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Old 07-31-2008, 02:19 PM   #1
06njsti
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Default BC Stroker kit or stay 2.5l

Okay guys the time has come to start building my beast. I just picked up a daily driver and am going to start to build an engine i have in my garage. I want this block to handle 700whp so i can safely run around 600 through it(race gas and meth). i am going to build the block completely from sleeves to cams and am debating going with a 2.71 stroker kit. What do you guys run who are putting down the HUGE numbers. I plan on running just a 35r but hopefully pushing around 35+ psi. Also are stroker kits harder to tune then a regular engine? i emailed my tuner and havent heard back from them yet.
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Old 07-31-2008, 02:52 PM   #2
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I have a 2.7L and wouldnt do it again. Instead I would still sleeve big bore 101mm-102mm and run a 2.0 wrx crank (destroke) and long rods. I would have the 2.0 crank turned down on the rod journals for honda rods (way more choices for length) and a bunch of measurements for custom pistons
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Old 07-31-2008, 03:19 PM   #3
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do you have 15k laying around?
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Old 07-31-2008, 04:47 PM   #4
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It doesnt take 15k, maybe 6-7k. action machine did my sleeves and all materials for less than $1600, pistons $800, modified crank $200-$300, rods $500 then the rest of the standards lik oil pump ect, ect... Its more your time, calculations and educating yourself... I have less than 7k in my 2.7L
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Old 07-31-2008, 05:05 PM   #5
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Quote:
Originally Posted by 06njsti View Post
I want this block to handle 700whp so i can safely running just a 35r .
Quote:
Originally Posted by Sinister redlines View Post
It doesnt take 15k, maybe 6-7k. action machine did my sleeves and all materials for less than $1600, pistons $800, modified crank $200-$300, rods $500 then the rest of the standards lik oil pump ect, ect... Its more your time, calculations and educating yourself... I have less than 7k in my 2.7L
Let me quote a few highlights for you out of this guys build.

You forgot THOUSANDS in headwork also. He better just start with brand new subaru castings and go from there

And you forgot the little stuff to.

I still stand by my 15k

and the 2.7l isn't just a "modified" crank. you know that (well, assuming you stroke it and don't have some crazy bore diameter).
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Old 07-31-2008, 05:17 PM   #6
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I have the BC 2.7L, its a new crank and a big bore w/sleeves. I was telling him to run a big bore, short stroke long rod engine NOT the BC kit. OK spend 3500 on cossie heads.... The little stuff doesnt = 5K.. I just disagree and I have the setup so I am not just guessing, no reason to argue. Plus he can do alot himself to save $$
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Old 07-31-2008, 05:55 PM   #7
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For the turbo a gt35r isnt the best pick for those #'s you state. Take a look at the t4Z

http://www.atpturbo.com/Merchant2/me...egory_Code=GTB
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Old 08-01-2008, 01:15 AM   #8
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Quote:
Originally Posted by Sinister redlines View Post
I have a 2.7L and wouldnt do it again. Instead I would still sleeve big bore 101mm-102mm and run a 2.0 wrx crank (destroke) and long rods. I would have the 2.0 crank turned down on the rod journals for honda rods (way more choices for length) and a bunch of measurements for custom pistons
what a good idea
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Old 08-01-2008, 01:34 AM   #9
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I have a 2.71L motor sitting currently waiting installation. But I am currently in the same boat as sinister redlines. I would like a free breathing destroked big bore motor.
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Old 08-01-2008, 02:34 PM   #10
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Originally Posted by MartinSTi05 View Post
I have a 2.71L motor sitting currently waiting installation. But I am currently in the same boat as sinister redlines. I would like a free breathing destroked big bore motor.
I just put a down-stroked EJ257 in my car last week, preliminary results are good so far.
It revs like a 2.0, feels like a 2.5....

Stage 1 dyno comparison:
Red plot = stock 04 sti longblock
Blue plot = down-stroked 05 sti hybrid (2.35L)

Same boost (17 psi), same turbo, same intake manifold, same exhaust, etc.. same car, same dyno.

This is with full stock exhaust with cats and stock manifolds...




35R is going on when it gets 2,000 miles on it :-)

Last edited by Turbo_Mike; 08-01-2008 at 02:41 PM.
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Old 08-01-2008, 09:45 PM   #11
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^^ Looks like the 2.5 has you licked early on there...and there are 2.5's capable of spinning to 8500rpms on without drysump, and 9K with drysump.

These comparos are hard to make sense of since the tune has changed in addition to the components themselves. It's hard to know if the difference is due to the destroke or the tune applied to the destroked engine.
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Old 08-02-2008, 02:35 AM   #12
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I've been throwing around the same idea as well. I wanted the BC 2.71 but started reading and realized that destroking while increasing bore could be very benificial in stretching the power band. I'd love to toss a ver.8 crank into my 2.5 with 102mm pistons and call it good but it's not that easy. The issue that I'm finding is the lack of help and OTS parts to support destroking. The people that have done this aren't really into sharing how they have, or so that's what I've seen.

Turbo_Mike are you willing to share your measurements with us.
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Old 08-02-2008, 11:36 AM   #13
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Its really not as difficult as you think, some measuring and some math probs and your there. CP or any other custom piston manufacturer can make what you need you will just need to have the measurements done. Yes its not OTS but do some reading and educate yourself as there are many good books with the math in them.
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Old 08-02-2008, 12:00 PM   #14
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ahh finally a destroker! ...ive been talking about that for two years...

idiots with srt-4's cant grasp the concept yet... it nice subarus have begun too...

(wants to do a 2.2ltr srt-4 that rev's to 8k+)
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Old 08-02-2008, 06:14 PM   #15
Sinister redlines
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Well I have an extra head and turbo from a srt 4 if you want it LOL Cheap...
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Old 08-03-2008, 02:40 AM   #16
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Quote:
Originally Posted by Sinister redlines View Post
Its really not as difficult as you think, some measuring and some math probs and your there. CP or any other custom piston manufacturer can make what you need you will just need to have the measurements done. Yes its not OTS but do some reading and educate yourself as there are many good books with the math in them.
Do you have any references that you could point me to. I'm just looking for the right direction. Any help that you have would be greatly benificial not just to me, but to everyone interested.
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Old 08-03-2008, 01:52 PM   #17
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Do you have any references that you could point me to. I'm just looking for the right direction. Any help that you have would be greatly benificial not just to me, but to everyone interested.
Personaly I prefer the books but I have used the desktop dyno programs and the new ones have the compression calc and all the math built in. Simply plug the #'s and it will give you your rod ratio, comp, ratio, ect. Just use the info on the stock replacement forged piston for piston top cc's and for deck measurements. Then measure wrist pin to piston top, ect,ect and the program calc can on the fly show measurements.

Alot of people turn thier heads at this program but it has all the math built in and it even has a subie application on there. Plus you can see how cam profiles will effect power bands and there is a pretty good list of turboes on there..

http://www.proracingsim.com/desktopSCdyno.htm
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Old 08-03-2008, 01:55 PM   #18
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right on, thanks for the help.
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Old 08-03-2008, 02:21 PM   #19
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erm.... my heads were clse to 5k but whatever
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Old 08-03-2008, 11:19 PM   #20
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yeah...paying for built heads and shortblock...you can usually ball park a $10k longblock. All that small stuff adds up quickly.
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Old 08-04-2008, 12:06 AM   #21
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erm.... my heads were clse to 5k but whatever
Well its all relative, I ported and flowbenched my own including installing bigger seats for 1mm oversized valves. I have about 1k into them (cause I had to buy some tooling). It just depends on what you do or what someone does for you...
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Old 08-04-2008, 02:15 PM   #22
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Originally Posted by jigga View Post
^^ Looks like the 2.5 has you licked early on there...and there are 2.5's capable of spinning to 8500rpms on without drysump, and 9K with drysump.



These comparos are hard to make sense of since the tune has changed in addition to the components themselves. It's hard to know if the difference is due to the destroke or the tune applied to the destroked engine.
Yeah you can expect a loss of low end torque both due to the displacement decrease and the reduction of stroke, which reduces low rpm torque.

Both engines used the same exact rom with the same exact timing curve(base timing map), althouth the de-stroked motor took about 8 degrees more total timing due to having less compression(applied using flattened knock correction map). Both engines were tuned to the point of spark knock on pump gas.

The 2.5 "could" have kept going, but from experience and the graph, its clear that the power has already nosed over and would be a waste of effort to rev the motor any higher.


Quote:
Originally Posted by domestic_abuser View Post
I've been throwing around the same idea as well. I wanted the BC 2.71 but started reading and realized that destroking while increasing bore could be very benificial in stretching the power band. I'd love to toss a ver.8 crank into my 2.5 with 102mm pistons and call it good but it's not that easy. The issue that I'm finding is the lack of help and OTS parts to support destroking. The people that have done this aren't really into sharing how they have, or so that's what I've seen.

Turbo_Mike are you willing to share your measurements with us.
I agree, there is little to no info available on the subject so I just went ahead and did it to see what happens.

Its 100mm x 75mm... stock length rods. EJ257 block. EJ205 heads.
I used a JDM ver7 sti ra spec c crank, eagle H beam rods, 100mm wisecos.
Really isnt hard to do. Stock size bearings work fine. Everything bolts right up.

Its got some negative deck clearance at TDC.... which I really havent decided if its a bad thing or not..

Last edited by Turbo_Mike; 08-04-2008 at 02:27 PM.
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Old 08-04-2008, 11:52 PM   #23
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when is your 35R going on and what do you think you're going to rev to? 11 or 12 mm oil pump??? For me to find this benificial I'd have to reach 8000+ rpms. I've seen many 2.5's rev to 7500 with no issues....I'm really interested in seeing your results!!
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Old 08-05-2008, 12:03 AM   #24
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Originally Posted by domestic_abuser View Post
when is your 35R going on and what do you think you're going to rev to? 11 or 12 mm oil pump??? For me to find this benificial I'd have to reach 8000+ rpms. I've seen many 2.5's rev to 7500 with no issues....I'm really interested in seeing your results!!
I'm using a shimmed 08 sti oil pump. With 10W30 it has 53 psi hot idle and 97 psi @3k up hot.... (its an 11mm pump)

All the parts should be good for close to 10k RPM, but I'm going to rev it to just past where the power noses over, wherever that may be. I'm expecting roughly 8400 rpm.

I'm picking the turbo up on friday, we'll see how ambitious I am... but it will definately be done within the next couple weeks... motor's got ~1600 miles on it now

Last edited by Turbo_Mike; 08-05-2008 at 12:20 AM.
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Old 08-05-2008, 09:59 AM   #25
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Quote:
Originally Posted by Turbo_Mike View Post
Its 100mm x 75mm... stock length rods. EJ257 block. EJ205 heads.
I used a JDM ver7 sti ra spec c crank, eagle H beam rods, 100mm wisecos.
Really isnt hard to do. Stock size bearings work fine. Everything bolts right up.

Its got some negative deck clearance at TDC.... which I really havent decided if its a bad thing or not..
yes, that would be your quench height and leaving it loose isn't ideal and lowers your detonation threshhold. Part of the reason I started my setup with custom rods...then decided going with a much better & bigger bore (flow numbers and ring selection) I've now completely designed a long rod, big bore package. Also keep in mind that with any off the shelf EJ25 piston will have a lower CR than what they say.
There are a lot of things you can do to improve the package and probably why I spent so much time in my piston and rod design.

Shoot me a PM if you have any questions.
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