DWC's 1968 Camaro project

[colorado80439]

Beautiful build, clean and smooth, love the color. The fire extinguisher may be a little difficult to get to if you ever need it, lol. Good luck with that vibration

[jmac]

Nice clean car. Love the grille. Great job!

[ADY]

Nice to see a similar '68. I went through several rounds trying to figure out vibration, and for me it came down to driveline angles. Even with a Speedtech tunnel cover I can't get the T56 high enough to get rid of a minor vibration. Glad you'll be able to enjoy it this summer.

[WSSix]

Very clean! Love the work you did on the car. Enjoy driving this summer.

[SSLance]

It really sucks that such a beautifully finished car is giving you fits like this. Vibrations are so subjective, it would really help if you had a video of the vibration taking place, and from different angles (especially the underhood one). They can be great diagnosing tool.

My 383 always had a vibration I couldn't get rid off under a high load, low RPM situation, like 16-1800 RPM in 6th gear on the highway. Once I put the Holley Fuel injection on it, we figured out it was a miss (more like a shudder, not a hard miss) and we tuned about 90% of it out by fiddling with the timing and fuel in that area on the map.

There seems to be something about the stroker engines that enhance that type of harmonic and send it thru the whole car.

My builder putting my engine back together this time demanded that I bring him the pressure plate so he can balance the crank with the clutch assembly attached. He says if the clutch is out of balance you will definitely feel it. I'm interested to see how that turns out this go around as well.

Meanwhile, go enjoy your car... It's a beaut!!

[F'in mine]

[QUOTE=DWC;702651]I got the new trans installed the other weekend and went for a drive and...the vibrations are still there.

I guess we've eliminated one more possibility= the trans. So, it seems the issue is somewhere between the front of the engine and forward of the trans.

I've been reading various vibration threads and I'm wondering if the vibration is a result of a physical imbalance (i.e.- internal rotating assembly out of balance, flywheel counterweight incorrect) or an imbalance related to tuning (i.e.- misfire, incorrect timing, etc)?

Wouldn't a physical imbalance begin to vibrate at a certain RPM and continue to increase in severity through the RPM range?

In an effort to be concise, I'm going throw out some facts from what I know at this point:
-Vibration is not speed related.
-Vibration occurs around 1900-2100 RPM's, then goes away and returns around 4000 plus.
-Vibration decreases when I push the clutch in and engine speed begins to drop.
-Vibration seems load dependent.
-Vibration isn't noticeable/present when engine rev'd in neutral at a standstill.
-Engine seems to have normal water temp, oil PSI, power.
-Engine DOES have run-on/dieseling when I shut off the ignition. Usually around 3 seconds of continued rough idle before finally dying.

Regarding physical imbalance- I ordered a few different flywheel counterweights and was planning on trying to find a counterweight "sweet spot" via trial and error. Someone mentioned that the rotating assembly could have originally been balanced with the flexplate that came with the engine and now that I've installed a flywheel, it could be out of balance.



Just throwing out some suggestions so don't take this as offense to you. What type of stroker do you have? 2 pcs. rear main seal or 1 pce. seal, one is internal balance the other is external balance. Could you possibly have the the wrong type of harmonic balancer.
How about the frame mounts.
http://www.pozziracing.com/camaro_engine.htm
Could the flywheel or clutch assembly be out of balance?
Wrong throw-out bearing? There are a few different heights available.
Adjustment of the clutch pedal play & engagement?
Reciprocating assembly needs to be re-balanced, sorry its a possibly.
For the run on....try running a pvc system on the drivers side and a passenger side to air cleaner hose?
This one might be bull$#!t to do but how about running the distributor without the ignition box. I have a billet distributor on my SBC without a box and it runs great compared to the old points.
If its any consolation your car is looking too nice to be giving you trouble.

[DWC]

Thank everyone, I appreciate the compliments.

F'in mine-
No offense taken. I welcome any ideas to help troubleshoot.
I have a 2 pc rear main.
I installed a brand new externally balanced harmonic balancer the end of last year while troubleshooting. No change in vibration.
I verified the motor mounts are correct a few months ago.
The engine came with a flexplate and I installed a new flywheel. Both external balance. I think the flywheel/clutch could be the culprit.
The thow-out bearing came with the McCleod clutch and it's spec'd for my combo.
Clutch pedal/adjustment was verified when I installed the new trans.
Reciprocating assembly needs to be re-balanced- I think this is it. I think the original rotating assembly was balanced with the flexplate and the new flywheel/clutch is not quite balanced to match. I plan to pull the engine in the winter and have a shop install a new, internally balanced, rotating assembly.
Thanks for the run-on tips and the compliment!

Daniel

[Musclerodz]

Any possibility that the vibration might be detonation?

[DWC]

Mike- I suppose it could be. Any tips on how I can rule that out? Here's a quick rundown on what I'm running.

93 octane gas
14.25 AFR at idle
15*/36* timing
180* thermostat (avg 190* driving)
13hg vacuum at 1500rpm
Aluminum radiator
New Holley 4779 carb (750 DP)
New MSD Street Fire ignition
New MSD billet distributor 85551
New MSD Blaster SS coil
New Taylor plug wires
New spark plugs
Aluminum heads- 64cc/210cc
TDC and firing order verified multiple times
Dynamic compression ratio is estimated to be about 9.5:1

Thanks,

Daniel

[F'in mine]

Daniel, you mentioned its a 2 pcs. rear main seal, if its a aftermarket crank then its probably internally balanced. It could have a 400 crank with spacer bearings for external balance.
Any chance you might know this or could ask from whoever you got the engine from about the internals. Do you have a pic of the crank flange?
As inexpensive 60 buck option to try an internal balancer?

Do you know the cam specs and what are the plugs like?