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There is some talk about the C5 and newer cars having an advantage in Track Width. While I find this certainly true on a skid pad, I would also consider it both and advantage and disadvantage when you need to turn both left and right as long as you are in the confines of a given coarse. Put a Corvette and a Miata on a tight Autocross and the smaller car has such an advantage that it makes up for lack of Track Width to a point. And I would consider the faster and wider the course this would reverse at some point. Just like any other suspension change there is always a compromise to be had.
I totally missed this post earlier. Sorry. Yes, everything you wrote here is accurate. All else being equal, a car with a wider track width will skidpad better because it has less lateral weight transfer. And yes, on a tight autocross element a narrow car has an advantage because it literally doesn't have to turn as much. There are offset slaloms where a Miata barely has to turn the steering wheel at all whereas a big-*** C8 or Camaro/Mustang requires major steering inputs to negotiate it. That advantage always disappears on a road course, though: no road course has any elements that tight. But yeah, this is where all the arguments about "Miata courses vs musclecar courses" in autocross competition come from.
Thanks for all the great info! As stated the post was just an interesting thought i had about skid pad and how it is mostly about rubber compounds. My initial premise has finally started to come out in that some of you agree the numbers would be close between the older and newer cars. I never said anything about handling better auto cross or road coarse performance at the beginning. I just thought it would be interesting to see. Having a C7 and C4 street driven cars i can appreciate both for what they are dare i say raw vs refined. That said i learned a lot about C4 handling and race handling in general through your experienced knowledge of these cars.
i seem to recall cheverolet having to retune the MRC of the C7s at some point to “fix” them i thought because of the performance deficits which showed up in real world driving. Correct me if incorrect.
I still have to argue, maybe my non engineering mind struggles with, on weight transfer of a vehicle. Drag racing for example is all about transferring “weight” to the rear to increase traction to the rear tires. I am sure that the engineering behind it is about changing COG, centrifugal and centripetal forces etc and obviously not moving components (mass) of the vehicle but to the simple minded novice effectively weight is being moved/transferred from one place on car to another to improve specific performance parameters. Road course i imaging the same is true to load a tire or unload a tire for better lateral traction. Perhaps weight is the wrong term and maybe force is more technically correct but i am just a simple minded guy.
Computers, ie traction and stability control parameters and devices including MRC (which is computer controlled to an extent) proven by chevys MRC tuning via software which was done in 2017 I believe are helping you drive any modern car. Now based on power levels and drivers to dumb to know their limitations i think they are a good thing and most instructors tell new drivers to keep that stuff on, again good advice for newbees like me. But everyone should know by now that modern cars are computer controlled and those computers are able to adjust faster than people can. In aircraft technology computers are so “good” they can literally fly an airplane with almost no lift capability based on outward design. Computers are co-piloting pretty much every modern car and they are getting better. To learn i think a low powered less computer controlled car helps, me anyways, learn better than relying on computers to bail you out. Hence learning everything you can on inexpensive slower more analog vehicles makes sense to me. Everyone learns differently but as many pointed out seat time is the best way to gain that experience and learn those vehicle dynamics as is the book knowledge and learning from smart folks like you all.
Last edited by Admiral1996; 07-09-2022 at 02:47 PM.
i seem to recall cheverolet having to retune the MRC of the C7s at some point to “fix” them i thought because of the performance deficits which showed up in real world driving. Correct me if incorrect.
I'm not aware of them having to "fix" anything with the MRCs. I do know for a fact that Chevy has been sending their engineers in test cars to various autocross and track events over the years to gather more data and keep refining their product. At the 2018 SCCA CAM Challenge, for example, they brought several Camaros and Corvettes with two drivers each, including their all-conquering 2.0T 1LE Camaro. I watched them connect laptops between each run and review data and tweak settings. The dampers and active LSD would be the areas they were tuning. They have kept making the setup faster and better. However, I am not aware of any time since the C7 came out where the MRC car was slower than the non-MRC car. As I said, in every stock class national event I'm aware of, C7s and Camaros that win are equipped with MRC dampers, even though we could remove those shocks and put in expensive JRI or Penske dampers. It's one of the big attractions of buying a C7/8 or Camaro: you don't to spend $5k on shocks to win in Street classes like you do on most other cars.
I still have to argue, maybe my non engineering mind struggles with, on weight transfer of a vehicle. Drag racing for example is all about transferring “weight” to the rear to increase traction to the rear tires. I am sure that the engineering behind it is about changing COG, centrifugal and centripetal forces etc and obviously not moving components (mass) of the vehicle but to the simple minded novice effectively weight is being moved/transferred from one place on car to another to improve specific performance parameters. Road course i imaging the same is true to load a tire or unload a tire for better lateral traction. Perhaps weight is the wrong term and maybe force is more technically correct but i am just a simple minded guy.
Terminology first: weight is the force of gravity acting on a mass, so when we talk about tire loads the terms load/weight/force are interchangeable.
In drag racing and road racing, unless you change ride height or wheelbase/track you cannot change the amount of weight that is transferred for a given acceleration force. As I wrote before, even with no suspension at all, the weight still transfers. Pages 6-7 of this article give you the diagrams and math that shows this. The CG moves very slightly as the car rolls or pitches, but not enough to make meaningful change. However, suspension kinematics and wheel rates definitely can change the rate at which the weight transfer takes place. The higher the roll centers or anti-squat/dive and the stiffer the springs, suspension, and damper rates; the faster the weight transfer takes place. This is where a fair amount of the "magic" of suspension design and tuning takes place. We know a lot more about these transient conditions in 2022 than we did in 1982, since we now put cars on 7-post shaker rigs with high-resolution load sensors and use lots of computing power to see what's happening as the car moves around on it suspension in every conceivable way.
Computers, ie traction and stability control parameters and devices including MRC (which is computer controlled to an extent) proven by chevys MRC tuning via software which was done in 2017 I believe are helping you drive any modern car.
You can believe what you want, but it's really easy to see that this is not the case (or doesn't have to be, at least). If it were really true that modern cars do the driving for you, then in an autocross or road course run, a crappy driver would be just as fast as a great driver. But that's not how it goes in most modern cars. For example, in a C7/8 or 6th-gen Camaro (the cars I have some knowledge of), all the driver aids can be turned off, and that is the fastest way to run them for autocross courses. You still have active damping rate adjustments and an active differential, but they are helping the car adjust its balance to go faster under various circumstances rather than doing the driving for you. Put it this way: if you put a national champion autocross driver and an average local driver in a C4, and the national champ completes an autocross run 5% faster than the average driver in that car, then the champ will also be 5% faster if you put them both in a C8 with all the nannies off.
Now based on power levels and drivers to dumb to know their limitations i think they are a good thing and most instructors tell new drivers to keep that stuff on, again good advice for newbees like me. But everyone should know by now that modern cars are computer controlled and those computers are able to adjust faster than people can. In aircraft technology computers are so “good” they can literally fly an airplane with almost no lift capability based on outward design. Computers are co-piloting pretty much every modern car and they are getting better. To learn i think a low powered less computer controlled car helps, me anyways, learn better than relying on computers to bail you out. Hence learning everything you can on inexpensive slower more analog vehicles makes sense to me. Everyone learns differently but as many pointed out seat time is the best way to gain that experience and learn those vehicle dynamics as is the book knowledge and learning from smart folks like you all.
You certainly can do your runs with some or all of the nannies turned on in a bunch of different modes, and the car will try to help save you from yourself. That is "driving the car for you," or at least helping. This is the setting all these cars are in by default when you start them up, and so on the street most people do have help from getting themselves into too much trouble. And I agree, that's not a bad thing. But that's not how anybody fast drives their cars when they want to go fast. Again, turn all the nannies off in a modern Camaro or Corvette and you are responsible for 100% of the driving duties. The car won't save you from yourself at all. And these cars will teach you good driving just as well or better than the old ones. I've owned/autocrossed/tracked a 1975 Firebird, a 1898 Mustang 5.0, a 97 SVT Cobra, a 92 Camaro B4C (like a 1LE but with a/c and a radio), a 96 Corvette, and a 2020 Camaro SS 1LE. I've also driven a number of other cars at least once or twice in these settings. You can believe what I'm telling you or not, but I'm telling you based on a fair amount of experience how it really is.
Yes, you are correct: moving a 35lb battery from over the front axle to over the rear axle would be a 2% weight distribution change. My mistake.
The worst I've seen is from a Road and Track review that showed 52/48, but that was an estimate with driver, so it's pretty much useless. I found another resource that says the 1990 ZR1 had 1750/1729 on its front and rear axles, which is 50.3/49.7. And Corvette Action Center says the LT5 was 39lbs heavier than the L98. The LT5 wasn't actually 200lbs heavier than the L98 or LT1, and I seem to recall seeing that there was a big confusion with whether the engine weight listed for the LT5 was with trans or without, thereby causing people to mistakenly believe it was 200lbs heavier when most of that was actually trans and clutch.
I don't know what to believe for sure. However, I find it incredibly hard to believe that an all-aluminum engine with the same bore spacing and displacement weights 150lbs more than an iron-block LT1. I realize the LT5 heads are much bigger and contain four cams total and that it has a more complex intake, but there is typically 75-80lb extra in a standard iron SBC block than an aluminum equivalent (like Brodix or Dart), and the LT5 block should be similarly light. It seems to me that in similar "dressing," the LT5 probably weighs 30-40lb more.
In the book Corvette Specs by Michael Antonick, the dry weight of a dressed LT5 for a 1990 is 596 lbs and the dry and dressed L98 from the same year was 557 lbs (see pic below). The LT1 weight is very similar to the L98. This is where the 39lb difference comes from, and I would put my money on this being correct. I think a lot of the goofy-huge weight differences include a transmission and flywheel on one engine and not the other, or confuse pallet/crate/shipping weights with a dry/dressed engine weights, or include a 40lb flywheel on one engine and featherweight flex plate on the other. Some of these are the same specs that say an LT4 weighed about 150lb more than an LT1, which of course insane.
It certainly isn't that easy to ascertain LT5 or ZR-1 weights....that's for sure. Conflicting and dubious data...and that's when you can find any. I don't think comparing an aluminum small block to the LT5 block is all that valid. The LT5 block is a brick **** house with deep skirt, plus the ladder girdle for the bearing caps that is aluminum encapsulating cast iron. Then you got the weight of the heads, that gigantic intake, I could see it being heavy. I am not sure I see 150 lb more heavy, but more than 39 lb, I can see pretty easily.
I will be doing some top end work on a '90 ZR-1 later this month. I'll throw it on some Corner scales and then do my LT1 so we can compare. Then we will have some real info.
Modern tires and modern shocks really help the car but it's old. If you drive them hard you can embarrass people. 😂
THe C4 is retired from national events now but I happened to run a Divisional for Great Lakes Division at WVU Parkersburg.
Maybe I should delay retirement since BS is weak, new set of tires and go hunt unsuspecting victims. Hopefully without cone issues, feel like I'm driving better this year too.
I was the fastest, oldest, and stockest Corvette on site. On 192 run 5k mile Goodyear Supercar 3s no less.
Wait, you beat an 06 C6 and a 06 as well!? How....wha....
Something that cannot be measured on a skid pad is driver mod. I was getting 98% of the potential out of the car. They weren't even coming close to that. The one car was on Hoosiers....get gud scrub.
I'm not even really fast. I'm quick but I'm not fast.
I know. I agree with you. Driver mod, tires, those are the places that you find massive improvements or differences.
Not so much in a few percent of weight distribution one way or the other.
Nice to see you post, by the way. My son and I went to an auto cross race two weekends ago, it didn't go that well. You should search up my posts and read about it.
It certainly isn't that easy to ascertain LT5 or ZR-1 weights....that's for sure. Conflicting and dubious data...and that's when you can find any. I don't think comparing an aluminum small block to the LT5 block is all that valid. The LT5 block is a brick **** house with deep skirt, plus the ladder girdle for the bearing caps that is aluminum encapsulating cast iron. Then you got the weight of the heads, that gigantic intake, I could see it being heavy. I am not sure I see 150 lb more heavy, but more than 39 lb, I can see pretty easily.
I will be doing some top end work on a '90 ZR-1 later this month. I'll throw it on some Corner scales and then do my LT1 so we can compare. Then we will have some real info.
The Z weighs about 120lbs more than a standard 6 speed coupe. The freakishly heavy flywheel and beefier 6 speed weighs more than the base auto so base auto is tough to compare to a Z. Base Auto to Z is a couple hundred pounds. The Z has a different weight distribution too, so it adds up. I believe 52/48 Front/Rear on the Z. Coupe was 51/49 and 'vert was 50/50 if I remember right.
Even though the LT5 is aluminum the parts inside that make the thing run aren't... and these items aren't necessarily light. LT1... smaller aluminum heads, 1 cam, 16 valves with one simple timing chain. LT5... 4 cams, big *** heads with 32 valves and the associated springs, 3 timing chains that loop over heavy gears all the way up to the heads. The intakes on both are aluminum but I think it's pretty safe to say the LT5's weighs way more. All of that stuff is heavy. And to add to it... LT1 holds 4.5 quarts of oil, LT5... 12.
None of these items individually are all that much, but 10 pounds here, 15 there, etc. certainly add up. And like I already said part of the issue is if the engines are weighed with the dual mass flywheel or not, and if they are dry weighed or measured with fluids... I mean the LT5 holds about 15 extra pounds in oil alone.
Anyway... tires. Man these new compounds are some serious business. Even for street tires. I just put Michelin's on my GS and it's like the car is glued to the ground. Compared to the factory GS-C's it is just not in the same neighborhood
I don't know what to believe for sure. However, I find it incredibly hard to believe that an all-aluminum engine with the same bore spacing and displacement weights 150lbs more than an iron-block LT1. I realize the LT5 heads are much bigger and contain four cams total and that it has a more complex intake, but there is typically 75-80lb extra in a standard iron SBC block than an aluminum equivalent (like Brodix or Dart), and the LT5 block should be similarly light. It seems to me that in similar "dressing," the LT5 probably weighs 30-40lb more.
I don't know the correct answer, but despite being aluminum, the LT5 should be significantly heavier because of the DOHC heads. That is 4 cams vs 1, much physically larger heads, much larger larger timing set, much larger timing cover etc. This is going to make the engine both bigger and heavier. Also I bleive the LT5 has Iron Cylinders. All that siad I agree the basic block is should be lighter on the aluminum engine, but not by enough to make up for the rest of the motor I don't think.
I don't know the correct answer, but despite being aluminum, the LT5 should be significantly heavier because of the DOHC heads. That is 4 cams vs 1, much physically larger heads, much larger larger timing set, much larger timing cover etc. This is going to make the engine both bigger and heavier. Also I bleive the LT5 has Iron Cylinders. All that siad I agree the basic block is should be lighter on the aluminum engine, but not by enough to make up for the rest of the motor I don't think.
The LT5 does not have iron cylinder liners. In fact, as I recall, the porosity of the aluminum cylinder walls was an issue at first. I agree that the heads and related hardware are heavier, but the block is a lot lighter too. I posted an itemized list of all those differences earlier in this thread (Post #87). I'm not saying the LT5 is lighter than an L98 or LT1. It's heavier, but only by about 40lbs, not the 150-200lb that is often thrown around.
I disagree on the block being "a lot lighter". It's deep skirt. It's got a cast iron, aluminum encased girdle. I found more references from. HOTB where they actually put the dressed engine weight at 600 lbs -which jives with the earlier post where they said 150 more. We can debate LT5 weights all day and get no where. I'm going to be working on a '90 ZR-1 in a couple days. I'll try to corner weigh it, then my '92. Put this lore to bed.
Back to the value of skid pad numbers....I kept my mouth shut earlier when they were lambasted as "useless", but I'm going to say, "sorry, but no". I did another track day yesterday and the reality of being on a real track, is there is a LOT of time spent, mid turn, just grinding the tires off the car. If you set up for the turn decently, that kind of turn is steady state, max G cornering. What is a skid pad test? "" "" ""
It's relevant. It ain't everything, that's for sure, but at those points on the track, a car that can skid pad higher, will drive away from the car that G's lower.
I am likely to agree with you (MM) much more strongly, if we're talking Auto-x; because there are way, WAY more transient maneuvers, less looooong, steady state cornering and throttle/braking transients are more violent due to the lower speed/higher wheel tq, in auto-x. But on a big track....Skid pad performance matters because there is simply SO much time spent, mid turn, max G, steady state cornering.
I disagree on the block being "a lot lighter". It's deep skirt. It's got a cast iron, aluminum encased girdle. I found more references from. HOTB where they actually put the dressed engine weight at 600 lbs -which jives with the earlier post where they said 150 more.
Even the reference I posted above says the LT5 weighs 596lbs. So I don't think we disagree on that weight. But the L98 and LT1 are way heavier than the 450lb you imply (at least fully dressed, as per the LT5 weight). The L98 is more like 550lb dressed (557lb per my reference above). An LS1 is more in the range of 450lb.
Back to the value of skid pad numbers....I kept my mouth shut earlier when they were lambasted as "useless", but I'm going to say, "sorry, but no". I did another track day yesterday and the reality of being on a real track, is there is a LOT of time spent, mid turn, just grinding the tires off the car. If you set up for the turn decently, that kind of turn is steady state, max G cornering. What is a skid pad test? "" "" ""
It's relevant. It ain't everything, that's for sure, but at those points on the track, a car that can skid pad higher, will drive away from the car that G's lower.
Grip is absolutely vital to any kind of performance, yeah. My point about skidpad numbers is that they are so easily manipulated and they are largely tests of tires and alignment specs rather than any inherent qualities of the overall car. IME, two cars that have somewhat similar weights, track widths, CG heights, and tire widths can skidpad very similarly on the same type of tires. OTOH, those two same cars may behave very differently on the brakes, throttle, or transitions; and that's where you're going to find the most meaningful differences between two cars. IOW, skidpads usually don't tell you much about the qualities of the car, except the most fundamental aspects of it.
Even the reference I posted above says the LT5 weighs 596lbs. So I don't think we disagree on that weight. But the L98 and LT1 are way heavier than the 450lb you imply (at least fully dressed, as per the LT5 weight). The L98 is more like 550lb dressed (557lb per my reference above). An LS1 is more in the range of 450lb.
Well....let's find out.
Originally Posted by MatthewMiller
Grip is absolutely vital to any kind of performance, yeah. My point about skidpad numbers is that they are so easily manipulated and they are largely tests of tires and alignment specs rather than any inherent qualities of the overall car.
Right. That is the essence of what the OP's point was....in post #1! Test the same car; a C4 Corvette, with new rubber, see how it compares with period test(s). I think we can all assume that the car would have OEM alignment specs in either test, b/c...that's how the cars are tested.
Originally Posted by MatthewMiller
IME, two cars that have somewhat similar weights, track widths, CG heights, and tire widths can skidpad very similarly on the same type of tires. OTOH, those two same cars may behave very differently on the brakes, throttle, or transitions; and that's where you're going to find the most meaningful differences between two cars. IOW, skidpads usually don't tell you much about the qualities of the car, except the most fundamental aspects of it.
No. The MOST meaningful diff's (after the driver) is the tires. We (I) just re-learned that, as you know, on my own car, and that is where "massive" is found. Skid pads tests ARE a narrow focused test, no arguing that from me...but I'll reiterate that a large portion of time on a road course is literally spent, doing one "skid pad test" after another. Of course that one, single test won't pick a winner at the track (no test will), just like a dyno test won't tell you a winner at the drag track. Too many other factors. But the OP wanted to see a 30yo tire vs. today's tire, test. I'd love to see it too. Love to see a C4 slalom on a brand new tire, too. That ain't gonna tell us a 'track winner' either....but it's interesting. A then/now skid pad test is interesting and yes, it is translatable date, just like dyno tests are.
07-09-2022, 11:09 AM
