| Author | Message | ||
     Martin |
My winter project was to build a 42mm twin t/b inlet for my xb9 First dyno runs netted 83rwhp, which is about 10 up on my previous best with the FAST kit and Luckys exhaust. (Same dyno, which I guess is a conservative one) Still weak everywhere, from idle upwards. worked better with the O2 setting at ''2' (Richest)on the PC Maxed-out on the fuel added with the PC111 so we are getting some bigger injectors. Just to put my mind at rest I am going to look for air leaks first. Strange things: very hard to get an O2reading below 5000 rpm. anyone else had this problem? maybe the probe doesn't go far enough in? Engine doesn't return to idle for a short while, even though throttle is shut. This is affecting throttle response/feel, which is one of the things I was looking to improve. 'Feels faster' but mostly at the top-end. More news/dyno charts as it happens. | ||
| Stinkybritches |
Do you have fully independant runners to the ports, or are the siamesed? Independant are FAR superior, and MUCH easier to tune as there is no charge robbing from cyl. to cyl across a shared intake. I am planning to go to 90", cams, dual TB/intakes and paint over the wet winter here. Please keep us updated. | ||
| Wyckedflesh |
Martin, just wondering why you chose a twin 42mm throttle body? Wouldn't it be better to run a twin 36mm throttle body instead? | ||
| Martin |
I was looking for a twin t/b with the smallest distance between the bodies. The one I ended up with was based on a weber dncf pattern, of which the smallest stock size was 40mm but the stack for that t/b was only available in 42mm. I had at the back of my mind that I might later enlarge the motor. | ||
| Wyckedflesh |
It very well could be that the TB size itself is to great, and that the motor just can't pull that kind of CFM on individual runners. If it is based on the DNCF design, then see if you can get some machined inserts that will let you downsize the throats. | ||
| Martin |
presumably they would go in below the butterfly so as to restrict the runner? | ||
| Wyckedflesh |
IIRC the "kits" had a piece that went above, and then another that went below, and a resized butterfly. If your good with a lathe I am sure you could make one yourself and then just use a resized butterfly. | ||
| Alex |
How can it be that the motor canīt pull that kind of CFM on individual (42mm) runners when itīs capable of pulling enough CFM through a stock 45mm runner? Remember that the motor does not pull with both cylinders simultaneously but with one at a time. Best regards Alex | ||
| Blake |
Bingo. | ||
| Wyckedflesh |
Ok guys, your right my bad, the MOTOR itself can pull the single 45mm throttlebody, but the FUEL system can't handle the airflow of the twin system at 42mm each since from Martin's description he feels its running very lean. Otherwise he wouldn't keep adding fuel to the mix. So if he has maxed out the fuel flow, then what happens if we drop the throttle body size by 20%? 36mm is 80% of 45mm, which should bring the amount of air flowing back into the range of the injectors in the stock fuel system. Also, I think there is a little more intake scavenging going on between the cylinders then you might think. Once you get on the revs, the intake pulses smooth out noticebly when you hold your hand over the opening of the throttle body which means the airflow isn't getting stopped as much as each cylinder fires. I think the valve timing is such that as the front cylinder is tossing its exhaust, there is enough overlap that its helping to pull air into the tract as the rear cylinder starts its fill, and vice versa. Not exactly stopping the airflow dead, but just kind of keeping it moving. Where as when you go to an individual intake tract, its just that cylinder by itself keeping the airflow moving. | ||
| Alex |
-----So if he has maxed out the fuel flow, then what happens if we drop the throttle body size by 20%? 36mm is 80% of 45mm, which should bring the amount of air flowing back into the range of the injectors in the stock fuel system. ----- How can You expect to increase hp when You restrict air flow to match the range of the injectors? BTW the stock injection system can handle more air the You might think. Best regards Alex M-TeK Engineering | ||
| Wyckedflesh |
I am thinking tuneability more then max HP at the moment. Going based on his comments of not being able to add more fuel to the mix, then it would stand to reason that for tuneablity that cutting down the volume of air would help. If you can advise on how to add more fuel at the moment then I am all ears. I am just trying to offer a suggestion based on what he is saying. | ||
| M1combat |
"How can You expect to increase hp when You restrict air flow to match the range of the injectors? " Correct me if I'm wrong... Too much is too much. IF the TB's are too large, you'll lose velocity. Just right is right. What size are the intake valves? (Message edited by m1combat on July 12, 2005) | ||
| Craigster |
What do you mean, 'he feels it's running lean'? Is the AFR actually lean or do you have a reversion in the exhaust sucking air (oxygen) into the pipe and contaminating the mixture? | ||
| Wyckedflesh |
Craigster do you add fuel to a motor that is running rich? | ||
| Craigster |
Martin said his tuner told him he thought it seemed lean. Seems funny that a bike running the same EFI that has supported far more than 80 RWHP is un able to feed enough fuel. That's where a dyno that shows real time torque is a great advantage. Add fuel watch for power increase and observe AFR. Subtract fuel and watch for power change while observing AFR. if the Wideband cannot be inserted far enough, or if the pipe lends itselft to revesion, you can resort to watching the torque rather than relying on a possibly erroneous AFR meter. Just curious how they arrived at the idea it's lean. Perhaps it is, and if so would be a very interesting learning experience. | ||
| Martin |
wow! I'm just away for a day and look what I started. I was very suspicious about the need to add more and more fuel and also the occasional backfire whilst idling. I sprayed wd40 round the inlets and got a slight reaction so ordered-up the bigger injectors and then started stripping-down the injection. As I got closer to the intake I realised that it was moving about a bit! All the bolts were only finger tight. the wd had made its way round the inlet seals so that must have been a hell of a leak. I fitted the Pico 330cc injectors (Those things are tiny, so the fuel rail needed altering)then reinstalled the inlet with loctite/spring washers and an extra brace to the coil mount to help stop it moving. Once it was all back together I took a deep breath and woke up next doors teething baby as the motor fired-up with a steady,although fatly rich idle and a crisp throttle response. Incidentally, before the dyno was only giving an O2 reading over 4-5000 revs at first. this has also happened before on previous runs. Has anyone else had this with an XB? Obviously the massive air leak was leaning off the mixture all through the range (making the 83rwhp dangerously impressive. Great tip about watching the torque figure to spot O2 effects without the meter. Back to the dyno, then! | ||
| Opto |
which is about 10 up on my previous best with the FAST kit and Luckys exhaust Well that's got to be impressive to start with...you're not going backwards. |
