# Downdraft carb challenge: MK1 Rabbit 1.8 16v



## NSH57 (Jul 6, 2011)

I'm deep into this project right now... and about to fab up a custom intake and header for the 16v in my 81 Rabbit. This thread shows a bit more about the car http://forums.vwvortex.com/showthread.php?5396991-The-penny-squeezer-rabbit-build!!!

Hopefully pics will be coming soon!

The plan is to remove all old computer connections except for gauge senders. The distributor will be fired off by an MSD box, and will also be used to control the advance curve. 

I'm using a downdraft 2 barrel carb that flows about 200 cfm. I'm hoping this will be adequate for the 16v. 

I am open to any input or opinions on this setup.


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## vwpat (Oct 25, 2000)

According to the formula, a 200 cfm would be fine but in practice a much larger carb would be needed. The problem on a 16V is where it sits and sticks up through the hood that is why most people use sidedrafts. You can run it on your injection without "electronics" especially if you use a rocco intake, use rocco 16v fuel lines, mount the WUR on the side of the head. Make sure you have the larger (80mm) sensor plate. It would be easier to just get a raceland header rather than fab your own but if you have the skills...
edit: and use a saab 900 8v dizzy. Best I remember it is 82-85 and your stock TCi-h harness will plug in.


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## NSH57 (Jul 6, 2011)

Do you know what a "good" cfm rating would be? I think I have the height thing figured out so I won't have to cut the hood. I'm fabbing my own intake to make this happen, as I don't have any other parts to fit, or $ to buy them. If I make my own stuff, it's much much cheaper.

And excuse my lack of knowledge... but what is WUR? 
I'm planning on using the stock dizzy with a MSD ignition box. I don't have any wiring harnesses to use.


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## vwpat (Oct 25, 2000)

I would say close to 600, that is about what dual sidedrafts flow I think. Sam used a Holley 4 bbl 600 or 650 on his one time. warm up regulator (control pressure regulator) bolts to the front of the 8V block. Will MSD control the stock knock sensor 16V dizzy? I meant the 8V harness that is in the Rabbit.


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## NSH57 (Jul 6, 2011)

I shouldn't need a warm up regulator (using a cable choke) and the msd box accepts the hal signal from the dizzy, and will also give it an adjustable advance curve. It's the new programmable 6al-2 box. I think I should be able to tune it and run without a knock sensor, as I will be tuning it on a chassis dyno that I happen to have access to.


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## vwpat (Oct 25, 2000)

The WUR was only if you kept CIS.:thumbup:


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## NSH57 (Jul 6, 2011)

Here's the pics... 

First the old block.


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## NSH57 (Jul 6, 2011)

The intake flange is finished, and I started work on the runners tonight. It's a little snug, but they should go just fine. Plans are to try to keep them as equal length as possible. Carb mocked up at the height that should work, and it looks like it will squeeze under the hood.


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## L33t A2 (Aug 5, 2003)

*FV-QR*

I dont think fuel is going to like dripping down and then fight gravity to go back up to the head, especially at idle. Down drafts are meant to be fully above the intake port...


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## NSH57 (Jul 6, 2011)

L33t A2, 
I've been worried about this from the beginning, and I have a backup plan in mind if it doesn't work. But I'm going to try it and see where it goes. 

Here's a little more progress. It sure is hardto get things done only working on it a few hours a week.


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## antichristonwheels (Jun 14, 2001)

what carb is that?


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## NSH57 (Jul 6, 2011)

I figured someone would be asking about the carb... it's a Holley 94. Popular on Ford vehicles from 1938 to the mid 50's. I know it's an odd choice, but I have tons of them laying around.


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## oopseyesharted (Mar 2, 2005)

this is very cool!!!


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## Swallow Tail (Sep 4, 2012)

It will work. Chrysler had a dual crossflow manifold that put the carbs outside the valve covers and lower than the covers to clear the hoods. 

Did you make the intake flange? What size tubing are you using.


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## NSH57 (Jul 6, 2011)

Swallow Tail said:


> It will work. Chrysley had a dual crossflow manifold that put the carbs outside the valve covers and lower than the covers to clear the hoods.
> 
> Did you make the intake flange? What size tubing are you using.



Yeah, the intake flange is 1/4" thick stainless, and I used a plasma to cut it. The tubes are 1 5/8" diameter 16 gauge stainless as well. I'm in the process of building a header out of the same materials.


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## Bootlegger213 (Jul 29, 2012)

Very cool ill be watching

_Posted via *Topify* using Android_


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## pistol-mcgee (Sep 20, 2011)

NSH57 said:


> Yeah, the intake flange is 1/4" thick stainless, and I used a plasma to cut it. The tubes are 1 5/8" diameter 16 gauge stainless as well. I'm in the process of building a header out of the same materials.


is 1/4" thick enough to not warp when cutting with plas or welding on it? I figured that thing would turn into a wave being so thin.


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## NSH57 (Jul 6, 2011)

Here's a bit more progress. Intake is all welded and finished, and carb rebuilt. I also wired up the MSD box and dumped a little fuel in the carb to see what happened. It fired up for a few seconds  so now it's on to building the header. And removing all the extra wiring that won't be used anymore.


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## NSH57 (Jul 6, 2011)

So I had 2 hours tonight to start on the header, and I feel I've already made decent progress. The header is much simpler and straightforward on design. Same size tubing and flanges as intake.


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## NSH57 (Jul 6, 2011)

pistol-mcgee said:


> is 1/4" thick enough to not warp when cutting with plas or welding on it? I figured that thing would turn into a wave being so thin.


I've never had any 1/4" plate warp when plasma cutting for flanges. (I've make dozens of intakes and headers) I have had problems with warping when welding though. You have to go REAL slow and check the flange often when doing this. Whenever I have one that warps, I just face it on the mill after I'm done. 

I do have concerns about the heat on the header side. I don't know anything about exhaust temps on these motors. Anyone know?


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## NSH57 (Jul 6, 2011)

Progress.


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## Antikrist~86CGT~ (Mar 24, 2009)

This is so fukkin awesome.. :thumbup::thumbup:umpkin:


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## NSH57 (Jul 6, 2011)

Alright guys... I need some input. I need the distributor advance curve points or graph for the 16v engine. The header is done and I finished the fuel system and wiring this weekend. It fired up, ran, and even idled down pretty good.  I haven't searched lately for the curve info, but I looked a bit earlier in the project and didn't find much.


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## NSH57 (Jul 6, 2011)

Here's the fuel pump I went with... I removed the stock pump and accumulator, and used the stock line to the engine to keep it simple. It's a Carter electric that only runs 6 psi.


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## NSH57 (Jul 6, 2011)

Here's the advance curve I have so far. I am locked out at 30 degrees advance as 0 on the graph, so all points on the graph are retarding from there!

I'd really like some more input on the points between 1100 and 2800 rpm.


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## NSH57 (Jul 6, 2011)

Round 2. It's amazing what you THINK is going to work vs. what works in the real world. (I'm sure there will be revisions to this curve as well.)


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## vwscotty (Jun 1, 2012)

This is really cool! Cant wait to see more of this :thumbup:


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## NSH57 (Jul 6, 2011)

Ok... so it has been all winter, and I haven't done much till last week. 

Here she is ready to roll. (I'm sure I'll still be working out bugs for a while, but I have about 100 miles on her so far.)






And after the engine was under load on the road, the spark curve got modified again. Sometimes simplifying it works better... so far it pulls pretty strong.
I've been doing a bunch of different styles of driving and pulling plugs to read them for mixture. A little lean at first, but the 2 barrel Holley 94 with #57 jets has been working quite well. I have a diesel geared 5 speed trans, and it pulls harder than my 84 GTI in every gear. I think I can tune out some more power, but time will tell.

I'll be running it on the dyno soon and I'll post some numbers.

(Remember... 0 on the chart is 30 degrees advance and the chart numbers are subtracted from 30.)


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## Lowenough (Dec 6, 2010)

Is that air filter custom or something you bought? I am looking for very slim filters for my bike carbed 16v.


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## NSH57 (Jul 6, 2011)

Filters are bought from this place...(I am into early 30's Fords)
They are a little pricey, but very thin and work decent.

http://macsautoparts.com/early-v8-ford-mercury-air-cleaners-filters/camid/F30/cc/548/


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## NSH57 (Jul 6, 2011)

Quick Update...
350+ miles with no troubles. Noticed the odometer was stopping for a few miles every once in a while, but still the last tank was 32 mpg. So after that is fixed, I'll see how it does.


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## Italian308 (Sep 15, 2010)

Any video of this running. I would like to hear it. Nice build btw


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## CantKillDaWabbit (Jun 5, 2011)

Looks great!! Cool to see it with a different motor!


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## NSH57 (Jul 6, 2011)

It's time to move on to other projects so this one's going up for sale!

Here: http://forums.vwvortex.com/showthread.php?8159049-FS-1981-Rabbit-16v-5speed


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