Great but simple explanation of how a carb works, keeping the air speed up for fuel delivery & atomisation is paramount on a carb , bigger isn't always better as you've shown us.
sir post more on DCOE tuning, its great since kiddos nowadays didnt know how powerfull dcoe it can be. In fact im building DCOE 55 for Drag Car this year with alcohol fuel. going to post the build soon
Interesting. Here is an idea for you. It would be interested to take an EFI itb setup, and install carbs to it instead of intake runners. ( Carbs without fuel feed) that would allow to test various combinations with identical AFR. Would be interesting to see how big an air restriction a carb is.
Interesting infomation. I Recently purchased a single DCOE 40 to install on a 1.0L K10 Micra with a Draw-thru supercharger setup. Be interesting to see how it copes.
Hi Graham, Kart engine 45/32mm 13k rpm I got the 32's working, the kart will pull away with full throttle from walking pace. We fitted the 40's and on the stand mixture weaking was as you said, but initial blip throttle was the same as 32's. It would pick up, go weak, then completely lose the will to live at higher rpms. 22+ I'll do the rejet when we track test, when the weather is better. An intersting test for you would be to compare auxiliary Vents, no one ever does that.
Ive been spending ages trying ti get ny 4G54 cammed 2.6 4cylinder with twin DHLA40 Dellortos running well, my first move was to put 36 chokes in (replace the 32s). I must have a better go at getting the 32mm chokes back in and test it out.
@@PenguinMotors you are correct, I went from 36mm chokes to 32mm and same mph at the drag strip and far better driveability, with 36s it had massive lean spot part throttle as the main jet too too long to be activated street driving.
Great video! Although the difference between a diameter of 33 and 37mm is only 4mm, a 37mm diameter orifice is 25% larger than a 33mm diameter orifice. But yes, as the venturi/choke size gets closer to the same size as the actual carburetor body (bigger venturis), the difference in areas becomes less and less causing there to be less of a velocity increase and less signal/vacuum past the jets. Love your content! Could you possibly do a dyno test video with DCOE 45's instead of the 40's to compare the differences with 30, 32, and 34 mm venturis? It'd be 6 different runs + test runs, but it'd be really great to know! Always wondered. Anyways, great video. I look forward to more in the future!
will do another 45 choke test at some point, i already did one 36 and 38 chokes on the same 170bhpish engine. trouble is takes ages, setting up and rejetting for each test, plus to get an accurate result you need to do numerous test pulls each time, you could easy use a whole days dyno testing
Absolutely spot on 👍 very interesting and food for thought, could you possibly tell us what the actual main and air corrector jet size differences were for both the 32 and 33 chokes?
Tried 30mm chokes on my 1640 Escort once. Got all round better performance than the 33mm's, even good top end! I was truly amazed, but that's how it was.
Hi sir Graham!! I own a Pug 205 Rallye 1.3 swapped to 1.6 which equips two Webers 40 DCOM. Not sure if these carbs are so diferent from the DCOE's but, on the DCOM's I have, the inner diameter on the intake horns and aux venturi is 45mm and it only measures 40mm on the rear end outputs/throotles after main venturi. The strange thing is that these carbs mount 34mm main venturis stock and the original engine is only a 1300cc!!! Also I've tested 36mm main venturis on the 1.6 and it doesn't rev faster, but definitely there's a noticeable difference at the peak power and max rpm's so I've been using the 36mm for years, maybe I'll purchase a pair of Weber 45 soon lol... Maybe the 40 DCOE's you tested are different from the DCOM's? If I fit 32mm venturis I would lose power for sure. Not saying you are wrong, your theory has actually much sense and you showed dyno numbers, I'd just like to find an explanation of why Peugeot mounted these BIG 34mm chokes in the 40 DCOM's fitted in a 1.3, if this really could be counterproductive for the performance. Cheers!
You can never know 100% why a vehicle manufacturer does something. maybe it was for exhaust emission purposes or they wanted to change power delivery or even homologate them for competition? I tried bigger chokes on one engine, gained no power but left them in. Why? because i had less fuel stand off with the bigger chokes, its not always about peak power!
yes Ross long aux vent do help reduce stand off, its not so much that air speed is lower, but fuel blown back stays in the aux vent rather than being blown into outer space
hello Graham, we'd talked already before. Good video by the way, but there is something i want to discus if you dont mind. Now choke size matters indeed, but you've got to consider auxventuri how its shaped and the diameter. I know standard most at 4,5 as used to call it on aux venturi. Now you can modifie those for example. Correct about what leaves at intrance across / casting bore and aux venturi stacks. High velocity at high rpm may do @33 chokes, as for lets say a 1600 at 7500 rpm, but lost and gain on some, depending on cam. So why do they sell even 34mm chokes on #40 carburettors IDF or DCOE, if it does not do anything really for performance? Production cars in the 1970ties i have read, do differ at using a single dcoe carb or twin choke-wise and thus choke size also. Please do indepth video's on this item. A learning curve. I am doing my test and see what does and most by feel driving, i do not have an engine dyno. Less is ( often ) more like i said on the phone, as you know. I did prepped and shaped my aux venturis, for flow/pickup at working rpm's. Thank's and lets go a bit further in this matter if you like. 👍
they probably sell chokes too big for the same reason a lot of exhaust are too big, bigger must be better right? bigger sells well, whether its better or not!
lost some bottom end for no gain basicly, i rather sacrifice the last 500rpm of 1-5hp for gains in the bottom than look for minute increase where i almost never drive personally.
Very, very interesting video. Thanks for sharing your knowledge! Does the engine capacity have an influence on choke size or is the 32mm choke the ideal size also for a 1300 or 1600 engine? What would be the sensible maximum choke size for the 45 dcoe (1.9/2.0l engine)?
engine capacity will have an effect, 32mm chokes are just fine on most 1600, but a very mild one might be better on smaller, most 1300s would definitely work better on 28 or 30's. most sensible size for a 1.9/2.0 on 45's is 36, but 34's will work well on a mild engine and 38's on something hot
if your happy with it dont worry, but reducing them a bit along with the main jet size would probably make for an engine which will respond bit better at lower speed bigger throttle openings, for what its worth a dellorto only has one leg on the aux vent, so a 33mm choke MIGHT give a bit more benefit in a dellorto than a weber
@@PenguinMotors I have not fitted the twin 40’s yet. It has the fully modified 32/36 as per your video on it at the moment I set up the 40s with 34 choke from info in the Des Hammill book it is a modified 2.0 your videos are awesome it’s difficult to find someone who wants to tune a pinto and knows carbs. Last time on the dyno I was doing all the tuning and he just did the tests when I said I want to change cam timing he talked me out of it saying your not going to make any more power that’s about all you going to get. Disappointing attitude.
@@flatchatcharlie what is modified how far? Mild cam on SOHC standard internals on 40 mm sidedraft Carbs no larger need as 32 chokes. Jetting and ignition timing perfect, you wont believe how much it can do for daily road. Not to speak of clutch and endgear ratio. wich does contribute how an engine responds with given power output and curb weight of car.
Your engine has bigger problems than the carb, the bigger venturi should have increased the power. But the engine falls over at 5000rpm so any venturi sized for more than 5000rpm (in this case 32mm) is pointless due to that particular engine and the way it's built. Back to the drawing board to find an engine with more power, then try the carb test again?
That's what I would have expected and yet interesting at the same time? Do you have a video showing the 45 specs and dyno run ? What would be an excellent comparison is 32 and 33 venturies in the 45s ?@@PenguinMotors
