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maschinenbau (I live here)
maschinenbau (I live here) UltraDork
2/23/21 1:35 p.m.

I got 12th with a car I built in 10 days, even taking the 12 in concours. Well, "built" is generous...more like we kept cutting parts off of it in the name of lightness. I think Stampie got top 10 with the same strategy in his Q45. 

I wonder how high I could place in a chop-top Jaaaag wink

bobzilla
bobzilla MegaDork
2/23/21 2:22 p.m.

In reply to maschinenbau (I live here) :

I was 29th in autox on 218k mile suspension and 420 treadwear westlakes. 32nd in drags with ... well the same crap. finished 36th overall. basically, I sucked. still loved it.

frenchyd
frenchyd UltimaDork
2/23/21 2:32 p.m.
stukndapast said:

RANT ON -- Having been a drag racer since the late 60's, competing in countless NHRA and IHRA events, setting NHRA records, and only recently having discovered the pleasures of autocross, track days and road racing, I would like to respectfully request that y'all stop talking about a DRAG RACE in the CHALLENGE.  THERE IS NO DRAG RACE IN THE CHALLENGE.  There is a 1/4 mile ELAPSED TIME RUN in the challenge.  There is NO RACE.  A drag race is a competition between two cars from a standing start for a specified distance and whoever gets there first wins.  (Yeah, I know, breakouts and all that E36 M3, let's not go there).  The vast majority of the skill in drag racing is the start and the finish; properly staging, cutting a light, hitting your shift points and taking just enough stripe to win.  In handicap racing it also depends mightily on choosing the right dial-in.  None of that comes into play in this challenge thing.  It's not drag racing, so stop calling it that.  -- RANT OFF

For the OP's question, from a technical ET perspective, you want the suspension set up to provide the as much weight transfer on the initial movement of the car as is needed to provide necessary loading of the drive tires such that they don't loose traction, i.e. spin.  On a low powered car, you don't need a lot of weight transfer with decent tires.  On a high powered car with a great suspension designed for a standing start launch, it is what is needed, and no more.  On a high powered car with a lousy suspension you need a lot of weight transfer, even with good tires.  Watch a "pro-stock" car launch.  It doesn't do a ridiculous wheel stand.  It just barely pulls the front wheels off the ground, which means, obviously, that the weight of the car is being handled by the rear tires.  The multi-link suspension is set up just right to direct all available energy to planting the rear tires.  Putting the front of the car 4 feet in the air is wasted energy in that case.  Watch an older "stock" or "super stock" car launch and it is completely different.  Older high powered cars do crazy high wheelies because they are saddled with old, obsolete or structurally compromised rear suspensions.  Standing the car up on the rear tires is the best way to increase the rear tire loading in that situation.  You can't tune a leaf spring and shackles to work like a multi-link suspension.  Newer cars, like "factory stock" (which are anything but stock) have much better (i.e. modern) designed suspensions and, even though they are far, far faster than the "old" cars, they launch much more like a tube chassis, purpose built "pro-stock" car.  Small, low wheelies, even on a 9" slick (which is tiny in the drag race world).

For the OP's situation, with a fair amount of power in a light car, he will need as much weight transfer as he can get to keep from spinning the tires, and he needs good tires first and foremost.  If treated like an "old" drag race car, he wants a low friction front suspension with virtually no rebound damping, literally none.  I have known guys that actually drill a hole in the shock and drain all the oil out of them because the rules say you have to have a shock, but they don't really do anything.  The car is going to bounce though, and you have to be ready for it.  That is where the "90/10" shocks came in way back in the dark ages.  Very little rebound but tight compression to dampen the motion when the car comes back down.  They still bounce, but not as bad.  Most people just run double adjustables these days that have very light rebound settings and are velocity sensitive.  Before the urethane and Del-alum days some guys used to loosen the pivot bolts for the front suspension arms so that they would rotate more easily and not have to deflect the rubber bushings.  There was some scary E36 M3 stuff going on at the local drag strip.  The OP also wants as much weight as possible off the front end, dinky front wheels and tires, battery in the back, maximize the weight at the rear of the car.  Take the sway bar off.  He has an automatic with a torque converter and the converter is going to be the determining factor in how hard the car hits the rear tires on launch.  If it is a street converter with a low stall speed, he isn't going to hit the tires very hard unless he is making massive torque at 2500 RPM, and won't need as much traction, thus less weight transfer, as it would with a high stall speed converter.  I assume that he will not have a trans-brake, which could hit pretty hard even with a low stall speed.  A high stall speed converter would give better ET results, but will generate a lot of heat in a road course type of application, probably not the best thing to do for the "challenge".  He can control the hit to some degree by experimenting with launch RPM, i.e. how much RPM he puts against the converter while on the brakes at the start.  He can only go to the stall speed, of course, but the amount of "power braking" at the starting line can make a big difference in how hard the tires are hit and it is highly dependent on the car itself.  You just have to experiment to see what works best.  A lot of people think power braking to the stall speed gives the best launch, but many times "flashing" the converter from a lower RPM lets the converter torque multiplication work to your advantage provided you have enough traction to hold the power.

There is another HUGE factor that is completely unknown is track prep.  Starting line prep is everything to a high powered, small tire drag car.  Where are the ET sessions going to take place and how well is the starting line going to be prepared and maintained?  If it is prepped to a competition level expected by the small tire drag race community then the traction worries drop drastically.  If it isn't, well, then who knows what to expect.

I'm sorry to offend you. I call it a drag race because to a Newbie that's what it looks like.  I now understand the difference but I hope you won't be offended. It's just shorter to type.  
   Here are the details of my car.  It's a Jaguar V12 XJS Think big block Camaro size and power.  Somewhere in the 500+ horsepower. Around 2700 pounds race weight. 
    It has a IRS  that with a few typical modifications plants the tires pretty well. ( no knowledge of what a launch from a dead stop will be). But I expect to have Drag slicks since it has a Chevy bolt pattern. 
The only numbers I have are in 1982 one went 9.710@ 137 mph in the quarter. I don't know if that's good or typical or what. 
Edit;  I'm slightly wrong. The XJS has 106 wheelbase to the early Camaro's 102 inch wheelbase.  Also the Jaguar is about 3 inches wider than the early Camaro. 

Stampie (FS)
Stampie (FS) MegaDork
2/23/21 2:54 p.m.

Is that a factory big block Camaro you're saying has 500hp?  Net or Gross?

jfryjfry (FS)
jfryjfry (FS) Dork
2/23/21 2:59 p.m.
Stampie (FS) said:

Is that a factory big block Camaro you're saying has 500hp?  Net or Gross?

We should have a separate thread for that. 
 

 

Ha?

frenchyd
frenchyd UltimaDork
2/23/21 3:17 p.m.
Stampie (FS) said:

Is that a factory big block Camaro you're saying has 500hp?  Net or Gross?

I honestly don't know.  Whatever the dyno numbers are. I suspect it's gonna be someplace in between.  It won't have any of the restrictions needed to be legal.  Which tends more towards gross but it will be on a chassis dyno so  it won't be the same as crank horsepower either.  If it's 12 horsepower I won't care as long as it's running properly. 
 Since we are talking about a car that isn't normally drag raced it could launch beautifully or or it could just sit there and spin it's wheels. 
The only guidance I have is in 1982 a Jaguar XJS. V12 turned a 9.710 @ 137 mph. No details other than that were given. 
    
    

Stampie (FS)
Stampie (FS) MegaDork
2/23/21 4:21 p.m.

In reply to frenchyd :

Well if that 82 XJS is better than all the other racers and just as good as you at weight reduction, @ 2700lbs in theory it made 650hp.  I'm guessing more like 800hp in the real world to make that time.  

frenchyd
frenchyd UltimaDork
2/23/21 4:53 p.m.

In reply to Stampie (FS) :

OK thank you. So do you think It'll need NHRA ROLL BARs ? I mean I could be heavier in the weight and lower in the power. I'm just going by what my 1975 weighed and the Engine analyzer program is telling me. Is the cut off 10.99?  

Stampie (FS)
Stampie (FS) MegaDork
2/23/21 4:55 p.m.

Honestly your goal is where you need a cage but honestly I don't think you'll reach that goal.  But always better safe and slow than fast and dead.

 

11.5

https://grassrootsmotorsports.com/forum/2000-challenge/nhra-regulations-thread/155054/page1/

frenchyd
frenchyd UltimaDork
2/23/21 5:11 p.m.

In reply to Stampie (FS) :

It will have a chump car legal cage but to meet the challenge budget limits it probably won't go in  until after. As far as a cage for a "speed event " where it's not wheel to wheel I'm not sure I can agree of the need.  I still race in Vintage group 1 without a bar and the reason is in  over 40 years I have  never seen a car roll or collide with another car with anything other than minor tin damage. In fact over the same period I've never seen a group 3 car do either one. Those are some brutally fast cars with, ummm,  challenging drivervrequirements compared to today's cars. 

Stampie (FS)
Stampie (FS) MegaDork
2/23/21 5:59 p.m.

In reply to frenchyd :

Today I saw a van that had rolled over.  Pretty sure it was the drivers first time rolling a vehicle.

frenchyd
frenchyd UltimaDork
2/23/21 6:30 p.m.

In reply to Stampie (FS) :

Well you and I seem to have a different tolerance to risk.  I'll respect your feelings completely. But reserve the right to my own opinion. 

stukndapast
stukndapast Reader
2/24/21 9:15 a.m.

In reply to frenchyd :

No offense taken.  Just wanted to make it clear that the information that you are asking for has little to do with the process and procedures of an actual drag race, as opposed to an ET time run.

9.71 @ 137 MPH is very quick. Consider that when the Hellcat came out it was 707HP and could run around 11.2 ET @ 125 MPH on stock tires and around 10.8 seconds with drag radials.  It is heavy though, but still, it pales in comparison to a 9.70.  It also has modern electronic traction control which is a massive advantage in getting the car moving.  As for the IRS, in general, they suck for drag racing.  In NHRA stock and super stock racing, old cars that came with IRS (essentially just Corvettes) are allowed to rip the whole rear end mess out and replace it with a solid rear axle.  The modern "factory stock" or "factory shootout" cars from Dodge (Challengers), Ford (Mustangs) and Chevy (Camaros) all are purpose built drag race cars from the manufacturers.  All have IRS on the showroom car.  But the race car versions all have solid rear axles, Ford 9" or Dana 60's, with spools.  I surely hope that the Jag rear end has some sort of effective posi-traction or your right tire is going to be on fire.  If the car is really capable of an ET in the high 9's or low 10's, it will have to dead hook on launch and I would be worried about breaking a half-shaft under those conditions.

If you want to mess around with ET estimation based on a variety of factors like weight, HP, ET, MPH, ad nausem, I might suggest using the calculators at   Drag Race Calculators  Since acceleration of a mass is essentially a physics problem, these calculators are fairly accurate as long as you understand that there are a lot of second and third order variables left out.  There are a bunch of different scenario calculators and they are fun to do "what-ifs".

eastsideTim
eastsideTim PowerDork
2/24/21 9:29 a.m.
stukndapast said:

In reply to frenchyd :

Since acceleration of a mass is essentially a physics problem, these calculators are fairly accurate as long as you understand that there are a lot of second and third order variables left out.  There are a bunch of different scenario calculators and they are fun to do "what-ifs".

And those second and third order variables get more and more important the faster the car.  I'm reminded of a joke from the late 90s/early-2000s:   What do a 400 HP Supra, a 600 HP Supra, and an 800 HP Supra have in common?  Answer:  12 second time slips.

SVreX (Forum Supporter)
SVreX (Forum Supporter) MegaDork
2/24/21 9:31 a.m.

In reply to stukndapast :

I agree. IRS sucks for drag racing. But it's wonderful for cornering (like autocross and road racing)

Like I said. Everything about this event is a compromise. This is why they call it "The Challenge"

frenchyd
frenchyd UltimaDork
2/24/21 9:39 a.m.
stukndapast said:

In reply to frenchyd :

No offense taken.  Just wanted to make it clear that the information that you are asking for has little to do with the process and procedures of an actual drag race, as opposed to an ET time run.

9.71 @ 137 MPH is very quick. Consider that when the Hellcat came out it was 707HP and could run around 11.2 ET @ 125 MPH on stock tires and around 10.8 seconds with drag radials.  It is heavy though, but still, it pales in comparison to a 9.70.  It also has modern electronic traction control which is a massive advantage in getting the car moving.  As for the IRS, in general, they suck for drag racing.  In NHRA stock and super stock racing, old cars that came with IRS (essentially just Corvettes) are allowed to rip the whole rear end mess out and replace it with a solid rear axle.  The modern "factory stock" or "factory shootout" cars from Dodge (Challengers), Ford (Mustangs) and Chevy (Camaros) all are purpose built drag race cars from the manufacturers.  All have IRS on the showroom car.  But the race car versions all have solid rear axles, Ford 9" or Dana 60's, with spools.  I surely hope that the Jag rear end has some sort of effective posi-traction or your right tire is going to be on fire.  If the car is really capable of an ET in the high 9's or low 10's, it will have to dead hook on launch and I would be worried about breaking a half-shaft under those conditions.

If you want to mess around with ET estimation based on a variety of factors like weight, HP, ET, MPH, ad nausem, I might suggest using the calculators at   Drag Race Calculators  Since acceleration of a mass is essentially a physics problem, these calculators are fairly accurate as long as you understand that there are a lot of second and third order variables left out.  There are a bunch of different scenario calculators and they are fun todo "what-ifs".

The rear end is a Dana 44 with positraction. 
I understood the issues of an IRS from the beginning.  Even if I can keep the rear wheels straight, there will be camber change as the rear end squats. So traction is least when it's needed most. 
     I think the reason for the high speed is remarkably the XJS has an extremely low CD. It's shocking when you compare it with its predecessor the XKE.   
Numbers don't lie. A stone stock XJS did 150 mph while the famous XKE needed every trick in the book to touch that speed. Remarkably the XKE had 265 horsepower to the XJS's 262. 
and the XJS was a foot wider than the XKE 

My goal is not to set a record,  simply to be respectable  

Robbie (Forum Supporter)
Robbie (Forum Supporter) MegaDork
2/24/21 10:59 a.m.

meh.get a car, take it to a drag strip for a test and tune night. 

If the car is capable of anything faster than a 15, you'll quickly find that the driving is much more nuanced than "floor it and shift".

Also, look at the challenge results in the GRM issues that cover it. Faster than a 15 is normally in the top half of competitors ET-wise. 

frenchyd
frenchyd UltimaDork
2/24/21 11:51 a.m.

In reply to Robbie (Forum Supporter) :

That's been my concern.  I know Nothing about drag racing,  nothing about autocross.  But I'll do my best.

 
I'm not building it for those reasons. I want  a wheel to wheel car. Yet, It's too new for Vintage and not even listed in SCCA   
If I have to I'll run Champ Car ( Chumpcar )  as it will sit I have 400 points so I can find 100 points of go fast stuff still. 

Floating Doc (Forum Supporter)
Floating Doc (Forum Supporter) UberDork
2/24/21 6:33 p.m.

This has been a useful discussion for me. I'll be a Challenge rookie too. 

Stampie (FS)
Stampie (FS) MegaDork
2/24/21 6:39 p.m.

In reply to Floating Doc (Forum Supporter) :

But have I told you how cool your car is?

Floating Doc (Forum Supporter)
Floating Doc (Forum Supporter) UberDork
2/24/21 7:50 p.m.
Stampie (FS) said:

In reply to Floating Doc (Forum Supporter) :

But have I told you how cool your car is?

Uhh, before anyone else did. Before I owned it. Before I saw it for the first time.  And, how about email you sent me before I even knew that it existed?

Honestly, I'm not sure I thanked you enough.

frenchyd
frenchyd UltimaDork
2/24/21 8:16 p.m.
Robbie (Forum Supporter) said:

meh.get a car, take it to a drag strip for a test and tune night. 

If the car is capable of anything faster than a 15, you'll quickly find that the driving is much more nuanced than "floor it and shift".

Also, look at the challenge results in the GRM issues that cover it. Faster than a 15 is normally in the top half of competitors ET-wise. 

Robbie; 

My test and tune night will be my drag race portion of the Challenge. Good bad or ugly  it's what goes on 1/2 the speed portion. The autocross event will be my second half. I don't know of any way to do the concours. Send in photos?   

frenchyd
frenchyd UltimaDork
2/26/21 7:31 a.m.

In reply to SVreX (Forum Supporter) :

Thank you SVreX your guidance about the challenge  portion has been very helpful. It's given me the confidence ( something I don't normally lack ) to go ahead and try something completely new. Not easy for an old geezer to do. Especially since I have so much successful experience  at Wheel to wheel racing. I just hate the idea of looking stupid.  The relative success of the XJR's tells me big full sized  sedans can do respectably. 
      Without  your support and explanations I doubt I would have gone ahead.  Thank you again 

rslifkin
rslifkin UberDork
2/26/21 8:02 a.m.
frenchyd said:

In reply to SVreX (Forum Supporter) :

Thank you SVreX your guidance about the challenge  portion has been very helpful. It's given me the confidence ( something I don't normally lack ) to go ahead and try something completely new. Not easy for an old geezer to do. Especially since I have so much successful experience  at Wheel to wheel racing. I just hate the idea of looking stupid.  The relative success of the XJR's tells me big full sized  sedans can do respectably. 
      Without  your support and explanations I doubt I would have gone ahead.  Thank you again 

Don't worry about looking stupid at a test and tune night no matter what happens.  Plenty of people bring all kinds of junk, daily drivers, etc. out to those just to see what they'll run.  So even if you run slower than you'd like, you're still going to be faster than something else there. 

frenchyd
frenchyd UltimaDork
2/26/21 9:52 a.m.

In reply to rslifkin :

Our nearest drag racing track is over in Wisconsin so I can safely go over there and fall on my face completely and the laughing won't be heard at home.  
The autocross might be a little different. I know some go up to Brainerd which is a 3 mile track  but they put a lot of cones on the straights to keep speed down.  However there have been shorter events in the twin cites area. I just don't know who to contact. 

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