3,2SS to 8k RPM

atelier14 · 02:22 AM

I am currently configuring my 3,2SS which will see 60% fast road/ 40% DE use in a 1972 911 with 2050 lbs. I will need driveability on low RPMs but due to the ratios of my 915 gearbox and the tracks I plan to use I want to spin it up to 8000 RPM - Power could start to drop at around 7600 RPM.

It will have slightly ported 3,2 heads with IN 41mm/ OUT 38mm ports and standard valves. I plan to use MFI with bored 42mm butterfly E throttle bodies.

I have two questions still left unsolved:

1. What would your suggestions regarding cam be for this one?

2. What is needed to let this engine live at periodic use up to 8000 RPM? Can I stay with the standard oiling on the crank or should I have it cross-drilled? Will I need RSR rockers? Are there any other suggestions for durability up to this RPM?

Many thanks for your help,
Chris

Steve@Rennsport · 03-08-2010, 07:37 AM

Chris,

I would talk to a camshaft provider to optimize what you need. Bear in mind that the space cam inside the MFI pump must match the camshaft profile and the person doing your pump should be consulted, as well.

For reliable 8K operation, you must do all the oiling mods to the lower end as well as install good valve springs & retainers. RSR rockers are not necessary in your situation.

I would also use Pauter rods for durability.

atelier14 · 03-08-2010, 07:57 AM

Steve,

Thanks - my MFI pump rebuilder suggests to choose the SCRS/ 954 engine cam profile for my desired usage profile. As he has not been into contact with perhaps more "modern" cam profiles for MFI applications recently there might be a better cam for my engine.

Could you strongly recommend the Pauter Rods for this engine & RPM? Are Carillos worth to consider?

Many thanks,
Chris

Steve@Rennsport · 03-08-2010, 08:27 AM

Quote:

Originally Posted by atelier14

Steve,

Thanks - my MFI pump rebuilder suggests to choose the SCRS/ 954 engine cam profile for my desired usage profile. As he has not been into contact with perhaps more "modern" cam profiles for MFI applications recently there might be a better cam for my engine.

Could you strongly recommend the Pauter Rods for this engine & RPM? Are Carillos worth to consider?

Many thanks,
Chris

We use Pauter 4340 rods in every race engine as they are very strong, lighter than OEM, less $$$ than Carrillo's and available. Some of these poor things get accidentely revved beyond 10K.

Call me if you need a set.

kenikh · 03-08-2010, 09:31 AM

Talk to John Dougherty on cams. From my experience, the Sprint Cam is a great one for this application. You might also consider his DC62 or DC44 on a 101 lobe spacing, although the DC44 might top out too quickly on such a large motor.

Any of the rods mentioned are great for this application. A third option are the R&R rods from LN Engineering. If you are still building and buying parts, I'd just settle in with Steve and go with his recommendations, as he'll get you set up right with a motor that meets all of your needs. He knows all of the details that will result in a motor that is greater than the sum of its parts.

Henry Schmidt · Henry Schmidt's Garage

+1 on the RR rods from Charles @ LN Engineering.
If you truly want to run at 8000 rpm you might consider a custom rod with a longer center to center length. Charles has made 130mm rods for 70.4 cranks and they are beautiful. Of course custom pistons are required but 8000 rpm is not really a bolt and go proposition.

kenikh · 03-08-2010, 03:14 PM

FWIW, I went with the GT3 spec R&R rods, then underground a 66mm crank to accomodate the smaller SC bearings, while maintaining the 66mm stroke. I like the member design of the R&R rod a bit better than the Pauter, but admittedly, there have been no cases where the Pauter design has had any issues that I can find, so basically, find the rod that meets your budget and run with it. R&R and Pauter have had none of the issues reported that seem to have plagued Carillo in recent years...

Walt Fricke · 03-08-2010, 10:06 PM

Stock rods with ARP or Raceware or other high strength steel bolts aren't too shabby. I've spun mine up to (and occasionally over) 8,000 in a 2.7 race motor for years. Never had a rod problem. Plenty of others, but not rod failures.

But for the 2.8SS I am building I have a set of Pauters. Had I known about the RRs I would have compared them. Carillos were the gold standard, but as Steve points out they are a bit expensive (everything involved with engine performance is expensive, so it is a matter of degree). But these aftermarket rods not only add strength, they also are lighter. Always a good thing, all other things being more or less equal.

Those of us with advanced Holiday Inn Express engineering degrees wonder about the Pauter design. Porsche uses an I beam with a nice broad web. Carillo (and its imitators) uses an H beam with two wide flanges. Easy to see where they get their stiffness. No one has explained to me how the cross shape of the Pauter does the job. But do it it does. I have seen it said that the Pauter also has less windage. Pauter has been making hot rod stuff for a very long time. Plus you can, for not too much more $, get custom rods if you need different lengths, journal diameters, big end widths, etc. if your innovative design calls for that.

lvporschepilot · 03-11-2010, 11:45 AM

Jeez I had no idea it was so hard to make a 911 engine safely spin that high. My '76 Ferrari 308 is all stock components except for cams and pistons and lives at 8500.

kenikh · 03-11-2010, 02:25 PM

Think about it - the car is a 3.0L V8. The bore is so much smaller on these cars, so the valves can be smaller/lighter even if the car is the 2V version. If it is the 4V version, no wonder it can rev to 8500RPM - the valvetrain is even lighter! When you are taking like displacement from 8 to 6 cylinders, the bore and valves get bigger/heavier. It is easier/cheaper to spin a light valve train.

As a result, Porsche was astute enough to know not to overbuild their cars for revs they wouldn't need to reach. So if you want to really spin a big bore 911, you need to spend a lot of money upgrading the parts that were not designed for those speeds:

Valve retainers
Valve springs
Valves (sometimes)
Rod bolts
Crank cross drilling

This is where the cost comes in.

joetiii · joetiii's Garage

well said

lvporschepilot · 03-12-2010, 05:56 AM

You have me curious now. What are the valve sizes in the 911. I know mine are 41mm intakes and 38mm exhausts. The 308 engine is actually closer to 2.9L so your explanation makes perfect sense. That and the crank journals are small and ludicrously well-oiled (identical bottom end in F40 and 288GTO and racing engines).

Very well stated!

lvporschepilot · 03-12-2010, 06:01 AM

I think I answered my own question. I am finding about 46mm intakes and 38mm exhausts to be right around the norm.

Walt Fricke · 03-12-2010, 03:19 PM

Las Vegas

I am confused when you ask what 911 valve sizes are, and then think you have found a norm of 46/38.

Here are sizes as the engines got larger from 1965-1989 for the pre-964 stock (not race) engines:

39/35; 42/38; 45/39; 46/40; 49/41.5, per Wayne's 911 engine book.

The last is for the 3.0 and 3.2, whose heads I bet Chris is planning to use. He doesn't specify an intake valve diameter to start this discussion, but says he is looking at 41mm exhausts, where I am guessing he meant 41.5.

The 964 is 49/42.5, and the 993 is 49/43, then 50/43.5 with the Varioram, per Frere. After that Porsche went with water cooling and 4 valve heads.

Walt

lvporschepilot · 03-15-2010, 06:18 AM

Many thanks for the clarification