The Rodding Roundtable
Motorhead Message Central => Rodder's Roundtable => Topic started by: 1939coupe on December 29, 2004, 08:42:59 AM
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
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.
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
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.
Quote from: "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.
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 :lol:
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.
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)
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
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!!
Thanks, that will be the first thing I try this Spring when I get the car out of hibernation.
Randy
Quote from: "1939coupe"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.
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.
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
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.
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 :D
The Total Timing on the engine is 36 deg. 6 initial and 30 centrifical.
As for the Vac advance can, right now it addind about 6 deg. and I have it connected to Manifold Vac. I runs cooler at Idle this way.
Randy
Quote from: "1939coupe"The Total Timing on the engine is 36 deg. 6 initial and 30 centrifical.
As for the Vac advance can, right now it addind about 6 deg. and I have it connected to Manifold Vac. I runs cooler at Idle this way.
Randy
=====================
As you probably know, there are adjustable vacuum advance mechanisms on the market.
....Perhaps, more vacuum advance and late centrifugal advance will eliminate the light-load ping, without affecting full-throttle performance??
I think there are also after-market ignition boxes that can use a knock-sensor to retard timing when needed.
It all boils down to how many $$$ you want to throw at the problem.
Quote from: "1939coupe"The Total Timing on the engine is 36 deg. 6 initial and 30 centrifical.
As for the Vac advance can, right now it addind about 6 deg. and I have it connected to Manifold Vac. I runs cooler at Idle this way.
Randy
My book shows the timing figures for a 66 Pontiac 421 with three 2 barrels or one 4 barrel to be:
6 degrees BTDC initial.
22 degrees centrifugal, all-in @ 2300 rpm.
10 degrees vacuum, all-in @ 16" vacuum.
Disregarding vacuum, that gives you 28 degrees centrifugal all-in.
An entirely reasonable figure.
36 degrees all-in sounds like a Small Block Chevy timing figure.
Fwiw, I run a 455 Buick and all-in centrifugal timing on it is 32 degrees.
Some of the Buick guys running a more radical build than my mildy cammed, 9/1 compression engine run 32, 30 and 28 degrees all-in timing at the strip and on the street.
Ae you timing the engine with the vacuum advance line disconnected at the distributor?
And perhaps using a degreed balancer or timing tape to show you exactly where you're at?
If so, one small experiment you could try would be to set the initial timing at zero degrees (vac line disconnected).
That would give you 30 degrees all-in centrifugal timing.
Then, reconnect the vacuum line and take the car for a drive.
If the pinging goes away - and I'm betting it will - the next step would be to reinstall the original distributor weights and springs.
The factory distributor curve on these engines is a good choice for a performance engine whether factory stock, mildly cammed, low compression (9/1) or a more radical build.
Even with a radically built engine, this timing curve is a good one to start with.
Once you get things sorted out, you may be able to run the middle octane gas or even the 87 octane stuff.
Fwiw - the 87 works well in my 455 Buick winter and summer.
The only thing on the engine that is NOT stock is the Dist.
I'm running a Mallory Uni-light.
As for the amount of money I'm willing to Spend, I drive the car a lot and want to fix it RIGHT. I don't want to breakdown somewhere and find out the breakdown was caused by a Pinging or a Timing problem.
Randy
1939 coupe,
Well the "right way" is probably lowering the compression with dished pistons or larger combustion chamber heads or both. do you know what the compression ratio is rihgt now and what type piston , dished, flat ect and combustion chamber size. I have some friends that are pontiac nuts Ill ask them what the largest chamber head would be.
Happy New year
Dj
Quote from: "1939coupe"The only thing on the engine that is NOT stock is the Dist.
Mallory Uni-Lite's are easy to change the timing curve on.
Seems to me that'd be the easy way out - and the cheapest and the least work.
Get it back to baseline and see what you have as far as how well it runs.
The following two links are to the same article posted in different forums.
Whilst the info does not specifically address Randys problem, it is very informative, and anyone who has followed the thread this far is bound to find it interesting reading.
http://www.streetrodstuff.com/Articles/Engine/Detonation/
http://www.germanmotorcars.com/Detonation.htm
Quote from: "Dr Flowgood"1939 coupe,
Well the "right way" is probably lowering the compression with dished pistons or larger combustion chamber heads or both. do you know what the compression ratio is rihgt now and what type piston , dished, flat ect and combustion chamber size. I have some friends that are pontiac nuts Ill ask them what the largest chamber head would be.
Happy New year
Dj
My heads have a Casting Code of 092. And they are 1966 heads, so the Compression Ratio should be 10.5:1. And I know that the Pistons are Flat on top.
Thanks
Quote from: "C9"Quote from: "1939coupe"The only thing on the engine that is NOT stock is the Dist.
Mallory Uni-Lite's are easy to change the timing curve on.
Seems to me that'd be the easy way out - and the cheapest and the least work.
Get it back to baseline and see what you have as far as how well it runs.
What step should I take first:
1- Cut back on initial timing (right now 6 deg.)?
2- Make Centrifical Adv. start coming in later than the present 1000 RPM?
I would rather NOT take initial timing out OR adjust my Vac can to put in Less than the 6 deg it is set for right now because the less Advance it has at Idle the Hotter the engine will run.
I just don't want to give up to much POWER.
QuoteWhat step should I take first:
1- Cut back on initial timing (right now 6 deg.)?
2- Make Centrifical Adv. start coming in later than the present 1000 RPM?
I would rather NOT take initial timing out OR adjust my Vac can to put in Less than the 6 deg it is set for right now because the less Advance it has at Idle the Hotter the engine will run.
I just don't want to give up to much POWER.
Too much advance takes away from power as does not enough advance.
Limit the amount of centrifugal advance until you match the Pontiac factory recommended limit. IE: 28 degrees total.
Even if you did spend lots of $$ on heads, pistons and the like, if you run too much advance you'll still have your problem.
Here's an address for Mallory tech instructions.
Just click on the style distributor you're running.
http://www.centuryperformance.com/mallory/mallorytech.asp
Note that there are two types of centrifugal limiting devices.
One - the older style Uni-Lite I believe - has bendable tabs.
The other has keys to set the advance and then lock it down.
I'm fairly sure the keys are available at Summit and the like.
Like my dad used to say, get it back to factory specs and go from there.
Worked every time for me.... :lol:
like C9 says , mayb start over again from tthe baseline with timing curve?
Quote from: "PeterR"The following two links are to the same article posted in different forums.
Whilst the info does not specifically address Randys problem, it is very informative, and anyone who has followed the thread this far is bound to find it interesting reading.
http://www.streetrodstuff.com/Articles/Engine/Detonation/
http://www.germanmotorcars.com/Detonation.htm
Thank you very much for this Link. I learned a LOT about Detonation and how Timing and Cumbustion Chamber Design can be used to eliminate Detonation.
I also learned that Detonation (pinging) is NOT as bad as I thought.
I'm going to use the info in the article to alter my timimg curve.
Anyone who builds and works on there on engines should read this article.
Thanks again,
Randy
Randy......the real way to fix it right is find out not only what the static compression ratio is.....but more importantly do the arithmetic on dynamic compression ratios.
Rereading the posts here I don't think you have a "load" of too much timing here even tho tweeking it first might show some improvement..certainly 30 is a more realistic target. I have set ponchos up with both 400s and 455s to run over 30 degrees total....nary a problem on 92 octane but they have been engineered to run that way. Just about every muscle car ( or big block from that era) that I have driven with the factory cams, heads and timing profiles ping under moderate and light loads with regular 92 pump gas. It's the combination of compression ratio, cam profile, timing and lack of octane in today's fuel.
I also will admit that I don't know where the piston is sitting in the hole either with the 421. And, yes I believe you have flat tops with reliefs. I am guessing that your gasket is .028" which is pretty standard for these. This all figures in to dynamic compression ratios and there are plenty of online calculators to help you accomplish the correct values.
I recently did a 70 GTO almost with the very same issues. 3800 pound 1970 GTO, 400 +.030 over, factory dished pistons, stock 1.5 rockers, stock Q-jet, 3.55 rear gears, 4 speed, dual exhausts; stock point distributor used mostly for local shows, cruises and some road trips. The goal was to improve stock performance, at the same time lower 9.5 to 1 compression to run on pump gasoline. The engine came with the OEM "S" camshaft (068); 212/225 @.050" duration. The inherent problem with this engine was the lack of "overlap" that created a high DCR. It pinged like a mother on pump gas under light and moderate load.
The results were spectacular! The Edelbrock heads are a vast improvement and the power to the rear wheels was upped almost 100hp in combination with a newer comp cams, intake and HEI upgrade. Milage improved almost 25% too. I personally think it's worth the cost....just on the fun factor.
Now....down to spending your money....hopefully smartly. I would suggest that you can do several things here with new heads and a different camshaft which will improve performance/power/torque, milage, and work all on pump gas if you do the homework. The cam profile and heads in your engine is TERRIBLE with a capital T.....compared to today's OEM heads and performance cam grinds. I will guarantee you if you do the Edelbrock RPM Performer head series with these........keep your quench design between .035 - .045 and dynamic compression ratio below 8.2 to one, (and you can keep your bottom end) you will be very satisfied with the outcome. But bottom line.....do your homework first.
Good luck with your problem here, I hope it comes out to your liking :)
Don't know if you have found your answer yet. But had the same issues with a .030 over 398. It sucks - I know. Debated most of the solutions listed here... tried a few, as well.
I was told - the vacuum advance was primarily to promote better gas milage, and that the car would run fine (although Lopey ) without it.
I disconnected the advance & drove the car like this for another year. While this DID NOT totally eliminate the mid throttle pinging - it did reduce it greatly. If you are running a quadrajet - also look into the setup of the rods - a little extra fuel at mid throttle, while a band-aid, can help too.
The best solution - as stated earlier, is to reduce compression.
A set of 6x heads would be easy to come by, flow pretty well stock, and can be modded to flow like crazy. The next step up would be 96 - these are a little more desireable ($400-500) because they have the larger exhaust valves.
I was lucky enough to pick my 96's for $150 - added hardened seats & new valves for a total investment of less than half the price of the edelbrocks....
BTW the edelbrocks are around 87cc
Check out the Q&A on CLASSICALPONTIAC.COM - lots of compression talk going on there - from all the guys building 455's.
Good luck!
Chuck