Help with compression ratio
22 February 2017, 08:22 AM
#1
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Help with compression ratio
Can someone throw some light on this please ,
I've got a hybrid engine running 99.75mm Mahle WRX209927P10 pistons with a 9:1 dish , 1.1mm thick 100mm head gaskets and standard ( unmachined combustion chamber ) STI V6 cylinder heads .
I'm not making the power expected and think it may be down to a too high of a compression ratio ??
I've got a hybrid engine running 99.75mm Mahle WRX209927P10 pistons with a 9:1 dish , 1.1mm thick 100mm head gaskets and standard ( unmachined combustion chamber ) STI V6 cylinder heads .
I'm not making the power expected and think it may be down to a too high of a compression ratio ??
22 February 2017, 11:51 AM
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I thought it would be higher than that ? running the Turbo Dynamics MDX555-500 , APS 65mm cold air intake, APS front mount intercooler , 800cc injectors , I think the week point maybe the ECU , still running WRX ECU on Ecutek ,
peak power of 400 at 5600rpm .
peak power of 400 at 5600rpm .
Last edited by mikey-p; 22 February 2017 at 11:53 AM.
22 February 2017, 01:06 PM
#4
Were the heads fully rebuilt, ie recut seats & valves, what springs ?
Those pistons fitted in the bores are around 24.5cc you will not see 9:1 on them even on 2.0 heads, on 2.5 heads it will be 8.2:1, some don't like the 2.0 heads as std, they usually require the chamber to be chamfered to suit the bigger bore, but the extra compression ratio will help spool & driveability, as long as your using at least 99ron.
Those pistons fitted in the bores are around 24.5cc you will not see 9:1 on them even on 2.0 heads, on 2.5 heads it will be 8.2:1, some don't like the 2.0 heads as std, they usually require the chamber to be chamfered to suit the bigger bore, but the extra compression ratio will help spool & driveability, as long as your using at least 99ron.
22 February 2017, 02:49 PM
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Yeah , fully rebuilt, valve seats recut, standard STi valves, springs and cams . Had to have the maf rescaled when mapped due to air flowing past sensor too fast causing issues . Could go big maf intake ??
14 March 2017, 12:05 AM
#6
what did your mapper think? better ecus give better safeguards and features/logging-" but" a good map is a good map it just takes a bit longer with ecutek-
most 500bhp turbos need 2 bar in a 2 litre engine to make the numbers - set up is very important at this level -i lost circa a 100bhp just through the wastegate arm being loose!!(made boost at 6200rpm lol)
dont remember a recent heavily tuned engine still running a MAF though- standard mafs would be at their limit at 400 bhp .
if its a fresh built engine you can proably discount any major faults-and start looking at the ancillaries -assume its decatted? what uppipe? 3" exhaust?quality headers? any decent tuner should be able to tie it down quite quickly
most 500bhp turbos need 2 bar in a 2 litre engine to make the numbers - set up is very important at this level -i lost circa a 100bhp just through the wastegate arm being loose!!(made boost at 6200rpm lol)
dont remember a recent heavily tuned engine still running a MAF though- standard mafs would be at their limit at 400 bhp .
if its a fresh built engine you can proably discount any major faults-and start looking at the ancillaries -assume its decatted? what uppipe? 3" exhaust?quality headers? any decent tuner should be able to tie it down quite quickly