Single port carb selection

[oilstain]

I am debating on using kadrons or center zenith.
The heads have 8:5 compression.
Engle 110 cam and lifters
C/w crank
S/s 1 3/8 header.

Any suggestions

Transaxle selection is either 4.37 or o 4.12 swing axle.

Need suggestions

[modnrod]

If you have yet to get either set up........

The centremount will "shake" a bit at idle, it will have a "cammy" note at the lights, the back of the car will slowly rock a bit.

The twin carbs will be smooth across the board, won't spit or splutter anywhere, and will get maybe 5% better economy and mid-range.

[hotrodsurplus]

The centremount will "shake" a bit at idle, it will have a "cammy" note at the lights, the back of the car will slowly rock a bit.

The twin carbs will be smooth across the board, won't spit or splutter anywhere, and will get maybe 5% better economy and mid-range.

What he said. I wouldn't exactly call a W110 with Kaduds smooth but it'll run a fair bit smoother than it would with the Zenith. Here are some other things to consider. It may sound as if I have something against the NDIX but I don't. I love them. They just have their application.

NDIX carburetors aren't exactly expensive to buy but they can get quite spendy to prepare. The brass throttle shafts wear. Replacements are available but they're not cheap. The manifold truly designed for an NDIX differs from the more common ones designed for the Holley Bug Spray. The true Bug Spray manifold mounts the carburetor very high and to the left of where it should go.

It's difficult if not impossible to route the throttle cable through the shroud and directly to the NDIX linkage when using the non-offset oil cooler. Most throttle cables met the linkage at painful angles. Many people eliminated the in-house cooler and drilled the tube hole where it needed to go. I have no experience with the NDIX on an offset-cooler (doghouse) engine. 

Manifold heat is a serious issue with any single-mount two-barrel carburetor if you live in an area that gets cool and damp. If not properly heated these carburetors ice like crazy. No header that I'm aware of routes the riser-heat tubes properly (from #2 to #4 is merely convenient but not as effective as routing from 2 or 4 to the collector). A few existed in the '70s and early '80s but I haven't seen one in probably 20 years. The limited contact area between the heat risers and the manifold tubes doesn't transfer heat well, either. A few people on Samba have modified the heat risers to heat the entire center of the manifold. Not difficult but time consuming. And they really work best if you run a preheat tube from under the cylinders to a bonnet over the air-filter housing. Heat is your friend.

The long intake-runner tubes damp the signal which diminishes response. The long tracts also give the fuel plenty of opportunity to fall from suspension during low-velocity applications (like anything slower than 3,500rpm on a small-displacement engine with a W110 cam).

The NDIX is nearly infinitely tunable. You can even alter the air bleeds in the idle circuit and they have a true high-speed enrichment circuit (activated by the accelerator plunger when the carburetor hits wide-open throttle). NDIX parts are getting a bit hard to find and have been expensive for some time. Unmodified NDIX jets are a bear to find.

Unless you stumble into an NDIX from an early Super (not likely) then you'll get more power out of the Kaduds. The Duds have 28mm venturis whereas the Normal NDIX has 24s. The Super NDIX has 28s but as noted they're not very common and expensive when you find them.

Kaduds are cheap and easy but their quality is questionable. The throttle-shaft bores wear out rapidly. Re-bushing the shaft bores isn't always a sure-fire fix as the butterfly often wears a groove into the throttle bore once the shaft bore wears out. That will make them impossible to achieve a sufficiently slow idle speed.

Single-port Kadud manifolds got quite valuable because we threw them all away in the '80s and '90s. Kadud linkage SUCKS. It's more responsible for their bad image than any other thing. Copy the linkage that Berg copied from Speedwell and they behave nicely (I have such a setup on a car right now).

Kaduds are easily modified for a vacuum-advance distributor. I recommend a combination mechanical/vacuum advance like from a '70-and-later car and use only the advance port on the vacuum canister. Leave the retard port open to the atmosphere.

Kadud jets are easy like Sunday morning. They're the same ones that all Solex PIC-series carburetors use and you can get mains from the local motorcycle shop (Mikuni is a Japanese Solex copy). 

That's not everything you need to know to make a truly informed decision but it's enough to make a reasonable one. Personally I'd run the Kaduds. They're not ice prone; they'll run smoother with that cam; they'll make better power than Normal NDIXs; their shorter runners really help throttle response; they're cheap and fun like two-dollar whores; they won't run you crazy looking for obsolete parts; you probably have a friend who has a set holding a door open. 

hope it helps.

c

[Zach Gomulka]

^^^ Bang on right there.
I loved my Zenith. If you don't want to mess with duals and your engine is mild, it's the way to go. Bolt on and go. I was lucky enough to get a box of jets when I found mine, so I really played around with the jetting a lot. Another thing, mileage isn't that impressive. I averaged 22-23 on my old original dual port engine. I also found a couple parts carbs, one from Ratto (a 28 vent Porsche carb) and the other (a 25 vent PO10) for $10 at the Vegas show. I tried the 28's but could not get them to run right, but the 25's worked well. I also removed the center brace in the carb top and had to richen up the mixture as a result of the increased air flow. It was a lot of fun and virtually maintenance free, I'd do it again but only because I've still got access to the jet box (sold all the bits to a friend).
Kads are great, too. Personally I'd keep the cam smaller than a 110, displacement under 1900cc. After that, dual 2 barrels REALLY wake the motor up. I've still got my first pair kicking around, just in case I find a nice stock car that needs some more pep. And I've never had the linkage issues that everyone seems to complain about

For the engine in question (1600cc??) I'd go Kadrons. Then eventually put some dual ports on it and 36 Dells, it will come alive! The motor is pretty narrow I bet considering the compression, you'll have some fun getting the one piece single port manifold to seal up without cutting it.

[hotrodsurplus]

Kads are great, too. Personally I'd keep the cam smaller than a 110, displacement under 1900cc.

That's a really relevant point. You haven't told us what displacement this engine is.

Bear in mind that cam timing is a tradeoff and you don't get something for nothing. Increasing the duration increases the engine's power potential at faster speeds but at the cost of low-speed performance. And even though it's mild by comparison, a W110 cam can really gut a small engine like a 1600. In fact nowadays I'd run something with less duration than a W110 even in a 1776.

But there's another thing in this particular case that is probably even more critical: your heads. I love single-port heads but only for the right application. And for me that application is stock. Simply put, they do not flow very well. Even with extensive port work they flow just a little bit more than what a stock dual-port head does. And those aren't screamers right out of the box.

Stock single-port heads can just barely feed a stock 1600. Volkswagen's engineers really earned their pay with that combo. The heads have a very hard time just trying to keep pace with one of those engines that spins any faster than stock. The 1-2-5/1600 and Class 9 and 11 engines get away with aggressive cam timing but they also run split-duration profiles (more intake duration and lift than exhaust), lots more compression ratio, and make their power in a really narrow speed range. They plain suck to drive on the street: you work tirelessly to keep them in their power band. They're on or off. And they idle like hell even at 1,200rpm. And you gotta feather the clutch to get them moving. I haven't driven a single port with a W110 but I can imagine that it's somewhat similar but with even poorer low-speed performance. Just a hunch.

Displacement only aggravates things. Increasing displacement has the same net effect of spinning the engine faster: it requires more port capacity. Which, as I've indicated, is likely to outpace a single-port head.

That's not to say that increasing displacement will make a single-port engine miserable. Quite the contrary: it will make the engine outright explosive the moment you release the clutch which is fun for a daily driver. In fact one of the strongest daily-driver engines I built was a single-port engine that was stone stock save for 90.5 bores. It would beat everything across the intersection. But as usual it's all a tradeoff: the engine landed on its face at about 4,000 to 4,500rpm. And that's about 1,000 to 1,500rpm short of where a W110 makes peak power.

If this were mine and it was a 1600 I'd keep the cam super-duper conservative (like only a touch more intake duration and stock exhaust duration) or even stock. If it were any larger I'd definitely run the stock cam and maybe ratio rockers. Don't underestimate the stock cam: its ramps are faster than many 'performance' cams and it has a respectable duration for what it is. A stock cam will make peak power at 5,000rpm if the rest of the engine is up to the task. And that's the key: the rest of the engine has to be up to it. A more aggressive cam will ask more of the rest of the engine at the cost of low-speed performance. 

I know you didn't intend to talk cam timing but it's absolutely critical to engine performance and it will make or break any engine and even crush a small one. Choose wisely.

[Martin S.]

One thing we tried with my 90.5 x 74 low compression (7:1) semi-hemi stock cam 1.25 rockers motor with stock dual port heads and kads, was to enlarge the crossover pipe that tied the two manifolds together. My engine guy Steve pointed out the size of cross over pipe that VW used on the T4 bus motors. Larger than the typical hose that comes with the Kad kit. He drilled out the bosses on the manifolds and added the larger metal pipe and it made a huge difference in smooth low end running. He said it was the first Kad motor he had seen that idled on all four cylinders.

[hotrodsurplus]

One thing we tried with my 90.5 x 74 low compression (7:1) semi-hemi stock cam 1.25 rockers motor with stock dual port heads and kads, was to enlarge the crossover pipe that tied the two manifolds together. My engine guy Steve pointed out the size of cross over pipe that VW used on the T4 bus motors. Larger than the typical hose that comes with the Kad kit. He drilled out the bosses on the manifolds and added the larger metal pipe and it made a huge difference in smooth low end running. He said it was the first Kad motor he had seen that idled on all four cylinders.

If the cam is stock and the butterflies fit properly then Kaduds really should idle beautifully right out of the box. I run a pair on a 1600 with a stock cam and 8.1 static and it idles better than it did when it was stone stock--it's downright fluffy.

Two things kill idle: poorly fitting shaft bushings which administer unmetered air and intake reversion created by greater-duration intake events. Closing the intake valve later (a consequence of greater duration) increases the opportunity for the piston to push the intake charge back up the port. Because cylinder 3's filling event follows 4 so closely (and 1 follows 2 so closely) the positive pressure that 4 and 2 create in their respective manifolds diminishes the negative-pressure signal that cylinders 3 and 1 need for the carburetor to administer fuel properly. So keeping the reversion to a minimum really creates the smoothest idle. Short of that, giving each cylinder its own venturi eliminates that crossover pressure interruption which makes a radical-cammed engine behave so much smoother at slower speeds.

[oilstain]

I have access to both items.
I got an early Empi manifold and zenith carb.

Also, picked up a pair of aluminum single port with 70s Berg linkage.
I got them from my travels.
It's amazing what you find at garage sales. 

By the way, the heads are for 90.5.
So engine could be 1679 or 1776 depending on piston selection.
This is part of a Autodynamic Hustler project. 
It looks like Lotus Elan.
It only weighs 1300 lbs somewhat light weight.
 

[hotrodsurplus]

Also, picked up a pair of aluminum single port with 70s Berg linkage.
I got them from my travels.
It's amazing what you find at garage sales. 

Aluminum Kadud single-port manifolds? Man that's a hell of a score. That and the Berg linkage make the Kadrons the inevitable choice for me. That will make a sweet setup. I have Berg linkage on my setup and it's wonderful.

By the way, the heads are for 90.5.
So engine could be 1679 or 1776 depending on piston selection.

So they're bored 97mm? If so you'd have a hell of a time finding 90.5mm bores with that register. They were super popular in the '70s and early '80s but they're quite uncommon now. Not impossible but uncommon. A 1680 with Kadrons would make a really good single-port combo with a stock cam or a high-lift cam with just a touch more intake duration and basically stock exhaust duration. And it would scream 1973. It would also outperform the same engine with the Zenith.

[oilstain]

I have noticed the new thick wall 88 pistons.
Suppose to fit 90.5 head but fit into a 85.5 case.
Anybody have any experience with them?

The cam selection is not set in stone.
I like the old school Norris type.
The 329 or 330 sound like they would do good
W/ dual Kduds. 

Another option might be a single carb kad.
I have read about Joel Mohr's Quik and Dirty.
Just thinking outside the box.

The Hustler has a small wheel area.
I can only use 13 or 14 wheels.
This brings up my next question.
Tranny selection?
With those size tires will 4.37 or the 4.12 r/p be better?
I have both the 8 hole 4.37 K.
And thing O 4.12 with gearing has 4th .93.

[brian e]

Not sure if this will help much, but here is a SP 1679 I finished late summer and have a few thousand miles on now.  Don't mind the ugly messy engine compartment.  Its my ugly daily beater.  I was shooting for a early 70's feel, and it was kind of an experement.  I used a 40mm DCNF, I did a bunch of home brew port work on the heads, 8.8cr, and a CB Bigfoot 2208 cam, and a 10lbs flywheel.   The cam is somewhat noisy, but it really rips right out of the hole, and then quits about 5200rpm.  With the compression (I live at 3300ft) and the light flywheel it revs really quick, and most riding in it are surprised how quick it is.  I added a real recirculating manifold heat tube tied into the collector, and when winter came, I had to added a stove pipe to the air cleaner.  It will pull the long 60mph grade on the way home in 4th all the way to the top, without dropping below 60mph.  Our 2.5 Outback cant even figure out what gear it wants to be in on that hill.   

I have a set of Kad's I really want to try.  I think it will make it even more snappy, and better in the cold.  I just need to build or find some manifolds. 

[brian e]

I have noticed the new thick wall 88 pistons.
Suppose to fit 90.5 head but fit into a 85.5 case.
Anybody have any experience with them?

These are what I used for my 1679cc in the above post.  AA brand.  They were less than 1gr off on balance, ring gaps were good, and skirt clearance was good.  2nd set i have used.  They are super thick walled.

Brian

[Zach Gomulka]

My last engine I built was with 88 Mahle's trimmed down to fit in a stock case. Worked great, but you might as well just bore the case. There's no real benefit unless you are already working with an existing engine and aren't splitting the case.
Since the cost is the same with 88's or 90.5's, might as well go 90.5.
I haven't used the Norris grinds, but the 329 looks good to me on a 1776 single port with Kadrons.
Considering the super short tires, extremely light weight and loads of torque this engine would produce, a 3.88 trans would suit it best.

[oilstain]

Thanks for the info on the AA pistons.

[Lee.C]

Interesting thread.....

You might want to check out my "1600sp BUS MOTOR" thread.... Lots of useful single port stuff in there 

[oilstain]

Thanks Monk great info.

[oilstain]

Well it looks like I wont be using an Empi single port intake does anyone need one?