Ignition timing tech you probably did not know!

In this, episode 120 of PowerTec 10, DV details what an engine needs for the most efficient use of the fuel involved.
Knowing the "why's" of ignition timing can result in a far smoother and lower idle RPM as well as a more authoritative "lope" when a big cam is used. He talks about one big cammed 500 inch test BB Chevy motor that, on the dyno, idled at an amazingly low 200 RPM!
All the advice applies to both carburated and EFI motors be they street or race. A smooth and consistent idle, whether it has a big cam lope or not is the mark of professionalism. This video shows just how to do it.

[philzellmer]

Great video David! I've been trying to convince others about manifold vacuum for street use for nearly fifty years now. Some get it, others don't. It's ok though, my car pulls their's in straight line accell anyway!....Thanks again for the great work!

[Crazyts]

this guy is a mastermind of mechanical knowledge

[gergatron]

I have one thing to note about using vacuum advance straight from manifold. When using a stock-style distributor, I did achieve a very smooth and quiet idle (heard through the exhaust), along with great steady-state cruise and light throttle performance with direct manifold advance.

However, when the throttle was opened under even moderate acceleration, there was a moment of severe detonation as the vacuum canister responded to load. No matter what timing setting I tried, there was no compromise or getting around the slow response time of the vacuum advance. In the end, I installed an MSD 6AL programmable which has a MAP sensor input (equivalent to a vac advance) but you can fully customise the entire vacuum curve, as well as the rpm curve, and the timing response is instant.

I am currently running around 28 degrees at idle on a closed chamber, 10:1, mild-cammed 302 Cleveland. Approx 45 degrees total under vacuum, back to 35 under load.

It starts first kick with no choke and one pump of the throttle (even in winter). Idles beautifully at 850, only time I ever see a hint of detonation is when in traffic on a hot day and the temp is above 3/4 (which is rare). I run E10 exclusively, which my engine loves the most.

I most certainly agree that the vac advance at idle should be maximised, but in my experience, using the canister (which requires physical actuation) does not pull timing back quickly enough to allow safe acceleration. Using a programmable electronic ignition provides an instant response.

[danielmauter]

Dr.David!!. Excellent as always!!. I've been following you for 35+ years following a purchase of one of your books at a Swap meet. Then every time a new one came out. I jump on it. I'm sure I have a dozen already. Take care and God Bless..😊

[tylervassar]

Thank you so much! I've screwed around with timing and mixtures for years but never pit it into the proper sequence. It's like a slap in face looking at it now.

[Adrenacyde]

DV: In the next installment of this Topic, can you please include the nuances between in and out of gear idle when using an automatic transmission? There usually isn't a lot of clarity here.

Take care!

[dadalebreton]

For the common backyard mecanic who always been learning from usual mecanic so called "experts", its hard to know the difference sometime from what is good and what is best when we were tought "This or That" way. Realizing some teachings were not always the BEST, is sometime difficult to master without starting all over again. Thanks for sharing these gold knowledges. I respect you and Andy very much for what you and everyone who does there best to help us, New and old backyard DIY mecanics and race lovers. Happy New Year everyone !

[petercermak]

Hello Mr. Vizard. New subscriber here. Been watching your videos and taking notes. Wish I found you back in 76 when I started building my street cars. Saw a recent video from Richard touting the benefits of LSA selection. Looks like he switched camps!

[alanwilliams]

Regarding the comments on your Holley book, I would just like to say that I own many of your books, starting with your Mini books when I was a young man starting out modifying and racing cars, I would consider any book or article written by you as the best on that subject, and your videos here are the same - and thank you for being so generous with your knowledge.

[AlexJonesWasRight]

Proud to say I have a Progression Ignition HEI on my 400 SBC!

[sidecarbod]

My understanding is that as long as an engine conforms to the accepted standards such as conrod ratio, bore to stroke ratio and things like that then any engine will want peak cylinder pressure to occur between 14-20 degrees ATDC, this is a purely mechanical thing, it is to do with the angle that the conrod forms with the crank, the likes of Ricardo worked this out years ago. The graph at 15:34 shows peak pressure a little later at around 20-22 degrees but at least its in the 'ball park' with what I have read. All of the tricks that we have to do with mechanical advance and vac advance is all to achieve peak cylinder pressure at the right point in crank degrees on the power stroke. Obviously an engine operates in many different 'modes' and at a range of RPM's such as peak RPM at WOT and mid range RPM with the throttle just cracked open (and different AFR for different modes), all of this stuff effects the burn speed which is why we need to adjust when we light up the mixture in the first place. I read some interesting things about how to select a vac canister, basically if an engine pulls lets say 18" on idle then you must select a canister that is 'all in' with 1.5-2" less vacuum, otherwise the timing will bounce in and out. I found it quite hard to find suitable canisters for some engines, the programable MSD 6AL running a locked out dizzy and a MAP system solves the problem nicely!

I recently had a big argument with a "professional" 2 stroke tuner here on youtube, he stated that he was working towards getting peak cylinder pressure at TDC! I quickly concluded that he is an idiot!

[goldsgarage]

Great video David. An affirmation of a video I made recently on ignition timing.
I also enjoyed an article you co authored with Steve Davis DUI ignition strategies. I would like to Post it on my channel, credits to you and Steve. Allan Gold
I am planning to be in NC in April. I would enjoy meeting with you.

[rotaxtwin]

That's good info. I had a reasonable understanding of combustion chamber events but DVs deep explanation & gripping sound effects help to bring it home.

I think i will be watching parts of this again & again.

[mechanknuckle]

I'm a classic car mechanic (currently at a British Specialty shop) and even though I now deal with Jaguar, MG, Austin Healey and Triumphs with SU, Stromberg and Weber carbs, I keep the How to Tune a Holley Carb book in my box. Ignition and Air/Fuel principles apply across all cars with carburetors. From time to time we get Holley's coming in on something, and even though I can rebuild a Holley with my eyes closed-- TUNING one to perfection is always worth opening the book.

[brocluno]

Good episode. Some aviation folks have been flying "Lean of Peak" for decades. That is they keep leaning their mixtures to peak EGT and then they keep going until the engine gets to weak to maintain RPM. Then slightly fatten up and fly on. This is to save fuel on long cruises. Airplanes don't have vacuum advances. But they do have wide ranging mixture controls 😊

[monadking]

You always have great information. I am still a carburetor guy. I remember when Excell was in Branford Ct. and went to their car shows and have one of their duel ponts distributors. Now they are in Meriden, which I have driven by many times and remember the good old days. I can't wait for warmer weather now to get back to my 55 Chevy with a 355.

[PetesSnakeBiteKit]

This is one of the best videos so far. You stretch my brain like Smokey did. Thanks!

[groundpounder]

I'm sitting here wide eyed wishing I could just open up my head cheese and scoop this knowledge in. When I was a teenager 25 years ago, I felt the same way when cousin John came to town and tried explaining the principles to me out of his notebooks filled with equations, telling me the stories from racing on John Bradley's team before Manthis engineering came about. All them family members aren't here anymore for me to ask now that I am trying harder to comprehend the knowledge. Gentlemen like you willing to share the intricate details of their knowledge are priceless. Let's face it, quickly becoming a lost piece of the passion for the hobby when the technology exists for my kids to just bolt stuff on and let computers take over. I would stand in line for a tech seminar or event, just to try and absorb what I need to really enjoy my old Fords. I'll get there, just need to set your channel on repeat

[markerwin]

David, I cannot thank you enough for making this video.

This information is priceless, and nearly impossible to find online, as there are too many people out there with opinions rather than facts. I've been searching for this *exact* information for months, and you sir are the ONLY source I could find with reliable, specific, universally applicable step-by-step guidance on how to set up a Holley idle circuit perfectly.

While this information might be in a book somewhere, us young guys dont have mentors with enough experience to tell us what books we can turn to for this info, and most book stores don't carry the good stuff like they used to.

Again, I thank you. I thank you A LOT. You are a true hero to the hot rodders.

[andrewforrest]

When it comes to reviews on anything, I’ve always said most people that leave bad reviews on products are also the ones who are expecting that product to do or contain something that wasn’t even advertised. I’ve been reading David’s books and watching these videos for awhile and he is one of very few people that actually wants to pass on all of the knowledge he has for those willing to pay attention and listen. I would be more than happy to know just the things that he’s forgotten. Keep up the amazing work Mr. David