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Advice: 2.4 7R Engine Rebuild

Hi,

I recently purchased a 73.5 2.4 7R engine and need some help figuring out what my options are for a rebuild. I want something that a bit more powerful than the stock engine. I was thinking about building a 2.5. Any suggestions?

Thanks,

Buddan
Old 10-31-2016, 11:22 PM
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There are A LOT of options with the 7R case. I think your best bet is to get Wayne's rebuild and Bruce Anderson's performance book and start reading. In the end, you'll have a much better feel for what's possible and pretty good roadmaps to get there. You say it's a 73.5 2.4? Halfway thru 1973, Porsche moved away from 2.4l with mechanical fuel injection and started building "middies" with 2.7L and CIS. Typically, if someone posts they have a 73, it's a 2.4, if 73.5, it's a 2.7. It would help to post a pic of the engine and provide an engine serial number to determine exactly what you have.

I want to throw this out there that there's very little chance of doing this on a tight budget. Unless it's already been done, you are looking at a significant machine shop bill just to get the case and heads ready for reassembly.
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Old 11-01-2016, 10:54 AM
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2.4 7R CIS vs 2.7 7R CIS

tharbert -
1973 E and S cars are all MFI. 1973 T early cars where also MFI. Starting mid year in what is known as a 1973.5 model, Porsche put a newly revamped 2.4 engine in their T cars. These cars sported a 2.4 liter 7R case with the new CIS fuels system. I have one of these cars and can confirm that it is a 2.4 liter, not a 2.7 liter. I think the confusion is that the 2.7 liter case also has a 7R case, but it has bigger spigots than the 2.4 liter 7R case.

I am not aware of any 73 cars with a 2.7 engine. I was under the impression that 1974 was the first year of the 2.7.

I do have the same question as Buddan regarding the rebuild options. I have been told that a 73.5 with a 2.4 CIS 7R engine has limited rebuild options if you want to keep the CIS fuel system. If anyone has information on how to upgrade these engines I am interested in the info, as I am looking to rebuild mine too.
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Old 11-01-2016, 07:37 PM
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Ooops, right. I think I knew that but had overlooked...6 months of 2.4/CIS then 2.7 in MY74. I was flipping back and forth in the Tech Specs page and got carried away.

Wayne

The money it takes to rebuild even a 7R is getting to be breathtaking. I kind of wish I had gone shopping for a 3 or 3.2 at this point and mothballed my 2.4 MFI.
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Old 11-02-2016, 01:43 PM
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The biggest drawback is the magnesium case itself. It doesn't have the oil bypass (1976) and it will most certainly need the head studs and select web bolts time serted. That pretty much means the case has to be split. This will get very $pendy very quickly.

You can indeed do a 2.5 (86mm p/c) for higher compression without widening the spigots and upgrade the cam to something suitable for CIS without getting into the case if the machine work already been done. Hot rodding these engines used to be done all the time without the case work but it goes against prevailing wisdom these days.

7R cases
CIS Heads
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Old 11-03-2016, 08:26 AM
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You could ditch the CIS go to carbs. Then the build is easy. Higher compression pistons, hotter cam (Mod S or DC 30).

With more HP comes more heat so oil bypass mod is a good idea. Followed by Case Savers for the head studs. If you do the work your self but send out the case and heads for the mods, probably looking at around $12k and 200 HP.

Chris

73 E
Old 11-03-2016, 01:09 PM
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Thanks for all the advice. Greatly appreciate it.
Old 11-05-2016, 10:09 AM
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