Topic: performance potential between K heads and F2/3 heads

[dragracer]

Rear of bearing halves.

[NitroHunter]

Keep in mind the cam limitation when using the F2 head, the valves get really close in a hurry. When I put a RC 315 cam in the stock head, the valves were clipping each other after some spirited riding. After the head was reworked it was all clear. I never tried a larger cam in that head.
The ratio of exhaust to intake valve area percentage is unfavourably large in the 410 castings (from a hot rod perspective). The exhaust easily outflows a ported intake. Interestingly, the intake flow numbers on my particular head showed few gains progressively beyond .350" lift. Serious port rebuilding to get to that next step was beyond where I wanted to go and larger intakes were out of the question.
Using 36mm intakes in a suitably ported K head worked well for Dale Walker and Tommy Bolton back in the day.
Hope this helps.

[MRieck]

Keep in mind the cam limitation when using the F2 head, the valves get really close in a hurry. When I put a RC 315 cam in the stock head, the valves were clipping each other after some spirited riding. After the head was reworked it was all clear. I never tried a larger cam in that head.
The ratio of exhaust to intake valve area percentage is unfavourably large in the 410 castings (from a hot rod perspective). The exhaust easily outflows a ported intake. Interestingly, the intake flow numbers on my particular head showed few gains progressively beyond .350" lift. Serious port rebuilding to get to that next step was beyond where I wanted to go and larger intakes were out of the question.
Using 36mm intakes in a suitably ported K head worked well for Dale Walker and Tommy Bolton back in the day.
Hope this helps.

I have run into the F2 valve to valve problem when I built a specialty head with Harmon Super F #'s/ground 110 lobe centers. Initial valve job had them to close and both sides had to be sunk and it was still close. I used custom 5mm valves so they were lighter than stock (a good thing when dealing with close valve to valve) but I still could not get the seat pressure I really wanted because the 5mm guides are so short on top. Kibblewhite could increase the height .040 or so and still clear any cam made for the SOHC 750. The engine was for an LSR bike.
 Absolutely correct on the exhaust valve OD being to large. I would be great to pull the seats, weld it up and stick in a seat bored to 85% of a 29mm valve. Valve to valve issues gone.
 I totally agree on the .350 lift too without a 36mm valve and floor modification. At least that's what I think on a "stock" port. If you start straightening the port after R/R the spigots things cange change quickly but that is a lot of work. You could large RS's on it at that point too.

[754]

I am curious how the cut the domes...?
Do they use a swinging radius attachment, or a CNC. Lathe ?

One thing to note if you bore out the small end to 17mm.. You can shift the hole by about 35 thou..higher or lower. Just mentioning it in case, you are running out of dome thickness, on these pistons you are modding..

[dragracer]

I decided to grab up some rods to see how they compared by weight. I'm fairly certain at this point i'm going with the MA3 ( CB1000) rods as they have the correct pin diameter for the KZ pistons i want to use under my F2 head. The pistons have a noticebly higher dome on them than the 73mm, 12.5:1 K model pistons i have so they should fill the F2 chamber pretty good.

Find attached a picture of the rods. Beginning left to right they are arranged by weight as follows.

* HD rod                   = 392 grams
* Stock CB1000 rod   =387 grams
* Unknown alloy rod  = 365 grams
* Carillo "A" beam rod= 343 grams. (Busa rod for comparison)

[dragracer]

In addition to weighing the rods, i also weighed the 4 different pistons i had on hand for reference to the 72mm KZ piston i want to use under the F2 head.

Top to bottom in the picture the weights are as follows:

* 73mm Arias, 12:5-1 =190 grams (k model)
* 71mm MTC, 11.5-1  = 229 grams (k model)
* 70mm MTC, 12.5-1  = 218 grams ( k model)
* 72mm Wiseco, 10.25-1= 208 grams (KZ) - shown in a seperate picture

I weighed the pin for the Arias piston at 41 grams, the KZ pin at 58 grams. 

[dragracer]

I attempted to test fit  the Cb1000 rod on the KZ piston but had a minor set back. It seems the small end of the rod  has an odd shape just below the pin hole that would not  allow the rod to fit low enough to push the pin through. I took my dremel tool out and slowly ground away some of the metal in order to get the rod into the piston, so the pin would push through. Since this rod already seems to be compromised, I'll use it as my prototype, so to speak. I only removed enough material from each side at this point to avoid interference with piston movement. I intend to work with just one cylinder right now in case this doesn't work out, it will be less work to correct later. The chamber on the head  has to be opened up a little to get the dome of the piston to fit.

Find attached a few pictures of where the material was removed ( shiny area).  I've also included a few pictures of the HD rod and alloy rod that shows that neither will slip into the piston due to the wide of the SOHC rod versus the width of the KZ piston rod area. There is a picture of one of the 73mm Arias, K model, 12.5-1 pistons attached to the HD SOHC rod in comparison to the 72mm, KZ 10.25-1 piston on the CB1000(MA3) rod.

[dragracer]

Mike and Nitrohunter, thanks for that detailed information on the F head. This discussion has been enlightening, to say the least, about the limitations of the larger valve F head versus the K head. I'll be looking into my options further, based largely on your experiences with the head. I think it will still work well for my purposes and budget. The F head on my current motor has provided sufficient horspower to propel my bike into the mid 10 second zone consistently, without any exotic work. This happened in spite of using k model pistons. I'm not out to build the quickest SOHC- that ship sailed a long time ago. I'm just trying to see what happens when building a similar platform with high compression pistons. Your input will surely be of help once i get into the actual head work. I've still got a lot to sort out right now before i begin port/valve work. Old Scrambler has also provided valuable insight on his engine program that i hope to use as well. A few others chimed in and gave good information.

The wealth of information shared on this forum is unparalleled elsewhere. Keep it coming gentleman. I'm sure others are just as interested in knowing more about the F head versus K head performance potential. 

[bwaller]

Frank if it was possible to find a used/scrap KZ piston you could cut it right through the middle to see exactly how much meat there is for removal from both the dome & valve pockets. It sure makes the measuring easier.

[MRieck]

Frank if it was possible to find a used/scrap KZ piston you could cut it right through the middle to see exactly how much meat there is for removal from both the dome & valve pockets. It sure makes the measuring easier.

Got to be plenty of those dead soldiers laying around.

[MRieck]

I decided to grab up some rods to see how they compared by weight. I'm fairly certain at this point i'm going with the MA3 ( CB1000) rods as they have the correct pin diameter for the KZ pistons i want to use under my F2 head. The pistons have a noticebly higher dome on them than the 73mm, 12.5:1 K model pistons i have so they should fill the F2 chamber pretty good.

Find attached a picture of the rods. Beginning left to right they are arranged by weight as follows.

* HD rod                   = 392 grams
* Stock CB1000 rod   =387 grams
* Unknown alloy rod  = 365 grams
* Carillo "A" beam rod= 343 grams. (Busa rod for comparison)

I think the A beam Carrillo would be the best choice for the 750's (or 550's for that matter). It is plenty strong enough and pretty light. As far as I know I it is a custom rod for the 750 etc and it more expensive than the H beam. I have a set in my FJ and that has over 155HP.