After keeping up with this thread for a while now, I'm wishing I had given the 38 more consideration when I purchased my 32/36.
What performances differences would I realistically see between the two?
BTW, I hope you're feeling better.
I think what you'd see is a big increase in off-idle and midrange throttle response and torque.
I know I'm going to piss off a dozen guys with 32/36 carbs and I really don't mean to but I'd size a Weber 32/36 on a fairly stock 1,600 to 1,900 cc Volkswagen.
I ran my first Webers in high school on a built (if you can imagine such a thing but it's true) 1,915 cc Volkswagen with ported heads and an Engle cam. I went with a pair of 40 IDF Webers and the damn thing would take full throttle without a hiccup at 1,000 rpm, even though it loped at idle.
I believe those carbs are good for around 212 cfm per barrel and I had 4 barrels. If you do the math, I should be way over carbureted for the engine size. That's why I always want to slap a guy in the mouth when he talks about some cfm calculator on the internet. Please appreciate my humor when I talk like that.
I guess that story doesn't really apply because it's an I/R application and we're talking about common-plenum carbs. I digress
There was a guy on the forum a couple of years ago with a Solex 34 who carried on and on about how a 38 was a race-only carb and how his Indonesian knock-off 34 was the cat's meow. That dude did more disservice to Weber, forum members and engine tuning in general than you could imagine.
Ok, I'm getting carried away, lol. My opologies.
I suppose the point is that cfm calculators don't tell the whole story and can easily lead guys astray. What's more important than some arbitrary airflow number at max flow is the carb's ability to meter fuel and deliver the appropriate mixture under all conditions.
From what I've seen, the Weber kicks the snot out of other carbs for low-speed metering accuracy. One thing you have to keep in mind is that the idle/progression circuits were designed with a certain amount of air flow in mind. 4200cc on a single 32mm throttle plate with a single idle jet wasn't in the plan, lol. That's actually a testament to how well a Weber works!
A 38 with slightly larger venturi but double the idle/progression circuit area, it is much easier to tune with more accuracy and provides more useable torque. It's most-certainly not "over-carbed" on a 258.
My opologies to those who've had to suffer through this post. Matt, I'm bored stiff, can't leave, on meds, waiting on the Mayo Clinic and apparently terrorizing other people with my opinions is somehow helpful? I don't mean to.
Please bear (bare?) with me. And thank you for asking!
Edit: Please also try to forgive all of the mispelled and/or missing words. Work with me here huh. I ain't quite right lately but we're working on it.