WHAT . . . DID . . . I . . . DO?!?

[hornetball]

13 minutes ago, speedracer said:

Your build comes out looking like a show car. 

It's not as shiny in real life.  It IS a race car after all.

[hornetball]

I swapped the location of the oil cooler and fan to get the cooler into fresh air.  Used bulkhead fittings to get through the radiator support.  The cooling changes worked well.  By running my fan, I was able to maintain 210F water and 250F oil on a 95F day.  I can still do some sealing to improve things.

 

Also built up a mirror mount to hold a racing mirror, the iPod I use for TrackAddict, and a GPS.  This should improve my video vibration issues.  Unfortunately, the iPod holder is a bit soft, so I ordered a firmer one.  It will just rivet in place when it arrives.

 

Put name and class graphics on the car.

 

Here I am demonstrating proper line and engine sound to a GT3 Cup Car.

 

Obligatory video.  Vibration issues are improved.  Car was running 1:23s in the heat.

Aaaannnddd . . . corded another set of fronts.  What do you guys make of this wear pattern?  I ended up with two circumferential wear grooves.  I think my pressures may be high making the tire tread bulge.  Remember, these are bias-ply tires, so they wear a bit differently than radials.

[Captain Buddha]

Very nice!! What size tires? I used to run bias ply on my GTA and my previous TA2...they were 27/10-15 though...probably more of a balloon than you've got...we still run very similar cold/hot pressures in our similar sized Pirelli Radials though....what are you starting at? It almost looks like you might be running too little of pressure (wear on the outside edges). I'm no tire expert though...it'd be worth it to get pyro readings across the tread though.

[hornetball]

The spec tires for this car are 25.5x8.5-15 (front) and 26.5x9.5-15 (rear).  The picture is a front tire.

I was initially thinking underinflation too, but I'm not sure if I would call the worn areas the "edges."  They seem a lot more inboard from the true edge.  Plus, I've been running my pressures on the high side for bias plies (going out at 25 and bleeding off to 32 hot).

I've got a pyrometer but lack assistants.  I'm also wondering if the classic pyrometer reading method (edge-middle-edge) would have picked up the hot spots?

Confused.

[Max]

^In order to rule out driver error- I would be happy to test drive it in the name of research of course..hahahahahahaha

[Matt93SE]

I would say underinflation as well, but those pressures are very high for a bias.  I used to run 14 cold on my RX7.   but I was running nearly same width tires on a 2000lb car with 200whp and no torque.  you have a different beast..

something to think about on bias is that the sidewall and shoulders are VERY stiff.  low inflation wear may not necessarily manifest itself on the outer edges like a radial tire, but further in where the stiffened parts of the shoulder taper down to the tread face.

I will also mention that I run DOT radials pretty low and have seen similar wear patterns on them where they will cord on the outer edge but have another wear mark roughly where the "tread bars" are on a hoosier on the inside of the tire.   someone mentioned a while back that's from underinflation and from the inner sidewall deflecting in turns, causing the tire to deform and push out right there.

seems plausible, but like Brad I'm no expert.

I'd go the pyrometer route, but maybe even take 5 readings across the tread for a little while and see if that brings you any useful information.  I would think you could "hire" someone at the track to help you tune things in like that.   I'm usually a 1-man-band at the track as well, and have enlisted the help of others when needed.  so far the only one that's refused to help was already in their clean clothes and about to leave, so I can't blame them for not wanting to climb under a hot car on pit lane.

[Captain Buddha]

If you every come run at ECR I'm more than willing to help you - in the paddock or on pit lane!

So...with bias ply's on our 2,830 lb tube frames we'd start at 17-18 cold with a target of 26-28 hot - really 27-28 hot.

An idea: start out with a little higher pressure and go make a few laps...bring the car into hot pit...have your helper take pyro readings across all 4 tires...then drop 2 psi and repeat...several times. 

[Max]

On 7/12/2021 at 5:13 PM, Max said:

^In order to rule out driver error- I would be happy to test drive it in the name of research of course..hahahahahahaha

As a side benefit- It would allow "you" to take tire temps upon pit in- Just trying to help out a friend  🙂

I too would be glad to help out and take tire temps if I am there when you are there.  As another option- make your next student help out.  It could be part of their "track education" to get some learning on taking tire temps.  hahahahahahaha

[hornetball]

Now that's an interesting idea.  Make the students earn their keep.  🙂

 

[RCman]

I would also be happy to help

[hornetball]

I noticed some play in the driver's rear.  It was coming from the diff.  On old Corvettes, the halfshaft serves as an upper control arm, so it is important to minimize the play in the stub axle so that camber and toe stays put.  Ideally, this should be .005".  I measured .012" on the passenger side (OK), but .030" on the driver side (too loose).  There are two possible causes:  (1) wear on the stub axle end where it meets the posi shaft (easy fix); and (2) wear in the posi clutches (harder fix).  I pulled the diff and inspected the stub axle ends.  They were perfect (sigh):

 

So, into the diff I went.

And, sure enough, worn clutches:

This is what it should look like:

Parts on order.  In the meantime, worked on radiator sealing.  I used foam tape on the top and bottom, side-bulb edge seal on the sides, and aircraft cowl seal for the top of the radiator support to hood.  Worked well!

First time I've torn apart a diff.  Wasn't too hard.

[Captain Buddha]

Interesting stuff...so...you've torn it down...the fun part is ahead...putting it back together...correctly...better you than me! Curious if you'll need more tools...or is this a case of "tighten it all to torque spec and it's all good?" (since you're not putting in a new R & P?).

[hornetball]

Since the gears and bearings are good and I haven't disturbed the pinion, all I need to do is reassemble with all shims in EXACTLY the same place and with the ring gear remounted to the carrier in EXACTLY the same orientation (according to the Chevy service manual).

Fortunately, I'm OCD.  That's a good thing for this work.

Putting the carrier back in the case is a tight fit on purpose (you get about .010" of stretch when you put the shims in).  I'm buying a set of shim drivers as Plan A.  If Plan A doesn't work (i.e., looks like shims might get damaged), then Plan B is to homebuild a case spreader using square tubing.

Once again . . . everything from Summit arriving in one day and reasonably priced.  Gotta' love old Chevies!

[Captain Buddha]

Very cool!! Good luck with it!!

[hornetball]

New clutches are in and diff is reassembled and back in the car.  All clearances checked good with a good gear pattern.  I'll be doing my own diffs from now on.

Since I've been getting tidbits here and there from the "Corvette Forum," I went ahead and joined.  Monitoring the traffic and topics . . . I'm definitely not a "Corvette Guy" (despite owning two).  Those guys really fit the stereotype.  LOL.

[Captain Buddha]

The Autocross / Roadrace subforum is legit though....the rest of it....a LOT of stupid....and such.

[hornetball]

So, all back together and to the track.  It's running cool and strong with greatly improved video capability.  It's ready for CVAR next month.

Did the 1.3 today.

Here's a "race" between a 1964 Corvette and a 1995 Miata.  Amazingly close.

http://www.youtubemultiplier.com/61181509b88e0-1964-corvette-vs-1995-miata-msr-cresson-1-3.php

[Matt93SE]

There is no way you can take that to CVAR. you will be kicked off the track.  no way an old Vette can handle like a Miata, nor be driven like one.   They will tar and feather you with 120wt gear oil and send you home if you drive a Vette like that on one of their weekends.

[Captain Buddha]

Very nice!!!

[hornetball]

Did  CVAR's racing school this weekend.  The racing school was interesting because they mix all the groups together.  This was the last session of the weekend. Got in four laps and the transmission let go. I have a few weeks to get another transmission in before the CVAR race at Hallett.  Hope I can get one with all the stupid COVID supply issues.

 

[Matt93SE]

do you have to run a stock box, or can you run a 4 spd dog box?  look at Jerico, G Force, and the like?

[hornetball]

Stockish.  Car had a Richmond Super T-10 in it, but that's close to the limit of what they allow.

I tore into it a bit yesterday.  Diff is OK and transmission is OK.  Probably broke the clutch disc.  A little more digging and I'll know for sure.

[Matt93SE]

Gotcha.  well clutch disc is cheaper than the rest of the parts!

There are several T101a boxes on racingjunk.  just don't tell em it's a dog box? 😉 

[hornetball]

Clutch is fixed, and I added a cage.

 

Cages need to be tested, right?

 

[hornetball]

COTA!  First time there.  In retrospect, I would definitely change some shift points and set the MSD for a 7K redline.  If I was really serious . . . different rear end gears.  Still, great weekend with classic Texas wacked out weather (had sleet on a session the day before).