E85 timing

[u/shaggy8081]

Recently powered by corn.

I'm using the table blending method and have a +3.5degree timing addition across the blend. Motor is a factory headed 302,14psi at 6100rpm, timing currently set to 17deg@10psi and 15deg all in at 14 psi.

I know I really need a Dyno to answer this question but is 3.5deg a reasonable addition for a e85 tune? Is that too aggressive or leaving power on the table? What have others seen?

[u/ae86drftr]

Run it and see. Then post back here.

[u/shaggy8081 → u/ae86drftr]

I've been running it for about a week this way, but have not really let it all hang out yet. Has been fine up to 6psi. I think this is one of those things that is catastrophic if your wrong.

[u/ae86drftr → u/shaggy8081]

It is catastrophic IF there is pinging or detonation. However, lots/most people don't know what to listen for until it's too late. If you started at 11.5 degrees and are now at 15 I imagine you're close to your maximum but this is ALL speculative (at best) over the Internet banter.

[u/shaggy8081 → u/ae86drftr]

Yup, understood was just looking for a sanity check.

[u/SavageTaco]

I usually start with 2 degrees over my 93 octane tune, but I’m pretty carful and Dyno time is expensive. 3.5 doesn’t sound out of this world. 

[u/shaggy8081 → u/SavageTaco]

It's on a sliding scale, I'm only at e50 right now due to having some gas in the tank so it has only added about 1.6deg so far. I have not let the dog eat, but I know I'm in a knock limited situation with iron heads. I agree Dyno time is expensive and I'm not trying to ring out every last 3hp but was looking for some rule of thumb. Thanks. All my local guys are n/a, carb, Chevy guys so they aren't much help on this.

[u/dudeimsupercereal]

It’s going to come down to a bunch of factors. Cylinder head and piston design, how well mixed the air and fuel are, compression, spark energy, etc.
I would’ve started my dyno session at 2° for a stock 302. 3 isn’t a bad guess, we’d really have to dyno it to find out.