bonkas Posted August 14, 2017 Share Posted August 14, 2017 Hey Guys, Trying to find pistons for my 4g63 SOHC to up the compression and possibly overbore to 87mm (Same as 4g64) I am having a hard time finding anything that suits SOHC as I dont think the recesses for the valves are in the right place for DOHC pistons?. Does anyone know who could supply me something that will work. Quote Link to comment Share on other sites More sharing options...
Mr Vapour Posted August 14, 2017 Share Posted August 14, 2017 Do you know the compression height required? Why cant you just use a 4g63 piston in 060 or 1.5(same thing) ?? ring segedin STA 092561120. They may have the 4g64 pistons you need and will also be able to tell you the compression height and pin size. Quote Link to comment Share on other sites More sharing options...
bonkas Posted August 14, 2017 Author Share Posted August 14, 2017 I believe a 4g63 piston in 060 oversize should be the same as a 4g64 but cant find any solid info that this is true - What I can find is the different stroke with different rods and crank in the 64 but pistons remain the same albeit a larger bore size... I am unsure what compression height I require to be honest.. I am learning as I go with this, know what I want to acheive but unsure how to get there so relying on engine builders etc to assist me but no-one is happy to do the work for me or want to charge an unreasonable amount to "look into it". Will give STA a call, hopefully they are happy to help a clueless punter out! Quote Link to comment Share on other sites More sharing options...
chasinthemirage Posted August 14, 2017 Share Posted August 14, 2017 I have zilch experience with Mitsubishi's but @fuel may be able to provide you with some advice? Quote Link to comment Share on other sites More sharing options...
fuel Posted August 14, 2017 Share Posted August 14, 2017 1997cc 4G63 is 85mm bore 4G64 is 86.5mm bore, 4G69 is 87mm bore The bigger bore engines are cast with more material around the cylinders to account for the larger bore size. You can't bore a 4G63 out to 4G69 size and expect the bore to hold together. The highest compression SOHC 8V 4G6x engine would be about 9:1 at the most - the early engines were quite conservative with their compression ratios. You will probably have better luck increasing the compression ratio by milling the head, but then you might run into valve clearance issues. There are tons of aftermarket issues for the DOHC 4G63s, and as you're finding out, barely anything for the SOHC engines. If you want to stick with the SOHC, be prepared to go custom made with many of the parts. Quote Link to comment Share on other sites More sharing options...
smokin'joe Posted August 15, 2017 Share Posted August 15, 2017 20 hours ago, bonkas said: Hey Guys, Trying to find pistons for my 4g63 SOHC to up the compression and possibly overbore to 87mm (Same as 4g64) I am having a hard time finding anything that suits SOHC as I dont think the recesses for the valves are in the right place for DOHC pistons?. Does anyone know who could supply me something that will work. conrod Chris Bowden up Norf would be a worthy enquiry Bowden Engine Parts Quote Link to comment Share on other sites More sharing options...
bonkas Posted August 18, 2017 Author Share Posted August 18, 2017 Chris was unable to help with anything forged or higher compression. I may have a lead from Spool Imports in Australia who can custom make a forged 10.5:1 set for me almost half price of what I can get made here of my research so far. Engine builders where most of my work is getting done rates them highly also so that might be a goer. Quote Link to comment Share on other sites More sharing options...
smokin'joe Posted August 18, 2017 Share Posted August 18, 2017 21 minutes ago, bonkas said: Chris was unable to help with anything forged or higher compression. I may have a lead from Spool Imports in Australia who can custom make a forged 10.5:1 set for me almost half price of what I can get made here of my research so far. Engine builders where most of my work is getting done rates them highly also so that might be a goer. how far can STD pistons go ? skim the head and mod the cam pulley to bring compression up ? Quote Link to comment Share on other sites More sharing options...
bonkas Posted August 20, 2017 Author Share Posted August 20, 2017 From the research I have done so far and people I have talked to.. 9:1 will probably be near to max I will get with stock pistons. My planning was not to give theh ead an aggressive skim as I am increasing valve lift and duration so need to make sure I have enough clearance. Stock the motor is 8.5:1 Quote Link to comment Share on other sites More sharing options...
smokin'joe Posted August 20, 2017 Share Posted August 20, 2017 3 hours ago, bonkas said: My planning was not to give theh ead an aggressive skim as I am increasing valve lift and duration so need to make sure I have enough clearance. if you don't increase compression ratio in the head by planing, then the chamber area is reduced by the increased piston crown. main piston to valve issues are reduced by flycutting piston and very careful camtiming Quote Link to comment Share on other sites More sharing options...
bonkas Posted August 21, 2017 Author Share Posted August 21, 2017 Yup, Sending my head and Cam to Kelfords so they can fit larger intake valves and if any further head work is required. Once I have this back I can do some clearance tests and then order the pistons to suit as they wll need to be custom anyway as there are no off the shelf options. Quote Link to comment Share on other sites More sharing options...
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