I have a 355 (30 over 350), 64 cc 375 horse factory GM heads , with 10:72.1 semi dome TRW pistons , Elderbrock Performer intake with a 650 DBL pumper Holley w / modified performance main body. Have a 274/286 Comp extreme energy cam .

I am having major Ping (valve clatter) problems . I have backed the timming down to try and quiet the engine down and it helped but it hurts the performance terribly . I want to raise the timming back up where it needs to be .

The gas available today is awful !

What can I add that will cure the valve clatter problem I am having without getting too expensive ..... The intake has no EGR application so what can I do ?

 

Assuming your cam is installed at 106* ICLA, your dynamic compression ratio is just entirely too high for pump gas. DCR isn't the only concern when engineereing a good street engine, but failing to take it into account gets a lot of people in to this kind of trouble. Here's a link to a good article on DCR, which includes a comprehensive DCR calculator download. I'm afraid there's probably no cheep way out, as simply retarding the timing won't come close to solving this one, and increasing duration will only lead to very bad manners for a street mill. You need to reduce your CR.

http://www.empirenet.com/pkelley2/DynamicCR.html

btw, that carb is too small for high perf.

 

Carb is too small even though I installed the modified performance main body to it ?

And also , You dont think that Octane Boost additive will help ?

Thanks for the info !

 

I'm not familiar with what your mod has done to cfm capacity, but with a high perf 350 SB, you can safely go with a 750 for improved top end. If you've got a stick, the 750 DP is fine. With an auto, the vac 2nd's would be more likely to work out. 650 cfm will do the job, and probably provide easier tuning and a touch more bottom end, but will limit high rpm performance when it becomes a restriction to be overcome. Depends on what your priorities are as to which is really best.

Bear in mind that your DCR is significantly higher than practical, and though a dose of 104+ would help, I'm not sure it will be nearly enough. But, it's sure cheaper than tearing into your engine, so I'd definitely give it a shot. However, I'd keep an eye out for signs of detonation by frequently checking the plugs even if you don't hear it rattle. Oh, and don't ever spill a drop on your paint, unless you're ready to strip it off and start over.

I know this isn't exactly what you are wanting to hear, and I'm no expert, but that's my $0.02. So you're aware, you'll probably get a whole lot more advice on this issue, including those who dissagree with my prognosis, over in tech/perf. There are a few guys over there claiming to safely run as much as 11:1 on pump gas, but IMHO they'd have to be rediculously over-cammed to actually get away with it.

I failed to ask what your ignition curve was.

 

Its original , the distributor is all stock HEI

I had a buddy reccomend a water injection system , Ive never seen one and havent a clue as to the expense .

 

Ya know , what doesnt make sense to me is that 6 years ago .... I ran an identicle engine with the same heads but had 11:50.1 pop up pistons and never delt with a bit of clatter . The cam I ran wasnt quite as big but still ???????????????

Gas must really have gone to chit !

Naw , Pistons are staying put ... I spent way too much to tear back into it and downsize them .

Theres got to be something out there to fix this problem . I wonder if running colder plugs would help ?

 

Do you know what your dist. timing is? Could possibly make a significant difference in your favor should any of the following be occuring: 1) initial timing too high, 2) total advance too much, 3) total is coming in too soon, 4) vac is advancing too much. Take the time to plot it out if you aren't sure. If you haven't already, read up on Barry K's timing "sticky" in tech/perf. The original post includes links to some very good reference material on tuning.

Another item that may be effecting this engine could be insufficient quench between the head and piston. If it's not down around 0.040", could well be aggravating the situation.

And, not to be overlooked, are you running a hot thermostat or a 180*? Just trying to find something that helps out...

On gas quality, some name brands are "cheating" by running up the research octane to bring up the R+M/2 rating (for marketing) without spending the money it takes to raise motor octane (the one that counts).

Here's a great article from May 2006 Pop Hotrodding on pump gas.

http://www.popularhotrodding.com/tec...p_gas_secrets/

Hope you find a cure that suits your needs. I'm pulling for you.

 

I really dont know what the timming is sitting on to be honest .... set it by ear . All I know is that by backing it down to elliminate the spark knock effected the performance dramatically . It needs to go back up .

The quench between the head and piston , I couldnt tell you .

I was running a 195 thermostat but changed it this past weekend to a 160 . Also put a fan and fan clutch back on it today . The flex fan wasnt getting it !

Youll laugh at this one .... I had a guy today tell me to throw a few mothballs down in the gas tank .... said his dad used to do this to elliminate ping . I'm in Mississippi .... that may tell you a lot .... lol

I thank you for your assistance , the links and articles ... youve been mighty helpful !

 

1 option would be to change the heads to a larger cc like 72 that would drop your CR and you wouldnt have to touch the lower end?

I dont think any of that off the shelf octane boost is worth a crap, but you may try running like 50/50 raceing fuel with premium gas to boost the octane like a half a tank full of each??

 

Yea , I used to do that with my ole Chevy II and its 327 . Back in my Navy days , I would fill half of my tank with Avgas and then the rest with regular .... Made a great combination .

 

The moth ball thing has been around for years and years. The claim was it improved/raised the octane,something like that,I forget.
I agree,you need to lower the compression a bit. Larger chambers would be the easiest way I suppose. Dont know if putting on the thickest set of head gaskets you can get would help. I do know what the Preignition/knock that you have,will do to pistons/rings. That knock,ping you hear isnt in the engine...its dollars in your wallet knocking to get out.

 

Nope , not tearing my engine apart what so ever .... no need for this .

I'll find a alternative solution .... if its adding aircraft fuel ... so be it !

 

Short of a tear down, I 'm hearing possible solutions of: back down the timing, run a colder thermostat, higher volume water pump and or radiator, colder plugs, thicker head gaskets, higher octane fuel.

Did I get these correct and, any thing else?

Jay

 

Am I late for class ?

 

Flat tops and a .041 head gasket, other wise 1970 making a return!

 

Yea , your about correct !