Hi!

Ever since the DIY EFI project was mentioned on the 'Turbo GS' thread, I can't get it out of my head. I feel like it would solve all my 'problems' and make my GS stay with me another season or two. Of course, a DIY project will generate a bunch of problems on its own, but hey - it's all DIY fun! :lol:

Anyway, I've been talking to some guys on the Megasquirt forum and they said, that if the engine would benefit from a larger carburator, I should get a slightly larger than 34mm throttle body (just slightly larger cause TBs generally flow better - they have less obstacles in the air path).

Now - would a GS engine benefit from a larger carb? I really have no idea.

Thanks, D.

some racers have punched out the sleeves replaced them with early gsxr 1100 sleeves and bored hell out of them, inorder to feed those lungs theve run anywhere from 36mm Gsxr 600 carbs to 38mm Kien's


Btw, the gsxr 600 carbs are nearly identical and bolt right on the gs500 rack.

OK, racers...

But would a bigger carb do anything good for a stock engine (just exhaust and maybe air filter are aftermarket - more flowing)?

Can anyone take an educated guess?

D.

Well bigger carbs will make the top end better, and lower end worse...
Ironically ... a GS is not a high spinning motor ... so Your experiment with bigger carbs may end poorly... And EFI ... ok more trouble than its worth, cos most efi bikes even from the factory, people want the bike to behave like a carbureted bike ... EFI is mainly for fuel efficiency and cleaner exhaust... which make for a bike that barely runs ...
Cool.
Srinath.

you can take 1 engine, carberate it tune it and get ok hp, now if you put FI on it and map it right you can increase HP. throttle respose is generaly improved.   Mileage and emmisions only cuz theres less waste

Here is a tech page on constructing a custom plenum:

http://www.sdsefi.com/techinta.htm

 It was made for a Toyota 20r but there are alot of really good applicable ideas, mostly the plenum itself, injector bosses and fuel rail.

Edit: doh

Someone suggested that with EFI a larger throttle body shouldn't cause problems as the maximum air flow is limited by the port size. And EFI can adjust the mixture based on O2 readings.

This sound's reasonable, doesn't it?

D.

Wouldn't a larger throttle body negatively influence throttle response?

Is there a stand alone FI system that would work with 2 cylinders?  I know there are systems available for cars but are there any for bikes?

An EFI system would probably cost more to buy and tune than our bikes do

I would guess air flow through the heads and cam specs would be limiting factor with a well tuned EFI.  I can't imagine you'll get much more power than you would with a pipe/filter/nice jetting without porting the heads and getting custom grind cams.  There just seems to be easier ways to get more power :dunno:

Quote from: 70 Cam GuyWouldn't a larger throttle body negatively influence throttle response?

I don't know - would it? :dunno:

QuoteIs there a stand alone FI system that would work with 2 cylinders?  I know there are systems available for cars but are there any for bikes?

http://www.megasquirt.info/ - I've read about it and asked some questions and it seems it should work!

QuoteAn EFI system would probably cost more to buy and tune than our bikes do

Given that the above is a DIY project, it shouldn't cost a lot (I think they sell the kit for ~140 US$). It has a computer port

The MegaSquirt communitiy has produced some tools and software for tuning. And some guidelines.

Quote
I would guess air flow through the heads and cam specs would be limiting factor with a well tuned EFI.  I can't imagine you'll get much more power than you would with a pipe/filter/nice jetting without porting the heads and getting custom grind cams.  There just seems to be easier ways to get more power :dunno:

I'm not really after more power - 45 HP would do. But my bike is running like crap (30 km/h short of declared top speed - even on slightly downhill highway) and I'm tired of not finding the real reason for that.

And I think a DIY EFI would be a great learning project too.

D.

I didn't realize you already had an idea for the FI system

Sounds like fun!  probably a bit challanging still

I wish you luck, sounds like a bit of work ahead  

QuoteBtw, the gsxr 600 carbs are nearly identical and bolt right on the gs500 rack.

If that's true then maybe a throttle body from a later gsxr would be just right.

Anyone got one FS?

D.

you have to play with configuration alittle to use the 2 middle carbs (Gsxr600) and plug up the fuel crossovers and some extra venting.  dont ask me about the jetting, i have no clue where to begin. my stock carbs dont even like the 40 pilots, but then i still need some stock slide needles.

Srinath, you got some layin around needing a home perhaps?

running bigger throttle bodies then are necessart will hurt all partial throttle usability and if they are so huge then can hurt full throttle performance as well.  one big advantage to carbs is that you dont have to mount a fuel pump and ECU on the bike.  many cars that have huge throttle bodies usually have a smaller primary throttle body to make partial throttle more manageable

Quote from: raceratbrunning bigger throttle bodies then are necessart will hurt all partial throttle usability and if they are so huge then can hurt full throttle performance as well.

Just to make sure I understand - is that because a little movement of the throttle (and the big flap) will make more air pass through than a smaller TB would?

Would that also mean that maximum air flow would require less throttle twist? Actually, that would be good.

Quoteone big advantage to carbs is that you dont have to mount a fuel pump and ECU on the bike.

Of course, that's true. But they have a lot of disadvantages too.

Quote
many cars that have huge throttle bodies usually have a smaller primary throttle body to make partial throttle more manageable

Primary throttle body? What's that?

D.

most throttle bodies are "primary" , some carbs however to combine low end driveablitly and full throttle perfomance, use a progressive 2 ventri setup, using a smaller Primary thottle plate, and a larger secondary plate to massivly increase Airflow.   weber, holly,rodchester,hitatchi, and keinhin have all done this.  the problem with large openings, is the drop in air velocity when the plate opens.     the larger opening means more air comes in, but it dosnt have to move as fast to fill the cylender.  with a smaller throat, the air moves faster tring  to fill the same space.  too each size larger you go, you have to open the throttle slowly till enginespeed picks up before you can reach wide open and then you might have a happy engine. to compensate for that, one opens ports, larger valves, bores cylender, extends the stroke even.  there is a touchy ballence to maintain.

ok, i've forgoten the reason  got in this deep so im stopping now.

This is my project www.suzukiGS500efi.blogspot.com . It si 70% done.