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High Comp And E85

Simon-S14
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Super Drager Mentor

Super Drager

Posted
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Ok so theoretically say we have two engines of the same spec apart from compression.

One is 10.5:1 comp and the other is 8.5:1 comp. If the 10.5:1 motor is on 7psi, would it make the same power as the 8.5:1 motor on the same boost?? Sorry i'm a n00b.

TiTAN Grand Master

TiTAN

Posted
Posted

no, you would expect the higher compression motor to make more power for the same boost and start making its boost earlier, however if you are running the turbo out of flow then you may end up with similar peak power figures given everything else in the engines are equal.

kitto Mentor

kitto

Posted
Posted

How about an RB25 or 26 Block, 26 crank, 25/26 conrods but use NEO pistons to bump up the CR. The extra 2mm of stroke will bump up the compression ratio (you'd need to use a calculator to work out the final compression ratio). But a NEO is 9.0:1 factory so you'd gain a reasonable amount from that stroke.

It may go too far though and cause the piston to stick too far out of the deck. Possibly hitting the quench pads. You definitely wouldn't want a heavily shaved head or block.

Just an idea, it might be easy to get it to work, or it might be nearly impossible.

XKLABA Grand Master

XKLABA

Posted
Posted

How about an RB25 or 26 Block, 26 crank, 25/26 conrods but use NEO pistons to bump up the CR. The extra 2mm of stroke will bump up the compression ratio (you'd need to use a calculator to work out the final compression ratio). But a NEO is 9.0:1 factory so you'd gain a reasonable amount from that stroke.

It may go too far though and cause the piston to stick too far out of the deck. Possibly hitting the quench pads. You definitely wouldn't want a heavily shaved head or block.

Just an idea, it might be easy to get it to work, or it might be nearly impossible.

the rb25 pistons are all the same, the neo head has a smaller combustion area which is what gives it the higher cr, the 26 pistons have a different comp/pin hieght to account for the extra stroke, but you still have to work out the static comp ratio when chopping and changeing crank/rod/piston setups.

as long as you keep a 0 deck hieght and have a 1mm+ head gasket you wont have piston/head clearance problems, piston/valve comes down to cam duration and timing more then anything, if its to close for comfort then you can get/have the pistons flycut for valve clearance

to get the cr up you have to reduce combustion area, where it be by shaving the head or getting pistons with bigger domes the end result is the same.

lifting comp ratios has the same effect on turbos as N/As, the higher the cr the high the PSI in the combustion camber at TDC, the higher the pressure the more force on the piston pushing it down and in turn giving more power.

adding boost means your compressing pressurized air( boost pressure ) inturn increasing combustion pressures which gives more power

JustinP Mentor

JustinP

Posted
Posted

Wrong. 9.0:1

I think the misconception here comes from the fact that the commonly used "off the shelf" pistons that CP sells for the RB25DET (which are not suitable for use in Neo's) are 8.5:1 rather the the OEM 9:1.

When you buy CP pistons for a Neo they are a custom non stocked item and they simply copy the exact Neo OEM piston, so the standard offering is still 9:1 unless you want further customization.

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