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i will give the IDA48's a second chance.... when i didn't got it good running 10 years ago , i think ( and hope) i started with to big venturis of 40 mm.... and on a "old" '82 engine.
Now i have a more "sound" '86 engine ( still 16V ) and will start tuning with 36 mm venturis.
CC's per cilinder are the same as my rally BMW 3.5l CS running perfect with triple DCOE 45 Webers.... with 36 mm venturis.
i will give the IDA48's a second chance.... when i didn't got it good running 10 years ago , i think ( and hope) i started with to big venturis of 40 mm.... and on a "old" '82 engine.
Now i have a more "sound" '86 engine ( still 16V ) and will start tuning with 36 mm venturis.
CC's per cilinder are the same as my rally BMW 3.5l CS running perfect with triple DCOE 45 Webers.... with 36 mm venturis.
Barry, 40mm venturis is absolutely not too large. I once had a BMW 323i E21 (386cc per cylinder) with three Dellorto DHLA 45 carbs. Going from 35mm to 38mm venturis made quite a power increase.
The fuel pressure must be right (0,20-0,30kp/cm2) and the float level correct. Get one of these so you can monitor the air fuel ratio when tuning the carbs. https://www.innovatemotorsports.com/products/MTXL.php
Online you can find plenty of information about tuning the Weber carbs. https://www.jiminglese.com/weber-tech http://www.clubcobra.com/forums/arch...php/f-127.html
Åke
don't know Ake, as i found on the net some diagrams for venturis per cilinder cc : 36 ...max 38 mm for our 580 cc at 6000 rpm. So with bigger jets a 40 mm would work but i guess the smaller the venturi is , the better respons mid range , what i want.
If i get i right i will soon see if the engine gets out of air at 6000 rpm. As long that's ok , i don't see the need of bigger venturis.
goal is a rally car , so respons,torque is more important than HP at 6000 rpm.
PS i do have Innovate AFR gauges...
don't know Ake, as i found on the net some diagrams for venturis per cilinder cc : 36 ...max 38 mm for our 580 cc at 6000 rpm. So with bigger jets a 40 mm would work but i guess the smaller the venturi is , the better respons mid range , what i want.
If i get i right i will soon see if the engine gets out of air at 6000 rpm. As long that's ok , i don't see the need of bigger venturis.
goal is a rally car , so respons,torque is more important than HP at 6000 rpm.
PS i do have Innovate AFR gauges...
Barry, it is your choice, a smaller venturi will in theory enhance the middle range. A rally car need more mid range torque. The power range of my small BMW was between 4000 and 8000 rpm.
Åke
indeed Ake, i start with 36 mm and can always go bigger…. also i hold 6000 rpm max as oem , i want to keep the engine reliable. It is a V8.... 8000 rpm , as you mention, is another story for venturi diameter.
If i look at the diagrams i used for the 580 cc/cilinder : 6000 rpm gives 37 mm ( so i took 36 for mid range ) but 8000 rpm gives 47/48 mm !
here is my BMW regularity rally car/engine … with the longer trumpets /airbox we went from 240NM to 300 NM !
Barry, the BMW Coupe of yours is almost too nice to be used as a Rally-Car. You are one more that has find out that long tuned intake ducts is the way to go. It seems hard to convince our american friends how important intake length tuning is.
Åke https://mechanics.stackexchange.com/...curve-of-a-car
yes Ake, on the E9 forum they find it "horror" that i use the coupe for rallies…. but ok, most of those guys are restoring them to the last bolt and have "garage queens" they don't daire to drive in rain….haha.
And for what/who ? perhaps we are the last generation who "may" drive those oldtimers.... ?
Out of respect i also restored another one and keep it oem… idea was a spare shell but ended in a restoration.
Barry, that is a very nice BMW Coupe. I have a 635CSI of the same color. Right now the engine is out and will be replaced by a highly modified 3,5L six. No racing though, just for fun. I have had the car since 1980.
Åke
11-15-2009, 07:43 PM
i also restored another one and keep it oem… idea was a spare shell but ended in a restoration. 
