New guy here, looking for some turbo ign timing help

[Idiocracy]

Hi all, let me start with the build. Its a chevy inline 6 (250) with forged internals, bigger valves, mid lift turbo cam, and a turbo obviously. EFI done by Fitech 600hp power adder system. I am not cntrolling timing with the fitech because I am currently running an HEI on mechanical advance only.

My issue is I have bad spark knock as RPMs climb because I am not pulling timing as boost climbs. I am also learning as I go. So I know I have several electronic options to pull timing, but I don't have the components to do that at the moment. I would like to try to use the vacuum / boost reference as a timing adv / retard control.

I am trying to understand what will happen to the idle and drive characteristics in the two following configurations

1. Lock HEI and set base timing without vacuum advance connected. Direct vacuum source.
2. Lock HEI and set base timing with vacuum advance connected. Ported vacuum source.

These are the only two scenarios that I can sort of make sense of in my head...I am sure there are others, which I would be very interested in learning.

This is kind of a rat rod thing, so if I can make it work without the digital timing control then that would be cool. If there is no way to get good starting / idle and driving characteristics in boost and regular, then I will swap to a conventional dist and MSD setup and let the fitech control the timing.

Whew...thats one hell of a first post. Thanks in advance guys.

[rebelrouser]

I have a LA mopar with a procharger and a Fitech, buy an MSD distributor and program the timing curve. I trtied a differant aftermarket one and the Fitech did not like it. I assume you have the one that is capable.
What I did was use performance trends engine software to plot a advance curve, I plotted one for the engine normally aspirated, and plugged that into the computer map for timing under vacuum, and then inputed a supercharger, and then plugged that curve into the computer map for boost, it worked like a dream, no knock, good fuel economy, and it runs scary good, on pump gas.

[Idiocracy]

I appreciate the feedback and that is seeming like what I am going to have to do but I was hopeful that I could get it functional (cruiser, not racing it) with the vacuum/boost reference.

[rebelrouser]

I am not smart enough to tell you how to retard timing for boost mechanically. I don't see how it would work. The only way I could see it would work was if the vacuum advance diaphragm, under pressure would rotate the plate attached to the points or pickup coil, in the distributor and pull timing out. Every mechanical distributor I have seen only adds timing as rpm and vacuum increases. Under load they will return to the starting point. But with boost they have to retard past where they would run good under no boost. I have seen adjustable vacuum advance units where you could control how much timing they add, but never seen one that will pull timing out.

[motormonkey]

The old turbo buicks and Pontiacs had vacuum/boost cans for distributers. With that said.
Your best and only option I believe is a map able electronic ignition. The biggest gift efi has given to us is the fact we can program where and when things happen. No reason not to use the tech to our advantage. Your half way there already.

[Roundybout]

I believe there are different versions of the hei module (Toronado comes to mind?) that will retard the timing 5-10 degrees when the 5th pin is grounded through a pressure switch. Sort of a budget home built spark retard for just your scenario.

[Firechicken]

I run my street turbo engine with hei locked timing below knock threshold which is 18 degrees for my setup. Vac advance connected to manifold source so I get good cruise timing and any boost pressure takes it back out.

Not very sophisticated - obviously - very simple and old school but it works well for me with no electronics needed.

[David Redszus]

I am not smart enough to tell you how to retard timing for boost mechanically. I don't see how it would work. The only way I could see it would work was if the vacuum advance diaphragm, under pressure would rotate the plate attached to the points or pickup coil, in the distributor and pull timing out. Every mechanical distributor I have seen only adds timing as rpm and vacuum increases. Under load they will return to the starting point. But with boost they have to retard past where they would run good under no boost. I have seen adjustable vacuum advance units where you could control how much timing they add, but never seen one that will pull timing out.

I am currently building a distributor for a BMW Turbo. The distributor uses mechanical advance and vacuum retard.
It could easily be adapted to provide boost retard. But getting the correct boost vs timing curve might cost a few
engines as part of the development cost.

Man, it's hard enough to get the boost vs fuel curves right.