MIKE-FORD Posted June 28, 2007 Share Posted June 28, 2007 Does any1 no if a rs200 throttle body will fit a 1800 xr3i or is it best to do the 2ltr modeo ? Link to comment Share on other sites More sharing options...
Stu Posted June 28, 2007 Share Posted June 28, 2007 It's best to leave the standard one on. Link to comment Share on other sites More sharing options...
MIKE-FORD Posted June 28, 2007 Author Share Posted June 28, 2007 may i ask why as ive been told if i do change it i will gain a tiny bit of bhp and better throttle response or sumthin like that? Link to comment Share on other sites More sharing options...
Stu Posted June 28, 2007 Share Posted June 28, 2007 Everyone on the internet will tell you to change it because their mate did it and his mate told him to do it and so on and so forth. It's complete crap. Putting a larger throttle body on will give you full power with less pedal action. Yes, a different "throttle response", if you wish. Personally I prefer to have 0-80% throttle control instead of 0-30% (eg, 1/3 throttle movement goes from idle to full throttle). Link to comment Share on other sites More sharing options...
Craig855S Posted June 28, 2007 Share Posted June 28, 2007 cud u please explain in more detail stu as to why a larger hole doesnt let in more air therefore more power??? does it let in just teh same amount of air??? or does it let in more air and not give any more power?? Link to comment Share on other sites More sharing options...
Trig Posted June 28, 2007 Share Posted June 28, 2007 you need more fuel with the increased air intake to get more power, if you dont, it runs lean. Link to comment Share on other sites More sharing options...
rogerthecabbyboy Posted June 28, 2007 Share Posted June 28, 2007 basically if you can get more air and fuel into a cylinder at the correct ratio you can create more power. I can appreciate the larger 54mm throttle body won't flow a huge amount more than a 45mm one but surely provided the fueling is matched to airflow this will aid in the production of power? As for having a smaller throttle opening range i don't see how that is true provided the throttle can still open fully and the fuelling is matched to flow. i.e at half throttle for example the butterfly will still move to the same degree, but the pontential for flow is greater with the larger body as there is more of an open area. Link to comment Share on other sites More sharing options...
Stu Posted June 28, 2007 Share Posted June 28, 2007 Great theories chaps, all wrong though. A normally aspirated engine will draw in whatever it can. It's just a vacuum pump afterall. Something on that engine will choke it. Choke means the maximum airflow possible. Airflow equals power. A 40mm throttle body can flow 140hp worth of air in atmospheric conditions whereas a 50mm one can flow 170hp worth (not exact figures, but a reasonable comparison). If your engine/head/manifolds/etc. can only flow 130hp, then there is no gain in going from the 40 to 50mm throttle body. That is how my throttle response description works. Lets assume your engine chokes flowing 200CFM of airflow (~130hp). Your 40mm TB can flow 200CFM at 75% throttle. The 50mm TB can flow 200CFM at 40% throttle. Anything after the 75% and 40% respectively, is no extra power. That is what it's all about. Go search google for information on gas flow in pipes and you will soon find it quite astonishing what you can flow through a pipe at atmospheric pressures... Under boost.. thats a whole other story.. i've seen over 500bhp through a 50mm throttle plate.. I hope this explains it.. Link to comment Share on other sites More sharing options...
Craig855S Posted June 28, 2007 Share Posted June 28, 2007 you need more fuel with the increased air intake to get more power, if you dont, it runs lean. the MAf wud solve that problem surely Great theories chaps, all wrong though. A normally aspirated engine will draw in whatever it can. It's just a vacuum pump afterall. Something on that engine will choke it. Choke means the maximum airflow possible. Airflow equals power. A 40mm throttle body can flow 140hp worth of air in atmospheric conditions whereas a 50mm one can flow 170hp worth (not exact figures, but a reasonable comparison). If your engine/head/manifolds/etc. can only flow 130hp, then there is no gain in going from the 40 to 50mm throttle body. That is how my throttle response description works. Lets assume your engine chokes flowing 200CFM of airflow (~130hp). Your 40mm TB can flow 200CFM at 75% throttle. The 50mm TB can flow 200CFM at 40% throttle. Anything after the 75% and 40% respectively, is no extra power. That is what it's all about. Go search google for information on gas flow in pipes and you will soon find it quite astonishing what you can flow through a pipe at atmospheric pressures... Under boost.. thats a whole other story.. i've seen over 500bhp through a 50mm throttle plate.. I hope this explains it.. thats explained it fine stu, but why did ford put the big TB on the 130?? and why does the 2.0 mondeo use a big TB if it only needs one big enough to flow for 136BHP?? and are u saying that opening the throttle on a 2.0 TB'd 1.8 40% wud give u just as much acceleration as if u were to put the pedal to the metal??????? i find that REALLY HARD to believe Link to comment Share on other sites More sharing options...
Stu Posted June 28, 2007 Share Posted June 28, 2007 The 130/136PS engines used the larger throttle body to give the engine different throttle characteristics. Here are some real figures for you... Flowing 220 CFM (about 140hp) @ 37C (100F) through an orifice... = 42mm = 246 feet/second flowrate (ideal is around 320), pressure drop 0.5psi (6%)50mm = 168 feet/second flowrate, pressure drop 0.25psi (3%) Considering sonic (Mach 1) occurs at approx 1100 feet/second, do you really see either of those throttle bodies choking at 140hp? If you don't understand this, then it's most likely a topic you shouldn't be discussing The topic is considerably more complex than this as it greatly relies on the inlet manifold design... everything is relative. Link to comment Share on other sites More sharing options...
Craig855S Posted June 28, 2007 Share Posted June 28, 2007 The 130/136PS engines used the larger throttle body to give the engine different throttle characteristics. Here are some real figures for you... Flowing 220 CFM (about 140hp) @ 37C (100F) through an orifice... = 42mm = 246 feet/second flowrate (ideal is around 320), pressure drop 0.5psi (6%)50mm = 168 feet/second flowrate, pressure drop 0.25psi (3%) Considering sonic (Mach 1) occurs at approx 1100 feet/second, do you really see either of those throttle bodies choking at 140hp? If you don't understand this, then it's most likely a topic you shouldn't be discussing The topic is considerably more complex than this as it greatly relies on the inlet manifold design... everything is relative. so a 40mmTB in that situation wud be better than a 42mm as it wud flow nearer to 320ft/sec? but then wouldnt the pressure drop more than 6% u dont want the pressure to drop do u Link to comment Share on other sites More sharing options...
Stu Posted June 28, 2007 Share Posted June 28, 2007 It's all about compromise.. when you design an engine you have to take into account engine response, torque, rather than just peak power (which is why the 130PS 1.8 is crap compared to the 115 one).. Link to comment Share on other sites More sharing options...
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