Yeh, well hopefully it will see me good in the set up of my 40's on my current 1600 when the time comes.
yes will be a later mk2 eng,what sort of price are you paying for it?might also be worth having a look inside to see what has been done?
No price agreements yet, before i agree anything, i'l need to know the full spec of everything thats been done, everything thats needed to run it, and why.
i don't have the engine, i have only seen the bottom end built up and the head on the bench. the guy runs 2 rally cross cars and a rally car all are mk1 golfs either 1600 8v, 1800 8v or 2.0 16v depending on class. the guy said it needs 48mm carbs then it needs 48mm carbs. no offence guys but i would tend to believe someone with the knowledge of designing, building and racing the engines on what components will make it work for the application which it was designed for... oops also meant to say it should use mapped ignition to get the potential out of the engine. Edited by: pol8
48's can go all the way down to 34's by the looks of what is in the book I'm reading and the maximum size for 45's looks to be 40mm Although I think someone mentioned a percentage rule that worked? 6-7% of the venturi size or something?
alright james i heard a 90% of the carb size type rule. so going off those sizes,either should be able to be set up to run on maybe more than you would think?
dex,seems like your into this stuff do you wanna throw a wild guess at what you think i would need,think you know the spec im after? basically am i just best off giving the 45's a chance to be set up? cheers,neil
Neil, as I think I've said before you've got nothing to lose by trying the 45s and if they're not big enough you can then go over to something bigger. Once you've finally decided on your engine spec and what it's going to be used for you can make a better choice! It was interesting to hear that H8SV8S and RobT seem to be reaching the limits of the 45mm throttle bodies, though. If your engine's going to be to a similar spec then it would seem that you may end up needing to run DCO/SP48s or even bigger. This theory's all well and good (and useful for getting started) but it means absolutely nothing when it comes to tuning the car. A good carb expert won't ask what rpm you expect to make peak power and then read off a little chart to work out what choke size you need, he'll listen to the sound of the engine, put his hand over the trumpets, smell the exhaust fumes... Then, to finish off he'll check how the changes to choke sizes affect the car on the rolling road and even more importantly how they affect the way the car actually drives. You just can't work that out until you build the engine and try out different setups.
For the 1600 engine Scott has mentioned, if the engine is to rev to 8,500rpm then you could use either 45's with 40mm chokes or 48's with 40mm chokes. A particular engine of this type - albeit a highly developed long-stroke 1600, with the 48's and a suitable semi-race cam and the right lift produced 189bhp at 8,250rpm (6,200-8,500 powerband). 48's with 42mm chokes would be suitable for an engine that revs to 9,500rpm. So for Neil's, which I think you mentioned you wanted to see 8k-8.5k? 48's or 50's with 42mm chokes would see you in about the right area. There will be exceptions to the immediate above but generally they will be pretty close.
yeah! cheers for clarifying that greg its just that if the general opinion was to go for 48's for definate then id be selling the carbs now to fund other stuff for the moment thats all but i thought it would be best to keep hold of them as i know they havent had much use really and they are a good matched pair. i cant wait to see the guy setting em up
sorry james,i took ages to reply. people agree with james's thinking? sounds good to me? obviously im just tring to understand this in simple terms,all will be found out when its on the rollers time after time maybe. Edited by: riley
That 9,500 is in relation to the 1600 engine (400cc cylinder displacement) by the way. It shows the recommended Weber carburettors and recommended choke sizes with regards to cylinder displacement and state of tune. Are you still aiming for a 2.1l engine Neil? Race-spec 2180cc VW engine used 48 IDA's with 40mm chokes. Going back to a table that shows the recommended carb and choke size to use... I will just put the 3 levels of tune that will be more relevant for you to look at, rather than including the lowest and highest state of tune recommendations. Buy the book - Four-Stroke Performance Tuning book by A. Graham Bell. There will be exceptions to the above information. Food for thought nonetheless and a bit of knowledge into carb and choke selection. The author is very thorough in his explinations throughout the book. As you say, all will be revealed with regards to what does and doesn't work on the rollers, the above figures are generally very close to what will work best. There is a lot more to it than just carburettors. (And a lot more to carburettors too!) Going back to your original question, I do believe that 40's and 45's share the same manifolds and 48's and 50's will require their own, as I think someone has already mentioned previously in this thread. Edited by: mk1 driver
No offence James because I see where you're coming from with those but they're totally useless in the real world. The "tuning" you can do from a book will get your engine running and maybe help you to choose carb sizes but in terms of actually setting up the engine, nothing comes close to an experienced tuner having a play with the engine. It's not an exact science and every setup will respond differently to changes in choke and jet sizes. By the way, that race-spec VW 2180cc engine - it'll be a Beetle engine so it won't be much use to Riley unless he's going aircooled.
but if you haven't bought the engine yet, just fit a 16v in there rather than a very fragile, modded 1600
There is a rough indication of the choke sizes you need, as already said its alot better to fit smaller chokes, once you get it tuned up you'll soon see if you need to go bigger as the curve will flatten off, and peak will be lower than expected. I know the ins and outs as i started off with a stock 1600 running 30s, this was really torquey but wouldn't pull much high up so i went to 32s and noticed a difference straight away, on a stock engine with 4-1, i made 122bhp@5667 fly and 114lb/ft at about 5k. But i was disappointed, the car went well but the engine was peakign too low, my box was designed for a 7000+ limit... so i eventually got a worked head (alot of work done,cut back valves, worked seats/guides, porting on inlet/exhaust 10.6:1, reshapped combustion chamber etc) and a 277/280 cat cam, 36mm chokes (in 40s) had it all setup and now the car makes 125bhp@6800 wheels and the same torque as before, incidentely i done back to back tests with no trumpets and trumpets and i gained 10lb/ft and 1000rpm lower peak torque with the 90mm trumpets as apposed to none (of course i ran these all along but wanted to see the difference). The car certainly flies but low down i still think 34mm chokes would have been better, of course this is a peugeot engine so principles will be similar but you will have to make different choices on choke size, just get someone decent to set it up who has chokes in and swap them on the rollers, it only takes 5 or ten minutes and mine are at the back of the bay, just make sure you fit the auxillary venturis in correctly as if they aren't the car won't rev because the main circuit won't work
I haven't said those figures are bible, whereby only that particular carb with that choke size will produce the best figures. Those figures arise from development on a whole range of different capacities and specifications of four cylinder engines over many, many years and therefore for a given cylinder capacity and engine specification you may find you are in the same region as stated in table, in the book. Obviously there are many variations from engine to engine in varying states of tune but the figures I showed are from what has been known to work over the years for a given cylinder capacity. You never know with Neil but you could see from the recommended carb's and choke's I put up before that they were close to what was actually used on the air-cooled 2180cc engine. To sum up, those figures were in relation to cylinder displacement various states of engine tune (which alone will also differ from engine builder/tuner to the next..). It will be a big case of trial and error but picking up information from people with similar specification engines will be invaluable.... if you can get any that is.
Dex, its not a case of if he says it needs 48's but cant say what choke size it needs, more a case of me asking him if 40's would be suitable, with him replying that they wouldnt be suitable and it would need 48's. I cant remember if he stated a choke size in any of his emails to me, so all i can do is ask him. Edited by: scottmk1
no need to get cheeky, the reason i believed what i was told in this instance is because this person has knowledge in the engines he has built. I don't know about you, but I don't disregard information given to me by someone who has more knowledge on something than I do... i would have asked more questions and got more information about the engine and the spec of it and why certain parts should be used but i was to busy getting advice about the engine i am building. i think he will be able to tell you much more than what chokes the carbs it will run...
