1969cutlassS

I have a 69 rocket 350 (number 5 heads) rebuilt with mid RV cam and converted it to TBI EFI using a late 80s 307 distributor and late 80s TBI used on GM trucks. The computer has been modified with an EBL Flash daughter board allowing complete tuning of the setup. Everything runs great but I'm questioning what the base timing should be? The computer controls all the advance and timing but needs a reference as to what the base timing is. I've set it at 10deg but the factory spec for the 307 olds that used this HEI EFI distributor in the 80s is 20 deg base. Any thoughts on what the base on an older non emissions 350 with this distributor should be?? Noting again that the advance and timing are all controlled via the ECU.

Also, if anyone has done a similar conversion I would be interested in the timing curve/table best suited for this.

olds 307 and 403

Having a custom curve will help a lot. I still say 20 degrees is a good base timing. What compression ratio and cam? I ran right around 20 base with the lazy 94 sbc swirl port 350 curve. I had 8.5 to 1 and a 204/214 cam, it had mid 50's part throttle timing. I just pulled a 454 TB off my shop floor, has me thinking TBI again.

1969cutlassS

69 350 so about 9.5:1 compression, cam.... not sure the exact one. Engine guys said it was just a mild RV cam better than stock.

So here is a quote from the guy that created the EBL Flash setup I mention. He is quite the EFI guru. I guess on a total computer control setup the base timing is only used for cranking, other than that the ECU controls it all. The EBL even lets you set the idle timing etc a long with changing everything in regards to the SA timing tables. So if I'm following as long as the engine starts fine at base below 20, like the 10 I've got it at, it gives you more wiggle room to tune above and below this value where required. I'm still trying to figure out why the stock 307 from the factory was 20deg.

Quote:
The base distributor timing affects two areas:

It sets the at-cranking spark advance. It cranks at the base timing. 20° is usually too much.

It affects the minimum and maximum possible spark advance when running. Only so much retard or advance can be programmed into the distributor before the cap/rotor cross fire.

RetroRanger

I think what the quote is saying is 20* base will be the min value, and 20* + mechanical advance + vacuum advance will be the max value.

I don't know if 20* is to much, but if you knew the vac advance and mech adv amounts you could guess where to start. Usually something like base setting plus mechanical is around 34* add in vac adv to reach 48+ total *

I realize your set up is CCC but if you know the other advance numbers base timing works w those

1969cutlassS

Well it's not a Computer Controlled Carb setup but a Throttle Body Injection setup. The distributor itself doesn't have any mechanical or vacuum capability at all. It's just static. You could possibly use some none computer controlled values from another engine to construct the SA (spark advance) table but in reatity if you know your starting point and ending point it's not hard. The Base timing in the case of EFI computer controlled is just as he says, for cranking purposes. The rest of the timing is all entered in your SA tables and can be changed. There is places to set your idle SA etc. All table you enter that work together. They are not added to the base value but it's rather just telling the computer that this is what the distributor is at so it can advance and retard from there your tables etc. It's actually quite a slick setup. Check it out on his website and also read his Intro to Tuning 1&2 if you're interested on the same page. dynamicefi.com

RetroRanger

Sounds pretty cool, I will check it out.

FYI my current base on a BBO is 12ish when I had a sbo I ran 16-17. much more than that I would run into starter push back when hot

olds 307 and 403

The low compression Olds V8's like/needed a lot of part throttle timing for emissions and decent performance, hence the 20 base number. You probably have a 204/214 cam, which is small with 9.5 to 1. I hope you are running 91 octane and non ethanol if possible. I tried various base timing and close to 20 ran best but you have a point higher compression. I would add 5 degrees base timing, especially if you have A/C, it will help stabilize the idle. You should be able to put your spark advance wherever you like, how quick it comes in, how much part throttle and full throttle timing. Make sure the knock sensor is good and torqued to 11 ft/lbs.