421 pontiac PINGING, need help!

[1939coupe]

I have a '66 Pontiac 421 with a TH-400 in my '39 olds. The engine is original with cast iron intake and heads. I put a 185 deg thermosat in to see if the engine would run cooler and it does. On the highway or when the elec. fan is on it runs at about 195. The original thermo was a 195 deg.
unit. At what Temp should I have the fan turn ON? Right now it turns on at
200 deg But while the car is not moveing the temp gauge fluctuates between 195 and 210, and the fan cycles is that OK?

Problem:The above may be linked to the problem I have. After the engine is up to Temp. it pings under moderate acceleration. I run 92 octain fuel. If I add some octain booster it stops pinging but Id like to get away from having to buy booster all the time. The inital timing is set at 6deg btc. and the vac. can is set to add about 6-7deg more for a total of about 12deg at idle. The centrifical advance starts coming in at 1200 rpm, could this be to early?
I was told the problem could be solved if I replaced the 60's style cast iron heads with a set of Edelbrock alum heads. The resons givin where:
1-the new heads have hardened seats.
2- the Alum heads transfer heat better than the Iron heads.

Is any of what I was told TRUE ? I put a lot of blood,sweat and tears into my Olds and love driving it But I want to fix this problem before it causes ENGINE DAMAGE! I would be greatful for any help.

Thanks, Randy

[kb426]

I believe the heads won't make any difference for the reasons you listed. If you have a closed chamber head and the alum. are open chamber and reduce the compression ratio, you might gain something. I don't know how old the engine is so this is just a guess. If it is high milage and has lots of carbon buildup that could be a problem. If you don't want to retard the timing all the time, by a MSD knock sensor with the retard unit built in. The only other suggestion I'd have is to lower the compression ratio by using thick head gaskets or cutting piston domes. If you have flat tops, you're in trouble. There is a chance that the cam profile is one that causes real high cylinder pressure which could also be contributing to your problem. Might be something simple like wrong heat range of spark plugs or weak ignition. So much for my guess's.

[1939coupe]

kb426,

The engine is a 1966 Pontiac 421. The engine was built when leaded fuel was in use, but now you can't buy leaded fuel at the gas station.
So I'm running Unleaded fuel in a engine designed to use Leaded fuel, what kind of problems does that cause? And how do I fix them?
The compression Ratio on my engine is about 10.5:1.
How much power will I lose by lowering the compression ratio to say 9.5:1?
Thanks,
Randy

[enjenjo]

about 15 hp. You might call Crower, they were making some cams that were designed to bleed off some of the excess compression, just to solve this problem.

[Dave]

I believe the heads won't make any difference for the reasons you listed. If you have a closed chamber head and the alum. are open chamber and reduce the compression ratio, you might gain something. I don't know how old the engine is so this is just a guess. If it is high milage and has lots of carbon buildup that could be a problem. If you don't want to retard the timing all the time, by a MSD knock sensor with the retard unit built in. The only other suggestion I'd have is to lower the compression ratio by using thick head gaskets or cutting piston domes. If you have flat tops, you're in trouble. There is a chance that the cam profile is one that causes real high cylinder pressure which could also be contributing to your problem. Might be something simple like wrong heat range of spark plugs or weak ignition. So much for my guess's.

The head gasket thing is a good idea heres what we did on the old 427 chevys.
Buy a steel head gasket set and a composition gasket set  then coat em both real good with avaition permatex then install em and torque the heads. I ran a jet boat with 12 1/2 to one pistons with regular low lead with no pinging. The 2 gaskets knock the compression down to where it will run. Id think although its gonna be some work it will be the cheaper option to curing the pinging . I had a great engine builder in brighton Mich show me this trick years ago. The idea with the permatex it i guess to ensure good sealing with 2 gaskets. I had my 427 apart a couple of t imes and i was supprised how easy the block deck and heads cleaned up even with the aviation permatex on em.
Dave

[kb426]

If you want to go the fat gasket route, try the solid copper ones. I don't know about the availability for Pontiacs but for other engines they are available in increments up to 80 thousandths.  I use to run .090's on my blown alky racer.

[SKR8PN]

The aluminum cylinder heads WILL stop the tendency for detonation,simply because of the aluminum being a better "heat sink" than the cast iron. If I were in your boots(running unleaded in an older engine without hardened seats and higher compression)and if it fit the budget, I would consider aluminum heads and/or a different cam profile,providing the rest of the engine is in sound condition(no oil/water leaks,CLEAN inside,bearings OK, and no ridge at the top of the bores when you get the heads off)

[1939coupe]

SKR8PN,

I was also told that with Flat Top pistons(which I have in my engine) the heads would lower my Comression Ratio to 9.5:1 which I can live with.
The engine is very sound, it only has about 40,000 mi on it and runs great except for the pinging. I think if I'm going to shell out the money for a set of heads and take the engine apart I'm going to spend a little more money and get a Cam and Intake alone with the Heads from Edelbrock.

Thanks for everyones help,
Randy

[topless]

Hi, you say the pinging occurs under moderate acceleration? Well if it was my engine I would try stronger springs on the mechanical advance to allow the advance to come up later, this is easy and cheap and might just take care of your problem.  Good luck!!

[1939coupe]

Thanks, that will be the first thing I try this Spring when I get the car out of hibernation.
Randy

[Scrap Fe]

Thanks, that will be the first thing I try this Spring when I get the car out of hibernation.
Randy

Another thing, don't run the reformulated gas if you can avoid it.  That gas doesn't have a shelf life over 30 days and tends varnish and drops octane.  I spent  mega $ on my wife's fuel injection system to get it running correctly.  I have also had problems with my garden tractor.  The mechanic told us to avoid the reformulated gas which we have the past two months and no problems.  I'm fortunate in that I'm only 16 miles away from Jefferson county where they have real gas.

[HOTRODSRJ]

While I could suspect SOME timing issues....I really think that the dynamic compression ratio of these old engines is typically over 8.6 to one....which means that you will have pinging with the timing curve.  It's the cam timing moreover than anything else that builds higher cylinder pressure.  A higher duration cam would be better and could fix the problem, but do the math first.  Also, bringing the operational temperature of the engine down to 160 will help too.  

I am NOT a fan of playing with the gaskets per se.  The reason is it SOMETIMES screws up the quench which should be as close to .040 as possible. Sometimes it's okay. I don't know where your pistons are sitting in the hole.....so???  Also, It's the dynamic compression ratio that you should be looking at....not the static for solutions. Do your math and you can easily engineer your way out of this. Study how this works.

New aluminum Edelbrock heads are a great alternative.  I would say that the power will INCREASE due to the increase in VE of the improvements in heads.  Those 50/60 era iron heads flow terrible. Yes, the static compression will go down, but the increase in VE of the system will be at least 15%! Combine that with a new more efficient cam grind and I submit that you will make another 50hp!  I have done similar things to the Pontiac 400s.  

Also if you are buying octane booster and it works....your very close to the octane you need.  The octane boosters in a bottle only move your octane about 0.1 points (not 1point) and are fairly innert.  Use and google the use of Toluene or Xylene for octane boosters.  You will learn alot about octane.

[1939coupe]

Just to clarify, The Octain Booster I've been using is not the stuff you by at the Auto Parts store. I't is a Lead Additive that I buy Online at BatteryStuff.com. I use 2oz. per gallon which raises my octain from 92 to 98, a 6 point increase. It works great but it is expensive!! 12$ for 32oz.

Thanks,Randy

[Mikej]

What is total timing?  What  carb are you using?   You can limit the mechanical timing to 28 and richen up the carb alittle. This will let you run on 92 but may still ping at 210 degrees. Going to be alittle doggy.  I'm running 454+.030 and cast heads. To much compression and to hot of temps are a problem.

[Dr Flowgood]

Hello Folks.  Doug the plumber here. First time caller,  love the show.  heh.  I live around the corner from that 348 tripower guy and thought Id join the fun here.  
I agree with a lot of what hotrodsrj said. Adding thicker head gaskets to lower compression is not a great idea because it screws up the quench height . your motor will resist detonation better with  the correct quench height of about .040" than it will with a larger QH. even though the compression goes down some, it will usually make it ping worse.  Also , your motor may have the pistons -.020 or more below the deck already and may have originaly had a thin steel shim head gasket  and now has a composistion type head gasket that may be twice as thick as the factory one was (just speculating on that)    The design (shape) of the combustion chamber is probably not a real effecient design and that directly effects how much octane you need at a given compression ratio.  An example of a really effecient head would be like a sbc Vortec head that makes max power at about 32 degrees total timing and with the right combo of parts run at over 11 to one compression with 94 octane gas. compared to the Poncho head that probably wants 36 or 38 degrees total timing and want race gas at even 10 to one.
The Edelbrock heads may be better in that department and I KNOW they flow better and will make more power  but your wallet will be lighter by about 16 hundred dollars.

The valve seats being  hardened wont matter other than they will wear down(sink) faster without the lead to protect them.

If you havent already , you might try to hook the vac advance line to manifold vac. That will give you more timing under low load conditions (like idle) and pull some timing when your foot is heavy (acceleration) This wont help at wot  but for cruising it might be enough to make it livable.  Is 94 octane gas avalable in your area?  that might be all you need.  But in the end, that ol poncho motor just might  not like the pump gas we have today.


Sorry to make my first post to the board a novel .

Doug




Problem:The above may be linked to the problem I have. After the engine is up to Temp. it pings under moderate acceleration. I run 92 octain fuel. If I add some octain booster it stops pinging but Id like to get away from having to buy booster all the time. The inital timing is set at 6deg btc. and the vac. can is set to add about 6-7deg more for a total of about 12deg at idle. The centrifical advance starts coming in at 1200 rpm, could this be to early?
I was told the problem could be solved if I replaced the 60's style cast iron heads with a set of Edelbrock alum heads. The resons givin where:
1-the new heads have hardened seats.
2- the Alum heads transfer heat better than the Iron heads.

Is any of what I was told TRUE ? I put a lot of blood,sweat and tears into my Olds and love driving it But I want to fix this problem before it causes ENGINE DAMAGE! I would be greatful for any help.

Thanks, Randy