I have a question what would be the better way to go ITB's or Carbs?
on the itb's i will need a standalone engine management system and on Carbs all that gets eliminated. right? so what would be better? Give me your opinion.

 

Really depends on what you want to do with your car. ITBs keep you with an EFI system whereas carbs get rid of all the electronics and makes it all nifty but you still have to tune the carb for your application, which if I am not mistaken is still easier then a EFI system. The only draw back to a carb is they generally dont flow enough to provide fuel for a high power system unless you got a DIY custom setup then anything is possible.

 

ITB's and ECU will give you perfect fuel/air delivery throughout the entire RPM range.

A carb can be dialed in to work great in approximately a 1000 RPM range. So between 2000 and 3000 you run perfect, everywhere else is less than perfect. (generalized example for you nit-pickers)




But Carbs look SO cool!!!!!!

 

yeah i cant decide! so carbs are only good through certain rpm's?
what systems can i use to tune ITB's?

 

go to the stand-alone section, any of the ones in there, on the cheap, theres megasquirt, sds, haltech, and then **** just goes up. it all depends on level your car is at, if it were me and i was going itb on the cheap i would go with a distributor and an sds to control the fuel with some home made itbs. its all about how awesome town you want it to look, with around 5k i could whip up some gangster *** **** but im not going to do that when i can accomplish something similar for a lot less. b.p. with a modified downdraft swinging an sds with a good tune, **** the glitter and gold. good luck

 

do you think i can use the toyota itb's off a 20valve?
with some customization i think it will work.
what do you think?

 

You can use as system out there for ITBs its basically the same as a stock throttle body setup; however instead of having a huge 70mm throttle body for your two rotors you would have two probably 48mm throttle bodies. I think megasquit is probably the cheapest unit out there but make sure you get the PnP version or you are going to have to build the ECU yourself :P

Edit: You could make the toyota ITBs work; however you will still need a standalone to run the ITB and Injectors. As mentioned before and I have seen it myself but people have even used the throttle bodies of a Hayabusa (1.3L super bike) to do a DIY ITB setup it just depends on how much time you want to spend creating and tuning it

 

oh i have all the time in the world. its just a matter of getting everything i need. like materials and info. so you think i can use the toyota unit?

 

All else being equal, the ITB's will be more powerful, have better drivability and better fuel economy.

Read this: http://www.twminduction.com/ThrottleBody/carb_vs_fi.pdf

 

I have twin DHLA 40s on my 13b, i got the setup for cheap and it works awesome, but I wish I had the money for a big ITB setup. I drive in mostly mountain areas so elevation is always going all over the place, and the weather is always different, so some days the car is awesome and others its meh.

 

That depends on the EFI in question.

I still haven't seen EFI that cab give the efficiency of a Nikki carb. There's something really nice about a properly sized progressive carb setup.

 

Like I said, all else being equal, compare a shitty EFI to a good carb and it can very well be a different situation. If you're comparing a higher flowing, more powerful EFI to a carb, then it might well give worse efficiency.

Key words: all else being equal, which unfortunately it never is, this is a generalisation that's true much of the time.

 

I guess that's why all the professionally built race cars use injection, unless required to use carbs by the rules.....

 

There are also cases where you can run webers or stock EFI where the carbs are preferable, but he was specifically speaking to the efficiency point, which probably just comes down to size and power potential.

 

I love how any discussion revolves around what racers do...

For *street efficiency*, it is difficult to beat a properly sized carb because of atomization and granularity issues with EFI unless you get a Really Nice Setup.

I don't know of any race series where they drive at 60mph at 50KPA for long periods of time. Probably quite boring to watch.

 

our race car is either wide open, or closed throttle about 95% of the time. its kinda weird to see the datalog

 

Modern fuel injected cars get very good milage while making better power than their carbed counterparts from long ago, while providing better drivability, much, much lower emissions and making more power. How can you really say that carbs are better for efficiency just because in one case you've observed that carbs can get decent milage? Besides, what was the power of the competing carb and EFI setups? If the EFI was making a bunch more horsepower then it's not a fair comparison.

 

Under the same circumstances EFI will always be superior to carburettors. Just by their very nature as mentioned earlier. EFI can be tuned across the entire rev range for a chosen A/F mixture. This means a wider powerband, more torque, better driveability and better fuel consumption. Injectors also give superior fuel atomization which further enhances the above-mentioned properties. The only advantage I can see to carbs is simplicity. Less to go wrong (although a properly done EFI setup is perfectly reliable) and easier to install. I was going to say easier to tune but it actually depends on the setup, with a wideband O2 sensor and a standalone management system its relatively easy to tune an EFI setup whereas with a carb its a case of trial and error when it comes to jets etc. which is not how I like to tune. Just my 2 cents, im a fuel injection man all the way but I wont bash people for going with a nice Weber setup. It is cheaper than a good ITB setup and we wouldnt be driving rotaries if we were really worried about fuel consumption

 

I forgot to mention. My full-bridgeport 13B, ITB, megasquirt 2 EFI setup gives as good if not better fuel consumption than my old nikki on a stock port 13b(if im driving normally ofcourse). My EFI allows me to run a lean mixture at low loads and revs and yet still be able to supply plenty of fuel at high revs and power output because I can tell the injectors precisely how much fuel I want going into the engine at different loads/rpm. This would not be possible with a carb setup such as a Weber as one would have to use large jets to allow for enough fuel at high revs which would make low rev/load fuel consumption horrible. Especially with the long intake stroke of the bridgeport which would be "sucking" a lot of fuel from the carb with each stroke. The efi counteracts this by only putting in enough fuel to achieve the desired mixture regardless of how long the intake stroke is.

 

What kind of power are you putting down with your setup?

Interesting reading for those who haven't taken the plunge:

The costs: https://www.rx7club.com/canadian-forum-42/real-costs-my-itb-set-up-661987/

This and that: https://www.rx7club.com/canadian-forum-42/itbs-ftw-648413/

 

Still breaking in my engine. Should have it done by end of this week and then im just going to get the tune perfect. Will post the results once I get it dynoed. What are you getting on your setup?

 

It still stands that carburetors get better atomization.

Part of the problem with rotaries is that the fuel injectors are huge. A ~150hp engine has no business needing four 42lb injectors. That's just nuts. It'd be better off (but more difficult to do on the software level, probably) to run some nice, small, let's say 19lb-hr injectors for the primaries so the pulsewidths are longer and the atomization is better. Mazda didn't do that and people in the aftermarket just seem horny to run massive giant injectors when they don't even need them.

I know I have 680s in my car right now... but I have only two of them, and they're still enough injector for my needs. My car makes just a little bit more power than a stock N/A I could go to quad 340s and see efficiency benefits. Most people making about my power are stuffing in TII injectors, or even GSL-SE injectors on the *secondary* side.

Note that Mazda *did* got to smaller injectors, and more of them, for the RX-8.

PS - I was getting 30-33mpg with the Nikki. (In Imperial gallons, that is about 36-40mpg) The trick was to drive it with the throttle right up against the secondary opening point. The primaries encountered a lean spot there. I haven't been able to get EFI to run as lean as I could with the carb, because the carb is a constant fuel scenario, the engine is fasically getting air with a fog of gasoline in it. With the EFI it is just a stuttering blorf of fuel and the combustion ends up being less stable. (Yes, I do have the air bleeds functional)

As least, that's my thinking for why I can't get my engine to run well leaner than 14:1 AFR.

 

pretty much any stock ecu 80's car is setup to provide enough fuel for wot+full rich coolant correction and still be under 80-85% duty cycle. that means when its warmed up, its only running 60% or so.

newer cars like the bmw's, and the 09 rx8, limit revs when the engine is cold, so they do not have to run full revs with full coolant corrections.

i agree, its hard to get it to run leaner than 15:1. its probably doable, things like injector phasing, maybe smaller injectors etc would help.

 

That's about all they do and offcourse they are cheaper!

 

SOME carbs get better atomisation.