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I have a 67' GTO, 36000 miles, completely standard unrestored PHS documented correct engine, YS code. The only changes are header, large KN filter and the Rochester is a 85 model. The carb is completely renovated, cleaned, all new internals from Cliff Ruggles. The ignition is standard with points and set to 6 degrees at idle and approx. 36 degrees under load, I have taken the vacuum advance away as this would go above 50 degrees. It will start pinging under load, not full throttle but around where the secondaries may start to open I believe. I have tried some alterations to the carb, latest from 73 to 75 jets for the primaries but it continues. It idles well revs quick runs well. Spark plugs have alle the time been completely clean, not brown so my suspicion has been that it runs lean. Haven't checked then after chancing the jets though. The car is in Denmark and runs on She'll V-Power 99 octane. Any tips are highly appreciated :)
 

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Ikki: "The ignition is standard with points and set to 6 degrees at idle and approx. 36 degrees under load"

PJ: #1 .You could try to change the dist. advance curve using different springs.

#2 . 36 may be too much. Drop it back to 34, then 32, and see if the pinging stops. Don't be concerned with the 6 degrees at idle at this time. You just want to see if the pinging stops. If it does, then you may need to limit the total advance to that number.

You can add a bushing or small piece of vacuum tubing to the advance pin : "M point type distrbutors made from 1955-1968 have a advance slot that is oval shape. The GM point type distributors made after 1969 have a advance hole that is nearly round. The shape of the hole for the advance pin was to changed in order reduce the amount of mechanical advance as the octane of pump gasoline was reduced. GM then started using open chamber heads with less quench area. Put a small piece of vacuum hose on the advance pin that is located in the weight plate advance slot and reduce the mechanical advance."

SUMMIT has a kit that will do both: https://www.summitracing.com/parts/mrg-928g/overview/

Ikki; "I have taken the vacuum advance away as this would go above 50 degrees."

PJ: Yep, it is supposed to do that for better gas mileage in cruising mode. It is important to have this. You can get an adjustable vacuum advance can from Summit and dial it in. Many say to use direct manifold vacuum versus ported vacuum as it may work better - something you have to play with.

PJ: Have you tried one step colder spark plugs? Use regular type plugs, nothing fancy like titanium tips, split fire, etc. as these are not made for older type engines and can cause too much heat in the chamber - and pinging.

PJ: Run a colder thermostat. Assuming your radiator/cooling system is in good shape. Just because the car has 36,000 miles, time has a way of corroding internals through electrolysis and you could have poor flow in your cooling system so as not to cool efficiently. Might want to get one of the hand held infra-red heat scanners and check a few spots around your engine to ensure cooling is uniform/adequate.

PJ: My experience with the older cars is that they can build up a layer of carbon, especially high compression engines. You have to blow out the carbon by opening the engine wide open a couple time, like accelerating onto the highway. Babying the car can cause problems and it just may need a good cleaning out.

Just a few thoughts on the subject. :thumbsup:
 

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Hi PontiacJim, thanks for your feedback, great :) My sparkplugs where AC Delco43S I believe it is a step colder already. They where Clean! not brown... I bought a set of NGK XR5IX, running fine and more smooth, however also completely clean, not brown, am I running lean? This is all happening as long as I am running on the primaries on the carb. Tried to take the ignition back this morning and it helped out although not gone. I will try to take it further back. Already got a colder thermostat :). My fan clutch wasn't working ok also, engine running really hot so I just bolted it secure, that helped a lot! I bought a new fan clutch and it seems to be working now. I don't have that excessive heat in the engine compartment.

I don't do massive burnouts, but it is allowed to stretch out frequently.

I will check my sparkplug tonight, after driving some 30 miles to see if the color has changed.

Would a modern MSD ignition with this 20 degree firing range help?
What about a higher voltage coil?
 

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Hi PontiacJim, thanks for your feedback, great :) My sparkplugs where AC Delco43S I believe it is a step colder already. They where Clean! not brown... I bought a set of NGK XR5IX, running fine and more smooth, however also completely clean, not brown, am I running lean? This is all happening as long as I am running on the primaries on the carb. Tried to take the ignition back this morning and it helped out although not gone. I will try to take it further back. Already got a colder thermostat :). My fan clutch wasn't working ok also, engine running really hot so I just bolted it secure, that helped a lot! I bought a new fan clutch and it seems to be working now. I don't have that excessive heat in the engine compartment.

I don't do massive burnouts, but it is allowed to stretch out frequently.

I will check my sparkplug tonight, after driving some 30 miles to see if the color has changed.

Would a modern MSD ignition with this 20 degree firing range help?
What about a higher voltage coil?

OK, sounds like you are having some success and moving in the right direction. Gauging the carb's rich/lean condition by the spark plugs can be difficult - honestly never go the hang of it myself! LOL. You could back out the idle adjustment screws to get the carb to run a little richer. If it likes it, then you might go up another jet size, but this will only affect the primary side.

I don't know if you have Cliff Ruggles book? He says to test the primary calibration, warm the engine completely up then turn your fast idle screw (on the side of the carb) to increase your engines speed to 2,000-2,200 RPM's. Then gently tip in the choke flap, but not enough to close it or choke out the engine. If the engine speed increases 50-100 RPM's, then this will indicate that your primary settings are on the edge of lean. If no RPM increase or RPM fall off, then pull a small manifold vauum hose from the carb and see if the RPM increases at all. If it does, then the mixture is a bit rich.

He also mentions that the mechanical advance in the distributor is usually too much and total advance needs to be reduced. He also recommends the adjustable vacuum advance on the distributor. Again, this is where I think (my opinion of course) you may be able to fine tune the engine's total advance and the advance curve to get the pinging out.

I don't know if the MSD would help with the engine pinging. However, I have used the MSD6, along with an RPM limiting tachometer, in one of my long ago past builds and it did cause the car to idle better, not foul plugs, and in general ran smoother. Now building a nice 455CI for my car and I have purchased the MSD6AL BECAUSE you can set the built in RPM limiter to the RPM's you want the ignition to cut out - thus preventing the engine to over RPM and do damage, especially if you do burn-outs or miss a shift with a 4-speed. It might also be a good thing in lowering your RPM's if you drop your car off at a shop and don't want the shop guys pushing the engine into upper RPM's or anybody else who may drive the car.

MSD also has an add-on module/kit that allows you to manually adjust your ignition timing right from inside your car - you can advance or retard the timing. Might help if you can't get top grade gas and you need to retard the timing a bit so it doesn't ping. This may work for you with your situation right now, however, I would first try to get your engine right/dialed-in as is before I added the adjustable timing feature - I would not use this as a quick fix and then have something go wrong with your engine. https://www.msdperformance.com/products/rpm_and_timing_controls/timing_controls/parts/8680
 

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Thanks, PontiacJim. I have the book from Cliff, a must when you restore old Rochesters. Had some mail conversation with him on the details of the carb. I know the sentence, tried it too :smile3::smile3:, but will do again. I am gonna take the advance further back until it eliminates the pinging to see where i end up (and how lame the engine gets :frown3: ). I have ordered adjustable vacuum canister, advance kurve kits and a new coil. Have fun with the 455 :grin2:
 

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Thanks, PontiacJim. I have the book from Cliff, a must when you restore old Rochesters. Had some mail conversation with him on the details of the carb. I know the sentence, tried it too :smile3::smile3:, but will do again. I am gonna take the advance further back until it eliminates the pinging to see where i end up (and how lame the engine gets :frown3: ). I have ordered adjustable vacuum canister, advance kurve kits and a new coil. Have fun with the 455 :grin2:
OK, sounds like you know what you are doing and have a handle on it. You will just have to play around with the timing which is part of, and why, we own these cars. :thumbsup: This is one of the reasons when rebuilding an engine you want to drop the compression down - but your car is far from ready for that with its low mileage, but when it's time, it is the best way to go for street driving.

Another thought is to add a water injection system. I have never personally used one, but have looked into them as a possibility to reduce detonation. They use a water/alcohol mix to cool the incoming air charge. I believe they can be used manual or set-up to be activated off your throttle. Not inexpensive in my opinion, but it could be an option.

Depending on how often you drive your car, you could put an octane booster in the gas. Might be good to have some in the trunk just in case you can't get any high octane gas. The stuff is not what you get at a auto parts store, its a real octane booster. This is what geeteeohguy has been using in his '65 389 for years because of the high compression. "I've been using this stuff for the past 10 years off and on with my '65 GTO. I may need to use it in my recently acquired '61 Corvette, which pings badly when the second carb is kicked in. Octane Supreme 130 is the only octane booster I've ever used that really works, and I've tried them all. Don't even waste time on any of that Autozone crap." Click on here to go to the link: Octane Supreme
 

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I took it back further yesterday evening. Further I connected the vacuum hose again, but took the vacuum from the manifold, not from the carb. I have no vacuum on the carb at idle. The combination worked :smile3: I have no pingning and it revs. quicker from idle when i flip the throttle now because I now have vacuum advance at idle. Ok, its not pulling a hard as before but now I have a starting point. I ordered the advance curve kit, adjustable vacuum advance and new ignition coil. I will post the results here Also did the test on the primary side, behaves just like described. You're right, the engines are for a different era, not modern days fuel :crying: I will try to find he octane booster here in Europe, but might be hard, but will try.
 

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I took it back further yesterday evening. Further I connected the vacuum hose again, but took the vacuum from the manifold, not from the carb. I have no vacuum on the carb at idle. The combination worked :smile3: I have no pingning and it revs. quicker from idle when i flip the throttle now because I now have vacuum advance at idle. Ok, its not pulling a hard as before but now I have a starting point. I ordered the advance curve kit, adjustable vacuum advance and new ignition coil. I will post the results here Also did the test on the primary side, behaves just like described. You're right, the engines are for a different era, not modern days fuel :crying: I will try to find he octane booster here in Europe, but might be hard, but will try.
Excellent, sounds like you are on your way. As long as the pinging is gone, that's the key as you don't want to damage the engine -and I'll trade off a little power loss to save my engine. :thumbsup: This gives you a base line and now you can play with the timing curve and vacuum can. You may be able to fine tune it a bit more.

You may have to mail-order the octane booster. I see they do sell it in a quart size. You might want to email the guy and get a quote on shipping. Might be worth trying a quart of the stuff.
 

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Your combination will require at least 100 octane US grade fuel...I believe, but am not certain, that your Euro 99 octane is about 93 US. The only octane booster that actually works is TEL130 Octane Supreme. That, or add race gas. I've had my stock '67 since 1983, and could not run it on pump gas until I lowered the compression on the engine in the early '90's. I installed an adjustable advance can in my '67 and '65 GTO's, and found out they could be adjusted one time only. Re-adjustment a second time would break/strip the screw because it is of inferior quality. (both Accel and Crane units). I ended up (in both cars) physically limiting the vacuum advance with a blockage plate. Google "Lars Grimsrud''....and Corvette ignition timing. His articles are excellent. As Jim said, you are clearly on the right path. Good luck.
 

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Thanks, geeteeohguy for Your feedback. I guess there is only a few solutions this, either adjust the ignition as best you can or modify the heads! Can you actually modify the 670 heads on the 67' engine? How is the modification, open chamber like on the 68' or something completely different?
I found the article by Lars regarding Rochester rebuild, but it seems that this corvette page has a lot of valuable info. I found something similar I the UK for octane boosting TetraBOOST seems to be similar to what you can buy in the US. Right now I will try to optimise my ingnition the best I can and then look into heads modifications. In the long run the octane booster is to expensive ending up costing the same as modifying the heads :) so if you can give some tips on the heads modifications i would appreciate it. All my friends have Chevys, Fords, Mopar none have Pontiacs so good to have a forum like this.
 

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Ikki, I have had my '67 since 1983. 670 closed chamber heads need a lot of octane and like a lot of spark advance. Not the head to run today. Some guys on the AMES forums open up the chambers and squeak by.....with a razor-sharp tune under the right conditions. I retarded my timing, and the car ran hot, guzzled fuel, and was a slug. No fun to drive. I tried water injection. No go. I ended up installing 1970 455 heads, number 15, for the 87cc chamber and about 9.3 CR. I upgraded the studs, but left the small valves. My engine runs well on 91 octane with this combo, with only slight detonation on 105+ summer days up long grades. I tried for YEARS to cheat physics and run high compression in a Pontiac on pump gas....and it doesn't work. Your best bet is race gas or octane booster. If I were to build a Pontiac today, I would install dished pistons and use the original heads. These pistons were not available back in the '80's when I rebuilt my GTO's. Your easiest solution, right now, would be to research and buy a set of used 87-90cc iron heads (look up Wallace Racing) or a set of new 72cc aluminum heads. Problem solved.
 

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Update on the Mod's i have done. I have updated my iginition with a few parts; Purchased the springs for the mech. advance, with the limiting collar so that it cant advance the that much, adjustable vacuum canister, new MSD coil and resistor. On top of that a friend og mine had an electronic ignition laying around(Pertronix). The original ignitions system coil has a resistance of 2.4 ohm and the build-in wire resistor is 1.4 ohm total of 3.8 ohm which gives you a charching current of 3.15 Amps. The Pertronix requires only 1.5 ohm total and fits perfectly with the MSD system as the coil has 0.7 ohm and the resistor 0.8 ohm. This allows for a total current of 8 amps, more than double! whereas the voltage across the coil is slightly lower than stock=7.56V and MSD 6.4V This will roughly double the power to the coil and consequently to the sparkplugs. I have now the strongest springs in the advance and static advance is actually now around 38 degrees and idle around 8-10 degrees, only little vacuum advance at the moment. This has really helped. I believe the more precise ignition and alot more power to the sparkplugs is key to minimizing engine pinging, its gone :smile3:
Ok, i have also tweaked the carburetor a little. My Rochester is from a 85 Chevy truck with the APT system and it is the 800 CFM version too. My pingning was primarily at part trottle and at changeover from primaries to secondaries. So i adjusted the APT 3 turns up which raises the primary needles, this to make a real difference. I can just floor it from standstill and hold it there gear change from 1 to 2, and continue, no pinging. Ok i might be running a bit rich, i will try som more tweaking :nerd: Right now i have 75 jets in, and they should actually be to large but on the other hand i run an open KN filter så more air can get in, not so much restriction. Headers too. A few words on the fuel, as said it's Shell V-Power 99 octane according to the RON standard used in Europe. This compares to 94-95 octane AKI(Anti Knock Index) used in the US. Ok, fall is coming here in DK and we may have 1 more week to drive in, then the rain comes, shitty weather, vinter a.s.n.:crying: So no more driving this year. looking forward to 2017 :grin2:
Thanks for feeedback guys...But, i will open a new thread on TH400 , i have a small issue :|
 

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Sounds like you got it! :thumbsup: The ignition & distributor curve is more important than most think. Getting it dialed in just takes a little trial and error and time.

The APT adjustment is another great feature that allows you to fine tune the primary side of the carb. It may have been running a little too lean and by richening it up that helped. That too is a trial and error type of adjustment.

You may want to also use a vacuum gauge to adjust your idle screw mixture setting - this may lean out the carb a little to balance out the richer APT setting. I would take notes on everything so you will have your original settings should you need to go back to them. I found this easy explanation on the web:

"got the idle mixture set using a vacuum gauge... lean best.. and got the idle properly set.. for those not familiar.. vacuum gauge hooked up to manifold vacuum. engine warmed up.. the choke should be wide open at this point. start by turning the idle mixture screws inward till the manifold vacuum starts to drop. then go back until the manifold vacuum does not increase.... do both screws... then turn them in until the manifold vacuum just starts to drop.. go back to the point where its right at the spot where it starts to drop.. using the vacuum gauge. i turn the screws in just slightly so with both adjustments i have reduced manifold vacuum by 1/2" of vacuum on the gauge. if you have assembled the carb properly.. both screws should turn about the same fraction of a turn to reach this. its usually 1/8 to 1/4 turn.. sometimes only 1/3 of a turn. this gives you lean best idle.."

And here is the follow-up to finalizing the adjustment on the APT after getting the mixture zero'd in:

"now.. with an educated driver behind the wheel.. lots of room behind and in front of the vehicle.. nothing to hit.. have them do a part throttle acceleration. i did this in the length of 2 parking spots. you only need a part throttle test.. if it backfires.. you need to raise the APT adjustment 1/4 turn.. back the vehicle up and try it again... if it backfires. give it another 1/4 turn upward.. continue this with 1/4 turns upward... soon it will be accelerating really hard.. you will find a point where the acceleration no longer gets better.. start turning it the other way.. you want to reach the point where the acceleration is the best..

your APT adjustment is now done.. its that simple.."


The main thing is that you got the pinging under control. :cheers
 

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Took it out for a Spin today with my 12 year old son. He managed the stop watch and without much effort and a Little wheel spin it Stil manged to do 0-60 mph in Approx 6.5 sec. Rear end code is WD 2.93. Think that's ok for a 1st try :)
 

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Took it out for a Spin today with my 12 year old son. He managed the stop watch and without much effort and a Little wheel spin it Stil manged to do 0-60 mph in Approx 6.5 sec. Rear end code is WD 2.93. Think that's ok for a 1st try :)
Your are right on the money. Found a 1966 GTO 0-60 time of 6.6 seconds with 3.23 gearing, so you don't have any problems with that kind of time. :thumbsup:
 
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