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Old 10-16-2017, 12:14 AM   #1
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Question Odd Shudder From Mid-Full Throttle

Hey guys! I'm new to this forum, and recently after taking my car out to the strip Oct.13th, this weird shudder was noticeable.

My car is a '77 Nova, 305SBC with headers, true dual 2.5" exhaust with glasspacks, Holley 650CFM 4-barrel on a dual plane 210?CFM manifold. Also has new high output dizzy. The transmission is the forsaken THM250 (non-lock-up) but still shifts firm. Stock heads, internals, cam etc.

The Scenario: Drove up to Raceway Park no problems, smooth ride as always. Passed tech and went to run.
1st run: Green light to exit lane no problems.
2nd run: Green light to exit lane again, although this time I thought towards the 1000ft mark, I felt like I had solid mounts suddenly, as I could feel every power stroke through the chassis.
Problem wasn't noticed until leaving the track on the way home. In any gear from 1/2-Full throttle you can feel it again, until the gear revs out towards it'* end rpm'*.

Just to note, I pulled all the new plugs today, they looked proper so I re-gapped them and set them aside. I did a dry (no oil) hot compression test on all cylinders.
Results: 1)180. 2)170. 3)178. 4)168. 5)175. 6)165. 7)175. 185. Based off the 10% rule, for an engine over 130K miles, these are sound numbers. Timing is correct, fuel system is good, ignition based off plugs seems great. Internally the test showed nothing bent/burned from the 2 passes. Still daily-ing it and nothing is getting worse or better.
Other things to rule out: new U-joints, axle bearings are solid, differential oil replaced and sound, new balanced tires on all 4, nothing modified between the time I left my house and when I returned, just the passes.

Any and all ideas/help will be considered and appreciated! Sorry my post is long, I just want you guys to have as much detail as I can give.

-Chris
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Old 10-16-2017, 08:11 AM   #2
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I would check your engine/transmission mounts to make sure they are still intact and functioning as designed.
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Old 10-17-2017, 12:57 PM   #3
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Quote:
Originally Posted by rjolly87 View Post
I would check your engine/transmission mounts to make sure they are still intact and functioning as designed.
Thanks, ive thought that but wanted some other opinions to confirm it
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Old 10-17-2017, 11:04 PM   #4
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Thankfully it'* an easy check. Just goose the throttle while holding the brakes in both drive and reverse, and if the engine tries to climb out of the engine bay, it may be worth checking further in to.
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