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ignition timing at WOT question

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ignition timing at WOT question

Postby Belgian1979 » Sun Nov 02, 2014 3:02 pm

This is a question related to EFI, but with some comparison to the conventional distributors used on SBC gen I's.

Let's assume WOT. Usually a SBC is given 36° or around that as maximum advance coming in at around 2800-3000 rpm. It stays there in a conventional distributor because the weights are maxed out.
In an EFI system it is possible to put less spark in at higher rpm, like 33 or 34 or so. Would this be benificial because the mixture is more homogenous and due to the higher compression pressures the burn rate is supposed to be faster or would it be better to have it stay at the 36°.

I currently have 36° from 2800 rpm onwards to max rpm. I was thinking of bringing this down somewhat to say 33° at above 4000 rpm. However my engine is a large bore short stroke, long rod combo which would play a part as well.
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Re: ignition timing at WOT question

Postby BOOT » Sun Nov 02, 2014 3:44 pm

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Re: ignition timing at WOT question

Postby lada ok » Sun Nov 02, 2014 3:47 pm

Hypothetical question really
Only you'll know by testing.
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Re: ignition timing at WOT question

Postby MadBill » Sun Nov 02, 2014 5:38 pm

It would take a fair bit of dyno time, but with the full control of spark advance in small RPM increments as provided by most EFI systems, you can develop the 'perfect' curve then adjust overall or 'here and there' as required, guided by street and/or track results. For example the old TPI long runner Camaro/Corvette pulled out several degrees in the resonant tuned RPM range (~ 3200 RPM, AIR). You might find that above peak torque slight increments are required every 500 RPM up to red line.
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Re: ignition timing at WOT question

Postby 140Air » Sun Nov 02, 2014 9:02 pm

MadBill wrote:It would take a fair bit of dyno time, but with the full control of spark advance in small RPM increments as provided by most EFI systems, you can develop the 'perfect' curve then adjust overall or 'here and there' as required, guided by street and/or track results. For example the old TPI long runner Camaro/Corvette pulled out several degrees in the resonant tuned RPM range (~ 3200 RPM, AIR). You might find that above peak torque slight increments are required every 500 RPM up to red line.


Bill is right, this is the way to go. I'll just add that IMHO if you have a ping detector (and you should have one) and especially if you have automatic ping retard, you need to monitor it. You might make best power at the verge of pinging or not, but you definitely don't want to get into heavy ping and you don't want to trigger automatic retard.
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Re: ignition timing at WOT question

Postby nitro2 » Mon Nov 03, 2014 10:03 am

MadBill wrote:It would take a fair bit of dyno time, but with the full control of spark advance in small RPM increments as provided by most EFI systems, you can develop the 'perfect' curve then adjust overall or 'here and there' as required, guided by street and/or track results. For example the old TPI long runner Camaro/Corvette pulled out several degrees in the resonant tuned RPM range (~ 3200 RPM, AIR). You might find that above peak torque slight increments are required every 500 RPM up to red line.


or......... the perfect curve could be dialed in, in 3 engine tests, even without a dyno, using our equipment. The first test to see where the engine is at, as is, the second test to see where the engine is at with the recommended adjustments made, and the third test only if the second test was not perfect.

Automatic optimization of the combustion process relative to TDC (for all rpm blocks), saves a lot of time and brain power :)
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Re: ignition timing at WOT question

Postby Sweet P » Mon Nov 03, 2014 10:43 am

nitro2

"or......... the perfect curve could be dialed in, in 3 engine tests, even without a dyno, using our equipment."

Can you educate me on your equipment?
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Re: ignition timing at WOT question

Postby nitro2 » Mon Nov 03, 2014 4:26 pm

Sweet P wrote:nitro2

"or......... the perfect curve could be dialed in, in 3 engine tests, even without a dyno, using our equipment."

Can you educate me on your equipment?



Our combustion pressure analyzers do the regular things like record cylinder pressure and/or port pressures relative to crank angle, determine IMEP, IHP, IT, VE per cylinder per combustion cycle, energy release and energy release rates per combustion cycle etc. etc. etc.

However, not so commonly found, and relative to my statement above, our equipment will automatically go through every combustion cycle of every instrumented cylinder and determine how much sooner or later (in degrees) that the entire combustion process should have occurred, in order to have made the most uumph (IMEP, IT, IHP) for each and every combustion cycle. The software then automatically plots how far off of optimal the combustion process is located (in degrees) vs. rpm. The end user uses that knowledge to program in the relevant changes in ignition timing, so that the combustion process will be optimal for all rpm blocks for the very next test. If the programming changes were done correctly timing will be perfect for all rpm blocks on the second test, if not then one more iteration (test) will do the trick.

Obviously if after that some other kinds of significant mods are made to the engine, it might change things enough that the combustion process location has to be re-adjusted again, but that only takes another 1 or 2 more tests.
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Re: ignition timing at WOT question

Postby jmarkaudio » Mon Nov 03, 2014 9:32 pm

Where do you get the pressure readings from? Do you have to drill holes to the combustion chamber or can it be done with a modified spark plug? I actually have a set of SB2.2 Hendricks heads that have combustion pressure ports drilled.
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Re: ignition timing at WOT question

Postby nitro2 » Mon Nov 03, 2014 11:09 pm

jmarkaudio wrote:Where do you get the pressure readings from? Do you have to drill holes to the combustion chamber or can it be done with a modified spark plug? I actually have a set of SB2.2 Hendricks heads that have combustion pressure ports drilled.



The combustion sensor can either be in the spark plug, or in the head itself.

I always find it curious that OEMs have been tuning with combustion pressure for years, but they never make the production heads with the combustion pressure ports left in them.
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Re: ignition timing at WOT question

Postby Belgian1979 » Tue Nov 04, 2014 5:59 am

I agree that something like that looks like a great tool and I remember you spoke about this before, unfortunately this is way beyond my budget.
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Re: ignition timing at WOT question

Postby Sweet P » Tue Nov 04, 2014 8:15 am

Nitro2 do you have a website?
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Re: ignition timing at WOT question

Postby jacksoni » Tue Nov 04, 2014 8:27 am

Sweet P wrote:Nitro2 do you have a website?

click on his name and the board takes you to the persons information including email, PM, websites etc to the extent the individual wants this information published. Clint (nitro2) is really good about information and emails about his system.
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Re: ignition timing at WOT question

Postby dieselgeek » Tue Nov 04, 2014 9:42 pm

I've used parts of Clint's equipment (the combustion pressure sensors and logging) and it worked really good once I got the hang of it. It's ridiculously easy to build the perfect timing curve in a few tests on the dyno. However, Implementing and characterizing knock sensors is not as easy as it would seem. I'm sure Yves can find the best timing and fuel mix using the standard practices hotrodders have used for years . If he wanted/needed to make changes to ignition timing based on RPM, MAP, coolant temp, inlet air temp, or just about anything else - he can do it pretty easily now. This is reward of seeing a first-time EFI project to completion.
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Re: ignition timing at WOT question

Postby nitro2 » Tue Nov 04, 2014 10:37 pm

Belgian1979 wrote:I agree that something like that looks like a great tool and I remember you spoke about this before, unfortunately this is way beyond my budget.


I remember. I wasn't suggesting our equipment as an option for yourself in particular, I was just giving Madbill some FFT :)
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