Compression for N/A build

Webers, Cam selection and Ignition upgrades.

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Compression for N/A build

Postby erikgetty » Sat Jan 28, 2017 5:44 pm

New to forum and just here looking for input. going back through my 3tc in the near future.

current:
87mm bore w/ stock pistons
eagle rods
arp everything (rod bolts, main bolts, head studs, flywheel bolts)
aasco flywheel
ported cyl head
+1mm ss valves
valve locks
crower cam (regrind 268 <i think i cant find the cam card>)
adjustable timing gear
hardened push rods
double valve springs
single DCOE 45mm weber
pacesetter header
probably missing something in there.
i made some compromises at the end of the build that i'm not proud of but i just flat out wanted to get back on the track and was running out of money. so i'm here now to fix those problems. it slides pretty good but id really like to set it up to make at least 200 whp N/A. as in without turbo or boost... so first thing that i wanna fix is the pistons. stock compression kinda blows and i have been told that i have too much cam for stock compression (this was by an "engine builder" i don't even know if that's a thing or not)

plans for redo:
efi conversion (trying to get a couple of those jenvey heritage throttle bodies in 45mm)
mega squishy
i would love to ditch the dizzy for a COP system (maybe LS coils) dont know yet how that works with oil pump
better header/exhaust (doug thorley?)
high compression pistons

which is where yall come in... called my buddy the wiseco dealer and asked what they have for "off the shelf" pistons in a 89mm bore (because that's just free power through added displacement). he said 8:1, 10.5:1, and a completely insane 14.2:1. (i may be wrong on the 8:1 but i don't care about that one cause i'm not building a turbo charged engine) so its between a 10.5:1 and some weird machining voodoo or a 14.2:1. i was imagining a 12.5:1 (custom piston i guess and if it doesn't make enough i suppose laughing gas fixes everything). so my question is what have people done in the past to make my power goals NA. is that much compression necessary (14.2:1). if so do those pistons fit the combustion chamber or will i have to run some stupid thick head gasket (i will of course still clay it). my hesitation for 10.5:1 is that i want something that's easily repeatable when/if the motor lets something go. i don't want some crazy one off machining job done to make this work and then forget how i got there. my hesitation with 14.2:1 is that i don't even know what kinda gas you need for that... will vp110 do that much compression? C16? also i don't know if those will even fit the combustion chamber without modification which brings us back to the "easily repeatable" point. and of course my hesitation with a custom 12.5:1 is that it costs a couple hundred more dollars for custom pistons. so there it is. my thoughts. now i would like yours.

to be clear.... by input/thoughts i mean you have assembled or have helped assemble an engine that is <insert what you tell me>. i don't need opinions here (citation or documentation would also be welcomed). i know this sounds rude but i've been on a lot of forums over the years and i know how these types of questions can go.

thanks in advance
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Re: Compression for N/A build

Postby BOBLOOK » Sat Jan 28, 2017 9:48 pm

The day we learn to think
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Re: Compression for N/A build

Postby erikgetty » Fri Feb 17, 2017 12:09 am

for the record... no one replied so i just went ahead and got the 14.2:1... hopefully this isnt a massive mistake.
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Re: Compression for N/A build

Postby BOBLOOK » Sun Feb 19, 2017 11:19 am

Okay the majority hang around fb instead of forums sadly :evil:
https://www.facebook.com/groups/3tcgara ... ts&fref=ts
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Re: Compression for N/A build

Postby oldeskewltoy » Wed Mar 08, 2017 5:15 pm

erikgetty wrote:for the record... no one replied so i just went ahead and got the 14.2:1... hopefully this isnt a massive mistake.


ahhhh, it might be...... :?

a LOT depends on what variables Wideco used when calculating the compression ratio. I know for a fact that they, and other piston makers screwed up 4AGE pistons pretty badly.

What you need to know is piston dome volume. With that, and chamber volume you can calculate the ACTUAL compression ratio of YOUR engine......
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