GMs in IT

[Ron Earp]

With the Mustang discussion last week I noticed that we don't have much GM participation in IT. However, I think there are a couple of places where the General can come out and play.

The 1993, 1994, 1995 4th Generation Camaro has an engine option that would fit well into ITS, the 3.4L 90 degree V6. Stock the motor is rated at 160hp and 200 ft-lbs of twist. Looks like it'd drop into ITS at around 2580 lbs before any adders for torque, so maybe a mid-2600 spec weight.

Another GM platform that Mr. Young pointed out is the C4 Corvette circa 1984. 205 hp, 290 tq, it should fit into ITR with no problem. Great motor, good brakes, reasonably light chassis that will probably need ballast at a spec weight of around 3100-3200 lbs.

I think I'll write a letter and ask to have both of these cars classed.

[JoshS]

While on the ITAC I lobbied the CRB for a new faster IT class which would fit the M3 and the C4 Corvettes. Unfortunately only the '84 is likely to fit decently into ITR and that's not a very desireable package compared to the later cars.

[Ron Earp]

While on the ITAC I lobbied the CRB for a new faster IT class which would fit the M3 and the C4 Corvettes. Unfortunately only the '84 is likely to fit decently into ITR and that's not a very desireable package compared to the later cars.

The 1984 C4 fits into ITR. While maybe not as desirable as later model C4s, it'd be possible to class it as is in ITR. Over 51000 1984 examples were built so there is plenty of race car fodder out there for cheap prices. Probably even get a leather jacket and gold chain to go with it.

[joeg]

No love for Fieros, Citations or Chevettes?

[Ron Earp]

No love for Fieros, Citations or Chevettes?

Au Contraire, I love Fieros. I still think a full on 100% Megasquirted built to the max Fiero could do some damage in ITA. Still haven't seen a 100% build yet, or close to it.

Those other two, no, no love there despite the common DNA with the Fiero.

[chuck baader]

Look at the intake manifold/ports on the Fiero and you might change your mind. cB

[CRallo]

I like the ideas. Good thinking.

3.4 needs a torque adder? What else does? Where is the line drawn?

[TomL]

"Torque adder"? Is that still around? I'll say it again. Horsepower counts, torque doesn't. "Torque monster" is noting but a synonym for "revless wonder". I wonder why things like torque adders are still even discussed, much less used. Color me disappointed.

[JoshS]

"Torque adder"? Is that still around? I'll say it again. Horsepower counts, torque doesn't. "Torque monster" is noting but a synonym for "revless wonder". I wonder why things like torque adders are still even discussed, much less used. Color me disappointed.

Tom, I agree, but here's why it is part of the Process:

What really matters is not only peak HP, but also, the breadth of the peak part of the HP curve. Until we are all using CVT transmissions, we'll be spending some full-throttle time away from the HP peak. We need something to approximate how quickly HP falls off on either side of the peak to account for this. Neither displacement nor peak torque are exactly related to this, but on average are decent indicators of this breadth and are easily available to the ITAC.

[Gary L]

Look at the intake manifold/ports on the Fiero and you might change your mind. cB
Put one on the track and you might change it back. :) I've posted this story on these pages before, but what the Hell...

In 2004 I took a nearly stock (I've owned it since new, so I know what's been monkeyed with and what hasn't) '88 Fiero GT to Hallett and did a few track days. The car had the muffler removed (converter still installed), was lowered an inch or two by chopping the stock springs, and had orange Koni street shocks front and rear. We mounted some used Hoosier SM's on 7" Kosei K1's, decambered it front & rear and went at it. We ended up 3.5 seconds off the ITA lap record, held at that time by Bob Stretch in the Nissan 240S. This was with nothing done to the engine - and I do mean nothing whatsoever; no chip, no headers, no tuning of any sort. Oh, yes... about the weight... we were 300 pounds (three hundred - it's not a typo) over current ITA minimum for the car. And remember, we're talking about a 2900+ lb car on used 205/50 15's!

I'm not saying it's an overdog in ITA, but I sure wouldn't dismiss it as an also-ran; in full prep and the right hands, the car is a potential front runner IMO.

[TomL]

Josh - I realize that high torque has sometimes been taken as an indicator of wide torque band. For a specific engine, I don't doubt that is the case. However, I have serious doubts that this is true across the huge variety of engines that are found in IT. Admittedly, I haven't seen a huge number of dyno sheets to confirm my impression, but I'll take that as true until I see otherwise.

Have you all done a systematic survey of all the data you have to demonstrate that peak torque is a reliable indicator of power band width? Is so, could I see it? I've been thinking about writing a paper on the whole torque vs. HP question, and would like to see what anyone else has discovered. Alternatively, could I get access to a selection of the dyno graphs the ITAC has so I could do my own analysis? This is a topic which has bothered me for years, and I'd like to see a definitive resolution.

Thanks

[Ron Earp]

3.4 needs a torque adder? What else does? Where is the line drawn?


Apparently it is a "We know it when we see it" thing. Empirically it is a "Domestic Penalty" - TR8 (ITS, maybe it has one, domestic motor), Mustang V8 in ITR (does have one), Camaro V8 in ITR (has one), Corvette (not classed but would probably have a torque adder in ITR) - all domestic powered cars with torque adders.

RX7s have no torque to speak of, but at 8000 RPM that twisting force makes a lot of horsepower, and horsepower tells us how much work we can do with the motor. There are many torqueless motors that perform just fine - Miatas, GSR, etc. because they produce good horsepower in the framework of the class they race. Their horsepower peaks are broad enough to get the job done.

Naturally I'd take a broader horsepower curver over a narrower horsepower curve as the area under the horsepower curve that is accessible with the gearbox is all that makes any difference. But in looking at a lot of dyno plots I'm not entirely convinced that 2V large displacement domestic engines are producing horsepower curves that are appreciably wider than small displacement imports. Especially when most of the import motors have four valve heads which provide for impressive breathing capability.

But besides all of that, those two GM cars should be in IT. Shame about the Camaro as it doesn't have disc brakes in the rear. Typically GM does ok on brakes but they left drums on the car until it got the more powerful 3.8L V6.

[GKR_17]

Tom, I agree, but here's why it is part of the Process:

What really matters is not only peak HP, but also, the breadth of the peak part of the HP curve. Until we are all using CVT transmissions, we'll be spending some full-throttle time away from the HP peak. We need something to approximate how quickly HP falls off on either side of the peak to account for this. Neither displacement nor peak torque are exactly related to this, but on average are decent indicators of this breadth and are easily available to the ITAC.

You have to admit that is is completely bogus to have an adder for torque, but not account for the transmission. We have cars getting deductions for low torque that also have ridiculously good ratios in 6-speed boxes.

[Z3_GoCar]

Apparently it is a "We know it when we see it" thing. Empirically it is a "Domestic Penalty" - TR8 (ITS, maybe it has one, domestic motor), Mustang V8 in ITR (does have one), Camaro V8 in ITR (has one), Corvette (not classed but would probably have a torque adder in ITR) - all domestic powered cars with torque adders.

RX7s have no torque to speak of, but at 8000 RPM that twisting force makes a lot of horsepower, and horsepower tells us how much work we can do with the motor. There are many torqueless motors that perform just fine - Miatas, GSR, etc. because they produce good horsepower in the framework of the class they race. Their horsepower peaks are broad enough to get the job done.

Naturally I'd take a broader horsepower curver over a narrower horsepower curve as the area under the horsepower curve that is accessible with the gearbox is all that makes any difference. But in looking at a lot of dyno plots I'm not entirely convinced that 2V large displacement domestic engines are producing horsepower curves that are appreciably wider than small displacement imports. Especially when most of the import motors have four valve heads which provide for impressive breathing capability.

But besides all of that, those two GM cars should be in IT. Shame about the Camaro as it doesn't have disc brakes in the rear. Typically GM does ok on brakes but they left drums on the car until it got the more powerful 3.8L V6.

First I've heard of a "Domestic" penalty... My car's made in Greer South Carolina, this might explain a bunch.

[jacklee]

Hey thanks for sharing such an good stuff. Good work. Keep it up.:)

[erlrich]

With the Mustang discussion last week I noticed that we don't have much GM participation in IT. However, I think there are a couple of places where the General can come out and play.

The 1993, 1994, 1995 4th Generation Camaro has an engine option that would fit well into ITS, the 3.4L 90 degree V6. Stock the motor is rated at 160hp and 200 ft-lbs of twist. Looks like it'd drop into ITS at around 2580 lbs before any adders for torque, so maybe a mid-2600 spec weight.



The only problem with that (well, not the only, but the major problem) is the same problem its younger cousin has in ITR, but worse; the weight. All the 4th gen cars all weigh about the same - ~3300 lbs. Add a cage and a driver, and you'll need to drop almost 1000 lbs to get to the ITS weight.

I'm pretty sure the ITAC & CRB don't agree (we should find out this month), but I think those cars should be classed in the lower class at a heavier weight, i.e. the 3.8 should be in ITS at ~3200 lbs and the 3.4 should be in ITA at the same weight. Even then I think they would both be mid-pack cars.

[Ron Earp]

The only problem with that (well, not the only, but the major problem) is the same problem its younger cousin has in ITR, but worse; the weight. All the 4th gen cars all weigh about the same - ~3300 lbs. Add a cage and a driver, and you'll need to drop almost 1000 lbs to get to the ITS weight.

I'm pretty sure the ITAC & CRB don't agree (we should find out this month), but I think those cars should be classed in the lower class at a heavier weight, i.e. the 3.8 should be in ITS at ~3200 lbs and the 3.4 should be in ITA at the same weight. Even then I think they would both be mid-pack cars.

I'm not a 4th generation Camaro guru and I'm assuming your not quoting marketing/magazine/web curb weights, but the Mustang hasn't played out as badly as predicted. With the stang it is more a question of dropping few hundreds of pounds, not many hundreds of pounds. Any chance of a real-world V6 T5 Camaro in street trim coming in at 3100-3200 lbs with a light driver sitting in the seat?

I haven't been asked but I don't think a 3.8L V6 Camaro in ITS at 3XXX lbs would be that attractive. It'd have the juice though. I'm not much up on ITA, but I wouldn't fancy my chances with a 3XXX lbs weight in ITA either. I think I'd rather race a 3.4L V6 Camaro a couple of hundred pounds over spec weight in ITS than race it in ITA at its curb weight. But, there again, I don't have much Camaro experience. Is the CRB/ITAC considering re-classing the Camaro?

I do like the Camaro classed in ITR though at around 2800 lbs. That weight seems obtainable, the chassis has some good features, and the motor should be able to make power needed for the class. Bummer that the 3.4L ITS version has rear drum brakes - I swore those off when I sold the Z.

[erlrich]

I'm not a 4th generation Camaro guru and I'm assuming your not quoting marketing/magazine/web curb weights, but the Mustang hasn't played out as badly as predicted. With the stang it is more a question of dropping few hundreds of pounds, not many hundreds of pounds. Any chance of a real-world V6 T5 Camaro in street trim coming in at 3100-3200 lbs with a light driver sitting in the seat?

I haven't been asked but I don't think a 3.8L V6 Camaro in ITS at 3XXX lbs would be that attractive. It'd have the juice though. I'm not much up on ITA, but I wouldn't fancy my chances with a 3XXX lbs weight in ITA either. I think I'd rather race a 3.4L V6 Camaro a couple of hundred pounds over spec weight in ITS than race it in ITA at its curb weight. But, there again, I don't have much Camaro experience. Is the CRB/ITAC considering re-classing the Camaro?

I do like the Camaro classed in ITR though at around 2800 lbs. That weight seems obtainable, the chassis has some good features, and the motor should be able to make power needed for the class. Bummer that the 3.4L ITS version has rear drum brakes - I swore those off when I sold the Z.

Ron - not a guru either, but I did stay at a Holiday Inn...err, scratch that - I did take my car ('02, V6, T5) across the scales at Summit a couple of years ago just to see what I would have to lose to get to ITR weight. With my 250 lb backside in the seat, and about 1/4 tank of gas (~4 gals) it came in at 3535 lbs. That was in full street trim - spare tire, jack, full interior, etc.

The V6 currently runs in SSB at 3300 lbs, and the V8 version is classed at 3530 lbs in both AS and T2. To the best of my knowledge, other than things you can change in IT trim (springs, sway bars), the suspension, diff, and brakes are identical on both V6 and V8 versions. I know 3300 lbs sounds heavy to us in IT-land, where 2600 lb cars are considered pigs, but I think that car will work at the higher weight. That said, I really don't think this will be a great car in either class; I think Andy summed it up well...something like "you can put lipstick on a pig, but in the end it's still a pig". :D

And yeah, I put in a request to have the V6 Camaros & Firebirds moved to ITS months ago; I just received an email that the ITAC & CRB have reviewed the request, and the decision should be in the next FT.

[Ron Earp]

I know 3300 lbs sounds heavy to us in IT-land, where 2600 lb cars are considered pigs, but I think that car will work at the higher weight. That said, I really don't think this will be a great car in either class; I think Andy summed it up well...something like "you can put lipstick on a pig, but in the end it's still a pig". :D


Time to get some pigs in IT. What are they making these Camaros out of, Tungsten?

I bet the car can make ITR weight with some serious work. Dick got his RX7 to make ITA weight, against all the naysayers, and it was apparently a lot of work. I can get Dercole's ITR stang to minimum weight and I think he's convinced of that too.

I can't get my ITS stang down to weight, but I think I can get close enough to weight that it'll be a threat in ITS, at the expense of many man hours of work, but it might just be possible. The Camaro could be a similar situation in ITR.

So in ITS trim the 3.8:

200x1.25x12.9 = 3225 (no "torque adder" applied, does it get one?). Dang ol. No doubt the 3.8L can make some power, but that is some serious weight to haul around. About 600 lbs heavier than the RX7, more than 700 lbs heavier than the Z. I've always liked those GM 3.8L engines. Powerful workhorses that didn't complain much. Man ol man, talk about parts aplenty.

In ITR trim it is considerably lighter, 2815 lbs. Let's say it can't make 2815 lbs and has to race at 2950 , still seems like a good package for ITR. I'd be surprised if they moved it to S, but you never know. S or R, I'd love to see some of them on track. High time to move away from the Mazda Car Club of America.

Earl, how user friendly are they? I haven't poked around them much, but the ones I have looked at seem like a definite "front mid-engine" design. The motor seems to live under the dash between the two occupants. Definitely a slick exterior. And, from the times I spent in the back seat of the 3rd gen cars in the 80s I know there isn't a lot of room there. The Mustang seems like a more usable package although maybe at the expense of handling.

[Andy Bettencourt]

Letter ID Number: #6637
Title: 1984 C4 Corvette Classification
Class: ITR
Request:
I would like to request the classification of the 1984 C4 Corvette. Specs are below needed to classify the car per the ITCS:

1984 Chevrolet Corvette
205hp@4300 / 290 lb-ft@2800
Curb weight 3200lbs
V-8 OHV
Bore and Stroke: 101.6mm x 88.4mm
Intake valve: 1.94”
Exhaust Valve: 1.50”
Compression Ratio: 9.0:1
Wheelbase: 96.2”
Wheel sizes: Base: 16”x8.5” Z51 package: 16”x8.5”F, 16”x9.5”R
Transmission ratios: 4 speed, 2.88, 1.91, 1.33, 1.00
Brake size: 292.1mm F&R (11.5”)
Independent front and rear suspension with transverse leaf springs.

Using the classification process, I would see it playing out like this:
205 x 1.25 x 11.25 = 2882.8 rounded to 2885lbs.

If you care to research these cars, you will find out that they share the ‘cross-fire’ injection with the 1983 C3 L83 cars. Horrible for revs but decent torque. Pre tuned-port-injection. Single year on a single spec line.

We have a build pending the weighting of the car. Thanks.

[Ron Earp]

I also wrote a letter a few weeks ago asking to class the C4 and 3.4L Camaro. Don't see any reason why both shouldn't be included in ITR/ITS respectively.

R

[erlrich]

Earl, how user friendly are they? I haven't poked around them much, but the ones I have looked at seem like a definite "front mid-engine" design. The motor seems to live under the dash between the two occupants. Definitely a slick exterior. And, from the times I spent in the back seat of the 3rd gen cars in the 80s I know there isn't a lot of room there. The Mustang seems like a more usable package although maybe at the expense of handling.

Ron - sorry, I missed this earlier.

They're actually pretty user-friendly - the 6 can borrow everything suspension-wise from the 8, so there are plenty of suspension pieces to pick from. Somewhat less for the engine, but still enough to do a decent IT build. And yeah, the 6 sits mostly behind the front wheels, so that helps. And you can tune the OEM computer. I do think it will make 250 HP with a full-tilt build, but that's about it.

Great brakes - I've done a few track days with mine, and with just HP+ pads it has brakes to spare (at 3500 lbs I would note). The only concern re brakes would be the aluminum calipers - I've heard tales of them deforming under lots of heat. Good brake cooling would be a must I would think. The AS guys talk about replacing front hubs often, so that may be a problem area. And then there's that live axle...



In ITR trim it is considerably lighter, 2815 lbs. Let's say it can't make 2815 lbs and has to race at 2950 , still seems like a good package for ITR. I'd be surprised if they moved it to S, but you never know. S or R, I'd love to see some of them on track. High time to move away from the Mazda Car Club of America.

Obviously the ITAC agrees. I just don't see anyone in their right mind building one - when you have the choice of a 2,800 lb E46, a 3,000 lb S2000, a 3,050 lb 968, and a 2,950 lb Camaro, I think the Camaro comes dead last every time. I would also love to see one built, but my guess is if you do it will be another one of those 'sentimental' cars guys build, and not full-tilt pro build that will show what it really is capable of. Maybe when the Camaros age out of SSB next year we'll see a few of them migrate to IT.

[Ron Earp]

I do think it will make 250 HP with a full-tilt build, but that's about it.

That is some serious power for ITS, even at 3300 lbs weight.



Obviously the ITAC agrees. I just don't see anyone in their right mind building one - when you have the choice of a 2,800 lb E46, a 3,000 lb S2000, a 3,050 lb 968, and a 2,950 lb Camaro, I think the Camaro comes dead last every time.

The thing is, the same, or functional equivalent cars exist in ITS . All of those cars exist in ITS (replace S2000 with Miata, 968 with 944 S) with larger weight differences compared to the Camaro (at 3300 lbs), so using your line of thinking the car would be a last choice car in ITS too.

Don't you think you might be assigning too large of a performance detriment to the live axle? Of the few cars in IT that use them, most notably in my area the ITB Mustang and ITS TR8, the axle doesn't seem to be a detriment at all. As long as the full rear axle allowances in IT are taken advantage of both chassis are SARRC Champion winners and podium material any weekend in their respective classes. I'm looking forward to using the axle in the Mustang compared to messing around with Datsun 240Z geometry.

I think a well-built ITR Camaro sporting 250 flywheel hp at 2815 lbs could put a hurting on some ITR regulars.

[DSeefeldt]

Ron:

I'm considering building a 4th Gen Camaro for ITR. I agree with you, I think if done right, it can be a very competitive car.

Back in the day, 1984, when ITA first started out here in the San Francisco Region, I built a ITA V6 Capri and did very well with it. Although everyone said it couldn't be done, we won some races and usually finished in the top 5 - 10. We would have 20 - 25 car ITA fields with mostly RX3's.

I sold that car back in 1992 and built an AS Camaro. Raced it for a couple of years and then took 15 years off. I got back on the track last year. I now have the itch to build one more car. This one for my son. I'm thinking a V6 Camaro could be a good build. Plus I want to build a car I can run in the annual NASA 25 hour enduro at Thunderhill Raceway Park in Willows, CA that gets better gas mileage than my AS Camaro gets.

Stay Tuned!

Darryl Seefeldt
AS Camaro #22
San Francisco Region

[StephenB]

We have a build pending the weighting of the car. Thanks.

Another ITR car for the NorthEast! Awesome :) We will be at 20+ car fields sooner than we know it!

Stephen

PS: Andy you should build an ITR car not that ITS miata! :)

[JeffYoung]

Of those choices, the Camaro is the cheaper build, by far, and may make the most power.



Obviously the ITAC agrees. I just don't see anyone in their right mind building one - when you have the choice of a 2,800 lb E46, a 3,000 lb S2000, a 3,050 lb 968, and a 2,950 lb Camaro, I think the Camaro comes dead last every time. I would also love to see one built, but my guess is if you do it will be another one of those 'sentimental' cars guys build, and not full-tilt pro build that will show what it really is capable of. Maybe when the Camaros age out of SSB next year we'll see a few of them migrate to IT.

Also, I agree with Ron on the live rear deal. I don't think there should be a weight break for it. Setup right, it is not, in my opinion, a real detriment. I do not perceive a handling deficit on my car to the best RX7s, 240s, etc.

[dickita15]

Also, I agree with Ron on the live rear deal. I don't think there should be a weight break for it. Setup right, it is not, in my opinion, a real detriment. I do not perceive a handling deficit on my car to the best RX7s, 240s, etc.

Interesting, so you do not think the advantage of adjusting rear camber and toe rises above the noise level in car differences.

[Knestis]

Point of interest - back in the early "stock car" era of TransAm (early '80s), some Corvette teams petitioned to use solid rear axles because they couldn't get their IRS to work the way they wanted...

K

[Ron Earp]

Interesting, so you do not think the advantage of adjusting rear camber and toe rises above the noise level in car differences.

I'm sure it probably does.

But, having driven Jeff's car and my Z back to back (he's done more of that than I have as I don't drive his in races) I feel the differences are negligible, at least at my level of driving.

I understand that the Z should have an advantage with tire contact patch while cornering, and should be superior in keeping the tire on the racing surface. But in practice, the TR8 doesn't seem to give up anything to the Zs or RX7s in tight corners, or long sweepers.

I feel (no data) that the independent suspensions would have a greater chance to shine if the surfaces were a bit more undulating or less smooth. But at Roebling Road and VIR, both very smooth tracks, the live axle works well.

Indeed, the latest Mustang live axle iteration comes from the factory with tri-link and panhard rod. It gets rave reviews even when compared against IRS designs from BMW, Nissan, GM, and others. What's old is new again.

Interestingly enough, solid axles aren't as heavy as you might think. The 7.5" rear axle, with stock arms and shocks, is lighter than the Z pumpkin, half shafts, batwing lower arms, and uprights. The former assembly I can struggle to move, the latter I have no chance in hell of moving. Maybe Nissan needs to get with the program and put a stick axle in the new Z.

[erlrich]

Of those choices, the Camaro is the cheaper build, by far, and may make the most power.

Agree on the cost part for sure.


Also, I agree with Ron on the live rear deal. I don't think there should be a weight break for it. Setup right, it is not, in my opinion, a real detriment. I do not perceive a handling deficit on my car to the best RX7s, 240s, etc.

Jeff - out of curiosity, at VIR are you using the curbs going up through the esses (except for the last one at the top of the hill), and going through hog pen? I don't have tons of track time on the Camaro, but from what I've done I just can't imagine those curbs wouldn't play hell with the rear end of the car.

[Ron Earp]

Agree on the cost part for sure.



Jeff - out of curiosity, at VIR are you using the curbs going up through the esses (except for the last one at the top of the hill), and going through hog pen? I don't have tons of track time on the Camaro, but from what I've done I just can't imagine those curbs wouldn't play hell with the rear end of the car.

Yeah, he runs them like most everyone else. Stable and good. Or, it seems as stable as my car did in the same situation.

http://youtu.be/JWXt8qLsRAY?t=51s

[dickita15]

Point of interest - back in the early "stock car" era of TransAm (early '80s), some Corvette teams petitioned to use solid rear axles because they couldn't get their IRS to work the way they wanted...

K

Ah yes and Group 44 ran a live axel in the TR4A in nationals in the 70’s

[billf]

Of those choices, the Camaro is the cheaper build, by far, and may make the most power.

Also, I agree with Ron on the live rear deal. I don't think there should be a weight break for it. Setup right, it is not, in my opinion, a real detriment. I do not perceive a handling deficit on my car to the best RX7s, 240s, etc.

While I agree that the live axle is not in itself a detriment, the linkages to it can be. Incidentally, the Live Axle is only one of two designs that accomplish all goals in suspension geometry: constant camber regardless of chassis attitude, whether it is acceleration, braking, or cornering. The other is the De Dion. All others offer compromises under some condition, or the other. Incidentally, as we all know, the give-away with the live axle is of course the unsprung weight. While a De Dion has less unsprung weight, it still has more compared to an Independent Suspension.

Back to my statement about linkages... All live axle cars do not have the same linkage setup. The Camaro has the best, with the factory torque arm, as demonstrated in AS. The Mustang has to have the worst, with the four arm setup, which inherently binds when cornering, or under hard acceleration (when it doesn't matter). (For those who don't know, these four arms are controlling all longitudinal, and, lateral movement of the chassis...at least that's what we would like to happen.) All solutions except two, modify the bind, but do not eliminate it...just make it happen at a different time. Any bushing material replacement has the potential of increasing the bind...it cannot be eliminated because of the dissimilar arcs of motion created by three different planes of control.

The two solutions are the aftermarket three link (not four), and the aftermarket torque arm. Unfortunately, the offerings of torque arms for Mustang are enginereed for the 8.8 inch rear, not the 7.5 which the car is produced with. Thus, no aftermarket torque arm for the ITS or ITR V6 Mustang. Also, a Panhard Rod, or Watts Link must be added to provide the lateral location lost when the upper arms are removed...more weight.

Unfortunately, all solutions to the bind for the Mustang will add weight to an already overweight platform. If it ain't broke...you might find that the car can be driven without the need for additional linkages. I did for years with an ITB.

Just my two cents worth after dealing with the identical suspension in my '87 Mustang...7.5 rear also.

Bill

[dickita15]

When I look at the four link in a Mustang I see the ITA/ IT7. The three link conversion on that works pretty good and has already been accepted as IT legal

[Ron Earp]

When I look at the four link in a Mustang I see the ITA/ IT7. The three link conversion on that works pretty good and has already been accepted as IT legal

Yep, and it does a damn good job on those cars and Jeff's TR8. We're designing our own with the 7.5" in the stang and we have access to some CNC milling in ally. Putting it together in CAD we can design a tri-link setup that is very light and strong, thus minimizing the weight addition. Of course the physical pad/attachment to the car is done with steel. We could do a torque arm for the 7.5" but the weight there is pretty high, even with extensive use of ally. I'm also not convinced the torque arm is ideal.

Ford's tri-link on the new stangs is light and it works well I'm told. If we could reliably weld bosses on the 7.5" cast housing it'd be ideal, but that piece wouldn't be easy to attach to after the fact.

http://www.blogcdn.com/www.autoblog.com/media/2009/06/mustangirs_lead.jpg

[JeffYoung]

Correct.


Interesting, so you do not think the advantage of adjusting rear camber and toe rises above the noise level in car differences.

Dick/Earl, having driven Miatas, the 240z, the TR8 and Ron's Lola at speed at VIR, CMP, Roebling and others, I've yet to really see where the TR8 is at a serious disadvantage to the others.

Once we eliminated bind and settled the axle down with a good tri link and panhard setup, the back end does not mover around. I obviously don't get any camber back there, and that hurts some, but as someone pointed out I also don't get toe and camber change as the axle moves.

By subjective feel, the only place the TR8 seemed at a disadvantage to the Z and the Miatas before the tri-link was Hog's Pen. But now even there I pull most good RX7s and Z cars out of the hole -- watch the vid Ron posted (and that was BEFORE tri link).

Earl, yes, I can run the curbs at VIR fine. The car doesn't like the channelled FIA curbs at CMP, which I understand are coming to VIR for next year, yay, but not sure any of our cars really do.

I think with our 150-180 whp cars, the live rear just isn't that much of an issue.

Bill, no off the shelf fix for me either, but it was not hard to have one, a good one, fabricated given how open the rules are for a live rear axle with the 'traction arm" allowance.

[billf]

Want to know what happens to a live axle when jumping curbs??? Just watch ONE V8 SuperCar race from Australia, and you will see EVERY car jumping curbs. They are mandated a live axle, even though the chassis are originally built with IRS, and mandated to run a spool at all events.

When the cars jump the curbs, the wheels have liters of air under them. The effect is minimalized by the spool which delivers 100% power to the opposite (still in contact with the pavement) wheel.

Quite the lesson in drivetrain dynamics...

Jeff,

Sometimes the live axles "bend":rolleyes: in service and acquire some camber... I'm not sure the mechanisms are fully understood....:)

But the lack of camber and toe changes surely make the live axle a good choice if one can tolerate the expected unsprung weight.

Finally, I believe the lack of toe and camber change, in addition to the ability to harness the axle torque reaction, gives the live axle an advantage in traction out of the corners with especially high horsepower cars. The new generation Mustang is certainly competitive with the competition, all of which have IRS...and its corner exit is impressive. Only Porsche is better, and that probably is because of its greater rear weight percentage.

Bill:024: