Fullauto Head Count

NKN · Sep 19, 2016

I received one this morning from AN-GB, it's a 850 and number is 164.

Looks nice, can't wait...

Clanger · Sep 19, 2016

jseng1 said:
... twin carbs give you twice as much throttle opening as a single for a given amount of twist grip turn and that's a big boost of bottom end grunt. And most single carbs do starve for fuel at WOT.

Maybe a perceived boost, because for a given amount of twist the twin carb set up will present twice as much opening. But I can't see how that translates into any real power difference from a single carb opened to the same degree, unless there's some aerodynamic difference in the different inlet tracts. I won't mention dyno's at this point...

I agree on the top end, but as a single carb user I'm perfectly happy with what its got below 5000.

74ok · Sep 19, 2016

jug said:
Fullauto said:

Any performance Commando really needs twin carbs. A single carb goes flat above 5000 RPM and even at low RPM, twin carbs give you twice as much throttle opening as a single for a given amount of twist grip turn and that's a big boost of bottom end grunt. And most single carbs do starve for fuel at WOT.

Click to expand...

Maybe I need to put it on the dyno before and after. I wonder why no one has suggested that before?

Click to expand...

Ouch, might touch a nerve. LMAO.

lol

manx850 · Sep 19, 2016

I have #24 850.......I noticed there is not a small metal rod to register the inlet valve cover to as on an original head, are people removing this from other heads or inserting an appropriate size piece of rod?......Thanks

Fullauto · Sep 19, 2016

manx850 said:
I have #24 850.......I noticed there is not a small metal rod to register the inlet valve cover to as on an original head, are people removing this from other heads or inserting an appropriate size piece of rod?......Thanks

Yep. The locating dowel is a standard part. order from your parts supplier or use the one off your standard head.

manx850 · Sep 19, 2016

Thanks, just heat up and pull out?......it sizes to about .2....might be easier to get a pice of rod...?

manx850 · Sep 19, 2016

Oh by the way , i put the head on a Dyno.......It produced 10 BHP on its own without the rest of the engine!...looks promising!.............LOL

dennisgb · Sep 19, 2016

manx850 said:
Oh by the way , i put the head on a Dyno.......It produced 10 BHP on its own without the rest of the engine!...looks promising!.............LOL

Do you have a chart on this?

Mark · Sep 19, 2016

Rohan said:
But no-one seems to have put one on a dyno to say how great.

Is this true ?
If so......... I'd say Rohan has a pretty valid point.

EDIT:
after a bit of research, I found this post from comnoz in another thread:

comnoz said:
The amount of power increase you will see depends on a lot of other things, just simply bolting the head in place of a standard head may get you ten horse more if you have twin 32 or larger carbs and a good working exhaust system. If the flow is restricted with a poor manifold or an exhaust system that does not scavenge very well then you would likely only see a bit more midrange torque. Jim

baz · Sep 19, 2016

pete.v said:
jseng1 said:

[Any performance Commando really needs twin carbs. A single carb goes flat above 5000 RPM and even at low RPM, twin carbs give you twice as much throttle opening as a single for a given amount of twist grip turn and that's a big boost of bottom end grunt. And most single carbs do starve for fuel at WOT.

Click to expand...

Their are exception to this "opinion". I will give you the fact that you mention "MOST single carb starve for fuel at WOT", most certainly not all. In addition, with your upgrades installed on my Commando, I consider mine as a "performance Commando".

Sorry to get off topic cause I sure would like one of these heads too.

My commando has a single 40mm flatslide mikuni ,there is no comparison between this and the single 34 or 36mm VM round slide mikuni set up ,my bike will pull to 7500 rpm if I want to ,I can't really tell the difference on the top end between the twin amal set up and the 40mm flatslide but where you do notice it is in the midrange the way it pulls out of corners is brilliant and at 5000rpm it's really starting to pull hard cheers

worntorn · Sep 19, 2016

I don't see why a request for dyno test of a given engine before and after fitment of the FA head is at all off the mark.
This is exactly what Nigel is doing for us (and him) with his RH 10 modified by Jim Comstock.

I imagine everyone that purchases a Fullauto head is looking for a bump in performance and by all reports, that is the result.

It would be nice to see if the improvement is all along the curve, just in the middle or just at top. And how large the improvement is.
Many of us found the head thread to be great entertainment/learning and that was all flow results.
While it's clear that dyno numbers can be misleading, they do give some substance to all of the flow work, which I'm told doesn't always pan out in horsepower quite as planned.
Personally, I would be more interested in the effect all along the curve than the peak number.

Just a Curious Cat.

Glen

WZ507 · Sep 19, 2016

baz said:
pete.v said:

jseng1 said:

[Any performance Commando really needs twin carbs. A single carb goes flat above 5000 RPM and even at low RPM, twin carbs give you twice as much throttle opening as a single for a given amount of twist grip turn and that's a big boost of bottom end grunt. And most single carbs do starve for fuel at WOT.

Click to expand...

Their are exception to this "opinion". I will give you the fact that you mention "MOST single carb starve for fuel at WOT", most certainly not all. In addition, with your upgrades installed on my Commando, I consider mine as a "performance Commando".

Sorry to get off topic cause I sure would like one of these heads too.

Click to expand...

My commando has a single 40mm flatslide mikuni ,there is no comparison between this and the single 34 or 36mm VM round slide mikuni set up ,my bike will pull to 7500 rpm if I want to ,I can't really tell the difference on the top end between the twin amal set up and the 40mm flatslide but where you do notice it is in the midrange the way it pulls out of corners is brilliant and at 5000rpm it's really starting to pull hard cheers

Baz,

Kelly George would likely agree with you as his single carb Norton 850 flat tracker surely doesn't go flat above 5,000 rpm and is a consistent winner where ever it is campaigned.
Gives late style HD XR-750s a good run for their money too. Even hobot whole heartedly endorsed the single carb!

Knoxville Win

#66 digging hard and leading into turn 1

Wauseon Win. What else is there to say if hobot endorses it?

jseng1 · Sep 19, 2016

Clanger said:
jseng1 said:

... twin carbs give you twice as much throttle opening as a single for a given amount of twist grip turn and that's a big boost of bottom end grunt. And most single carbs do starve for fuel at WOT.

Click to expand...

Maybe a perceived boost, because for a given amount of twist the twin carb set up will present twice as much opening. But I can't see how that translates into any real power difference from a single carb opened to the same degree, unless there's some aerodynamic difference in the different inlet tracts. I won't mention dyno's at this point...

I agree on the top end, but as a single carb user I'm perfectly happy with what its got below 5000.

Yes - it is a perceived boost - you just have to twist the throttle more to get the same amount of power. And a single is smoother and easier to tune - it just doesn't come on as quick.

jseng1 · Sep 19, 2016

WZ507 said:
baz said:

Their are exception to this "opinion". I will give you the fact that you mention "MOST single carb starve for fuel at WOT", most certainly not all. In addition, with your upgrades installed on my Commando, I consider mine as a "performance Commando".

Sorry to get off topic cause I sure would like one of these heads too.

Click to expand...

My commando has a single 40mm flatslide mikuni ,there is no comparison between this and the single 34 or 36mm VM round slide mikuni set up ,my bike will pull to 7500 rpm if I want to ,I can't really tell the difference on the top end between the twin amal set up and the 40mm flatslide but where you do notice it is in the midrange the way it pulls out of corners is brilliant and at 5000rpm it's really starting to pull hard cheers

Baz said:
Kelly George would likely agree with you as his single carb Norton 850 flat tracker surely doesn't go flat above 5,000 rpm and is a consistent winner where ever it is campaigned.
Gives late style HD XR-750s a good run for their money too. Even hobot whole heartedly endorsed the single carb!

Jim says:
Whatever Kelly George uses to win is OK with me - but how big is that single carb and is the manifold modified? A 40 mm carb as mentioned above is a completely different story. And no one that I know of has compared the power output of the #66 dirt tracker with a single carb and then dual carbs.

lcrken · Sep 19, 2016

Might help to look at the cross sectional area of the different carb combos. I went through this in some detail for my Rotax powered race bike. For persepective, consider this.

A 40 mm carb has just a tiny bit more venturi area than a pair of 28 mm carbs.

When I was running the Rotax, the largest carb I could manage was a 45 mm flat slide that I JB welded and bored out to 47.5. That was still only equivalent to a pair of 34 mm carbs. It wasn't enough, and I ended up running a pair of 41 mm flat slides. If you have a built Commando race motor, and run the long circuits, you need more than a single carb for maximum top end power.

That doesn't mean a single carb isn't just fine for a street bike, or even a short circuit race bike, but if you want to be running with the big dogs at the fast tracks with a Commando, you'll be running twin carbs.

Ken

Brooking 850 · Sep 20, 2016

I have FA head number #10 that was worked slightly by Jim C, it was originally for one of his bikes.
Since I have had it, my engine porter had a little play with it and I have had it volumetrically balanced .
It has been gas flowed before and after these little mods.
Original flow figures that Jim supplied a potential of 78 HP (the inlet Vv/s are 1.5mm larger) latest flow figures show a potential of 82 + HP
Once the motor is complete I will have it dyno'ed for my own data base and post on here.
Regards Mike

pete.v · Sep 20, 2016

Brooking 850 said:
I have FA head number #10 that was worked slightly by Jim C, it was originally for one of his bikes.
Since I have had it, my engine porter had a little play with it and I have had it volumetrically balanced .
It has been gas flowed before and after these little mods.
Original flow figures that Jim supplied a potential of 78 HP (the inlet Vv/s are 1.5mm larger) latest flow figures show a potential of 82 + HP
Once the motor is complete I will have it dyno'ed for my own data base and post on here.
Regards Mike

You do know that JimC is not comnoz and comnoz is not JimC don't you?

Brooking 850 · Sep 20, 2016

Hi Pete, yes I do, as we were talking about head porting and FA heads, I thought the forum members on this thread would be aware of who I was talking about.
For those not so clear, Jim Comstock is the guy I purchased the head off.
Regards Mike

Madnorton · Sep 20, 2016

Watch this space, I'll be lending out my FA head in the spring for testing.

At the moment I suggest no one has a point - it is just a replacement head and sold as such.

74ok · Sep 20, 2016

Madnorton said:
Watch this space, I'll be lending out my FA head in the spring for testing.

At the moment I suggest no one has a point - it is just a replacement head and sold as such.

nope

there is this

manx850 said:
Oh by the way , i put the head on a Dyno.......It produced 10 BHP on its own without the rest of the engine!...looks promising!.............LOL

this
fullauto-head-count-t25400-15.html#p336169

comnoz wrote:
The amount of power increase you will see depends on a lot of other things, just simply bolting the head in place of a standard head may get you ten horse more if you have twin 32 or larger carbs and a good working exhaust system. If the flow is restricted with a poor manifold or an exhaust system that does not scavenge very well then you would likely only see a bit more midrange torque. Jim

and of course

Rohan said:
But no-one seems to have put one on a dyno to say how great.

Fullauto Head Count

NKN

Clanger

74ok

manx850

Fullauto

manx850

manx850

dennisgb

Mark

baz

worntorn

WZ507

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