The Huntress - AWD '69 Vert Ghia Project

[Piledriver]

The closest setup I can think of would be something like a modern AWD 911.
Power/weight ratio and weight distribution about same.
You could do much worse.

Perhaps use the ~whole front suspension?
With your fab skills (And Porsche parts) a Mendeola front suspension is an expensive paperweight.

[56SemaRag]

Thanks for the input Pile, I am still reading on the subject when I have a bit of down time.

Trying to get the bulkhead fitted permanently so I can start the front suspension, but I have to finish the pans first. As expected the channels near the end were tight against the pan so I reshaped the ends.

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[Piledriver]

Nice steady hand!
I cannot imagine life without a plasma and TIG anymore.

[GS guy]

Super nice beads on those welds! I can only dream my welds could look that good.
Not sure about adopting a McPherson strut design to a Ghia front end? Are you staying with the VW torsion bar design with AWD front knuckles? - see the Subarugears thread: https://www.thesamba.com/vw/forum/viewt ... &start=400
Unfortunately - like many threads the pics went away with photobucket. They're working on a VW style knuckle that works with a Subaru stub axle.

For growing your own unequal length a-arm suspension - I highly recommend getting a suspension design software package. I use Performance Trends Roll Center Calculator:
http://performancetrends.com/rc.htm
It's at the bottom end of PTs available suspension software packages - but provides a lot of information for quick analysis of roll center/camber changes during bump and roll for various suspension designs. Trying to "hand draw" to scale minute suspension pick-up point changes and see their effect on RC and other factors can take days - vs. seconds with the software. Their may be other similar software packages out there that do the same? I've only used PTs software and it helped me out immensely in designing the front and rear suspension for my Deserter.

If you're thinking about going with an entirely new front suspension design, have a look at adapting the Subaru front uprights as a knuckle for an a-arm style suspension, as Factory Five racing has done with their 818. While the 818 doesn't utilize the AWD hardware, the upright is ready-made for it.

Unless you're building your own spindles, you'll have to use whatever SAI is designed into the knuckles you're using. Typical I've seen for a MII style and many other spindles is about 9-10 degrees. Wilwood has a nice custom knuckle similar to the MII with dimensional info. I believe the new Corvettes are closer to 7 degrees (maybe less)? As the SAI gets lower (which I gather is better for handling), more suspension "stuff" has to get tucked inside the wheel, requiring larger diameter wheels. In the end, it comes down to what you can fit into the chassis/body of the vehicle with A-arm lengths, spindle height, SAI, etc.

Jeff

[Piledriver]

Cutting a strut down and installing an upper ball joint also allows you to set the SAI ~as you wish.
Combined with a 914 or classic 911 lower arm setup as Nate used keeps the torsion bars, and makes it so you just need to add a shock and a custom upper arm.

I considered doing reversed 911 arms/springs, but the car handles on rails with the std T3 front suspension with coil overs and the bars.

[GS guy]

The terminology SAI - Steering Axis Inclination is a bit confusing (at least for my small brain!). I was referring to KPI in my above post - Kingpin Axis Inclination - which is dictated by the relationship of the ball joint pivots (or "kingpins") to the stub axle axis in front view. The BJ pivots can move in and out from chassis CL, but camber is (obviously) changed as the result in a fixed spindle geometry. I can visualize Pile's point of locating the upper BJ pivot where you want it at the top of the upright if you're custom making your own setup - could be a nice advantage being able to do that! The other "SAI" I can visualize would be caster, which is typically adjustable (front to rear) to where-ever you want it to be.

Here's an old photo of a modified McPherson strut to A-arm configuration. BJ appears to be fitted directly to the top of the shortened "strut" housing.

frontchassis2.jpg

Other strut designs use separate components for (bolt-together) spindle and strut, which is similar to the Subaru. FF uses custom brackets on top of the spindle to attach a BJ/a-arm instead of the strut cartridge.


Jeff

[56SemaRag]

All great points gentlemen.Thank you. I'll try to answer the questions and give a good picture of the front end design.

Are you staying with the VW torsion bar design with AWD front knuckles?

No, due to the mounting of the torsion bar and differential it seemed a conflict not worth solving. Really wanted the performance of a double A arm

For growing your own unequal length a-arm suspension - I highly recommend getting a suspension design software package.

I am using this Virtual Suspension Calculator to get the basics down. I have another one that includes the steering rack and drive axles. You are right, it has helped out a lot working with the variable dimensions once the physical limitations are known.

If you're thinking about going with an entirely new front suspension design, have a look at adapting the Subaru front uprights as a knuckle for an a-arm style suspension

I am using the Subaru knuckles, but due to their proximity the inside of the rim and to maintain a decent (SAI/KPI) I am going to mill them down (3 sides). I am going to drill anther mount hole and manufacture a bracket to hold a stud for the Del Sphere joint. This was one of my previous pictures of the knuckle to be cut down.

Knuckle.jpg

One of these will go on top with a cone spacer. Went this route because trying to fit a ball joint setup with a tapered cup would be more difficult. They are adjustable tension wise, allow 28 degrees movement and can be rebuilt.

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Unless you're building your own spindles, you'll have to use whatever SAI is designed into the knuckles you're using. Typical I've seen for a MII style and many other spindles is about 9-10 degrees.

When I make the bracket for the upper joint I can set it to pretty much any SAI and caster. Figure if I don't like it, all I have to do i make another bracket and position the stud where I want. It looks like I will be around 7-9 degrees which based on my hub,tire and wheel selection puts me under a 2" scrub radius which is ideal for AWD cars.

Cutting a strut down and installing an upper ball joint also allows you to set the SAI ~as you wish.

tireclearance2.JPG

The Suby knuckle is tall, The original strut reaches in to bolt up to the knuckle so there is very little vertical clearance to the wheel, can't mount the ball joint to the top of the strut due to the excessive length and angle of the upper A arm. It would also put the SAI / KPI too far out. It's why I am looking to trim down the upper part of the knuckle. Before I machine the knuckle I'll put all my dimensions on here to see if I am on the right path.

The terminology SAI - Steering Axis Inclination is a bit confusing

They are one in the same, since kingpins aren't used on modern cars I guess they had to come up with a new term. I was doing the same thing trying to figure out the difference, I guess if a car doesn't have a kingpin it can't have a kingpin angle. But if a car has a kingpin it can still have a steering inclination angle

I can visualize Pile's point of locating the upper BJ pivot where you want it at the top of the upright if you're custom making your own setup - could be a nice advantage being able to do that! The other "SAI" I can visualize would be caster, which is typically adjustable (front to rear) to where-ever you want it to be.

I was trying to think of a stable way to be able to move and lock the upper ball joint in different positions relative to the knuckle. It would allow caster or SAI to be adjusted before moving to the inner pivot A arm adjustments. With vertical space at a premium I figure I can slot the bracket I will make that will allow me a few degrees of camber / SAI to dial it in. Since I want caster to be adjustable without moving the inner control arm pivot points I am going to design the upper arm after the SPC style.

Adj Upper Control Arm.jpg

Every design I come up with has to remain clear of the axle and shock or push/pull rod for the shock. It has been a challenge, especially when I look at how simple the Mendeola is on my other car. The ball joints are only separated by a few inches vertically. Appreciate all the input and keep it coming, looks like I will shoot for 7-9 degrees on the SAI. My icluded angle (SAI + static camber) should be spot on. The last geometry question is the rising rate of the camber. What's considered ideal? For every inch of travel up, how much negative camber should be added. This will lock in the A arm dimensions and determine my mounting points for them. I have read some articles but many do not go into detail what good values are.

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Finished out the weekend clearing the body for the chassis bulkhead. Want to set it into position before welding it to the chassis. Then the front suspension that will get built on it is a go! Thanks again gentlemen for the valuable input and ideas.

[Piledriver]

The last geometry question is the rising rate of the camber. What's considered ideal? For every inch of travel up, how much negative camber should be added. This will lock in the A arm dimensions and determine my mounting points for them. I have read some articles but many do not go into detail what good values are.

Ideally it would match the deflection of the tire under load, the suspension flex and body roll.
That largely depends on how much body roll you are allowing/how stiff it is.
How to calculate? No idea. Cut and try likely required.

Another example is axle trail, not to be confused with caster.
Increasing caster increases trail. Moving the axle forward or aft in relation to the KP axis can increase or reduce trail...
They are not the same but effectively do the same thing via different methods if that makes any sense.
They are commonly used together effectively.

On big Mercs and a lot of SUVs, they use a LOT of caster, then offsets the axle to reduce the trail.
(similar is done on a LOT of cars, just to varying degrees)
This produces a LOT of camber gain/loss with large steering angles, allowing for body roll and tire/susp. deflection at the expense of steering effort, which is boosted to hell in any case.
This also provides more steering feedback than a "normal" setup where the axle is on or near the KP axis.

I have considered switching to a weld in CrMo axle spud, perhaps raising it an inch or so, and moving it aft for more positive trail... This will largely offset the effects of reduced caster in a lowered T3 front axle, without actually adding caster.

Here's a brief basic reference with some examples.
http://www.car-engineer.com/suspension- ... -behavior/

[GS guy]

I focused on reducing roll center movement, side to side during bump and roll in designing my GS suspension. Next level of importance was to get the lower a-arms as long as possible, within the design constraints of my chassis/body. My spindle was "fixed" as MII, selected for availability of matching components (brake kits, hubs, ball joints, a-arms, etc) to support it. After that, it was tweaking the upper a-arm inner/chassis pivot points to reduce RC movement, and finding a steering rack that would work with low bump-steer. Originally I ended up with ~ -0.5 deg. camber gain/inch of dive. My RC tracked vertical chassis movement near perfectly. In roll, RC stayed put up to 3 degrees of roll, but would start migrating out with 3 deg and past 1" bump, up to about 80" off center @ 2" bump (my max excursions from static).

Later, after doing more research on camber gain, which seems to be most widely available on circle-track race car suspension discussions, it seemed something closer to 1deg/inch of bump is more desirable. I went back to the drawing board (or computer) and re-worked the upper a-arm inner pivot location and was able to improve RC control and increase camber gain to -0.78 deg/inch of bump. In my max 3 degrees of roll, the outer tire goes to +2 deg positive camber (0 deg static) vs. +2.3 deg in the previous design, RC doesn't move. In max conditions of 2 inches bump and 3 deg. roll, outer tire camber is -0.7 deg, and RC movement only moves about a foot off-center (it only starts migrating off-center past 1" of bump combined with max roll). Easy enough to dial in a little negative static camber to compensate.

I think that's why all the pro-touring front suspension re-works universally raise the upper pivot point at the spindle (with taller spindles and/or longer ball joints) to increase camber gain in bump, and likely other benefits for the 40+ year-old designs.

At that point I figured "good enough" and modified the parts to match!

Jeff

[56SemaRag]

I have considered switching to a weld in CrMo axle spud, perhaps raising it an inch or so, and moving it aft for more positive trail... This will largely offset the effects of reduced caster in a lowered T3 front axle, without actually adding caster.

Here's a brief basic reference with some examples.
http://www.car-engineer.com/suspension- ... -behavior/

Great point and that link helped a lot. I ran across that several months ago but forgot to bookmark it. Thank you! It was one of the only places that I could find a list of cars and their KPI. Since the numbers were so varied, i kept searching to narrow it down within a few degrees considering it's a semi permanent value for the knuckle. Good thing I can only adjust the upper

...finding a steering rack that would work with low bump-steer.

Later, after doing more research on camber gain, which seems to be most widely available on circle-track race car suspension discussions, it seemed something closer to 1deg/inch of bump is more desirable. I went back to the drawing board (or computer) and re-worked the upper a-arm inner pivot location and was able to improve RC control and increase camber gain to -0.78 deg/inch of bump. In my max 3 degrees of roll, the outer tire goes to +2 deg positive camber (0 deg static) vs. +2.3 deg in the previous design, RC doesn't move. In max conditions of 2 inches bump and 3 deg. roll, outer tire camber is -0.7 deg, and RC movement only moves about a foot off-center (it only starts migrating off-center past 1" of bump combined with max roll). Easy enough to dial in a little negative static camber to compensate.

I am looking at front steer racks of the Mustang II variety. They have shortened ones that have inner pivot points reduced up to 4", so I should be able to keep bump steer to minimum. I should be able to get all three pivot points to line up.

I will experiment with the suspension calculator and shoot for those numbers. Thanks for the thorough feedback, it helps a bunch especially with monitoring RC changes.

[GS guy]

All my suspension books say keeping good control of the roll center - that is minimizing its movement during bump and roll - greatly improves the "feel" of the car when driving hard. Looks good on paper!
For the rack - take a look at the MGB/Cobra racks too. That one worked best with my geometry (without going custom $$$), plus came closest to providing a similar steering "rate" as the original VW box (with the MII spindles). Many manual racks have a pretty slow steering rate depending on the steering arm lengths on the spindles. Power racks are definitely quicker, with the power feature making for easier steering at slow speeds. I once drove a fiberglass buggy with a Saco-type or similar rack fitted, with very quick steering ratio. It was a bit of a bear to turn at slow speeds - I realized it was easy to over do it going for a quicker ratio.
Woodward has some good technical info on rack set-up:
http://www.woodwardsteering.com/PDF/tec ... 0guide.pdf

Jeff

[56SemaRag]

Woodward has some good technical info on rack set-up:
http://www.woodwardsteering.com/PDF/tec ... 0guide.pdf

That was a good read Jeff. Thank you.

Tacked the bulkhead in place. I'll finish out the transition to the floor pan and finish welding the sub frame joints this coming weekend. Going to order the majority of suspension pieces this week and finish out the design portion.

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[56SemaRag]

The link below will be close to the final design. I still have to add in the drive shafts and shock linkage. Practically zero bump steer through 5 degrees of body roll and roll center stays within a few millimeters in the worst scenario. The lowest part of the frame will be the tabs for the front differential at about 5-1/2" of clearance. Guess it's time to trim down the knuckles and start fabricating the front end.

AWD Ghia Front Suspension

[Ark]

You may already be a little too far down the Subaru path but did you consider using the front knuckles from a 4wd S-10? I believe they use a micro-stub hub and have an a-arm style design so it seems like they would be relatively easy to bolt custom control arms directly to the stock ball joints.

[56SemaRag]

I didn't. Kept everything Suby. Figured when it came to axles it would be easier to mate the diff and hub.

That's a good point about the S10 parts. If someone wants to attempt this in the future, they can compare what I've done versus an alternate path.