What grade fuel should I be using in an 89 TPI 350 engine? It seems to run the same on 87 or 91. I usually run 91 but filled it with 87 to save some money. The engine is stock except for roller rocker arms, 1.6 on the intake and 1.5 on the exhaust. It also has Tri Y headers and no cats.

Bump

I would run the 91 octane, i don't think its going to benefits the motor that much buts its gotta be better then 87... It also depends on how you drive it.

Thanks Skip. I have been running the 91. The engine is installed in a 72 El Camino with the 700R4 transmission and 3.73 gears. Primarily a daily driver but I tend to run my vehicles a bit harder then the avearage grand ma. The recent advent of unpaid furlough days plus the rising cost of everything has me looking any where I can to save a few pennies. Of course all those saved pennies are going into the Nova project :D

What's the compression, 9:1? 9.5:1?
What grade of fuel does Chevy recommend?
Check the owners manual, or just look by the gas cap. On my vette, printed next to the gas cap is "PREMIUM UNLEADED FUEL ONLY"

Regular 87 shouldn't be a problem.
Midgrade 89 certainly is not.

There's no such thing as "better gas" at least relating to octane. Octane is a measure of a fuels knock resistance, as in how much cylinder pressure will the fuel handle without knocking. You only need and want the minimum octan your engine requires.

[QUOTE=Philip;1159654]What grade fuel should I be using in an 89 TPI 350 engine? It seems to run the same on 87 or 91.

You answered your own question.she runs the same with 87.Most likely fires off quicker on a cold start also.There is no advantage to slowing down the burn unless detonation is an issue..not commonly seen with an oem installed knock sensor.Run the fuel the manufacture recommends for this application..take advantage of the millions of dollars they spent on r&d.

You answered your own question.she runs the same with 87.Most likely fires off quicker on a cold start also.There is no advantage to slowing down the burn unless detonation is an issue..not commonly seen with an oem installed knock sensor.Run the fuel the manufacture recommends for this application..take advantage of the millions of dollars they spent on r&d.

:hurray:George that is exactly what I am trying to find out, what fuel was recommended by GM. Sorry for not wording it properly in my previous posts. I never saw the donor car, an 89 Camaro, it is now in a 72 El Camino. With the stock heads and dished pistons I do not think the compression is much over 9:1. I know that detonation can occur without it being heard by the driver (especially an old guy :) ) and I do not want to cause any damage.

Jim sums up very well
There's no such thing as "better gas" at least relating to octane. Octane is a measure of a fuels knock resistance, as in how much cylinder pressure will the fuel handle without knocking. You only need and want the minimum octan your engine requires.

And it is not how hard you run, it all has to do with CR and DCR and cam and the rpm range and how the timing cyrves are setup , and in the case of ECU how that works for that model.

the higher the octane , the lower the sg, hence less btu/volume (which is how it is measured at the pump..not my mass) the slower the burn and more advance required, but higher CR and higher DCR the less advance needed.
So for a non stock engine the whole thing is rather a complex situation, for a stock engine the manufacture and ECU have already done the maths for you