Does anyone know the formula to calculate the required fuel octane given compression, boost and timing?

Like if I have a B16A with 10.4:1 compression, and I want to run 6psi of boost at stock timing set by a P72 ECU. What octane fuel do I need to run to avoid detonation?

I also would like to hear from anyone that has played with their cam gears to dial out overlap to keep more boost in the cylinder chambers.

Thank you

 

6 psi should be fine on 10.4
If your nervous you can pull a degree or 2 of timing....I wouldnt personally for only 6 psi. You always want to run the highest octane fuel on any turbo car. Seeing your in Pa, 94 octane is readily available. b16 cams shouldnt have any overlap, so no need for the gears to be changed around---besides the setting will vary from motor to motor and the only way to tune cam gears is on a dyno.

 

Unfortunately, there is no chart or formula because there are too many variables. Simple little things such as piston design, combustion chamber design, and rod ratio play a big part in how much timing you can run w/o detonation.

 

Also, even though 94octane is available in PA, just keep in mind that it is not available everywhere. If this is a daily driver, it might not be wise to tuned on 94 just to take a trip out of town and be stuck with 91.

 

One of the guys we know is running 13.0:1 in his full race car and wants to boost 25lbs.+... We're going to be dynoing the car so I guess we'll see how that works... I'm not keeping my fingers crossed, anyone know what kinda dynamic compression we'll be seeing with stock cams, hehe I won't go over 10.5:1 on a built motor but that's with the intension of boosting 35lbs+... Peace

 

I agree w/the 6lbs being ok possibly even 8lbs, but if I were you I would not wanna dial out overlap to keep more boost in ur cylinders if you ever wanted to boost higher, it would kinda make sense to me if you dialed in overlap... less chance of octane being a problem, and it could cool down your exhaust valves and exhaust temps more... maybe?

I dunno but your doin the same thing im gonna be doin basically, and im just gonna be sure to get it tuned well @ about 7-8lbs.

You must have a thinner head gasket also?

 

im building my d16 and will be using 10.5 pistons, crower rods, sleved block with the intention of boosting 14 psi.. (using 93 octane)

think its too much compression for 14psi?

some people say its a 'go' other its too much cr for that much boost. an other thing it wilb e pretty much daily driven but not necesarely hotdoged 24/7

 

You should be fine with that, you begin to near the limit where your car will have to be either run on race gas or tuned for pump and race gas (depending on if you are boosting or not) If you just wanna drive really nice and calm on the freeway (not boosting up) then you could probably get away with 93 and even race gas tuning... We tune on race gas and drive everywhere on race gas so it really doesn't matter, but when you run low and need pump gas then I absolutely would NOT boost on it... Even if you do, you'll notice the power just isn't there... I would consider just bringing down the boost a bit if you wanna drive on the street, playing with the static compression raises your overall (dynamic) compression a lot... Don't get me wrong tho, I love 10.0-10.5:1 with boost, and there is NOTHING wrong with going that high... If it turns out to be too much then back down a couple lbs... Just my $0.02, Good Luck

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by stierhund &raquo;</TD></TR><TR><TD CLASS="quote">I agree w/the 6lbs being ok possibly even 8lbs, but if I were you I would not wanna dial out overlap to keep more boost in ur cylinders if you ever wanted to boost higher, it would kinda make sense to me if you dialed in overlap... less chance of octane being a problem, and it could cool down your exhaust valves and exhaust temps more... maybe?

I dunno but your doin the same thing im gonna be doin basically, and im just gonna be sure to get it tuned well @ about 7-8lbs.

You must have a thinner head gasket also?</TD></TR></TABLE>

You mean do I have a thinner head gasket to go from USDM B16A 10.2:1 comp to 10.4:1? I have a JDM SiR II B16A which comes with 10.4:1 comp. Maybe you're right about the keeping the overlap to reduce boost. I even have my intake cam gear advaced to create more overlap currently.

I guess I'll give the following a try:
Turbo or JRSC @ 6-7psi, 94 octance, 10.4:1 comp, +2 deg Intake Cam advance, P72 ECU with stock ignition timing..

If I get stuck with 92 oct gas, I can always limp home shifting at 3500rpms. I haven't been stuck with lower than 92oct yet.

Thanks for the info guys.

 

with 94 it shouldn't be a problem IMHO

 

hopefully my setup wont knock. i WANNA use stock injectors and stock timing.