Topic: Big intake heads from Cycle X

[PeWe]

Dennis, which cam do you use to that engine?

[Jerry Rxman Griffin aka MuthaF'er]

It's a Megacycle 125/Dennis 

[MRieck]

 The stock spigots are a choke point....F2 or K.

[scottly]

I have thoughts about not going too big loosing midrange response/acceleration.

I think your on the right track Per.

The question is, what is too big?
120whp on not that high rpms with 33mm carbs indicate a good combination as you have shown, Brian.

The Weber DCOE 40's can be tuned, just use smaller or bigger rings for the throat/venturi. 26-36mm as I have seen. Very flexible carburetor.

More carbs should have that possibilty.  The carbs on my K6 that finally joined the +100whp club are 32mm. It would be fun to test bigger. I miss the tuning possibility with rings.
Different sizes depending on application. Before or after ~6000 rpm something.

I experimented with both 30mm and 32mm chokes in my Webers, and only found a small (1HP?) increase at the HP peak RPM. This was with an 836 with a stock, non-ported K1 head. I suspect a better flowing head would show a greater difference with the 32's?

[dragracer]

Lots of good discussions going on here.

I go back to my original question: Has anyone purchased one of these big spigot heads and can you give some feedback on the performance??? Looking for REAL world experience with your package with this head up top.  I'm not a "dyno numbers guy" but if you have that info it would be helpful.

[PeWe]

Dennis, which cam do you use to that engine?

A dyno chart would be very interesting too.
With data from 4000 rpm or lower to its top. 34mm carbs, 35mm valves and 761cc is very interesting to see if this is mostly a top end power combo or if it produce relatively good power from lower/midrange.

I have seen +86hp dyno a 761cc bike produced. CR31 carbs,  5mm stemmed 34/28 valves. It's head not that much ported, piston crowns and chambers adapted to each other.
Cam not known. I have to ask the bikes owner.

[Jerry Rxman Griffin aka MuthaF'er]

PeWe, this combo has him knocking on the door of 150mph on Bonneville minimal traction Salt Flats

[PeWe]

That's really good! Asphalt should allow higher speed, right?
I admire the rider that can manage to ride a CB750 based bike very fast on that surface!

The dyno graphs to see how and when the power kicks in would teach me and several others, I suppose.

This is an interesting thread, the beginning of it about CycleX larger inlets, when and how this will apply extra power.

Dennis salt racer might have use for it or is more displacement  needed?

[dragracer]

Dennis, does your head have the big spigots?? That combination of yours is impressive for the cc.

[754]

 I was at Bonneville in teardown  as Dennis opened up his engine. .. he explained what he had done to it.
 I have failing memory, but pretty sure it was a late head with bigger spigots, and it had beehive springs.

This was after I tore down the other fellows cb 750,  with only half the needed tools. Dennis or Jerry had volunteered  me for that,  unknown  to me..
  I arrive at the Salt, and they  say to me.... Guess what You are doing later this afternoon..... too funny..

[slikwilli420]

I'm going to have one sent to Mike with the big spigots. Goal is to run 33 mikuni carbs and squeeze the biggest intake valve I can into a 72mm bore for my AHRMA superbike. 120hp is the number I'm dreaming of. Of course it won't be ready until the 2022 season so no real world performance to speak of... yet.

[Old Scrambler]

I've been relaxing after my morning at PT...............Megacycle 125-29 on my card.........its a wide-angle 125-30

The big spigot F2 head and rubbers were reamed to 33mm IDs............Just my (bench racing?) that the larger intake runners reduce the harmonics affect when the valves close so MAYBE the inductive flow at the jet is always positive.

Not all Beehive springs are alike........some have 2 or more windings of the same size. My Ferrea springs can actually be compressed without adverse harmonics or potential for coil-bind.

I have talked to Ken about his big-spigot heads and agree with his opinion that they would be best used on a 970cc or larger motor.

[scottly]

How big are the cycle x spigots? There is such a thing as too big; the Boss 302 was a good example.
 Dennis' bike at 10,000 RPM is pumping as much as a 900cc bike at 8,000, and he is running the engine at or near the peak HP RPM for extended periods of time, while Frank's engine only hits the HP peak for instants between shifts. Drag racing makes better use of a broader power band than LSR or road racing.

[PeWe]

Easy to imagine, trickier to make....
Not possible to modify the valves and seats? Use 2 smaller valves on inlet side. Lighter 28mm valves beside each other with lighter springs.
A mechanism push them both in parallel by stock rocker arm.
2x28mm ca: +30% larger area than 1x35mm when just calculate the area.
For 70mm chambers if there will be room for 2 smaller in the curved area...

Alu printer or billet if stock cannot be modified

[seanbarney41]

Easy to imagine, trickier to make....
Not possible to modify the valves and seats? Use 2 smaller valves on inlet side. Lighter 28mm valves beside each other with lighter springs.
A mechanism push them both in parallel by stock rocker arm.
2x28mm ca: +30% larger area than 1x35mm when just calculate the area.
For 70mm chambers if there will be room for 2 smaller in the curved area...

Alu printer or billet if stock cannot be modified

Take a look at 07' era crf250/450...single overhead cam in a 4 valve head...rockers are probably way to big to work on a 4 cylinder though

[Old Scrambler]

It may be more beneficial to add a second sparkplug

[dragracer]

It may be more beneficial to add a second sparkplug

Dennis,

Are you planning to make the flats in 2021??

[Jerry Rxman Griffin aka MuthaF'er]

Frank, plenty of room for you guys for your stopover if you drive. Or fly into Salt Lake City and we'll see you there.

[Old Scrambler]

Planning for August on the salt is well underway...........solving leaky fuel delivery before going for dyno-tuning with new lightened rockers.

[754]

 Ooh man , that is starting to sound good... may try to make it..

[PeWe]

That dyno will be very interesting read, Dennis!
If published on the Dyno thread or your own.

[Old Scrambler]

On my thread and on the Dyno thread.........when I get it

[dragracer]

I think I'm going to contact Kenny soon to ask about the I.D. and O. D. of the spigots on his modified head. At this point, I don't feel I can break into the 9's without more airflow. I'm trying to avoid installing a stroker crank to achieve this goal.

[simon#42]

It may be more beneficial to add a second sparkplug

i doubt it , you need a very big piston and a very poor head shape for it to be of any use

[scottly]

I think I'm going to contact Kenny soon to ask about the I.D. and O. D. of the spigots on his modified head. At this point, I don't feel I can break into the 9's without more airflow. I'm trying to avoid installing a stroker crank to achieve this goal.

How big is your motor now, Frank?