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Track day with Turbo84

3K views 16 replies 5 participants last post by  lsejlowe 
#1 ·
Caught up to Mike yesterday afternoon at Raceway Park of the Midlands (MAM). It was a beautiful day to be at the track, and plenty of people realized that so there was quite a turnout. I only got there in time for the last few sessions, but it was great to meet Mike and see his '69 on track and chat about all the work he's done to cut weight (about 2800# dry!) and put on the C4 suspension.









 
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#2 ·
Jason, I enjoyed visiting with you last Friday. After exchanging PMs for the past three or four years it was nice to finally meet and talk in person. As I mentioned, I'm planning on doing a headlight modification somewhat like yours in the future, and when time permits I'd appreciate your input on a couple things.

Had fun on the track, and got the "what do I fix/change over the winter" information I was looking for. In general, I was pretty happy with most aspects of the car's drivability. I don't have the horsepower of the C6 and C7 Z06 cars, but I don't have the additional 400-750 pounds they carry around either, so that helped even up things, thankfully.

Like we talked about, this winter's project is to tweak the front suspension geometry a touch more for a bit better camber curve, and hopefully an attending improvement in front grip in the slower corners (I'm pretty happy with the rear grip at the moment). Also got a couple aluminum fabrication projects planned that should pull another 20 pounds off the car.
 
#3 ·
Hey Jason, just an update on things. It's been a busy non-car related year so far. Had a lot of family obligations up in SD this year, which sure slowed down progress on the '69, and hasn't allowed me any opportunities to get back to MAM. I put on a lot of miles running up and down I29, and drove by MAM what seems like a couple dozen times.
Only got a couple things completed over the winter. I changed the front suspension UCA mounts to reduce the camber gain on the front. I think I was getting a touch too much with the old geometry.
Also, I spent some time trying to fix some of the road rash on the left side muffler and tip after smashing some of the pipes every time I bottomed out on that big dip in the RH turn before the long straight. After spending a couple hours messing with that 16 pound piece (muffler, entry elbow, and exit tip) I came to the conclusion that that's just too much weight to keep accelerating and decelerating the whole track day. I decided to weld up a replacement muffler that would hopefully be a bit lighter. I made a jig to capture the exterior dimensions of the present muffler, and then welded up an aluminum replacement. I've been running an aluminum muffler on my '84 for quite a while with good durability, so hopefully this new one on the '69 will work as well. Here's a picture during a test fit prior to polishing the tip and painting the housing black to match the right side muffler.



The new muffler setup weighs 9.9 pounds, for just a touch over six pounds off the left side of the car. I've only had time too put some street/highway miles on it, but it sounds as quiet as the righthand muffler (a Dynomax turbo muffler, which are good flowing quiet mufflers). For some sort of comparison test, I cranked the throttle setting up to 2000 RPM, and then used my sound dB meter to measure the amplitude out of each exhaust pipe. The readings were damn close. The tone is slightly different, but that's to be expected due to the difference in internal design. If things work out well I'll replace the righthand muffler with a similar aluminum replacement this winter.

The next project (if I can keep the interruptions at bay) is to swap out the C3 batwing and put in a C4 batwing. The C3 batwing is about 18-19 pounds, while the C4 batwing is about 12 pounds. The present batwing took about 15 pounds off the car due to getting rid of the heavy cast iron cover and the steel crossmember. This C4 crossmember to get me another half dozen pounds off the car.
 
#7 ·
I appreciate the kind words. Thank you.

I've got a couple pictures of different stages of progress with the C4 batwing. I'll dig through them and post a couple here in a bit.
 
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#5 ·
Hey Mike, good to hear from you. New muffler looks great! I appreciate your willingness and ability to dive in and fabricate anything and everything. Definitely keep us updated on how the batwing project goes!

I can relate to the busy non-corvette times. I started a new job in March and we just had our first child, so I doubt the 'vette will get much attention in the near future. That said, I do have the top end off the motor right now. I've been burning a little coolant on the driver's side for quite a while and it started getting worse so I decided I better get after it before things got worse. Found a crack in the intake valve seat on the #3 cylinder. I'm planning to just find another set of old '186 heads and stay pretty stock. Would be a good chance to upgrade, but I don't want to set foot on that slippery slope...

 
#6 ·
Hey Mike, good to hear from you. New muffler looks great! I appreciate your willingness and ability to dive in and fabricate anything and everything. Definitely keep us updated on how the batwing project goes!

I can relate to the busy non-corvette times. I started a new job in March and we just had our first child, so I doubt the 'vette will get much attention in the near future. That said, I do have the top end off the motor right now. I've been burning a little coolant on the driver's side for quite a while and it started getting worse so I decided I better get after it before things got worse. Found a crack in the intake valve seat on the #3 cylinder. I'm planning to just find another set of old '186 heads and stay pretty stock. Would be a good chance to upgrade, but I don't want to set foot on that slippery slope...
Hey man, congratulations on the new addition to the family. I'm happy for ya. :thumbsup:

ps: I weighed the car today at a local truck stop. 2780#. Every pound gets a little harder to dispose of while maintaining the factory interior.
 
#8 ·
Here's just a few steps along the way of trying to fit the lighter weight C4 batwing onto my car, which presently has the late C3 batwing attached to the older C3 iron differential.
The first thing needed was to make a 3/4" thick aluminum spacer to clear the C3 ring gear. The C4 cover is quite shallow compared to the C3 cover. Once there's clearance, I centered the batwing and put a couple tack welds on the spacer and cover to hold things together while I drilled the cover for the C3 pattern. Here it is bolted to an old spare 3.70 rear end I've used quite often for building and mocking things up. (The two parallel black marks near the outer mounts are explained later.)



Here's the separate pieces after welding up the original C4 bolt pattern holes in the cover.



And here's the cover a bit further down the process. Years ago I narrowed the C4 suspension on the car 3" to match the stock C3 trackwidth (so I can use stock C3 wheels on the street), so I had to cut (at the black marks) and reweld the the batwing after removing 1 1/2" on each end for rear knuckle clearance (the same as I had to do with the previous C3 batwing.



Here's the mostly finished cover bolted onto the mockup rear again. I welded the spacer to the cover both for aesthetics and so that I did not have two layers of cover gaskets that needed to seal. Due to clearance issues, and the desire to not have to do additional cutting and welding), I had to use a special small-head bolt in the upper right position to clear the plastic vent tube near that location. Also, I replaced the rubber bushings with new polyurethane units while it was handy.



Here's the initial test fit of the C4 batwing onto the differential that's in the car. Oh, I also had to weld/drill/tap a place in the cover for the lube plug, as the plug on a C4 is in the housing, not the cover like a C3. Thankfully everything fit. (I've got some steel material temporarily welded into a jig to keep the differential assembly from moving around until I can get the outer frame tab mounts fabricated and welded in.



Right now I'm still cutting and grinding to remove the remnants of the old frame tab mounts so I can weld in the new mounts.

This C4 batwing swapout will take an additional 5# off the car compared to the C3 batwing, which was a 15# reduction in weight compared to the original iron cover and steel crossmember.
Years ago, because I have a C4 suspension and a C3 differential and cover, I had to make several (steel) adapter brackets to mount the C4 spring and the C4 (and later, C6) toe rods. With the usage of the C4 cover, I should be able to delete most, if not all of those adapter brackets, resulting in an additional 6 pounds removed, for a net reduction of 11# with this conversion.
 
#9 ·
looks great, Mike! You make it look so easy.

Can't even tell you shortened the batwing 1.5" on each side. Looks totally stock to the untrained eye.
 
#10 ·
Jason, just a quick update. Finally had an opportunity to get back up to MAM for a track day yesterday. Last year was full of extra family obligations and I never had an opportunity to do any track time (anywhere).

I put about 90 miles on the car yesterday. Car ran well, and nothing broke! I had some durability curiosity/concerns about the new aluminum muffler and pipes, but everything held up fine. Exhaust has a nice note, and thankfully not loud either. Made some changes to the front suspension geometry and alignment, and the understeer issue I've fought for the past few track days is gone. Very happy about that. The new lighter batwing worked out well, so I'm glad the time and effort on that wasn't a waste. The track there is getting pretty bumpy at places, and I might pull off the '84 Z51 rear spring and put on the base '84 rear spring to soften things up a touch.

Over the winter I found out that my accelerator pedal upper arm was bent, and the carb wasn't at WOT when the pedal hits the floor. I took the pedal assembly out and rebent it, and the acceleration at WOT is noticeably improved now. Apparently the upper arm bending is not an uncommon thing in C3s, and something to keep in mind if the engine just doesn't seem as strong as it should be.

Heartland Park is open again, so I'm hoping to get over there next month for a track day.
 
#11 ·
Great work, I appreciate your engineering skills and willingness to push it hard. :thumbsup:

Would love to see a photos of the engine and front suspension. Food for thought......... the Dana 44 HD (Dana 60 pinion) out of a Viper has an aluminum housing. Street Shop makes a billet bat wing, minor mods to the housing are needed but with your skills you won't have a problem.

The upgrade does require moving to coil over shocks, fairly easy to fabricate mounts. Photo below.

:cheers:
 

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#15 ·
The truck is a work in progress, so I don't have many pictures. It's basically a stock bodywork standard cab '51, with an '85 front suspension and a '93 rear suspension. The engine is the original 350 from my '84, hooked to a turbo 400 transmission. I'm running out of ideas for modifications on the '69, so I'm hoping to start making progress again this winter on the pickup.
 
#13 ·
Hey Mike, glad to hear it's running well! I had a similar thing to your bent pedal. Carb linkage was all out of whack and wasn't getting much out of the secondaries. Quick adjustment and shaved a second off my 1/4 mile time. Too bad those kinds of gains don't happen more often! :laughing:

Let me know when you're planning to head to Heartland Park. Not sure if I'll drive the 'vette all the way there, but I might meet up with you and then head over to my in-laws by Lawrence.

I did get the top end of my motor back together. I have a bunch of loose ends to tie up, but struggling to find time to work on any of it... We all know how that goes.
 
#16 ·
Hey Mike, glad to hear it's running well! I had a similar thing to your bent pedal. Carb linkage was all out of whack and wasn't getting much out of the secondaries. Quick adjustment and shaved a second off my 1/4 mile time. Too bad those kinds of gains don't happen more often! :laughing:

Let me know when you're planning to head to Heartland Park. Not sure if I'll drive the 'vette all the way there, but I might meet up with you and then head over to my in-laws by Lawrence.

I did get the top end of my motor back together. I have a bunch of loose ends to tie up, but struggling to find time to work on any of it... We all know how that goes.
The track days at HPT don't seem to be fitting into my schedule so far this year unfortunately, so I'm shooting for heading up to MAM again sometime this month. I'll drop you PM when I think I'm heading up there.
 
#14 ·
Finally got the other (RH) aluminum muffler completed. Got it as close to a mirror image of the left side muffler as I could. Still need to spend a bit more time polishing the tips.



The weight was similar to the LH muffler (10#), allowing another 6# off the car. Ran my first autocross in years last week when I hauled the car back to Indiana to visit some old friends and have a bit of fun with the car. Got some compliments on how the exhaust sounded at WOT, and also a comment that the exhaust was "pretty quiet for that kind of horsepower". That was welcome news, given all the work it took to fabricate and weld up the mufflers, as I hadn't mentioned to anyone there that these mufflers are new to the car.

The narrowed/modified C4 batwing seems to be working well with the stock C3 differential. So far no leaks or structural problems. The modified C4 batwing is about 5# lighter than the late C3 batwing I previously had on the car, which is 15# lighter than the original iron cover and steel crossmember. The car should be about in the 2765# range at the moment.
 
#17 ·
Sounds like the mufflers turned out great (pun intended :laughing:)!

Keep me posted on your plans for MAM, I'll try to swing over and meet you there.
 
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