Compression ratio for 2056, While i am at it |
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Compression ratio for 2056, While i am at it |
worn |
Aug 22 2019, 08:20 PM
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#1
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can't remember Group: Members Posts: 3,150 Joined: 3-June 11 From: Madison, WI Member No.: 13,152 Region Association: Upper MidWest |
Pulled the motor after several years of service from the 2056 build. Two problems have plagued me. The reason i pulled the engine was to seal persistent oil leaks. I am going after the oil pump and some gaskets and seals. The second problem has always been cylinder head temps. They are kinda high. I built the motor to have a 9.0:1 compression ratio, which works in my cast iron block, water cooled TR6. On further consideration, that may be a tad high. Especially after a few hours of highway driving in the summer.
The internet has lots of calculators to do the math. I can get or may already have cylinder shims. What ought it to be? The goal is dependable gobbling of miles with some increased power due a 2056. Suggested ratios? Guess i should have asked this question some time ago. Thanks folks. You are great. |
falcor75 |
Aug 22 2019, 10:25 PM
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#2
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Senior Member Group: Members Posts: 1,579 Joined: 22-November 12 From: Sweden Member No.: 15,176 Region Association: Scandinavia |
I'm running 10,3:1 in my 78x96 engine so if everything else in yours is up to par it should be ok. At cruise my CHT's sit around 150-160° C (300-320F)
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76-914 |
Aug 23 2019, 08:05 AM
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#3
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Repeat Offender & Resident Subaru Antagonist Group: Members Posts: 13,494 Joined: 23-January 09 From: Temecula, CA Member No.: 9,964 Region Association: Southern California |
@McMark might be the person to ask. He's built several of them. (IMG:style_emoticons/default/beerchug.gif)
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yeahmag |
Aug 23 2019, 11:43 AM
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#4
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Advanced Member Group: Members Posts: 2,421 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
The engine is a combo. We would need to know what cam, heads and headwork, and exhaust you are running.
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worn |
Aug 23 2019, 11:52 AM
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#5
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can't remember Group: Members Posts: 3,150 Joined: 3-June 11 From: Madison, WI Member No.: 13,152 Region Association: Upper MidWest |
The engine is a combo. We would need to know what cam, heads and headwork, and exhaust you are running. I am running a cam from webcam described as using the "Raby grind". The exhausts are backdated from 1976 to a 1974 era SSI exhaust. I am using the stock EFI and I tweaked the MPS. I want to keep the fuel injection. #3 cylinder head plug has reached 400° F on uphills in the summer (when everything isn't frozen solid here). |
yeahmag |
Aug 23 2019, 12:03 PM
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#6
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Advanced Member Group: Members Posts: 2,421 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
I'm guessing that's a Webcam #73 variant for DJet. I would say that 8.0:1 to 8.5:1 would be more appropriate, but I'm not an expert on that cam. So, next you need to consider timing and AFR. What are those set to?
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worn |
Aug 23 2019, 06:35 PM
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#7
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can't remember Group: Members Posts: 3,150 Joined: 3-June 11 From: Madison, WI Member No.: 13,152 Region Association: Upper MidWest |
I'm guessing that's a Webcam #73 variant for DJet. I would say that 8.0:1 to 8.5:1 would be more appropriate, but I'm not an expert on that cam. So, next you need to consider timing and AFR. What are those set to? Timing is set stock. If i run much leaner than 10:1 the engine runs hot. However the engine gives better performance around 13:1 or even leaner. Yes, the cam is a 73 plus 2.5 degrees as i recall. Have to look at the card to be sure. |
yeahmag |
Aug 23 2019, 10:22 PM
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#8
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Advanced Member Group: Members Posts: 2,421 Joined: 18-April 05 From: Pasadena, CA Member No.: 3,946 Region Association: Southern California |
John Connolly of aircooled.net (who I trust) recommends 7.8-8:1 on that cam. I’d guess that’s a smoking gun assuming everything else is good.
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worn |
Aug 23 2019, 10:38 PM
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#9
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can't remember Group: Members Posts: 3,150 Joined: 3-June 11 From: Madison, WI Member No.: 13,152 Region Association: Upper MidWest |
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porschetub |
Aug 23 2019, 11:20 PM
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#10
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Advanced Member Group: Members Posts: 4,697 Joined: 25-July 15 From: New Zealand Member No.: 18,995 Region Association: None |
I'm guessing that's a Webcam #73 variant for DJet. I would say that 8.0:1 to 8.5:1 would be more appropriate, but I'm not an expert on that cam. So, next you need to consider timing and AFR. What are those set to? Timing is set stock. If i run much leaner than 10:1 the engine runs hot. However the engine gives better performance around 13:1 or even leaner. Yes, the cam is a 73 plus 2.5 degrees as i recall. Have to look at the card to be sure. What is your stock timing?,with that comp maybe a dial back a touch,just saying,cheers. |
Mark Henry |
Aug 24 2019, 11:05 AM
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#11
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Web #73 cam a 8.5 CR is about the max, make sure to check both sides. You can stack base shims, 3 max.
Big engines, oversize intake/exhaust, large duration (overlap) carb cams (or aftermarket FI) are the ones that can run higher CR. |
rbzymek |
Aug 28 2019, 02:43 PM
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#12
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Member Group: Members Posts: 195 Joined: 5-April 19 From: Northville, MI Member No.: 23,013 Region Association: Upper MidWest |
So I will be receiving my SCAT 2056 long block in a couple weeks. I requested a Web 73 cam and 8.5:1 CR. They did the build with new type 2 heads and 42x38 valves. This will allow me to re-use my tin and intake system. The exhaust valves will be sodium filled, with SS 2.0L heat exchangers. I plan to use my L-Jet FI from the 1.8 that I am rebuilding. After reading this thread I am wondering if I will have temperature issues. I do have a taco plate temp gauge but it only has a red zone, no numerics. I also have a wide band AFR meter for tuning. The engine is ready to ship at this point. Any suggestions or things to look out for? Better temp gauge? How hot is too hot? Thanks in advance.
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rbzymek |
Aug 28 2019, 03:53 PM
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#13
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Member Group: Members Posts: 195 Joined: 5-April 19 From: Northville, MI Member No.: 23,013 Region Association: Upper MidWest |
Make that 40x33 valves.
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worn |
Aug 28 2019, 08:16 PM
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#14
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can't remember Group: Members Posts: 3,150 Joined: 3-June 11 From: Madison, WI Member No.: 13,152 Region Association: Upper MidWest |
Web #73 cam a 8.5 CR is about the max, make sure to check both sides. You can stack base shims, 3 max. Big engines, oversize intake/exhaust, large duration (overlap) carb cams (or aftermarket FI) are the ones that can run higher CR. Thanks. I probably should mill thespigots, but don’t want to split the case. Deck heights on one side are about 0.010 different between sides. Is it ok to use shims under the cylinders to even things up? Have to re-read the Wilson book again. |
worn |
Aug 28 2019, 08:19 PM
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#15
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can't remember Group: Members Posts: 3,150 Joined: 3-June 11 From: Madison, WI Member No.: 13,152 Region Association: Upper MidWest |
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rick 918-S |
Aug 28 2019, 09:12 PM
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#16
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Hey nice rack! -Celette Group: Members Posts: 20,441 Joined: 30-December 02 From: Now in Superior WI Member No.: 43 Region Association: Northstar Region |
Carb cam. The overlap is likely causing a pulse in the intake thumping the maps. Not ideal. I would install a FI cam, leave the compression as is, add a lightened flywheel, and tune the injection with a exhaust sniffer if you can get the air fuel ratio right at cruising speed the engine should run cooler.
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Mark Henry |
Aug 28 2019, 09:16 PM
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#17
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that's what I do! Group: Members Posts: 20,065 Joined: 27-December 02 From: Port Hope, Ontario Member No.: 26 Region Association: Canada |
Web #73 is a stock FI duration cam with a hair more lift.
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rick 918-S |
Aug 28 2019, 09:25 PM
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#18
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Hey nice rack! -Celette Group: Members Posts: 20,441 Joined: 30-December 02 From: Now in Superior WI Member No.: 43 Region Association: Northstar Region |
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Bleyseng |
Aug 29 2019, 02:03 AM
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#19
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Aircooled Baby! Group: Members Posts: 13,034 Joined: 27-December 02 From: Seattle, Washington (for now) Member No.: 24 Region Association: Pacific Northwest |
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