32/36 jetted or 38/38 Weber

[Daily02]

Hello,

I am looking for an opinion here on whether a 32/36 Weber properly jetted would FEEL as fast a 38/38 Weber, or does anyone know why the 38/38 feels faster? Is it quick throttle action, larger venturi's, and (or) jetting? Fire away. 

 

Regards

 

Dono

[Son of Marty]

More noise, less flexibility with the 38/38.

['76mintgrün'02]

Much touchier pedal with the 38-38. 

 

(Makes it feel peppier than the 32-36).

[TobyB]

I know why.

 

Many do.

 

The 32/36 is a progressive carb, where the 32mm bore opens first, and then the 36 follows on a bit later.

 

the 38/38 was originally meant for a V6, with each bore feeding one bank, and it's synchronous, with

both 38mm bores opening at the same time.

 

So for the first 20 degrees of throttle shaft rotation, the 38 flows a LOT more air.  Too much for a 2 liter, really,

but having run one for a few years, it was still a blast.

 

There is a 'sync link' out there for the 32/36 that opens the secondary 36mm barrel along with the 32.  Never tried that.

 

I DID find that lap times with a tired stock engine didn't much care if I was running a 32/36 or a 38/38- with a 6k

rev limit and 8.2:1 compression, the 32/36 isn't a flow restriction.

 

The 38/38 is more fun.  

 

t

 

[John76]

@'76mintgrün'02 makes a nifty throttle linkage adjuster that lets you adjust when the secondary throttle kicks in.

 

[Daily02]

It sounds like the quick throttle action is it, and as for the feel:

"The 38/38 is more fun."

This is really what I am looking for. That seat of the pants kick. It doesn't need to be actually quicker. Thanks!

 

Regards

 

Dono

[Tom Daley]

For what its worth my 32/26 set up is below.

 

Good throttle response and pulls throughout the RPM range. I worked on this for a while with an air fuel (AF) O2 sensor kit installed just after the header pipe and temporarily wire tied to the hood vent ribs in front of the driver. 

 

NOTE: I installed throttle shaft bearings and a linkage synchronization kit so its not progressive, its a  2bbl.

 

FINAL SET UP

1976 2002 M10 original block.

Altitude ~370ft above sea level, Ambient as of this writing, 50deg.

Flat tops w/1 step overbore

274 cam with 2mm added lift (turbo or M30 grind)

E12 flowed head, stainless valves

Exh manifold air injection tubes removed and plugged

Stainless Irenald exhaust, fully heat wrapped header pipe, AF wideband just after the header

Throttle linkage synchronization kit

Fully ovaled out the manifold opening at the carb, ported the manifold also

Petronix, Timing 40deg at 3500. No vacuum retard or advance

Float 38MM

Primary

Main 140, Air 155, F50 Idle 60

Secondary

Main 135, Air 170, F50, Idle 55

 

UNPLUGGED the Secondary Enrichment Circuit. (This fixed my lean WOT AF 16-17:1). Still can't find out why its recommended to plug off. Made my WOT lean.

 

AFs now,  Idle 13:1. 12-14:1 through all throttle position and rpms including WOT with one exception, I noticed a blip at just before WOT where it hit high 14s:1 to and sometimes 15:1 for an instant. I'll check spark plug temperature/color. I.e. want it to be a tan marshmallow. and I should be done.

 

Good throttle response, pulls like a mule, no throttle lag at any RPM, no burn your nose drain oil, no exhaust fumes. 

 

[Daily02]

Hello Tom,

 

That is a great argument on keeping what I already have. I like the way you kept the secondary enrichment circuit. It is there for a reason. Thanks!

 

Regards 

 

Dono

[Dick R]

Last year, I faced pretty much the same question you have now.  Keep the 32/36 or go for the 38/38.  Here's my story and the thoughtful responses. 

 

https://www.bmw2002faq.com/forums/topic/333502-3838-surprise/#comment-1621198

[John76]

18 hours ago, Tom Daley said:

Exh manifold air injection tubes removed and plugged

Just curious...how did you plug the threaded air-injection ports in the exhaust manifold?

Thanks,

John

[Tom Daley]

I unscrewed the tubes and purchased 4 bolts of the same thread. Preferebly stainless. Cut the threaded end off at a deduced length based on hole depth. I then slotted the cut off end of it to use as a screwdriver slot. Chased the hole threads for easy install, basted the theads of what is now essentially a heavy machine screw with JB weld and screwed it in until just flush or slightly .030 or so below flush. I then staked it in at 3 or 4 points and let the JB set up. Lastly I used a ball stone to "dress" the entire cavity. 

[Tom Daley]

Hi Daily02,

 

Data rules all. AF ratio gauge is very helpful.    Just remember that your altitude, engine arrangement etc... will have effects in set up and make sure your normal power valve is good first.

 

Depress the spring and hold your finger over the orifice on the lower side of the top cover, release the spring.  It should stay depressed. If its bad it'll not deliver the extra fuel as designed under low vacuuum (throttling for power) conditions. 

 

High vacuum, no extra fuel (i.e. idle). Low vacuum, (given it the beans) extra fuel. 

[jimk]

5 hours ago, Tom Daley said:

Hi Daily02,

 

Data rules all. AF ratio gauge is very helpful.    Just remember that your altitude, engine arrangement etc... will have effects in set up and make sure your normal power valve is good first.

 

Depress the spring and hold your finger over the orifice on the lower side of the top cover, release the spring.  It should stay depressed. If its bad it'll not deliver the extra fuel as designed under low vacuuum (throttling for power) conditions. 

 

High vacuum, no extra fuel (i.e. idle). Low vacuum, (given it the beans) extra fuel. 

Doesn't the power valve open when the small round disc on the end of the spring loaded rod is pushed against the power valve stem when vacuum is insufficient to hold the rod up, i.e. vacuum pulls the rod up and the power valve in the bottom of the bowl closes.

[Tom Daley]

Yes. Did I  not say that? High vacuum lifts the disc and closes the valve. i.e. idle. Low vacuum at calling for power releases the spring depressing and opening the valve. Did I say it backwards.

[Daily02]

Good data does rule! I wouldn't start tuning without an AFR and a vacuum gauge. 

 

The input has been great here. Several different opposing opinions of end users with the pro's & cons. 

 

Regards

 

Dono