.:HSTuners::

*AzCivic* · 03-06-2003, 10:45 PM

Whats the highest compression ratio you can go with 93octane gas?? I'm thinking 11.5:1, what do you think(or know)?

ebpda9 · 03-06-2003, 11:08 PM

hmm i've heard that cr running with 87 octane (toyota echo), but for your question i can't really answer

03-06-2003, 11:34 PM

i think 12.0 is the highest i'd go, but i've heard people with good tuning people running 12.5

03-07-2003, 01:47 AM

93 Octane can utilize a pretty high comression ratio (12-13:1) *only* if the camshaft has been ground (custom or bought from a parts supplier) to compensate for the higher static compression ratio.

The static compression ratio is the cylinder volume + the combustion chamber volume divided by the combustion chamber volume. These are the numbers you regularly see posted.

But the compression ratio that counts as far as fuel octane is concerned is the dynamic compression ratio or for purposes of simplification the 'effective' compression ratio. This is the compression ratio measured at the point at which the intake valve closes. The volume of the cylinder is smaller because the piston has already started moving up on the compression stroke.

The reason that this ratio counts is because there is little to no pressure (compression) in the cylinder until the intake valve is closed and the combustion chamber is completely sealed. For an engine running 93 octane (combustion chamber design, size of the intake and the exhaust ports, piston crown coatings and the general design of the engine alters this greatly) you can usually get away with an effective compression ratio of around 7.5 - 8.0:1 (some cars even higher, Honda's are built quite well).

What this boils down to is the intake cam duration (and therefore the point at which the intake valve closes) is for the most part dictated by the static compression ratio. Calculating this ratio requires some trigonometry, unfortunately.

High compression ratios benefit the power of the engine at higher RPM's so it is best to have a 'built' shortblock and the rev limiter set to a new, higher maximum RPM (redline). This allows you to spend more time in lower gears, thus taking advantage of the higher torque multiplication.

Thanks,

-Scott Tucker
The static compression ratio is the cylinder volume + the combustion chamber volume divided by the combustion chamber volume. These are the numbers you regularly see posted.

But the compression ratio that counts as far as fuel octane is concerned is the dynamic compression ratio or for purposes of simplification the 'effective' compression ratio. This is the compression ratio measured at the point at which the intake valve closes. The volume of the cylinder is smaller because the piston has already started moving up on the compression stroke.

The reason that this ratio counts is because there is little to no pressure (compression) in the cylinder until the intake valve is closed and the combustion chamber is completely sealed. For an engine running 93 octane (combustion chamber design, size of the intake and the exhaust ports, piston crown coatings and the general design of the engine alters this greatly) you can usually get away with an effective compression ratio of around 7.5 - 8.0:1 (some cars even higher, Honda's are built quite well).

What this boils down to is the intake cam duration (and therefore the point at which the intake valve closes) is for the most part dictated by the static compression ratio. Calculating this ratio requires some trigonometry, unfortunately.

High compression ratios benefit the power of the engine at higher RPM's so it is best to have a 'built' shortblock and the rev limiter set to a new, higher maximum RPM (redline). This allows you to spend more time in lower gears, thus taking advantage of the higher torque multiplication.

Spazum888 · 03-07-2003, 03:02 AM

wut site did you get THAT off of?

*AzCivic* · 03-08-2003, 06:30 AM

Quote:

Originally posted by scottrtucker
93 Octane can utilize a pretty high comression ratio (12-13:1) *only* if the camshaft has been ground (custom or bought from a parts supplier) to compensate for the higher static compression ratio.

The static compression ratio is the cylinder volume + the combustion chamber volume divided by the combustion chamber volume. These are the numbers you regularly see posted.

But the compression ratio that counts as far as fuel octane is concerned is the dynamic compression ratio or for purposes of simplification the 'effective' compression ratio. This is the compression ratio measured at the point at which the intake valve closes. The volume of the cylinder is smaller because the piston has already started moving up on the compression stroke.

The reason that this ratio counts is because there is little to no pressure (compression) in the cylinder until the intake valve is closed and the combustion chamber is completely sealed. For an engine running 93 octane (combustion chamber design, size of the intake and the exhaust ports, piston crown coatings and the general design of the engine alters this greatly) you can usually get away with an effective compression ratio of around 7.5 - 8.0:1 (some cars even higher, Honda's are built quite well).

What this boils down to is the intake cam duration (and therefore the point at which the intake valve closes) is for the most part dictated by the static compression ratio. Calculating this ratio requires some trigonometry, unfortunately.

High compression ratios benefit the power of the engine at higher RPM's so it is best to have a 'built' shortblock and the rev limiter set to a new, higher maximum RPM (redline). This allows you to spend more time in lower gears, thus taking advantage of the higher torque multiplication.

Thanks,

-Scott Tucker

Dont know if you wrote this or what but anyways, I'd want the intake valve to close when its not allowing anymore air into the combustion chamber, if i let it stay open longer the air in the chamber will go right back out(lowering compression whether it be static or whatever).

Anyways i'm thinking of getting some CHEAP high comp pistons (10.5:1 - 11:1) and doing some other crap so i'll have a somewhat rebuilt engine that can handle a 50shot of nitrous every now and then.

Anyone have any experience with any of the aftermarket cams out there for the D16Z6? And will low end be sacrificed for top end? I would think not since thats what Vtec is supposed to be preventing.

03-06-2003, 10:45 PM	#1
AzCivic Moderator Join Date: Feb 2002 Location: Az Age: 43 Posts: 3,804	Compression ratio Whats the highest compression ratio you can go with 93octane gas?? I'm thinking 11.5:1, what do you think(or know)?

03-06-2003, 11:08 PM	#2
ebpda9 Repost Wagon Join Date: Dec 2001 Location: over here Age: 44 Posts: 17,266	hmm i've heard that cr running with 87 octane (toyota echo), but for your question i can't really answer __________________

03-07-2003, 03:02 AM	#5
Spazum888 3rd Gear Join Date: Aug 2002 Location: Orlando Age: 42 Posts: 550	wut site did you get THAT off of? __________________ Girls are like internet domain names, the ones I like are already taken. well, you can stil get one from a strange country :-P

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03-06-2003, 11:34 PM	#3
96coupe Posts: n/a	i think 12.0 is the highest i'd go, but i've heard people with good tuning people running 12.5

03-07-2003, 01:47 AM	#4
scottrtucker Posts: n/a	93 Octane can utilize a pretty high comression ratio (12-13:1) only if the camshaft has been ground (custom or bought from a parts supplier) to compensate for the higher static compression ratio. The static compression ratio is the cylinder volume + the combustion chamber volume divided by the combustion chamber volume. These are the numbers you regularly see posted. But the compression ratio that counts as far as fuel octane is concerned is the dynamic compression ratio or for purposes of simplification the 'effective' compression ratio. This is the compression ratio measured at the point at which the intake valve closes. The volume of the cylinder is smaller because the piston has already started moving up on the compression stroke. The reason that this ratio counts is because there is little to no pressure (compression) in the cylinder until the intake valve is closed and the combustion chamber is completely sealed. For an engine running 93 octane (combustion chamber design, size of the intake and the exhaust ports, piston crown coatings and the general design of the engine alters this greatly) you can usually get away with an effective compression ratio of around 7.5 - 8.0:1 (some cars even higher, Honda's are built quite well). What this boils down to is the intake cam duration (and therefore the point at which the intake valve closes) is for the most part dictated by the static compression ratio. Calculating this ratio requires some trigonometry, unfortunately. High compression ratios benefit the power of the engine at higher RPM's so it is best to have a 'built' shortblock and the rev limiter set to a new, higher maximum RPM (redline). This allows you to spend more time in lower gears, thus taking advantage of the higher torque multiplication. Thanks, -Scott Tucker The static compression ratio is the cylinder volume + the combustion chamber volume divided by the combustion chamber volume. These are the numbers you regularly see posted. But the compression ratio that counts as far as fuel octane is concerned is the dynamic compression ratio or for purposes of simplification the 'effective' compression ratio. This is the compression ratio measured at the point at which the intake valve closes. The volume of the cylinder is smaller because the piston has already started moving up on the compression stroke. The reason that this ratio counts is because there is little to no pressure (compression) in the cylinder until the intake valve is closed and the combustion chamber is completely sealed. For an engine running 93 octane (combustion chamber design, size of the intake and the exhaust ports, piston crown coatings and the general design of the engine alters this greatly) you can usually get away with an effective compression ratio of around 7.5 - 8.0:1 (some cars even higher, Honda's are built quite well). What this boils down to is the intake cam duration (and therefore the point at which the intake valve closes) is for the most part dictated by the static compression ratio. Calculating this ratio requires some trigonometry, unfortunately. High compression ratios benefit the power of the engine at higher RPM's so it is best to have a 'built' shortblock and the rev limiter set to a new, higher maximum RPM (redline). This allows you to spend more time in lower gears, thus taking advantage of the higher torque multiplication.