DCOE VS Throttle Body DCOE VS Adapted Bike Throttle Bodies

noypiesky Wrote:
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> heymagic Wrote:
> --------------------------------------------------
> -----
> > I worked on a sand rail last year with a
> pro-built
> > 2.3 Ford. It had 4 Mikunis off of some bike.
> They
> > were mounted with rubber hose to a home made
> > intake, stub pipes on a flange. Started
> easily and
> > ran like a scalded dog.
>
> That's the Esslinger Racing Mikuni set-up. The
> Mikunis are off some snowmobile application.
>

It's been a while and my memory is not so good but that looks about right.

Interesting question - but something to consider is displacement of the motor the carbs are going on. I know a guy that had a bugger of a time fitting some carbs off a 1000cc bike on his 2000cc VW - just had a bugger of a time trying to even getting it to idle. Figured since it was flowing double the air at idle it was maxing out the idle circuit / jet and it was just hard to tune in general since the flow was so different. He eventually got it with LOTS of trial and error though - and the sound alone was worth the effort.

On your NSU however - the displacement is much closer to that of a liter bike, so you should have very little tuning in order to have a pretty sweet set up.

So in cases where you're fitting them on a car motor of similar displacment as the donor bike - I think it's definitely worth a try as it'd be great bang for the buck if they dialed in easy.

Something to be wary of buying used carbs is there's no garantee the carbs were working on the bike to begin with, so if you can start with known good carbs that's a big plus.

Rabin

bean Wrote:
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> So in cases where you're fitting them on a car
> motor of similar displacment as the donor bike - I
> think it's definitely worth a try as it'd be great
> bang for the buck if they dialed in easy.

For idle, displacement may be of some concern. But when it comes to the actual sizing of the TB, then it's more important to compare power of the engines.
The ID of the TB is basically what limits the amount of HP the TB will flow air for.
With big bike engines producing 160-170 hp or more on a 4 cyl, we are seing +60 hp pr. cylinder.
This is what should be compared when choosing a bike TB or carb for at car.

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Brgrds
Brian

There are a bazillion old bikes running around just fine with original carbs. Not hard to clean them. My son just re-jetted his quad carb and he had never seen one before. BTW it is a single cyl 500 Polaris making over 60 hp on one carb. Do the math...

It may take a bit to get the jetting right but having driven the 2.3 Ford buggy they work and with places like Bent Bike salvage yards it isn't totally unreasonable to get an affordable set-up.

Have a look at this link to the VW Vortex. It is an inventory of all bike carbs and ITBs. http://forums.vwvortex.com/zerothread?id=2838896

Robert.

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Robert.

"You are way too normal to be on Rally Anarchy." Eddie Fiorelli.

That's juicy Robert, but I wonder what the woking end dims are for the bike INJECTORS?


And of course that would be even more interesting if we knew bore center to center on some of the likely candidates like all those Faule Vays.

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John Vanlandingham
Sleezattle, WA, USA

Vive le Prole-le-ralliat

www.rallyrace.net/jvab
CALL +1 206 431-9696
Remember! Pacific Standard Time
is 3 hours behind Eastern Standard Time.

I've modded junk Weber DCOE's into throttle bodies. A 40 mm throttle body flows like a 45 DCOE w/40 mm venturi, so by using a 40 mm DCOE with the venturi removed, all passages epoxied up and otherwise gutted, you get the same effect.

I've picked up 40 DCOE's from ebay for as little as $15 (usually missing jets and whatnot). Only thing remaining is to decide where to run the injectors...intake or TB. Or even the 'above the airhorn' Extrudabody setup.

Bob

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Opel is a 4-letter word...
http://www.flickr.com/photos/10498579@N07/sets/

wildert Wrote:
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> For idle, displacement may be of some concern. But
> when it comes to the actual sizing of the TB, then
> it's more important to compare power of the
> engines.
> The ID of the TB is basically what limits the
> amount of HP the TB will flow air for.
> With big bike engines producing 160-170 hp or more
> on a 4 cyl, we are seing +60 hp pr. cylinder.
> This is what should be compared when choosing a
> bike TB or carb for at car.
>
> Brgrds
> Brian

That is a good point, but your numbers need to get scaled down because of RPM. Also - a lot of the big numbers you're talking about are mostly injected bikes. Numbers come down a bit for production bikes on carbs, and when you factor in the RPM peak of 6-7000 RPM of the NSU (if that?) the power numbers are MUCH closer than the peak numbers you posted.

So while there is a crap load of variables - it'd still be easier to tune if the carbs came off a big engine of similar displacement to the NSU. While they're capable of flowing for 10 - 11000 rpm - the little NSU will never see that, They're still capable of proper fueling right through to that range so it shouldn't be too hard to set up.

Rabin






Edited 1 time(s). Last edit at 04/17/2009 11:58AM by bean.

bean Wrote:
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> That is a good point, but your numbers need to get
> scaled down because of RPM. Also - a lot of the
> big numbers you're talking about are mostly
> injected bikes. Numbers come down a bit for
> production bikes on carbs, and when you factor in
> the RPM peak of 6-7000 RPM of the NSU (if that?)
> the power numbers are MUCH closer than the peak
> numbers you posted.
>
> So while there is a crap load of variables - it'd
> still be easier to tune if the carbs came off a
> big engine of similar displacement to the NSU.
> While they're capable of flowing for 10 - 11000
> rpm - the little NSU will never see that, They're
> still capable of proper fueling right through to
> that range so it shouldn't be too hard to set up.

I don't know how to put it nicely - other than: You got it wrong :-).
RPM has nothing to do with how much diameter you need for X amount of horsepower.
1 HP is 1 HP is 1 HP, and it requires the exact same amount of air and fuel, regardless of how many RPM it takes to develop that 1 HP.

HP is a product of torque and number of repetitions over time (the RPM's).
This is simplified a bit, but it is still valid:
If you make 1 HP from X amount of torque being repeated 10 times in one second (10 revs pr. second), or you make it by 10 times X amount of torque being repeated once in one second (1 rev pr. second) - it's still 1 HP, and it still requires the exact same amount of air and fuel pr. second to enter the engine.

So you only need to look at peak horsepower, when trying to figure out when increasing the ID of the carb or TB, will cross the point of diminishing returns (maybe even the point where you'll hurt performance due to low air speeds).

Look at ads for performance carbs for those big V8's you guys have over on your side of the pond. They're all quoted for x amount of CFM (cubic feet per minute) that they can flow. Thus a 600 cfm carb will fit equally well on a slow reving big block, and a faster small block, provided that they develop about the same amount of horsies.

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Brgrds
Brian

Rallymech Wrote:
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> Have a look at this link to the VW Vortex. It is
> an inventory of all bike carbs and ITBs.
>
> Robert.

Blows my mind that there's so many different ones. oy!

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Andrew M
Onterrible
30ish

wildert Wrote:
-------------------------------------------------------
>
> I don't know how to put it nicely - other than:
> You got it wrong :-).
> RPM has nothing to do with how much diameter you
> need for X amount of horsepower.
> 1 HP is 1 HP is 1 HP, and it requires the exact
> same amount of air and fuel, regardless of how
> many RPM it takes to develop that 1 HP.
>
> HP is a product of torque and number of
> repetitions over time (the RPM's).
> This is simplified a bit, but it is still valid:
> If you make 1 HP from X amount of torque being
> repeated 10 times in one second (10 revs pr.
> second), or you make it by 10 times X amount of
> torque being repeated once in one second (1 rev
> pr. second) - it's still 1 HP, and it still
> requires the exact same amount of air and fuel pr.
> second to enter the engine.
>
> So you only need to look at peak horsepower, when
> trying to figure out when increasing the ID of the
> carb or TB, will cross the point of diminishing
> returns (maybe even the point where you'll hurt
> performance due to low air speeds).
>
> Look at ads for performance carbs for those big
> V8's you guys have over on your side of the pond.
> They're all quoted for x amount of CFM (cubic feet
> per minute) that they can flow. Thus a 600 cfm
> carb will fit equally well on a slow reving big
> block, and a faster small block, provided that
> they develop about the same amount of horsies.
>
> Brgrds
> Brian
>
>

I think you're mis-understanding my point. I agree with everything you've said, but it has nothing to do with what my point is.

My point:

My ZX-10 (1000cc) makes 130 HP at 11000 RPM. At 6000 rpm it's making 70 HP. If the carbs are tuned great, I can unbolt them and put them on a 70 HP 1000cc Austin Mini motor and have very little tuning to do to get them dialed in.

* Power numbers quoted are just to illustrate a point.

I made no claims as to the HP potential of the carbs, but tuning wise they have the same air flowing through at idle all the way to 6000 rpm - so getting them to work on the Mini should be easy.

So my only point was ease of tuning bike carbs on a car motor for cheap bang for the buck results.



Rabin

You're absolutely right - I never caught that point :-).

What I was trying to prove, was that if you trying to make 170 horsies on a 1800 cc engine, then throttle bodies (or carbs) from a 1300 cc bike producing 170 horsies are just fine.

Two completely different points we are trying to make :-).

I do have one beef with your point though. From a jetting point of view, it makes sense.
But you do suffer from an overly large bore on the carb or throttle body though. This could easily hurt low end driveability, and thus also torque.

Going for carbs or TB's from a 70 peak horsepower bike would be better for driveability. I'd even venture the guess that the power characteristics would be more similar.

---

Brgrds
Brian

wildert Wrote:
-------------------------------------------------------
> You're absolutely right - I never caught that
> point :-).
>
> What I was trying to prove, was that if you trying
> to make 170 horsies on a 1800 cc engine, then
> throttle bodies (or carbs) from a 1300 cc bike
> producing 170 horsies are just fine.
>
> Two completely different points we are trying to
> make :-).
>
> I do have one beef with your point though. From a
> jetting point of view, it makes sense.
> But you do suffer from an overly large bore on the
> carb or throttle body though. This could easily
> hurt low end driveability, and thus also torque.
>
> Going for carbs or TB's from a 70 peak horsepower
> bike would be better for driveability. I'd even
> venture the guess that the power characteristics
> would be more similar.
>
> Brgrds
> Brian
>
>

Yep - Ideally you're correct, but getting those carbs to idle worth a damn with twice the air coming through them is a BITCH. Idle jet sizing and needle settings all have to be done basically by trial and error. Once you figure idle, then you gotta make sure there's no nasty flat spot when you transition to the main jets. It's possible for sure - just a bitch.

As a point of interest - I met Jay - the owner of a dyno shop in Colorado in 04' that said bigger carbs are always better - you just need to know how to tune them. (He's a carb GOD!) http://www.thecarburetorshop.net/bigger1.html

So with proper tuning you might do really well with the 140 HP carbs on a 70n HP motor. Out of the box and getting it running ASAP I think a lot less fiddling would need to be done with my scenario.

Rabin

So all of this bike carb talk with the jetting and relative engine displacement, does this all come into effect with ITB's from bikes? Because then you would have the bikes displacement, the receiving engine's displacement, and the bike ITB diameter.

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Welcome to the cult of JVL drink the koolaid or be banned.

Dazed_Driver Wrote:
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> So all of this bike carb talk with the jetting and
> relative engine displacement, does this all come
> into effect with ITB's from bikes? Because then
> you would have the bikes displacement, the
> receiving engine's displacement, and the bike ITB
> diameter.

For ITB's it's much easier to tune, since it implies that you some sort of programmable engine management solution available (or you at least should have :-)).

So you really only need to find ITB's with an ID that suit the sort of peak power you are looking for. There's a lot of info on this from manufactureres of ITB's, etc. - but it's also not far off to just compare the peak power pr. cylinder for the bike.

Displacement means nothing in that case, since you have 100% absolute tuneability from you EFI, thus stuff like engine characteristics and power band for the donor engine is irrelevant.

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Brgrds
Brian