Why is it that the TPI system seems to like having less timing in it than an older engine? FOr example: most people seem to say that when retuning a TPI engine with iron heads, about 29-30 degrees should be your maximum all-in spark advance. But with a carburetor like on my dad's 67 Camaro with a 406 and a holley 750 (or really any other iron head small block), 35-36* all-in is recommended, and typically earlier too, like at 2500rpm. Is it all about the heat management that comes with fuel being in earlier and therefore air temperatures a little cooler, or is it something to do with early and later head designs?

I ask this question because I have a 350 in my car with heads off of a '69 Camaro Z/28 302 engine, but a TPI manifold on top. I don't want to risk hurting the motor with 36* of spark when everyone on this site seems to agree that 30 is a maximum safe limit for TPI, but at the same time I can't help but feel that 35-36* would improve performance if it was all based on the design of older heads against a vortec head.

 

Typically the lower rpm peak torque area, 2800-3200 rpm, has less timing. Its the highest cyl pressure, more so than other sbc stuff. Nothing has the peak torque of a tpi motor like that, since carb intakes dont have runner length like that. At peak hp i found 34-35 still makes best power. Especially past peak rpm of 4200-4500. Usually helps power carry.

L98 heads are ok heads. But not like a vortec. So 32-35 deg at peak hp should be expected depending on compression fuel and other engine specs.

corvette aluminum heads however usually want more. 36 deg is typical. But still may be 2 deg less at peak torque, maybe.

non computer controlled timing setups using mechanical advance may have to set timing to come in early in order to have timing where you want it. Tpi being computer controlled you can command what you want it to have. But that 2800-3200 range is where you typically need to be careful with.

 

I would say the range is a bit wider, 2,400-4,000 rpm with a stock style LTR setup, 3,200 rpm being the lowest point of the dip. It is actually not uncommon for the timing to be lower around peak torque. This is a LS for reference. Good size dip in timing near peak torque at WOT.

 

Also in the TPI's GM put some of the total timing into the Power Enrichment subroutine. So the main table is not reflective of everything you get when you're not at WOT.

 

In my case, I zeroed the PE spark advance so my spark curve is all bound to the main SA table.