A few Questions on the DOHC head Swap

[Galant306m]

It has to do with combustion chamber volume. The volume of the combustion chamber on the EVO head is smaller than volume of the SOHC head, this is what causes the increase in compression ratio.

exactly there is a formula that you have to do to figure it out mine raised .8:1 with the new head over stock i just call it 10.5:1 cause it sounds better then 10.3:1 lolz...

[mko]

I understand that, but still its alot. 1.5 in CR raise is insane.

the difference between SOHC and DOHC on 7g is 0.5:1. From 9.5 to 10.

people that want to have high CR NA engines use 1.8L Hyundai 4g37 DOHC head with 37cc chamber that bumps it from 10.0:1 to 10.5:1

Its weird for me

[Galant306m]

Oh my head had .015" removed from the deck that's where the other .3 comes from i thing, she was a low in the middle so he had to take off more to make it flat again.

[duh2150]

Yea it only should just by about 1.0:1 at most.

I hope you know that the pistons you are going to be looking for are not going to be custom right? Manley makes a really nice set for a good price and all 4g64 blocks have the same bore so even if you find one that says application for a 1996 eclipse spyder it will still work cause its the same piston.

Kia head is basically the same thing as the evo head minus mivec and minus the evo cams, and most likely smaller intake and exhaust ports and valves which could be fixed by having the head ported and putting in evo cams and valves. Mivec is pointless to me, really so go with a evo 8 head or the kia head and you will be happy.

the 4g69 head will not work because the head is narrower and the bolt pattern is not the same so move away from that idea right now unless you want to plug and and retapp the block.

(yes and no) the pistons have to be made bidirectional like the ones I'm using in mine from wiseco 7g and 8g pistons if your using them on a 8g they HAVE to go in backwards why because of the pin offset

and seriously the ports are huge between the kia and evo there are no differences from what ive seen evo8's don't even have mivec, but im pretty sure you can use the kia cams you just have to use 2 non adjusting 8g cams(i'm pretty sure it never been done) but it should work.

[Stewi]

(yes and no) the pistons have to be made bidirectional like the ones I'm using in mine from wiseco 7g and 8g pistons if your using them on a 8g they HAVE to go in backwards why because of the pin offset

and seriously the ports are huge between the kia and evo there are no differences from what ive seen evo8's don't even have mivec, but im pretty sure you can use the kia cams you just have to use 2 non adjusting 8g cams(i'm pretty sure it never been done) but it should work.

did you mean 2 non-adjusting 8g cam gears? If so, you are wrong. Its been tried by the likes of AMS, Magnus and Buschur and its not right, the same way using stock EVO cam gears is not right.

You can look on google and find the formula for compression ratio. Any good engine builder will know the formula off the top of his head. My engine builder actually had a computer program he input all the data into, and it told me the required headgasket thickness in order for me to achieve my target compression ratio.

Also for NA, I think 10.5 would be OK on a stock bottom end if you ran 93 octane full time and had the car tuned. Hell there are EVO guys with 2.4 bottom ends running 10:1 comp ratio and 20psi on 93 octane, at that point its all in the tune.

[duh2150]

oh the 2 8g cam gears don't work? i didn't know anyone even tried that just a theory i had, now i can mark that off out of my head :)

[mrg7243]

Man this shit is getting confusing with stewi and galant 306 saying similar things and DUH saying other things. Here is my target goal, put the DOHC head on stock block. Run NA untill i can get the money to run boost. yes i could have my motor built like the evo guys do with riduclous compression. I could talk to a guy i know who builds race motors and see what he says. Does anyone know for sure roughly what the compression ratio for a stock 2001 4g64 block with an evo head would be. i have heard 10.1 10.5 9.5..

[blue8g]

there's nothing wrong with 10.5:1 on NA............

[mrg7243]

Yeah i know that pretty good, i would still like to know what it would be so i could know what fuel to use ect

[duh2150]

I'm pretty sure the stock c/r is 9.0:1 the manual says 9.5:1 other places say 9.0:1 I don't think anyone really knows 100 percent if you do speak up, I'm running 8.5:1 and using premium gas

[duh2150]

Plus we all are right we just did differnt swaps and we found differnt quetions to Ask other info will be given they know what's needed for the evo swap I mainly know the Kia one simmilar but still a little differnt

[mrg7243]

thanks man for your help, i am looking to do what stewi and galant306 did with an evo head. maybe kia it just depends what i can get ahold of first.

[duh2150]

It's not really all that hard after you start I had a build thread on GF but it's gone now many I could try and recreate it it has a shit ton of input on the pistons and stuff because I was asking the same questions you are right now, I just ended up buying another engine and building it to what I wanted now it's in it runs 16.2 in under summer FL sun, trying to get it there before it's summer again and before the turbo I'm putting together 8.5:1 C/R so you'll see I hope you done the 5 speed or atleast doing it while you do this it's like amazing and I think everyone agrees

[mrg7243]

planning on the five speed, looking at a few trannys right now. the DOHC will come after tranny and cat back. i was just trying to get a feel of the DOHC head stuff

[mysticj]

I'm pretty sure the stock c/r is 9.0:1 the manual says 9.5:1 other places say 9.0:1 I don't think anyone really knows 100 percent if you do speak up, I'm running 8.5:1 and using premium gas

9.5:1cr on fed spec 3G/8G(99-00) and outlander
9.0:1cr on cali spec and all 01+ 4g64

Evo head will raise compression by .5; Kia head will lower compression by nearly 1.0

[mrg7243]

thanks man that what i was looking for

[duh2150]

THANK YOU MYSTICJ good info i been looking that that info for ages

[Prophet]

It's not really all that hard after you start I had a build thread on GF but it's gone now many I could try and recreate it it has a shit ton of input on the pistons and stuff because I was asking the same questions you are right now, I just ended up buying another engine and building it to what I wanted now it's in it runs 16.2 in under summer FL sun, trying to get it there before it's summer again and before the turbo I'm putting together 8.5:1 C/R so you'll see I hope you done the 5 speed or atleast doing it while you do this it's like amazing and I think everyone agrees

http://www.dnaelite.com/gf/phpbb/vie...hp?f=63&t=6000

[mrg7243]

whoa its the galant forums back from the dead

[mysticj]

THANK YOU MYSTICJ good info i been looking that that info for ages

No problem