My 69 Z/28 "building find"!

[Z28Project]

Yeah James.  And combine all of that with the 5.86 rear that was in it and I'm sure it was a wild ride!

[firstgenaddict]

wow set up for the 1/8 mile... aluminum rods set below the deck... to allow for stretch... oh I know too well those drag engines.

[jdv69z]

So, why aluminum Rods?

[Z28Project]

I believe the lower reciprocating weight allowed the engine to rev high and rev quick, so they were used in all-out performance builds.  The downside is the properties of aluminum only allow so many high rpm stress cycles, so after so many 1/4 mile runs you were supposed to change the rods.  From what I understand that makes it not a good choice for a long term street engine.

In todays engines, they do it with titanium connecting rods which allow the very low reciprocation weight and long term durability, at a fairly high cost! $$$   The C6 Corvette LS9 and LS7 (also in 5th Gen Z28) use titanium connecting rods.

[firstgenaddict]

I believe the lower reciprocating weight allowed the engine to rev high and rev quick, so they were used in all-out performance builds.  The downside is the properties of aluminum only allow so many high rpm stress cycles, so after so many 1/4 mile runs you were supposed to change the rods.  From what I understand that makes it not a good choice for a long term street engine.

In todays engines, they do it with titanium connecting rods which allow the very low reciprocation weight and long term durability, at a fairly high cost! $$$   The C6 Corvette LS9 and LS7 (also in 5th Gen Z28) use titanium connecting rods.

Not only reciprocating but also rotating mass (big end of the rod)

removing a few ounces of weight from the rotating and reciprocating masses will yield a larger improvement in lap times than removing a few hundred pounds in vehicle weight... why? a few ounces accelerated through the RPM range many times per lap takes more horse power than one could imagine.

[Z28Project]

I had decided from the get-go that I wouldn't service the front drum brakes if there were any issues, and one of the wheel cylinders started leaking, so off with the drums and on with a front disc swap kit.  Not an upgrade, just getting the car back to where it once was. 

Front drum brakes:




Off the car:






New discs going on:






Some fresh wheels and tires coming next!

[BULLITT65]

I am surprised anyone would go through the trouble of putting drum on a disc car. I have heard that because the disc pads slightly drag, that drum are faster, but geez I gotta think the extra weight would negate any small gain like that.

[Z28Project]

Agreed!  I asked him about that a long time ago.  He said he thought it would be quicker with drums.

Probably something he read at the time, or heard from somebody else.

[69Z28-RS]

I don't think there is any doubt that for DRAG RACING, it's better to have drum brakes than disks...   In the late sixties, when one could order disk brakes or use the drums (on most performance cars), if one was intending to to use it for 'acceleration testing'.. ...  They always went with the drums, and then back off a little on the adjustment so the wheels rolled very easily...

[Z28Project]

That makes sense!  I forgot about backing the adjustment off a little.

[BULLITT65]

Gary, I have doubts...
Maybe in the late 60's there were no doubts?
 

[ZLP955]

Very common to see serious racers swap out front disc brakes for drums back then. Mine had it done too, looked like the original owner knocked the disc assembly out of the ball joints and pulled a complete '68 drum/spindle setup, including the drum master, from the junkyard to replace it.

[69Z28-RS]

Gary, I have doubts...
Maybe in the late 60's there were no doubts?
 

Austin...  to prove it to yourself, go PUSH a car wtih disk brakes vs a car with drum brakes! 
that will convince you....

[ZLP955]

John where did you source the two-piece rotors from? I know there are several suppliers who offer US-made and imported reproductions, but interested in opinions on quality, fit, finish etc from anyone who has used them. I have my original take-off parts, but the rotors are close to minimum spec and have a few pits.

[ban617]

I think with the drum brakes will hold the car better when doing a burn out vs using manual stock disc brakes.