ive noticed some aftermarket pistons lower ur compression ratio. What is the advantage of dropping the compression ratio from stock compression to say 8:1 ??

can run higher boost,

can run higher boost,

 

but if u drop compression dont u lose power ?? fair enough u can boost a bit higher but apart from that any advantages?

nope. As I understand it, you need the extra area for the increase in combustion pressure. Im sure one of the techs will elaboate.

Mainly, CR and octane dictate the boost you can run safely (as long as you're in the efficient region of your tubs).

Dropping the CR allows you to run higher boost. You're right though, you loose power at the same boost level (or off boost). Really low CR, laggy turbo cars are hideous.

Less Torque more bhp!

 

Sounds familiar ;)

still dont really see the advantage yet . Wouldnt it be best to have a higher cr ?? why would u want less torque but more bhp ? more bhp means what exactly ??

It just means you can run higher boost safely.

It just means you can run higher boost safely.

 

but if ur dropping the torque and raising the boost , dosent that pretty much cancel itself out??

No, at the bottom end you loose torque/power as you're still at the same boost (or vacuum) levels generally. At higher rpm you can run more boost so make more power/torque. It is a trade off though. On a road car, best stick to smallish turbos and relatively low boost levels + highish CR to keep it driveable.

No, at the bottom end you loose torque/power as you're still at the same boost (or vacuum) levels generally. At higher rpm you can run more boost so make more power/torque. It is a trade off though. On a road car, best stick to smallish turbos and relatively low boost levels + highish CR to keep it driveable.

 

so with hybrid t25's with running at max 21psi with 555's and intercoolers ect and a compression ratio of 8:1 should be a good setup then , especially with the n/a ratio rear diff.?

so with hybrid t25's with running at max 21psi with 555's and intercoolers ect and a compression ratio of 8:1 should be a good setup then , especially with the n/a ratio rear diff.?

 

 

T25s running 21psi? What would be the point of doing that? you won't get any more power out of them thats a fact LOL

T25s running 21psi? What would be the point of doing that? you won't get any more power out of them thats a fact LOL

 

Any more power than over what psi then? they are Stage 2 Hybrid 360 Thrust Bearing, Larger Compressor Housing and Wheel, High Flow Exhaust Wheel and Housing, Adjustable Actuator, VSR Balanced 12-22psi

Any more power than over what psi then? they are Stage 2 Hybrid 360 Thrust Bearing, Larger Compressor Housing and Wheel, High Flow Exhaust Wheel and Housing, Adjustable Actuator, VSR Balanced 12-22psi

 

 

Oh Dear Karl what power have you been told they will make?

Oh Dear Karl what power have you been told they will make?

 

 

you know who would of told him anything,jock also has T28s same as karl and IIRC 21-22psi is achievable probably maxed out but achievable and havnt seen any mention of what power it will make

you know who would of told him anything,jock also has T28s same as karl and IIRC 21-22psi is achievable probably maxed out but achievable and havnt seen any mention of what power it will make

 

WTF is that all about?

I'm running t28's karl is running t25 hybrids

WTF is that all about?

Mac Karls might not be as quick as yours top end but my god will he leave that funky back side of yours for about the first 5 miles :rolleyes: untill your turbos have finally breathed enough air to get your car into a forward motion :tongue: :tongue: :rofl:

 

Karl has a T25 Hybrid which is capable and efficient ut to 21 psi (same as a sport 500) with the new Diff that has been fitted any more power would be silly because you struggle to change gear quick enough as it is :p

I'm running t28's karl is running t25 hybrids

 

 

sorry thought karl was running t28s?

WTF is that all about?

 

LOL i dont know either

Mac Karls might not be as quick as yours top end but my god will he leave that funky back side of yours for about the first 5 miles :rolleyes: untill your turbos have finally breathed enough air to get your car into a forward motion :tongue: :tongue: :rofl:

 

Karl has a T25 Hybrid which is capable and efficient ut to 21 psi (same as a sport 500) with the new Diff that has been fitted any more power would be silly because you struggle to change gear quick enough as it is :p

 

PMSL The day a T25 pulls away from a Greddy TD0518G is the day that pigs will fly FFS LOL

 

Keep taking these mate :rofl: :tongue: :slap:

WTF, T25 Hybrids?!!!! That's not what Karl or Ryan told me I had in that car :mad: I think an explanation is due please!

WTF, T25 Hybrids?!!!! That's not what Karl or Ryan told me I had in that car :mad: I think an explanation is due please!

 

he changed them since then mate, don't worry!

So the Turbos were changed twice in 8 months?!!! Why would anyone do that :headvswal

they were changed as car went back to ryans for additional engine work, T25's came out and sold to a forum member and the Mitsi tubs were fitted. Reason was I wanted more power !!

Dropping the compression ratio so that more air fuel mix can be pressured in before reaching det points can give more power but at the expense of crap running at low throttle openings. Saab has a novel design with a variable compression ratio to get you the best of both worlds, high CR at low throttle and low CR at high throttle. This design has the cylinder block and head on a kind of hinge from the crank case meaning the big end bearing centre to top of the cylinder bore dimension can change thus changing CR

 

Then you can have good mpg and power

 

Saab variable CR engine