"go fast" chassis setup for your 308

YOU DA MAN LOL

 

Your Tq/HP gains are from not aerating and slinging oil around in the crank case. Any vacuum you pull in the CC is miniscule compared to what would be required to reduce air friction losses, i.e, you would suck in your cam seals and gaskets if you had enough CC vacuum to significantly reduce windage.

Typical Tq numbers for a large (400+CI V8) are ~20 Ft-lb loss in wet sump, no windage tray, 10-12 ft-lb loss with windage tray as compared to dry sump.

Doug

 

maybe i'm wrong but that seems still pretty soft?

I used to rally my audi but also did some tracking. For this I used springs of 340. The audi however was much lighter, about 1800 lbs, hé, i even had a set of 450 spring made and used them ( they turned out to be a little to short so not much usage)

So for a 308, especially in track trim, so a fair bit lighter than stock ( assume 2500-2750 lbs) i would think about a spring of somewere in the region of 450-500


Or are these 375 only still a sort of compromise to give at least a little confort on the road?

Were does my thoughts go wrong?

 

Careful when comparing the springs in different cars….the effective rate can be quite different even with the same spring do to different arm lengths, mounting points, ect.

That said I run 450/400 on the street and am quite happy. ..although the back might like 375 better. For track only I would be thinking more like 800/650

 

yes that's a valid point.... ( i'll will think of that..)

That's funny because i was thinking likewise but were a bit afraid you all would call me stupid...

For (dry-only) track racing i always thought there is no real boundery for increasing spring stiffness.

Edit: when i think of it, on the audi (= mcpherson) the effect was only bigger compared to the levertype suspension on a 308. Taking that into account the rate on a 308 should be considderbly higher than just the weight-ratio formula

 

I'm not sure

increasing (partial) vacuum in a wet sump will/can cause boiling of the oil i guess. I go along that ambient pressure would be best but with normal sumpventilation ( don't know if that's the correct term) I do think the pressure WILL NOT be substantiallly higher than ambient, even if the leakage on the pistonrings is huge.

I think that the "mist" of air/oil in the sump will have a considderable effect on internal powerloss, I always thought that that's on of the reasons dry sump are used ( beside among more the increased cornering ability, increasing the ways of cooling the oil, bigger amounts of oil etc etc)

 

Isn't that the wrong way around? i was always learned that the spring (and only the spring)should be able to press the wheels to the floor at all times and the shocks should only follow the springs movement. You simply cannot use a shock to compensate for the "lack" of spring.

If you harden the shock beyong the springs capacity it will cause a reduction of the force pushing the wheel on the track resulting in a decrease of control.

 

thanx,

What do you think of my feeling on "endless" increasing the spring capacity? What will turn out to be maximum, or isn't there any?

 

Oh there is a maximum. Too high and the wheels will bounce the chassis over every bump, taking the tires off the ground. You want the softest springs you can run with the suspension bottoming.

Spring hold the car up
Sway bars control body roll
Shocks control oscillation.

 

must be a language thing so pardon my question but what do you mean by

the suspension bottoming. ?

 

Full compression of the suspension hits the rubber snubbers, frame hits the ground, or wheel hits the body, which ever comes first….hopefully it’s the snubber.

 

I don't understand that completely. Stiffening springs will indeed make a lower car height possible for the reasons you mentionned but there's not a direct relation between height and stiffness so why would this create a boundery for increasing the springs stiffness?

 

With a combination of the modified wet sump baffle, front mounted oil coolers (adds more oil), and an Accusump (still more oil and additional pressure control), I have not been able to drop the oil pressure while doing hard sweeping turns with slicks. If retaining oil pressure on the track is a concern, this seems to work - FWIW.

 

The boundary condition is when the tire will no longer follow the road and bounce the whole car into the air instead. This is VERY bad in a corners. You want the softest spring you can get away with as this will produce the most grip. On a smoother track you can run a stiffer spring and lower the car a bit, on rougher tracks you need softer springs to keep the tires on the ground, that means taller ride height.

 

i'm lost now.

i will sleep things over and return tomorrow ( it's about time to go to bed over here )

 

Well, i'm going the pull the trigger on new shocks, the first step to put the gtb on full track-mode. So they will be very stiff and very low..

Now i wonder, what should be the best closed and open length? And what about the overall lenght?

I will use heavy springs (probably about 700 front 625 rear) and the shocks I set my eye on ( spax ultra light double adjustables with adjustable spring platform height) looks quite suited for this job.

Can anybody give me some advise on this? Or maybe does someone has some experience with this particular brand to share?

 

Most of us who are modding seem to run QA-1's Steven. I've got them too and they work brilliantly. I can look for the exact part numbers and lengths if you'd like.

Regarding springs (a question of yours on page 1): Stock depends on GTB or GTS and probably USA or Europe too. I should have a table somewhere, but from the top of my head, they were 175 / 175 front/rear for the GTB. WHEN NEW!!!

I've got 300/300 on my GT4. I ride minde pretty low and I have yet to have it bottom out on me. Seems plenty stiff.

I reasoned that with OEM being equal front and back, why should I go for the more common front-stiffer-than-rear approach? If anything, that will get less grip on the front and more on the back. Read: understeer. With these cars understeering enough as it is, I stuck to equal spring rates. I'm totally satisfied with my 300/300 for street use and would chose the same again next time. I'm sure that you could go stiffer on a track, but what would be the goal of that? It will get you less grip, and believe me, you don't need that much spring to keep the car flat and not diving under hard braking! Uprated anti-roll torsion bars seem a better investment there!

I run the shocks at setting 3 out of 12!! I used to run them at 4, but after I changed all the suspension rubbers to new poly bushings, I found that the shocks at 4 would get the car dribbling on its tires, as if it were a basket ball. NOT good for handling, I can tell you! It would just bounce of of any corner. Going back to setting 3 remedied that. The car is still VERY stiff!

Will you be at Bart CCC's meeting next Sunday? If you are, make sure you take my GT4 for a spin around the block to get a feel for the suspension!

Cheers,

Hans

Edit: one more good thing about the QA-1's is its price: around $800 for shocks and springs, if I remember correctly. Dual adjustable shocks (in/out separately) available too. And adjustable ride height standard issue

 

Hi Hans,

I have a few questions for you - hope you don't mind. Anyone else, please chime in too!

I want to "renovate" my suspension for my 308GT4 and so this thread is very timely. I don't do a lot of street driving and do occasional track days so I am happy to bias the car a bit towards trackability.

In a different thread, you posted a photo of your 308GT4 pushing pretty hard around a track (some dice dangling at a very oblique angle from your mirror showed how hard you were pushing) and the car looked very stable. So it seems that you have a very good set-up for a 308GT4 and maybe I should replicate what you did!

So, to summarise your set-up and ask the questions:
* QA-1 shocks set at 4 for front & rear - What specific QA-1 model? Same front & rear? But, as far as settings go, Luckydynes talked about setting the shocks at 10!
* Springs, 300 both front and rear - what brand? Does brand really matter anyway? Also, Mk e talked about running 450/400 on the street and suggests for track maybe 800/650? Comments?
* Poly suspension bushings
* Uprated front torsion bar - how thick?
* Uprated rear torsion bar - how thick?
* Also are you running 16" rims, 7" front, 8" back?
* What size tyres do you have on these rims? Some people seem to push these quite wide and Luckydynes mentioned 245-45-16 rear, 225-55-16 front.
* Have you changed camber? Again, Luckydynes mentioned -2.5 rear, -2.3 front with modifying the front suspension forks.
* Luckydynes also mentioned toe and caster about factory. Its this what you did?

OK, those are my questions - any thoughts welcome with thanks!

Cheers,
Grahame