Performing open heart surgery on a Bischoff 3/73:
(more info and photos in this thread: https://www.early911sregistry.org/fo...light=Bischoff )
as in the infamous modification drawing:
Performing open heart surgery on a Bischoff 3/73:
(more info and photos in this thread: https://www.early911sregistry.org/fo...light=Bischoff )
as in the infamous modification drawing:
Last edited by swisscheese; 01-15-2022 at 02:43 AM.
911S 1973
Early 911S Registry #176
Hello.
No not yet. I had pull the engine and slip in three other engines for seat and tuning. I’ll do the back to back test on the 2.7 in about a week and will post the results.
Back in march 2021 I did a back to back on a 2.4S with 9.5/1
The leistritz made 203.5@6741 and the bischoff pulled 206.2@6724 and added just under 2lbs extra torque.
[SIGPIC][/SIGPIC]Robert D. Groß
The biggest difference I see in compared to a Dansk are the perforated holes and style in the out pipe.
Regards. Robert
[SIGPIC][/SIGPIC]Robert D. Groß
Doing the dual outlet mod is not worth the effort of roughly 2 additional peak Hp on an S cam engine (but it does free up a bit of drop off power at the upper end.. but it still useless unless you have the means to tune and mod the mfi pump for the added fuel needed. Carbs would be easier too tune for max but are no comparisons to what the mfi can yield overall.
Unless your motor is spinning up past the 8000rpm zone it’s not worth the work put in and the excessive sound on the street assuming your car is not for the track !
Regards.
[SIGPIC][/SIGPIC]Robert D. Groß
thnx Robert, just added the graphic for reference (I wasn't particularly planning on going to track, nor going to dual outlet). I have a high-compression 2.7RS MFI engine (with correct 2.7RS space cam) and have an Eisenmann exhaust, which, as I understood, is a derivative of the Leistritz/Bischoff examples. The Bischoff was/is date-matching the rest of the car, so took the effort of surgery. Haven't driven yet, nor on dyno, so have no clue re. HP loss/gain. Will hopefully find out this year! Thanks for the informative thread, look forward to the 2.7RS measurement. Tom
911S 1973
Early 911S Registry #176
Hi Tom.
The best thing you can do for that engine is put a 2mm bigger butterflys and use mag stacks opened up to 40-46.
With a 9.5/1 it’ll touch 250hp and well over 210lbs torque.
The low compression motor I’m running has 39mm butterfly’s , mag stacks opened 39/46, 89 octane.
233hp and 199lbs torque.
Don’t alter the 36mm dimension below the butterfly and into the port.
Find a dyno shop with mfi knowledge that can tune it.
Best, Robert
[SIGPIC][/SIGPIC]Robert D. Groß
thanks for the advice Robert! I used all parts of my 2.4 S engine, except the '74 cases, Mahle 2.7 cylinders+Wahl pistons and altered MFI pump. "2mm bigger butterflys and use mag stacks opened up to 40-46", are those modified/custom parts, or standard parts from other models? thnx, Tom
911S 1973
Early 911S Registry #176
Hi Tom. It’s purely custom.
Eurometrics can supply and modify throttle bodies. I don’t know who is doing it in Europe.
I do it in-house as well and or can also just supply the butterfly’s if you can’t find anything and or just the taper machining.
Best to find a clapped out cheap 2.2T setup and do the modifications. Leave the S bits alone.
Also, the plastic 72-73 stacks are too thin, That’s why I recommend the mag plus the mag with trumpets combined are taller.
Regards, Robert
It seems like bischoff overstamped their abbreviated number for a while presumably for those getting the different tailpipe for impact bumper but still using stocks the main part so likely the same. There is an overstamp of the other number that I referred to as “911/x”. In both my cases the “x” is 1 but here is 3 ( overstamp). Seems like 911/“x” is some sort of version number denoting some change maybe pipe shape but not clear what it denotes? These are not my exhaust silencers just came across this 574 example on www so can’t tell if outer wrap is stainless or regular steel.
Steve
[QUOTE=911MRP;1116361]It seems like bischoff overstamped their abbreviated number for a while presumably for those getting the different tailpipe for impact bumper but still using stocks the main part so likely the same. There is an overstamp of the other number that I referred to as “911/x”. In both my cases the “x” is 1 but here is 3 ( overstamp). Seems like 911/“x” is some sort of version number denoting some change maybe pipe shape but not clear what it denotes? These are not my exhaust silencers just came across this 574 example on www so can’t tell if outer wrap is stainless or regular steel.
I have one of these Bischoff 911/3 (9/74) California emissions mufflers with the extra air tube currently on a 69’ 911E engine that I just finished tuning.
I did a back to back test with my usual Leistritz test muffler.
This motor is running original 80mm mahles 9.1/1.
All I’ve done was valve tweaking and seat geometry and retained stock ports dimensions.
Both mufflers produced the exact same power of 170hp@6950.
[SIGPIC][/SIGPIC]Robert D. Groß