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Technical Thoughts on decreasing idle vibration?

Discussion in 'The Hokey Ass Message Board' started by strangepanel, May 8, 2015.

  1. Not necessarily so Rusty,,,some time witness an out of balance tire..it will get better at higher speed..same is true with a simple clothes washing machine on "spin cycle" when its all said and done,,my bet is still on engine unbalance..original poster just want to find a solution that suits his thinking,,or pocketbook
     
  2. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,992

    2OLD2FAST
    Member
    from illinois

    After picking our collective minds & us trying to help......" I'm going to take it to a guy ".....checkbook 'rodder ..
    dave
     
  3. I don't know what your motor is or its build but it sounds to me like it is idling too slow. If that is where it is idling in park where does it idle in gear?

    I got to ask is that just the way that it was when you got it? Have you tried tuning it different? Have you tried hooking a different tach up to it to see if it is actually idling where you think it is? The reason I am asking is that number one it sounds like it is idling too slow and number two it maybe just needs to be properly tuned. unless it is a full on race motor it should do way better then what it is now.
     
    X38 likes this.
  4. tommyd
    Joined: Dec 10, 2010
    Posts: 11,999

    tommyd
    Member
    from South Indy

    If its shaking apart I would look real hard at the balancer deal. 50oz and 28 oz. Hit a Mustang forum and chat with them.
     
  5. tommyd
    Joined: Dec 10, 2010
    Posts: 11,999

    tommyd
    Member
    from South Indy

    That is a Jegs Blueprint engine. A 347 cost about the same as a 302 from them. May be why it sounds so nasty. I would also think that it would have come with the correct balancer as a 347. As a 302? who knows?
     
  6. tommyd
    Joined: Dec 10, 2010
    Posts: 11,999

    tommyd
    Member
    from South Indy

    A quick trip to the Jegs site says nothing about including a balancer. That's where I'd start.
     
  7. jetnow1
    Joined: Jan 30, 2008
    Posts: 2,194

    jetnow1
    ALLIANCE MEMBER
    from CT
    1. A-D Truckers

    Seems like if you just changed the trans it would have been the time to address the torque converter.
     
  8. Who said I didn't? His advise was that motor mounts wouldn't do much, but his assistant seemed to think they might. So it was somewhat split. It's a 351W bored out to a 408. Cam specifications are: .510/.512 lift, 224/230 duration @.050 with 110* lobe separation angle. I've had a couple of options on cams recommended from Comp Cams. Which brings me to perhaps another question. Just how much power will I loose switching to a milder cam? One other complication, I've been told is that the engine has a 10:1 compression. Which is about as high as you want to go on a 351W, so a cam that is too mild may over pressure things at idle. Someone also asked about firing sequence. 1 3 7 2 6 5 4 8. She's in the order that she is supposed to be.
     
    Last edited: May 9, 2015
  9. And it is exactly these differing opinions that keep me looking at all of the options. The cam guys thought it was the cam, but then they sell cams.

    I still need to catch up on all of the comments. Been a busy weekend. I do appreciate all of the comments. I'm learning a lot. This is my first and somewhat unintentional hot rod.
     
  10. I did have that changed, but just went with a mild one of 2500 rpm. I had the idle at around 1000 once and it was still very hard to hold back while in drive. I live in the city, so I have about 30-40 minutes of stop and go traffic before I hit the highway. I didn't find that practical.
     
  11. stimpy
    Joined: Apr 16, 2006
    Posts: 3,546

    stimpy

    the convertor is still too tight if you cannot hold it back at 1000 rpm idle . if you the dyno sheet that came with the motor you will see the max torque figure , you shoot for 1000 rpm under that for the convertor stall speed and use a proven convertor , I have see so called 2200 -2500 convertors that were loose stockers for a different application (5-10 ton truck ) and flashed 300 higher than stock ( which is apx 1500 ) . if you have low power on the power brakes you might have to add a vac can or aux vacuum pump ( best bet ) to help the power brakes ..
     
  12. That is true, but that's because I don't have a lift and a cam or engine mount change is beyond my meager capabilities. Maybe one day I'll get there. As to pocketbook. That's somewhat true. I'm just trying to avoid the endless cycle of doing some pretty expensive modifications and ending up not fixing the problem. I guess my biggest worry is that I do change the cam (which I think is probably the most expensive option) and the problem is still there. I admit I'm going to the guys with more experience than me to try and avoid making a mistake that more experienced would have had me avoid. I greatly appreciate all of the insights!
     
  13. I have a vac can, but now that you mention it I'm going to look into an aux vacuum pump. That has to help a little more.

    There has been a bit of a discussion about tuning and raising the idle rpm. I always thought you wanted to lower the rpms as much as possible to when it still ran well. Something else to think about that I wouldn't have normally jumped to.
     
  14. ROADSTER1927
    Joined: Feb 14, 2009
    Posts: 3,283

    ROADSTER1927
    Member

    Your engine doe's not sound to me like it runs good at your idle speed and it has to be worse in gear. It sounds like it needs to idle faster and you need a looser converter for sure. You also are going to need some help in the vacuum department for your brakes. Good luck on your truck, Gary:)
     
  15. A 110 LSA is affecting your vacuum at idle. The sweet spot to run vacuum for brakes is around 112-118 which is why a vacuum canister was recommended. The engine is out of tune. It's stumbling in a cyclical manner at idle/misfiring. A proper tuning would fix it. The lift and duration suggests running an idle speed at around 1000rpm, it's a breather and your choking it at such a low idle which would load up the cylinders, foul plugs, and generally be too rich. A stall convertor for that engine would be better suited at around 3000rpm, which will affect mileage, but will let the engine breathe a little better in the lower register. JM2$.
     
  16. seb fontana
    Joined: Sep 1, 2005
    Posts: 9,113

    seb fontana
    Member
    from ct

    First can't bore a 351 to 408, need stroker crank...Cam is really not that much for a 357 cube if its just bored .030, even at .060 its only 364 or so and even with a stroker and at 408 cube the cam is pretty small.... Point is that if it runs smooth at higher rpm its probably the tune at idle, 750-800 rpm should not be a problem and vacuum should be in the 12-14 range at least...As an example I have a 292 [289+ .030] with 242° at .510 cam with maybe 10:1 compression and it idles at 1100 rpm with 5" vacuum..Yes it lopes and shakes some but doesn't vibrate stuff loose...Point is I have way less cubes and way more cam and have no vibration issues...Something wrong with idle tune as previously stated posts....
     
  17. Relic Stew
    Joined: Apr 17, 2005
    Posts: 1,237

    Relic Stew
    Member
    from Wisconsin

    Some stroker cranks use the 50 oz-in balance factor, even though it's for a 351W. Could also be neutral or the standard 28 oz-in. Check the specs for the crank you have, and make sure the damper and flexplate match the crank balance factor.
     
  18. Thank you for your response. Sorry, me being a little too loose with my terminology. She's bored .04 over and has a stroker crank, SCAT crank 9-351-400-6000-2100W. 28 oz flywheel, according to the engine builder. So displacement is 408. I'd have to add a aux vacuum pump I guess, but this is an interesting proposition about just pushing the idle up to 1050 rpms or so. I'd have to switch to a higher torque converter, but it may solve the issue. I agree she sort of 'wumps' a little at this idle speed. She doesn't really move down much in terms of rpm when I put her in gear.
     
    Last edited: May 10, 2015
  19. Rusty O'Toole
    Joined: Sep 17, 2006
    Posts: 9,756

    Rusty O'Toole
    Member

    A milder cam should increase power at lower RPMS and decrease it at higher RPMs. In other words you trade a smooth idle and more power in the 0 - 60 range for less power above 90 MPH.
     
    strangepanel likes this.
  20. I also prefer the stock style side mounts, and in almost all cases I use a solid Moroso saddle on the drivers side mount (the Tension side), and a stock rubber saddle mount on the other side (the side under compression).

    As far as the miss, it could come and go (or just get covered up) by higher rpm if it was due to a weak spark.

    Posted using the Full Custom H.A.M.B. App!
     
  21. I can't say I'm doing the work myself, but I've found someone to start trying to deal with this vibration issue. I'll probably put in a milder cam (considering switching to a full roller setup) and trying to find a knock that turned up. Current thought is the knock may have been caused by a bad wrist pin. Gave a noise that sounded like piston slap. We'll see how it goes, but for anyone that has been following my story you can see that it is definitely turning into a major job.
     

    Attached Files:

  22. When do you hear the knock? On start up, at idle, under acceleration? Really loud, or kind of quite. I'm not there to hear it, but if you pull each plug wire off individually, it "should" go away, identifying which cylinder has the problem. If it's piston slap, it'll probably run for years. My Dually has it, and a noted big block expert told to just ignore it! It's been running for years with no adverse effects so far. Mostly, a matter of personal preference, I suppose. My coupe started rattling on startup this month (the 5.7 Hemi's are pretty notorious about it), and I changed the oil and filter immediately. New, genuine Mopar filter (they have an internal anti drain back valve in them), and presto, noise gone! Hope yours is something simple as well.

    Posted using the Full Custom H.A.M.B. App!
     
    Last edited: Jul 14, 2015
  23. Hello Blownfuel,

    the knock was constant, from idle to speed. I guess I'd place the sound as average. Definitely clearly audible. I changed the oil and the spark plugs and the filter. No real change, still knocking away. I also somewhat felt like there was a slight decrease in power, but I may have been imagining that. Maybe I could have continue to run it, but the guys in the area that heard it recommended I have it fixed. No metal in the oil, so at least that is one less concern. Engine is out and on a stand. It should be torn down this week.

    Now the other question. while it is all apart do I switch to a roller cam or stick with my flat tappet style setup? I want to get the idle smoothed, which is where this all started. Thanks for the good wishes!
     
  24. I agree, but it is making the car difficult to drive at the moment. It almost sounds like it has real tight valve lash as well as the ungodly knock.
     
  25. finn
    Joined: Jan 25, 2006
    Posts: 1,438

    finn
    Member

    Hard mounts in a street driven car are half-assed cobble jobs.

    The auto makers have gone beyond rubber to hydraulic and electronics to reduce nvh transmission to the chassis, and they are starting with input from powerplants that are orders of magnitude smoother than our crude hot rod engines.

    My 36 Ford / sbc pickup was assembled by who knows who with crap aftermarket solid engine mounts and a crude aftermarket poly trans mount. First thing I did was to replace the garbage solid engine mounts with proper rubber mounts. Major improvement.

    Replacing the trans mount is on the bucket list.
     
  26. Hello Finn,

    Those are definitely on the list. Seems I need to deal with this first:
    20150715_121713.jpg 20150715_123606.jpg

    Detonation damage?
     
  27. At least you found what that horrid noise was.... detonation? How did the plug look?
     
  28. pitman
    Joined: May 14, 2006
    Posts: 5,148

    pitman

    Great discussion on street issues. The 301 Chev's of old, were tightwinding track motors. (somewhat similar in terms of peak output builds)
    If you want to enjoy the street driving, I'd recommend the roller and (in your case) milder cam.
    Mid-range torque is real plus, rather than going to the moon rpm-wise.
     
  29. 2OLD2FAST
    Joined: Feb 3, 2010
    Posts: 5,992

    2OLD2FAST
    Member
    from illinois

    Either detonation or too tight ring end gaps , what a bummer !!
    dave
     
  30. indyjps
    Joined: Feb 21, 2007
    Posts: 5,393

    indyjps
    Member

    Throw a matching piston in the hole and move on.

    That cam power band is up to about 6500 or more. Needs a 3000 to 3500 stall and 4.10 gear. No reason putting power brakes on it.
    Unless you race regularly, I'd suggest a smaller cam, it will work with your converter, will be better to drive - much more midrange power.

    Ford guys can give you better advice than me on a 347 cam spec, Hydraulic roller or flat tappet. You can make plenty of power with flat tappet. You should be shooting for 470-490 lift and lots less duration, that will be the range that works with your converter.

    At that lift, not a lot of reason for a roller unless you just want to spend more. There's some reduced friction advantage, etc, can you say the engine is so dialed in and perfectly machined that you'll notice the incremental friction reduction gain.

    What rear gear ratio are you running. If you don't know, mark the driveshaft, and tire, spin them and count the revolutions, it will get a close approximation.
     

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