Track question, SRT10 coupe vs GTS

[Janni]

The wag remains on the Comp Coupe.

Unless you are doing some bonzai manuevers - the tail doesn't swing around - but it is unsettling.

Chuck is right about some alignment adjustments will help this. I also suspect that the rear toe brackets from Snake Oyl would help keep the toe stable during hard braking.

Henry has felt that he's consistenly leaving time on the table by not utilizing the Comp Coupe's excellent braking. He did some test runs at VIR a couple of weeks ago and at one point on the back straight - I overlayed his data from his 1:59.6 qualifying lap on good tires and his practice laps on O-L-D tires and he increased his braking g's from 1.1 to 1.7 by braking deeper and STILL not getting into the ABS.

Of course, he then spun later in the session trying to see how far he could push it.... but there is still alot left out there....

 

[Dave Moore]

Quote:
Tail wag under heavy braking can be reduced with castor and toe in adjustments.

Thanks Chuck ...any more specifics on the adjustments?

 

[valentine_viper]

Quote:
and unsteadiness under maximum braking (basically a side to side movement), which reduces confidence during high speed braking


I have a 05 copperhead vert and noticed the same tail wag with heavy breaking...thought it was me becuuse I'm new to putting a car on a track. I am in the process of putting in SS break lines and the comp coup 2 piece rotors.
Has anyone done this and found it helps eliminate the wag?
I have to admit to the near need to change my shorts when I hit the breaks @150MHP heading into the tunnel turn at Pocono and I got this tail wag going on.
Dave Moore

Are you on stock suspension or lowered? Mine is stock and I didn't notice the tail wagging when I was at Pocono. But then again, it was my first time on a road course and I was so focused on just keeping the car on the track that I may have not noticed.

Tail wag under heavy braking can be reduced with castor and toe in adjustments.

 

[Catwood]

Quote:

Tail wag under heavy braking can be reduced with castor and toe in adjustments.

On the front or rear?

 

[Andrew/USPWR]

Catwood, can we be expecting a Coupe in your future? I've yet to track the SRT/10 but, I like the feedback your getting from the pros.

But I did love tracking the GTS.

 

[Catwood]

Good question. I love tracking my GTS also. It had headers and cat back on it when I bought it. I've added 6 point harnesses, coil over shocks, trap doors to the oil pan, 40 MM rear calipers, Forgeline wheels, tracked aligned, bump steer eliminated, SST brake line, PS cooler and 315 fronts. With everthing I've done I sit at 7 points with safety equipment.

I could add a roll bar and fire system or race seats and run super stock or I have 3 points to play with within Prepared.



Or I go shop a new coupe and start all over....and get it into prepared.

 

[Shelby3]

Good question. I love tracking my GTS also. It had headers and cat back on it when I bought it. I've added 6 point harnesses, coil over shocks, trap doors to the oil pan, 40 MM rear calipers, Forgeline wheels, tracked aligned, bump steer eliminated, SST brake line, PS cooler and 315 fronts. With everthing I've done I sit at 7 points with safety equipment.

I could add a roll bar and fire system or race seats and run super stock or I have 3 points to play with within Prepared.



Or I go shop a new coupe and start all over....and get it into prepared.

How much improvement did you notice on the 40mm rear caliper upgrade?

 

[Chuck 98 RT/10]

Quote:

Tail wag under heavy braking can be reduced with castor and toe in adjustments.

On the front or rear?

If your suspension is already aligned the way you want then I'd start with bringing the rear toe in a bit.

 

[Fast Freddy]

Stock for stock comparison for you guys that have owned both.

On stock tires is the SRT10 coupe really faster on the roadcouse? If so...how much.

my brother owns a srt-10 coupe

the srt-10 coupe has a longer wheelbase and better suspension geometry other than that every advantage that the srt-10 coupe has over a gen-2 gts coupe can be equalled by upgrading the gen-2 coupe to the srt-10 coupe specs. ie: the brakes on a gen-2 can be upgraded, etc. i can think of one disadvantage that a srt-10 coupe has versus a gen-2 coupe and that is at .35 the coefficient of drag on a gen-2 coupe is better than the srt-10 coupes .39

as far as weight goes i think their is less than 100 lbs difference. the gen-2 i think is slightly lighter. there is less cockpit space in a srt-10 coupe than a gen-2 gts. i have yet to see how anybody has installed a 4 point roll bar in a srt-10 coupe

 

[Chuck 98 RT/10]

FF, the question was "Stock for stock comparison."

Once you mention "upgrades" or "mods" the discussion becomes moot. And as I mentioned earlier, even with a brake upgrade the SRTC would still beat the GTS.

 

[Tom F&L GoR]

The normal rear toe pattern produces a toe out direction with rebound (droop.) Therefore under braking (nose dive and rear up attitude) the rear goes to more toe-out. As Chuck said, it makes sense to add more rear toe-in to keep the rear behind you.

 

[Tom F&L GoR]

Chuck 98 RT/10

Catwood is having some login issues (!!) and asked if you would recommend some rear toe settings. Thanks.

...only 12 posts from being a top 75 poster...

 

[CCBrian]

Having owned and tracked my 2001 ACR, and now my '06 FE Coupe, the new one is way faster and easier to drive. The tail wag in high speed braking that is mentioned is really not a problem. My Comp Coupe (CC64) does the same thing but the ABS will pull it straight. I will admit the first time out it felt a little unnerving but it will stop straight. I don't care how good a driver your are the ABS is better than you are.Dodge did a grat job with these new brakes.That said, stock for stock, an new SRT-C will walk away from a Gen 1 or 2 and it is much easier to drive fast.

 

[PatentLaw]

CCBrian - are the brakes that much better between the ACR and the 06? Above, most people have non-ABS Gen II cars-like comparing apples and oranges. Brakes were significantly improved with 01 and 02. Significant improvement?

 

[SylvanSRT]

the change from '01 and '02 to the '03 is very dramatic. the brakes on the gen 3 cars transformed the Viper from a hot rod into a world class sports car!

 

[Warfang]

I've driven both and the gen3's kicks @$$ on the brakes alone... and it pulls a bit faster too

I'm just a stickler for the older styling ,but have low confidence in the brakes. Tom... just finish a bunch of maintanence stuff (new clutch, tires, etc)... your brakes will be next.

 

[Tom F&L GoR]

PatentLaw points out the apple/orange issue, so it's tricky to understand what exactly is the comparison in people's comments.

In a previous post, I documented the 0.8G to 1.0G (spikes up to 1.1G) braking improvement from just the rear brake change, and GR8 ASP added the SRT braking data which showed a 1.1G (spikes to 1.2G) performance. The '94 RT was a customer car I was driving (poorly, perhaps) and did not have the prop valve disabled, so there's possibly a little left on the table, and of course, doesn't have the ABS that the SRT does.

http://www4.forum.viperclub.org/showflat.php?Cat=&Board=UBB14&Number=558609&fpart=1&PHPSESSID=

The missing data is a similar test with an 01-02 car. They had same front caliper as the Gen 1 car, a 43mm single piston rear caliper, and ABS. On paper, that is more than enough rear brake, so I am of the opinion that it should equal an SRT in brake balance (assuming the ABS algorithms are equal) and stopping performance.

SylvanSRT and Warfang, I've admitted my presumptions, so if you could expand on your comments, I would appreciate learning what the 01-02 car to SRT car difference is. If the SRT is still "better", are we looking at the details of suspension geometry during braking or vehicle weight balance?

Lastly, I have word from Tom Sessions that Viper Days will not add points for the use of 40mm calipers. Maybe you'll see some more of them (or current owners will admit it) on the track and the performance comparisons will be more readily available.

 

[SylvanSRT]

yes SRT's are lighter, different suspension set up, the car also has a system that will adust brake pressure on the calipers to suit the given situation(electronic brake distribution ? i think). bigger rotors all around. the rears on gen I & II cars have calipers that are no match for the cars abilities. Gen 3 also has a seperate system for the parking/E-brake. The stopping distances have improved greatly i checked some old mags i have a

'98 gt1 replica 60-0 147'
'00 rt/10 60-0 117'
'00 ACR 60-0 115'
'03 srt 60-0 99'

 

[GR8_ASP]

Tom, Mike hit the main points. The SRT seems to have a suspension that allows weight transfer somewhat quicker than the Gen II. Enough that my butt feels it, but slower than some others. It also have electronic proportioning so even when ABS is not invoked the balance front to rear is near optimum. That is what allows the system to have equal braking capability front to rear.

Note please do not ask what happens when the ABS fails on the track (unbeknownst to the driver) and disable ABS and the proportioning valve).

 

[Warfang]

Tom, my gts is a 97, so no ABS, and more "pray when you brake". I also haven't driven an ABS gen2 before for comparison. When I have to brake sudden and hard to avoid an accident, the car pitches right (or left... don't remember as I was too busy holding my *** in).

 

[Tom F&L GoR]

Wow, gang is all here.

I didn't know SRTs had a brake pressure distribution system; I have read about them on Mercedes cars. It seems to be an electronic version of the mechanical-hydraulic proportioning valve.

I would be worried about EBD failing; allowing rear lock up gets you in trouble maybe faster than ABS failing and allowing front lock up! (blatant scare tactic for when a Gen 1 and Gen 3 are braking side by side... )

Anyone have an '01-02 braking distance number? I'm actually surprised the '00 cars were that good.

Warfang, you'll be happy to "hold it" when you make the caliper switch.

 

[Chuck 98 RT/10]

I researched the stats to compare the ABS GenII Vipers againts the non-ABS GenII Vipers and every published article I found was identical.

Warfang, it shouldn't pull to one side under hard braking. It probably needs a caliper rebuild.

Tom, your rear brake upgrade works great.

 

[Warfang]

I researched the stats to compare the ABS GenII Vipers againts the non-ABS GenII Vipers and every published article I found was identical.

Warfang, it shouldn't pull to one side under hard braking. It probably needs a caliper rebuild.

Tom, your rear brake upgrade works great.

Would Tom's upgrade negate a caliper rebuild? Or is there more to it than that?

 

[Chuck 98 RT/10]

At the time you swap out for Tom's calipers you could change the rings in the front calipers. Not much to it and you'll have to bleed the system anyway.

 

[PatentLaw]

Not to disagree....but I am going to....

Edmunds tested a 2000 GTS (non-abs) 60 to 0 in 155ft.
Edmunds also tested a 2001 ACR (abs) 60 to 0 in 115 ft. In other words...worlds of difference.

Most recent test of Road and Track August 2006 - SRT10 Braking 60 to 0 113 ft. Not making this stuff up.

Wow....a HUGE world of difference (2 ft). I am a really embarrased Gen II owner.

Of course, that test has nothing to do with fade and continual track usage...which prompted my question from CCBrian as he has owned both of the cars. I am pleading ignorance here. I am not trying to start something, but the numbers that I have reviewed do not necessarily bear out the worlds of difference. Moreover, if the difference is a mere 2 ft, different road surfaces, weights of the drivers and weight in the fuel tank can play a major role as there is less than 1 percent difference. Just something to consider.

 

[REDSLED]

Catwood, all of this talk of brakes and lap times is based on the assumption that better brakes lower your lap times. You know that is not the case. Assumptions on the race track are very dangerous. Also, haveing ABS doesn't necessarily mean you'll be faster on the track as well. it may give you a warm, fuzzy feeling of confidence knowing that you have them, but the average racer probably won't engage them as much as they think. Look at the most recent World Challenge winners (Gigliotti C6 & Emery 997 Porsche)neither had ABS.PM me and I will shed some light on you for some suggestions.

 

[Warfang]

Not to disagree....but I am going to....

Edmunds tested a 2000 GTS (non-abs) 60 to 0 in 155ft.
Edmunds also tested a 2001 ACR (abs) 60 to 0 in 115 ft. In other words...worlds of difference.

Most recent test of Road and Track August 2006 - SRT10 Braking 60 to 0 113 ft. Not making this stuff up.

Wow....a HUGE world of difference (2 ft). I am a really embarrased Gen II owner.

Of course, that test has nothing to do with fade and continual track usage...which prompted my question from CCBrian as he has owned both of the cars. I am pleading ignorance here. I am not trying to start something, but the numbers that I have reviewed do not necessarily bear out the worlds of difference. Moreover, if the difference is a mere 2 ft, different road surfaces, weights of the drivers and weight in the fuel tank can play a major role as there is less than 1 percent difference. Just something to consider.

You're right, and I guess in regards to braking, the differential should be abs/non-abs, and not gen 1-2/gen3. That said, the additional power and better handling still gives the srt's a slight advantage on the track, and the cup holder just puts it over the top!

I just might have to trade my 97 in for an 02.

 

[Tom F&L GoR]

Formula courtesy of Stoptech:
http://www.stoptech.com/tech_info/The%20Physics%20of%20Braking%20Systems.pdf

Stopping Distance = (original velocity^2)/(2 * deceleration rate)

velocity in MPH times 1.4666 gives velocity in ft/sec
deceleration rate of 1 G = 32.2 ft/sec^2

examples for 0.8, 1.0 and 1.2 G
distance from 60 MPH = (1.4666*60)^2/(2*32.2*0.8) = 150ft
distance from 60 MPH = (1.4666*60)^2/(2*32.2*1.0) = 120ft
distance from 60 MPH = (1.4666*60)^2/(2*32.2*1.2) = 100ft

So non-ABS cars stop at roughly 0.8 G's, ABS cars are a little better than 1.0 G's, with 40mm cars only slightly behind.

PatentLaw, that fits more with the testing of a '94 and my (amateurish) track experience. I'm sure Chuck would modestly agree that his braking performance is closer to that of ABS cars than the OEM setup.

 

[Chuck 98 RT/10]

Edmunds tested a 2000 GTS (non-abs) 60 to 0 in 155ft.
Edmunds also tested a 2001 ACR (abs) 60 to 0 in 115 ft. In other words...worlds of difference.

Correct. That is worlds of difference. But something doesn't seem right. When the 01 came out there wasn't much fanfare about it's braking capability other than it had ABS.

I'm gonna have to borrow a GenII ABS and test it for myself at Sebring sometime.

 

[SylvanSRT]

gen II with ABS were much better but the issue of fade did not go away after only 10-15min of a 20 min session the fade would start to appear with the pedal going almost to the floor