My friend is swapping in a B20VTEC setup consisting of a JDM 98 B20B block (P3F) and a USDM 98 GSR head. The question comes up, which octane does he have to use? According to C-speed Racing.com (http://www.c-speedracing.com/h...c.php), compression ratio will be at 9.2:1, whereas a stock B20B is at 8.8:1 and requires 87 octane. Would the addition of a GSR head require 91 octane or is compression ratio still low enough to run 87? For reference, stock B16's are at 10.2:1 or something like that, and require 91 octane.

Thanks for the help.

 

I'd go with 91/93 depending on where you are, but thats just me.

I thought B20VTECs had higher comp. than that...

 

With stock b20 pistons that is what the comp ratio is. If you were to use b16 or gsr pistons, that changes it. You can do all sorts of mix match stuff on cspeed's comp calculator.

 

you cant put b16/gsr pistions in there i thought..

 

oh...right, not 81mm, they are 84 mm cylinders huh? I don't know why i was thinking that it was just a longer stroke?

 

compression ratio will determine octane requirement.

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by littleredcivic &raquo;</TD></TR><TR><TD CLASS="quote">compression ratio will determine octane requirement.</TD></TR></TABLE>

Exactly. So with the comp. ratio being at 9.2:1, it would be safe on 87 correct?

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by christhereefer &raquo;</TD></TR><TR><TD CLASS="quote">Exactly. So with the comp. ratio being at 9.2:1, it would be safe on 87 correct?</TD></TR></TABLE>

Not with variable valve timing.

 

how do you figure with variable valve timing, the octane requirement will be higher? i would use 87 if i had your setup. i don't believe in using higher octane than needed. run with 91, then dilute to 89, then to 87 if you want to be safe. if you see no drop in performance and no measureable knock, then you are good IMO

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by littleredcivic &raquo;</TD></TR><TR><TD CLASS="quote">how do you figure with variable valve timing, the octane requirement will be higher? i would use 87 if i had your setup. i don't believe in using higher octane than needed. run with 91, then dilute to 89, then to 87 if you want to be safe. if you see no drop in performance and no measureable knock, then you are good IMO</TD></TR></TABLE>

Cool, I'll do that. Thanks for the help

 

what about in a 1.5 SOHC D15b7, W/ intake, header, 2.5 mandrel bent exhuast, d16y8 head gasket(thinner)
Ported head?

I was told im waisting money using 93 octaine??

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by zx2gotboost &raquo;</TD></TR><TR><TD CLASS="quote">what about in a 1.5 SOHC D15b7, W/ intake, header, 2.5 mandrel bent exhuast, d16y8 head gasket(thinner)
Ported head?

I was told im waisting money using 93 octaine?? </TD></TR></TABLE>

yep

 

so 87, 89?

 

was the ported head milled at all?

 

no

 

https://honda-tech.com/zerothread?id=1475335

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by littleredcivic &raquo;</TD></TR><TR><TD CLASS="quote">how do you figure with variable valve timing, the octane requirement will be higher? i would use 87 if i had your setup. i don't believe in using higher octane than needed. run with 91, then dilute to 89, then to 87 if you want to be safe. if you see no drop in performance and no measureable knock, then you are good IMO</TD></TR></TABLE>

I agree with this. HOnestly in the end its only about $0.20 cents on average a gallon more. an extra $2.40 or so per tank

 

run the 91 it will be better for the motor

 

how is a higher octane fuel better for the motor? octane ratings only determine the anti-knock value of a fuel, not the fuel quality.
hey! 2.40 is a lot of money man!! you can go buy yourself 2 tacos and a jumbo jack!!!