Jaguar XJS progress.

Stampie said:

In reply to Tom1200 :

True but the opposite effect is he'll lose some traction without weight over the tires. I think the rear is fine. It's supposed to be a decently strong rear. I think all the other factors will keep him in the 13s. I know with Michael's Miata I had to do everything perfect to get a 14.0 run when the calculators said it was a 12 second car.

 So a formula 1 car has even less weight over the rear until the air forces it down?  
 Weight is one of those cursed if you do and cursed if you don't things.  It's harder to accelerate  weight but weight provides added traction. 

Captdownshift (Forum Supporter) said:

frenchyd said:

In reply to NOT A TA :

My best guess is the car will weigh about 2500# dry.   I'm hoping for around 550/600 hp.   Anybody know what times I should expect in a quarter mile?  

Spectacular failure trophy award winner. Although that trophy is no more. (I'm not being snarky either, I just question the amount of Tire, power and VHT that the rear end will effectively be able to handle.) 

Don't forget it's patterned after the Group 44 cars. ( 3 XJS's made  76,77,78 ) each was lighter than its predecessor   The 78 which had only the roof in steel was actually underweight and had to be ballested.   The 78 was also heavy in the rear. 

Skip the asphalt circle track nascar tires. You'd have better luck with a used soft compound roundie round dirt tire.   Even then, you'd be further ahead buying a dirt cheap pair of used up drag radials or slicks or street tires.

Nascar slicks just aren't going to work for what you are trying to do. At all. Super stiff sidewall, wrong tread compound and so forth. Everything and anything that could possibly be wrong with them for use as a drag tire, is.  

Street tires would be better. 
 

Yes, weight is part of the equation. But autocross is a race that lasts less than 60 seconds. Stock car tires run for long periods of time at speed. Autocross needs  grip at the very first turn. 
 

frenchyd said:

Captdownshift (Forum Supporter) said:

In reply to frenchyd :

What's your plan to get heat in them for the autocross? Stock car slicks are notoriously greasy prior to getting up to operating temperature, which won't occur on an autocross course. I'd be wary of going that route unless you're packing tire warmers. 

  I've watched those 900 horsepower stock cars leaving the pits and they tend to be done slipping within 10 feet or so even the guys at the front who are not limited by pit lane speed limit. 

How much hard braking and transitional turning are they doing on those cold tires? Oval racing isn't autocross. On cold stock car rubber it's going to be like CAM class on meth. 

IMSA says that rubber selection is gonna be a bad time without tire warmers. 

We ran Hoosier f40 in the challenge and local autocross on my amc.

They sucked HARD for autocross. No grip the first few runs in july. Ince hot, no end of grip but tbey couldn't keep up with steering inputs. They lagged by a non insignificant amount. Fast slalom they were an element behind the car. 

Id reccomend against them for autocross. Great for hpde and open track, bad for autocross. 

Stampie said:

In reply to Tom1200 :

He's claiming to take it down to a weight that knowledgeable people on the Jaguar forums say it very difficult.

Stampie. They are both right and wrong. For the street getting it down under 34-3600 pounds is near impossible.  However mine is built as a Group 44 tribute car.  While the 76 was almost 360 pounds overweight in racing trim that was with a 30 gallon fuel tank full.   
By the time it got to the 78  he was ballesting to meet weight plus the engine was moved back 8 inches which made the car rear heavy.  
I'm paraphrasing  from Jaguar V12  race cars . Born to win. Osprey pub 1986 

    I crawled all over and under that car the 3 years it raced at Brainerd and Elkhart Lake. They were very generous and open about everything.  The first year only the trunk  and fenders were fiberglass both were chopper gun and I thought overly thick.   By 1978 the roof was the only steel body part the rest was all fiberglass 

 IMSA allowed the front spark plug to be equal with the front spindle but that wasn't taken advantage of until 1978 which moved it back the 8 inches. 
   I don't use a chopper gun or mat because they are too weak and too heavy.  Instead I use fiberglass cloth. Much stronger and I use a squeegee to remove the excess resin which further lightens  the whole thing.  While cloth is more expensive than matt.  My advantage is all the cloth I bought to make my Fiberglass trailers.    That was decades ago.   the last one I sold was 1985.  I bought that roll in the 70's .  There is enough left to do a couple of cars. 

In reply to Captdownshift (Forum Supporter) :

I honestly don't know.  I don't know past the challenge how much autocrossing the guys do.  I doubt much drag racing. I hope a lot of Vintage racing. We will work it out. 

GaryC83 said:

Skip the asphalt circle track nascar tires. You'd have better luck with a used soft compound roundie round dirt tire.   Even then, you'd be further ahead buying a dirt cheap pair of used up drag radials or slicks or street tires.

 

Nascar slicks just aren't going to work for what you are trying to do. At all. Super stiff sidewall, wrong tread compound and so forth. Everything and anything that could possibly be wrong with them for use as a drag tire, is.  

 

 

 

Thanks. That makes sense. A long time ago I started to use Hoosier dirt stockers in Vintage sports car racing.  One gentle warm up session for the first cycle was  all that was required. From then on I could use them hard until  the tread got too hard.  Typically a year &1/2 to 2 years 

SV reX said:

Street tires would be better. 
 

Yes, weight is part of the equation. But autocross is a race that lasts less than 60 seconds. Stock car tires run for long periods of time at speed. Autocross needs  grip at the very first turn. 
 

 

 The guys should make their own selection. They know a lot more than I do on that subject. 

SV reX said:

Street tires would be better. 
 

Yes, weight is part of the equation. But autocross is a race that lasts less than 60 seconds. Stock car tires run for long periods of time at speed. Autocross needs  grip at the very first turn. 
 

 

Fair enough,  you know how little autocross experience  I have.  I'll let the guys decide what tires they want.  They have a lot more knowledge than I do. 
 

I really don't expect great things in the autocross.  This is the biggest race car I've ever built and with the fender flairs and wide tires making it even wider I seriously hope it's not too much like threading a needle for them.  
I just have visions of cones flying.   

Captdownshift (Forum Supporter) said:

frenchyd said:

Captdownshift (Forum Supporter) said:

In reply to frenchyd :

What's your plan to get heat in them for the autocross? Stock car slicks are notoriously greasy prior to getting up to operating temperature, which won't occur on an autocross course. I'd be wary of going that route unless you're packing tire warmers. 

  I've watched those 900 horsepower stock cars leaving the pits and they tend to be done slipping within 10 feet or so even the guys at the front who are not limited by pit lane speed limit. 

How much hard braking and transitional turning are they doing on those cold tires? Oval racing isn't autocross. On cold stock car rubber it's going to be like CAM class on meth. 

 

 

 

 

IMSA says that rubber selection is gonna be a bad time without tire warmers. 

See, that's my lack of autocross racing experience .  I'm thinking of road racing with slightly lighter but less powerful cars than NASCAR uses on the road racing tracks.  So thanks.  The guys will decide what tires to buy for autocross.  Heck I may even go into the 21 century and use a different wheel size than a 15 inch 

TWR  was kicking BMW's butt and everybody else in Europe with their XJS  

 They used 17 inch rims (13 wide in the rear )   So maybe we can find some junkyard take offs off a Camero or something?   
 Only Vintage will require 15x10's 

In reply to frenchyd :

Just changing gears here,  thinking of my next car.  I've been whining about the size and weight of the XJS 

 In the shop I've got all sorts of XKE molds.  The next one won't be the MGuar , instead I'll build a Jaguar XKE 

   Same sorta horsepower but 5-700 pounds less weight and a lot less frontal area. Besides it will qualify for SVRA Group 6 

I've got most of the mechanical  and I'll use wire wheels to  boot.  I wonder if I could build it under the Challenge budget?  Hmmmm

Stampie said:

Stampie said:

I put the over/under at 13.5.

Now that I know the tires I'm going with 14.0.

Like I've said.  Repeatedly. I don't know anything about drag racing.   For example when the rear end squats  the rear end geometry gives a slight rising rate camber gain.  Should I start out with a slight positive camber,  have it flat on the launch and then allow it to go negative?   
   Or just start off flat, keep the springs heavy to hold it there through the quarter?   
    The trouble with that is the guys would have to pull the springs out of the rear end  and put the softer ones in for the autocross.  I suppose it wouldn't be that difficult if they had a spare  4  coil overs  to just bolt and unbolt in the parking lot.  I've got plenty of spares, and  I'll be in the class where it won't count anyway.  
     Heck since I don't have to worry about budget  I can send some drag slicks down  with them.  Just Chevy wheels. Should be able to buy those cheap enough
   Yeh!   If I'm not worried about  budget. They can swap the turbo's from those little T3's  for the autocross and use some T4's or even T6's. For the drag race.   
    The engine is sure strong enough and I've got  spares.  If the engine blows up drag racing. I'll bet it's only a couple hour swap now that most of the  luxury junk is gone.  It came out in 10 minutes.       Plus replacement if it's the same OEM is allowed at no budget hit.  
   1000 + hp 
    Think with drag slicks I might even have a shot at the Nelsons? 
 They have been running in the 9's in England. 

In reply to frenchyd :

No

Seeing "like I've said, repeatedly " gets quite old. Every one has heard you repeat stuff... usually off topic. 
You are the one, on here, that asked how fast anyone thinks your car will be. If you do not like the answer you get, there is no reason to start replying "I said" followed by "bla bla bla bla bla. 
yes, we know. 
For the record, I have no clue how fast your team will make the car go, so I have no opinion. 

In reply to 03Panther :

 Neither do I until it's together and I try it a bit. Basically it's all conversation.  But it will be interesting to see won't it?  

In reply to frenchyd :

I'd imagine twin t3 turbos will do a bit better even for drag racing than swapping to twin t4 or t6 turbos. Especially if you're not trying appropriately match the turbos to the engine setup and tuning.

In reply to yupididit :

You may very well be right.  And definitely are right regarding road racing /autocrossing.   The lag, spool up time of a bigger turbo would kill autocrossing. ( which is why Calvin isn't faster in the autocross. 
Bigger will work at Bonneville though. 
    I'll bring a spare engine or two and if it goes ca-Bang!!! Aw, so what!!   I'd just like to see what 30 pounds of boo

Frenchyd!

How is this car coming along?

Gonna turn a wheel in anger this season?

Rog

In reply to boulder_dweeb :

I have been fight bronchitis the last two months. Just when I thought I was over the hump I caught a cold.   Back to hacking, wheezing, coughing up major phlegm.   Right to the point of blacking out.  Checked twice and nope not Covid.  
   Then on top of that, my wife's mother passed away and we had to clear out her town house.  Which means a whole lot of furniture and stuff got worked into our place. 
  So it's coming up on 3 months without any work.  
   To answer your question;  schools ended and it appears I won't be driving for summer school.   So there will be serious progress and I expect noise coming out of the car by this fall. 

AWESOME!

yupididit said:

In reply to frenchyd :

I'd imagine twin t3 turbos will do a bit better even for drag racing than swapping to twin t4 or t6 turbos. Especially if you're not trying appropriately match the turbos to the engine setup and tuning.

The T3's I've got are as  close as I can guesstimate  without actual experience. 
   I'm going to start out conservative with about 12 pounds of boost max.  Then  find out what the pair is capable of making.    
  The factory tach goes up to 7000 so anything above that is guessing.    I know both Group 44 and TWR used   8000 RPM as redline   

In reply to frenchyd :

Even with the e85 you plan on putting in the tank 12psi is not a small amount of boost when coming from na. Get those wastegates down to 4-6psi and start there. 

12psi is almost 1 bar, which means ignoring a whole bunch of other factors your almost doubling the VE of the engine. Yours almost doubling the pressure of the air rushing into the cylinder when the intake valves open. 

Ya I strongly recommend starting at 4-6 lbs of boost. Build the system for 18 lbs in terms of intercooler, fuel etc but start at 4-6 and get the tune perfect then creep up on 12 or what ever your goal is.  
 

12 lbs is a lot for a motor of that displacement and if something  goes wrong it will really go wrong (as in motor destruction). Trust me on this one I am an expert on this. (The adding to much boost to fast and blowing up motor part).   ;-).