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2.45 Build Questions

Im looking to build a 2.45l (70.4x86mm) and fuel it using my current 69S MFI setup. I am currently collecting parts and have got a crank, 4-rib pump and some 2.4S heads so far. I have been reading a lot on here but I still have many questions.

1) Im not sure what manifolds/heat exchangers my car currently has but they are original MFI ones by looking at them. Were all MFI manifolds the same diameters 2.0-2.4? if not, will I need to ideally change out to presumably 2.4 ones? If they are all the same, I presume my current stock MFI ones will suffice to run a 2.45?

2) Im not sure if DC30 or DC40 cams are the way to go or to stick with my S cams as is? Can anyone give an idea of the power bands these cams operate in? e.g. is the DC30s peak 1k lower than the DC40? Ideally I would like to not have to port my heads from the current 36mm, which is the best profile for 36mm ports?

3) My engine case is 1R but Im told has had squirters installed, and the IMS shaft bearing done too as a minimum, I would do the oil bypass mod also. Im not sure if this would effectively make it a 3R case? Would people have reservations about running a 1R case on a 2.45build? What exactly would be the concern? I am sure I have read a thread where Henry has said that 2.45 builds don’t really even need case savers to be installed and that pulled studs are almost unheard of on 92mm spigot cases. I would rather not invest in a 7R case if it is of no real benefit and simply a “nice to say you have” item.

4) I would like to keep my engine looking like a 69S from the engine bay. That means running a engine cover without the additional ducting to the oil cooler of later engines. My assumption is that as long as there is sufficient cooling capacity by way of other external coolers etc that this would not be an issue?

5) Im in Europe so our fuel is 95 octane as standard. What CR is safe with our fuel and single plugs? It seems like in North America 9.5 is generally the limit for 91 octane. Is 10:1 safe for 95 octane? Or is that going too far?

6) Further to the above is there any way to to lower CR on an engine and then higher it later on? On previous engines I have built you have been able to lower CR by using thicker head gaskets etc. I was thinking that it may be possible to buy 10.5 CR pistons, use thick gaskets etc to lower the CR to 9.5 or 10:1 for a single plug setup, leaving the option of going twin plug and reverting to 10.5:1 using standard gaskets at a later date. (this could all be totally unfeasible on 911 engines, until I tear one down I am not very familiar with the intricacies of them as they are quite unique in design)


Thanks all in advance!

Old 03-03-2021, 03:36 PM
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1) All the S throttle bodies have identical dimensions. The 69S has a larger Air horn @46mm, identical to the Weber. The rest of the S stacks are 42mm approximately.

2) The Solex has is place, but if I was building with S ports I would do a Mod S

3) The Mag cases are getting old, I would do all the recommended work to ensure you have success in your build

4) I use early shrouds and late and as long as you are running an aux cooler up front you will be fine

5) I believe Europe has a different method for octane than the U.S. does so I am not sure what you have. Compression is dictated by cam choice. So whatever you choose, you will need to make that adjustment

6) Try to avoid compromises in the build. Build it with the way you want it to turn out. Personally, I would Twinplug it, Mod S and 10.5/1. It will have fantastic midrange torque and about 200Hp
Old 03-03-2021, 06:08 PM
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DC 30's with 9.5/1 CR and MFI is an amazing combination. It's at peak power beyond 7,200 RPM redline. Consider ways to lighten the valve train for increased RPM's. Mapping the MFI to any non porsche cam profile will be impossible but you can get it close enough.

Chris
73 911 E
Old 03-05-2021, 09:29 AM
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A 7R case has significantly more inside bracing , good to have with the longer stroke crankshaft .
With a 1R case there will be significantly more movement or shuffling of the main bearing webs .
Old 03-06-2021, 05:42 PM
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Thanks for all your input guys, sounds like a 7R is required really. All other opinions are still welcome!

Neil
Old 03-07-2021, 06:27 AM
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The killer for mag cases is heat. If the case has been overheated (all 2.7, 75-77 delivered with thermal reactors) issues will ensue.
Keep the operating RPM under 6500, keep it cool (add a cooler) and you'll find that any mag case (within reason) will work to make 200hp.
If using a mag engine case other than 7R, try not to bore the spigots.
That was the point of the 2450cc. It is largest engine you can build without boring the spigots.
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Old 03-07-2021, 07:18 AM
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Quote:
Originally Posted by cmcfaul View Post
DC 30's with 9.5/1 CR and MFI is an amazing combination. It's at peak power beyond 7,200 RPM redline. Consider ways to lighten the valve train for increased RPM's. Mapping the MFI to any non porsche cam profile will be impossible but you can get it close enough.

Chris
73 911 E
The DC 30 is generally a modified "E" cam that is reground to be a Mod Solex.
Although I haven't used this exact combination, I have used the Solex grind with RS spec engines (Carb & MFI) and love that combo. The addition of more compression would have to be a stellar improvement.

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Old 03-07-2021, 07:23 AM
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