well im building a obd0 sohc zc engine and i've got a chipped pm6 ecu. my dilemma is that i am not sure if i should mill the block and run 8.5:1 compression or just grab a y8 head gasket and run 8:1 compression.

if i mill the block to run 8.5:1 i would need to mill .060" of an inch or 1.5mm and im afraid that would mess up the timing because i might not beable to get my timing belt tight enough...or would it?

if i run 8:1 compression ratio that'll be another 40 bux down the drain for a different head gasket...

if i do neither and run with a d16a6 head gasket i'll be at 7.8:1...which would suck...so helpage...

oh planning to run 14 psi on a tdo5h and i want to be making atleast 250hp.

 

I wouldnt use anything but a metal headgasket (z6/y8) regardless, especially for boost, and don't mill your block either

 

I heard 8:1 pretty much is *** too. If you only want 250hp, 10:0:1 cr would help you get it so much easier. Stock SiR-IIs run 10:4:1 and make 300+hp reliably. I wouldnt be afraid to run 10:0:1 cr

 

don't be afraid of the lower compression on a sohc. Its not that big a deal.

 

well with an 8:1 compression ratio wouldnt it kind of bog the car down because its no producing enough power when its not in boost? i mean i dont think it'll be that noticable because the 14b kicks in sooner than most turbos.

for the guy that said dont mill the block...whys that? i mean the vitaras do sit 1.5mm lower than stock pm6 pistons and if i mill it i would have the same deck clearence. so you guys would recommend a 8:1 eh? i'll look into that.

but anyways i still want more thoughts on this.

 

well i'm assuming you are gonna be running Vitaras? What makes the Vitara setup so attractive is the low cost. Once you start factoring in all the machine work to get the CR up closer to 9:1, you might as well just get some 9:1 forged pistons.

There are already a couple dozen of people who have successfully built some Vitara set ups that put out decent power, with little complaints about the lower compression.

I went from a boosted mini-me to Vitara, and i honestly can't tell the difference.

 

your not going to like that low compression, stick with a 9.5 or 10:1 forged piston. Higher compression helps spooling time and will give you a little more kick in the lower revs with a D.

 

haha the funny thing is that its already getting built by me. .040" over pistons and tuner toy rods...now the question is should i keep the 8:1 or mill it .060" to get 8.5:1.

 

i personally don't like the 76mm bore idea with stock sleeves, but my point is if you are going down the road of "low budget" then just put it together and boost it, otherwise spend the money and get forged pistons.

compression ratios on Ds have been discussed before, just look at what the big HP d series guys are running.

 

I ran 10.3:1 when I had my turbo sohc .60/.63

 

<TABLE WIDTH="90%" CELLSPACING=0 CELLPADDING=0 ALIGN=CENTER><TR><TD>Quote, originally posted by ej8 &raquo;</TD></TR><TR><TD CLASS="quote">I ran 10.3:1 when I had my turbo sohc .60/.63 </TD></TR></TABLE>

That dosn't really tell us much though. What HP levels? forged or cast piston?

 

Personally.. I'd bump the compression up

 

so i wasnt really talking bout 10:1 compression...i should just make a poll out of this...8:1 or 8.5:1...anyways...i dont think this thread is helping so if a mod is reading this..just close it down.