DWC's 1968 Camaro project

[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?

[DWC]

Simon- It had an external balancer and flexplate on it when I bought it. I was able to watch it run, on a stand, before I bought it. Only thing I changed from it running on the stand was an external balance flywheel. I've since installed a new external balancer during my troubleshooting as well.

This is the best picture I have of the crank flange. The crank flange is cast with a counterweight on it.

Here is my cam:
https://www.summitracing.com/parts/lun-60105

Here are the #3 and #4 cylinder plugs from last week. BUT, this was just after having the engine warm up at idle. I haven't done a proper shut down after WOT plug reading.

Daniel

[F'in mine]

Daniel, just throwing out all possibilities. If you're able to check with the guys you bought the engine from, try to see if you can find out the specific crank they used. I realize it had external components but just in case the wrong parts went on.
You purchased a new flywheel, is it the one with the weight pad that's bolted on? I realize this is a alot of bs but maybe take the weight off and see what happens.

The plugs look okay, the cam specs seem to be a bit high for the compression you're running. I'm wondering if that has an effect on the run cause Lunati says it requires a minimum of 10.5 compression.

[DWC]

Simon- I appreciate ANY ideas, really. At this point, I've resigned myself to pulling the engine this winter. So, I don't mind chasing any possibilities up until that point.

After I bought the engine, I removed the oil pan to verify it was a 383 stroker and see what the cylinders looked like, etc. I've attached the photos I took while the pan was off (sorry for the low quality). The number cast into the crank counterweight is hard to read. After a lot of research time online, I *believe* the crank is made by CAT (Cal Auto Transpeed). A lower quality, chinese import, that subsequently is out of business from what I can tell.

The guy I bought it from said PAR Racing in Spartanburg, SC assembled the engine for him. I'm waiting for a return phone call from them.

Yes, the flywheel I bought has removable weights. I've tried running without a weight and it was clearly not happy. I've also tried different amounts of weight trying to "sneak up" on the correct balance, but no luck.

As to the compression ratio, I used online calculators and the specs I was told to calculate the ratio. With that cam's overlap, the dynamic ratio estimate was about 9.5:1, with the static ratio about 10.5:1.

[ScotI]

Originally Posted by DWC

Simon- I appreciate ANY ideas, really. At this point, I've resigned myself to pulling the engine this winter. So, I don't mind chasing any possibilities up until that point.

After I bought the engine, I removed the oil pan to verify it was a 383 stroker and see what the cylinders looked like, etc. I've attached the photos I took while the pan was off (sorry for the low quality). The number cast into the crank counterweight is hard to read. After a lot of research time online, I *believe* the crank is made by CAT (Cal Auto Transpeed). A lower quality, chinese import, that subsequently is out of business from what I can tell.

The guy I bought it from said PAR Racing in Spartanburg, SC assembled the engine for him. I'm waiting for a return phone call from them.

Yes, the flywheel I bought has removable weights. I've tried running without a weight and it was clearly not happy. I've also tried different amounts of weight trying to "sneak up" on the correct balance, but no luck.

As to the compression ratio, I used online calculators and the specs I was told to calculate the ratio. With that cam's overlap, the dynamic ratio estimate was about 9.5:1, with the static ratio about 10.5:1.

Here are the details-
383 stroker engine I purchased in person and we ran it on an engine stand to verify it ran good and all looked/sounded fine
Aluminum 64cc heads
Lunati hydraulic flat tappet cam- https://www.summitracing.com/parts/lun-60105
Hyper pistons
5.7" rods
Aluminum roller rockers
Edlebrock Performer 2701 intake manifold (new)
Windage tray
7 qt oil pan
Full length headers
Summit Racing external balanced harmonic balancer (called Summit to verify this)
Energy Suspension poly motor and trans mounts (new)
93 octane fuel

The calcs I used indicated 10.51:1 static/8.67:1 dynamic @ .020 deck height (or 10.89:1/8.98 w/a .005 deck) using typical generic 383 numbers & that Lunati cam. Seeing your cranking compression >200psi would suggest your in the ball park. I've been advised exceeding the 200# number on pump gas is pushing things & for worry free operation things needed to be optimized for every different combo.

Have you tried just backing off the timing to see what happens w/the 'run-on' scenario?

[Musclerodz]

Originally Posted by DWC

Simon- It had an external balancer and flexplate on it when I bought it. I was able to watch it run, on a stand, before I bought it. Only thing I changed from it running on the stand was an external balance flywheel. I've since installed a new external balancer during my troubleshooting as well.

This is the best picture I have of the crank flange. The crank flange is cast with a counterweight on it.

Here is my cam:
https://www.summitracing.com/parts/lun-60105

Here are the #3 and #4 cylinder plugs from last week. BUT, this was just after having the engine warm up at idle. I haven't done a proper shut down after WOT plug reading.

Daniel

that plug does not look happy. have you verified which advance springs are installed? Are you using a non-digital timing light to time it?

[DWC]

ScotI- No, I haven’t had the timing lower than 36* total. I’ll decrease it 1 or 2 degrees and see what i get.

Mike- the 21* bushing is in it. I’m using a basic, non-digital, Craftsman timing light.

Daniel

[DWC]

I backed the timing down to 13*/34* and went for a short drive this weekend. The vibration did not change at all, still there.

Interestingly, the engine run-on still occurred as well. It *may* have been a bit less run-on then previously, but not a significant change.

Daniel

[ScotI]

Originally Posted by DWC

I backed the timing down to 13*/34* and went for a short drive this weekend. The vibration did not change at all, still there.

Interestingly, the engine run-on still occurred as well. It *may* have been a bit less run-on then previously, but not a significant change.

Daniel

Try 32° total. This would be strictly for the run-on issue as I think there is something different causing your vibration.

If still experiencing run-on @ 32°, I would seek out some higher octane rated gas & utilize it to eliminate octane as a possible cause.