switched to 91 octane......now what

[oldred95]

I figured enough is enough with 87 octane. The hottest we've got here is 91 but I bit the bullet and put it in anyway. So now what should I do? Never ran anything or tuned around anything but 87 octane and I'm not sure where I need to start. Timing?

[91chevZ71]

it's not that much more if you think about it, IMO.
maybe datalog some WOT runs and see what your truck can handle.
My experience has been that sometimes more isn't better- you already knew that, though. Maybe raise it in a particular area that you're looking to modify and then see what it can handle, then move to a different area. Kpa vs power felt, vs MPG, etc etc
who knows. Tuning timing has been interesting for me
keep us posted on what you change and notice, man. good thread

[oldred95]

it's not that much more if you think about it, IMO.
maybe datalog some WOT runs and see what your truck can handle.
My experience has been that sometimes more isn't better- you already knew that, though. Maybe raise it in a particular area that you're looking to modify and then see what it can handle, then move to a different area. Kpa vs power felt, vs MPG, etc etc
who knows. Tuning timing has been interesting for me
keep us posted on what you change and notice, man. good thread
Talking to Fast and my timing curve was lame and way too fast. It started low and leaped high. He said I need to start it higher and ramp it slower so I've got a new curve and it looks good on the screen but I haven't tried it yet.

[91chevZ71]

start it higher and ramp it slower

mine is like that too. I'm using one of his 355 vortec tables with some changes.

[oldred95]

Well I put about 25 miles on it today with the new timing table and it responds completely different then it did before. On the highway its running 16-17% throttle now instead of the 20-24% it ran before. Its not falling on its face after the shifts either. Need to recorrect the VE's but so far I think it was worth the switch to 91.

[PHATSPEED7x]

I can't afford 91 octane, but I can get mid grade 89 octane for the same price as regular at the station I fill up at so I just go with that.

[oldred95]

Price gouging son of a beeches here are rediculous. Down south the posted price for unleaded was 2.85 so I pull in and look at the pump and 91 octane is 3.15 a gallon. Nothing like 30 cents a gallon markup over 87. So I went to the station by my house and its 2.89 for 87 and 3.09 for 91 so I filled up. I don't even like a 20 cent markup but its better then paying 10 cents a gallon more for the same thing at the other station.

[PHATSPEED7x]

Do they even offer mid grade where you live?

[oldred95]

Do they even offer mid grade where you live?
Yea...

[GarnerZ]

i started to run high test in my white truck right before i sold it and with tuning it make a difference

[oldred95]

Doing some more datalogging and I haven't really gotten into it but so far the most knock counts I've accumulated was 2 and I'm betting that one on engine noise because I have some rockers ticking like mad. I am still experiencing a little bit of a soft spot in the power band after shifts and when the engine is lugged. Also at cruise I can tell its running so much freer but it feels like there might be a little more left in it. Seeing that there are no knock counts and I'm only getting 12 mpg city I bumped the timing another 3 degrees or so over the entire table (just for now and adjust it accordingly where it needs it after logging) and I'm going to see what that does. I really didn't expect to see this kind of spark knock reduction with just 91 octane. On 87 octane with a lame timing curve I was still picking up maybe 10-15 knock counts over a period of several WOT runs. The thing I'm curious about is come summer time when the air gets nice and hot. Got this bad feeling its going to spark knock like there's no tomorrow.