# timing 428cui, 670 heads



## Chris-Austria (Dec 23, 2010)

Hi!

Now I'm sure what setup I bought with my GTO and I think the timing might be incorrect, because I used values from the original 389 cui.

I have:

- 428 cui from 5.14.1969
- 670 heads from 1967
- tri power setup from rochester
- headers and 3" exhaust
- flowkooler high volume aluminium waterpump
- high flow thermostat 160°
- msd ignition (distributor...)
- accel 137 spark plugs
- mallory spark plug wires

If I use the highest available octane the engine sounds good, is my compression too high? I'd like to run 95 octane without engine knocking, could it be a timing issue?

Chris


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## BearGFR (Aug 25, 2008)

Hi Chris,
670's on a 428 are going to put your compression "up there", but the real test is whether or not the engine knocks and/or you're finding tiny shiny specs of metal on your spark plugs. 670's are closed chamber heads and as such their combustion efficiency isn't as good as the open heads, so to make the most power they're going to need a little more ignition timing than an open chamber head would. 

Is the motor knocking now? When you examine your plugs, are you seeing tiny shiny specs? (A motor can be not knocking but still detonating and damaging itself - the shiny specs are bits of piston).

Bear


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## Thumpin455 (Feb 17, 2010)

That combo with flat top pistons is going to be well over 10:1, not far from 11:1. Depending how Austria tests for octane, 95 might not be enough. I know it isnt enough here with our gas, that thing would knock the upper rod bearings flat in a few hours. Been there done that with a 400.


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## Chris-Austria (Dec 23, 2010)

I'll remove one or two plugs and check them.
If I use 95 octane (would be 91 in the US) the engine knocks.. if I use 98-100 (would be 94-96 in the US) it sounds pretty good. I also add some lead additive..
Timing is now at 7-8° I think, but it has been at 10° before I set it down... should I use 10°?
Motor isn't knocking now since I use 100 octane and lead additive! But that makes fuel pretty expensive.. it consumes about 25 liters/100km (9,5 mpg)


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## BearGFR (Aug 25, 2008)

The big thing is making sure the motor doesn't knock and isn't slowly eating pistons. Everything else is secondary to making sure of that. 

That being said, with 670's I'd probably start with timing at 34 degrees TOTAL (vacuum advance disconnected, engine at 2800 rpm or higher) and see how it likes that. Add more a degree or two at a time until you find the point where performance starts to decrease (or you start to see/hear signs of detonation), then go back to the previous setting. Then measure to see what that works out to on the initial side (motor at idle, vacuum advance disconnected) just so you'll know where to set it the next time you need to.

You want to run as much timing as you can until either performance degrades or you see/hear signs of detonation, which ever happens first.

Bear


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## Chris-Austria (Dec 23, 2010)

Like always a very good advice, I'll try that  The vacuum advance is a part of the distributor? Mine doesn't have such a thing at all.
Maybe I'll ask the shop to check my compression ratio as well if that isn't to complicated and expensive.


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## freethinker (Nov 14, 2009)

Chris-Austria said:


> Like always a very good advice, I'll try that  The vacuum advance is a part of the distributor? Mine doesn't have such a thing at all.
> Maybe I'll ask the shop to check my compression ratio as well if that isn't to complicated and expensive.


with 670 heads on a 428 there is no need to have anybody check it. its too high for pump gas. period. 
you can try retarding timing to less than 6 and try limiting the advance but those are bandaids. you need different heads.


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## BearGFR (Aug 25, 2008)

Chris-Austria said:


> Like always a very good advice, I'll try that  The vacuum advance is a part of the distributor? Mine doesn't have such a thing at all.


I keep forgetting you don't have a factory distributor. The vacuum advance would be evidenced by a vacuum line connected between the distributor (usually on the side next to the bottom edge of the distributor cap) and either the intake manifold or the carburetor. For distributors that have them, it's important to make all timing adjustments with the vacuum line disconnected and plugged.



> Maybe I'll ask the shop to check my compression ratio as well if that isn't to complicated and expensive.


There's no way that I know of to measure compression ratio without removing the cylinder heads. Checking cylinder 'cranking pressure' with a gauge doesn't provide an accurate measurement because that measurement is heavlily influenced by the cam profile --- the "later" the intake valve closes, the less pressure will be - because compression can't begin until that valve closes. Speaking of, that's another "band aid" that's available: if you use an "adjustable" timing chain/gears you can retard cam timing "a little" to delay that intake valve closing event some and it just might be enough to keep the motor out of detonation if it's already "close". Retarding cam timing has other consequences though - it shifts the torque curve higher in the rpm range so the motor's going to have less torque at low rpm and also will need to turn to a higher rpm in order to make maximum power.

I just ran "numbers" for 670 heads on a standard 428 (4.12 bore, 4.00 stroke) and assumed a standard factory compressed gasket thicknetss of .042 with the pistons .020 "in the hole" at TDC - which is what Pontiacs "usually" are from the factory unless the block has been decked. I also assumed flat top pistons that have about 6 cc's worth of clearance volume in the valve reliefs. Factory specs for 670 heads state that their chambers have 72 cc's of clearance volume. However Pontiac heads have been known to vary from factory specs quite a bit in either direction, and also we don't know if your heads have ever been milled/surfaced, so the only way to know for sure would be to pull the heads and measure the chamber volumes directly. With all the "disclaimers" out of the way, that combination works out to 10.549:1 static compression using nominal factory measurements. That's probably too high for any pump gas we have available here in the States, I'm not sure about what you can get there in Austria. It might be possible to squeak by with a really nasty (long duration) cam and top notch cooling system, but I wouldn't try it myself. Just on numbers alone it's not worth it to push compression to the limits. On my 400/461 the difference between 9.4:1 and 10.5:1 is only worth about 14 peak horsepower - not worth it to me to take the risk of destroying the motor for just 14 HP.

To see the effect of chamber volume on static compression ratio, if we just add a measley 6 cc's of volume to each chamber 'somehow' (piston dish) that drops SCR to 9.96:1. If we triple the volume to a total of 18cc's (acheivable with off the shelf D-dished pistons) that makes SCR 9.44:1 - streetable on U.S. 93 octane if you're careful and have 'enough' cam. 

Aluminum heads would be a different story. Aluminum doesn't retain heat like cast iron does so you can get away with more compression. 10.3:1 or maybe even 10.5:1 with aluminum heads is doable (given the right cam and a good cooling system).

Like with lots of things on cars, it's all a compromise and there's no hard and fast rule due to all the interelationships between the various components and the overall condition. A poorly planned/sloppily built motor might rattle like a load of loose bowling balls in a box car even at only 9:1 on 93 octane, while a very carefully built and meticulously maintained one might be ok at close to 10.1 if everything is always "dead on" and the fuel mixture/tune up always "perfect". 

And... it's not that I'm an expert or anything on this topic, it's just that I spent BOATLOADS of time and effort researching it during the time I was planning and building my own 461. I was in a situation similar to yours. I had a set of original 1969 #722 Ram Air IV cylinder heads that I -really- wanted to use just for the cool factor, but in order to get the compression ratio down to something reasonable on a 461 I had to jump through a lot of hoops to do it, when it would have been "easier" to just get a good set of aluminum heads (which probably would have made more power than the IV's anyway). As it is though, I've got a 461 that makes fairly decent power that I can point to and say "yeah, it's just the factory 400 - nothing special" and MAYBE get away with it except with Pontiac-heads that know how to interpret all the various codes and numbers - at least until I start it up 

Bear


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## Rukee (Feb 8, 2007)

I though NASCAR had a tool that inserted into the plug hole and did some whistle thing and they could determine compression ratio??


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## Chris-Austria (Dec 23, 2010)

Thank you for calculating how high my compression would be, if everything is still like it was build. The guy at the shop told me the same thing.. it's not possible to measure the ratio and I shouldn't worry too much if it doesn't sound to bad when using the highest available octane (would be about 96 in the US). I'll drive it empty (now I use 94) and fill it up with the 96 and add some octane booster.


Which heads would fit best to the 428? (Many hp and a good compression?) 

I like it if an engine looks factory and has a setup that is good for some surprises


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## BearGFR (Aug 25, 2008)

You've got options depending on your budget and availability of parts where you are. If you want to run cast iron Pontiac heads and preserve the stock look, then some of the later model heads with larger chambers and hardened seats (6X-4 for example) would be a good starting point. There's always the 455 SD head but they are incredibly hard to find and hideously expensive when you do. If you want to go that route (keep the stock look) and have the budget for it, then what I'd do would be to contact Dave Wilcox at Central Virginai Machine (Central Virginia Machine Service - Home of the ***** Engine!) and have him work up a set of later model D-port heads. Dave's one of the best there is when it comes to head porting and he'll be able to get everything out of a set of heads (either iron or aluminum), performance wise, that there is to be gotten. If you're interested more in power than you are preserving factory looks, then aftermarket aluminum is definitely the way to go. First into the market were the Edelbrock Performer heads, based loosely on the Ram Air IV port design. Worked over by Dave they will make more power than any iron head. There are others on the market now too, CV-1, Tiger, Kauffman, newer Edelbrock D-ports, and others. Some of them are mostly for racing, some deviate quite a bit from the original Pontiac design and appearance even to the point of not being able to use any factory Pontiac intake manifold. It's all just a question of what you want and how much you want to spend.

There's another option too. If you have good availability of E85 fuel where you are, you could convert to that and run all the compression you like with the heads you have. Thumpin455 on here is very experienced and knowledgeable about doing that.


Bear


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## BearGFR (Aug 25, 2008)

Rukee said:


> I though NASCAR had a tool that inserted into the plug hole and did some whistle thing and they could determine compression ratio??


Well hush my mouth -- I didn't know about this tool. I did some searching and found it. It's made by Katech, is called "the Whistler" and costs just over $2000 to purchase.. I went to Katech's web site and read about it. From reading the doc I got the impression that it works by somehow using a calibrated air flow into the cylinder with the piston stopped at TDC to measure the volume of the open space (resonance maybe?). Once the volume is known (clearance volume) then compression ratio can be calculated if the cubic inch displacement and number of cylinders are also known. To provide a measurement, you have to enter the displacement, number of cylinders and engine temp (within 5 degress) into the tool.

Hah! It DOES use resonance. I found this link that explains the process: http://ieeexplore.ieee.org/xpl/freeabs_all.jsp?arnumber=352029


Bear


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## Thumpin455 (Feb 17, 2010)

If you can find some 70-73 350 heads, casting 46, you can add larger valves and they are quite similar to 96 and 7K3 heads. All of which give you a 9.5:1 455 so about 9:1 on a 428.

I know you can get E85 and ethanol in Europe, I just dont have any idea where. We export a huge amount of the stuff over there. That would let you run the engine like it is, since that is low compression for E85.

I have 670 heads on a 455, it used to run on 110 race gas, and with that stuff it liked 52 degrees total timing. Yeah, fifty two, and it would slow down considerably with less timing. Those chambers arent exactly efficient. Also on the 400 with these heads it didnt knock at all, no ping, no rattles, nothing but lots of power, and then it spun a rod bearing. It had flattened all the upper rod bearings with inaudible knock. It literally crushed the bearings in the rods. Its the stuff you cant hear that kills engines.


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## Chris-Austria (Dec 23, 2010)

I've done some research and found Edelbrock cylinder heads, either 72cc or 87cc and they write that the compression ratio will be about 9.5:1 on my engine. Whats the difference between the 72cc and 87cc? Which produces more power? (the 670 heads also have 72cc)

If the compression ratio with the same heads is a little bit higher on a 455 instead of a 428, so I might have luck and the highest available octane with octane booster will just be good enough (would be similar to 100 octane in the US). Thats what I'll try.

Are used 670 heads worth some money if I sell them after buying for example the Edelbrock heads?

I don't know where to get E85.. (Didn't even know something called E85 exists )


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## BearGFR (Aug 25, 2008)

Chris-Austria said:


> I've done some research and found Edelbrock cylinder heads, either 72cc or 87cc and they write that the compression ratio will be about 9.5:1 on my engine. Whats the difference between the 72cc and 87cc? Which produces more power? (the 670 heads also have 72cc)


Just that - the difference is the chamber volume and the resulting compression ratio. Remember that with aluminum you can get away with (and also need) more compression than with iron because aluminum doesn't retain as much heat as iron. In the States it's generally recommended to be in the neighborhood of 9.3 to 1 with iron heads on 93 octane, 10.2:1 (or so) with aluminum. As mentioned before the specifics of the motor involved and the cam shaft can affect these ranges. Couple things here: The Edelbrocks are pretty good out of the box, but some have said that if you buy the heads ready to run the valves and springs that come with them are of suspect quality. "If it were me" I'd buy a set of bare heads, ship them to Dave at CVMS and have him work his magic on them and outfit them with good parts while he was at it. You might be able to just buy a set ready to go directly from CVMS. The advantage of that is that you'll have the opportunity to work with both Dave and Jim (Mr. PBody) and they'll be able to tailor everything to your specific situation - and that's worth a lot.



> If the compression ratio with the same heads is a little bit higher on a 455 instead of a 428, so I might have luck and the highest available octane with octane booster will just be good enough (would be similar to 100 octane in the US). Thats what I'll try.


If you want to play around with it, I have a spreadsheet that I can send you that does CR calculations taking into account all the various measurements (bore, stroke, head gasket thickness, piston valve relief/dish volume, deck height, etc.). There are also web sites that have similar tools.



> Are used 670 heads worth some money if I sell them after buying for example the Edelbrock heads?


Indeed they are. They'll be worth something to someone restoring a 67 400 because they are specific to that engine/year. They also flow pretty good for a D-port head and quite a few performance oriented folks like them a lot. Personally I'm not a fan of the closed chamber but that's just me.



> I don't know where to get E85.. (Didn't even know something called E85 exists )


Thumpin455's the expert on that one. I spose it might be called something else in Europe. It's 85 percent methanol fuel.

Bear


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## Thumpin455 (Feb 17, 2010)

85 percent Ethanol, not methanol. Methanol mixed with gasoline is M85 and it is very corrosive, so you need special fuel system parts to run that. Ethanol is not a problem in most fuel systems.

Here is a listing for stations in Germany that carry E85. Some companies might have it in Austria, or you can go over the border if one is near you.

http://www.e85.biz/media/archive1/ethanol-tankstellen-d.pdf

Another site that can provide more information. 

AGRANA SuperEthanol - SuperEthanol E85 - Der Kraftstoff

Some searches on E85 in Austria will give you locations. The thing is, with a carbureted engine, you have either a gasoline carb, or an ethanol carb, and a methanol carb is too large for ethanol use. So if you want to run gasoline, you need a carb set up for that, but then you also need high octane so that means expensive race gas. If you have an E85 carb you dont need to worry about the octane since it will handle your engine easily. You just cant fuel it with gasoline like a flex fuel vehicle, its one or the other.

I can build you a carb, show you how, or I know others who can as well who have businesses that cater to E85 fuels. It isnt difficult to convert them if you know how to rebuild a carb.

E85 is cheaper than gasoline in Austria, just like it is here, you use more of it but the price difference between 100+ octane and E85 is quite a bit more than the cheapest gas and E85. The cheapest gas and E85 is about a break even point on most vehicles, higher octane with higher prices widen the gap considerably, and there is no worry of hurting the engine despite what some people say. Its an option for you there.

I can give you as much information about it as you would like, but if you like power, less vibration, cooler operation, and vastly reduced wear in your engine, then its something to look into. The only problem right now is how many stations have it, and there are more sprouting up daily.


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## Thumpin455 (Feb 17, 2010)

Also the compression ratio on a 400 with 670 heads is too high for 93 octane gasoline, increasing the displacement to 428 isnt going to make it better.


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## BearGFR (Aug 25, 2008)

Thumpin455 said:


> 85 percent Ethanol, not methanol....


Told you he was the expert ... :rofl:

Bear


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## Chris-Austria (Dec 23, 2010)

Thank you for all the information!
I've been in Germany this night and saw something they call "ultimate super" with 102 octane (would be 98 in the US). Maybe I'll try this one... but it is very expensive 
I asked some guys from Germany.. nowbody knows anything about E85 and there is no gas station near my location listed.

If I think of new heads I'll keep in mind what you told me of Dave! Larger investments will have to wait until next year..


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## Chris-Austria (Dec 23, 2010)

Now I have been driving about 3000 miles with my 428cui and 670 heads without having any trouble. I use 100 octance gas and lead additive.

I am still not sure, what timing setting will fit best. 
If you click following link you can see the possible settings of my distributor shown on "Figure 4". Which curve would be best?!

http://www.msdignition.com/WorkArea/DownloadAsset.aspx?id=15032386309

And what might me the best iginition timing? (This is what I can change by moving the distributor?) I think now it has 8°.


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## lars (Sep 28, 2004)

A 428 with a 4.12 bore diameter and the 670 heads wants 36 to 38 degrees total timing for best power. If you have a non-vacuum advance aftermarket distributor, you need a short advance curve and quite a bit of initial timing: You want initial timing in the 18 - 20 degree range, which means you need to shorten your advance curve to about 18 degrees to get the 36-38 total timing. This will produce best power and idle quality, but you may not be able to run these "best numbers" with the compression you're running:

If you have a stock 4.12 bore with the 72 cc heads, .045 compressed gasket thickness, 5cc valve reliefs and about a .010 deck height, your compression ratio is about 10.82:1. Chances are good that your engine is not the stock bore, and has likely been rebuilt at a .030" over-bore. This will give you a compression ratio of almost 11:1.

Run the timing numbers up as close as you can to the numbers I outlined above while staying out of detonation with the best fuel you can get. You'd be better off with a set of the 87cc Edelbrock heads and paint them to match the engine color to make them look stock. This will give you a 9.51:1 comp ratio if the engine is bored .030 over.

If you need instructions on setting total timing, drop me an e-mail request for my "how to set timing" tech paper.

Lars
[email protected]


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## BearGFR (Aug 25, 2008)

For these engines, timing is best set by setting the amount of total advance you want to have when the engine is at rpm. To do this yourself you need a timing light that is capable of measuring total advance, something similar to this one:

Actron/Digital advance timing light with LED screen and mode indicator lights (CP7529) | Timing Light | AutoZone.com

The process is to disconnect and plug the vacuum advance line so that there's no vacuum leak, then take the engine up to an rpm where the centrifugal advance in the distributor is "alll in" -- usually somewhere in the vicinity of 3000 to 3500 rpm. With 670 heads and their closed chambers, they usually "like" a litte more advance than the open chamber heads do because their combustion efficiency isn't quite as good. I'd start with about 37 to 38 degrees total advance with those heads at rpm. If you really want to find the optimum you need a way to objectively measure performance --- something like e.t. clocks on a drag strip. You'd establish a baseline then start varying the timing up (and maybe down) a degree at a time until you find the setting that provides the best performance. Once that's found, then check the timing the "normal" way with the engine at idle and see what the setting is. This is so that you will have a reference point to return to the optimum setting in the future without having to repeat the rpm testing.

The point is, there are a lot of small things that can influence what is the "best" setting for a particular engine. The intial settings that someone might recommend are really just generalizations of a reasonable 'starting point' based on experience.

Bear


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## geeteeohguy (Feb 2, 2008)

I agree with these gentlemen. Altitude, humidity, air temperature, operating temperature, and load all change, and will affect the optimum timing for each situation. The outlines described will work in most driving situations. I can't get away with as much total advance where I now live, where it's hot with very low humidity--- as I could when I lived in a cool coastal climate. Just something to consider.


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## Chris-Austria (Dec 23, 2010)

Thanks for the responses.
I have no vacuum advance on my distributor. I'll change the initial timing from 8° now to 18° and give it a total timing of 38°. If there is no detonation with the best fuel I can get I'd be pretty happy. Maybe my heat-problems are related to the retarded timing. 
If the vacuum advance control unit (which I don't have) will add about 20° to the initial timing that was set, a stock distributor would give about 28° initial timing. Thank you Lars for telling me this thing that I didn't know and my mechanic didn't know either when he retarded the timing to 8° without a vacuum advance. The reason why I cannot use such a high initial timing is because it wouldn't start at all, did I get this right? So the stock vacuum advance is there to allow a good start with let's say 8° and push the initial timing once it has started to 28° for a better idle, lower temps and more power?

Where I live the altitude is about 400 meters above see level, air temperature of about 90° in summer and a humidity of 60-70%. No load in the car except a pretty girl and myself 

Hope to find the best setting now with these new information.


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## Chris-Austria (Dec 23, 2010)

One question because I always read "set the timing to 6° initial"
There are two options:

1. my 428cui and a distributor with a vacuum advance => initial timing 6°
2. my 428cui and a distributor without a vac. advance => initial timing at 16-18°

Is that correct? If so I will try the setup from my last posting next Tuesday.


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## BearGFR (Aug 25, 2008)

Hi Chris,

Don't fixate too much on initial timing. The only reason it's specified as initial is to make it easy to set (much easier to work around an idling engine than it is to work on one while it's running at 3000 rpm or better). The setting that really matters is the amount of ignition advance your engine "sees" when it's at wide open throttle under load. Under those conditions, vacuum advance is also out of the picture because manifold vacuum is so low it won't activate the vacuum advance, so it doesn't matter if you have a vacuum advance installed or not. (Vacuum advance exists to provide additional advance only at part throttle, lightly loaded, cruise conditions in order to get better fuel economy and lower engine temps)

If you really want to get the timing "right", work off of total advance at 3000+ rpm. Get that set to the point your engine "likes" for best performance first. Once you've got that, then let it idle and use the light to see what initial timing setting that is so that you'll know how to return to the same setting in the future without having to run the engine at RPM.

Pontiac service manuals specified the intial setting at 6-degrees because the factory "knew" how much mechanical advance was built into the stock distributor and also what amount of total advance provided the "best" compromise between economy, cooling, and performance. If you know what total setting you want, and how much advance is "in" the distributor, then arriving at a figure for the initial setting is as simple as subtracting the distributor mechanical advance from the total advance - and that's where the 6-degrees came from.

If you're running a non-stock distributor, or even a stock one that has been altered so that it has "more" or "less" mechanical advance than it originally did, then the amount of initial timing MUST be adjusted to compensate for that in order to place the total advance where it needs to be for the motor under load at wide open throttle. It's the total that matters.

Bear


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## Chris-Austria (Dec 23, 2010)

Finally I have a plan of the timing-thing, thank you.
I'll test it on Tuesday and report the effects.

I'll set the distributor to bring in the full advance of 38° at 3000rpm and use a stop bushing that gives 20-22° of advance, so I have to start somewhere between 16-18° initial timing. Will this "high" initial timing have any other effects than better fuel economy, lower temps and higher HC?

If I can hear detonation with 38° I'll adjust the whole thing down to a point where it works better, but I'm pretty sure that I now have about 36 or 37° and that seems to work fine, but there is a bushing on my distributor that gives 28° of advance and a spring that brings in the full advance at 3200rpm.


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