terret725
New member
ok i did some porting on my sxr 700. well i didnt a friend of mine did. all he did was take the lip off where the exhaust port meets the flanges and smoothed it out. he also just took the blunt edges off the fins in the transfers. made them a little more pointy. now I've already had this done so there's no going back and some one told me that u cant port with PI center dumps cause it will blow the motor. could u guys confirm this or is what i did OK or is there anything i can do so it wont blow now?
RJH
New member
I don’t think you will blow you motor - but you just made it slower - flowing gas does not like knife edges. If it did, the factory would make it that way.
Have you ever seen Yamaha's engine test department....these guys’ very life or job depends on engine development...the equipment and testing would be beyond belief....
How can some guy with a grinder, sitting in a heated garage have any possible idea on modifying an engine?
Maybe in the early 80’s , you could improve it.
Ask any so called tuner to show you a real dyno chart of just porting NOTHING ELSE – there would be no difference – if not less.
Have you ever seen Yamaha's engine test department....these guys’ very life or job depends on engine development...the equipment and testing would be beyond belief....
How can some guy with a grinder, sitting in a heated garage have any possible idea on modifying an engine?
Maybe in the early 80’s , you could improve it.
Ask any so called tuner to show you a real dyno chart of just porting NOTHING ELSE – there would be no difference – if not less.
Terret, by knife edging the transfers did he smooth and flow them alittle? if he did the air flow over the edge and through the port will improve just a lil bit. By opening up the exhaust you just made the flow into the manifold more efficient which will help you way up top at WFO and wont really be noticeable. Did you open the exhaust port itself at all? if not no big deal, you just wont gain anything. T
terret725
New member
i don't think he did the port its self. he was just copying some of the things we see on our open mod sleds when we get the motor back. he said he wasn't gonna really open anything because he didn't have a flow bench to balance the flow. he said it wouldn't be much other then maybe some better throttle response and maybe a hp or 2. i wasn't expecting much and he did it for free so i'm not complaining if i really don't notice it. but im more worried now that some oen told me that teh PI center dumps dont liek porting and may blow my motor. id liek to hear from people that ahev center dumps and porting.
Hey RJH... whats an exhaust port have to do with flowing gas?
RJH
New member
BBlueSRX said:
Couple of ways to answer…..I guess.
1:
1st. …..gas does flow out the exhaust then gets pushed back in.
Fresh unburned fuel that is introduced into the combustion chamber is mixed with the flamed used exhaust and is pushed out the exhaust hole. The pipe is designed and timed to push some of that unburned “gas” back into the cylinder as the piston is coming back. That is how pipes work.
Taking that lip out is a good idea. I didn’t think he put a knife edge on the exhaust port – it was the casting lip he removed. Polishing the exhaust and making it straight can be done as that port does not cause conflict with clean fuel as we try to atomize it better. You would not want a knife edge on the exhaust bridge as the piston needs that for support and the wide face needs lubrication. Usually, a hole is drilled in the piston to help lubricate that area.
2:
I assumed – it would be understood I was talking about the transfers only.
Thanks for reading.