Big Bores for 70 degrees
- Thread starter jon andersson
- Start date
Joined Jul 2016
596 Posts | 281+
Australia, Beechworth, Vic.
Weighed some pistons and pins
Std 570 piston assy including pin 371 gms
Wossner 362 gms
CP610 437 gms
Pins
Std pin 66 gms
CP pin 80 gms
The 610 piston in my Berg is then weighing 66 gms more than the OEM piston attached to the std crank. That’s the total weight of one std pin! Any wonder it vibrates!
Std 570 piston assy including pin 371 gms
Wossner 362 gms
CP610 437 gms
Pins
Std pin 66 gms
CP pin 80 gms
The 610 piston in my Berg is then weighing 66 gms more than the OEM piston attached to the std crank. That’s the total weight of one std pin! Any wonder it vibrates!
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Joined Jul 2016
596 Posts | 281+
Australia, Beechworth, Vic.
I also received from Ola a balanced crank and spare CP piston kit both new unused so I can make another 610. I just need to get the spare cyl he gave me taken out to 104mm.
Joined Jul 2016
596 Posts | 281+
Australia, Beechworth, Vic.
Its very hard to see from a pic whats going on, different camera, what wide angle, light and so on.
What is clear is the oem head wont flow well enough, so for a 570 at least and a big bore for sure the head needs addressing to make use of the top end.
Ill see if I can find the flow chart of the head FP-engineering did for me.
Flowing a head is far from an absolute truth when it comes to power, however its helpful for some things. brb!
What is clear is the oem head wont flow well enough, so for a 570 at least and a big bore for sure the head needs addressing to make use of the top end.
Ill see if I can find the flow chart of the head FP-engineering did for me.
Flowing a head is far from an absolute truth when it comes to power, however its helpful for some things. brb!
I saw you were discussing the heads on FB, Im not a fan of FB, so Ill write my few lines I have here. All in my humble findings.
Mototune is a joke right, its just ******** all of it, I have actually tried that crap and built stuff and dynoed in the noughties, it is that old yes. The idea is pretty good but wont work in reality.
What you want to do that works is aiming at an intake stream around 300 feet per second at the valve stem, which will be your max speed, that sets the minimum diameter of your port, just a tad over 30mm from memory on the 570 aiming at 70hp. I used vanniks softy to get in the ballpark, which matched FP's work.
After the stem part you need to slow the speed down to up pressure by introducing a bowl to fit (bernoullis principle) , this combination is the culprit plus the seat cuts, along with enough stack length to keep air velocity adding on to the pressure. Cam timing on top of this!
How the ports look to the human eye is of no importance, its just a selling feel good point, it can be really rough un-round and not shiny no worries
Ask the engine
Mototune is a joke right, its just ******** all of it, I have actually tried that crap and built stuff and dynoed in the noughties, it is that old yes. The idea is pretty good but wont work in reality.
What you want to do that works is aiming at an intake stream around 300 feet per second at the valve stem, which will be your max speed, that sets the minimum diameter of your port, just a tad over 30mm from memory on the 570 aiming at 70hp. I used vanniks softy to get in the ballpark, which matched FP's work.
After the stem part you need to slow the speed down to up pressure by introducing a bowl to fit (bernoullis principle) , this combination is the culprit plus the seat cuts, along with enough stack length to keep air velocity adding on to the pressure. Cam timing on top of this!
How the ports look to the human eye is of no importance, its just a selling feel good point, it can be really rough un-round and not shiny no worries
Ask the engine
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I'd love to bench with my ported head and my stock as comparison! I'm not saying my ported head is bad but I dont like the characteristics on road. Ice for sure it spinns away.
It's good with different inputs and if you have dynoed different heads I believe you. Nothing beats empirical data.
What I also start to believe is a part of the truth is different end goals with the tune. Mix in really good ports, straight out **** and as most often too many variables changed at the same time (not only head but other parts at the same time) and peoples opinions will differ.
Like me talking, out of my *** maybe, about the head. My tuned engine had so many changed variables so I shouldnt be concluding anything really. I know that.
All I know is that I didnt like the top revvy character of my old engine. Now when I will go 660 I will not touch the head, but later I might swap to an original head to compare
It's good with different inputs and if you have dynoed different heads I believe you. Nothing beats empirical data.
What I also start to believe is a part of the truth is different end goals with the tune. Mix in really good ports, straight out **** and as most often too many variables changed at the same time (not only head but other parts at the same time) and peoples opinions will differ.
Like me talking, out of my *** maybe, about the head. My tuned engine had so many changed variables so I shouldnt be concluding anything really. I know that.
All I know is that I didnt like the top revvy character of my old engine. Now when I will go 660 I will not touch the head, but later I might swap to an original head to compare
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Joined Jul 2016
596 Posts | 281+
Australia, Beechworth, Vic.
My 610 was wearing the ThumperRacing head. The power/torque spread was ideal. I don’t need over 9,500rpm. I like to operate in the ‘fat’. Always have. Going back to my opened up but standard head 570 which is running very nice, a rather quick rider who owns a late 500 EXC didn’t like the 570 for the fact it didn’t rev. We are all different with different requirements. The ThumperRacing head had minimal work done to the point I could see that it would’nt have made a noticeable difference. I’ll do some more work on it. It was interesting reading what Mr Vizard said about the level of effect with just some blending and reducing the boss width. With Tom mentioning a port size of 30mm is interesting and would like to work on that on one of my standard heads in the future. Determining that dimension throughout the port (except the bowl) won’t be an easy feat. Rewarding nevertheless. The feel of this 610 ATM doesn’t make me feel like the port is lacking, ok it can be improved but it doesn’t drop of like it is lacking.
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Sorry for late reply due to the shock of being at work again this week
My post about appearance of the head intake surface was more aimed at others reading this thread in hindsight, not the posters(ie you).
I have tried it, the theory is the return pulse somewhat dont get back into the chamber messing up the incoming overlap stream.
A wet dream in my eyes, never found any evidence its working.
(Engine builder selling point imho, something the customer can see + theory = sold)
@jon my stock head did 260 on intake oem and after FP 308 fpm.
Edit: I never noticed any drawback at low rpm porting and there should be none done right
My post about appearance of the head intake surface was more aimed at others reading this thread in hindsight, not the posters(ie you).
I have tried it, the theory is the return pulse somewhat dont get back into the chamber messing up the incoming overlap stream.
A wet dream in my eyes, never found any evidence its working.
(Engine builder selling point imho, something the customer can see + theory = sold)
@jon my stock head did 260 on intake oem and after FP 308 fpm.
Edit: I never noticed any drawback at low rpm porting and there should be none done right
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Joined Jul 2016
596 Posts | 281+
Australia, Beechworth, Vic.
I’ve been lead to believe that step was implemented by the tuner.
My assumption would be if the raised exhaust floor did assist against reverb, the neg to this would be hurtful turbulence off that step when exhausting. I’d be looking for some other method of preventing reverb if it was a concern. Chamber in the header pipe for instance would reduce some pressure. All conjecture on my part of course.
My assumption would be if the raised exhaust floor did assist against reverb, the neg to this would be hurtful turbulence off that step when exhausting. I’d be looking for some other method of preventing reverb if it was a concern. Chamber in the header pipe for instance would reduce some pressure. All conjecture on my part of course.
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