Compression ratio for 2.5 shortblock swap, 11.5 or 10.3
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Compression ratio for 2.5 shortblock swap, 11.5 or 10.3
I want advice. I'm thinking I should go for the 10.3 CR unless a thicker gasket is available. Advice?
I used the specs from http://wac.addr.com/auto/obs/turbo/ejcalcs.html with the calculator http://www.bgsoflex.com/cr.html -
* Cylinder head Volume (CC) = 40.00
* Piston Top Volume (CC) = 14.50
* Cylinder Bore (Inches) = 3.9
* Cylinder Stroke (Inches) = 3.11
* Deck Height (Inches) = 0.000
* Head Gasket Thickness (Inches) = 0.060
# Computed Compression Ratio is 10.2 to 1
If I use the SOHC gasket thickness of 0.023 # Computed Compression Ratio is 11.3 to 1
For fun I entered the stock EJ22 specs -
* Cylinder head Volume (CC) = 40.00
* Piston Top Volume (CC) = 14.50
* Cylinder Bore (Inches) = 3.8
* Cylinder Stroke (Inches) = 2.95
* Deck Height (Inches) = 0.000
* Head Gasket Thickness (Inches) = 0.060
Computation Results:
# Computed Compression Ratio is 9.4 to 1
Background - This is in my beater Legacy. I've driven it like I stole it every day for the last 130k miles. It runs perfectly, good compression, passes smog great but cylinder #3 is consuming oil at the rate of 1qt per 350 miles. I got the EJ25 for free since the spark plug broke and put a few dents in the piston top (easily removed with the dremel).
Same post can be found here http://forums.nasioc.com/forums/showthr ... p=22679362
I used the specs from http://wac.addr.com/auto/obs/turbo/ejcalcs.html with the calculator http://www.bgsoflex.com/cr.html -
* Cylinder head Volume (CC) = 40.00
* Piston Top Volume (CC) = 14.50
* Cylinder Bore (Inches) = 3.9
* Cylinder Stroke (Inches) = 3.11
* Deck Height (Inches) = 0.000
* Head Gasket Thickness (Inches) = 0.060
# Computed Compression Ratio is 10.2 to 1
If I use the SOHC gasket thickness of 0.023 # Computed Compression Ratio is 11.3 to 1
For fun I entered the stock EJ22 specs -
* Cylinder head Volume (CC) = 40.00
* Piston Top Volume (CC) = 14.50
* Cylinder Bore (Inches) = 3.8
* Cylinder Stroke (Inches) = 2.95
* Deck Height (Inches) = 0.000
* Head Gasket Thickness (Inches) = 0.060
Computation Results:
# Computed Compression Ratio is 9.4 to 1
Background - This is in my beater Legacy. I've driven it like I stole it every day for the last 130k miles. It runs perfectly, good compression, passes smog great but cylinder #3 is consuming oil at the rate of 1qt per 350 miles. I got the EJ25 for free since the spark plug broke and put a few dents in the piston top (easily removed with the dremel).
Same post can be found here http://forums.nasioc.com/forums/showthr ... p=22679362
Last edited by ciper on Thu Jun 19, 2008 4:21 am, edited 1 time in total.
I found a Subaru compression ratio calculator!
http://www.jonesboy.com/Media/Matts_CR_calc_v1_01.xls
Using it I get 10.33 for DOHC gasket and 11:5 for SOHC gasket
http://www.jonesboy.com/Media/Matts_CR_calc_v1_01.xls
Using it I get 10.33 for DOHC gasket and 11:5 for SOHC gasket
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I would be tempted to do some minor porting of the heads and go for the high compression with the PP6.
Reddevil, Awaiting new heart, will it ever happen?
1990 wagon, EJ25 12.3 @ 116.5 FAST Family wagon getting new motor soon
1992 wagon, wifes daily, high compression
1992 Touring wagon, should I keep it?
1990 wagon, EJ25 12.3 @ 116.5 FAST Family wagon getting new motor soon
1992 wagon, wifes daily, high compression
1992 Touring wagon, should I keep it?
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This is meant to be an inexpensive daily driver. I'm using the stock heads.
Both of those ratios seem too high for regular gas. Are those of you who did this swap using premium?
BTW using a piston volume of 21cc gets a 9.4:1 comp ratio. That not only happens to be the stock ratio but the EJ257 pistons are 21cc IIRC.
Both of those ratios seem too high for regular gas. Are those of you who did this swap using premium?
BTW using a piston volume of 21cc gets a 9.4:1 comp ratio. That not only happens to be the stock ratio but the EJ257 pistons are 21cc IIRC.
A well respected VW builder/tuner made a suggestion today. If I use one DOHC gasket and one SOHC gasket together I get 9.6:1 compression... (assuming the resulting thickness is .083). He said they have built many turbo motors this way and would help me fix it if it leaks. The stock CR of the 90-96 2.2 is 9.4 where the 97+ 2.2 is 9.7! This is only .023 more than the DOHC gasket so would my manifolds fit properly?
Three SOHC gaskets gives me 10:1
I know the newest design of EJ25D gasket from Subaru is MLS, Do you know if the SOHC gasket is of similar material and could mate properly in this configuration?
Three SOHC gaskets gives me 10:1
I know the newest design of EJ25D gasket from Subaru is MLS, Do you know if the SOHC gasket is of similar material and could mate properly in this configuration?
Last edited by ciper on Thu Jun 19, 2008 4:24 am, edited 1 time in total.
i got the 2.5 bottom end with my 90 2.2 top, i got some thicker gaskets from a company in Ohio, but they were made for the swap as well, they line the water jacket holes up better. I just ran 93 in it and it was fine. Only problem i had was the oil pump in the 2.5 wasn't up to pair and after 6 nights of racing on it, i blew a hole through the block
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Ok guys help me out here. I want to make damn sure I order the right size. I don't trust the numbers I posted originally.
Secondly give me your advice. Is a 9.7:1 ratio good if I plan to use 87 octane gas?
Response from cometic -
We can gladly make the gasket thickness what ever you like as long as it is a possibility for us. However, I cannot confirm nor deny if your calculations are correct or not. When it comes to volumes I can tell you it is never a safe bet to assume anything or trust information you find on the internet. In theory your numbers make sense but like I said I cannot do the math to verify.
Kevyn Kistner
Technical Sales
Cometic Gasket
Secondly give me your advice. Is a 9.7:1 ratio good if I plan to use 87 octane gas?
Response from cometic -
We can gladly make the gasket thickness what ever you like as long as it is a possibility for us. However, I cannot confirm nor deny if your calculations are correct or not. When it comes to volumes I can tell you it is never a safe bet to assume anything or trust information you find on the internet. In theory your numbers make sense but like I said I cannot do the math to verify.
Kevyn Kistner
Technical Sales
Cometic Gasket
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I am already driving my 2.2l SOHC heads with the STi short block set-up and I love it!
Use the 4 layer steel OEM Subaru 2.5l headgaskets and you'll be able to run 87 oct. pump gas no problem!
My dyno test showed 125 ft./lbs. of torque at the wheels!
Use the 4 layer steel OEM Subaru 2.5l headgaskets and you'll be able to run 87 oct. pump gas no problem!
My dyno test showed 125 ft./lbs. of torque at the wheels!
1991 Subaru Legacy BJ 2.2L/2.5LSTi Block Hybrid N/A w/ over 250,000 miles! 1992 Yamaha Seca II 2004 Dyna Super Glide My other car is a Go Kart Redhair...Black Leather...My favourite colour schemes. If it's not Scottish...it's Crap!
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IIRC the C.R. is closer to 10.3
BTW the SOA part # for the H.G. I used is 11044AA610 4 layer multi-steel 2.5
I carefully drilled holes to match-up to the 2.2L heads.
End result is it works GREAT!
BTW the SOA part # for the H.G. I used is 11044AA610 4 layer multi-steel 2.5
I carefully drilled holes to match-up to the 2.2L heads.
End result is it works GREAT!
1991 Subaru Legacy BJ 2.2L/2.5LSTi Block Hybrid N/A w/ over 250,000 miles! 1992 Yamaha Seca II 2004 Dyna Super Glide My other car is a Go Kart Redhair...Black Leather...My favourite colour schemes. If it's not Scottish...it's Crap!
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Since you appear to be at Sea-Level, I would say go with the 4-layer MLS Subaru head-gaskets...but I think you'll still have to run premium. The phase II 2.5 short block in combination with your 2.2L heads will have a higher C.R. than with a STi short-block and SOHC 2.2L N/A heads that I am using and I am at altitude of 5,280 feet
1991 Subaru Legacy BJ 2.2L/2.5LSTi Block Hybrid N/A w/ over 250,000 miles! 1992 Yamaha Seca II 2004 Dyna Super Glide My other car is a Go Kart Redhair...Black Leather...My favourite colour schemes. If it's not Scottish...it's Crap!
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If you match the block bore, compression will lower... Match the 2.2 head, compression will be higher....
I have done both, both worked.
I have done both, both worked.
Reddevil, Awaiting new heart, will it ever happen?
1990 wagon, EJ25 12.3 @ 116.5 FAST Family wagon getting new motor soon
1992 wagon, wifes daily, high compression
1992 Touring wagon, should I keep it?
1990 wagon, EJ25 12.3 @ 116.5 FAST Family wagon getting new motor soon
1992 wagon, wifes daily, high compression
1992 Touring wagon, should I keep it?
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If I remember correctly, the only time I had issues with the cooling/oil passages was when using ej22t gaskets on ej22na heads.
I have used 2.0 DOHC heads and 2.5 DOHC heads on 2.2, no problems with the gaskets, and 2.0 heads on the 2.5, no problems. But as for the 2.2 na heads, not so sure.
I wouldnt sweat the extra thickness, as its spread out over the entire belt.
I have used 2.0 DOHC heads and 2.5 DOHC heads on 2.2, no problems with the gaskets, and 2.0 heads on the 2.5, no problems. But as for the 2.2 na heads, not so sure.
I wouldnt sweat the extra thickness, as its spread out over the entire belt.
Reddevil, Awaiting new heart, will it ever happen?
1990 wagon, EJ25 12.3 @ 116.5 FAST Family wagon getting new motor soon
1992 wagon, wifes daily, high compression
1992 Touring wagon, should I keep it?
1990 wagon, EJ25 12.3 @ 116.5 FAST Family wagon getting new motor soon
1992 wagon, wifes daily, high compression
1992 Touring wagon, should I keep it?