NicD

iTrader: (7)

No need to apologize, I don't advertise for a reason and I didn't take any offense. I just share lots of information to try to help people out.

I just see no real gain after a certain amount of timing on these lower compression truck motors and don't see a big benefit to running premium in them after LOTS of time and testing.

budhayes3

iTrader: (19)

Very nice gains, and you didn't have to give anything up down low either. Interesting about the low octane/ 26* of timing also, I'd be interested to hear more about this.

Fast355

This is what I found on a fairly modified 5.3. Keep in mind that the high octane spark tables in these PCMs are fairly unique and work very well, even on a modified engine. This is what I found on a fairly mild 2003 5.3 build running long tube headers, LS6 cam, and 2002 LS1 engine management system/tune. The first test was on 87 octane and the stock timing map. The second test was the same engine, running 6* more timing on the high octane map and Shell 93 octane. On an engine dyno, running NO accessories, and a truck intake/exhaust setup. I honestly did no see enough difference to run the extra octane and additional advance.

--------Test1------Test2-----Difference
RPM----HP---TQ---HP---TQ--HP--TQ
2,500--139--291--141--296---2---5
3,000--172--301--173--303---1---2
3,500--208--312--209--313---1---1
4,000--250--328--252--331---2---3
4,500--290--338--291--340---1---2
5,000--324--341--327--344---3---3
5,500--340--325--344--328---4---3
6,000--344--301--353--308---9---7

NicD

iTrader: (7)

Yea that was the part I really liked about it, nothing was really given up down low at all.

As far as the lower octane timing stuff goes I just don't usually see these 9.5:1 motors being octane limited much if at all. Meaning you can feed timing in to them at 87 octane and make just about as much power as you can with 91 octane. Just adding timing for the sake of running higher octane doesn't necessarily give you a noticeable gain when you are not octane limited. IE it may knock above 27 deg of timing on 87 but is it really making more power if it's set to 32 deg on 91 octane? Not in my experience but of course every combo is different but I am just talking in general.

NicD

iTrader: (7)

Just a few more things....

The stock 24.5 lb/hr injectors that are in my truck are very much at their limit. I am seeing ~95% at 6300 rpm at a 12.5:1 a/r ratio. I am not really worried about any problems arising from this but I am going to be looking for some bigger factory injectors to swap in at some point. Going to the marine 44 lb/hr injectors seems like a bit of overkill but I don't really see any other injectors in the mid 30 range that would work other than maybe stock car LS2 injectors but even then those aren't the right length, etc correct?

I found my good mic last night so I will probably try and take an idle clip tonight or tomorrow if anybody is interested in what it sounds like.

dlt76028

iTrader: (13)

regular 8.1L are direct swap and their 31 lb

NicD

iTrader: (7)

Ahh, but I won't have much luck finding those around here since most people don't pull them out like the vette and GTO crowd does for bigger ones. I am pretty sure I know of a couple of sets of the stock car LS2 injectors at some of the local shops that I can get my hands on for cheap, just don't know if they are a direct swap like the 8.1L injectors.

dlt76028

iTrader: (13)

might want to jump on these...

http://cgi.ebay.com/ebaymotors/Injec...ayphotohosting

budhayes3

iTrader: (19)

I got my 8.1 31# injectors on ebay for less than $100 shipped

NicD

iTrader: (7)

Yea, just looked at some LS2 car injectors and that's a no go. Only reason I wanted the LS2 car injectors is because I could take a set or two for free.

I will look in to the 8.1L injectors, thanks for that link on Ebay. Guess I just have to figure out what I really want to do with the near future and if it's worth it to get the 31# injectors or not.... cough... TVS...