Was ITB size for 2270 motor Now Single plenum 2270 Options

[cgnj]

I have been running 45 dells on 2270 with 34mm vents. Not sure if it was the cam choice (163/86b0, but it was much easier to drive with than with the 38/39 vents.

I was going to gut my spare dells for this project, but I think they are worth more in the box.

So, for street 2270 what size motorcycle from wich bike tb should I be looking at for a first build?

Thanks in advance,
Carlos

[DBCooper]

Talk with Mark Henry, who has bike ITB's on one of his motors. I have some GSXR1000 throttle bodies in a box somewhere, which are either 38 or 42 mm, but never used them in favor of a single TB. Thinking at the time was that bike's red line is twice what my 2270 was and throttle bodies don't have a venturi so they can move more air than a similarly sized carb, plus the injectors are already sized right. Sounds logical enough, but MH has direct experience.

[Mark Henry]

I'd look for something around 40mm, mine are 46mm, but I have a 2.6L engine.

You need to find an bike TB assembly that comes apart into 4 separate ITB's, late 90's GSXR are a common choice but there are others.

This is not a project for a beginner, you need access to a mill, lathe, welder etc..
Also if your time is money you might want to consider the CB TB's.


http://www.914world.com/bbs2/index.php?sho...p;#entry1862152

[cgnj]

Hi Mark

I was hoping you would chime in. I read your thread 3 times.

I guess my question is with the larger bores, the intake velocity slows. Is this a non issue with ITB's? Do we choke the bores of the carbs to compensate for an analog fuel delivery system? That would make sense to me. But I'm a dope. Ask my ex.

Carlos

[r_towle]

great to see the annual motorcycle ITB project will start.
I hope you document how you do it.

rich

[McMark]

ITBs that are too big will limit part throttle resolution. A small change in throttle makes a big change in air flow.

ITBs that are too small can choke off the top end.

I agree with Mark that 40s would probably be a good choice, but you could go up to 44. There probably isn't a distinct advantage to any size in that range, unless you're planning on dyno tuning everything and swapping ITB sizes to check everything.

[falcor75]

If you want something that goes in pretty easily get the ITB's sold by Mario at Thedubshop, they mount right onto a EMPI IDF intake, complete the kit with Tangerineracings Cable throttle kit and you'll have a nice setup.

I went with the 40 mm size for my stockish 2.0 but I have a spare 1,7 that I'll have built into a 2270 or 2316.

http://www.914world.com/bbs2/uploads_offsi...458131052.1.jpg

[Mark Henry]

Hi Mark

I was hoping you would chime in. I read your thread 3 times.

I guess my question is with the larger bores, the intake velocity slows. Is this a non issue with ITB's? Do we choke the bores of the carbs to compensate for an analog fuel delivery system? That would make sense to me. But I'm a dope. Ask my ex.

Carlos

Actually the choke in a carb the proper name is 'venturi' and what it does is it speeds up the air, creating a substantial turbulence to atomize the fuel for a proper burn. It also helps to suck the fuel from the carb (bowl) at a metered rate.
A fuel injection TB doesn't need this as the injector atomizes the pressurized fuel.

Search the venturi effect.

[aircooledtechguy]

As a general rule, you step one size DOWN for ITBs when switching from carbs. ITBs flow like crazy. I wouldn't go bigger than a 40mm. That said I have 45mm ITBs on my 2316cc and they are a bit too large. 42s would probably be more appropriate.

I second Mats suggestion of the ITBs from Mario (www.thedubshop.net) and Tangerine racing's cable linkage. The linkage is like butter and I havent touched it in 18 months (20K miles) and it was still spot-on 2 weeks ago when I checked with my flow meters. You'll NEVER say that abut X-bar or even twist style linkage.

[Mark Henry]

You'll NEVER say that abut X-bar or even twist style linkage.

I've never touched my center pull, but I did build it myself. Also never had to touch Gene Berg cross bar, but that's T1 only...just saying it can be done right, but rarely is. (IMG:style_emoticons/default/shades.gif)

[Alapone]

If you want something that goes in pretty easily get the ITB's sold by Mario at Thedubshop, they mount right onto a EMPI IDF intake, complete the kit with Tangerineracings Cable throttle kit and you'll have a nice setup.

I went with the 40 mm size for my stockish 2.0 but I have a spare 1,7 that I'll have built into a 2270 or 2316.

http://www.914world.com/bbs2/uploads_offsi...458131052.1.jpg

this is awesome.......valuable comment I know

[Mark Henry]

You know the one thing I would do if I had a T4 (your size, 2270) 914 again would be to modify a a D-jet intake for a single mustang 75mm TB. Then drive it and learn how to tune the FI system.


I know for sure it would be easier to tune and you could take your time building an ITB system for later while still driving.
I did this on my first build with a 2.0, mild cam and all stock intake (stock 914 TB). I admit it was the smoothest, most stock like operating system I've ever built.
Systems...I've done a few stock engines like this.

I know Jake doesn't like a single because you lose some HP, but to me sometimes it's worth it.

Programmable FI is a steep learning curve and it would be one less thing in the mix while you are learning.

[McMark]

(IMG:style_emoticons/default/agree.gif) Single TB intakes are more friendly.

[cgnj]

You know the one thing I would do if I had a T4 (your size, 2270) 914 again would be to modify a a D-jet intake for a single mustang 75mm TB. Then drive it and learn how to tune the FI system.


I know for sure it would be easier to tune and you could take your time building an ITB system for later while still driving.
I did this on my first build with a 2.0, mild cam and all stock intake (stock 914 TB). I admit it was the smoothest, most stock like operating system I've ever built.
Systems...I've done a few stock engines like this.

I know Jake doesn't like a single because you lose some HP, but to me sometimes it's worth it.

Programmable FI is a steep learning curve and it would be one less thing in the mix while you are learning.

Mark,

I have kicked this around also.
Mustang MAF, 1.8 914 or 2.0 bus plenum, 944 throttle body. Upsides is that I would only have to source the MAF.

Carlos

[colingreene]

its not a non issue but its less of a issue because the throttle is not depending on air speed for mixing fuel the injector atomizes it for you.

you likely want anything you can find in a 40-46

[Mark Henry]

I have kicked this around also.
Mustang MAF, 1.8 914 or 2.0 bus plenum, 944 throttle body. Upsides is that I would only have to source the MAF.

Carlos

Why do you need a MAF? are you trying to mod an L-jet system?

Most aftermarket systems use a MAP sensor and this is what causes issues with low vacuum, hot cam, ITB engines.
Simplified explanation is this causes issues with low MAP signal resolution resulting is a bad accel curve.

[cgnj]

[quote name='Mark Henry' date='Mar 16 2016, 11:25 AM' post='2316528']

[/quote]

Why do you need a MAF? are you trying to mod an L-jet system?

Most aftermarket systems use a MAP sensor and this is what causes issues with low vacuum, hot cam, ITB engines.
Simplified explanation is this causes issues with low MAP signal resolution resulting is a bad accel curve.
[/quote]

MS will do heated wire MAF which would take care MAP resolution problems with cam.

My big valve heads were made on a 1.8 casting. I still have 4 bolts intake setup, so I have to use 1.8 runners.

Using a 1.8 or 2.0 bus plenum will allow room to install the MAF, since the throttle body is on the side instead of the top.

I reread your post and a 75 mm mustang throtte body seems huge.

Carlos

[r_towle]

humor me please,

a 40mm weber or dell gets sized down to 34mm with the venturi.
ignoring the reason, to get the fuel to atomize better, the net result is still a 34 mm hole letting air into the intake, not a 40mm hole.

So, why would a 40mm hole work fine (magically) for a FI system?
The air charge will now be slower.
I understand the fuel atomization is no longer an issue, and its not what I am talking about here...its purely the volume and speed of the air.

I know the motor will only take what it needs for air, that is reality.
Would it not work fine with 34mm ITB's?

I have a set of 40mm duel throttle bodies sitting here....the super long term project if i ever get up the nerve to do a programmable FI system.

Also, if I have say 46mm intake valves....wouldnt I want 46mm throttle bodies?

[DBCooper]

Well, air can be compressed, so it's temporarily squeezed through the 34mm venturi, but afterwards expands back to 40mm. Means that on either side of that 34mm venturi the air is flowing in a 40mm tube, same size tube as that 40mm throttle body, with the same velocity and volume.

And when that 46mm valve opens it doesn't get totally out of the way leaving an empty 46mm hole, there's still some obstruction there, so a 40mm throttle body can supply what's needed, and at a pretty nice velocity.

[gereed75]

I have been running 45 dells on 2270 with 34mm vents. Not sure if it was the cam choice (163/86b0, but it was much easier to drive with than with the 38/39 vents.

I was going to gut my spare dells for this project, but I think they are worth more in the box.

So, for street 2270 what size motorcycle from wich bike tb should I be looking at for a first build?

Thanks in advance,
Carlos

I suggest that you look at Al Ikosmal threads on pelican. http://forums.pelicanparts.com/911-engine-...fi-systems.html as one example

There are many other ITB threads over there and a few on the VW sites. The displacements from 911 to 914 are similar per clyinder so sizing will be somewhat comparable

I would not go against Marks knowledge and experience but I seem to recall that Al uses smaller ITB's with great success. His go to is from the triumph speed triple I think.

Check it out