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Old 02-19-2013, 01:43 PM   #1
jacky599r
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Default any qualms with 101mm cosworth HG on 100mm bore?

I am a little paranoid about my compression ratio now. My ej255 setup:

100mm wisecos
oem crank
manley h beams
acl race bearings
arp headstuds
CNC Ported heads and polish combustion chamber
Kelford 264s

I have freaking two HG with me and still unsure which one to bolt right up...or should i go with cosworth's but i couldnt find a 100mm one. So, i am left with 0.03 Cometic's or Stock HG. How bad would the compression be? I have RON98 fuel and would be planning for meth down the road, but meanwhile...i don't wanna regret choosing the wrong parts.
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Old 02-19-2013, 02:59 PM   #2
vicious_fishes
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100mm bore and stock HG here. no issues.
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Old 02-19-2013, 03:40 PM   #3
aboothman
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Depends on the dish on your pistons. I assume you have d25 heads?
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Old 02-19-2013, 09:24 PM   #4
jacky599r
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Yup d25
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Old 02-20-2013, 10:36 AM   #5
aboothman
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What about piston dish cc? You only answered one of the questions needed to answer yours...
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Old 02-20-2013, 10:41 AM   #6
No Limit Motorsport
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The 101mm bore headgasket will not cause a problem what so ever. Non-issue.

If your combustion chambers were ported to match the EJ257 chambers than you at this point have an EJ257 engine setup, and as long as your heads or block have not been decked, your compression should be in the realm of 8.8:1. Perfect.

Just make sure you have at least .030 clearance between piston and heads and you are good to go.
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Old 02-20-2013, 01:52 PM   #7
jacky599r
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i didnt have them matched to ej257 since it is a ej255 block. I did, however, decked my heads to make sure they are straight but machinist could not recall how much he removed but said it was checked and straight and removed less then 0.1mm of material.

And i have the regular wiseco pistons so i expect it to be 19cc
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Old 02-22-2013, 02:01 PM   #8
jacky599r
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Sorry, what would be my rough CR again?
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Old 02-23-2013, 11:03 PM   #9
aboothman
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From my calculations your CR will be around 9.2-9.3:1 with the 19cc Wiseco pistons and D25 heads.

You are in the same boat as I was recently with my 17cc JE pistons and D25...9:1+ CR. Thicker gasket meant crappy quench height. So I ended up going with the +2 rods and running a Manley stroker piston with a 26cc dish to bring me back down to 8.5-8.6:1

Hopefully one of the senior builders will check my numbers before you go out and spend a bunch of money

Last edited by aboothman; 02-23-2013 at 11:14 PM.
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Old 02-25-2013, 06:36 AM   #10
jacky599r
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Ah man, 9.3 is high!!!! I have Ron98 fuel though and not sure if that would keep detonation at bay... God damn it. Other cheaper alternatives?
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Old 02-25-2013, 10:50 AM   #11
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Not an expert on fuels bud so I do not know how your ron98 compares to our 91 or 93. Either way it is not a deal breaker it just means you will go running lower boost. See what your tuner thinks

I opted to keep my CR lower, but I had other reasons for changing my build...
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Old 02-26-2013, 03:08 PM   #12
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what would be a good HG thickness to get? U mentioned crappy quench...and that affects?
This sucks...im neither here nor there now...
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Old 02-26-2013, 03:47 PM   #13
aboothman
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The thicker your HG the higher your quench. IIRC OEM HG gives you around .030"-.035" quench depending how much has been removed from your heads and block. Add the increased HG thickness to that figure. So for a .040" HG you would have: .030+(.040-.020)= .050" quench

Thats off the top of my head....again, hopefully some more experienced builders can chime in on ideal quench and some more details.
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Old 02-27-2013, 01:54 PM   #14
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help to fix my high CR....
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Old 02-27-2013, 01:59 PM   #15
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i also have kelford 264 cams and how does everything come into play now?
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Old 02-27-2013, 03:37 PM   #16
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The 19cc dish gives you a 9:1 CR on an otherwise stock wrx engine. The fact that you decked the heads and used 10mm pistons brings it up to ~9.3. If there was any material removed from the combustion chamber during polishing it will be a bit lower than that maybe 9.2. Normally I'd say it's slightly high but where I live we get crappy gas. According to wikipedia
Your 98 Ron gas is like 93ish octane here which is decent. With the headwork, and decent fuel I think your compression ratio is fine with a stock gasket.

What turbo are you going to run?
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Old 02-27-2013, 11:52 PM   #17
jacky599r
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Yeah, you are right, there are some materials taken off when i sent the heads for porting. Machinist told me they wanted to balance the combustion chamber.

How does the kelford cams change dynamic compression?

I ordered a twin scroll TD06SL2 20GTX 10 cm and planning on meth down the road
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Old 02-28-2013, 12:35 AM   #18
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The cams will allow for a bit higher cr. how much I don't know enough to say. Maybe an expert can say lol. There are people here who have done similar builds with a higher cr and cams though. Jr even did I think 9.8:1 manley pistons on pump gas with the heads and block all decked. He seemed to really like the way that setup worked out. Although I believe the bigger 35r hotside probably helps his efficiency a little bit more than the 20g will. Still though you're more than half a point lower in compression. He mentioned that he ran a lot less timing in that engine. Hope you have a good tuner.
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Old 02-28-2013, 04:26 AM   #19
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appreciate it!

Now, are there experts out there willing to chime something in?
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