acdrey

Hey all,

Figure I'll through a twofer in here to avoid clogging up the forums.

I'm seeking some expert advice with two issues I'm seeing with my track car

1) Car sees boost spiking by up to ~3psi over target especially <~3.8k RPM in gears 3 thru 5 when shifting.
I'm running a Vitesse stealth S turbo with TurboXS standard MBC (bleeder type), M-tune, TiAL WG, stock head (bottom end internals are not stock, but stock displ.), stock IC, and race exhaust, on E85. What have you guys done to eliminate overboosting? Is my problem with hardware, or is there something I should look into with vacuum line routing, etc.?


2) I can't find the right damper settings in the rear - I've got JRi 2-way adjustables (low speed compression/rebound and high speed rebound), with 850# springs up front and 1200#'s in the rear. I get stuck between setting the dampers too hard (through low speed adjustment) so that the rear ends up rotating too much and hopping over bumps, and setting it too soft so the rear squats too much when accelerating or bouncing through rough turns. I can't seem to find a great high speed setting, either. I haven't really had a chance to play with 2-ways until this season, so I'm still trying to figure out cause and effect with these. The car feels decent otherwise, I'm just having trouble figuring out what I need to do to help me power out of turns sooner, as that's where the faster cars in TT3 are really killing me. Any suggestions? I've got a couple lousy videos below.

Gingerman (most recent event). See ~1:05 when the car starts skipping through the long sweeping left hander. It sounds like the wheel lifts and hangs for a moment, as the RPMs jump up and down a bit.


Mid Ohio (two events ago). The rear slides a bit through turn 1 at 0:05, but then jumps a bit over the crest of Madness at 0:55, and same through the transitions from 1:05-1:15. You can really see the car hop at 1:30.


Any advice you guys can throw out there would be appreciated.

Dwane

350# difference front to rear seems a bit much....I was advised 150-250 difference.

Paulyy

Try a different boost controller. Seems as though there might be a ball and spring in the controller causing a spike.
Don't get me wrong, but it can be useful when you're shifting gears as it gives you a slight boost on torque after each change.

mahoney944

I used that same MBC before and had issues. It uses a controlled leak to regulate boost. Which isn't ideal for a sealed boost system. You want one like Lindsey offers, or at least that styling

Dave W.

Have you considered that you might have too much spring for the course? If the tire is skipping off the ground it might need more compliance.

disasterman

I think your spring rate is too high in the rear. I was at both events racing in ST1 with my 944. I am currently running 900 up front and 1100 and we are backing down to 750 front and 1000 rears.

Gingerman - there is a significant bump just past the apex on turn 9. While changing your springs & shock settings will help, you can also apex later and run parallel to the bump/groove.

Mid Ohio - That's a lot of hopping around on the exit of the carousel.

I would recommend you start at the bottom range of your settings and work up. On tracks where we don't have data we begin 2 clicks off the bottom and make adjustments from there.

Paulyy

My MBC was a "controlled leak" type. no issues.

There is probably a ball and spring there causing the issues.

mahoney944

No the kind he got has no spring. It uses the body as a chamber and that chamber has a hole in it. the **** simply exposes more or less of the hole and allows air to leak right out from under the ****. This is why its called a bleeder valve. A restrictive valve(ball and spring) uses the spring to load pressure against the flow of air restricting it. Turning the **** raises or lowers the spring pressure in the controller effecting boost respectively. The brand he has is the junk one found on eBay at a decent price, which is why I tried it and found it caused boost to come on lazy. Minor of course but noticeable.

The style "bleeder type" is OK for a single port if you don't mind it venting to atmosphere but on a dual port the MBC "T's" into the main boost supply line causing a leak on both sides of the diaphragm. You might as well poke holes in the vac lines.

67King

What rear bar are you running? In my experience, most people tend to want to run more rear bar than they need to. You might back off on the bar in conjunction with more firm compression settings on the dampers.

FWIW, I run 700 front, 1000 rear.

rlm328

I do not know what type of aero that you are running but you have way too much spring for your car's grip. My car (in the signature) is running 800 in front and 1000 in back on a car whose race weight is 3050. It also appears that you have some over steer, I would look at loosening up (moving towards the ends) the rear sway bars.

I assume that your g-meter is set to 1 g per ring for a total of 2 g's. The car should be capable in stock form to pull 1.1 g about all I can see on the gauge maybe a tad more at times.

Get a decent MBC from Lindsey.

acdrey

Thanks for the advice. If you don't mind me asking, what's your comp weight, and what size tires do you run on your car - are you at 285s? I'm limited to 275s based on classing, and my comp weight is 3000# even. What motivated your decision to back off spring rates - have you been at 900/1100 for a while, and just recently decided to change? Any suggestions on what might be more ideal for my setup?

I think I'll reset the damper settings and work up from the bottom range as you suggested, I've got a bit more rebound in them now than I probably should so hopefully backing that out should help with some of the hopping issues at Mid-O. I'll probably try that before swapping springs, unless you think these rates are just too high.

Thanks for the tip on Gingerman, not having to cross the bump seems like a safer way to take 9.

acdrey

I've got the MO30 3-way rear, set to the middle setting right now. I'll try backing that off to the softer setting to see if that helps out.

Just curious, what tires are you running, and what's your comp weight?

acdrey

Thanks for the reply. I'm running a Good Aero wing with a slightly longer splitter from Scott up front. My comp weight is 3000#, and I'm running 275s all around. I'll try backing off the rear sway to the softer setting, as it sits it's in the middle now.

The g-meter in the video is kinda crappy in terms of resolution, looking at the data, the car peaks at 1.4-1.2g depending on the corner/course, holding more steadily around 1.2-1.1g, but I will admit that "steady" is sort of subjective, and the curve is a bit jagged. It also seemed to be able to hold the same running 245s on a softer suspension setup, so there's something to be said there, I guess.

Any recommendations on spring rates for my weight/tire size? I assume your setup is a good reference since you seem to run a similar weight and aero setup, though I'm curious what iterations/different rates you went through to arrive where you are now? Are you happy with the current rates, or have you thought about changing one way or the other?

Thanks for the help.

acdrey

Thanks for the replies, all. I'll check through older forum posts to see what MBCs everyone's happy with. Lindsey and Hallman seem to come up frequently, so I'll check into those.

As far as spring rates go, any recommendations for my setup? I think a good portion of my issues lie within damper settings, but it seems that there are a few of you suggesting the rear rate is too high. Any suggestions? I run a large front splitter and rear wing, 3000# race weight, 275s on all four corners.

By the way, are any of you guys running stiffer springs also running helper springs? Mine now come unseated at full droop (car jacked up) since switching to the higher rates, and I wasn't sure if others just dealt with this, or if you guys were using helper springs.

disasterman

I have been using that spring rate for a long time, starting out as an E class racer in PCA then as a GTS 2/3 car and finally as a ST2/1 car. Weight gradually dropped from 2900's to 2700's. Raced ST2 with BFG R1's 275/35 with a best time of 1:31:1 at Mid O during the 2012 NASA Nationals week.

Current car is racing ST1/2
2650 with driver and fuel.
405 HP
Moton Club Sport
Pirelli/Michilin 305 front 322 rear
6 degrees of negative castor
3.8 degrees camber front
2.6 degrees of camber rear

I am going to switch to a lighter package this week 750 & 900 to give that a try. I will be testing out the new spring setup next weekend racing SCCA at a local track - Waterford. Will let you know how it pans out. Our next NASA race is in Pittsburg which is a rough track which will be a light spring rate track.