Finished rough preliminary tubbing on the frame, now to start designing the suspension linkages.

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radXR650R@reddit

Ummm need more info. Searched previous posts so I see it's a 3000GT with a 8.1.... but is that a dually axle in the rear? Why the cut area in the trunk? What is the plan here?

Also, this is awesome.

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SillyTr1x@reddit

My Wild Ass Guess is the “dually” wheels are stand ins for some phat meats to be selected later.

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Vengeful-Wraith@reddit (OP)

Yes! But to be honest, it looks badass to me that dually setup... It'll actually to give me that meat (comes out to the equivalent of 450mm wide tires) to really help plant that 8.1liter torque down.

Maybe I'll do proper wide tires one day, we'll see.

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Special_EDy@reddit

Tires don't work like people intuitively think.

Wider tires in theory have exactly the same amount of grip as skinny tires.

Amontons' First Law: The force of friction is directly proportional to the applied load.
Amontons' Second Law: The force of friction is independent of the apparent area of contact.

That second law is important. friction-force = coefficient-of-friction × normal-Force. Or in English, Traction = tire-compound × weight-on-tire. So, the only way to increase the traction of the tires is to increase the weight on the tires, or to increase the stickiness of the tire compound.

There's some factors about tires being a pliable material which make it more complex: The tires deform into the rough surface of the road. But in the real world this just means that there is an optimum amount of contact patch for a given weight of vehicle on a particular texture of road surface. The same width of tire on your car will not be optimal for concrete pavement as it will be on asphalt, for example.

You associate wider tires with more grip because Motorsports tires are wider than production car tires. But Motorsports tires have more grip because they are super-soft racing compounds. Some are actually soft enough to be sticky, your road tires will never be sticky. Racing tires have a lot of other reason for being wider too, longer tread-life on a track car by having more material, increasing surface area to reduce pressure for sidewall deformation on a drag radial, and opting for a wider contact patch instead of a round one for cornering on a track car.

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Vengeful-Wraith@reddit (OP)

And what of the principal of suspension geometry causing artificial downward load on the tires imitating a change in weight?

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Special_EDy@reddit

It's the downward force applied onto the tire. So aerodynamic forces, suspension forces, and weight transfer can all act to increase the grip of the tire.

This is why the majority of your braking force will be on the front tires: besides a forward weight bias being typical, the weight transfers onto the forward tires under heavy braking and thus the front tires have proportionally more tractive force under heavy braking. Tire compound and normal force(weight) are the main factors in grip.

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Vengeful-Wraith@reddit (OP)

That makes sense... I guess more than anything this build is more show that being serious about true performance, but if I do want to go that route it's more the tire properties needing to be adjusted.

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Special_EDy@reddit

You just need good tires back there. Two skinny tires, one wide tire, what will matter is the compound.

You will need to adjust the tire pressure since you will have the load spread across 4 tires instead of two, but that would be true of a foot and a half wide drag radial as well. Pressure is more about the sidewall construction than contact patch.

And perhaps most interestingly, skinny tires are honestly better than wide tires for acceleration, in theory. Given a similar tire construction, a skinny tire will offer a narrow contact patch which is long front to rear, while a wider tire will offer a wide contact patch side to side but short front to rear. The narrow but long contact patch should perform better in straight line acceleration, while a wide contact patch has benefits in cornering. With a similar tire construction/compound/pressure, the contact patch will have the same surface area bur a different profile.

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Vengeful-Wraith@reddit (OP)

That's fascinating. I can visualize the theory on the contact patch geometry... Also in regards of pressure, would it be a linear change? As in, one tire rated for 35psi in this case actually means 17.5psi on both because it's a dually? Or is it not straight forward you think?

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Special_EDy@reddit

It's not linear, it tapers towards a plateau at the maximum pressure and load rating.

There is typically a minimum and maximum pressure. A certain amount of pressure is required to support the sidewall structure. Once this is met, additional air pressure will mostly put force on the tread of the tire.

You'll wear out the tires significantly faster with an under inflated tire, the whole tire will flex and heat up which will break it down. An overinflated tire will wear out the center portion of the tread faster.

A higher pressure will give you a smaller contact patch, but that contact patch will have more pressure between the road surface and rubber per square inch. Same static friction regardless of tire pressure and contact patch size, in theory.

Ideally, your tires will have a load rating versus tire pressure chart. Some truck tires are going to be built for higher pressures and a lot of weight capacity. Passenger tires, Motorsports tires, or better yet some drag tires, will likely have lower capacities for a given tire pressure.

Really, you're not needing to set any speed records or win strict races. So you just need to get above the minimum recommended pressure of the tire manufacturer, and get into the ballpark of proper load rating for your vehicle. Some light Passenger car tires with summer-tread and a fractionally lower pressure than normal( for example 25-30psi), will be fine. You can definitely find some stickier tires if you go shopping on Jegs or Summit, there will be plenty of appropriately narrow car tires for Motorsports and probably even tires for people wanting to drag race dually pickup trucks.

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Vengeful-Wraith@reddit (OP)

Wealth of knowledge my friend! Mind if I keep you in my Rolodex for future questions?

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Vengeful-Wraith@reddit (OP)

Will make for quite a show doing burnout competitions though

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Syscrush@reddit

If you swap out those duallies I am going to find you and wag my finger in your face.

Such an exciting project, good luck with it!

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FalseRelease4@reddit

oh no keep the duallies they're too cool 😂😂

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Vengeful-Wraith@reddit (OP)

Plan is for a high torque build. And yes that is a dually setup tucked into the original body. It's a Ford 9in axle with custom spline shafts and a Torsen differential for good power distribution. The hole is where the fuel cell will be partially inserted. (Also helps to stand and cut/fabricate the inside).

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radXR650R@reddit

Wild. Gona need some popcorn to watch this progress. Do you have a technical background? Can weld? This looks like quite the project.

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Vengeful-Wraith@reddit (OP)

I appreciate!

Also, sorta. I'm an inventor, so I've quite the experience with fabrication and connections with job shops in country and overseas.

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mxpower@reddit

I wish I could get by saying I'm an inventor, kudos to you good sir!

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bizzaro321@reddit

Okay, now I have to see where this goes

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pushingair@reddit

u crazy

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Vengeful-Wraith@reddit (OP)

Proper Daft B)

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Nutsack_Adams@reddit

This is the best thing to do to a 3000gt. Cut it up and put a different engine in it.

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Vengeful-Wraith@reddit (OP)

The original 6g72 was cool, but could only be taken so far .

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Nutsack_Adams@reddit

Are they cool? They aren’t that cool. The 4g63 is cool. Tell me why they are cool. I’m sure you know more about them than me. I think they are overcomplicated and under powered

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TP_Crisis_2020@reddit

6g72 was a very well built engine with few flaws, enough that mitsubishi used it in many different models of cars, even in the Montero/Pajero and Pajero EVO which was a Dakar rally homologation vehicle. The TT 6g72 in the 3si cars was an awesome engine that was essentially a "big block" 4g63 in power and durability. It never got its shot as a top tier tuner engine because of the 3si chassis mostly being a flop.

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Nutsack_Adams@reddit

Good to know! I kind of thought it was just a montero 3.0 truck motor with twin cam heads and turbos

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TP_Crisis_2020@reddit

Yeah, they used it in a lot of stuff.

https://en.wikipedia.org/wiki/Mitsubishi_6G7_engine

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Vengeful-Wraith@reddit (OP)

Pure nostalgia is why. Yes, underpowered, under beefed... Mine was different, I built an upper intake adapter to attach a M90 supercharger which kicked up the low end torque a bit, but ultimately I knew I had to replace it if I wanted to go further.

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Nutsack_Adams@reddit

At a shop I worked at I inherited a job from a tech who got fired. It was a vr4 in boxes. I think it had blown a head gasket, but the entire bottom end was taken apart too. I had to put this thing together. I have basically hated them ever since

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Vengeful-Wraith@reddit (OP)

I fully understand your pain. It's a level of complexity and cramped space.... Actually it's probably what killed aftermarket and tinkering on those cars that made them mostly forgotten.

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