Ultimate ST thread

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Originally Posted by varunan123

Chuck

Even going into 1972 Porsche was still recommending weber carburation for circuit endurance racing.It was not until the displacement grew further into 73 that the switch was consistently made to MFI.The Performance difference between MFI and weber negligible but reliability was supposedly better with the weber.That's what i was told but who knows

raj

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I thought I read in Fere's The Racing Porsches about how the factory was developing their engines with MFI starting with the 906E. They found that the shutoff solenoid and injection below the butterfly eliminated the pooling of fuel on the butterfly during part throttle- good for races like the Targa but probably irrelevant for LeMans. I also read that the injection eventually gave better fuel consumption after a couple years of development. I did not hear mention of unreliability. The pumps seemed rather robust- from a diesel truck, no? The carburetors have those tiny jets and such to clog, it would seem.

Raj is right,

To this day the fastest ‘contemporary vintage’ raced early 911’s both in sprint as well as enduros (VARA, HSR, HSR/West) 2 through 2.5 liter, and some bigger, are virtually all carbureted.

The early 911s and 914'6s I've helped out with at the track were all BIG compression, BIG cams, and BIG carbs....


I’ll check the Pascal book tonight to see how many 911s were injected at Le Mans in ‘72


Cheers

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Originally Posted by letsrollbabe

Another interesting fact with that Ginther ST as restored is that the engine, done by Jerry Woods has a red S engine cover (not natural FG) and although it was twin plug, it did not have high butterfly induction as most ST factoriy engines had...

Is this engine still in the car? I know it has been restored again with the blue stripes on the sides, but was the engine redone with HB?

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Hugh, Gib, Raj, Chuck, Harvey, et al.. I managed to grab a quick shot of the recently restored Ginther ST engine compartment at RRIII as it was being shown to the judges. No HBs.

It is interesting to note that the Sports Circular or Bulletin that Raj posted sent to Stanley Palmer lists a 2.492 L (70.4 x 86.7 mm P/C) engine with twin plugs, racing cams, 46 Weber carbs, but with an "approx. 210 HP at 8000 rpm". I don't know if this was a misprint or what, but we know from other documents that this engine was factory rated at 270-275 HP at 8000 rpm. And the factory often listed the MFI versions with 10 hp more than the Weber carb. engines.

The rally STs got the standard 911S engine with MFI, not carbs, so I don't think reliability was a factor as rally events were often longer endurance. As we all know, the MFI systems are pretty much bullet proof once set up correctly, and carbs are more tempermental often requiring different jets for varying conditions.

Chuck, I think the reason carbs are used by vintage racers today is simply that they do deliver the power and are simpler to get set up initially. MFI pumps need the proper space cam to match racing engine parameters, and they are not available from the factory. Standard T, E, S or RS space cams must be modified by pump rebuilders to achieve the results required to be competitive, especially with CRs as high as 14:1 that many Vintage racers use these days. These modified space cams are not a science and are more of a black art, and therefore require a lot of tuning time to get things right for a particular engine/exhaust set up. Most vintage car builders don't want to spend the time or money to go with MFI, so they use Webers or PMOs, which can fit a wide range of engine performance parameters.

Ok,

Pascal's book says in '72 of the 7 911s entered in Le Mans only 2 were carbed and 5 injected......... one year and more confidence

Cheers

Just a thought...

Rally cars might benefit more from the MFI's built in barometric compensating cell than track cars would, due to the changes in altitude on hillclimbs that would carburetors cannot adjust for. Race tracks (except for maybe the Nordschleife or original Spa-Francorchamps) would not have such extreme variation in air density. Not to mention changes in temperature and huidity throughout the rally's different days.

Interesting Raj... please, if you don't mind. What publication is this?
thanks

Paul Frere, in his famous Porsche 911 Story states that the from March 71 the STs with the 66 mm crank engines went to 87.5 mm P/Cs providing 2380 CCs, and that 'Engines of that size were built with fuel injection only.' Prior to that, the ST engines with 2247 cc used both MFI and Webers to achieve 230 hp. For the 2.5L ST engines with the 70.4 mm stroke, the factory used 86.7 mm P/Cs to achieve 2492 cc...and according to Frere, "The engine, which was made only with Bosch plunger pump fuel injection, was otherwise similar to the 2380 cc unit, but the power output was raised to 275 hp at 7900 rpm and the torque to 27 mkg (196 lb/ft) at 6200 rpm." That engine had vibration issues, and the factory went back to the 66 mm stroke with an 89 mm bore 'producing the same power', but Frere is silent on the induction.

In Anderson's book, the 2247 cc (66 mm x 85 mm P/C) ST was listed at 230 hp with both Webers and MFI, and the 2380 cc is listed only with mechanical injection at 250 hp....the same specs as Frere describes. Anderson lists the 2.5L ST engines (86.7 mm x 70.4 mm stroke) with 270 hp using MFI, and the alternate version (89 mm x 66 mm stroke) at 275 hp also with MFI.

It seems there are conflicting comments here from what has been shown in other documents regarding a privateer's choice as to using Webers or MFI for the 2.5L engines....and so it goes with these very special competition versions...the documentation is always somewhat sketchy.

Edit: Just checked the Boschen-Barth The Porsche Book, they say that 2.5L ST engine modifications included..."Bosch racing injection system or twin Weber Type 46 IDA carburettors to choice". So there you go....

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Originally Posted by varunan123

christophorus: Mark notice how it suggests the wheels are 400mm in diameter and not smaller? When are you going to give up on that ugly wheel of yours and on top of that it's completely the wrong diameter, i'll give you 50 bucks for it,you can use it to get yourself a proper 400mm wheel without all those defects.
raj

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Raj, I know I have to let it go. I'm the OCD poster boy for Early S Registry. :o

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Originally Posted by varunan123

christophorus


Mark notice how it suggests the wheels are 400mm in diameter and not smaller? When are you going to give up on that ugly wheel of yours and on top of that it's completely the wrong diameter, i'll give you 50 bucks for it,you can use it to get yourself a proper 400mm wheel without all those defects.

raj

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I'd take it to mean a replacement of the factory 380mm ST (914-6/RS) wheel, not the factory 400mm wheel.

I'll have to take another look at my period MOMO brochure but, I don't remember a 400mm Prototipo.

I got your back Mark. :D Your pictured wheel is the same as shown in the Christo article. Differences in overall wheel diameter are easily seen in the spacing and diameters of the "lightening holes in the swiss cheese style":D:D:D