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returf
While most of you guys are nearer the end of your racing season, we are just beginning down here in New Zealand. I finally managed to get my car to it's first meeting last weekend. A classic meeting that is in it's 31st year of running and right at my local track. Practice went well but i noticed that I still had the wheel shake up front under brakes. Race 1 was going well with a demon start but unfortunately a lower arm on the left front broke and that put me out for the rest of the day. Day two, and another good start and went from grid 18 to 9th before the first corner, gee it's got great acceleration!!! Race three and off to a flyer again but three corners from the chequered flag and an axle broke. But all'n'all a great start to the 914's racing. Here's a video of race three. check out the shaking. Once i get that sorted i'm sure i'll be able to brake a lot later.

https://www.youtube.com/watch?v=C4OPnfSt_Lw

Click to view attachment
stownsen914
You've got some serious straight-line speed there! What kind of hp is it making?

I did notice the shaking. I'm guessing you feel it pretty clearly in the driver's seat. Do you know what's causing it?

Sounds like it was a successful outing overall.

Scott
Toast
Great video. Thanks for sharing!
Good luck and enjoy your race season!
Which LS do you have? Or should I say what are your engine specs. (I dont get to the Paddock very often)
Andyrew
Are you still running really low boost?

Car looks like its running great!!
Andyrew
Whats the red nob for, boost?
returf
QUOTE(Andyrew @ Nov 17 2016, 09:17 AM) *

Whats the red nob for, boost?

Brake bias to the pedal box. I thought it might have too much front brake on, thus the adjusting
returf
[quote name='Andyrew' date='Nov 17 2016, 09:16 AM' post='2423786']
Are you still running really low boost?

Car looks like its running great!!

Yes only 8lb boost Andyrew. engine wise all i have to do now is fit a rear sump, Sump to it as looking at the data from the ECU it was dropping off oil pressure on hard acceleration ( thank goodness I had fitted an accusump)

returf
QUOTE(stownsen914 @ Nov 17 2016, 08:11 AM) *

You've got some serious straight-line speed there! What kind of hp is it making?

I did notice the shaking. I'm guessing you feel it pretty clearly in the driver's seat. Do you know what's causing it?

Sounds like it was a successful outing overall.

Scott


Its a standard LS1 un-opened, with bigger injectors borgwarner SX 475 turbo and Link engine management. Dynoed at 527ft/lb torque and 525hp ATW. It's a great feeling after all the years building it to finally race with other cars. Can't wait for the next event
wndsrfr
Crazy fast, thanks for sharing--especially like the left hand shifting arrangement, cool.
I'm betting on a warped rotor or at least uneven bedding of the pads/rotors. Put a dial indicator against the front rotors & rotate them to check warp/runout. Bedding a new set of pads/rotors takes a series of hard stops & then a cooldown time of about 5-10 minutes & never sit still with foot on the brake if they're at all hot. Keep us posted!
Cracker
Another potential issue is a wheel out of balance. Did you mount the outside weights on the inside of the drum or lip of the wheel? If inside, it gets too hot there - you will need to mount them on the lip (and tape them too). I bet you will find this is most likely the issue. The date says 2013 - wrong? What gear box are you running?

PS: I just watched the video...you might BOTH rotors and wheels out of balance. That is crazy amounts of shaking. Keep us posted...

Tony
flat4guy
Wow that sounds great, wish we saw more 914's out this way.......
returf

I'll check it out in the next few days Tony. the rotors are new J Hook AP's and I bedded the brake pads in at Friday practice. I suspect that some of the problem may lay in the attachment of the caster arms ( too light given the torque applied when braking) but I'll let you guys know what I find re runout ect.
returf
I've been out to the workshop and with the steering wheel locked solid you can get sideways movement of the wheels. I'm picking this will be from the steering joint under the fuel tank. is there any aftermarket fix for this and do you think this may be the cause of my violent wobble that happens only under brakes?
Cracker
Ok. A couple other possibilities: 1) There are four bolts that hold the steering column to the chassis mount - make sure they are tight. These are located underneath the column in the two slots; 2) The outside bearing on the same rack (in line with the turn singal stalk) can wear/enlarge its retaining bore. Due to the notch for the signal cancel its far from a perfect design. I once used a band clamp around this bearing and it helped a great deal before fixing it appropriately.

Tony
returf
Sorry Cracker, I didn't answer your previous question re gearbox. Its a 6 speed from a Subaru STI V7.

My steering column down to where it goes through the body is all different from stock. it's electric power steering and all the uj's are late model and secure. I'll check rotor run out today. what's an acceptable figure?
wndsrfr
QUOTE(returf @ Nov 17 2016, 09:11 AM) *

Sorry Cracker, I didn't answer your previous question re gearbox. Its a 6 speed from a Subaru STI V7.

My steering column down to where it goes through the body is all different from stock. it's electric power steering and all the uj's are late model and secure. I'll check rotor run out today. what's an acceptable figure?

There's a good guide that you can download from Centric Stoptech on rotor installation. Shoot for less than.002"....closer to .001" or less is desired. If they're off, try taking them off the hub & advance them one or two lug positions & measure again....keep us posted.
returf
is this coupler shagged?Click to view attachment
Cracker
I don't know (I can't tell exactly from that picture) but something is...

Tony

QUOTE(returf @ Nov 20 2016, 04:51 AM) *

is this coupler shagged?

stownsen914
I would think that if the steering coupler were the cause of that violent shaking, that the car would be darting all over the road, and you'd feel strong shaking in the steering wheel. Even if it's not the cause of the shaking, you may still need a new coupler if you're seeing movement ...

If the shaking happens primarily under braking, I'd look at your rotors.
Cracker
Trust me on this...I had thought I had a mechanical failure earlier this year due to the violence of the vibration on my car. We looked at everything and missed the most basic culprit. I had thrown wheel weights and was out 8 ounces. Mount the outboard weights on the lip and tape. You might be very surprised..I believe I've mentioned this before.

Tony

QUOTE(stownsen914 @ Nov 20 2016, 10:50 AM) *

If the shaking happens primarily under braking, I'd look at your rotors.

returf
QUOTE(Cracker @ Nov 21 2016, 05:26 AM) *

Trust me on this...I had thought I had a mechanical failure earlier this year due to the violence of the vibration on my car. We looked at everything and missed the most basic culprit. I had thrown wheel weights and was out 8 ounces. Mount the outboard weights on the lip and tape. You might be very surprised..I believe I've mentioned this before.

Tony

QUOTE(stownsen914 @ Nov 20 2016, 10:50 AM) *

If the shaking happens primarily under braking, I'd look at your rotors.



Thanks Tony, I will get them re-balanced before next event but did you experience your shaking only under brakes ? It's almost like when the shaking starts the play in the coupler won't control the wheels until i remove my foot off the brake pedal.I'll also replace the coupler with an alluminium coupler and get the rotors running with less run-out. I'll keep you all posted.
Cracker
Yes. Mainly only under braking - massive vibration - my rotors were new so it was baffling. A friend mentioned the wheels as a possibility and I thought he was nuts. Smooth as ice after having them balanced - I was shocked. This is not to say it's not something else, or in concert with something else, it would be the number two culprit behind the rotors.

Tony
JFJ914
QUOTE(returf @ Nov 20 2016, 04:51 AM) *

is this coupler shagged?Click to view attachment

Don't know if that's your problem, but I wouldn't reuse it.
stownsen914
QUOTE(Cracker @ Nov 20 2016, 02:08 PM) *

Yes. Mainly only under braking - massive vibration



Interesting ... I lost wheels weights once, and vibration was significant, but I felt it all the time, worse with increasing speed. Easy to check though, so definitely worth doing that ...
jmill
QUOTE(returf @ Nov 20 2016, 03:51 AM) *

is this coupler shagged?


Yes, that's garbage. Tangerine makes a Delrin one.

http://www.tangerineracing.com/otherproducts.htm

That's some crazy shaking. If the coupler doesn't fix it I'd look at your steering rack and how it's supported in the chassis.
Randal
QUOTE(Cracker @ Nov 20 2016, 08:26 AM) *

Trust me on this...I had thought I had a mechanical failure earlier this year due to the violence of the vibration on my car. We looked at everything and missed the most basic culprit. I had thrown wheel weights and was out 8 ounces. Mount the outboard weights on the lip and tape. You might be very surprised..I believe I've mentioned this before.

Tony

QUOTE(stownsen914 @ Nov 20 2016, 10:50 AM) *

If the shaking happens primarily under braking, I'd look at your rotors.



It is pretty amazing what happens after you throw off a few weights.

Been taping them on ever since Bontempi told me how important it was that they stay on.

And don't forget to clean the rim prior to having it balanced and adding weights.
returf
Thanks for all your advice Guys. I'm working through the list of things to change. Done new rear sump, working on relocation of exhaust system to accommodate the sump change, Made new steering coupler, Waiting on new axles from the driveshaft shop and I will get the wheels balanced. Thank you all for your guidance and have a great Christmas
Mike santa_smiley.gif
ablesnead
Nice car , will be fun when you get it sorted...I have only seen the one photo of the car , but in that one your wing is mounted too low in the turbulence too be effective as it could be.....
6freak
looks like alot of fun...good luck with the front ..id try adjusting toe,seems to me the tires are fighting to see who leads the dance,which causes shake/wobble under braking not vibration, your steering wheels not strait, is that a clue?..if its not vibrating any other time its not unbalance of wheels..did you corner balance and align the car so you have equal weight on front tires..good luck this season ,hope you get it pinned down to a root cause

smile.gif

returf
Just a bit of an update on the vibration issue. I seem to have got things under control now. I took your advice and got all the wheels balanced, skimmed the new brake rotors and replaced the steering shaft coupler. Hey presto the shakings gone. Had a meeting yesterday and the car ran well. Three races and three good results. I gave the car 2mm toe in on the rear and 0 at the front and it's transformed it into something that doesn't want to swap ends at the slightest hint of steering input.
Cracker
Bravo! FWIW: I have 5mm of total toe-in on the rear; zero at the front. With allot of power, such as you have, the trailing arms can be splayed quite severely causing a very tricky condition to handle. Good to hear solid improvements have been made.

PS: What is your oil temp? How are you cooling it? What is your shift point?

Tony
returf
Sorry Tony, I meant to say 2mm toe in each side. You had to ask the tricky questions dont you. I have an oil cooler mounted between the rear inner guard and the new outside guard so it gets plenty of cold air. Yep thats one of the other jobs i have to do ( install a temp sender unit and integrate it into the computer to log). Shift point is 6000 rpm but it's really easy to hit the rev limiter at 6200 as you will see when i upload the latest video. I always yearned for a close ratio box and now i have one ( six speed) theres no holiday from shifting gears haha
Cracker
Excellent. I look forward to viewing the latest videos...regarding a modern, close-ratio box - I agree (I have said it is almost like cheating)! Which unit did you install?

T
Cracker
Very much improved - night and day really! As you get more seat time - it appears you will be able to carry a fair more amount of speed through the twisties. I understand it is easier said than done - first hand experience! beerchug.gif

Tony
stownsen914
Big improvement! I'm sure the beast is a blast to drive ...
returf
QUOTE(Cracker @ May 18 2017, 02:07 AM) *

Very much improved - night and day really! As you get more seat time - it appears you will be able to carry a fair more amount of speed through the twisties. I understand it is easier said than done - first hand experience! beerchug.gif

Tony



Yes, seat time will help a lot as will changing the 6 year old second hand Porsche cup slicks for something a bit fresher haha. driving.gif
porschetub
QUOTE(returf @ Nov 17 2016, 05:58 AM) *

While most of you guys are nearer the end of your racing season, we are just beginning down here in New Zealand. I finally managed to get my car to it's first meeting last weekend. A classic meeting that is in it's 31st year of running and right at my local track. Practice went well but i noticed that I still had the wheel shake up front under brakes. Race 1 was going well with a demon start but unfortunately a lower arm on the left front broke and that put me out for the rest of the day. Day two, and another good start and went from grid 18 to 9th before the first corner, gee it's got great acceleration!!! Race three and off to a flyer again but three corners from the chequered flag and an axle broke. But all'n'all a great start to the 914's racing. Here's a video of race three. check out the shaking. Once i get that sorted i'm sure i'll be able to brake a lot later.

https://www.youtube.com/watch?v=C4OPnfSt_Lw

Click to view attachment


What a beast,interesting mix of cars in that race,is it just an ''all in'' class or just a warm up race.
returf
Yes there's a great mix of cars alright. This is what is called "Allcomers" at a classic meeting. Anything that runs slicks and doesn't quite meet the COD (certificate of description) for the classic movement gets to race in this class.
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