balbains324

Theory

I have currently CP Pistons 8.8:1 Compression, since I am using a supercharger that only puts out 9psi I need to get all the gains I can.

I was thinking about using 1.8 rods and increasing the compression in the engine back up to 10:1 to increase power.

Questions

As I understand the 1.8 rod is longer then the 2.0 rods....is this true?

Is this possible?

Can I get forged 1.8 rods, do I need them?

Is there an easier way?

Can I do this myself?

Would the gains be worth it?

Does anyone have a set of 1.8 rods that they feel like posting to the UK? laugh.gif

SOCKS_old

1.8L rods are shorter. which is why the 1.8L rod and piston combo gives you about ~7.7:1 compression

if you put 1.8L pistons on 2.0L rods, you get around 11:1 compression. 1.8L pistons are more domed on top, i believe.

if you use 1.8L rods and 2.0L pistons, no compression LOL.. no, but it will be LOWWWW.

so if you have 8.8:1 compression pistons now, and you used 1.8L rods, your compression would be SUPER low.


at 9psi, i would sell your CP pistons, buy some stock 2.0L pistons and run the stock 10.3:1 compression.. gains would be worth it IMO

heres the numbers i believe are correct for compression ratios.

1.8L rods-1.8L pistons = 7.7:1 compression
1.8L rods-2.0L pistons = 5.5:1 compression
2.0L rods-2.0L pistons = 10.3:1 compression
2.0L rods-1.8L pistons = 11:1 compression

so your setup with 8.8:1 compression AS IS, with 1.8L rods would put you at like 4:1 or so since you already dropped from 10.3:1 to 8.8:1.

balbains324

oh.....so it's the 1.8 piston that increases compression. I had it the other way round.

This means I need to source some forged standard compression pistons.....damn!

My CP pistons cost me shit loads getting them delivered to the UK and stuff!!

Does anyone know where I could get some rods to increase the compression of these pistons?

SOCKS_old

i doubt anyone knows where you can get custom longer rods from, but someone might.

as far as the pistons go, at 9psi, theres no need for forged pistons.. just get some stock 2.0L pistons and sell the CP pistons for a nice chunk of $$$$$. would be much cheaper than getting a forged set of stock compression pistons.

balbains324

The reason why I got forged pistons was because the stock piston didn't hold up, I think it was mostly due to the tuning but I will try and get a set of custom rods or something to restore my compression. Here are the dimentions of rods for Hyundai.

Accent/Scoupe
Pin diameter = .709"
Big End Bore = 1.890"
Length = 5.154"
Big End Width = .900"
Weight = 491g

Tiburon 2.0L 4Cyl
Pin diameter = .787"
Big End Bore = 1.890"
Length = 5.753"
Big End Width = 1.015"
Weight = 600g

1.8L Tiburon
Pin diameter = .787"
Big End Bore = 1.890"
Length = 5.551"
Big End Width = 1.015"

Sonata 2.7L V6
Pin diameter = .827"
Big End Bore = 2.008"
Length = 5.548"
Big End Width = .780"
Weight = 658g

balbains324

I emailed Pauter and thought people might be interested in the response.

"While we can make any length rod you wish, it is not likely you can accomplish your desired result through altering rod length in this case. A minimum deck height of about .040" (1mm) is required at top dead center to ensure the piston does not come into contact with the cylinder head. The most common method of raising compression is to use custom high-compression (domed or at least flat-top, if current pistons are of a negative dome design) pistons. Be advised that piston to valve interference issues must also be looked into."

So in conclusion.....does anyone want to swap some forged 10.3:1 pistons for some 8.8:1 CP Pistons? laugh.gif

SOCKS_old

if your stock pistons failed.. getting forged stock compression isnt gonna help.. they will fail also eventually.

you need to fix w/e tuning issue you have, and just go with OEM stock 10.3:1 compression pistons, and you will be fine..

9psi is nothing for the stock internals.

also at the same time, have the rods cleaned up and strengthened. get some ARP rod bolts.

optimoprime

what i dont get is that its been proven TIME AND TIME AGAIN that stock stuff will hold up if you have your tune right. but people will still go out and buy the forged parts for crazy amounts of cash. KDM shops are using 1.8 combo, hell SFR's black GK was on 29psi with stock 1.8L internals

SOCKS_old

the 1.8L combo is the cheapo half assed way to do things..

yeah it works, and you can push MAD JDM boost yO, but its the cheap way out of doing it right..

7.7:1 compression FTL. so to hit the same power, you need to push more boost, wearing your 1000$ turbo out faster.

bragging rights for pushing crazy boost, yes.. good setup.. not really, unless your just plain cheap.

i know id rather spend 400$ on some 9:1 compression forged pistons, and push 18psi, than spend 300$ on stock 1.8L combo and have to push 21-22 psi for the same numbers.

David Dickson

If you have a shop that knows what they are doing you can mill the head and block to gain about 1 point in compression. I stress they NEED to know what they are doing though as your messing with valve to piston clearences.