3SGE BEAMs Bike Carb Conversion + Dual VVTi

[SeductiveDuck]

Hi all,
I have a bit of an odd inquiry but thought that this would be the best place to ask, I'm in the process of putting together a build plan for a future engine swap into a 1980 Toyota Celica RA40 and the engine I have chosen is a 3SGE BEAMs. Recently I have been interested in motorbike carburetor conversions and wanted to know if it's possible to keep the variable valve timing functional on 3S if it has been converted?

Briefly, here is why I want to convert from EFI to Carbs. Firstly I am NOT chasing power, the 3SGE will give me double the horsepower of the 18R-C anyway. My main goal is to build a car that's reliable, easy to service & tune, fun to drive, long living in both durability & future parts availability and most importantly reflects its original heritage in a modern restomod (hence the swap from the 18R-C to 3SGE; both are 2.0 i4's, as most of you already know). I feel as though a bike carb conversion fills these requirements perfectly.

Before the EFI master race chime in, I have no issues with EFI and I get that it's the superior fuel delivery method. If this conversion can't be done, then EFI will be the route I'll take it.

So back to the main question; Can you keep the Dual VVTi functional after a carburetor conversion on the 3S? A lot of forums I've browsed for the 3S & 4A suggest that you upgrade to non-VVT camshafts, and as a result everyone has done so. However, given today's advancements in aftermarket engine management systems, I can't see as to why you couldn't program an aftermarket ECU to engage the VVTi at a set RPM while running carburetors? Would I be correct in assuming that it's because you require a more dramatic increase in fuel flow rate at the programmed RPM that can't possibly be supplied with a carburetor? Or does it require specific sensors that carburetors lack to operate properly? If I've gotten something completely wrong, or missed something important then forgive me, I'm still a fairly new enthusiast.

For those that are interested in the conversion or don't know much about it:

https://www.classicfordmag.co.uk/wp-...bike-carbs.pdf

Bike Carb Conversion Pro's & Con's: https://www.youtube.com/watch?v=1fR1wBA9LV8

Bike Conversion How To in 5 Minutes: https://www.youtube.com/watch?v=YPbtXHqyh8g&t=52s

Carburetors of choice are Yoshimura Mikuni TMR MJN's, very interesting and efficient design that I feel would work wonders on a 3SGE.
https://www.bikebros.co.jp/vb/sports...carburetor-en/

[jonathan yee]

If power is not your goal then disabling VVTI would be silly.

Are you going to keep the electronic ignition side of things? if so I'm sure a decent aftermarket ecu can run the dual vvti and ignition. But I have no idea about carbs and if they will be able to fuel it correctly. VVTI is variable throughout the range and not really ideal when used like the old VVT with just a switching point based on RPM.

The sensors used to operate it are the crank and cam angle sensors and then a solenoids on the cam cover.

[SeductiveDuck]

Yeah I agree, that's why I want too keep the VVTi. As for ignition I will be running an aftermarket ignition module and may have too convert back to an older ignition system, say from a 20R/4A (I'm still researching this area), I'm just unsure of what one though. I know that guys who run performance carburetored engines use MSD AL2's because they can program timing & rev limiters/launch control but its capabilities won't extend as far as variable valve timing. Haltech have options for carburetored engines as well, however I haven't looked as far into their products, so I'll check out what they have. 👌

[andrew_mx83]

Why not keep the stock ecu for ignition and vvti but leave injectors unplugged (Might need dummy resistors to keep it from throwing codes)
Also just about any aftermarket ecu should do what you want, just ignore the fuel side of things and set it up as spark/vvti only. With crank + cam position inputs it should handle the vvti.

That said any of these options would be a big step backwards. For your stated goals proper efi wins hands down every time. You can get throttle bodies that look like webers if appearance is a concern.

[SeductiveDuck]

That sounds like a viable option, and I do understand that it will be impractical but their's just something about motorbike carbs in an engine bay that looks so good, better then ITB's in my opinion. I have seen the EFI look-a-like Webers, which are good for going from carby too EFI but on an engine that was EFI from factory you may as well go ITB's if all you want is the carb look. Worst case scenario is that if my carby conversion plan won't work, then I'll run ITB's. I'm really just chasing aesthetics, throttle response/fun factor and a pure sound. Like I said before, no matter what route I go with the BEAMs, I'll still have a pretty substantial HP increase, weight reduction & fuel economy improvement.

[jonathan yee]

I can't see it being possible to run an old school distributor ignition set up on the Beams, but ignore if that's not what your looking at doing.

But yeh I'd imagine with the VVTi being fully adjustable you'd be able to control them in such a way that you didn't get any drastic changes in airflow so the carbies could keep up?

Did any bikes come out with VVT and carbs? I know some honda's had vtec etc, but i'd assume they were all efi?

either way, keen to see what happens.

[SeductiveDuck]

Yeah it doesn't look like I'll have too. The Haltech Elite VMS is compatible with MSD's ignition systems. If this works out then it's going to be really interesting to see how well old school equipment can blend with modern tech, especially given how efficiently Yoshimura's Multiple Jet Nozzles atomize fuel, MSD's ignition modules spark fantastically well and paired up with the Dual VVTi I may see a respectable fuel economy (fingers crossed!). As far as my research has taken me I haven't come across any other articles about people aiming too keep VVT with carby converted engines, aside from a LS1 Forum.

[SeductiveDuck]

I did some research on how Toyota's VVTi works and I think that I may have found a potential issue. I watched a video that demonstrated how Toyota's VVTi works and it showed the valve overlap on one of the strokes, which I had not taken into consideration. This leads me too believe that it may increase the risk of an external/pre ignition of the fuel, either in the exhaust or at the carburetor, due to some of the fuel being either blown back out of the intake valves or by being sucked into the exhaust? Can anyone confirm if this is possible, or is it a wrong assumption? In saying that don't ITB's mount in a similar fashion, or is injection timed so as to not allow fuel in during the overlap stage?

[jonathan yee]

There's always been overlap in NA cars chasing power whether carb or efi.

[jondee86]

OEM's commonly inject on a closed intake valve, so the situation regarding charge reversion and fuel loss to the exhaust during overlap is pretty much the same with carbs or EFI. One difference is that EFI will usually cut injection on the overrun so you don't get the crackling and burbling that you do with a high performance carb engine.

Currently, tuning EFI to inject on the overrun to make flames, pops and bangs is a thing

Cheers... jondee86

[LittleRedSpirit]

I think downgrading from efi makes no sense on a high performance efi engine like a Beams.
However, I appreciate your goals and brief for the car. The carbs should fuel VVTI cam control engine just fine, because what the vvti does is boost air `flow through the motor, airflow that pulls fuel with it, so if the air makes it in there, the fuel will too. I wonder if you can get appropriate sized bike carbs, can you get appropriate sized jets to make a 2 litre motor idle and deliver enough fuel from them. I'd advise using an ecu to control the ignition and vvti, which will mean sensors and efi wiring all included, so you will still have a bunch of wires in the bay, its not going to be 5 wires like a typical carb setup, which might be counter intuitive for the curation of the build as you see it. If youre looking at FCRs I dont think they come big enough for a beams.

[jondee86]

There is a common misconception that carbs are hard to synchronize, hard to tune, too big for your engine, too small for your engine, lose bottom end etc., and generally are a poor relation to any kind of EFI. If this were true the scrapyards of the world would be piled high with the countless thousands of big sports bikes with carbs that have been sold over the last few decades.


https://danstengineering.co.uk/index...product_id=884

Now it is true that EFI offers many advantages (mainly to vehicle manufactures) but that does not automatically mean that carbs no longer have a place on the internal combustion engine. Just as the technology industries pushing electric vehicles will not displace the enthusiats love of the internal combustion engine any time soon

ITB's motorcycle carbs, sidedraft carbs, throttle bodies all offer a short and direct intake tract for better engine response. Unless you are building a landspeed record vehicle, you do not want to oversize the throttles. Correctly sized throttles give better response and more power in the part of the rev range that you use the most.

To the OP, it might be worth contacting danST engineering to see if they have a kit for the Gen 5 3SGE.

Cheers... jondee86

[LittleRedSpirit]

I appreciate your ideas, however find it very general in nature. To bring it back to data, FCRs come up to 41mm, is that enough flow for a Beams you reckon? Or CV carbs maybe a better option where ultimate response isnt the goal? Can get CVs up to 48mm.

[SeductiveDuck]

@LittleRedSpirit It definitely doesn't, I will admit that it's impractical. As for providing enough fuel and airflow for a 2.0 ltr engine the bike carbs will do the trick A-OK, I'm trialing it with the 18R-C engine that I have in the car currently. Swapping out the old economy carb for a set of Keihin CVK36's off a Kawasaki ZX-6R. I reckon 40mm upwards will do the trick for a BEAMs, especially Yoshimura's. From what I've read a lot of guys run 41mm on more performance orientated heads. @jondee86 I will definitely get into contact with DanST, I have heard some great things about his work and I'm sure it'd be a project that he'd be keen to undertake, if he hasn't already. Just trying to keep the planning as local as possible, since buying parts from overseas is so expensive these days.

[jonathan yee]

I would assume you just want bike carbies of a bike that can see 210hp as that is what the BEAMS was. I'm not overly a fan of people running the 4AGE silertop TB's on the beams. I think they are too small, the inlet ports are bigger than them so your doing weird stuff to the flow. I know your not after HP, but I see no point dropping HP from stock levels?

Use an auto BT motor for your setup(it'll be cheaper) the MT version would be wasted.

SamQ makes an ITB adapter plate I think? He may be able to help make/modify one to suit whatever carbie set you go with?
https://www.sq-engineering.com/produ...ottle-adapter/