Ghia Road Course Setup

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Steve Arndt
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Re: Ghia Road Course Setup

Post by Steve Arndt » Sun May 08, 2016 2:40 pm

CMaxxcliff,
There is a fab guy named Mike that builds combo spindles. He said he can set them to any angle of camber desired.
https://www.facebook.com/groups/dunebug ... 741621990/

Mike's Machine&Fabrication

cmaxcliff
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Re: Ghia Road Course Setup

Post by cmaxcliff » Thu May 12, 2016 8:10 pm

Thank you Steve. Mike seems to be "the man".

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FJCamper
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Re: Ghia Road Course Setup

Post by FJCamper » Thu May 12, 2016 11:12 pm

Gentlemen,

Excellent info. I think this is just the ticket.

FJC

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Piledriver
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Re: Ghia Road Course Setup

Post by Piledriver » Fri May 13, 2016 4:37 am

FJCamper, are you familiar with adding trail vs. caster?

Thinking about modding some spindles (making drop spindles teh old school way) and adding some addition caster-like effect with a little spindle trail, but the information of the actual effect is thin on the ground.

That tubular spindle setup is slick, kinda like what I was thinking modding rusty 911 struts for same purpose.
(lopping it off and install a ball joint above the spindle, and going ~dual a-arm, with the Porsche lower arm/torsion setup)
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CobraJet
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Re: Ghia Road Course Setup

Post by CobraJet » Fri May 13, 2016 7:14 am

Piledriver wrote:......
That tubular spindle setup is slick, kinda like what I was thinking modding rusty 911 struts for same purpose.
(lopping it off and install a ball joint above the spindle, and going ~dual a-arm, with the Porsche lower arm/torsion setup)
Neat idea Pile!

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FJCamper
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Re: Ghia Road Course Setup

Post by FJCamper » Fri May 13, 2016 9:20 am

Hi Piledriver!

No, I'm not at all familiar with trail. What difference is there between trail and negative caster?

We run positive caster on our Type 1's. That's all I know.

FJC

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Re: Ghia Road Course Setup

Post by cmaxcliff » Fri May 13, 2016 2:59 pm

FJC, what is the best road course set-up for the transaxle? The Porsche uses a very close ratio 4 speed with ZF lsd that gives us 4 on track gears with our engines that do not work below 5000rpm. Using the Rancho terminology which level of trans build would you go with and what diff is good?

Trail is the distance on the road between the tire contact and a line through the center of the steering axis.

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Re: Ghia Road Course Setup

Post by Piledriver » Fri May 13, 2016 3:02 pm

FJCamper wrote:Hi Piledriver!

No, I'm not at all familiar with trail. What difference is there between trail and negative caster?

We run positive caster on our Type 1's. That's all I know.

FJC
Gotcha.

Trail offsets the centerline of the spindle aft (? forward? See below) from the kingpin axis.
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ChadH
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Re: Ghia Road Course Setup

Post by ChadH » Fri May 13, 2016 4:50 pm

I'm playing along, just for the sake of understanding steering geometry in more depth. I understand "trail" from bicycle/motorcycle geometry. I'm guessing it's the same concept for cars, but let me know If I'm wrong.

Trail is the distance from the projection of the steering axis on the ground, to the tire's contact patch, and is what gives the tire a centering force when it's traveling forward. The caster angle affects trail (same as a bike's head angle), as well as the offset of the wheel center from the steering axis.

I take it that by talking about negative trail, you're moving the wheel center forward, which makes the actual "trail" less positive?

Image

I guess what I'm not clear on is why you would want to adjust the wheel center to reduce trail, rather than adjust caster angle?

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FJCamper
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Re: Ghia Road Course Setup

Post by FJCamper » Fri May 13, 2016 7:40 pm

Hi CMax,

I'm presuming you have the Devlin-D.

Two schools of thought here. If you are powering the Devlin with a full race 356 engine, then you follow 356 transaxle practices. The much lighter Devlin will pay off in extending the usable power band lower in the RPM range than in the heavier 356. The car will start accelerating at least a thousand RPM earlier.

This is dune buggy experience. Some buggies can't even use 1st gear in a stock transaxle. You have to start off in 2nd.

The 356 transaxle has the best ratio assortment. To compensate in the VW, you have to tune torque and powerband. You'll want them both to come in lower than in the 356.

In the VW, you'll find the offered ratios beyond stock are mostly for reduced RPM freeway cruising, or drag racing. The same is true with VW Type 1 cams. The SCAT C65 is one of the few advertised "variable RPM" cams, and it was intended for Super Vee. The SCAT C95 is the same, but for full-bodied cars. Here's what a C95 on a 2.2 litre dual single bbl Solex 44mm throttle bodies and 36mm venturis) can do to BMW 318's.

The clip is long enough to show there is no edit tricks. The E30 Bimmers come in midway.

https://www.youtube.com/watch?v=zvYgzPgBRaw

I don't know how much tire you can get under the Devlin compared to what you're accustomed to in the 356, and I don't know if you drive depending on adhesion or sliding.

A LSD dramatically changes the handling of a swing axle at the limit, adding adhesion and understeer at the same time. It may be this is the feel you want and in that case, you use a Porsche transaxle.

High power cars have LSD's for entirely different reasons, to stop wheelspin. It puzzled the younger 934-935 mechanics that the "under powered" 356's even used LSD's. They were not aware it started with factory cars and 356 handling became dependent on LSD for the best lap times.

Now, to conclude this overly-long response, the point is if you go Devlin-VW, 120hp, tune for a midrange power band, and with a 4.12 final drive and just stock ratios, you'll have a rocket. You'll make up in acceleration for what an LSD would have given you.

However, you'll always miss the beautiful 356 gearing, as Rancho (and the others) just doesn't offer the same Porsche ratios.

FJC

Here's what's in our close-ratio transaxle:

PROCOMP RANCHO PERFORMANCE TRANSAXLE

Super Differential (4 spider gears instead of two)
Aluminum Side Cover (stops flexing)
Welded GEM 3rd & 4th Gears
Steel Shift Forks, Hardened Keys
4:125 Ring & Pinion
Close Ratio 3rd & 4th
3rd 1.58 (stock 3rd is 1.26)
4th 1.14 (stock 4th is 0.88)

And our "long track" transaxle:

Super Differential (4 spider gears instead of two)
Aluminum Side Cover (stops flexing)
3.88 ring/pinion
1st) 3.78:1
2nd) 2.06:1
3rd) 1.26:1
4th) 0.93:1

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Piledriver
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Re: Ghia Road Course Setup

Post by Piledriver » Sat May 14, 2016 3:01 am

Here's the source of that pic, and the article had a good explanation and great source, it defines std suspension terminology.

http://www.car-engineer.com/suspension- ... -behavior/
That link probably belongs as a sticky at the top of this forum:


Caster and trail are discussed together, or at least next to each other.

As to "trail", the spindle on most vehicles we work with installed directly inline with the kingpin axis, so they would by definition huge negative trail, hurting stability.???

...not just older VWs, MacPherson struts are frequently made with spindle on-center of strut.
If moving the stub axle forward of kingpin axis helps stability, its at least interesting to know why.

The "cost" seems to be additional input from side loads, but getting trail to ~zero would be the typical use case most likely.

Adjusting caster more is often not possible or easy on acvws, but the stub axle can get moved a bit esp if its a bolt on.

I my brain jams up on the effects of moving the axle centerline ahead of the kingpin axis, but if doing it that way is standard... add a lot of straightline stability at the cost of (something) as there is no free lunch.
Seems it might be useful for a mfr to tweak steering "feel"

Another question that is probably relevant to this thread...

Anyone have good shock damping//valving settings for AX/track/road uses?

I'm thinking the off road valvings are perhaps too stiff, but the following info was pulled from ebuggies, which oddly never replied to a purchase query, along with another place. I was expecting at least SPAM, disappointing. :evil:

Bilstein 7100 Baja bug "Sport" valving (non race/streetable I have to assume)
"Sport" F 180/75 rear 360/180
"Prerun" prerun F 180/75, R 550/240 (rear w/2 shock equivalent)

Late T3 is not a Ghia, but the weight distribution and suspension are reasonably close.
I assume average Baja builds (not totally built and race loaded with gear and 2 spares) would be in a similar ~2200 lb range.
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cmaxcliff
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Re: Ghia Road Course Setup

Post by cmaxcliff » Sat May 14, 2016 6:31 pm

The common 356 race box is
1-1.765
2-1.35
3-1.13
4-0.96
final-4.429
The 356 engines are 1622cc and put out between 165 and 180hp depending on who is talking and which dyno you believe. Useable rpm is over 5000-7500 or 8000 depending. The car weighs 1687 pounds and first is just a bit tall for the hairpin at Sebring where some guys use a lower first. We use Hoosier Speedster 205/60-15 at 24.2" tall.

I have options with the Devin because I can use VW, Porsche, or a combination for engine, trans, and brakes. I have spare Porsche stuff but I would like to use the strongest and best performing parts that I can. My guess is that the Devin will weigh 1200 pounds but I am not certain. It has a smaller frontal area but may not handle as well, still not certain. The rules are very fuzzy on this car but I have been told officially that it will fit SVRA group 3 or group 1 depending on engine size etc. There is so much available for the VW that those engines and transmissions may be better but only if they are truly better performing than the Porsche options.

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Piledriver
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Re: Ghia Road Course Setup

Post by Piledriver » Sat May 14, 2016 6:37 pm

The shock valving reference from eshocks (off-road-centric, but a reasonable starting place (?) )
http://www.eshocks.com/bil_ORgd.asp?Manf=All
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Re: Ghia Road Course Setup

Post by cmaxcliff » Sat May 14, 2016 6:44 pm

Oh, yes I have the Devin already. The frame is already being replicated for obvious reasons.
rsz_img_0814.jpg
rsz_img_3751.jpg
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Piledriver
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Re: Ghia Road Course Setup

Post by Piledriver » Sat May 14, 2016 6:58 pm

Shock valving types explanation (originally from Circle Track magazine, but the original source has gone 404)

Should I put this sort of reference in its own thread?
Shock Types

There are three major categories of shock absorbers, which are based on the way they react to force. (Note: This is not a discussion of shock absorber design, meaning twin-tube versus mono-tube.)

The first shock absorbers were progressive, meaning that as shaft speed increases so does the damping rate, or the energy required to move the shaft at that speed. A progressive shock is the simplest design, and also the least useful in practical terms. It’s simply a perforated disk moving through a resevoir of oil. At slow speeds the oil passes through the holes in the disk easily. At higher speeds more energy is required to move the oil through the holes in the perforated disk.

Eventually this type of shock reaches hydraulic lock—no matter how much force is applied to the shaft of the shock, travel speed cannot be increased. A progressive shock is old technology, and it’s performance is unacceptable to the modern racer. Low, continuous forces like body roll through a turn are too poorly damped, and on the other end of the spectrum the shock is unable to absorb sharp, high energy forces: holes, ruts and otherwise rough tracks.

Linear shocks were the next big advance in shock technology. As shaft velocity increases, damping forces increase at a linear rate. On a shock dyno graph (Diagram B) both compression and rebound damping appear as approximately straight lines diverging from each other as shaft velocity (or force exerted on the shock) increases. This style of shock has been a boon for racers because it allows increased control at lower shaft speeds, which is vital for controlling a race car through the corners.

The third type of shock is a fairly recent development. Digressive shocks are essentially the oppostive of progressives. As shaft speed increases, damping forces increase at a decreasing rate. Diagram C is a shock dyno graph of a typical digressive shock dyno curve. Digressive shocks provide low-speed damping control without being unreasonably harsh on rough racetracks.
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