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08-28-2010, 12:24 AM | #201 |
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something also along the lines of the sharp angles that the air has to flow through, that get smoothed out when the compression chamber is altered.
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08-28-2010, 02:38 PM | #202 | |
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Thanks -- Ed |
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08-28-2010, 04:30 PM | #203 |
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Squidz, I'm really interested in what you come up with. I have a 2.0 that looks like it spun a rod bearing on my way to an autocross last week. I like the idea of a little more compression but it seems like a balancing act from what I could gather on posts. Too much compression can't be good but too little may leave you wanting.
My wife says the same thing. Build it once or sell off the rolling chassis, which I am considering doing. A cool sticky for people who currently have the so-called 2.5 / 2.0 hybrid would be what they're running for cams, gaskets, and so on. I'd prefer to learn from someone else's mistakes than make my own. Then folks could readily review these setups and mirror them as needed. For now, it's a lot of trolling trying to sort out the facts. Anyway, I'm interested in what you wind up doing. Good luck. |
08-28-2010, 04:46 PM | #204 |
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not only is it trolling for facts...it subaru owners trolling for the proper build.
some people say that the hybrid works...nuff said. i think what ed is doing to improve the performance of the 2.0 head on a 2.5l block makes sense. |
08-28-2010, 10:05 PM | #205 | |
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The biggest problem with the hybrid setup, however, is the shape of the combustion chamber and sharp edges from the 2.0l head. This causes inconsistencies in power and knock resistance and makes for horrible performance under pro-longed hard use. Thanks -- Ed |
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08-30-2010, 07:29 PM | #206 | ||
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Yes, on a road course, this isn't ever an issue...but i'm not building a road course car. So i'm not worried about affecting my top end. I am just wondering if this is a good way to create more low-end torque, or should i let the smaller head chamber bump the compression a bit. I just want to make sure i have all the information so i can make the right choice...i only get one shot at this. Why don't the sharp edges and shape of the combustion chamber have those issues on the 2.0L, is it the difference in the bore that causes the combustion chamber shape to be so out-of-whack? What causes the sharp edges to become a problem with the higher displacement? Last edited by Squidz; 08-30-2010 at 07:34 PM. |
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08-31-2010, 07:36 AM | #207 |
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Squids,
The 2ltr head is 92.5mm across and fits the 92.5mm bore perfectly. These sharp edges are flush with the perimiter of the stock 2ltr bore. However when you lay the stock 92.5mm 2ltr head on a 99.5mm 2.5ltr bore, the edges of the smaller head now protrude into the larger cylinder area. This is where you will have issues. These are my own Spec C heads with a CNC chambers of my own spec. These will be going on a forged/pinned EJ257 with a GT35R |
08-31-2010, 11:38 AM | #208 |
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Is the degree of the valve angle different on a ej205 head vs a ej257 head ? Also do you machine the combustion chamber to the identical volume and dome specs to that of the ej257 heads ? I don't have a hybrid just curious.... What are the combustion chamber differences between an ej255 and 257 ?
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08-31-2010, 11:40 AM | #209 | |
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08-31-2010, 05:12 PM | #210 | |
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I have had enough of these motors apart that i figured that is what we were talking about, but some of the posts make it seem as if the 'sharp edges' are in the shape of the cobustion chamber itself...that i just didn't see. Have done a lot of research on this over the past day or so...it looks like the machined 2.0L heads with custom 2.5L pistons to bump the compression ratio is going to be the best way to get where i'm going. Of course it is, that makes it about $1000 more expensive...lol, i'd rather it be right than cheap though. Thanks all. |
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09-01-2010, 01:44 AM | #211 | |
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09-01-2010, 01:58 AM | #212 | |
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Sorry for the mspaint edit, but I have some questions....
For the most part, the picture is self explanitory, however I have only seen images where people have "opened" up the combustion chamber on the sides (see "C" and "D"). This would equate to 3.5 mm of material from each side(99.5 - 92.5 = 7/2 = 3.5) to match the new piston and bore. However with the increased bore you also make the top and bottom (orange area) larger by 3.5 mm on each side as well (See "A" and "B" - 9.5-6= 3.5). Since this increased "lip" is what heats up and causes detonation, why hasn't this area been machined as well? (or has it???) Maxwell power also had this to say about the combustion chamber: Quote:
Picture in linky So with this logic, why isn't this extra "step" (orange area in my picture above) machined or how is it dealt with? Or is the real solution back to simply decreasing CR? For example, if the machined heads were used AND we somehow kept the quench area the same but managed to bump the compression ratio back up to 9.1:1, do you think we see the same detonation issues even though we have a "matched" combustion chamber for the new piston? However back to machining the lip(s), obviously the areas where we do eliminate the lip will lessen the chance of detonation. Right? Thanks! Last edited by paintbing; 09-01-2010 at 02:06 AM. |
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09-01-2010, 07:46 AM | #213 |
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Youre right my orange area has not been opened up and effectively the quench area is now larger than before.
With my gasket thickness i have a calculated 0.9mm squish clearance. |
09-09-2010, 01:32 PM | #214 |
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Ed you have done a remarkable and excellent job solving a common OBVIOUS problem. Anyone who has laid a 257 head gasket over 2 liter heads would see what the challenge is. Nice work and can I have your cnc code? haha!
This thread could have concluded with the same effect on page one if it weren't for the demagogues. I'll bet Ed has a dirtier workshirt and no-hobbies as compared to the slobbering hounds trying to look and feel relevant. The conclusion is still that this mod allows the hybrid to tune like a 257 longblock for cheap. Big score for so many 2.0 liter owners who are replacing their shortblocks these days. Ed, hats off for keeping your cool. My response would have been unpleasant to those who can't grasp simplicity. |
09-09-2010, 06:12 PM | #215 |
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^Just so that we're clear, I too think this is a fabulous upgrade from the knock-prone hybrid.
My post above is in no-way trying to downplay this mod, but merely trying to get answers(or a disucssion) with what is happening in the combustion chamber. Ed's work merely addresses the sides (which may be enough to solve the issue) and doesn't address the increased quench at the top and bottom. Just wondering. Thanks! |
09-09-2010, 10:20 PM | #216 |
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Someone didn't take their pills today....
I searched the thread, but didn't find anything on this: I have decided i'm definately doing this service, and raising compression with custom shortblock from Rallispec. I'm considering purchasing the V6 EJ205 big port heads from them instead of re-working mine... Any reason this service won't work on these heads? Would it be more cost effective/easier to have you work the USDM EJ205 heads that i have? Flow differences? Thanks, i'm finally getting close to having this all together...i'm actualy getting excited about it now. |
09-09-2010, 11:45 PM | #217 |
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so, with the EJ205 heads being notorious for developing cracks at the spark plug, how much material do you guys remove from that area?
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09-10-2010, 02:39 AM | #218 |
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I did some more reading - http://racingarticles.com/article_racing-10.html
This helps explain the increased quench area at the top and bottom. According to the article, leaving this area alone and shaping the combusiton chamber only (like ed is doing) will help increase velocity near TDC and actually increase the turbulance and create a more efficient burn(more power with less fuel). Also, the increased turbulance coming from the larger quench area will help cool any hotspots formed at this leading edge, but NOT on the two sides Ed's service ends up removing. Using a thicker HG seems to decrease the velocity of gasses and doesn't provide an efficent burn. Convesrely using Lower compression pistons has the higher velocity, but still has hot spots to cause detonation(pistons may last now that they're upgraded, but your bearings will quickly be destroyed). Either way, like Ed stated earlier - at a minimum, the two sides should be deshrouded to remove hotspots. I bet just touching them with some progessive wet sanding will help prevent the leading edge from heating up.(i'll be doing this since my build ended up taking a turn that didn't allow me to get my heads to Ed). Anyway, I want to thank Ed for offering this CNC service. Now only if your service created a nice swirl action to occur.... Last edited by paintbing; 09-10-2010 at 02:45 AM. |
09-21-2010, 09:55 PM | #219 |
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Hey guys! I've been out of town a while, so I apologize for not answering these earlier. I'll have to take some time tomorrow to go through the questions and do my best to answer them.
Thanks -- Ed |
09-21-2010, 10:22 PM | #220 |
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Ed what benefit could the sti guys get from reshaping the combustioon chamber to help with the inflow of the mix and thee out flow of the exhaust. i see that most of u guys are happy with just the stock design but if u mildelyy resape the intakke and exhaust flow to the valves can increase hp and also torque. i have been very courious to do and also see this but it seems that no one is even interested init?
thanks john |
09-26-2010, 07:17 PM | #221 |
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what is the cc of the new combustion chamber of a 2.0l head to a 2.5l clone?
stock 2.0l head...49cc? stock 2.5l head...59cc? i'm wondering if you can safely cut a 2.0l head to 59cc. |
09-28-2010, 01:55 PM | #222 | |
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Thanks -- Ed |
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10-01-2010, 05:36 PM | #223 |
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bump.
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10-03-2010, 11:45 AM | #224 |
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I am curious about the answers to these questions.
and another by Homemade WRX - so, with the EJ205 heads being notorious for developing cracks at the spark plug, how much material do you guys remove from that area? |
10-06-2010, 02:33 PM | #225 | |
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Thanks -- Ed |
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