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PostPosted: Sun Jan 17, 2010 2:24 am 
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How To - Dual Carb VTEC Mini-Me

This how to is a description on how to build a VTEC Mini, on OEM Duel carbs! it can be a cheap mod, with one of the best "Bang for Buck" mods!

Whats this mod in a Nutshell? Putting a VTEC cylinder head, on a Non VTEC Block, the VTEC Heads flow better aswell as provide a compression bump, with the added power increase of VTEC, it also uses the OEM D14a1 Dual carbs, for added simplicity!

Why? Because Carbs are cool! and you can also laugh at 100's of people at car shows saying, "VTEC Cant work and carbs and needs an ECU", What do they know :wink: , its also very simple to maintain, and with no ECU Involved, no worries of expensive tuning!

How VTEC Works! in simple terms, VTEC is a Solenoid Valve, which Opens with it receives a 12v Signal, This in turn lets oil into a seperate passway in the rocker assembly, which pushs, and locks Pins into the Inlet Rocker assembly, locking the rockers to the center rocker, to which the VTEC Lobe sits on, this in turn creates the longer duration and lift, on a Typical VTEC Car, the ECU Sends the signal, but in simple terms, you can set up a simple 12v button or switch to engage VTEC.

So, Down to business...

You will need.....

VTEC Head
Headgasket
Timing Belt
Adjustable Cam Gear
Electronic Fuel Pump
VTEC Switch

Explanations...

VTEC Head, D16z6 ones are the easiest to find! can be picked up pretty cheap to! i would recommend changing the Valve Stem Seals whilst the heads off the engine.

Headgasket, Must be matched to the Head, a D16z6 one will be fine! however, you can go for, i think, a D16y7 or D16y8 Headgasket, as this is the Thinnest D Series gasket (Unless you go for a Cometic etc - Expensive)

Timing Belt, The VTEC head sits higher than a normal Non VTEC head, therefore, the normal timing belt (D14 for example), wont be long enough to use! it "can" be done, but it will make the belt too tight, and stress and decrease the life of the belt, match the Belt to the Head! Buy a brand new one!!

Adjustable Cam Gear, when the Engine is all back together, and with the increased Height of the engine, even when timed up the cam timing will be out slightly, its only a few degrees, but its worth it

Electronic Fuel Pump, Dual carb engines such as the D14a1, run the fuel pump off the cam, and with VTEC engines being Fuel Injection, they usually run a pump inside the tank and high pressure, therefore do not run a pump off the cam! so youll need an electronic fuel pump to get fuel to the engine, you will need an In-Line pump, rated for a maximum of 5psi, a Facet-Posi-Flo is perfect for this! (Rated 1-4psi, ~£35), also, these type of pumps are noisy

VTEC Switch, the Easiest way to do this, would be a simple 12v Circuit off a switch, BUT! i highly recommend a Buddy Club V-Con! Why? its RPM Activated and adjustable and its easy to wire in and can be had cheap! (around ~£40)

Other bits that are not essential, but i recommend...

Fuel Pressure Regulator, an In-Line pump "pulses" so to speak, and this can cause a hunting idle, aswell as hesitation and float bowl over-flow, which can cause performance and MPG Issues, a Cheap one will suffice! Usually around ~£20 on ebay (Usually rated 1-5psi)

Fuel Pressure Gauge, This is isnt really needed, but you can monitor the regulator and pump with this! (Around ~£10 off eBay)

New Tensior and Water Pump, Why not, its so easy to change whilst the engine is in bits! Save you a few headaches down the road.

VTEC Stickers, Because VTEC Stickers make you cool!


Now, the build! Pretty strait forward if youve done a headgasket before, take the head off, remove bottom pulley, timing belt etc!

Now, once the old head is off, there is a small Oil jet between cylinders 2 and 3 on the Inlet side, this NEEDS to be removed! this is VITAL! Why? VTEC Heads have this jet internal in the head, and having Both jets would possibly starve the oil feed to the head! REMEMBER TO REMOVE THE JET! (Jet Circled Below)
Image

Now, just simply re-assemble the engine, you "may" need to remove some studs on the inlet side to allow the carbs to bolt up to the head, also fit new tensioner and water pump if you got one!

Remember to fit the adjustable pulley and time the engine correctly according to an OEM Manual (Most D Series time up the same), Once timed up, you need to adjust the Pulley to i think its 4 Degrees retard
Image

Now, the Distributer, a D14a1 Dual Vacuum Dizzy will not bolt up to a Z6 Head, you need to Extend and Widenen the holes on the Dizzy, Because of the Cam Timing Advance, the Ignition timing needs some more advance also! Below is a Diagram of what to do, and an example!
Image
Image

Next, Wiring up VTEC, Buddy Club V-Con, cheap, easy to wire up! looks like so, The VTEC Solenoid only has 1 Wire, 12V Signal Wire (Solenoid Earths through the engine)
Image
Image
Image

Fuel setup, most Inline Fuel pumps have a chart explaning were to locate the pump, with the Facet-Posi flow, it needs to be located near the tank!, Its best to put the pump in-place of the OEM Fuel filter (Located behind the RTA on the passenger side), its then best to mount any Regulators and guages on the engine bay itself so it can be easily adjusted and monitored.
Image

When Re-fitting the choke and throttle cable, it will be a tight fit and will rub on the rocker cover, but i ran it for ages like this, ran fine! i eventually Re-Routed the Choke cable to hide it out of sight.
Image
Image


End Result?

Image
http://www.youtube.com/watch?v=NtFVZN_SM38

Just FYI! The engine pictured and Documented is a JDM D15b Block with a D16z6 Head! i later changed to a Complete D16z6, although this How-To can be used as a reference!

Another thing to add! is people seem to be confused how carbs work, and people worry that they may, "lean out" at VTEC Crossover, OEM Dual Carbs overfuel ALOT, and they are limited to the maximum amount of fuel and air it pulls through, by the Main Jet, Needle Jet and Spring Pressure (I pulled a Dead, Flat 12.0AFR on WOT - Ideally around 13.8 for Max Power)

Carbs work on a Need for Need Basis, When the engine demands more fuel and air, the carbs will delivered, hense carbs are self adjusting for fuel (similar to the 02 Sensors sending infomation if the engine needs for fuel or air), but as above, are limited to what they can perform (or in OEM Setup case, to much fuel)

Any questions? Just ask!

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1988 RT4WD Shuttle - Supercharged, VTEC Swapped Track Toy.
1988 RT4WD Shuttle - Lifted Daily Beater.


Last edited by Gizmo on Sun Jan 17, 2010 12:36 pm, edited 2 times in total.

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PostPosted: Sun Jan 17, 2010 2:28 am 
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Just spent 2 Hours on this, i evem went through my old threads to dig out the Photos!

Enjoy!

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1988 RT4WD Shuttle - Lifted Daily Beater.


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PostPosted: Sun Jan 17, 2010 10:12 am 
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Thats somewhat impressive, And i am very much tempted, as like you say, its cheap bang for buck.... I think i need a little more research before i go crazy on it though 8)

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PostPosted: Sun Jan 17, 2010 11:21 am 
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Great write up Gizmo,

Its also worth noting down that to set the igntion timing and cam timing up properly you will need a timing light.

Your carbs will also more than likely need to be re-tuned afterward.

Although the tuning is "easier" on the fueling the ignition isnt so easy, as you have 2 different profiles on the cam, the lobe peak differs from on and off vtec. now you can just set the dizzy on tick over and leave it, but this wont be best interms of performance, on ECU controlled vtec system, the ecu changes the advance and retard of the timing dependent on wether its on or off vtec, how ar the throttle is open and what rpm its at.

Now yes this set up uses a vac advance dizzy but it only advances/retards a minimal amount for starting and running, not for cam lobe changing and performance.

For the best results a dyno tuning session is the only way to actually set the timing up to work well. how ever you are not going to get the best of both worlds ie it wont be perfect out of vtec and in vtec. as there isnt enough scope on the stock dizzy to do this.

I did this a few years ago now and it was a great fun project and very different, + with this setup there is alot more scope for the future.

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PostPosted: Sun Jan 17, 2010 12:30 pm 
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Cheers daz.

I was speaking to a good friend last nite regarding the carbs, and the trouble i had tuning them regards to overfuelling.

As a result, im taking my carb tuning research into new depths, once i get the LM-1 Wideband, ill be able to test these ideas out my on current GL, and hopefully see what can be done in regards to the fuelling.

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1988 RT4WD Shuttle - Supercharged, VTEC Swapped Track Toy.
1988 RT4WD Shuttle - Lifted Daily Beater.


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PostPosted: Sun Jan 17, 2010 12:38 pm 
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So does it run okey ? or is it abit dodgy ?


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PostPosted: Sun Jan 17, 2010 12:39 pm 
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Runs fine, see the video :)

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1988 RT4WD Shuttle - Lifted Daily Beater.


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PostPosted: Sun Jan 17, 2010 2:05 pm 
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i miss that vtec ef :cry: :cry:
sell it me back giz :oops:

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PostPosted: Sun Jan 17, 2010 3:13 pm 
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does it matter what head you use i.e D16z6,D16y8

Can it be a 1.5 vtec head??

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PostPosted: Sun Jan 17, 2010 3:32 pm 
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Colin_D13B wrote:
does it matter what head you use i.e D16z6,D16y8

Can it be a 1.5 vtec head??


best use a 1.6
z6 was used in this project
i think some yanks use the y8, but dont quote me

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PostPosted: Sun Jan 17, 2010 3:51 pm 
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meandmejulie wrote:
Colin_D13B wrote:
does it matter what head you use i.e D16z6,D16y8

Can it be a 1.5 vtec head??


best use a 1.6
z6 was used in this project
i think some yanks use the y8, but dont quote me


yeah thats true i was researching an saw alot using the y8
i was offered a 1.5 sohc vtec head but i was unsure whether to take it or not :?

Just gathering the bits now
and then i can begin :D

hopefully going to surprise a few at the drag day coming up :roll:

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PostPosted: Sun Jan 17, 2010 6:48 pm 
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Gizmo wrote:
Cheers daz.

I was speaking to a good friend last nite regarding the carbs, and the trouble i had tuning them regards to overfuelling.

As a result, im taking my carb tuning research into new depths, once i get the LM-1 Wideband, ill be able to test these ideas out my on current GL, and hopefully see what can be done in regards to the fuelling.


Yeah deffo, We will be meeting up soon enough any way when i collect those parts so we can have a good chat and if its on the road spend some time tuning it together.

I have a huge amount of data from when we did ours, and tuning Nicks d16a6 as well which i will bring so it should give you something extra to go with it, I just dont have the time for development of these proects any more and will happily help in any way for continued growth. I also have a tuning kit i put together for tuning the honda carb set up. Which i can bring up as well you can borrow it for a while.

Being able to actually data log the RPM and AR at the same time is invaluable as they change so fast you can never get a good eyes reading on the road.

big :top: for carrying on with it.

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PostPosted: Sun Jan 17, 2010 6:59 pm 
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Cheers daz, just love the carbs!

Daz, any idea of the Main jets are adjustable when you remove the float bowls? my mate has gave me the name of a company that custom grinds Needle jets (and seeing as i have the specs of a few sets of needles already, should be simples!)

We also came to the conclusion of the Carb springs (the mod which i didnt think worked...) and came to a conclusion around them, and instead of 1 coil, perhaps 2 or 3 coils lopped off (again, i have 2-3 sets which ill cut down and test with the LM-1)

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1988 RT4WD Shuttle - Lifted Daily Beater.


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PostPosted: Sun Jan 17, 2010 9:13 pm 
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With regards to cutting the springs, the more you cut off the less resistance the slide will have so theoretically the better throttle response you will have, I always used to remove 3 coils off the spring any way. There will be a point where to much resistance can be removed and this will result in the slide raising and falling to fast and running lean.

After a breif conversation with Nick earlier on today I am probably getting his 4G4D so may be tinkering with that :lol:

Daz

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PostPosted: Sun Jan 17, 2010 9:18 pm 
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Well, we came to the conclusion with the Springs.

For example.

OEM Springs at WOT, the Piston would be fully open at 1500rpm, then for example, if we cut one ring of the spring and stretch to same lenth, it would fully open at 1800rpm and so on....

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1988 RT4WD Shuttle - Lifted Daily Beater.


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