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Discussion Starter · #1 ·
So basically the engine in my car (05 forenza) currently was destroyed my an incompetent mechanic and i may have a chance to rebuild it... From what I hear, the x20xev pistons will go in the u20 block, on u20 rods, and will deliver 11:1 compression ratio... Would the stock engine management still suffice to run this? Basically I am curious about gaining a bit of power/volumetric efficiency by running higher compression and maybe porting the head( depending on the damage done from bits of valve floating around) but for the sake of simplicity I was hoping to retain the stock engine management(but running 91 octane fuel for the sake of safety)... Could such be safely accomplished?

I read the thread in daewootech here...
Daewootech.com ? View topic - Rebuilding the T20/U20 engine block

Any input welcome...
 

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Discussion Starter · #2 ·

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hi ill answer the question here. i think its better if we start a new thread about it. heres the deal. i went and did some double checking and as far as i can find out the compression ratio for the x20xev is 10.8:1 for the vauxhall version, the opel version is 10.5:1. i think the x20xev rods and pistons drop right into the u20sed. now, the c20xe compression ratio, i think, is 10:5:1. but there is a big plus. the plus is with the c20xe rods you get the floating wrist pin design needed to run aftermarket pistons. the other plus is oem forged rods. with the c20xe rods, if you use arp rods bolts i believe you can safely rev to 7500-8000rpm. also i think the xev rods are good for somewhere around 300-350hp. for my build i was able to get oem c20xe forged rods and oem mahle pistons. id have to double check the RPM and HP numbers but i think theyre pretty close. i really dont think the oem engine management would work but you could probably get away with using a piggyback fuel ignition controller like the AEM FIC.
oh yeah, i checked the wiseco link. you can get the pistons in 86 bore/stroke or oversize if you wanted to bore the block. ihave a bunch of the info and part numbers for various parts ive been getting together for my build. depending on what parts your looking for it might come in handy. i was going to post the list but it got eaten by my phone. i have most of the info back together i just need to add a few more things.
 

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I'll stay away from commenting about the interchangeability of X20 / C20 parts as I don't know enough.

But to your more general question - you could rebuild your U20SED with 10.5 - 11 CR and use the stock ECU - provided you don't significantly change other stuff as well. I'll explain. Our stock 9.5 CR U20SED is tuned (fuel and ignition maps) to run on 87 octane - which is a pretty low/conservative standard. If you bump up the compression a little and keep everything else the same I'd say you will be fine if you run 91+ octane as this will provide the additional knock resistance. Also keep in mind the car has factory knock sensor which should immediately detect any knock and momentarily dial back the timing. For the same reasons I'd say you would also be fine to run a ported head as well - just don't go super aggressive with the porting.

On my Optra I've had a ported head for 5 years - and the car ran just fine on stock ECU when I would unplug my emanage to test.

Having said that, you might be missing out on some gains to be had by not playing with the timing/fuel - but I really don't think you will hurt anything.

If you start changing other more significant things such as: cams, throttle body, turbo, etc then you definitely will need a way to tune it.
 

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Discussion Starter · #5 ·
Yeah I wouldn't be doing much to the head at all, just knocking down the casting imperfections... I know if I were to change the cams, the fuel map would need to be altered... I still planning on running the stock engine management with its 6500 RPM limit, so the rev capability of the c20xe rods is totally null... Would the bump in compression be worth the future need to run 91 octane fuel? In other words, all other things equal, would I gain a significant amount to go up to 11 or even 12 to 1 compression? And part numbers on the stock xev pistons would be great...
 

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Discussion Starter · #6 ·
For tuning, if I decided to... I was planning in maybe an apexi SAFC-II... How would that AEM FIC work? Similarly I guess, but with added ignition advance control?
 

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your missing the point about the c20xe rods. its not the rev limit that important, its the actual strength of the rods. theyre forged, basically that means theyre stronger. theyre weak point is the rod bolts. that can be fixed by using arp rod bolts. and as i stated above, they use the floating wrist pin design which means you can use them with the aftermarket pistons. you CANT use the x20xev rods with aftermarket pistons. on a side note, the ability to raise the rev limit means that you have the ability to make more power on the top end. that IS an important fact if your going NA. by upping the compression, with a proper tune, i believe you could possibly be looking at a bump of up to 20hp.
about the tune and what you use to do the tuning. ultimately it depends on who tunes the car and what theyre comfortable with using. i wouldnt bring and afc to someone to tune who doesnt have experience with the unit. you should really find your tuner before choosing what you want to tune with. one of the pluses with using aem is the availability of help if needed. its a USA co. so theyll be quick to help with any issues you may have and if theres a problem with the parts its quick turn around time. another plus is that aem is a widely used tuning aid. that means more people know the equipment and have the ability to tune it. but again, it all depends on the tuner.
 

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Discussion Starter · #8 ·
I don't believe I am missing the point of the c20xe rods... I was just assuming that I could put the xev pistons on my stock u20 rods, like I read in the thread on daewootech... That would be cheaper than getting pistons and rods from he c20xe... If I couldn't find the xev pistons i plan to get the c20xe rods and those 12:1 wiseco pistons...(I wonder if the car could run on 91 octane fuel at 12:1CR?) the point is to replace the broken u20sed pistons with better ones while the engine is apart, but not to completely build a high RPM screamer... Besides, I don't believe I've ever seen a piggyback ECU that could raise a rev limiter... So I would still be stuck at 6500... Would forged rods even be necessary with the maybe 20-25 hp I expect to gain from the higher CR and the head/ intake porting? It's not like I'm shooting for 200hp and switch into ITBs, lol
 

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yeah but higher RPM's aside you cant run aftermarket pistons on either the u20sed rods or the x20xev rods. youll either need to use the c20xe rods or aftermarket rods. the fact that there forged adds to the security of the build and your ability to push the car further in the future. you be able to find used c20xe rods on ebay for pretty cheap. you can actually get some pretty cheap forged rods brand new. $250-300 i think ive seen them. also youd basically be able to redline the car at every shift with no ill effects lolol you can put the x20xev pistons onto your oem rods. that would still be good for a bump in HP. as for running 91 octane with 12.1:1 i think you could it just depends on the tune. if your looking for a bump in HP without spending to much money i would just pop in the x20xev pistons do an exhaust and intake, then port the head.
 

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Discussion Starter · #10 ·
Yeah, this was intended to be a budget build... It's good to hear about the xev pistons going onto my u20 rods... Yeah I was just planning on porting the head a little(removing casting imperfections and cleaning up the port shape a little if needed) and porting the intake in a similar manner... Eventually going to build a short ram intake (probably will happen before the engine goes in lol), possibly a cat less mid pipe and an exhaust back from there... But that is basically all I plan to do... I hope for about 140bhp...
 

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Discussion Starter · #11 ·

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Discussion Starter · #12 ·
Got a new question, figured I would out it here...

So I got the head back from getting worked on, and it looks fine in most places... But the combustion chambers are pretty beat up from the valves breaking off... There is a pretty deep gash in the quench area in one of the cylinders that I would like to repair if possible... Given that there are no breaches into water, what are my options for repairing the gash? Is there an epoxy that could be applied to the area and then shaped down to proper shape with, say, a dremel? I plan on getting the head surface shaved to ensure proper seal to the block...
 

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Damn its that bad ... I don't think there's any epoxy type substance that would hold up inside a combustion chamber. IMO the only option would be to weld it and use filler... even then I'm not sure if that's really ideal. Can you post a pic?
 

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Discussion Starter · #14 ·
I will gladly post pics of both the short block and the head when they are both in my possession and I can photograph them and upload the pics...
 

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Discussion Starter · #15 · (Edited)
Accidental double post, lol
 

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Discussion Starter · #16 ·
Here's a pic of the damage to the block... Only have one on photobucket, it's being a total PITA...


Here is a pic of the cylinder head... Look closely at cyl 2, second up from the bottom...

 

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Discussion Starter · #17 ·
Here is a close up pic of cyl 2, the one with the deep gash that I was asking about... You can kinda see cyl 1 below, in great shape... Nothing happened there...

 

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Oh man.... that really sucks.

TBH if it was me, I would have just sourced a new (used) complete head or engine from a local wreckers.

I really don't know how effective it is to repair damage like that... I would think welding would work, but you have to make sure its formed correctly and that it doesn't compromise integrity of anything else in that area.
 

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Discussion Starter · #19 ·
The block appears totally fine, other than the piston damage... Cross hatching is still visible in the cylinders, so I assume I just need to find a head... I could probably just use the stock head off my u20sed, but I was hoping to reuse the damaged one and get it ported, polished, and milled... I can still port my intake and exhaust manifold though...
 

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hey. 60gbp doesnt seem to bad. thats for each piston though so it would be around 240gbp or around $398.86 plus shipping.
i just read an article about fixing things like that gouge in your head. they weld then shape down the new material to match. not sure how costly that would be though. also not sure exactly who would be able to do the work for you. might take a little bit of looking around. i wouldnt port the intake until you get the head done. that way they can port match the intake to the head. just easier to do it at the same time. same with the exhaust. what about cylinder number three looks like theres a problem there too? you might be able to get a remanufactured bare head for pretty cheap and use the damaged one as a core. might not be a bad idea since you need to replace the valves anyway.
 
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