I run twin 45 DCOE Webers on my full race / stroked 285HP L.C. Engineering Stage 5 Pro motor. I set up mine with larger chokes, etc. good to 6500 RPM. You can run 48s but unless you have a motor like mine and want to rev to 8500 RPM you will really have to install small chokes, jets, etc.
yea....... reading around on what people with the sidedraft setups use..... generally the biggest people go on a daily driver is a 45mm. only the guys runnig high output, high rev motors use the 48's.
I have to disagree... You should see some type of gain for sure... The more air you can cram into the chamber the better... You can always jet down but, you can never get as much air thru a 45 as you would a thru a 48... Just my .02
arent these better suited for top end though? i mean, he can jet down but if he does that and dont use them at the higher rpm, woldnt that kind of be a "waste" of carburetor upsize? i know i have seen this formula before but, i cant seem to find it. it calculates the size of a carbureator needed to run the motor at its best efficiency rate given the top rpm of the motor and displacement size....... you know what im talking about BYE?
Bigger is not always better, people have a tendency to over carburate thinking a huge carb will yield huge power, NOT a pair of 40mm sidedrafts is more than adequate for a 4cyl engine when properly tuned.
thanks for info guys...its very useful for a newb like me...recently i blew my engine, and WAS going to drop in a 22RTE, but i think im going to stick to the 22R for now and build it when i get back
I will agree that bigger is not always better but, in this case I've experienced it first hand so I will side by my experience... A pair of properly tuned 48's will out perform a pair of properly tuned 40's anyday in my book... *My buddy has a pair of 40 webers and a pair or 40 mikuni's... Anyone wanna trade their 44/45/48's?? We'll even pay the shipping both ways...
thats more along the point i was trying to make. BYE, your buddy wouldnt happen to have a manifold/s that would better suit a late 22R head would he? i have 20R manifolds on the mikuni's i have..... wont work for the head i am gonna use. I'd pay shipping my way of course...... edit: did you happen to notice a delay in power delivery with the bigger carbs?
What 20R intake do you have? Cannon? I'll check him... If we trade can we also trade carbs? No delay in power delivery bro, like I said properly tuned....
Anything can be tuned.. They make 36 vents for the 48's, so you could really make them run about the same as the 45's. Alternatively, they make 40mm vents for the 45's so same story there. 45's should be cheaper. usually, for balance between power and drivability, venturi size should be about 3-5mm smaller than intake valve on stock or mild engines, and close to the SAME size as the intake valve on high output engines. Depending on your head flow, intake valve size... if your intake valve is 45mm and you use 48mm carbs w/45 or larger vents, it will still flow only as much as the 45mm valve permits.
I used to have an 18RG TRD Full race motor in my truck when I raced. The motor produced 360-375 HP and I ran twin Mikunis. The red line was 10,000 RPM and typically it ran in the 7000-8500 RPM range. Whether you use Webers or Mikinis the carbs have to be matched to the engine. My current 22R stroked engine has 10.5:1 compression, 20R head with the biggest valves you can put in, hot cam, ported exhaust and intake runners, matched intake manifold, large matched exhaust tubular SS header, and all the other goodies. It produced 285HP on the dyno and is red lined at 8500 RPM but I typically do not go over 6500 RPM. I run twin Weber 45 DCOEs with 38 chokes and appropriate jetting. I could run 48's if I wanted to go up higher in the RPM range (Racing). Go to the Weber WEB site and you will find Charts and Formulas for helping you to decide which carbs are best for you. Be real about your motor performance and how you want to drive your truck. Like they said "Bigger is not always better".
Thing is, when you talk about a 40mm carb, you wont have a 40mm hole through the carb, you'll probably run a 33mm or a 34mm(which is pretty much the max size for a 40mm) choke. Thing is that the bigger the body the bigger you can go on the max side, but it will also limit the size you can go down. All in all, see what kind of choke size you need and get the carb body to match it.
