winter project - dual carb manx engine

[Lee.C]

well guys I thought it was about time I moved this thread over here in to "in da werks" 

Now I LOVE the looks and performance of my little 1641 old skool motor, its an AWSOME little motor, its starts first time every time, Sounds AWSOME (read as stupidly noisey ) and goes pretty well for a single carbed motor - she'll do a 100mph FULLY LOADED!

here are the specs at the moment:

AS21 case - full flow oiling
69mm counterweighted crank with lightened and balanced rods
87mm barrells and pistons
Engle 100 cam
Stock dual port heads 040's with stock valves (slightly ported to remove all the sharp corners)
32mm oil pump (race trim)
deep sump (race trim)
Boosh 009 dizzy with electronic ignition kit (30degs)
8mm silicon leads 
Power pulley (smaller 356 diameter)
Lightened and balanced and 8 dowelled 200mm flywheel
"Bolt up" rocker sharfts with swivel feet adjusters
Cromoloy pushrods
Straight cut timing gears
DDS center mount "RAM" type manifold with a single Weber40dcn14 Carb (with 24mm venturi's) the two end piece's of the manifold although stock have been heavily ported,

and all this little lot revs to about 5500rpm with the bulk of its power from 2700 - 5300

But as I have been talking about in other threads this little motor is VERY noisey and not very good on MPG (as low as 15 mpg )

So the first thing I am planning on is a full merged header and a single quiet pack - like my friend robs  Now the second is a little more complicated - Dual carbs 

I am planning on fitting a pair of weber 40dcn's (the same as the single I use at the moment) on a pair of old skool Race trim manifolds  along with an Original DDS linkage BUT there is a slight problem you see the body work on the back my manx won't allow me to use "standard length" manifolds so I am SHORTENING them 

So far I have had the machine shop make some new top plates for the new SHORT manifolds - I should have the manifolds next week and I will post some pic's as soon as I get them home.

I am planning on using 28 vents / 135 to 140 main / 200 air / f24 emulsion tube and 55 idles,

I am also moving the timing up to 32 degs and fitting 1.25' Rockers

So guys what are your thought 

[roland]

fun engine indeed! New plan sounds great, love the custom manifolds...

[Lee.C]

fun engine indeed! New plan sounds great, love the custom manifolds...

I forgot I let you drive it - fun ain't she  oh yeah I sorted out the play in the throttle pedal now 

I'm not going to work out just how much these manifolds will end up costing me but hey its only money  and they will be soooooo cool when they are done 

[vwcab]

Fun project,show us the pic's when the monifolds are ready.

[wolfswest]

nice, I will follow this topic!  Let the pictures and stories coming!

[thehanz DVK]

are type 3 manifolds from berg an option here ?? they are a lot lower..

[j-f]

Hope to see and hear again your Manx with the new improvements  Lee. 

I still remember the noise it did when you play in the quarry in Norway   

It's just ridiculously fun 

But, why not raise the compression ratio? If it is still at original specs, it should be good to raise it, no?  And why not put a set of 1.25 rockers?
As the rest of the engine is well built, why not try to exploit it?

If you want some advice for the MPG, I can help you  ( Do you remember the gas I use during SCC trip? I have translate to UK MPG and it's about 43miles per gallon  6.5l/100  )

[Lee.C]

are type 3 manifolds from berg an option here ?? they are a lot lower..

Na they are not an option as they are NOT Race Trim  

And thanks for the comments JF I had forgoten about the quarry - now that was fun  I will let you have a drive next time 

As for the engine I am already planning on 1.25's (Richie has a set for me  ) And I hope he is going to help me set them up so I will ask him about compression - I can get the heads fly cut at a local macine shop if needed 

I can't believe you were getting 43 mpg  I worked mine out "roughly" and it was somewhere between 15-20mpg 

[j-f]

I will let you have a drive next time

Can't wait and thanks guy

I can't believe you were getting 43 mpg

Stock engine and long ratio gearbox. 

[nicolas]

good you have the parts then. the raising off the CR is an option, but you allready run an external cooler don't you? then go easy on it as it can heat up too much.

the manifolds could come out nice. that will be great to see as well.

hope to see a before and after difference.
btw what 1/4 times do you have now with this setup? 

[Lee.C]

good you have the parts then. the raising off the CR is an option, but you allready run an external cooler don't you? then go easy on it as it can heat up too much.

the manifolds could come out nice. that will be great to see as well.

hope to see a before and after difference.
btw what 1/4 times do you have now with this setup? 

Hey dude - yep I almost have all the parts, my dds linkage turned up yesterday - I still have to get the venturi's and a few other little bits but I am nearly there 

As for the c/r - its just an idea - also I could quite easily run without the cooler so heat shouldn't be a big problem - The manifolds should be done in a week or so.

As for 1/4 mile times - I would be happy with low 15's (maybe a 14.99 )

[j-f]

I don't think that raise CR in a reasonable way will make the engine run hotter, if it's correctly tune.
The 1500s run a little more CR than the other VW engine without problems and have 5 more HP  (That's about 10% more hp  )

When I buy parts to built my 1600cc, the guy said me that if I don't raise the CR at 8 to 8.5 and with a deck height at 1 to 1.5mm with an W110, I will not have a correct combustion. It will run and well but I will not have all the benefits of what the engine can do. 
He explain me why, but I don't understand   
 

[Zach Gomulka]

When I buy parts to built my 1600cc, the guy said me that if I don't raise the CR at 8 to 8.5 and with a deck height at 1 to 1.5mm with an W110, I will not have a correct combustion. It will run and well but I will not have all the benefits of what the engine can do. 
He explain me why, but I don't understand   
 

He was right!
Lee, when you open it up, set your deck height to .040" and your compression to 8:1.

[Lee.C]

Looks like the heads are comin off then 

[Jim Ratto]

Looking at your venturi size, your main jet predictions are too rich. You don't need such a big main with those 28mm.
Try 115-120.

 

[Lee.C]

Looking at your venturi size, your main jet predictions are too rich. You don't need such a big main with those 28mm.
Try 115-120.

 

Here is the sugested base settings from Nicolas:

"i looked up what size jets you could use as a starting point for dual carb setup on a 1641

28 vents / 135 to 140 main / 200 air / f24 emulsion tube (on a DCNF42 there is a f25) / 55 idle (usually on a IDF a 50 works well) / squirters are 50"

So you think I should go for 115/120's instead of the 135/140's - correct

[Jim Ratto]

yeah, I'll tell you why.
I was told a long time ago that small motors running Webers "sometimes" needed big jets, in order to have carburetors "feel" what the little engine wants. It made sense... big 44, 45, 48mm carbs on a 1800cc or smaller motor isn't going to make the air speed and "pull" through circuits like on a big 2300cc motor, or like smaller carbs on big or small motor. Your 1641 with 28mm venturis should still have good air speed, so no reason really, to hang big main jets in there. The smaller jets will come in nicely at a lower rpm just fine. I actually thought a friend's 1776 was going to need big fat mains too, this was back in 1994 or 1995... it was a low CR 1776, stock cam, stock valve diameter, light port work, 1.25 ratio rockers, dual 40IDF with 28mm vents. I thought what I had heard about jetting a smaller motor applied universally across the board and screwed in 130 or 135 mains and told the guy "should run great"... which it didn't, it had poor power and was very soft. My friend said it had no pulling power in the mid or high rpm, like getting on the freeway. I couldn't figure out why, except that we put a stock cam in it. For some reason, my friend tried different main jets and went down to 120's I think and it came to life and made nice power, good mpg, good repsonse.
135-140 are better suited to a 34-36mm vent.
But of course, it is best to tune it and test it under real conditions.

[Lee.C]

Hmmm interesting - that does go along with ther other "rule" I have heard which is that the mains should be roughly 4 times the vent size ie 28x4=112 so 115's sound perfect

[Jim Ratto]

Hmmm interesting - that does go along with ther other "rule" I have heard which is that the mains should be roughly 4 times the vent size ie 28x4=112 so 115's sound perfect

I guess.... yeah. But those calculations are just so books can be published about "how to do it"
too many variables.

[Lee.C]

Hmmm interesting - that does go along with ther other "rule" I have heard which is that the mains should be roughly 4 times the vent size ie 28x4=112 so 115's sound perfect

I guess.... yeah. But those calculations are just so books can be published about "how to do it"
too many variables.

Yeah I know dude I was only given it as a very rough guide - I am gonna get some 115/120/130/135/140's then I can play around all I want.

What "Air corrections" would you put with the 115/120's

[Lee.C]

Just got of interest huys here what was in the "Single" 

50 idles - 160 Air correcton - 140 mains and F38 emulsion tubes - Any thoughts

[Jim Ratto]

Just got of interest huys here what was in the "Single" 

50 idles - 160 Air correcton - 140 mains and F38 emulsion tubes - Any thoughts

what chokes were in your single carb?

[Lee.C]

Just got of interest huys here what was in the "Single" 

50 idles - 160 Air correcton - 140 mains and F38 emulsion tubes - Any thoughts

what chokes were in your single carb?

a couple of 24's that I polished up

[nicolas]

i would go 200 on the air or maybe 180 but not lower.

[Lee.C]

I already post a pic of these but they are just soooooooo cool I had to put them in here too

I already had one of these COOL Race Trim Air boxes for "off roading" and I paid SILLY money for it a while back (black one) And then late last night before I went to bed I thought "I'll have a quick look on ebay" then about an hour later I found THIS! (grey one) a second race trim air box! it wasn't listed very well so at about 5pm today I won it for a grand total $38.00

Now I have a pair for my new dual carb set up - HOW COOL!?

[Diederick/DVK]

how cool!
congrats on the cheap steal

[beetletom]

cool!

will you have to modify then to fit the dcn's?

[Lee.C]

yep its gonna take a few mods but you know me I can make ANYTHING fit 

[beetletom]

ooh er 

any updates on the manifolds?

[j-f]

yep its gonna take a few mods but you know me I can make ANYTHING fit 

With a good hammer, everything fit 

Nice buy Lee.