2.7 with stock leistritz vs Dansk sport

[glaverbel911]

Last years testing with a 2.4S motor brought about very disappointing hp/torque figures using a stock Dansk muffler replacement with 57mm tip. I believe it was a 7hp loose compared to original factory Leistritz or Bischoff and even more hp loose at the high rpm scale. The Bischoff usually the winner with a 1.5 or 2hp advantage.

This year a lightly tweaked RS spec 2.7 engine still with 8.5/1.
Testing has been with a 78’ dated leistritz early muffler style replacement.
Horsepower is at 222@6570rpm and 194lbs. Correction factor was 1.05%
The owner has now supplied me with a Dansk large tip 70mm sport muffler hoping to crest 225 and I preformed a back to back test. It yeilded an instant -10hp. How Very disappointing .

Next test will be with the bischoff and I’m sure it will yield us the 225 mark we are after.

Cheers.

[911MRP]

Interesting test. Thanks for posting the findings. I look forward to the next instalment with the Bischoff. I have several stamped 72. One in mild steel and one wrapped in stainless still with square tip end. One of them is believed original on my RS — can’t be sure as I’ve only had the car for about thirty years but it certainly had 72 date stamped Bischoff when I got it. Car has its original engine— work was done by renowned engine bulder Bob Watson who will be well known to folks in the U.K. I spoke with Bob about it before he passed; he recalled working on the car as it belonged to a chap who raced and won class at Le Mans at the time. Bob’s dyno was well known to U.K. community particularly those who raced the 911— I never thought to ask if he had an opinion on the influence of different brand exhaust silencers so this thread adds knowledge.

Bischoff exhaust silencer are discussed here:

https://www.early911sregistry.org/fo...light=Bischoff



Steve

PS for those who knew of Bob they might be interested to know the story of how he got involved with Porsche. He was working for Len Street a Lotus dealer in Chelsea London. Street had been one of the people working for Chapman at Lotus in the Cheshunt ( pre-Hethel) era specifically at the airfield near Cheshunt where they had a satellite building for customer servicing. One day Bob popped in to see my late pal Chris Turner, who had started his independent Porsche business in north west London in 1974. Chris loaned Bob the keys to drive his 911. Bob was impressed and soon left Len Street to start his eponymous Porsche repair business. Bob became well known in U.K. club racing and fettling cars for people who raced them in things like the PCGB series of 80s. Chris and Bob were among the most highly experienced abs respected Porsche. independents in the U.K.

[glaverbel911]

Hi Steve.
I’ll run an original early bischoff tomorrow.
M preproduction 74’ Carrera still has it original muffler. A bischoff dated 4/73
I can’t remember what my first series rs had. Will look it up.

Today I still installed my early factory 3 pipe with caps, sport rallye muffler that bolts up to standard exchangers.
It yielded the 225hp I was looking for but not worth the 3hp to noise ratio. It Was cool when I was 18 but would only use it today for some race/rallye purpose today .

Regards,

[911MRP]

Interesting result with the three pipe. The fashionable “I got lost on the way to the race track” paraphernalia that is often seen can be OTT sometimes

Bischoff seems likely in 73 RS maybe some got Leistritz too probably depended on supply situation. Since my car came to me with a 72 date stamped Bischoff three decades ago and car is one of the about 300 calendar 1972 built Carrera RS examples it seems likely that is the original factory fitted item because I can’t imagine the PO of my car bothering to date match a replacement exhaust silencer — thought probably wouldn’t have occurred too many folks back in the eighties or early nineties to look further a date stamped item let alone to these guys who were involved in professional motorsport in addition to the Le Mans driver another was team manager for a well known F1 team (so not concours guys)

Your 4/73 example pictured has suffix .001/ rather than suffix 00/ is that a revision due to the different shape fit rear apron for impact bumper?

Steve

[sttoronto]

Good info. Do you think this apply to the 2L S engine also?

Last years testing with a 2.4S motor brought about very disappointing hp/torque figures using a stock Dansk muffler replacement with 57mm tip. I believe it was a 7hp loose compared to original factory Leistritz or Bischoff and even more hp loose at the high rpm scale. The Bischoff usually the winner with a 1.5 or 2hp advantage.

This year a lightly tweaked RS spec 2.7 engine still with 8.5/1.
Testing has been with a 78’ dated leistritz early muffler style replacement.
Horsepower is at 222@6570rpm and 194lbs. Correction factor was 1.05%
The owner has now supplied me with a Dansk large tip 70mm sport muffler hoping to crest 225 and I preformed a back to back test. It yeilded an instant -10hp. How Very disappointing .

Next test will be with the bischoff and I’m sure it will yield us the 225 mark we are after.

Cheers.

[glaverbel911]

Good info. Do you think this apply to the 2L S engine also?

Yes of course, even more so on a high rpm S.
If your running a Dansk and switch over to an original you will probably need to turn up the main rack on the pump 1 or two clicks.
Regards,

[sttoronto]

Yes of course, even more so on a high rpm S.
If your running a Dansk and switch over to an original you will probably need to turn up the main rack on the pump 1 or two clicks.
Regards,

I am not sure what muffler I have, I can't find any name one or part number on it. I'll get some picture post soon to get some help to figure out what it is.

What do you mean turn up the main rack on the pump 1 or two clicks?

[glaverbel911]

I had assumed you have an mfi 2.0 . When switching to an exhaust less restrictive the fuel burn will be leaner. The mfi will not self compensate. That is also Assuming your motor was already fine tuned beforehand for max efficiency and power.
Regards ,

[sttoronto]

glaverbel911, Your test muffler 78’ dated leistritz early muffler style would that be the same as the 69-70 dated? And 2 in 1 out? I thought those are only for engine upto 2.4. It's not too restrictive for the 2.7?

[911MRP]

I can’t speak for Robert’s choice of exhaust silencer box on these interesting experiments but this was the part no for 72/3 whether 2.4 or 2.7 (ie Carrera RS)



As stated, I believe it is likely the one on my car (the bischoff) might have been its factory original fit as was there with 72 date stamp when I got the RS on early nineties — still have it. I have both a mild steel and stainless steel one as discussed in the thread (see link Post #2)

I do see incorrect part number used ( or advertised) for 72/3 era but don’t know if these earlier ones were different externally /internally.

Steve