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Old 01-11-2013, 03:32 PM   #1 (permalink)
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Default 351C Ping Question

Howdy,

Other than Timing or Fuel .. Any other reason a 351C may Ping?

Seems right around 2500 rpm when a load is pushed.. I get a smal ping..

Messed w/timing and types of Fuel.. Used to run 106 octane mixed with 93 before my rebuild but should not have to now.

Been using Sunoco,Mobil,etc 93 pump fuel. Timing is / Has been between 8-12 Initial. About 36 all in.

Would my Carb add to this issue? Quick Fuel 680VS

Making me crazy

thx for any insight.

PJM1
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Old 01-11-2013, 03:36 PM   #2 (permalink)
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Hot spots on the piston? Poor flame front? Open or closed heads? What is the compression ratio?
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Old 01-11-2013, 03:44 PM   #3 (permalink)
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The 351 Cleveland is more resistant to pinging than wedge-head engines. So, something is likely very wrong.

Again, what's the static compression ratio?

Is it possible you've just got a lot of carbon in the combustion chambers? Or, are you saying in your post that it's a recent rebuild?

If it's not a recent rebuild, you could run some Chevron Fuel System cleaner. Use two bottles in a full tank. (Another option would be SeaFoam. Everything else I tried is a waste of time and money.)

Your carb would have to be running pretty lean for it to cause pinging. But it is possible. Check the size of the jets you're running. (Now that I think about it, that Quick Fuel carb is just no good. Send it to me and I'll throw it away for you. )
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Old 01-11-2013, 04:13 PM   #4 (permalink)
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That Hurt.. What's wrong w/the Quick Fuel? Will Not run an Edelbrock..But thats another can of worms to open.

Demon or go back to a Holley?

Engine was rebuilt by a VERY rep. Builder. So that is a non-issue. Comp. is about 9.5/10 to 1.
Rebuild was very standard 30 over. Cam is pretty mild. Not much over what stock would have been. was not looking for a Street Beast.. Just a nice driver. Cast Iron Intake.

So my options are?? May dump 10 gals of 106 back in and see if this does it. If is does.. Then what is this telling me?

Change Carb? give me an example of what you believe should be used.

Appreciate your thoughts.

thx
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Old 01-11-2013, 08:49 PM   #5 (permalink)
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How about trying something easy first? Disconnect the vacuum advance and see if you still get the ping. Then report back.

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Old 01-11-2013, 09:05 PM   #6 (permalink)
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Cam is too mild for compression ratio. (high cylinder pressure) Cam is advanced as well as mild. Timing curve is coming in too quick for the build.
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Old 01-12-2013, 11:12 AM   #7 (permalink)
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I'm confused w/your Cam response.. This compression is lower than stock. The new Cam is a little Hotter. Thinking it could now handle the build..

Am I missing something here? I agree w/your timing concern.. I believe this is where I need to start. Believe Crank has a rebuild kit.. Cheap.. so really not a wate of $$ to try..

Thank you
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Old 01-12-2013, 01:18 PM   #8 (permalink)
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You don't mention any specs other than 9.5-10 cr. A short cam (very low duration @ .050, tight lsa, early intake centerline, fast ramp, or a combo of..) with that cr can cause very high cylinder pressures/detonation. Have you checked cranking compresssion vs "build" spec? Might very well be simply a timing curve issue but there's a reason you'll be having to recurve it from the former build. And that would be higher low rpm cylinder pressure than it had before.
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Old 01-12-2013, 01:23 PM   #9 (permalink)
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Quote:
Originally Posted by rickgto View Post
Timing curve is coming in too quick for the build.
That is my guess.
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Old 01-12-2013, 01:35 PM   #10 (permalink)
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Thx for responding GTO.& Others.. Here are my Cam Specs.. Comp Cams FC270H-10
Cam Style: Hydraulic flat tappet

Basic Operating RPM Range: 1,800-5,800

Intake Duration at 050 inch Lift: 224

Exhaust Duration at 050 inch Lift: 224

Duration at 050 inch Lift: 224 int./224 exh.

Advertised Intake Duration: 270

Advertised Exhaust Duration: 270

Advertised Duration: 270 int./270 exh.

Intake Valve Lift with Factory Rocker Arm Ratio: 0.519 in.

Exhaust Valve Lift with Factory Rocker Arm Ratio: 0.519 in.

Valve Lift with Factory Rocker Arm Ratio: 0.519 int./0.519 exh.

Lobe Separation (degrees): 110

Grind Number: FC 270H-10
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Old 01-12-2013, 02:58 PM   #11 (permalink)
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Does it ping just on light throttle? ie. If you stand on it does the ping go away or get worse?

If just on light throttle, too much vacuum advance at that rpm. If worse the harder you press, too much mechanical advance at that rpm.
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Old 01-14-2013, 12:11 PM   #12 (permalink)
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Quote:
Originally Posted by pjmach1 View Post
That Hurt.. What's wrong w/the Quick Fuel? Will Not run an Edelbrock..But thats another can of worms to open.
Oh, sorry. You misunderstood me here. The Quick Fuel is a GREAT carb. I was saying that I'd like to have one myself, so, why don't you send me yours?

You say your compression ratio is lower than stock. So, what is it? Perhaps I missed it in one of your posts?

What rickgto is saying is that a mild cam will create high compression at lower RPMs, which can lead to pinging, while a more aggressive cam won't develop high compression until the engine winds up a bit. This is referred to as dynamic compression, vs. static compression.

EDIT: OK, I see you listed "9.5-10:1" for compression. This should run fine on pump gas. I suspect Bartl is correct about your vaccuum advance or mechanical advance. What type of distributor are you running? It may need a re-curve.

Last edited by Klutch; 01-14-2013 at 12:18 PM.
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Old 01-19-2013, 01:39 PM   #13 (permalink)
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Thx Klutch.. For the $$ I spent on that Carb.. It better work.. Also Pressure Reg and Gauge. Have the PSI set at 6 to 6.5. I did order the Crane Dist. Recurv kit. Having the shop that did my rebuild do the upgrade.. I just don't have the patience for it right now. And they offered.. I was worried that there was an issue w/the rebuild.. But they ran a compression and leak down. ALL cyl. were close to 200 with no leak.
They are suspecting Vacuum. But Vac Gauge reads 15-18. So either this Carb or Timing.. We'll see and I'll let you know. Thx for all the responses
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