I have an engine shake that is driving me crazy and I'm not sure what the cause is. Maybe some of you can give me an education!! New SBC 415, approximately 2k miles. Checked all potential vacuum sources for leaks (Carb, brake booster, trans modulator, intake) with no indication of such. Running a Comp Cams XE274, 750 Speed Demon, RPM Air Gap w/ 1.5 inch Wilson Manifold 4 hole spacer, DART 215cc Iron Eagle heads, 10.1-1 Speed Pro pistons, Comp Magnum roller rockers, Pertronix HEI w/ MSD 6AL ignition box, MSD 8.5 ignition wires, TH-350 w/B&M Holeshot 2400 stall. Timing checked, plugs good, WTF??? All of the parts on the engine were brand new. Is it because it's a "stroked" 400?? Any help will be greatly appreciated.......

The first two things that come to mind...and I've had them both happen to me are, 1. Check your harmonic balancer to make sure it hasn't slipped. If you're running a stock balancer with the rubber sandwiched between the two metal rings, it could slip, especially if it's older. 2. Check your flywheel to make sure it's tightened up, and there are no cracks in it. I've had both happen, and would only get a shaking in the motor at certain rpm's. I'd imagine it was happening at all rpm's, but wouldn't feel it until I got up there in the higher range. Good luck.

What about shot out motor mounts, my 350 rocked hard, come to find my motor mounts were barely hanging on :eek:

Too lean at idle...some people like Demon carbs, personally I don't and don't know anyone that does.

just a suggestion if ur car has been settin for a length of time over a month or so with out bein started u may have a little moister down in ur motor my motor was like that for about and hour or so but the engine had been settin for about 4 months. just a sugestion ;)

Thanks for all the replies fellows. It's not the carb. I replaced it with a new Holley Street Avenger with the same result. The harmonic balancer is a new Prostreet balancer. It hasn't slipped or moved. Flywheel is new as well. No noticable issues with that. The motor mounts were replaced with OEM mounts, so I didn't consider them as the culprit. I don't think it;s moisture in the fuel. I have changed the fuel several times over and drive it enough to keep the fuel fresh. Any other ideas or something I'm still missing??

At what RPM is the engine shaking? Is that the only thing that's wrong with it? Have you noticed a loss in power in any RPM? Any odd noises coming from anywhere?

Have you RE checked the timing? With/without the vacuum advance (if it's being used). Ported/manifold vacuum? What's your initial/total timing? Does the engine start easily?

Was the rotating assembly balanced at a machine shop before you installed it? Are the balancer and flexplate external balanced? Try disconnecting your torque converter and see if it still shakes.

Just some suggestions.

Had a brand new balancer(500 miles) slip on my 406
It took me a long time to figure that one out!
almost felt like a miss but was shaking

Did you have your flywheel,PP,clutch balanced?

Again, I want to thank you all for the replies. Casey, the engine was balanced within 1/2 gram with the flywheel and balancer attached. Starts easy and only shakes at idle, around 800-1100 RPM, including while in gear. No performance issues throughout the RPM range. No odd noises either. I did ask the builder and he claims it's because of the Comp XE274 cam I'm running. I initially thought that might be the case, but wasn't convinced. Anyone running this cam with the same issue??

I run the xe274 on my 454, I do get my engine not firing properly due to improper fuel/air/exhaust mixture at idle to around 1000-1100 rpm, but once it gets aove that she starts purring like a kitten, and the engine is sitting pretty. This is because the valves are now opening and closing the way they should for that cam, at idle you will get exhaust mixed in with your fuel air mixture and it can make the engine shake. I would call it a twitch since it's coming from certain cylinders. It's just got "RUMPH"