reuter

hey im getting ready to run a 150 shot on my car and was wondering how an lt1 would respond to 103 octane off the nitrous. is there a major loss in performance? im wondering because id like to use 103 on top of my 6 deg timing retard on the shot but am i going to lose a lot of power until i squeeze? im prob not gonna hit the juice til 3rd gear so i need as much get up as possible through 1 and 2.

its a stock block and head lt1 only mods are intake, exhaust, ported maf and by the time i run it a 150 shot and 3.73s. thanks guys

Injuneer

You can't really correlate energy content and "power" to octane. That isn't what is measures. Many high octane fuels have a lower density, and reduce the pounds of fuel supplied by our volume based fuel delivery system - i.e. the injectors. And, the numerous components that make up the fuel each have their own energy content in terms of BTU/#, so you can't really generalize about the effects of using 103 octane. Most likely, it will be similar in "specific energy" content (BTU/gallon) to your basic unleaded pump gas, and you'l never notice the difference, except in your wallet. If it happened to have a significantly lower specific energy content than the fuel you regularly use, it might cost you some power, but it could (but probably won't ) go the other way as well.

I would wonder why you feel 103 octane is necessary at all, on top of 6deg retard. I ran the NOS 5176 kit on 93/94 octane pump gas with a 150-shot on a setup similar to yours, no retard, and never had a problem with detonation. You do have to keep an eye on the plugs regularly, and the advent of the ScanMaster really made it a lot easier to monitor potential for detonation.

reuter

you ran on no retard at all? ive always assumed 2 degrees per 50hp of nitrous is the way to go. im just trying to make it as safe as possible because i dont plan on squeezing on the streets so when i do use the juice id like it to be as safe and controlled on my motor as possible. i know there are plenty of threads about it but injuneer what plug do you suggest?

also was your ignition upgraded?

Prorac1

Plus if you do use race gas, you have to make sure its unleaded, cause leaded gas will plug up your catalatic converter over time, and ruin your 02 sensors. You really dont need it on the spray because our cars adjust fuel enrichment and timing as each cylinder sees fit. Just plug, play, aim, and shoot. Hope this helps, prorac1

Injuneer

Changes I made from stock included:

-24# SVO injectors
-NGK TR6 plugs at 0.035 (Autolite 104's are OK too)
-MSD-6A
-electronic WOT switch
-FPSS set at 65psi

When I first bought the kit in late-94 or early-95, it was one of the first ones sold. There were no guidelines on timing retard, not using platinum plugs, changing the stock injectors, etc. I was the test mule, I guess. Rapidly found out stock AC/Delco plats did not like N2O... at least the ground straps didn't and had a habit of disappearing. Never had a problem with detonation after I got the plugs straightened out. Never had a stock injector lock up either, but I didn't want to take a chance, after I learned there was something else available. And when I bought the kit, I was living in CA, and I don't think they had any more than 92-octane pump gas.

There was always some question whether the 5176 kit was 125- or 150-shot with the 0.067 jet. My MPH improvements seemed to indicate it was about 130-135flywheel.

red

This is not true since the PCM does not use the O2's at WOT. At WOT the PCM uses the PE tables to determine the pulse width of the injectors. There is no adjustment of the AF ratio by the O2 sensors during WOT. The only way to adjust the AF ratio at WOT is to make adjustments to the PE tables.

The knock sensor will pull timing when under WOT but this will be for all cylinders. The knock sensor, or the PCM, has no ability to set timing for each individual cylinder.

Injuneer

Agree... the LT1 is not getting any feedback from the O2 sensors at WOT. It hasn't the slightest idea that the N2O is even there. And there is absolutley no way the PCM can trim individual cylinders under load... at best it could trim a full bank of cylinders, but it doesn't get the feedback to adjust anything in the way of fuel.

If I had the advantages of individual cylinder fuel and spark trim with the stock PCM, I wouldn't have invested a small fortune in a MoTeC M48Pro computer.