[69synfulSS]

Im trying to set the timing correctly on my street driven 383 Stroker. It has HEI ignition. I set the timing to 8 degrees before TDC and about 1400 rpms when it is in park...without the vaccum line attached to the carb. It has a large hydro roller cam and solid roller lifters, so my rpms have to sit a little high or it will shut off. When I attach the vaccum line, about where should I see the timing sit at idle with it in park? My idle RPMs shot way up and Im sure the timing did as well. Any ideas? Also, the motor will "diesel" a little when I shut the motor off if the vaccum line is not attached. This is really starting to tick me off so any info anyone could pass will be greatly appreciated.

[jrubakon]

You should read the timing 101 in the performance section. It talks about alternate vaccum canisters for motors that have too little vaccum at idle. I would start there. It sounds like your large cam is the issue.

[Steptoe]

Read Johns 101 to understand what and how timing works...And the difference in ported vaccuum and manifold vaccuum VA.
Get timing wrong and slow death to an engine is not uncommon...usually blamed on component failure. Detonation (melted pistons) is not the only issue, valve ressentio, burnt, big end and small end +crank failures all can be traced back to bad timing curves while th owner thinks the engine is running well..

There are 2 current threads and several older threads talking ppl over several weeks thru the whole dialing an engine, establishing tuning specs.

[ace's68]

Your vacuum advance can deploys way too soon.
You need a can, or an adjustable cam that starts to deploy a few inches above your idle vac. Common problem when using a big cam and a vac. can that isn't designed for that purpose.

[69-Pace]

Sometimes the search here at TC doesn't find it, but over at CRG its a menu item.
Here you go:
http://www.camaros.org/pdf/timing101.pdf
http://www.camaros.org/pdf/map_advance.pdf

[Steiner]

A true HEI vacuum can usually has way too much advance for a performance engine with the proper timing curve, and the rate is usually too fast.....usually 22 degrees or so pulled in at 20" of vacuum or around that. You want to set up your timing correctly without the advance hooked up. Then if you want to use the HEI canister you'll have to use a limiter plate to dial in the vacuum advance and reset your idle and mixture accordingly. If it's not an adjustable can for rate, that is also difficult to do. MSD makes limiter plates for theirs (used to run one myself) but I don't know about others.

[Steptoe]

Brian that map advance pdf thats very good...excellent.
note the 6 deg intial and 30 deg in the cent...
And the VA selection...
And that if the VA is removed idling on the intial advance, the car is likely to stall....for that to happen the carb idle circuits need to have been dialed in... if they have been it would be save to say the other carb ciruits also... and the only way to do that accruately is with 02 or sniff with the nose.

He is talking dwells...points, these are the curves of pre HEI era which we are replicating back.

I liked the masking tape rather than the taylors tape I have been using...makes marking and stamping the balancer as I do easier.

Put Johns 101 and that document together...

[cool rocking daddy]

8 degrees before TDC is woefully short of the initial that cam wants. What is the duration at .050? 220? You should have at least 12 degrees intial.

Here is an article on how to time an engine with an HEI and even gives you the vacuum advance can recommedations.

http://www.73-87.com/7387garage/drivetrain/hei.htm

I cannot believe how many people on this site are trying to time their engines using stock numbers but don't have stock cams. Anything other than a stock cam, throw the stock timing specs. away! You won't destroy bearings, burn valves, blah, blah if you don't put so much total timing in it that you are at detonation. My god, people, do an internet search, ask your local hotrodders at the next cruise. You'll find most people with even mild performance cams are running at least 12-14 degrees intitial. Many are running 18-20 initial. That high of initial means they are limiting the mechanical advance in the dizzy. That is a MUST when running the high initial your cam needs and wants.

[Steptoe]

You won't destroy bearings, burn valves, blah, blah if you don't put so much total timing in it that you are at detonation.

For Christ sake put a bloody sock in it....you keep prompoting old school bs with nil or very little understading of timimg, why it is there, mixtures and how they relate, nor the implications when these are wrong

My god, people, do an internet search, ask your local hotrodders at the next cruise

We have Dennis try explain, John with the 101

As many of you are aware, timing and vacuum advance is one of my favorite subjects, as I was involved in the development of some of those systems in my GM days and I understand it. Many people don't, as there has been very little written about it anywhere that makes sense

Now if u wish to discuss or debate the subject fine....but it seems all can be suppied is links....If you do have a good understanding of timing in these old pre pollution addon designed engines, you should be able to not only to state your case but the technical reasons inside the engine as to why.
You are unable to get your head around the simple concept of intial is what the engine fires up on and idle is intial+VA...
Or the concept increasing intial increases the curve and total which if over advanced cause issues like slowly burning holes in pistons, burning valve, resseetion and loading cranks and bearings
The concept of establishing each parameter of timing and carburation , then mapping that in the carb and dizzy
The concept of running knock sensors, TPI . IMAP, O2 on non ECU engines.. Hell I doubt if u are even a here what the 5th terminal is on a later model GM HEI....funny that its a knock sensor...before ECU and EFI.

You want to promote this old school tune by ear, wack the timing up which id the horror of engine builders and engine failure, rather than parts...which also gets into collapsed piston skirts, cracked pistons etc.
I doubt u have ever been into or even involved in engine failure forensics... that is a real eye opener.

http://www.camaros.org/pdf/timing101.pdf
http://www.camaros.org/pdf/map_advance.pdf

upping advance to limits does make a car with a carb with bad AFRs run better... because incorrect mixtures burn slower.....upping advance in this is simply a patch 'fix' that doesnt even come close to full potential of and engine..
And as you conceed, how many "hot rodders at a cruise" can afford a data logger?
Well as it happens, If u wish to go thru these forums, a lot do.....
Think about it spend a few 10s of thousands on a car, thousands on an engine, and not to be able to afford a data logger or have professionally tuned by a compentent dyn techniction (both about the same cost)...thats basical stupid
Thats like doing panel perfect, then not paint the car.

Now to quote from your link..this guy has a lot right BUT

Centrifugal advance: Stock the advance mechanism is pretty good but the stock springs are usually way too strong, causing the advance curve to come in too slowly, if it ever gets fully advanced at all. All you need are the right springs and the right initial advance setting. Most Small Block Chevys like about 32-38 degrees total advance at WOT. Since we know already that the HEI has 20 built into the stock mechanism the first thing we need to do is set the initial advance correctly- that means you need an initial advance between 12 and 18 degrees (you might want to retard it 2-4 degrees for daily street use just to build in a little safety margin).

This is because he doesnt know how to adjust number of degrees in a GM HEI... toi convert from a post pollution dizzy spec to a pre polltion manifold vaccuum dizzy, with out EGR!!!!!
So it seems u have no idea of the effect of EGR, or more accuratly the timing requirements of EGR over non egr..and the effects on the engine.

To be able to give a timing for a given cam is impossible....timing depends on mainly compression at peek pressure, bore to stroke ratios, fuel type and octane, and mixture. And how some of these relate back to cam design.

So I repeat... read Dennis explantion on how to tune in, those 2 links....sure there are a couple approaches that seem on the surface different.. but at the end of the day the results are accurate.

If you wish to debate a subject that you claim to be knowledgable about... tell us WHY we are incorrect, show u have understanding of the internal inplications from starter armitures to timing of peek pressure of a given engine, dynamic compression ratios.

You won't destroy bearings, burn valves, blah, blah if you don't put so much total timing in it that you are at detonation.

There is far more to timing than detonation, and detonation is not neccassry audable,
Like firing peek pressure out side the 12 to 18 deg ATDC,AND which is why I state do not exceed 40/42degrees all up without using a knock sensor.

Now sit down, actualy read ,not scim, understand what u are reading .....with an open mind... then tell me Dennis, John, and others, including those who have followed the process and end up with better, more reliable, more torque/HP, and economy..... why we are wrong.

[DjD]

Would you two quit having a public pissing into the wind contest! You keep chasing each other from thread to thread and all it's doing is taking away from your credibility... I don't agree with everything posted by others and I'm sure not everyone agrees with everything I post. Like most, the best way to do this is just post up your advice and let the readers sort it out based on their own research as well as what they read here.

[ace's68]

Originally Posted by DjD

Would you two quit having a public pissing into the wind contest! You keep chasing each other from thread to thread and all it's doing is taking away from your credibility... I don't agree with everything posted by others and I'm sure not everyone agrees with everything I post. Like most, the best way to do this is just post up your advice and let the readers sort it out based on their own research as well as what they read here.

Well said.

[cool rocking daddy]

Originally Posted by DjD

Would you two quit having a public pissing into the wind contest! You keep chasing each other from thread to thread and all it's doing is taking away from your credibility... I don't agree with everything posted by others and I'm sure not everyone agrees with everything I post. Like most, the best way to do this is just post up your advice and let the readers sort it out based on their own research as well as what they read here.

Agreed. That is the reason why I post the links that I do. These are industry experts that have taken the time to write articles that answer the very questions it seems a lot of people on this board want answered. The only reference I have made to our fellow member from down under is that it is disingenuous to bring up valve stems, starter armatures, and the like when addressing this issue. From now on my answers to questions like these will be addressed by me to the OP in private messages. Seems to be the only way to have an intelligent conversation about the topic.