companies that sell aluminum ones (but expect to pay bucks).
An "LS" engine, even if iron block, is significantly lighter than a Pontiac.
Hollow front sway bar (probably wouldn't weigh less than the solid stock, but would be much stiffer without adding significant weight).
Rack and pinon conversion (not simple or cheap though).
Headers instead of cast iron logs.
Lighter (and better bolstered) front buckets.
Manual trans. in most cases will be lighter than automatics with torque converters and fluids, plus won't require a trans cooler.
Manual brakes or hydraboost.
Front discs (rear discs I think would still be similar to drums because of the parking brake mechanism).

Neutral (not shifting significantly fore/aft):
Any structural bolts you remove, you could replace with titanium. Non-load bearing screws (like interior) could be replaced with aluminum.
Aluminum or carbon fiber driveshaft.
Aluminum wheels.

Less overall weight but removed from rear:
Sheet-metal fabricated 9" rear with aluminum center section.
Hollow rear sway bar (also more of a weight avoidance like the front).
Smaller gas tank or plastic-based tank.

[68Formula]

Almost forgot. I recently removed about 30lbs from the front of mine using a combination of intermittent fasting, limiting average daily calories to 1800-2000 calories, daily walks, occasionally biking or swimming, and resistance training 3x per week using a 5x5 program.

[TanMan]

Wow, quite the comprehensive list! Great stuff.

What I read was, “money, $$, more money, $$$, and BIG money”. So yeah, I read ya loud and clear. Shouldn’t deceive myself and pretend this will be affordable.

I do love that with all of these mods and creative weight reduction, these are still fully functional, street-drivable cars. Head’s in the right place, wallet’s not.

[TanMan]

And it’s funny, the 30 pound reduction in the driver’s seat doesn’t cost a penny..

[Tsaints1115]

Don't be a cookie cutter! That car is awesome.

And more weight can always be overcome with more HP. It's the power to weight ratio that is what you feel.

[gscherer78ta]

Just run it and have a lot of fun. It will take a while to learn the car and then to learn how to drive fast and then you can decide on what is the best direction for getting faster from that point! I love seeing different cars at events! Even the F bodies are getting to be cookie cutter cars out there- Dare to be different!

[sodak65]

That is an A body not a full size. Do some research.

[jimco84x]

I don't know actual numbers, but had a 69 Grand Prix and I can tell you that you could stand between the engine and the radiator if the fan shroud was removed. The engine is further back than the hood line would suggest. It's still heavy, and has a lot of overhang front and rear but don't let any of that dissuade you. I think it would be a cool car.

[OLDFLM]

Jeff Schwartz did it in a 1982 Cadillac Fleetwood Brougham nearly 20 years ago... you can too!

https://www.schwartzperformance.com/...wood-brougham/

"Cadillac Attack"

Measured Performance
•1.02 Lateral G’s on skidpad
•11.80 @ 118 mph in ¼ mile
•0–60 4.0 sec
•Top Speed: 150 mph

Frame & Suspension
•Schwartz narrowed and boxed stock chassis
•12" single piston GM brakes, front and rear

Engine
•Schwartz 700hp 500 cid Cadillac Eldorado engine (eg. big heavy cast iron V8)
•Holley 850 cfm
•Custom headers
•NOS Big Shot 225hp
•Ported heads
•custom grind hydraulic camshaft

Drivetrain
•TH400
•Custom driveshaft
•GM 8.5 ten bolt

Exhaust
•Custom 3” dual-exhaust system with Flowmaster mufflers

Wheels & Tires
•Centerline Forged Billet wheels; fully polished
•17x11 with 315/35/17 Nitto Drag Radials
•17x9 with 275/40/17 Michelin Pilot Sport PS2 tires

[WallaceMFG]

I agree, don't be a cookie cutter! Build it how you want, and have fun with it. That is the most important part. Plus, your car will be unique in stead of blending into the sea of Camaros.

That big car done up with the right stance and wheels will look pretty cool!

[68Formula]

I don't know actual numbers, but had a 69 Grand Prix and I can tell you that you could stand between the engine and the radiator if the fan shroud was removed. The engine is further back than the hood line would suggest. It's still heavy, and has a lot of overhang front and rear but don't let any of that dissuade you. I think it would be a cool car.

It appears the extra 5" of wheelbase is moving the front axle forward of the engine compared to the A-body. If that's the case, then the weight distribution may not be as bad as the OP thinks. Be interesting to get it on some scales and compare to a GTO.

[c4racer2]

Oh if that's a car you already own - by all means build it. Hell yes!!

I would add aftermarket AC to it as well!