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

[scottly]

Which head would out perform the other given  same basic port work, same size valves and utilizing the same cam profile? Also being able to source the correct piston to fully fill the combustion chamber In other words, all thing's being equal, which head would out perform the other?

If I'm not mistaken, the F2/F3 heads have larger ID intake spigots, so that may tip the scales? The K7 head has the same size spigots as the K1; 28.7mm ID, 33.7mm OD.
Hasn't anyone cc'd the different heads already???

[cbr954]

I cc'd my f2 chambers at 28cc.  the k heads that I have checked vary a lot..anywhere from 22 to 24cc.  You have to mill a f2 head about .060" to get it down around 24 to 25cc.

[scottly]

Thanks, cbr. 

[dragracer]

The F2 heads have proved to be the best option for my big motors Frank.

Cheers,
Brian

If I can get my hands on the pistons I want, the F head will be my preference also. Some things work in theory  but you guys down under have a tried and true combination in the real world of racing.

[scottly]

I pulled the K7 head today, and a quick-and-dirty check of the volume was about 22-23cc. The pistons do have a bit of a dome, but I don't know how it compares to early or late Fs?

[HondaMan]

I pulled the K7 head today, and a quick-and-dirty check of the volume was about 22-23cc. The pistons do have a bit of a dome, but I don't know how it compares to early or late Fs?

The F0 and F1 pistons I have are the same as those found in the K7 (-392- numbers). They have a small dome in the center portion of the top. The F2/3 pistons are a full-round dome (most, I should say, as I have seen some that had a flat shoulder, too).

[Jerry Rxman Griffin aka MuthaF'er]

Scottly,

Here are pictures of BOTH 392 pistons that were made. Mine had the 'complete' dome on the right which is part of the reason it ran so good. That and the cam has the exhaust lobe 0.1mm taller than my K8 and F3 cam. Note that both pistons have 392 cast into them below the wrist pin.



   

[Jerry Rxman Griffin aka MuthaF'er]

Mark, now that Scottly has cc'ed a -392 head do you have an earlier -300 head you could cc?

[scottly]

Jerry, can you take a pic of both pistons mounted on one pin? It looks like the pin is closer to the oil ring on the left one?
Thanks
(George, sorry if we're high-jacking your thread. )

[dragracer]

I just received a used set of 72mm KZ 10.25:1 pistons in the mail today. I test fitted them in the chamber of a stock F2 head and it seems to fill it up fairly well. Not much cutting needs to be done it seems. I need to make a mold of the chamber so i can do some comparison.

I took a picture of a new Arias 12:5-1, 73mm, K model piston alongside the KZ, 72mm, 10.25.1 so you all could see the difference in the pistons. If i can work out the piston pin issue, 15mm versus 17mm, this might be a viable option for me as i really do prefer the idea of using the F2 head over the K head for drag racing.

Give me some feedback on what you see guys.

[hotdog]

What's the crown thickness on the kz piston.? And what cr will you be aiming for.?
Probably been said already - dynoman offer a custom rod that takes 17mm pins.

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[dragracer]

What's the crown thickness on the kz piston.? And what cr will you be aiming for.?

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Unsure of crown thickness for purposes of fly cutting the piston. I can measure crown/dome height tomorrow. I'm shooting for no less than 12.5:1 compression with the F2/3 head, so if these don't give me what i'm after, i'll source a 13.5-1 set and cut down the dome some. Regardless, the valve pocket will have to be moved over just a bit to fit the position of the canted  F2 valves. Air flow into an SOHC head is limited as discussed many times on this forum. We're hurt by port size and cam lift selection as others have pointed out over and over again, so no matter which head we use, we're only alloted a certain volume of air that can be introduced into the cylinder. So, my idea is to get as much air into the cylinder as possible by adequete porting and cam profile selection, the cylinder bore being as big as practical, then compressing that given volume of air as tightly as possible inside the chamber followed by the biggest explosion i can get to send that piston back down as quickly as the energy can push it. Of course cam timing and ignition timing will play a  big part in the equation along with the proper octane fuel as detonation is always an issue with high compression. I could make it simple on myself and build a low compression engine and fill the cylinder with a huge dose of nitrous oxide but i want to make horsepower on all motor- not by a power adder like a turbo or nitrous. A small shot of nitrous could be added later for the WOW affect- lol. I'm also trying to acheive my goal on a tight budget so custom made pistons is out of the question. I'm hoping to find whatever i can off the shelf or easily at my disposal. Since the F2 head already has bigger valves and ports, its what i'll use to begin with. I can always switch over to a k head and use the 73mm 12.5-1 k pistons for comparison later.

I'm probably making this hard on myself, but we'll see where this takes me.     

[HondaMan]

Mark, now that Scottly has cc'ed a -392 head do you have an earlier -300 head you could cc?

Yep, let me check my book: I did a K2 head in that one. It is the same as the K1 and K3 head. The K4 got slightly bigger.

...
The chambers ran between 22.4+ and 22.5 (not quite) on the two K2 heads I used (in the "Cheap Performance" section. I have a near-sandcast head (serial number ...1838) that is also 22.4+ cc in the 3 good chambers (one is all torn up from water damage).

[Jerry Rxman Griffin aka MuthaF'er]

Jerry, can you take a pic of both pistons mounted on one pin? It looks like the pin is closer to the oil ring on the left one?
Thanks
(George, sorry if we're high-jacking your thread. )

[gschuld]

(George, sorry if we're high-jacking your thread. )

Actually, quite the opposite.  The thread has come around to the exact topic I had hoped it would.  I was thinking about Frankie's K vs F2 head conundrum so I brought up this thread to open the discussion about it.

Sometimes I get lucky

George

[dragracer]

Here's a side by side comparison with coorespoding pin location of the 72mm Wiseco KZ 10.25-1 versus the k model 73mm Arias 12.5-1 pistons.  Across the top of  each piston is a long screw driver. You can get an idea of the difference in the crown/dome height at this angle. I didn't get an actual measurement yet but will do so when i get to the next step in the process. I was able to get a set of MA3 (CB1100F/Cb1000) rods off Ebay today to match the KZ pistons, 17mm wrist pin. That was half my mental battle in this whole process. The rods are slightly (1.5mm) longer than the stock SOHC rods but the difference in the pin location of the KZ and SOHC pistons is fairly close it seems. I can work with my base gasket to get the proper deck height. Still need to verify valve angles of the KZ versus SOHC F2 heads in case the pockets have to be recut to the F2 valve angle. Hopefully its close.

Thanks for posting this thread George. We're getting someplace now.

[scottly]

Yeah, thanks George!
I did some more checking, and as close as I can come to K7 chamber volume with my crude measurement tools is between 22 and 23 cc. I also did a clay impression of the piston dome (warm, soft clay becomes quite firm and retains it shape well after 5 minutes on a 35*F piston ) and found that the dome displaces about 3cc. The flat ring around the dome, however, was about .030" below the deck, which would offset that 3cc by maybe .8cc compared to flush with the deck? Jerry, if your full-dome pistons are the same height as the partial domes, I would make a swag that they have about 1.7cc more volume, minus the volume of the valve reliefs.

[MRieck]

Late F's are about 28cc if I remember correctly....I don't have my notes.

[Old Scrambler]

Frank.........Good on you for finding the MA3 rods   I have a spare set now that I have found I got lucky on ebay   Last year about this time I bought two sets of ebay rods.........both turned out to be MA3 sets but only one has squirters.  I thought I was getting CB900C rods (as advertised) so the prices were right  

On a big-bore the valves will be significantly UN-SHROUDED........with the stock valves the heads cc'd at 28........but with my flat-faced replacement valves they are a little less than 27cc. We measured the rods at 1mm longer on center than the 750 sohc rods.........but we have old eyes My suggestion is to dry-fit the rods and pistons to your jugs and carefully measure the edge of the piston to deck differential with the standard base-gasket.  With K4 jugs and the MA3 rods and J&E high-dome pistons meant for a K-head...........the edges stood .030" above the deck. So I ordered a .035 copper head gasket at the same bore size..........and milled the edges of the chamber for clearance.

My cam has .408" lift but the pocket depth/clearance was very good. We had to fly-cut the pockets to fit the wider valve faces. The piston crowns displaced about 20cc so we have less than 7cc of 'open' space at TDC and hopefully at the maximum ignition burn.  Final compression tested at 12.8 to 1 with the carbs open.

Your deck-height my vary from mine.........and most importantly.........with the big bore you could shave a few thou from either or both surfaces.   Hint........the taller crown will require more ignition advance for max power and rpms.......when tested with VP-110 gas.   

Your build will be interesting for me because it mirrors my plan to run a motor at or just below 1000cc at the salt flats. You get to test yours almost year around

[dragracer]

Thanks for that detailed information on your build. Gives me hope about what I'm trying to do on my project. I've also got a set of high compression, 13.5-1, MTC pistons coming my way from a friend in Canada. I'm going to see if they have potential to fit the chamber after milling the dome. I've decided not to rush this project so I can concentrate on getting exactly the results I'm after. I do have a bike I can still race so there's no real pressure to push forward and screw up. I've done that enough in the past.

[Old Scrambler]

I'm with you on the 'take some time' to get it right attitude. We all know that once the parts are all prepared and laying on the bench..........it only takes a day or three to have a running motor

What sleeves will you use?  I like the Cycle-X chain tensioners because they are quiet and lighter-weight.  My intakes are now 33mm ID. Who will port your head?  I only ask because Mike has yet to tell us if his health is up to a full work load. Will you stay with the RS-36s? 

For my motor, the top ring is still well below the deck. The head gasket acts as an extension of the cylinder and allows the piston-crown to be pushed higher INTO the head-chamber. We measured the top of the chamber to be 1mm taller than a K-head. The valve-stems are 1mm shorter. They have the same angle as the K-heads but look different because the curve of the chamber is 'deeper' (semi-hemi). My pistons do not have the plug reliefs and have sufficient clearance with Irridium plugs and the standard crush-washer. 

Relax and have a Merry Christmas

[Jerry Rxman Griffin aka MuthaF'er]

Guys, I have 2 new spare sleeves if I don't end up using them. LA Sleeve I believe. Got them from Kenny when I had to break the 900 apart but didn't use them. Keep it in mind should you need.

[dragracer]

The plan on the head right now is to cut it just enough to get the dome of the piston to fit. I'll get my local machinist friend to help me with the head work. He usually concentrates in the area behind the valve and of course he'll open the port up appropriately. He does little tricks on the exhaust side so I'm fairly comfortable overall with his work. He's a funny bike racer from back in the day. He set some records along the way although they didn't hold once he got out of the game. I'll get Mike to do a head for me one day once I get my $$$ saved up

[dragracer]

Alright, I received the MA3 rods in the mail today. All I can say is I should have looked at the pictures and read the description more closely. Being impatient may have bit me. Actually, some of the pictures would not show up on my cell for some reason. So its obvious to me now why I got the rods were so cheap.

Long story short, this engine appears to have been suffering from oil starvation. The rod bearings show signs of wear on 3 of the 4 but not significant. However, the 4th rod seems to have spun the bearing to the point of breaking off the retaining tab on one of the halves. From what my visual inspection tells me is the inside of the rod itself appears useable. I'll have to mic all of the rods and compare my findings to the rod specs. Hopefully all of the rods are good. To err on the side of caution, I remember seeing a single rod for sale on Ebay also and after closely looking at the picture, I decided to purchase it as a replacement. Those 4- $189 rods just went up another $100 to a total of $289 because I had to buy the extra rod.  I'm still okay as long as the small end of the rod is fine. I see minor galling but I'm not concerned right now. I'll push a pin through and see how it feels. I feel a simple clean up will suffice.

I was going to balance my entire rotating assembly anyway, so the unmatched rod shouldn't be a problem after the machinist is done. The crank will be polished and oil holes chamfered as well. I'm mixing and matching parts so balancing is a must for me. This bottom end has to be reliable and able to withstand what I eventually intend to throw at the top end. I'm on a tight budget so buying new rods was out of the question and I wasn't 100% comfortable using the MTC rods for this project given the need to bore the rods from 15mm to 17mm.

 I'm pressing ahead with what I have now but I will regroup if something doesn't feel right. This engine is more of a test mule for what I'm planning next so I'm in no hurry to screw up with the build.

On the rods, Live and learn- or in my case, get better pictures.

[dragracer]

A few pictures to inspect.