ps374

My question concerns my 84 Crossfire. This car was set up by my cousin some years back before I became the owner. The car has the Xram intake which after taking it apart due to a vaccum leak, I also had to remove the intake that the Xram is bolted to.It is a Wealand High performance manifold and the ports are almost twice the size of the stock Crossfire intake which i still have in storage. My cousin also inlarged the throttle bodies to what size I am not sure, changed the fuel pump to a TPI pump, put in a different Fuel pressure regulator, and also added functional Ram Air which goes directly into the crossfire butterfly flaps which are welded open. He also has a computer ECM from a newer Camaro along with a free flow exhaust system minus the cat. All polution stuff is also gone. The car has some kind of chip that was reprogramed to work with the ECM. I was told to use 93 Octane when I was given the car by him some years back. I have been using 93 Octane as told but I am begining to wonder is it reall nessary. The car is pretty loud so if it had a gas knock I doubt I would hear it. My question does doing mods like this make the engine require higher octane?

Aardwolf

You can build an engine to require higher octane or not. In your case the tune is probably set so that it's required (higher octant like you were told). You could have it retuned for the fuel you want to use. Ruining an engine from incorrect fuel will cost more.

DanielRicany

You probably shouldn't need 93 octane if the compression ratio remained the same as stock.

You can however, install an LED bulb spliced off the EST to ECM signal wire. It will always be lit until there is knock. When there is knock it will shut off the bulb briefly for each knock that is detected.

With this set up, you can try running 87 octane under every condition you can achieve. You just watch the light to see if spark knock is detected. If there is no spark knock detected then you should be good to go and can remove the bulb.

I did this with mine and it does work. This is because you don't have the ability to view knock counts on an '84 on a scan tool.

Paul Workman

Conditions that result in knock stem from HEAT phenomenon first identified by Boyle, i.e., "Boyles' Law" is at work:

Increasing the amount of air/fuel in the combustion chamber by various passive and/or active (forced) means
e.g., supercharger,
or increasing effective compression by advancing the spark to initiate fuel burn before the piston reaches TDC
or valve timing (i.e., cam profile) affecting compression

Different fuels burn faster than others and/or are easier to ignite by either spark or due to glowing carbon fouling or simply dieseling (Boyle's Law again). Regular gasoline burns faster than high octane and thus spark advance is necessarily less with regular, and it will diesel more readily. Higher octane burns slower, less likely to diesel (self-ignite), needs more spark advance, can tollerate higher temps (compression). Other fuels such as alcohol will tollerate very high compression ratios (14:1 and higher) without self-igniting.

So, when you say "modifications", whether the mods result in greater heat (read: engergy!) either by additional air/fuel higher compression (effectively playing into Boyle's Law either way) HEAT rises, and it is that HEAT that = ENERGY.

So... not knowing exactly what was done, it sounds like steps have been taken to cram more air/fuel into the engine. Yeah, you may well need higher octane (as recommended).

1984Z51auto

My 1984 didn't require higher octane gas until I added L98 aluminum heads and raised the compression. I had a ported stock intake and the (then hot combo) Turbo-City computer and chip... still ran fine on regular. What made the premium fuel necessary was the higher compression. Your situation may be different as I am at 5280 ft. elevation but, our premium is also only 91 octane, regular here is 87 octane.

Lloyd Smale

the chip may have bumped up timing and that will make premium a nessisity