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2.5 Frankenstein possible with 9.5-9.7/1 compression?
Posted: Sun Apr 07, 2013 1:16 am
by Bender-san
So I've been searching throughout various forums, but I can't find anyone who's tried to build a naturally aspirated Frankenstein that came in somewhere close to OEM compression ratio. I'm not really interested in being married to high-dollar fuel. Is there an OEM piston combination out there that will acheive this or do I have to go aftermarket?
Re: 2.5 Frankenstein possible with 9.5-9.7/1 compression?
Posted: Sun Apr 07, 2013 1:25 am
by mike-tracy
I don't know the answer, but if you dug up the combustion chamber sizes, stock piston specs and played around with a compression calculator I bet you'd find the answer.
If you mean ej25 and ej22 heads, then perhaps oldie moldie 1st gen heads with any ej25 and ej257 castoff pistons, and the one of the two thickness of the stock ej25d HG's.
Like I said, all speculation till you run the calculator.
I spend around $3 more for a tankful for premium than I do for regular unleaded on my 96 leggy. Course the SS goes through it faster.
Re: 2.5 Frankenstein possible with 9.5-9.7/1 compression?
Posted: Sun Apr 07, 2013 6:14 am
by rallyak
I've be thinking of the same thing. My idea is 00ish 2.5 short block with the longer rods and more favorable rod and main journals with 97-99 2.5D heads that are opened to 50cc to keep the stock compression ratio of around 10.1. 2.5D intake with 2.2 wiring and 2.2 valve body and IAC. I believe this will work well, with more torque and better fuel economy.
Basically a 00ish 2.5 with the easiest fit in my car,so I can keep my OBX headers that are currently on my 2.2.
I will make a thread when I'm about to get started.
How dose it sound?
Re: 2.5 Frankenstein possible with 9.5-9.7/1 compression?
Posted: Wed Apr 10, 2013 4:01 pm
by Bender-san
mike-tracy wrote:I don't know the answer, but if you dug up the combustion chamber sizes, stock piston specs and played around with a compression calculator I bet you'd find the answer.
Where might I dig one of these compression calculators up? Any suggestions on a reliable/accurate one?
My current thought is going with the early 2.2 NA pistons. Since the 2.2 turbo pistons run the compression up to about 8.7/1, I figured the early NA pistons might put it in the 10.2/1 range, which can technically still run on regular or plus gas (premium in my neck of the woods clears $4/gallon all year long).
edit: Won't my combustion chamber size vary depending on if I'm using the 2.5 vs 2.2 pistons (I thought the 2.5 pistons cleared the deck while the 2.2 pistons did not)?