Rolling road dyno, worth doing?

Took the words right outta my mouth....

Meh, there are folks modifying much more expensive cars than ours....besides, it's still just a car, but I love it.....I love the 308. There, I said it.
But a streetable Gr. 4 car is my idea of the perfect 308 - maybe the perfect car for me - so I'm not overly concerned with cost or resale value. There is (should be) enough room in the hobby for all to appreciate the bone-stock car as well as the modified car (until you start plopping Honda engines into everything....hahahahahaha). It's the same car, just with a little different attitude.
- Dave

 

It's kind of a moot argument in any case since 99% of 3X8s - whatever their flavor - aren't being driven anywhere near the limit, along with the fact that 99% of 3X8 owners couldn't feel the difference in torsional rigidity between an S and a B anyway...myself included.
- Dave

 

I think 99% prefer to treat their cars with respect and understand there is a difference between using something to its full potential and just plain abusing it.

 

I measured the frame flex on my car a few years ago, its about 1/2" per g. I would expect a GTB to be more like 3/8"



1g is a pretty hard bump, stock 308 suspension is on the snubbers at about 1/2g in front, about 1g in the rear which is why it plows. In a hard corner the rear is on the springs but the front outer hits the snubbers so the effective spring rate shoots up which transfers weight onto the front outer tire and it slides (the front inner does almost nothing). the stock springs are like 200/200 or 180/800, something like that but the front rear loading and the suspension geometry is very different so to match the front springs need to be about 1.6 x the rear, that is where the 400/250 and 800/500 setups come from.

After years of wondering wtf the factory engineers were thinking with that setup I've convinced myself its because they originally had matching tires f/r. 1970s tires are good for about 0.8g dry and maybe 0.5g wet which puts the front on the snubber and makes it slide first. So they were trying to make sure that in the rain the car would have light, controllable understeer so its safe for 99% of drivers. That's the only theory I've ever come up with for he weirdness

400/250 yields about 3.5" droop...the springs need to compress about 3.5" inch to support the car, which is a 1g load. Something like 1/2" of preload in the springs and the car sits at normal ride height with about 3" to compress so not quite 1g bump travel available. the frame will twist 1/2" at 1g, so 0.5 / 3 + 0.5) x 100 =14% or the travel is due to frame twist

800/500 yields about 1.6" droop.so 0.5 / (1.6 + 0.5) X 100 = 24% of the wheel travel is form flex so there is proportionally less F/R weight transfer through the frame as spring rates go up so the suspension tuning at each axle becomes less forgiving.

 

I think most owners realise that the potential performance improvement with a 308/328 isn't going to be massive - You can make them "perkier", but you're not going to be scaring modern performance cars to any real degree (and quite a few family saloons/sedans. A 2.0 litre turbo charged Alfa Romeo Giulia Veloce will perform as well as, if not slightly better than a 328. Spend a few hundred on an ECU tune, and you can take the Giulia from the factory 280bhp to @ 320bhp easily - Gaining the same 40bhp on the 328 will cost a lot more and require much more work)

For most owners too, the cost of making them "perkier" isn't really worth the gains - 3*8's these days are 36 - 50 year old cars, and more about the driving occasion than on the limit, flat-out, engine at the redline driving.

Each to their own at the end of the day - Personally I've never felt my '89 328 GTS was too slow, and when it comes to other people in modern cars going faster than me: Well Whoopee doo for you!

(I've lost track of the number of people in modern diesels, electric cars and family saloons who seem to have a desperate need to overtake a 36 year old Ferrari - Quite often on blind bends/no overtaking sections of road etc., etc., etc. If they're driving right up my arse, I'll simply find somewhere to pull over and let them go on their way. If they start to overtake, I'll simply lift off or even brake slightly, and just let them go - My Ferrari has nothing to prove to any of them! )

 

Track and autoX are similar but differ because the speeds are different. AutoX is run at street speed and in the video I remember my car was just touching 80mph before I hit the brakes are the end...I was struggling with what gear to use 2nd in the turn and need to shift on the pull or 3rd in the turn and have a little slower drive out but save the shift, I settled on shift into 3rd entering the turn so no shift in the video run. Anyway, spring rates are similar on non-aero cars like a 308/328 but damping rates are usually a bit different. On the street and autoX speeds its pretty common to run quite a bit less compression than rebound but at the trach they get closer or equal. At least from my experience.


{quote]Spring rates, I Have yet discuss this, i told Intrax very specifically i wanted a car with a dual nature 80% Road 20% Track as a baseline , as compliant if not more plush than the original Koni set up while supporting the car through deep compressions and hard cornering controling pitch dive and squat, then when on a smooth track switch the balance closer to a track setup, lower the whole car and progessively be able to dial in the stiffness, adjusting dampers compression and rebound independantly front to rear to in effect change understeer/oversteer characteristics at the push of a few buttons. He reported this was all dooable with this system and the actual spring rates will probably be LESS than stock, which i found surprising, however the tech they use allows for this, it would seem to be their party trick. When i was considering buying a 930 Turbo i was looking at a Tractive set up which is similar, when i decided to get a 328 Intrax had a full system developed in much the same way but some additional mods included as an option which sold me.[/QUOTE]

For sure they can use an accelerometer to know when you are braking or cornering and momentarily alter the damping to help ease the transitions but in any corner long enough the car will settle to its natural position as determined by the springs and sway bars unless they are real time changing preload as well as damping? Do be careful on the springs though, stock 308 and I think 328 springs are sized quite strangely. Most of what you real as soft of harsh suspension is the shocks, it takes a lot of spring rate change to make the ride get harsh.

Suspension people like to use Hz when they talk about springs, how fast the car bounces naturally on the springs with no shock. the 308 is about 1.16hz front, 1.34Hz rear.

so stock 308 is just scratching at the bottom of sportscar...but its passenger car. the 400/250 setup is 1.74/1.58 sports car. 800/500 is 2.46/2.23 race car. Something like 300/225 (or 200) would be 1.5Hz so about like a stock subaru BRZ. I've been running the front Hz a little higher than the rear, opposite factory setup, so there is always inherently a touch of understeer but that is just preference and i realized recently that setup seemed to work best because I had lowered the car and the front roll center drops much quicker than the rear so the front needs a bit more sway bar or spring to compensate.

 

I think that is the answer. For most the car is quite nice to drive and they have no interest in spending $50k (or more) making it less reliable and harder to work on.

but you can absolutely build a 450hp naturally aspirate QV or 328 engine or a 500-800hp supercharged or turbo version. its expensive though. What's more common is when the engine is already tired or damaged and you're looking at a $30k rebuild or $50k rebuild/restore for the engine then more people are open to bumping the hp....new cams, or custom high compression pistons are generally cheaper than OEM pistons and out pops a 300-350hp engine that still looks pretty stock and isn't hard to keep running.

Suspension stuff is cheaper and more in the the DIY realm so lots and lots are running some combination or after market shocks/spring/wheels/tires.

But yeah, the overwhelming majority are stock and will stay that way and personally I think that is a good thing. My car I bought from a salvage yard, they had bough it but decide since it was sad not damaged they could do a quick flip. Money wise restoration made no sense which for me was perfect....I had an excuse to change just about everything.

 

Thanks Dave

Just checked back and the figures were actually 240 and 233 on 2 different roads 2 years apart. I seem to remember I took 237 as an average