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3 restos WIP = psycho
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,665
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Compression and 2.0S MFI
I wonder what the realistic maximum CR is for a 2.0S w/ MFI on pump gas. When reading Wayne's book, I noticed that (on p. 112) that a 2.4L w/ 2.2 pistons makes compression of about 10:1. It also says this motor will run on pump gas with single plug. From that, the question has arisen: WHY?
I realize that the 2.4 heads don't have piston dome interference problems like the 2.0, thus aiding flame propagation and increasing knock resistance, but they are larger, increasing flame travel distance. It is thus reasonable to assume you could run a 2 liter engine with even higher comrpession in single plug form and even HIGHER compression in twin plug. The problem with the stock 2 liter is the heads. Can a 2.2 or 2.4 head be run on a 2 liter to increase flame travel efficiency and compression when coupled with custom pistons? For comparison, the 2.0L HSR motor runs 11:1 compression and needs race gas (again from Wayne's book), but does not mention plug configuration. I will assume single plugs. In a nutshell, here are my big questions: What CR could you get on pump gas with single plugs in a stock 2.0? I assume the stock 9.8:1 is near the limit. What CR could you get on pump gas with dual plugs in a stock 2.0? What CR could you get on pump gas with single plugs in a stock 2.0 w/ 2.2 or 2.4 heads? What CR could you get on pump gas with dual plugs in a stock 2.0 w/ 2.2 or 2.4 heads? Any expert insights will be greatly appreciated. (edit) What are the squish band repercussions of using larger diameter heads on smaller pistons and cylinders?
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- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 Last edited by kenikh; 08-18-2005 at 01:57 PM.. |
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3 restos WIP = psycho
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,665
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Anyhoo...no one knows or no one cares?
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- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 |
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Registered
Join Date: Jul 2001
Location: Portland Oregon
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Kenikh:
You have asked some VERY complex questions that go far far far beyond the ability to answer/discuss on a BBS or by e-mail. If you want to call me sometime when I'm not swamped, I'll help as much as I can,..... ![]()
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Steve Weiner Rennsport Systems Portland Oregon (503) 244-0990 porsche@rennsportsystems.com www.rennsportsystems.com |
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3 restos WIP = psycho
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,665
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Yikes, I must be reading too many books. Steve, thanks for your offer. Let me know when you are not swamped.
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- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 |
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Registered
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Location: Portland Oregon
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Call me near or at the end of a business day,....
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Steve Weiner Rennsport Systems Portland Oregon (503) 244-0990 porsche@rennsportsystems.com www.rennsportsystems.com |
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3 restos WIP = psycho
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,665
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Thanks again to Steve. We haven't spoken yet, but I have thought more about my motivations for asking the previous questions and perhaps they are too complex for the actual answers I am seeking. I am getting ready to install a long absent, correct MFI for my 2.0S. My basic questions were:
1. Is it worth twin plugging my stock 2.0S during this install? 2. Would it only be worthwhile if I go with custom pistons to raise compression? 3. If so, how high is reasonable for a twin plug 2.0S? 4. How would these mods affect the character and longevity of the otherwise stock 2.0S? 5. Should I just be happy with the single plug MFI and spend my money elsewhere? My other questions were only tring to get to the heart of this basic issue. Sometimes I just geek out a little too hard and forget my basic motivations. (edit) I just did some perusing of the Rennsport site and it looks like the 2.2S heads are a bolt on upgrade for the 2.0S and help immensely with detonation. Very interesting. I promise I won't ask any squish band questions here...I promise...must resist. ![]()
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- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 Last edited by kenikh; 08-22-2005 at 08:34 AM.. |
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Tom Tweed Early S Registry #257 R Gruppe #232 Rennlist Founding Member #990416-1164 Driving Porsches since 1964 Last edited by ttweed; 08-22-2005 at 08:18 AM.. |
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3 restos WIP = psycho
Join Date: Feb 2005
Location: North of Exit 17
Posts: 7,665
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Thanks, Tom. You know how slippery the slope goes: MFI turns into twin plugs, turns into high comp pistons, turns into 906 cams, turns into... In the end you could have just built another motor for less money.
To answer the question: I am not into cool factor for cool factor's sake. All I was looking into was making my 2.0 the best it can be without going into stupid money like Pauter rods and a titanium valve train. My thoughts were that if I could do smart upgrades to my 2.0 in the $1500 range in addition to adding the MFI, I'd go that route vs. possibly building another motor. Plus, I like the looks from people when I tell them I only have a 2.0. ![]() P.S. I know that some of you will be skeptical of adding twin plugs as cheaply as stated above. It can be done utilizing a Ford crankfire setup, using a MegaSquirt II brain and twin EDIS coil packs or MSDs. Hardware total is less than $700. Some would say that using MegaSquirt without its fueling capabilities is stupid, but you can't argue with the economics of it.
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- 1965 911 - 1969 911S - 1980 911SC Targa - 1979 930 Last edited by kenikh; 10-08-2005 at 07:34 PM.. |
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