Can a cooler plug require a timing adjustment?

[65bug]

Hi guys,
    I made a few changes to my 2165 motor this weekend and wanted some opinions from you guys.
   I changed out my plugs from the Bosch W8AC to the NGK B6HS. I also added a Mallory Unilite electric filter. This goes between my coil and Unilite distributor. The electronic filter is supposed to clean up any dirty electricity, stop power surges etc. from getting to the electronic module in the distributor and frying it.
   Well, after installing the filter I noticed my idle dropped to about 600! After checking my CFM intake there was not much room for adjusting the idle without it soaring up to 7-8 on each barrel of my 48 dells, so I loosened my distributor and advanced the timing a bit to bump up my idle.
     Took the car for a spin and WOW! Like a different motor. Woke it right up. Feels like it has 30 more HP. So I got out my timing light and when fully advanced I am at about 38!!!!!! What do you guys think? No pinging, runs cool but a little lump at idle.
     Man I think a dyno tune may be really worth the money.

Thanks!

[Simpsonshoe]

An engine is happy where it is happy.. You don't tell it.. It tells you.. If it is running strong and cool.. no pinging , passes the dip stick test etc .. maybe it is happy.. Not every engine is the same.. And to answer you question.. Yes, sometimes, maybe, it depends.. But, basically, Yes...

[65bug]

Thanks Mr. Simpsonshoe. Nobody else was interested in answering this question. Too basic I guess! I was hoping it would start a discussion on the subject, as everyone is so fixed on keeping advances timing at 30-32 degrees.
     My car starts up better then ever now at a fully advanced 38 degrees. However, this is just what my timing light is giving me and it is a old gun. I have a feeling it may be off a bit. Does anyone know if you can check the vacuum on the Dellorto 48 port and get a accurate number. It is at the bottom of the drivers side carb.

Thanks

[hotrodsurplus]

So I got out my timing light and when fully advanced I am at about 38!!!!!! What do you guys think? No pinging, runs cool but a little lump at idle.

It's true that you should give the engine what it needs but your engine is telling you that it needs something at one end of the bell curve. It's sort of akin to a patient telling a doctor that he/she needs 5,000 calories a day. That very well may be true for that person but there's likely an underlying problem like a 500-pound patient. Ignoring either one will likely lead to undesirable consequences.

A number of things determine what an engine needs for ignition timing but the first ones I'd look at are combustion-chamber design (which includes deck height), insufficient compression ratio for the cam timing, and excessively rich jetting.

Very large combustion chambers (ones opened improperly to unshroud the valves and others cut for semi-hemi) require the flame to propagate over a larger area. You can also transform an otherwise very efficient chamber into a poor one by using a lot of deck height (the distance between the piston crown and the flat or 'quench' area of the chamber). Just as it takes you more time to walk across a larger parking lot, it takes more time to propagate a flame over a larger area. Advancing the timing increases the combustion duration which can help burn more fuel but at a whole bunch more cost like increased heat transfer into the heads and piston crowns. Also, latent fuel far from the plug in a large chamber is more prone to ignite independent of the ignition event. This preignition can be a great contributor to harmful detonation. Questions: Do your heads still have the step in the chambers? Have they been semi-hemi cut? What's your engine's deck height, at least from the piston crown to the barrel top?

Cam timing and compression ratio go hand-in-hand. The cylinder's swept displacement and the deck and chamber's fixed displacement determine the static compression ratio but the point where the intake valve closes determines its effective compression ratio. Here's the thing: you can't alter one without altering the other to compensate. For example, increasing the duration without increasing the static CR to restore the effective CR will result in a very slow combustion event. Advancing the timing will burn more of the mixture but not all of it and at the same expense as it imposes with large chambers, most significantly increased heat transfer into the heads and pistons. What's your cam and compression?

Excessively rich mixtures resist combustion and tend to burn very slowly. Advancing the timing will generate more heat which can increase the burn rate but it can also invite detonation. What's your jetting (idle jet, venturi, main fuel, and main air correction)?

Almost every Volkswagen engine out there (even performance ones) suffers at least one of those problems, many, suffer two, and quite a few suffer all three so don't think you're alone. I would start looking into things before I just lived with 38 degrees total timing. Of the 1300-1600 engines the dual-port head has the 'worst' chamber design but only because of the step in the head. But even then, the 'worst' still requires only 32 degrees total timing. Flycut the step out and the chamber is as good as any late single-port chamber and those usually required only 30 degrees total provided the rest of the engine is tuned properly. I suspect something is afoot if the engine runs best with 38 total.  

Oh yeah, to answer your original question, a colder plug shouldn't require additional advance. However, a colder plug tends to load up and foul easier unless you're wailing on the engine all the time. I ran the NGK 6s for two seasons and didn't like the way the engine ran if I drove it like a sane person in normal traffic. It loaded up frequently. I converted to 5s and the loading went away. You have to 'read' the plug to determine if the temperature range is correct for the engine but I can pretty much guarantee that the hotter stock-range plug is better for your application.  

One last thing: you made two changes at once but you're suspecting the ignition filter of the problem when it may well be the plugs. The 'lope' at idle might be the plugs starting to load up. Why did you go to the colder plugs in the first place?

[65bug]

Chris,
     Thank you for taking the time to reply! I know it's a basic question in this forum, but felt if I could get some good info it would be here! Let me try to answer all the things you touched on and your questions.
The motor combo is as follows:
2165 CC
9.7-1 compression ratio
268 intake/exhaust Pauter cam 550 lift at valve w/ 1.4 rockers
Tims ported stage 2 heads. 42x37.5 valves. 5 angle valve job. blend ported cb big beef manifolds. 58cc and 90 deck. No semi-hemi.
Dellorto 48 drla carbs. 40 vents. I cannot remember the jetting, but can check. tuned with LM1 meter.
Everything new about 7 years ago. Maybe 1000 miles on motor. Weekend fun car. Not a daily driver.
    On the plugs, I could not find the W8 Bosch plugs anywhere! That's what I used to run and liked them just fine. Thinking I may go back to them, but looks like I will have to order them and wait.
    Drove the car this morning. Seems to run very cool still with timing advanced. 180 oil temps. 150 block temps. Exhaust at merged collector is 350.
    Any good spot to check temps with IR temp gauge to give me a accurate head temp? Right by plug?
    Thanks and have a good holiday!
 
     

[hotrodsurplus]

Hey, you're welcome for the response. Here are a few things.

2165 CC
9.7-1 compression ratio
58cc and 90 deck.

That don't add up. A 94x78 engine with .09" deck and 58cc chambers yields an 8.33:1 static CR. That's sufficiently low CR to run a stock cam with mid-grade fuel (I'm at 8.1:1 with a stock cam and still run 87-octane fuel).

268 intake/exhaust Pauter cam

That's the other variable for your problem.

Okay, the cam sounds like an M3 (268@.050 and 292 advertised). I don't have intake-valve closing specs on that one but since it's on a 108 LSA it's quite close to the Bugpack 4063-10 which I have specs for. That has a 296 advertised duration and closes the intake valve at 63 degrees ABDC. So knock two degrees off to make up the difference and the intake valve closes at 61 degrees ABDC (damn close for what we're doing if not perfect).

That cam produces an effective CR 1.48:1 less than static. So that means the effective CR in your engine is 6.85:1. As a general rule, with a close deck, good chambers, correct timing, and close jetting 87-octane fuel will support a 7.5:1 effective CR and 92-octane fuel will support 8.5:1 (some engines with great fuel and spark control and super-duper chambers can bear much more). So 6.85:1 effective is really too low to develop adequate volumetric and thermal efficiency. That right there is why your engine doesn't complain at 38 degrees advance.

I'd be willing to bet (and frankly hoping) that your heads still have the step in them. That step is around .055" tall. If it's still in there your true deck (distance from piston crown to quench pad) is .145" which is nowhere near adequate for efficiency or quench effect. If that step is there then flycut it out. That will restore the quench and reduce the chamber volume to about 50ccs depending on the chamber design. All other things being equal and assuming a 55cc chamber, the static CR will increase to 9.22:1 and the effective to 7.56:1. Again, 87-octane fuel is adequate to support 7.5:1 effective CR.

Even with the smaller chambers and increased CR you're still leaving a lot of performance on the table (not just WOT either) by running a .09" deck. As a general rule quench effect starts to come into play with a maximum .06" deck. That will yield a 9.94:1 static and an 8.13:1 effective CR. That's getting fairly close to the end of the easy zone with 92-octane fuel but if you get the timing right (probably 28 total) and the jetting good then it should run happily and not detonate.

If it were mine I'd flycut the heads and open up the non-plug-side of the chambers until they come out to about 52ccs and tighten the deck to about .05". Even though the compression would come out to 9.9/8.1:1 the slightly tighter deck will make the engine even more detonation resistant than it would be with the looser deck. A really thoughtful tuner could tighten the deck to .04" with the 52cc chambers for a 10.17/8.32 and still not encounter detonation simply because reducing the deck even further reduces detonation sensitivity to an even greater degree.

As a caution, I think you're really going to have to watch temps with that low compression and excessive advance. The slow burn exposes the quench area and piston crown to the combustion event for a longer duration and that gives the heat more opportunity to transfer into those surfaces. Essentially your engine is suffering the same shortcomings that semi-hemi heads impose.

On the plugs, I could not find the W8 Bosch plugs anywhere! That's what I used to run and liked them just fine. Thinking I may go back to them, but looks like I will have to order them and wait.

You haven't changed plugs in a long time, have you? Bosch renamed the W8AC to 7902 about 2 1/2 to 3 years ago. I actually prefer the NGK counterpart. The B5HS is the same heat range as the W8AC/7902. Most auto-part stores specify the B6HS for some reason but that's a colder plug and would make your combination run worse. Order B5HS plugs and enjoy. They're really nice.

Any good spot to check temps with IR temp gauge to give me a accurate head temp? Right by plug?

From my experience IR readings are inadequate. The surface remains considerably cooler than the interior volume. It's not impossible but it's unlikely that you're getting 180 oil temps after sustained use--the best built engines even when loping along at really low output still get in the 190 territory. I would suspect gauge accuracy at that point--a number of things like poor ground can make a gauge read funny.

Thanks and have a good holiday!

You too. Don't blow off any of your fingers. 
 

[65bug]

Hi Chris,
     You are correct! I have not changed plugs in a loooong time. These NGK's where the firs tones I have changed in probably 3 years or better! I get so busy with work, family house etc. the car just sits in the garage.
   I did however find a few of my notes and was incorrect on the deck. The correct deck is .014 Does that sound right to you as
far as getting closer to my 9.7-1 compression ratio?
      I cannot remember what my CC's where on these heads and I am still looking through paperwork to find it. I am missing a Berg book that has alot of my notes in it. It will turn up. I have a business and alot of paperwork and things filed away. I will find it!

Thank you Chris!

[neil68]

I was hoping it would start a discussion on the subject, as everyone is so fixed on keeping advances timing at 30-32 degrees.
     My car starts up better then ever now at a fully advanced 38 degrees. However, this is just what my timing light is giving me and it is a old gun.

I've had my 2332 cc on the chassis dyno a few times and it always makes the best power at 34-36 degrees full advance.  I've tried it at 30-32 and it runs poorly.  This is with several camshafts and CR's.  As long as it doesn't ping, then I leave it at 34-35 degrees.

[hotrodsurplus]

I get so busy with work, family house etc. the car just sits in the garage.

i can identify. I had to let a '32 Ford roadster sit outside last season.

The correct deck is .014 Does that sound right to you as far as getting closer to my 9.7-1 compression ratio?

If the heads have the step still in them then the engine would live with the .014" distance from crown to barrel top. And yeah, the CR would actually be upwards of 9.95 with 58cc chambers.

That still doesn't make sense, though. With that cam and static CR the effective still comes out to 8.14:1. That much effective with that much timing should rattle like a bitch.

[65bug]

Neil68,
     I have heard of quite a few people running at those numbers for timing. I am just wondering if I should invest in a newer, better timing light. I am going to play with it more this weekend.

Thanks!

     Chris,
        Thanks for all the help. Going to invest in a new timing light I think. I will get it sorted for sure!

Thank you

[65bug]

Hi guys,
    I finally got some time to drive the car around a bit more. It has been hot here in so cal too. At fully advanced 38 degrees the motor pings a bit when lugging the motor down a bit. This is on 87 octane. I filled the car with premium 91 and it went away completely. Motor oil temps are 190 degrees.
    I am going to back the timing down to 36 and see how that goes. Any suggestions?

Thanks!