mikie 0 Posted January 31, 2006 I am running 45s with 36mm chokes on my mi 1.9. Would a set of 38mm bike carbs from a cbr1000 give the same amount of air flow or not?I have done a search and cannot find the answer.All input welcome Share this post Link to post Share on other sites
crogthomas 0 Posted January 31, 2006 How much power does your engine make and how much did a CBR1000 that the carbs came off make? Share this post Link to post Share on other sites
Richie-Van-GTi 71 2 Cars Posted January 31, 2006 how much power the bike made is irrelevant as the displacement is totally different. Its choke size that matters and yes you will get a similar amount of flow Share this post Link to post Share on other sites
Rippthrough 98 Posted January 31, 2006 how much power the bike made is irrelevant as the displacement is totally different. Its choke size that matters and yes you will get a similar amount of flow Eh? You need a similar amount of air to make a certain power figure no matter what the displacement. Share this post Link to post Share on other sites
mikie 0 Posted January 31, 2006 Hoping for about 170-175 bhp standard cams etc.Just a rebuilt engine.Dont know what the bike bhp was. Share this post Link to post Share on other sites
Ahl 4 Posted January 31, 2006 Your both right, but your misinterpreting what richie means Rippthrough (or you haven't read the post above his). Share this post Link to post Share on other sites
Rippthrough 98 Posted January 31, 2006 Your both right, but your misinterpreting what richie means Rippthrough (or you haven't read the post above his). I have, but don't agree with statement about displacement. Share this post Link to post Share on other sites
mikie 0 Posted January 31, 2006 So would these be ok or would they be too restrictive? Should i be looking for 42mm throttles? Share this post Link to post Share on other sites
DrSeuss 0 Posted January 31, 2006 I think bike carbs run without chokes. Personally i think the 'if it ain't broke' principle works. Rather then spending more money on changing carbs. Get ignition management and a nice fat cam. Or a decent set up. Share this post Link to post Share on other sites
mikie 0 Posted January 31, 2006 Its going in the back of a mini pickup so iwill be making a loom and want to run it on carbs for ease. I cannot afford another set of webers along with the build so trying alternatives to keep it interesting and on budget Share this post Link to post Share on other sites
Rippthrough 98 Posted January 31, 2006 Its going in the back of a mini pickup so iwill be making a loom and want to run it on carbs for ease. I cannot afford another set of webers along with the build so trying alternatives to keep it interesting and on budget In that case yes, they should flow enough. Share this post Link to post Share on other sites
Dom9 2 Posted February 1, 2006 The simple answer is that they will flow roughly the same... Bike carbs generally don't run with chokes, so they are 38mm all the way through... Your 45's will be 36mm at their smallest point, but this is quite a smooth transition so I would expect the flow to be similar to a 38mm bike carb... However, when choosing a carb, I tend to agree with crogthomas and rippthrough... You want to use the carbs from a bike that makes a similar amount of power as it is directly related to airflow. If the bike is 1000cc and makes 150bhp but does it at 10000 rpm, I would have thought these would be ok for a 2000cc engine making 150bhp at 5000rpm... That is a bit of a generalistaion, but you get the point. Look for set a R1 or Blackbird carbs, they are larger and the Blackbird puts out 160-170bhp as standard... I have set I might be willing to part with, discuss over PM if you want. Why don't you just stick to the 45's though? Better the devil you know! Share this post Link to post Share on other sites
crogthomas 0 Posted February 1, 2006 A 1994-2000 model CBR1000 makes approximately 135bhp, so I would suggest that they are a little too small. Share this post Link to post Share on other sites
Jonmurgie 2 Posted February 1, 2006 A 1994-2000 model CBR1000 makes approximately 135bhp, so I would suggest that they are a little too small. As has already been said the power of the CBR1000 is completley irelavent in this topic... mikie - you should take a look though some recent topics about bike carbs before going down that route as you will not doubt end up disapointed... as has been said already, get some mappable ingition (only just over £200 + VAT for KMS from http://www.enginemangement.co.uk) and a set of CatCams from QEP (http://www.q-e-p.co.uk) and you'll be much happier and easily make your target Share this post Link to post Share on other sites
crogthomas 0 Posted February 1, 2006 As has already been said the power of the CBR1000 is completley irelavent in this topic... You want to use the carbs from a bike that makes a similar amount of power as it is directly related to airflow. If the bike is 1000cc and makes 150bhp but does it at 10000 rpm, I would have thought these would be ok for a 2000cc engine making 150bhp at 5000rpm... That is a bit of a generalistaion, but you get the point. As Dom9 has quite correctly pointed out power is directly related to airflow. The sorts of engines we are talking about here have very similar mechanical and thermal efficiencys and therefore the power output will depend on the amount of fuel burnt. Since the amount of fuel burnt is directly related to the amount of air consumed then so is power. On the CBR1000 the 38mm carb flows enough air to make 33.75 bhp per carb/cylinder. A 38mm carb is common on some 125cc 2-stroke MX bikes and they make about 35-40bhp per carb. On an engine that couldnt be more different. Obviously there is some tolerance, you may be able to squeeze 145bhp out of the CBR carbs, but its a very simple way of matching engines to carbs. Fuel injection is best though, by the time your spent hours on the rolling road and ££s on jets, you may as well have bought a ECU. Craig Share this post Link to post Share on other sites
Dom9 2 Posted February 1, 2006 (edited) As has already been said the power of the CBR1000 is completley irelavent in this topic... Why? Why then do you buy TB's by size? Why do we know that 42mm TB's, for example, flow enough for 220bhp on a 4-cyl engine, even though we have no information on what engine that is on? It's because it doesn't matter what engine it is! Throttle bore is what governs air flow and air flow governs power... Any carb that makes 35bhp can make 35bp on any cylinder, it just might be at a different rpm etc... If you want a carb that can flow 40bhp per cylinder on an Mi16, find a carb that flows 40bhp per cylinder on a bike, say the Blackbird carb. When a 45 DCOE makes 50bhp per cylinder on a Vauxhall XE would we assume that it wouldn't make 50bhp on an Mi16 in similar spec? Yes, jets may need to be changed to suit power delivery etc, but all a carb or TB does is flow a certain amount of air, to give a certain power. Edited February 1, 2006 by Dom9 Share this post Link to post Share on other sites
Jonmurgie 2 Posted February 1, 2006 It's because it doesn't matter what engine it is! Exaclty, that was my point... it's pointless that the carbs help the CBR1000 produce the power it does as he's not on about fitting a CBR1000 engine to his 205! For example just because a 45mm throttle body makes 200bhp on one engine doens't mean fitting that to a compleltey different engine it's going to produce the same power. The flow thing, as you say, is what it's all about and I'm not arguing that at all Share this post Link to post Share on other sites
mikie 0 Posted February 1, 2006 I didnt want to start a fight Thanks for all your answers keep them coming they make for interesting reading. Share this post Link to post Share on other sites
Dom9 2 Posted February 1, 2006 Exaclty, that was my point... it's pointless that the carbs help the CBR1000 produce the power it does as he's not on about fitting a CBR1000 engine to his 205! For example just because a 45mm throttle body makes 200bhp on one engine doens't mean fitting that to a compleltey different engine it's going to produce the same power. The flow thing, as you say, is what it's all about and I'm not arguing that at all Ok, I think I see what you are getting at... But... If a standard Mi16 makes 160bhp and CBR1000 carbs produce 135bhp, they WILL produce 135bhp at some point... It's just that they may not be able to cope with the 'full' 160bhp, if you see what I mean? If an Mi16 makes 160bhp at 7000rpm, it probably makes 135bhp at 6000rpm, so the Honda carb will aloow it to do that, it might strangle it at higher rpm though. If he was putting a carb rated at 135bhp onto a 100bhp engine, I would agree that it may not necessarily produce the increase to 135bhp... But one spec'ed for less or similar power ought to produce the goods at some point, it just might take a bit of adjustment to run smoothly through a cars rpm range. Power is power, regardless of spec... If an engine has the ability to produce 200bhp and so does another engine, it doesn't matter how much their spec differs etc, they will LIKELY be able to use the same carb as their max power is the same... even if one produces it at 6000rpm and the other at 7000rpm... I didnt want to start a fight Thanks for all your answers keep them coming they make for interesting reading. Don't worry mate, this isn't a fight! If you think it is - you haven't been hanging around here long enough! Why are you changing the 45's? Share this post Link to post Share on other sites
mikie 0 Posted February 1, 2006 Im not changing the 45s they are on my daily driver.The motor bike carbs are to go on my mini pickup project (mi powering rear wheels,rear engined) Share this post Link to post Share on other sites
Dom9 2 Posted February 1, 2006 What gearbox are you using? Transverse or longitudinal? Share this post Link to post Share on other sites
mikie 0 Posted February 1, 2006 Its going to have a 1.9 or mi box.The whole lot is going to sit in the rear the same as it does in a 205.Full 205 brakes suspension and steering. 2 front sub frames one in the front and one in the rear.It has got the rear frame mounts done already but im space framing the whole thing at the moment and getting rid of the ussual mini rust.Long term project really Share this post Link to post Share on other sites
Dom9 2 Posted February 1, 2006 Its going to have a 1.9 or mi box. Awesome for drag racing with all that weight out the back, but not so great for the roads etc especially with the mini being so light! What are you going to use it for? This sounds like an exciting project! Get some photos up for us!! Share this post Link to post Share on other sites
mikie 0 Posted February 1, 2006 Its going to be for road use.Im going to get some weight up front by mounting things like rad,fuel tank battery and ballast to help balance it out.I dont know how to upload photos to the web site otherwise i would. Share this post Link to post Share on other sites
