Duke's '72 510 (Carbed KA Autocross/Hillclimb car)

[yealla 521]

dame you have done a lot of work

[Duke]

How did the autocross event go? Tried to come by and watch, but apparently you have to be a pre registered member just to watch and can't bring kids. They let me do a drive through and I saw your car, and I think I saw you talking with a group.

 

Read on and you'll see...

 

The club is really restrictive as to who can enter the location.  They had a problem a few years back and since then it has been pretty much locked down to only members. 

 

This past Sunday was the first autocross event of the season.  With the new changes to my car, I was very excited to see how it would perform.  The club that I run with is also trying a new format, which will take some getting used to for me.  In the past, all runs during the day (typically 8-10) would count toward points for the championships.  Now, only the first 3 times runs would count, and the runs after that would just be "fun runs."  I got accustomed to taking my first few runs a little slow in the past to get to know the course and then pick up my pace as the day went on.  Now the pressure was on to be fast right out of the gate.  This is especially difficult to do when you are in the first run group of the day and have to deal with cold and overcast conditions.  But that is how it will be for this year, and that is how most bigger clubs run, so I guess I'll have to get used to it.

 

Lined up for the first run, all I wanted to do was set a solid time and get a feel for the new tires.  I went out and promptly spun in a fast left hander...damn, not how I wanted my first run on new tires to go.  I dialed it back for the next few runs and put in an OK time to take second in my class.  The think that was really annoying me though was that I was slower than guys that I was beating last year when I was running street tires!

 

For the afternoon session I wanted to experiment with some things that were bothering me in the morning.  I had another big spin (went all the way off course and got stuck on a berm...car was OK though) in the same corner that I spun on in my first run.  I narrowed this down to a brake bias issue because it was a sweeping left that I was trail braking though.  With some adjustment of my driving and my rear brake bias I was able to get the car under control in this section.  I was still not super happy with my times though, I didn't feel like I had the grip that I should, and the car was bogging a bit in one of the slower sections of the track.  Taking some advise from a fellow racer who runs the same tires on a similar weight car, I dropped tire pressures from 30psi (which I had been running most of the day) to 27psi for my last coulple of runs.  Well, that made a difference!  I dropped almost a second from my previous runs, and started to experience that kind of "face bending grip" that is associated with r-compound tires.

 

This newfound grip has brought up some issues with the car though.  The major issue being it has started to miss on long sweepers.  It sounds to me like it is only firing on two cylinders, and it clears back up once I'm out of the corner.  To me, this sounds like a float bowl issue, perhaps fuel sloshing out.  Maybe some of you guys out there will have some more insight into this, because I would really like to get this figured out before the next event.

 

The next issue is that the rear inside tire has started spinning in turns.  I'm thinking that the added grip and added weight transfer of the new tires is to much for the differential (WRX STI R180 w/clutch type LSD).  Is there anything that I can do to help combat this?  Higher front spring rates perhaps?  I'm currently running 350# springs with a 1" bar up front so maybe a little more roll stiffness is needed.

 

Here is a picture from Sunday.

 

[Creepy Cruiser]

So Awesome.

[DottiBlue]

Glad you got the car sorted out by the end of the day. Soft sticky tires behave much different then street tires. I remember from my racing days that we would do the opposite to he air pressure on the soft tires that we did with the harder tires, not to mention that the soft tires were started at a tire pressure 15 ponds lower.

 

It sucks about the security at the airport. My wife grew up out there with her dad auto crossing. It was a big bummer to learn we couldn't come out and watch. We were also told even if we were members, our kids would not be allowed until the had learners permits!

 

Anyways, good luck with your future events.

[ptown green]

Dont those tires run on every corner? Or are you just running enough camber not to? I have 205-50-15 on 15x7 +15 and my tires always rub.

[Josh K.]

Where are the radiator install pics?? ;)

[Duke]

Dont those tires run on every corner? Or are you just running enough camber not to? I have 205-50-15 on 15x7 +15 and my tires always rub.

The fenders have been slightly flared, and the front fender arches have been raised.  I still have some minor rubbing problems in the front, but in normal driving conditions it doesn't rub.

 

 

Where are the radiator install pics?? ;)

I'll throw a couple up.  I'm not very good at taking pictures as I do stuff, mainly just post stuff once it's done.

[Duke]

Last Sunday was the second auto-x event of the year.  I spent most of the time between the two events working on the radiator installation so I wasn't able to make many other changes to the car.  The one thing I did was decrease the rear camber to X.X* in an attempt to curb the problem I was having with the inside wheel spinning when coming out of turns.

The morning session (the one that actually counts towards the points series) went OK.  At the last event I had ended up at 27psi for my last few runs and had found that to pretty fast so that is where I started.  I was able to get 2 solid clean runs that I was pretty happy with, but I still felt that there was a bit of time left, especially in the slalom sections.  For the last run in the morning I really wanted to concentrate on carrying as much speed through the slaloms as I could.  I was amazed at how much faster I was able to go when I really trusted the car, unfortunately this meant I entered the corner after the first slalom much faster than in previous runs.  This excess speed lead to a pretty good slide through the corner, pretty much canning what could have been a fast run.  Oh well, that's how it goes.  The car felt better, but I was still only able to get 2nd in my class, and comparing times to the guys I used to compete with last year on street tires, I knew I should be faster.

In the afternoon "fun run" session I decided to do some more experimentation with tire pressures.  Looking at my tire temperatures in from the morning session, the middle temperatures were always a little higher than the outsides.  This told me that I need to drop my pressures a bit to even these out.  In the last 4 runs my rear pressures went from 27psi, to 26psi, and then finally settled at 25psi, which gave me very even (within 2 degrees F) tire temps across tread.  In the front I went down to 26psi, which evened out my temps pretty well, but the outside of the tires were still getting about 10* hotter than the rest of the tire.  To me, this is an indication of not enough camber, or not enough roll stiffness.  I am already running 3* of camber in the front and I think that running any more would start to really impact braking performance.

This then leads me to think that I need to increase roll stiffness.  I also have two pictures from Sunday that point towards the same thing.  The first is coming out of a 180* sweeper, and the second is in the middle of a tight 120* turn.  In the first picture it looks to me like the car is rolling over the front a bit, but in the second picture, you can pretty clearly see the inside rear tire is off the ground.





So the question is, how should I address this?  I could go make a new solid 1.125" (or maybe a hollow 1.25) front anti roll bar, which would be a quite a bit of work, or I could increase the front spring rate.  I currently have 350# springs in the front, so I would be stepping up to 375# or 400#.  I haven't really heard of anybody running anything above 300#, so I don't know if this would be way to stiff, or if it may be necessary to handle the grip of these new tires.  Some input on this would be greatly appreciated.

[15om]

Looks like a blast. Cant wait till I can get out there

[510T]

I agree with the stiffer spring idea.  Way easier than building a new sway bar at least!  If the 350's worked great for street tires it makes sense to me that for slicks you would need moar.

 

How about increasing droop travel in the rear, to keep the tire down, would that be possible?

 

See you next time!

[Josh K.]

I would think more droop would be the best solution.

 

Josh-

[Busta Nut]

I think Draynor was or is running something like a 375-400lb spring rate.....and he's not on the track.....

 

Might try asking him how stiff it was.........

 

Sweet ride Duke!!

 

Don't know why I haven't seen your thread yet.........wait I know.........cause I'm fucking blind...

 

Hopefully by next year I'll be up there with you guys....

 

Keep up the great work and sweet autocross oics!!

 

 

-Antony

[Duke]

I agree with the stiffer spring idea.  Way easier than building a new sway bar at least!  If the 350's worked great for street tires it makes sense to me that for slicks you would need moar.

 

How about increasing droop travel in the rear, to keep the tire down, would that be possible?

 

See you next time!

 

Droop travel is sufficient.  After some advice from a member over on the510realm, I think it is more of a body roll problem.  I may initially go to stiffer springs but I do think I will ultimately go to a stiffer front bar.

[Josh K.]

How much droop?

[q-tip]

with how stiff the chassis are on the 510's I would think you could run a stiffer spring. what size sway bars are you running

[Duke]

with how stiff the chassis are on the 510's I would think you could run a stiffer spring. what size sway bars are you running

1" solid front and no rear bar.

 

I haven't measured droop, but it is most likely around 3-3.5".

[Josh K.]

I thought for some reason you had S13 rear coilovers?

[Duke]

No, I'm running old Carrera (now QA1) coilovers.  My droop travel estimation was based on the fact that the lip of the wheel and the lip of the fender are even at ride height.  When the car is in the air, the lip of the fender is above the tire.  With 205-50-15 tires this should mean about 100mm (or 4") of droop.  It could also be that the rebound dampening is to stiff, which could cause the wheel to lift.

 

Like I said earlier though, I'm pretty convinced it is a front roll problem.  I still have to figure out how I'm going to do this though.  It will most likely be in the form of a new sway bar, but I'm investigating some other possibilities as well.

[q-tip]

a rear sway bar will help with the body roll.

[Josh K.]

But will worsen the rear inside tire lifting problem.

 

Curious to see what helps.

 

-Josh

[Josh K.]

I would think the 1.25" front would help a little. 

 

Are you braking a little too late? Have you had anyone ride with you to give you feedback?

 

I'm just asking because sometimes our driving style/type causes these issues. I had a chance to autocross an STI the first year they hit the US and I declined and ran my S13 instead. Reason being it didn't fit my driving style. I ended up beating that same car with the S13 (with a stock KA)....

 

-Josh

[q-tip]

I'm thinking the rear inside is lifting because the rear is too soft and rolls more weight forward to the front outside corner causing the rear inside to lift

 

I agree with josh about the driving style, I did a similar thing that josh did and I drove my buddies fox body mustang in an autocross, ended up runnin faster times in my 510, with crap suspension and ridiculous camber. I did get him to run almost 2 seconds faster than is "uncoached" runs.

[ATP]

Are you having and under-steer or over-steer situation when going through the turns? Based on what you said happened it sounds like and under-steer thing, which would typically be solved by reducing spring pressure or reducing front roll stiffness. Its hard to address with a strut setup though, since compression reduces camber instead of increasing it. Is it in fact under-steer you are experiencing?   

 

 

 

Andrew

[q-tip]

I can't speak for duke but I have a car with a similar set up and I do indeed have under steer rather than over steer. only differences in out setup I think is I'm running a rear sway bar different rear coil covers and 25lb lighter front springs

[Duke]

Are you having and under-steer or over-steer situation when going through the turns? Based on what you said happened it sounds like and under-steer thing, which would typically be solved by reducing spring pressure or reducing front roll stiffness. Its hard to address with a strut setup though, since compression reduces camber instead of increasing it. Is it in fact under-steer you are experiencing?   

 

 

 

Andrew

 

The handling is fairly neutral.  The real issue that I am trying to solve is the inside rear tire spinning while cornering.  I think that it is getting unweighted so much that the LSD can't compensate for the traction differential.  I'm hoping to achieve this by increasing front roll stiffness.

 

I have an idea boiling in my head right now that should help me achieve my goal with minimal work and without having to make a new front anti-roll bar.  I'll post up some pictures when it comes together.