Im getting a ej257 block and using my V3 heads, my question is what thickness head gaskets do i need to get the correct compression ratio. Ive been told that using older heads on these blocks lower the compression so does that mean i need thinner gaskets

 

first, i would reccomend that you either professionally get your combustion chamber opened up to suit the 2.5 or do it yourself.

I done mine, by putting the new Gaskets on the cylinder head, and mark around the combustion chamber area using tipex. next i swapped the gasket for a 2.0 one, and i also marked this to compare the difference.

i then used a dremil and some grinding stones to open up the combustion chamber to suit the 2.5, ensuring i followed the contours.

Once complete, I went over the entire combustion chamber with varying grades of sandpaper working down to 1500 Grade, then i polished it up with Autosol. giving what looked to be a professional finish.

I also used the dremil to clean and polish the ports, as my heads were already ported, had they not i would have done this myself also.

Now as for your question on Gasket thickness this also varies on several factors.

first questions i would ask are.

1. is the EJ257 using std Pistons?
2. have your heads ever been Skimmed?

if yes to 1, then you would need to work out the cylinder volume at BDC - TDC
If No you should be able to find out the std cylinder volume, this will be needed.

2. if yes which is more than likely as you will probably be doing so before fitting them then you would need to calculate the volume of the combustion area in the cylinder head.

here is a usefull calculator

http://www.race-cars.net/calculators...alculator.html

and some data on the EJ257 etc.


Block
EJ257 EJ257 EJ257 EJ205 -EJ207
Head Type
US STI Heads US WRX Heads SpecC Heads US WRX Heads SpecC Heads
Bore (mm) 99.50 99.50 99.50 92.00 92.00
Crank Stroke (mm) 79.00 79.00 79.00 75.00 75.00
Rod Length (mm) 130.43 130.43 130.43 130.43 130.43
Piston Pin Offset (mm) 30.88 30.88 30.88 32.89 31.59
Deck Height (mm) 201.00 201.00 201.00 201.00 201.00
Gasket Thickness (mm) 0.80 0.80 0.80 0.80 0.80
Head Volume (cc) 57.00 51.00 50.00 51.00 50.00
Piston Dish (cc) 22.00 22.00 22.00 12.00 8.00
Piston Deck (mm) 0.39 0.39 0.39 0.38 1.48
Total Quench Height (mm) 0.99 0.99 0.99 0.98 2.08
Total Quench Volume (cc) 7.70 7.70 7.70 8.51 13.83
Total Deck Volume 29.70 29.70 29.70 18.51 19.83
Swept Volume (cc) 814.28 814.28 814.28 498.57 498.57
Compresses Volume (cc) 86.70 80.70 79.70 89.51 89.83
Static CR :1 8.09 8.61 8.71 8.17 8.14
Rocl~‘Stroke Ratio (na) 1.65 1.65 - 1.65 - 1.74 1.74
Engine Displacement (cc) 2457.00 2457.00 2457.00 1994.00 1994.00

 

i was just going to bolt my heads on and off i go but it looks like i need to do a HND in mechanical engeering, lol cheers for the info i`ll give it a go..