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Oliver
 
Join Date: Nov 2018
Location: Portland, Maine
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2.4SS vs 2.5SS

Folks,

I’m in the process of determining whether to build a 2.4SS with 87.5mm Nickies and 9.5:1 JE Pistons or a 2.5SS via the Bruce Anderson route with 90mm Mahle RS P&Cs and need advice. My goal is more power but maintain decent low rpm manners for spirited street driving and overall reliability. I would sacrifice a little horsepower for longetivity and reliability.

I have read many forums and the new/old BA books as well as Wayne’s version. I am set on using my 2.2T case and crank with 66mm stroke. I will perform the necessary upgrades as per both book’s recommendations, including shuffle pins. I have a set of IDS Webers for the fuel delivery and will install a 2 in 2 out M&K sport muffler with SSI heat exchangers. I am torn regarding the camshaft choice, but am leaning towards an “E” or Solex cam (or possibly a hotter DC40 or similar modified Solex or S cam) and will install Pauter Rods if I go with a hotter cam like the Solex or a modified cam as well as have the distributor recurved for whichever cam I choose.

These are my thoughts:

Both routes are roughly the same money wise, so it comes down to compression with a slightly smaller displacement or displacement with less compression... will it be a better idea to build a 2.4SS that doesn’t require the machining to the spigots and heads/cam housings or go with the machining and have lower compression with no issues of possible detonation or fuel quality issues? Will these both result in similar hp and torque outputs? Which would be a better set up?

Thoughts and comments are appreciated.

Happy Holidays,
Oliver

Old 11-23-2018, 06:42 AM
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Hi Oliver,
At 9.5/1 I would recommend a DC40

9.0/1 would be my target for the DC30 (Mod Solex) I have seen these ping @ 9.5/1 so keep compression reasonable.

I personally do not like to bore out the spigots.
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Old 11-23-2018, 08:23 AM
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Oliver
 
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Aaron,

Thank you for your reply. I think the 2.4SS option is probably best as well, at least as far as the magnesium case longetivity goes... that is the route I will take.

Is the 9.5:1 compression ratio too high for my intentions? Is it possible, or even a practice in the engine building world, to add a little height at the cylinder deck with bigger base gaskets to drop compression a bit, say to a 9.0:1 with the 9.5:1 setup from LN Engineering? My main concern is detonation issues, as I don’t want to twin plug do to the extra cost. I’m also shooting for an engine that doesn’t need to live in the 6K+ rpm range to be exciting or driveable, preferably something with solid performance in the 3K to 6K range. Will the DC40 be too “peaky” for a non counterweighted crank?

Again, thank you for your input, I’m new to the engine building world and want to cover my bases before I jump in head first.


Regards,
Oliver
Old 11-23-2018, 08:53 AM
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From my experience the case is not a problem when bored for 90s. I would want to research if the slip in 87.5s are durable considering their thin skirts.

I ran a SS2,5 built on a '71 case for decades, 80K miles, hundreds of autocrosses, etc. Was still running perfectly last year when I finally replaced it.

I was running 8.5-1 CR, since that is what the Carrera Mahles had that I used in the '80s when I built the motor. I originally had T cams but changed to E cams later with great results. I'm not sure you will ever have much torque below 4K no matter what configuration you plan with the sort stroke motor. Don't get me wrong, my motor would run beautifully at 3K rpm. But it really didn't come alive till it hit 4K then it would scream to 7K+.

If I had it to do over again, I would consider going with a 92 or 93mm bore and S cams and around 9.5 CR.

Then again a 2,4-2,7 crank may be worth considering, especially if you are serious about Carello rods.

In addition to boring out the case spigots, the heads will have to be opened up as well for the 90s.
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Old 11-23-2018, 11:53 AM
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Oliver
 
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Gordon

Thanks for the input regarding the 87.5mm setup, I never considered there could be an issue from the skirts being too thin.

Does anyone else have any comments on this???

What type of power did you get from the 90mm setup with an “E” camshaft? Did you use a counterweighted crank or a non counterweighted? As I don’t plan on thrashing this engine is the bored spigot issue something I am over analyzing? It appears many folks don’t have issues, but many suggest against it...

So tough with all this great information and feedback to make a decision. I’ve been hemming/hawing for months and just want to move ahead with a purchase so I can get this rolling...

Thanks again,
Oliver

Last edited by OCG911T; 11-23-2018 at 02:39 PM.. Reason: Missed information
Old 11-23-2018, 01:53 PM
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I got around 170 whp. So somthing like 190+ flywheel, I would guess. It was a non-counter-weighted T crank.

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Old 11-23-2018, 02:56 PM
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Oliver
 
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That would be perfect
Old 11-23-2018, 03:25 PM
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Oliver
 
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Update:

I’m going with a 2.4SS for this build. I like the idea of the old tried and true 2.5, but decided against it on account of the extensive machining required on the case and heads.

I just bought the 87.5mm Nickies with 9.5:1 JE Pistons from LN Engineering. Merry Christmas to me!

Now the final big decision is what camshaft grind to go with? I am thinking I will go with the DC40 that has been suggested on this forum and the early911Sregistry. I emailed Dougherty Racing to seek his advice and will keep this thread updated.

Thanks for the advice and thoughts, keep it coming!

Oliver-
Old 11-24-2018, 09:08 AM
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Oliver
 
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Anyone know what kind of horsepower and torque I can expect with a DC40 camshaft, 2.4 liters and 9.5:1 CR? I am going to open the stock 2.2T head ports up to either S specs or just between (34/34).
Old 11-26-2018, 03:02 PM
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Oliver,

That sounds like a great engine build. Any update on how things came along in the end?

Thanks
Jan
Old 01-03-2020, 07:11 AM
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did DC30's on my 73 E with 9.5 JE's (closer to 10.0 /1 after heads machined a few times), Was a screamer!!! 4,000 to 7300++ RPM's was pure power band. Would spend a little dough increasing redline as it was far from done at 7300 RPM's. The engine Porsche should have built!

Chris

Old 01-03-2020, 10:48 AM
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