QUESTION: Should I really sweat a .5 comp ratio point?

Im about to assemble my block and I've got a set of 81.5mm RS Machine ITR pistons, which the zeal calculator says will give me roughly 11:1 CR. I also have a set of 81.25mm JDM ITR pistons, zeal calculates roughly 11.5:1 CR for these. So in order for me to run the JDM ITR pistons I will need to sell the block I have, due to over boring, and the RS Machine pistons. Then go and get a OEM GSR block and hone it to the 81.25mm pistons. All of this for .5 compression point, worth it? or should I just stick with the RS Machine pistons?

SET UP-
Essentially Stock block with ARP rod bolts on p72 Rods
B18C1 head
RM valves and retainers
Skunk2 Pro1 cams

will the half a point compression actually make me much more power?

 

All you need to do is run a 1 or 2 layer headgasket, or plane the head or some combination of both to get 11.5:1. That's all I did with my setup. Keep it simple.

 

I've been considering that. I just didnt know if I'd even see the gains for the headache that switching blocks could cause. What pistons are you running?

 

Where could I get a single or 2 layer head gasket?

 

I'm running a stock USDM ITR bottom end. You can make a 1 or 2 layer headgasket or buy a 2 layer on here or ebay. Just look around.

 

Spoon sells 2 layer HGs. Or, 2 ply as they refer to them. Visit there website. I think a few guys on here deal in spoon goods too.

 

Spoon works(I've used one) or get an OEM gasket and grind the rivets off and use the outer layers.

 

Just mill the head...or run a thinner gasket. KISS is always the best policy.

 

OP from what I understand the RS pistons are the JDM ITR spec but even if they where not I would not sweat 0.5 compression point. There are many examples of that piston making good power in 1.8L motors without raising compression through milling or thin HG.

 

When I ordered them from RS MAchine they told me that the ITR replica pistons are the USDM spec. Is 200-210 whp realistic with my current setup and with out any milling or thin HG? And with making the oem into a 2 layer, has any one had any problems with leakage? Just asking out of curiosity

Thanks for all the info guys!!

 

The RS ITR pistons copy the USDM ITR dome - NOT the JDM profile

 

you can make 200 w/those pistons.. but you will need a good header and it probably wont make the power w/those cams.

 

i use dhracing.com single layer .0014 headgaskets in my builds. they claim to add .5 to the cr. my current setup is a 11.7 cr b16 on a 100hp shot of n2o and it's still holding up.

 

Cool I'll check out the site and see what they have have for HG's. And we'll have to see if those cams will hit the 200 whp point after tuning, I think it will be pretty close. I would have gone with the pro2's but I was told that I'd be risking over camming the car

 

is your head ported? s2pro 1's are pretty aggressive. should be close...

also, i say stay with the rs pistons because its .5mm overbore. this will yield more torque...

 

No didnt port, kinda ran out of funds when I was building the head. Im pretty sure that I'm going to go with the RS slugs because I may have a buyer lined up on the 81.25mm ITR's

 

are the pistons still down in the hole?

unless they are sticking up out of the hole you really don't have anything to worry about.

If they are sticking out then you will need a thicker headgasket, if they are flush w/the deck or down stick w/a normal headgasket.

 

Not real sure about that yet, the block is at the shop getting fitted for the new pistons now. I may just end up running the OEM 3-layer and maybe have the head resurfaced. The most Ill consider is a 2-layer, or just removing the center layer of the oem, and/or a possible .03" planing of the head. But from what Ive been hearing is that I should be able to make good power with my setup as is. Is there any noted reliability problems associated with removing the center layer from the OEM 3-layer HG?

 

with a stock bore changing hg thickness isnt going to gain you all that much in compression.

I would leave it be, and use a stock HG.. keep in mind that those cams may not get you to your goals. the header and cams you choose will make or break your setup way more than a layer of headgasket

 

cool cool, thanks for the Information! So for I am using an ITR header, but may change out if i stay under budget with my build