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Engine popping at high RPM.(5500-6400) Found the problem
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Ballaholic29414
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PostPosted: Mon Jul 20, 2009 12:54 pm    Post subject: Engine popping at high RPM.(5500-6400) Found the problem Reply with quote

There is a popping sound that I can hear in the 5500-6400rpm(I shift at 6400 as instructed by the dyno tuner). It isnt a loud pop and it doesnt pop everytime I go down the track, just every now and then maybe 1 out of every 3 passes, but when it doesnt pop it doesnt go any faster or slower, but when I used to turn it 7000rpm(before I actually found out my motor peaks at 6400rpm) it used to pop trying to get there also. When I shift into high gear and the rpm drops it stops and when im going through the traps its popping again. Nobody can hear the popping except for me (or maybe people on the big end). It almost sounds like a skip.

Im thinking its either (1):I need to do another valve adjustment (valves too tight) because I go down the strip at 170-180 degreez, but I adjusted my valves at about 120 degreez. (2):bad spark plug (only 15 passes on plugs), (3): worn spark plug wires 1.5 years old with 20-25 passes on em).

Any suggestions

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Last edited by Ballaholic29414 on Tue Jul 21, 2009 4:43 pm; edited 1 time in total
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Paul P
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1971 Chevrolet Chevelle

PostPosted: Mon Jul 20, 2009 3:35 pm    Post subject: Reply with quote

2 things if it is not tune up or lash adjustment related.

Weak valve springs,

or over rich fuel mixture.

My money is on the springs.

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Ballaholic29414
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PostPosted: Mon Jul 20, 2009 3:51 pm    Post subject: Reply with quote

How would I know if it is the valve springs?
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squeeezer
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1991 Chevrolet Camaro

PostPosted: Mon Jul 20, 2009 4:21 pm    Post subject: Reply with quote

Paul P wrote:
2 things if it is not tune up or lash adjustment related.

Weak valve springs,

or over rich fuel mixture.

My money is on the springs.






could be lean also
(if popping = laboring)

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squeeezer
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1991 Chevrolet Camaro

PostPosted: Mon Jul 20, 2009 4:22 pm    Post subject: Reply with quote

Ballaholic29414 wrote:
How would I know if it is the valve springs?






beg borrow or steal a valve spring pressure checking tool

some are better than others, but all are better than none Cool

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lun40119
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1967 Chevrolet Chevelle

PostPosted: Mon Jul 20, 2009 6:17 pm    Post subject: Reply with quote

I think some valvetrain details are in order here..........springs, pressures, valves, sizes, pushrods, diameter and wall thickness, lifters, HR, SR, flat tappet. All the ideas above are great, but how would one give a guess without knowing any of this. Ignition would get worse as the load increases, valvetrain would get worse as rpm increases, and well fuel can be kind of funny. Fill in the blanks please.............
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Ballaholic29414
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PostPosted: Mon Jul 20, 2009 7:44 pm    Post subject: Reply with quote

I bought this motor a year ago with only 50 passes on it since it was freshened (I pulled the heads off to check if it was really freshened and it was obvious that it was). I put about 20 - 25 on it myself. 2.250in/1.880exh valves. Dart Pro 1 heads. My valve train knowledge about this motor is limited. The fuel I used was in the fuel cell for 2 weeks. 116 Octane
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Big Dave
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PostPosted: Mon Jul 20, 2009 8:57 pm    Post subject: Reply with quote

Personally I like stiff springs and stiffer push rods. You will not be able to control the valves if your push rods are shimmying around deflecting. I consider a 7/16th inch diameter chromemoly pushrod a good start (you will have to change out the valve guides as well).

Though BBC valves are too small for the size of the motor they are still heavy and controlling that mass at speed is difficult. I also like to run an old fashioned rev kit as well to keep the lifters on the lobe letting the spring use it's power to control the valve. Anything you can do to lighten the valve train helps as well, but the added weight of the push rods are much more desirable than having them bend.

Big Dave


Last edited by Big Dave on Mon Jul 20, 2009 8:57 pm; edited 1 time in total
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clay
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PostPosted: Mon Jul 20, 2009 8:57 pm    Post subject: Reply with quote

Doubt it's a plug, but they are cheap to replace if they've been in there a while. I've used the same wires for about 7 years now and they're still fine. Make sure that none of the boots have gotten hot on the headers, etc. One quick way to check is to look at night (pitch black best) with the engine running. Stray sparks show up better. You can also take a spray bottle with water and spray the wires while it's running to see if you pick up a skip. I would definately get a spring tester as that's where my thought's are also. Even if it was freshened up, that may have consisted of just rings and bearings and not necessairly springs. Clay
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lun40119
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1967 Chevrolet Chevelle

PostPosted: Mon Jul 20, 2009 10:56 pm    Post subject: Reply with quote

What size motor, cam, cylinder head. You need to be very specific to get anything close to an accurate response. Without that, all one can do is guess. Like has been mentioned, ignition, springs, fuel. It would be nice to try and narrow it down for you. Is it a solid roller, hyd roller, flat tappet??????
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Ballaholic29414
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PostPosted: Tue Jul 21, 2009 1:13 am    Post subject: Reply with quote

496bbc, Solid Roller cam .697, Dart Pro1 325cc (heads were bought bare),2.25intake valve and 1.88 exhaust valve. He used 1.8 roller rockers (he said to raise the lift), dual spring valve springs, 4.25 stroke,6.385 rods, 15.1 compression, Dart intake, 1050 holley dominator, MSD pro bullet distributor.

Champion c63cx spark plug
Naturally Aspirated
Moroso Ultra 40 spark plug wires
I run Sonoco C16 race fuel

Hope I gave enough information.


Engine built by Performance Racing Engines in Morehead City, North Carolina.

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Ballaholic29414
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PostPosted: Tue Jul 21, 2009 4:47 pm    Post subject: Issue found Reply with quote

After we installed the heads after checking to make sure the engine was freshend earlier this year we didnt install the exhaust rocker on cylinder # 2 correctly so it wasnt opening much at all.
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lun40119
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1967 Chevrolet Chevelle

PostPosted: Tue Jul 21, 2009 5:24 pm    Post subject: Reply with quote

What does that mean............
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af2
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PostPosted: Tue Jul 21, 2009 5:54 pm    Post subject: Reply with quote

lun40119 wrote:
What does that mean............



Confused That means confused.
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Ballaholic29414
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PostPosted: Tue Jul 21, 2009 6:23 pm    Post subject: Reply with quote

lun40119 wrote:
What does that mean............


???

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