Motorbike Carbs

[zep]

What would you consider an apt comp ratio? Obivously the only real way to do this without getting lumpy pistons is to shave the head down, but that leaves concerns for a higher lift cam grind.

I had a look at this

http://www.pumaracing.co.uk/Chokes.htm

The R1 carbs have 40mm chokes. Assumming that the Aussie 4ZE1 on 48IDAs was taking the advice on that page, he would be using chokes 41mm or smaller. His engine was worked (not as much as the 190hp version, but a little), and this wont be (well not as much). I know they are different carbs compeletely, but reading that makes me think that the choke size is perhaps the most important aspect of choosing which carbs to use. Therefore, I feel that 40mm chocked R1 carbs could actually be quite suitable to this engine, or am I just making total speculations based on technical naivity and less than adequate engine information?

A further question. Some Vauxhall magazine article I was reading says that you can use Weber DGAV jets in R1 carbs. The Puma Racing Engines website above says that you can estimate the main jet size but multiplying the choke size by 4 and then go from there. Does this mean that if the R1 carbs were suitable I should start with a 1.60 main jet and then see how it goes from there? The Vauxhall article says to use a 1.8 for a 2lt XE, but I'd imagine that they would have a higher cfm so therefore more air/gas than the 4ZE1

[Spencer]

^ I agree isnowi, will run on the R1's no doubt. But I'd be looking at something in the 45mm range which kind of puts 4cly bike carbs out of the game. Biggest carbed CBR only had 38's, Bandit 1200 only has 36mm CV's and next biggest bike in that category is something like the Hayabusa which has always been injected.

I know it bumps up costs but EFI is probably the way to go using black top 45mm throttles, or most of the big injected bikes have 45mm+ throttle bodies, some with variable trumpets just to add more complexity . Build a nice tapered manifold with some 45mm's for ultimate lush times.

Or you could get a set of 43-45mm flat slides which would be awesome, would cost around $6-700 to do for a set of 4 knock offs. Would need an interesting linkage setup to get them working in unison as well.

I wonder what the biggest jet you can fit in a R1 carb is anyway? 2mm or so?

EDIT for zeps post:

You really shouldn't compare these to choked IDA's the CV"s have a variable venturi where as the 45's need to be choked to get it to run properly all over the rev range with their fixed venturi. Just because he's had to choke them to that size to run correctly doesn't mean his inlet isn't to small.

Man that took ages to post while trying to work. Probably looking too much into it, the r1 carbs will work, maybe not ideal though. Dont worry about jets, they are cheap as shit to buy and you just buy a decimal drill set and drill them to what ever you want. Start around 1.6 and move up with a wideband to check ratios

[zep]

Ah spence, you know I want to go to ITBs but man it's a whole lot more learning about ECUs and stuff. There is no way I'm shelling out for another LINK, that sheezy is expensive! I don't think I have the time or patience to learn about the MegaSquirt system either, unfortunately!

I just feel that if I went EFI with blacktop throttles I'd also need to throw more cash into the engine too!

Other option is to try and get a crashed MU, Rodeo or Jackaroo and use the standard ECU and loom from it. But damn it, how cool would the bike carbs look hanging off the side!

[isnowi]

With respect to other posters, i still reckon it'll be alright on the 40's, coming at things from another angle, big power harleys quiet often run a single HSR (flatslide) 45 for both cylinders, up to 1400-1500cc too.

I personally don't think that going to 40mm carbs will have too much effect on the motors potential, at least not until a great many other obstacles have been overcome, comp ratio, vlave and port sizes, revability...

I say do it, there needs to be another bike carb project on the boards.... I miss my one.

[zep]

The motor will run on the carbs, I'm pretty sure of that. I think I might just give it a go. Either way, if this fails to work properly on the 2.6, the same intake manifold can be used on all SOHC Isuzu petrol engines from 2.6 down to 1.6 so they're bound to be appropriately sized for something.

Oh and the other thing I was going to ask. In regards to carb size vs EFI throttle body size. I imagine that it dosen't work quite as easy as diameter of the 1 EFI throttle body vs diameter of carb x4. The 4ZE1 has a relatively small throttle body from factory.

I guess we can talk about comp ratio, etc later on!

[peteretep]

The area of the 4 r1 chokes is equal to a single 80mm throttle body if you compare the areas directly

[Testament]

The area of the 4 r1 chokes is equal to a single 80mm throttle body if you compare the areas directly

it doesn't work like that - 4x 40mm throats on an independant runner manifold is essentially the same as one 40mm thoat on a common manifold. the differences as far as the cylinder are concerned are only due to a common manifold having more pressure drop, generally not being able to have tuned length runners, and with a carb the issue of getting the fuel in the air to turn corners without falling out. But the straighout airflow calc is identical - onyl one cylinder is drawing through the throat at a time (on a 4cyl anyways).

the R1 carbs can definitely be made to work, if you have them I would say just go for it as it doesn't sound like you are trying to get an absolutely "perfect" setup. Otherwise IMO I would be looking for 45DCOE's or DHLA's it will be easier to set them up.

Still you should look for more info, what rpm was this 190hp made at? what are the factory cam specs? any pics of combustion chambers and piston shape? It looks like its twincam? yes?

Will definitely need to get the compression ratio up if you can - if you can find out the wrist pin diameter and compression height of the pistons might be able to find something from another engine that may work to give you more compression.

any idea what the factory rods/bottom end is like? can they put up with say, 6500rpm?

[BobbyBreeze]

R1 crabs will be fine. They are 150ish HP stock, and Joe's seen them used on up to 250hp n/a XE Redtops.

If they are a little small (which they wont be), it will just make the motor more driveable which = win for an engine like you are talking. Big stroke means its never going to to be a screamer anyway.

[mikuni]

Surely it would make a difference how far away the throttle is from the valve or port. If you are running 40mm throttles near the port I would imagine it would hinder performance less than if they were 400mm away from the port for example.

SBD and QED (the 2 main XE tuners in the UK) run the same logic as above with their throttle bodies on Opel XE engines. You can get taper throttle intakes that run from an outer diameter of 66 down to a port size of 42mm with a throttle of 45mm and these make more power than an intake of 48mm that doesn't taper down to the port in the same way. Heres the yarns about it so you can read it for yourself. http://www.sbdev.co.uk/Tapers_Over_MT.htm

Also, people run up to and over 200+bhp on XE's with R1 carbs. Its well documented. So I can't see a huge issue with producing that much power with any engine. Its all about air in, air out and losses so if they can provide enough air to produce 200hp on a high flowing 16v dohc 2litre, why wouldn't they be able to provide enough air to run an 8v 2600cc engine to the same output? My logic may be flawed but it makes sense to me atleast.

edit: beaten by above, but yeah I had a bigger story time so there!

[peteretep]

true didnt even think about cylinders sucking at different times

[zep]

Thanks guys, this is all very interesting. I'm learning a lot here and interested to start thinking a bit more in depth about this kind of thing... it's much more interesting than I had originally thought.

Damn, I wanna start working on this now!

[mikuni]

I know its easy to throw your own jets in the carbs, but when I had a set of these and I was researching putting them on my XEV I found what all the guys jet them to in the UK. Search Bogg Brothers, they do most of the conversions. I talked to a carby guy down here about it and he was really interested, said he always wanted to bust some bike carbs on car engines but hadn't seen it done before in NZ. The prices he was quoting for doing the re-jet were stupidly cheap, so I'd say thats probably worth looking into rather than mucking around trying to find jets etc.

[peteretep]

I just rang bogg bros and had a chat when I had some questions, they were real helpful

[Testament]

Surely it would make a difference how far away the throttle is from the valve or port. If you are running 40mm throttles near the port I would imagine it would hinder performance less than if they were 400mm away from the port for example.

Yeah thats why I said the difference is due to the pressure drop and tuning length which means you need a slightly larger flow area for a single, but only slightly, it's not 4x the flow area (for a 4cy).

Well if it's documented that people have made 200hp on r1 carbs on an XE then yeah, they should probably work fine on the isuzu motor.

[mikuni]

This is floating around on oldschool somewhere, but a repost because its quite helpful regarding R1 carbs

http://www.totalvauxhall.co.uk/resource ... h60697.pdf

[peteretep]

this guy is running 40 DCOE's on his 2.6 astron motor

http://www.cardomain.com/ride/3239743

[Spencer]

I know its easy to throw your own jets in the carbs, but when I had a set of these and I was researching putting them on my XEV I found what all the guys jet them to in the UK. Search Bogg Brothers, they do most of the conversions. I talked to a carby guy down here about it and he was really interested, said he always wanted to bust some bike carbs on car engines but hadn't seen it done before in NZ. The prices he was quoting for doing the re-jet were stupidly cheap, so I'd say thats probably worth looking into rather than mucking around trying to find jets etc.

Jetting is the least of his worries its so simple, Ive done it a million times on bikes. With a wide band and the bike on the dyno it's childs play. You just drill them out then go for a drive with the wide band its that simple. If you go too big buy another set of jets for $10. There's only the pilot, the main and the needle height to play with. For gas money I could grab the wideband off my cuz and come help, just weld a bung in the exhaust.

Also the statement about 250hp XE's is ridiculous. Sure it is possible but doesn't mean its right, if a stock 2L beams is choked by a set of 45mm throttles. What are 40's going to be doing to that engine with 50 or so more Hp

if your going to use HP to compare throttles look at some bikes zx12 Ninja makes like 180hp and uses 46mm throttles, most other bikes around the 1L mark use 44mm+ throttle bodies for under 200hp.

But you cant really use just a HP figure from another build/engine and say it works for that much HP so it must be fine for mine! Look at the rough calculations earlier the bike makes more power but zeps engine still sucks more air, zeps engine will eventually, rev abit more and suck more air. But he wants to suck through some carbs off an engine that are sized for less CFM.

They will work fine, I just think they are abit small

[vvega]

no matter the engine size .. bar the v.e calculation if a piston engine makes 200 hp its sucking the same amount of air as another engine making 200 hp be it a bike motor doing 50 billon rpm ... or 4 liter v8 doing 500

typically a carbied engine needs smaller chokes to fuel than a injected engine

..injected engine your just trying to get the air though with the least restriction and the fuel is feed in at high pressure

carbs need to create a pressure diff so the fuel form the bowl is forced into the airstream

to do this you need a to "choke" the airstream with a venturi

basically you cannot use injected formular to size for carbs ... its a different ball game

IMO for 250 hp .. id be wanting 48mm chokes

plenty of 300 hp cosworths used to be run on between 48mm and 50mm

if 250 is what your after then 45mm is a good starting point....

IMO

[zep]

I never said that 250hp was what I am after, the only mention of attaining a power figure that I made was that I would like to try and replicate the standard 89.5kw, which is 120hp. I've seen 1.6 SOHC G-series gemini engines make this sort of power.

Any upgrades to the engine, i.e cam grind, extractors/exhaust, increased comp. ratio, head work, and it would be a bonus to make some extra power/torque. That said, I'd say that the standard power/torque figures for this engine would pull a sub 900kg car along quite nicely.

[Ogre]

kinda on topic, but what about boat engine carbs?Every boat engine ive looked at has had multi carb set ups, i know my dads is about 1000cc and triple cylinder.Wouldnt the carb be bigger than a 1000cc quad?I guess the boats dont rev that high tho....like 7000rpm or somthing.