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I've written about ARB's a lot. The main challenge is to actually make them work. Leverages are very long, the travel path is very short, only a few cm when the suspension travels, so that's why there is no major difference in terms of body roll whether you run stock ARB's or not. What stock ARBs do is mostly suspension bind and it is bad. GMS ARBs will bind the suspension too but at least they will prevent body roll. So we need stiffer torsional ARBs with the least possible weight. We have the solution on a way. Still I suggest ARBs only as an fine tuning element. First tune your spring rates, otherwise the suspension binding will increase, weight will increase, inner wheel spin will increase, nose dive and squat will remain unaffected, only body roll will decrease. ARBs should primarly be used for fine tuning understeer/oversteer balance, not for masking other suspension problems. Don't look for shortcuts, there are none if you want to do it right. 🏁
Obviously there’s a lot of variables, and it is probably more correct to talk wheel rates, but for an aggressive street/occasional track setup how much stiffer than stock would you recommend for spring rates before fine tuning with ARB? I’m thinking relative stiffness to stock and ratio of front to rear as the mechanical differences in coilover design will change the literal number somewhat. Thinking typical fast street tire setup such as 215 or 225 front and 255 or 265 rear re71r or similar.

Seems like most of the available options are somewhere from 1.2 to 2 (3 in some of the race specs) times stock rates and from .6 to .75 ratio front to back.
 

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Cleared the codes, and disconnected the battery today (trying to clear one last stubborn code - it shows as “permanent”, and did not clear).

Went for an hour long drive on county roads which I know very well. I will agree now, that there is some low end torque missing. Not really understanding why, but that’s my ignorance. I’m sure there is a perfectly good technical explanation (and some of it was already posted here, so I’ll go back and read that.

Meanwhile, no new codes. But now I think that I understand what is going on.
When they did the install, they likely disconnected the battery. The code only came on after they did a long road test and I did a long drive. Today, on my road trip, I kept stopping to check the status and although there were no codes, the emissions system is still showing “not ready”. I’m expecting that the code will reappear when the test cycle is complete.

Meanwhile, I spoke with Chris and Toby at Euro Compulsion, and they are able to disable the emissions codes in their tune. I have an EC stage one for my LE, so I’ve sent that to them to unlock for use in the track car, and to nobble the onboard e-tests. The tune should also recover the missing torque. So, only have to wait for shipping, which is deadly slow because of Covid19.

Stay tuned (see what I did there? LOL).
 

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Cleared the codes, and disconnected the battery today (trying to clear one last stubborn code - it shows as “permanent”, and did not clear).

Went for an hour long drive on county roads which I know very well. I will agree now, that there is some low end torque missing. Not really understanding why, but that’s my ignorance. I’m sure there is a perfectly good technical explanation (and some of it was already posted here, so I’ll go back and read that.

Meanwhile, no new codes. But now I think that I understand what is going on.
When they did the install, they likely disconnected the battery. The code only came on after they did a long road test and I did a long drive. Today, on my road trip, I kept stopping to check the status and although there were no codes, the emissions system is still showing “not ready”. I’m expecting that the code will reappear when the test cycle is complete.

Meanwhile, I spoke with Chris and Toby at Euro Compulsion, and they are able to disable the emissions codes in their tune. I have an EC stage one for my LE, so I’ve sent that to them to unlock for use in the track car, and to nobble the onboard e-tests. The tune should also recover the missing torque. So, only have to wait for shipping, which is deadly slow because of Covid19.

Stay tuned (see what I did there? LOL).
You should have them bump it to Phase 2 or 3. 3" exhaust is probably a bit big for only a Stage1 tune. You can run Phase 3 w/o the intercooler and just get it later if you wanted. I did it for about 2 weeks while I waited on my IC to show up.
 

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Discussion Starter #285
Will you make straight ARB for those with OEM exhaust or different exhaust?
I'm not sure yet, but probably yes. The problem is that CNC bending and material. No one is willing to supply just a few pieces of HQ steel tubes. Minimal order is huge...a lifetime supply of ARB'S. And expensive. :LOL:

Obviously there’s a lot of variables, and it is probably more correct to talk wheel rates, but for an aggressive street/occasional track setup how much stiffer than stock would you recommend for spring rates before fine tuning with ARB? I’m thinking relative stiffness to stock and ratio of front to rear as the mechanical differences in coilover design will change the literal number somewhat. Thinking typical fast street tire setup such as 215 or 225 front and 255 or 265 rear re71r or similar.

Seems like most of the available options are somewhere from 1.2 to 2 (3 in some of the race specs) times stock rates and from .6 to .75 ratio front to back.
OEM SUSPENSION - SPORT
125 lbs/in front (22N/mm)
200 lbs/in rear (35N/mm)
22mm front sway bar (cca. 13N/mm)
23mm rear sway bar (12 N/mm)

GMS RECOMMENED SPRING RATES for fast street use and occasional track:
300 lbs/in front (52 N/mm)
400 lbs/in rear (70N/mm)
22mm front sway bar (cca. 13N/mm)
no rear sway bar (to prevent wheelspin on non LSD cars)

GMS RECOMMENED SPRING RATES for track use and fast street driving where comfort is not an issue
370 lbs/in front (65 N/mm)
456 lbs/in front (80 N/mm)
22mm front sway bar (cca. 13N/mm)
no rear sway bar (to prevent wheelspin on non LSD cars) For the cars equipped with LSD,that's another story in terms of ARB

Different coilover designs on 4C are just aesthetics. The linking points are the same, so there shouldn't be much of a difference between products.

You should have them bump it to Phase 2 or 3. 3" exhaust is probably a bit big for only a Stage1 tune. You can run Phase 3 w/o the intercooler and just get it later if you wanted. I did it for about 2 weeks while I waited on my IC to show up.
I agree, go with STG2.
 

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Discussion Starter #287
I see ARB's biggest plus is the ability to balance understeer/oversteer without changing spring rates. You have a base setup which you fine tune depending of the track and weather by tuning ARB's.

Cars without LSD will suffer more wheelspin with ARB's, especially on slower, tighter tracks. On bumpy tracks or driving over the curbs will unsettle the car more if running ARB's. Running ARB's will allow for less static camber and better braking.

There is always a trade off. Personally I see LSD as one of the essential track upgrades for our 4C and ARB's just as a fine tuning tool, not meant to mask the soft stock suspension issues.
 

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I would like for someone to actually test an LSD on the racetrack and measure the performance improvement. Clearly it helps with traction on low speed corners but our cars (with OEM or stage 1 power) have a good amount of grip. The benefit on medium and high speed corners would be zero.
I wonder if a more complex LSD is not adding some extra friction and less performance on the straights.
When you install one maybe you can do a before / after test on the race track under similar conditions.
 

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Discussion Starter #289 (Edited)
Almost every track, has a slow corner or two. If you get a wheelspin there or you accelerate easily not to wheelspin, then you're loosing time. LSD would increase rear weight, would add friction, but it would transmit the torque to the wheel with more grip so you can accelerate sooner and harder. It would also help with braking stability and it wouldn't hurt straight line performance. Car with properly setup LSD will be noticeable faster. The reason I don't have LSD yet is time consume for install (engine out job).

Here are few examples where I was loosing a lot of time due to the wheelspin or I had to accelerate easily to prevent one:

(my wheelspin)

(no wheelspin, easy and late acceleration)

(opponent wheelspin)

(my wheelspin)

(my wheelspin)
 

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Discussion Starter #293 (Edited)
Akrapovic is for sure the most complete exhaust silencer out there in my opinion. The material is superior, it's 1.2mm thick titanium, the welding is nice too and the exhaust sound is quiet when needed and loud when wanted. There is no other way to make 4C noise comfortable and performance optimized at the same time. Such solution requires a valved exhaust with a muffler. But even though being full titanium it still weighs about 5kg, so once again, a trade off. Performance wise, when valves are opened, it's pretty much free flowing, but when they are closed it's quite restrictive, so, a trade off once again. I like minimalism, so straight through muffled system is the one for me, but I respect and understand other opinions.

The rear muffler, whichever you run, shouldn't affect performance on noticeable level unless completely mis-designed. The bottleneck and performance killer is the stock downpipe and stock 800 cell cat, so whatever you run from here on it doesn't really matter. You can run straight pipe and the heatsoak and backpressure will still remain unsolved.

We are currently working on GMS stage I and stage II tune to fully utilize our 3" exhaust, but stock and tuned ecu's should gain some power and torque in mid and high rpm range, while tuned ecu's even more, but what's more important, the engine power will remain stable and not so heat dependent (IAT).
 

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Akrapovic is for sure the most complete exhaust silencer out there in my opinion. The material is superior, it's 1.2mm thick titanium, the welding is nice too and the exhaust sound is quiet when needed and loud when wanted. There is no other way to make 4C noise comfortable and performance optimized at the same time. Such solution requires a valved exhaust with a muffler. But even though being full titanium it still weighs about 5kg, so once again, a trade off. Performance wise, when valves are opened, it's pretty much free flowing, but when they are closed it's quite restrictive, so, a trade off once again. I like minimalism, so straight through muffled system is the one for me, but I respect and understand other opinions.

The rear muffler, whichever you run, shouldn't affect performance on noticeable level unless completely mis-designed. The bottleneck and performance killer is the stock downpipe and stock 800 cell cat, so whatever you run from here on it doesn't really matter. You can run straight pipe and the heatsoak and backpressure will still remain unsolved.

We are currently working on GMS stage I and stage II tune to fully utilize our 3" exhaust, but stock and tuned ecu's should gain some power and torque in mid and high rpm range, while tuned ecu's even more, but what's more important, the engine power will remain stable and not so heat dependent (IAT).


What intercooler are you running?
 

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Yes, right after we finish:

1. GMS 3" adapter to Akrapovic exhaust rear silencer
2. Performance rear arms
3. Oil catch can kit
4. GMS Stage I ECU remap, stage II ECU remap, TCT remap
5. Adjustable ARB
5. Rear hood carbon cooling hatch
LOL, looks like we’ll be waiting a while. Thanks.
 

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Ran a full day in 30C+ heat on track with GMS 3” full exhaust. This was my third outing with it, but the first full day, in real heat, and I was able to get some legit data.

First off, opening the boot after a session, things are a lot cooler. That is just anecdotal, but I can tell you that despite the ambient temperature, and driving hard, my lap times kept getting better through the session, and were consistent or improving all day. 3 groups in 15 minute sessions, so not much cool down time between. I think that is a pretty good indication that things are staying cooler in the engine bay thanks to the less restrictive cat, the larger diameter, and the heat wrap!
 
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