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 Post subject: Potentia v8
PostPosted: September 29, 2020, 10:23 pm 
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Posts: 101
1uz-fe with twin ebay turbos(roughly gt-28's in specs) mated to a 350z 6 speed, this will be controlled with an ms3x ecu and the idea will be to run low boost of 7-8 psi. Should put it in the 420ft/lb and 380whp based on the car most of these parts came from. The front brakes are 4 pot fixed caliper from a 99 ls400 on modified sc400 hubs, this is forcing a 17" wheel though tire width wont go past 245 on the front. Its all a bit ridiculous but the project was spawned from having most of these parts left over from an old Lexus sc400 project, its not going to be usable power but the main focus of this project is the act of building it more then an entirely friendly car. With the excessive drivetrain the chassis is going to get heavy to cope, its sticking with 16ga square tube but most of the sheeting will be 18ga steel for rigidity. In the long term its getting a full closed wheel body but that's its own undertaking once this thing moves under its own power. The goal is to be 1800lbs wet or less.
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Used the Gibbs book as a basis then built the car around the motor and transmission because of their immense girth, engine weighs roughly 370lbs and the transmission 125lbs. The garage floor was mostly level but shockingly the frame isn't true, its still very close and at the time it was more important to begin then it was to worry every detail.
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Shortened the sc400 steering rack.
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The lower A arms are 1.25" .120 wall, 5/8 heim joints, 3/16" plate, and rav4 Balljoints. Upper A arms are 5/8 heim for the joint, 1/2" at the chassis, and 1" .120 wall tube.
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Steering system is mounted though the rack is only tacked for now, the beams around the column have yet to be triangulated because there's not much reference material for building this upper structure. With the engine being so large it ate up all the space for traditional bracing through the bay so this 3/4 tube attempts to reinforce the engine mounts and upper beam. Some fiddling showed the chassis would deflect about 5mm on a rear corner when lifted with the drivetrain installed, I believe most of this flex is in the engine bay and above the transmission, hence building the firewall directly behind the motor(to eventually fill in with bracing)
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 Post subject: Re: Potentia v8
PostPosted: September 30, 2020, 8:04 am 
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Location: Charlotte, NC
Welcome to the club, that will be an interesting build. I recommend test fitting the brakes before settling on the firewall as I think the diagonal will interfere if using floor mounted brakes.

And, Instead of an upside down "V" to reinforce the front hoop, you might consider one diagonal going from passenger bottom to driver top. That would likely give you the room for your steering rack and provide enough strength.

Keep it up, this will be a monster to drive when you get it finished!

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 Post subject: Re: Potentia v8
PostPosted: September 30, 2020, 8:57 am 
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Joined: July 17, 2008, 9:11 am
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Location: West Chicago,IL
One alternative to the diagonal at the brake is to remove the diagonal altogether and weld a steel sheer panel in it's place. The passenger side too. I noticed that the cross piece that would be above the transmission is missing. That piece provides chassis torsional strength. If this is to clear the trans. Perhaps adding 2 diagonals to the cross piece above and including another sheer panel on that would work. You might even be able to add a cross tube above the trans to these 2 diagonals.

These (sheer) panels would be needed anyway for a firewall.

I'd like to hear some comments on that.


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 Post subject: Re: Potentia v8
PostPosted: September 30, 2020, 9:57 am 
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Joined: September 29, 2020, 8:24 pm
Posts: 101
Mnot wrote:
Welcome to the club, that will be an interesting build. I recommend test fitting the brakes before settling on the firewall as I think the diagonal will interfere if using floor mounted brakes.

And, Instead of an upside down "V" to reinforce the front hoop, you might consider one diagonal going from passenger bottom to driver top. That would likely give you the room for your steering rack and provide enough strength.

Keep it up, this will be a monster to drive when you get it finished!

This is an excellent community, glad to finally make an account after drooling over other builds for years.

I believe the V has to stay, the passenger side will be acting as a point for the steering racks 3rd mount. The driver side bar will get cut back slightly more, sheeting on the backside and 3/4 welded to the front? The shock angles are at or near 45° so the front end is going to be under alot of stress.

The plan is for the brakes and clutch M/C to face the driver, this will end up placing them fairly high but should below the steering column.


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 Post subject: Re: Potentia v8
PostPosted: September 30, 2020, 10:28 am 
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rx7locost wrote:
One alternative to the diagonal at the brake is to remove the diagonal altogether and weld a steel sheer panel in it's place. The passenger side too. I noticed that the cross piece that would be above the transmission is missing. That piece provides chassis torsional strength. If this is to clear the trans. Perhaps adding 2 diagonals to the cross piece above and including another sheer panel on that would work. You might even be able to add a cross tube above the trans to these 2 diagonals.

This forward firewall was born out of the need to brace the missing bar above the trans, it sits high because the drivetrain slides up and out requiring alot of room in that area. The yellow braces you drew in won't be able to touch but I've drawn an example.
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Not sure what to do about all the in between space of the firewall and column mount.

Diagonal at the footwell exists partly for accident protection, all of the occupant area is being stichwelded in steel sheet, though if i can find gauge thinner then 18 ill use that in some areas.


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 Post subject: Re: Potentia v8
PostPosted: October 1, 2020, 5:13 pm 
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Ended up needing to cut out the RH brace inside the engine bay because the alternator needed the space. Perhaps that beam should placed further back, but it dosent seem like any good triangulation if its just pressing against the side of another beam in an unreinforced direction. You can see how little room exists in front of the engine, its 2.5" from crank pully to the frame.
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The solution for this engine bay may end up being a removable brace that bolts over the engine, from the shock towers to the firewall. Maybe made out of bent 1" tube in an X brace?
Here are some more photos of as it sits since The original post was a bit light.
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 Post subject: Re: Potentia v8
PostPosted: October 1, 2020, 5:27 pm 
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Joined: April 15, 2014, 1:54 pm
Posts: 470
A bolt in X brace is a very good way to gain torsional rigidity with an otherwise open engine bay.


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 Post subject: Re: Potentia v8
PostPosted: October 1, 2020, 11:25 pm 
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Joined: August 2, 2009, 3:34 pm
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Location: Alberta
Those are massive wheel spacers!

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 Post subject: Re: Potentia v8
PostPosted: October 1, 2020, 11:58 pm 
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[url][/url]
Trochu wrote:
Those are massive wheel spacers!

2" adapters up to 5x4.75, they help clear the lca's at full lock and less importantly get the total width up to the 6ft mark.

Being such a light car excess bearing wear isn't a problem and the scrub radius will be tolerable. Things will change though, these rims are too wide to use for more then the testing phase


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 Post subject: Re: Potentia v8
PostPosted: October 2, 2020, 2:41 am 
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Location: Holden, Alberta, Canada
Hey sony, just a question for you.
Rule of thumb for front end/steering is that the inner control arm pivots (upper and lower) and the inner steering TRE (this is on a rack and pinion) should all line up if you draw a datum line through them at ride height and the steering centered. It's tough to see in the pics you've posted. Could you take a pic straight on at the front?
Another rule of thumb is the steering arms be parallel with the lower control arm.
This is from a guy that doesn't know crap about the mathematics of steering geometry but builds front suspensions using string and cardboard.
A straight on pic of your front suspension and steering rack at ride height would answer all my questions :cheers:

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 Post subject: Re: Potentia v8
PostPosted: October 2, 2020, 8:26 am 
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Relative to Perry's comment about the steering rack. You could try mounting the tie rod on top the steering arm. Would require reaming a straight hole in the arm and then fitting a Hiem joint. Make final bump steer adjustments with spacers on the steering arm. With that thick of a wheel spacer it is going to be a bear for slow speed parking. Are you going with power steering? As a rule of thumb for manual steering, keep the scrub radius under +/- 3/4".


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 Post subject: Re: Potentia v8
PostPosted: October 2, 2020, 11:06 am 
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horchoha wrote:
Hey sony, just a question for you.
Rule of thumb for front end/steering is that the inner control arm pivots (upper and lower) and the inner steering TRE (this is on a rack and pinion) should all line up if you draw a datum line through them at ride height and the steering centered. It's tough to see in the pics you've posted. Could you take a pic straight on at the front?
Another rule of thumb is the steering arms be parallel with the lower control arm.
This is from a guy that doesn't know crap about the mathematics of steering geometry but builds front suspensions using string and cardboard.
A straight on pic of your front suspension and steering rack at ride height would answer all my questions :cheers:

There will be bumpsteer because my rack is too narrow but height wise, its aligned with the lca. This is my best front end pic right now as its torn apart again.


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 Post subject: Re: Potentia v8
PostPosted: October 2, 2020, 11:10 am 
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davew wrote:
Relative to Perry's comment about the steering rack. You could try mounting the tie rod on top the steering arm. Would require reaming a straight hole in the arm and then fitting a Hiem joint. Make final bump steer adjustments with spacers on the steering arm. With that thick of a wheel spacer it is going to be a bear for slow speed parking. Are you going with power steering? As a rule of thumb for manual steering, keep the scrub radius under +/- 3/4".

In the end the its about getting to 0 offset, steering will be okay because the rack isn't a quick ratio plus it was fine with no P/S on a 3300lb car from which the hubs came(wheel on that where 265 with -2 offset)


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 Post subject: Re: Potentia v8
PostPosted: October 2, 2020, 3:31 pm 
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I think the inner steering tie rod joint should be offset from the inner control arm joint axis by the ackermann offset.


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 Post subject: Re: Potentia v8
PostPosted: October 2, 2020, 4:05 pm 
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Bobber wrote:
I think the inner steering tie rod joint should be offset from the inner control arm joint axis by the ackermann offset.

As in the steering rack should be located forward or backward based on degree of ackerman at full lock? Could you explain a bit more?


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