Is high test really necessary?

Red__Zed · 12-04-2013, 06:14 PM

Quote:

Originally Posted by Jordo!

Yes, and no. Higher compression piston heads tend to be more likely to have flame kernels dissipate irregularly, creating hot spots that may lead to knock by way of pre-ignition of the next combustion event.

This is one of the reasons that it is generally easier to tune a boosted car with more boost but lower compression pistons, rather than just assuming more pressure however its achieved is better. You still have to deal with knock and that's generally easier on a low CR high boost motor, at least using port injectors (in theory you can do more with less using direct injection).

In either case, the ignition advance tables were tuned based on the presence of 91 AKI, so to run optimally and safely, especially under load, going below the recommended octane is potentially risky.

.

You say "yes and no" but as far as I can tell you are agreeing with me. Plenty of cars run 11:1 fine on 87/85 octane gas, the Z simply wasn't designed for it.

Jordo! · 12-04-2013, 06:31 PM

Quote:

Originally Posted by winnre

All I can get here is 87/89/91. No 93. But there is 103 available for like $11/gal.

91 is fine.

Quote:

Originally Posted by Red__Zed

You say "yes and no" but as far as I can tell you are agreeing with me. Plenty of cars run 11:1 fine on 87/85 octane gas, the Z simply wasn't designed for it.

I'm saying that yes, it is possible to run a high CR piston on octanes < 91, provided the spark advance tables are properly tuned for it, but no, the Z was -- at least according to Nissan -- not tuned for it.

Also, there are indeed special considerations for octane needs unique to the design of higher compression pistons, and it is unknown (or at least not widely known) how the VQ37HR pistons behave in terms of hot spots under load.

So, I'm agreeing with you, but calling attention to the potential unique needs of higher CR pistons, in much the way that Sh0velman was pointing to potential exceptions associated with running motors at higher altitudes.

I don't know how much of a role the piston crown design and specific CR is playing a role in octane needs for the Z's motor relative to the tune alone, but it is indeed possible.

I do know this tho': In the owner's manual it says some light knock when chugging up hill is "normal"...

That alone tells me this motor prefers higher octane fuel.

Red__Zed · 12-04-2013, 09:02 PM

Quote:

Originally Posted by Jordo!

91 is fine.

I'm saying that yes, it is possible to run a high CR piston on octanes < 91, provided the spark advance tables are properly tuned for it, but no, the Z was -- at least according to Nissan -- not tuned for it.

Also, there are indeed special considerations for octane needs unique to the design of higher compression pistons, and it is unknown (or at least not widely known) how the VQ37HR pistons behave in terms of hot spots under load.

So, I'm agreeing with you, but calling attention to the potential unique needs of higher CR pistons, in much the way that Sh0velman was pointing to potential exceptions associated with running motors at higher altitudes.

I don't know how much of a role the piston crown design and specific CR is playing a role in octane needs for the Z's motor relative to the tune alone, but it is indeed possible.

I do know this tho': In the owner's manual it says some light knock when chugging up hill is "normal"...

That alone tells me this motor prefers higher octane fuel.

Always helpful to have an echo.

Jordo! · 12-05-2013, 01:50 AM

Quote:

Originally Posted by Red__Zed

Always helpful to have an echo.

Yeah... I see your point.

You know, the only thing more annoying than an "echo" post is someone who insists on having the last word in a thread.

( Click to show/hide )

Similar Threads
Thread	Thread Starter	Forum	Replies	Last Post
Bolts for High Flow cats/test pipes	Sh0velMan	Intake/Exhaust	3	07-24-2013 09:05 AM
Invidia High Flow Cats & Test Pipes! SALE!	marks370z	Exhaust/Intake	7	05-25-2012 01:56 PM
Gas prices for high test is $4 to $5 per gallon	andre12031948	Nissan 370Z General Discussions	37	02-24-2012 12:25 PM
high flow cats or test pipes	black09Z	Wanted	0	07-23-2009 10:28 AM