which one is better piston 74.5mm or 75mm

[Janki]

both with the same compres 9:5:1
i want run 1 bar of boost with this spec


fuel pump
turbo t25
manifold custom
exhaut 2.5
inyector 580cc
apexi s-afc2
port and polish head with angle job
ported admission
stock head bolts
stock trotel body

so , pleae give me your opinion

 

[Skalabala]

That CR is a bit high for the 4E. I would say go for 8.5.
What fuel are you going to use and what management?

Go for 74.5mm then there is still some meat left when something goes wrong and the cylinders gets damaged.

 

[weeJohn]

Piston diameter is determined by the size of the bores, no point in fitting 74.5 mm pistons if the rebore to get the bores true will leave them to loose.

 

[Janki]

That CR is a bit high for the 4E. I would say go for 8.5.
What fuel are you going to use and what management?

Go for 74.5mm then there is still some meat left when something goes wrong and the cylinders gets damaged.

the block is 5e fhe , the fuel is pump gas , the management is stock ECU with apexi s-afc2
and i am pretty sure that the combination that i want prove is cr 9:5:1

 

[Tim@TBDevelopments]

remember to use an engine builder than is going to use a torque plate and hot engine when boring/honing.

This seems to be a specialist thing that not many people do, because i'm a new trader and do this on all my engine builds i do plan on wiring a technical article on engine boring and preparation for my traders section to enlighten a few people on the "correct" way to build a performance engine.

Tim

 

[Janki]

remember to use an engine builder than is going to use a torque plate and hot engine when boring/honing.

This seems to be a specialist thing that not many people do, because i'm a new trader and do this on all my engine builds i do plan on wiring a technical article on engine boring and preparation for my traders section to enlighten a few people on the "correct" way to build a performance engine.

Tim

thanks my friend

 

[elison]

buddy,

74.5 would be the ideal option. If something goes wrong you still have meat on the block to rebore again.
You can get wossner pistons which will give you about the stock c/r or any other forged flat top piston.

If i was you i would atleast go with a aftermarket ECU if you want to run 9.5:1 on pump gas rather than a piggyback because you have to be very careful with timing and a/f ratios.

Or i suggest you lower the compression. This way you have more room when the boost bug start biting.

 

[Janki]

buddy,

74.5 would be the ideal option. If something goes wrong you still have meat on the block to rebore again.
You can get wossner pistons which will give you about the stock c/r or any other forged flat top piston.

If i was you i would atleast go with a aftermarket ECU if you want to run 9.5:1 on pump gas rather than a piggyback because you have to be very careful with timing and a/f ratios.

Or i suggest you lower the compression. This way you have more room when the boost bug start biting.

thanks for the information , but now i have a question what is the difference between 74.5mm and 75mm in WHP ?

 

[elison]

It will not be that much buddy. If you lower the c/r you can run more boost. Search the forum. There are allot of good info's and ideas on c/r and fueling and other mods. At the end it will all come down on a good engine management to get the most out of your engine setup.

One thing is for sure most poeple will advice for 74.5mm for the simple reason if something goes wrong you would not need to scrap the block. It can be rebored again if damage is acceptable.