JZA70 Time Attack Track and Street

[1jz-Rolla]

The heim joints definitely take any flex out of the equation, so your alignment stays true regardless of which way the suspension is loaded. Also stops energy being stored in the bushes (wasted) which can help eliminate axle hop etc. Bad side: shock loads are transferred directly to the subframe and chassis - read fatigue and cracking (eventually).

From memory, a simple version is that toe-out on the rear can help turn-in and general responsiveness, but makes the car a bit twitchy.... whereas toe-in assists stability, particularly at speed. Different tuners/aligners seem to give different stories on the benefits of each.

 

[LordDigital]

This is a juicy topic and I was just thinking about all of this on the way home from the workshop (they are just perfecting the cold start btw).

How much camber did the group A cars run at the front? John Smith mentioned something about 5.5deg of caster which is far from 10 so that's interesting. With the beech arms, I was planning on maxing them out so they're as short as possible and then having the wheel aligner fine tune the LCA settings. Is this a bad idea?

In regards to rear arms, I have the full set from beach but am reluctant to fit them all for fear of "heim maintenance" in case I feel like streeting the car a times. Is it unnecessary to have adjustable LCA, toe and traction in the rear or should I just fit the LCAs themselves? I've heard people say there is quite a bit of adjustment with the stock rear end anyway but every aligner you speak with tells you a different story...

IMO John Smith's Group A supra story is that the car was setup with a aggressive race caster from TRD Japan which was 10degrees or more ,BUT he had reliability issues with that much caster. As a result to keep the car reliable he had to reduc it to 5 degrees. It has a lot to do with the goal of his race program - to have a reliable car - he simply had absolutely no theoretical chance of winning over the sierras ans skylines because FIA rules penalized the Supra in terms weigh way to much in the post 1988 regulations.

To be absolutely sure how much the caster helps ,someone will have to perform analyses on the dynamically induced camber of lets say 6 ,9 and 10 degrees of castor. I tried that but can't claim my results to be conclusive ,at ~10 degrees turn I gained 0.4 camber when moving from ~7 to 8.x caster. Even tough my analysis results were not conclusive ,I still strongly believe that the curve is non linear and decided to run my car with 9 degrees castor.

Camber settings are vehicle and track specific. Not sure what GroupA cars ran ,but these cars were tanks (1450KG minimum weight) and were also heavily caged... The best approach to determine good settings for your car will be to start with -3 front and observe internal tire temperature distribution. To do this I'm using pyrometer that actually punches my tires ,and I found that on my car with 9 castor and 3.1 camber results in 20degrees F deviation on the front tires (170degrees F in the middle) . I can get the deviation close to 0 by going -3.5 or maybe even -4 ,but my breaking will suffer greatly. On the rear it was IIRC ~30degrees delta and I wish that I could go to -2.5 camber in the rear (currently at -2) but with 500WHP and 500torque this will be suicidal... BTW Alexandar Strik supra is running -4 in the rear and -3.5 in the front in historic races on SPA (GroupA cage ,1350KG weigh)...

 

[spiller]

Thanks guys, that all makes sense. I guess a lot of it is down to trial and error. Alex you are right, I remember John saying all of that castor induced powersteering failures. Perhaps I will try something in the 6 range and start with 3.5 deg neg camber front and 2.5 in the rear and go from there. Suspension settings really are more suited to a physicist than a layman such as me haha.

That Alexander strik guy running more camber in the rear than the front...I've never heard of that but I'm sure it comes down to his driving style. I'd kill to have a lap of Spa.

 

[1jz-Rolla]

That's pretty much it - with added caster you are actually lifting the weight of the front of the car each time that you turn the steering wheel, puts increased loads on the power steering (or your arms in a non-assisted vehicle!).

Just remember with your camber - the more you go on the front, the less braking performance you will have...... and the more you set on the rear, the less traction you will have. So you have to find a balance for both.


Cheers
Phil

 

[LordDigital]

Thanks guys, that all makes sense. I guess a lot of it is down to trial and error. Alex you are right, I remember John saying all of that castor induced powersteering failures. Perhaps I will try something in the 6 range and start with 3.5 deg neg camber front and 2.5 in the rear and go from there. Suspension settings really are more suited to a physicist than a layman such as me haha.

That Alexander strik guy running more camber in the rear than the front...I've never heard of that but I'm sure it comes down to his driving style. I'd kill to have a lap of Spa.

Skirks (Father and Son Supra fanatics IRC) geometry settings always remind me of one of the picz in my "race MA70 collection" (Just make sure that you do not setup your car like this

It is difficult to justify that much camber ,but I guess that is what works for them. Looking at the history - Minolta colours was the pre-88 FIA homologation Supras ,and it is a fact that they ran STOCK CT26 with absolutely no upgrades! Regardless of that this is the only config where Toyota had any success whatsoever with Supra in GroupA ,on their debut in JTCC in September of 1987 at Sugo TRD MA70 scored a win in the round. Of course the privatly ran Sierras got DNF ... details ,details

BTW Skirks times on SPA in 2011 were 8 seconds behind TRD cars and 9 behind Bemani ,I guess track config changed for 21 years tough ... and I would also kill to drive there

 

[spiller]

Phil: Car is only making about 230rwkw currently so 10.5 inch slicks on the back could possibly even cope with more than -2.5 degrees. I hear ya though, I guess it all comes down to who ends up aligning the car. Ideally id like to have someone corner weight it at the same time. Some of those guys charge the earth though! It is nice to have an idea of what specs I should be going for in mind too though.

Alex: The set up on that car is insane, it almost looks photoshopped. V8 Supercars competing here in Aus (decedAnts of what the Aus GROUP A Supras competed against in the ATCC) run close to that much camber also.

 

[josbeat]

will be a good idea to open a new thread where we can write our setting and experiencies ehh??
I will order those upper arms anyway to have more room at the front now -1,5º with 265-660 slick 18kg spring and 1.9 bar
at the back and like my engine is pushing arround 700 hp I will keep the rear at -0.5º with a 285-660 slick 10 kg spring and 1.9 bar
I will be at the track on 7th of october and I will do more test and i will check the temperature of the tyres to be posted here but now I am playing more with the weight distribution and aero helps than with the suspension settings because at the end of the day the "used slicks" looks mutch better than in the bigginin of the day!!!! the last time in the track with the setting I posted so I was happy also with the handly .

my next project is to move the fuel tamk inside the car but just at the back of the drivers seat where the rear seat was, the heigh is almost the same as the stock one but the weigh will be between the wheels !! the plan is to fit a 8 or 10 quarts tank also with weight reductions what do you think matessss??

 

[spiller]

The fuel cell is definitely a good idea if you don't use your car for long hauls. I was thinking about doing this when I eventually go E85 but it takes dedication to the cause to cut your floor pan up!

Jose, how is it with the 10kg spring in the back? That is quite soft for slicks, no? I have 18kg for the front and 16kg for the rear that I am going to try but I can use also a 14 or 12 in the rear as well.

 

[josbeat]

I tryied the same setting of the Tein RA the racing ones.

allway is a good idea going form soft to hard

too much hard at the rear wheels = low traction

the rear of the supra is where we can remove more weight than other part of the car ( now will be the fuel tank, soon the rear glass, the spare wheel hole, I have 15 kg less with the rear brakes I have..... and more like the rear hatch in carbon fibre..... ) I am using the rear wing to compensate the difference of front-rear weight but with a too hard springs uhmmm I don´t see it.

I am still using the Supra on a public roads and till I have time to fit the new track dampers I have in the box, I will keep with the Tein Flex with those springs (remember I have a helper spring also, I am really happy with that setting)

if you plan is to go super low suspensions , yes you need a very hard springs
I prefer to have suspensions and compensate it lowering the body weight with carbon doors , carbon hood , low seat possition , the battery low and back in the car..... to minimize the body roll.
and lowering the rest of the body aero helps like the front bumper , side skirts, air vent on the fenders front and back....... really modifying a racing car is a world.

 

[oldsking]

The fuel cell is definitely a good idea if you don't use your car for long hauls. I was thinking about doing this when I eventually go E85 but it takes dedication to the cause to cut your floor pan up!

I got the ATL well cell.. check it out, fits right into the wheel well of the car perfect. Only thing is yes its 12 gallon but that should be plenty fine for time attack runs

 

[josbeat]

I got it
http://www.summitracing.com/parts/JZP-252-012-01/

 

[spiller]

I tryied the same setting of the Tein RA the racing ones.

allway is a good idea going form soft to hard

too much hard at the rear wheels = low traction

the rear of the supra is where we can remove more weight than other part of the car ( now will be the fuel tank, soon the rear glass, the spare wheel hole, I have 15 kg less with the rear brakes I have..... and more like the rear hatch in carbon fibre..... ) I am using the rear wing to compensate the difference of front-rear weight but with a too hard springs uhmmm I don´t see it.

I am still using the Supra on a public roads and till I have time to fit the new track dampers I have in the box, I will keep with the Tein Flex with those springs (remember I have a helper spring also, I am really happy with that setting)

if you plan is to go super low suspensions , yes you need a very hard springs
I prefer to have suspensions and compensate it lowering the body weight with carbon doors , carbon hood , low seat possition , the battery low and back in the car..... to minimize the body roll.
and lowering the rest of the body aero helps like the front bumper , side skirts, air vent on the fenders front and back....... really modifying a racing car is a world.

Jose, this is true. I have stripped everything out of the car that does not need to be there and as you said, the rear of the car ends up being much lighter than the front. So, this is of concern to me in regards to brake bias and overall handling/traction. I will see how the 16kg springs go but I also have anti-roll bar settings to play with as well. I had the workshop move my battery to the rear passenger area on the opposite side to where I sit, and I need to find a new seat that will get me lower in the car. I also have a rear wing ready to go on and material to make a front splitter but I want to get the mechanical grip working well before I introduce aero to the equation - otherwise I will confuse myself and wont be able to track my progress with the car if I throw too many new parts on all at once.

 

[HKS_TRD]

Just found this new thread, good to see that you have started to sort the car out.
Seems you have been collecting alot of nice parts too!

 

[spiller]

thanks mate, I actually drove the car for the first time in 18 months on tuesday when I picked it up from the shop. it was nice to finally drive a supra again although its a different experience with a locked diff and no interior.

I now have a dilemma as to whether I want to go along the lines of track only or track and occasional street. I love driving the car too much! the definitive factor is the heim jointed arms which I dont want to fit and generate a whole heap of upkeep unless there is a significant benefit from the alignment perspective.

My racepack dash has been mounted and is operational, the car made 225rwkw at 18psi and has no problems lighting the 265s at 2/3 throttle. It has a very high final drive gear ratio in there at the moment (4.3 or 4.55) which may have lowered the dyno no. (not sure?) because it feels just as powerful as it did before with a claimed 255rwkw. Not fussed either way as the drivability of the tune is great. The valve stem seals have developed a leak in its time sitting around workshops though but ill be going to a thicker oil for track use anyway so hopefully that helps the issue a bit, otherwise I will have them changed.

In other notes I have secured a spare rear cradle ready for bracing
I have a TRD 2 way in 3.9 ratio lined up also
Inspecting a pair of fixed back seats this weekend which will improve my safety and seating position
All components for evo brembo/sti rotors lined up ready to go

Hopefully get out to the track before the end of the month with the car in its current format.

I will post up some pics on the weekend but at the moment not much has changed.

 

[1jz-Rolla]

Be patient on the valve-stem issue, and you could get lucky. It may rectify itself after a few heat cycles to soften up the seal material. My motor showed exactly the same symptoms when first fitted (ex-jap import with ??? km), but came good.

I see your dilemma with the track vs street issue.... there can never be a good compromise for both unfortunately, if you want to chase those last few tenths.

 

[spiller]

Yeah I thought about that, hopefully the 15w50 and a few floggings will improve it. The guy who tuned it today said either weld a cage in and go wheel to wheel racing or do a bolt in and stick to club events etc. TBH the paint work is too nice for a race car but reshelling is more expensive than a paint job haha.

 

[spiller]

got the car back from the workshop about a week ago and have been enjoying driving it over the last few days. Havent had the chance to give it a good flogging yet as its a lot louder than I remember and
given that it has no interior bar dash and front seats, I fear the first cop who looks inside the car will send it on a one way trip off the public roads. I am itching to get it on the track, next prac day at Mallala is mid november so ill aim for that.

Its now using a Haltech PS2000 ECU, HPS6 igniter and Racepak logger dash. Makes a modest 225rwkw at 18psi and the powerband seems to be all midrange so its been interesting getting used to the new power delivery. AFRs are pretty conservative too which suits me. Bare in mind this is all just a baseline. The aim is to get it steering, stopping and turning properly before I invest more into the grunt side of things.

I spent some time today swapping over the wheels. What I had on the car are now my track wheels and the ones you see below are my new street wheels. They're XXR 527 18x9.75 all round +20 at the back and +24 at the front. Pretty happy with the fitment and i think its an improved look overall.

Have been Nulon in the Evo with good results so trying this in the Supra.

Its pretty thick but will be better for higher temps at the track. My valve stem seals have become leaky given the car wasnt run for 18 months so hoping this will help with that too.

And now the battery lives back here.

And the racepak. Havent had a chance to play around with it yet but it will tell me the important stuff and does lap timing, splits and predictive lap times too which should be cool.


I have a whole bunch of other shit taking up our spare bedroom that will be added in due course, just gotta find the time!

 

[1jz-Rolla]

Wheels look great But i'm not biased or anything! haha. Shame we're so far away, our cars would make a good evil pair cruising the streets together!

That 10W-60 Nulon should be good - I ran the Castrol Edge equivalent in my old JZ cause I was experiencing low oil pressure at idle after longer circuit stints without a big oil cooler, the thicker [when hot] oil did the trick, without affecting cold running.


Bet you can't wait to get out at Mallala soon

 

[spiller]

thanks mate. I'm not gonna lie, ive had these wheels sitting in their boxes for 8 months and had no intentions of using them on the street until I saw the pics of yours and thought "fuck it, they look too good to be just track wheels", and so here they are!

with the oil, those were my precise thoughts. I dont yet have any oil cooler other than standard so didnt want to risk it with the 10w40 motul i had in there. plus this is fully synthetic as opposed to the semi of the motul turbolight I was using.

 

[1jz-Rolla]

Haha, that's funny, we're doing the reverse with our rims. What size tyres are you running on the 18's?