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PostPosted: Fri Jun 02, 2017 8:42 pm 
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Something I typed up years ago, found it on a flash drive in the shed in a box of 'stuff' and thought what the hell someone might be interested. :lol:

Holley Four Barrel Conversion For Nissan L Series Six Engines. November 2011

A Holley four barrel carburetor is a large capacity carburetor designed primarily for use on large capacity engines such as V8's. When any attempt is made to adapt one of these units to the smaller capacity L series sixes, internal modifications need to be performed to some of the fuel passageways and delivery systems or over enrichment of the mixtures will occur. Failing to make these changes or the lack of understanding of how this carburetor works are the reasons why most people stay away from them. With the correct tuning modifications, they can be made to work quite well on small capacity L Series engines.

Tuning a carburetor to your engine combination is very important to optimize performance. With the prices of Oxygen Ratio meters falling to affordable levels, I bought one from Innovate. After hooking it to my L28, fitted with a Holley 600, I could immediately see that my mixtures were quite rich in some areas and lean in others. The Innovate wideband oxygen sensor device is an invaluable tool and I STRONGLY recommend that you get one if you wish to properly tune and develop your engine safely. I now consider the two should go hand in hand when upgrading to a Holley.

There is the lack of information about how to tune these carburetors with Nissans. Most people will run SU's or Weber’s and ignore Holley's as a viable induction alternative. Other people just hate them and will discredit them whenever the topic arises. Some good information can be found on the Datsun forums, so looking there can be helpful. Dozens of Holley books are available and some get close to describing what is needed for smaller engine calibration. I own most and have read these books carefully.

How much detail you require depends on how perfect you want your setup to be. You can spend a lot of money to get very little return and I have spent way too much money trying almost everything out there to see if it will help or hinder engine performance. I can help you with parts selection and the chances are, I have tried the combination that I'm recommending. Most of my experience is to do with hot street performance, not racing. Holley carburettors specifically built for race engines don't do very well on the street for several reasons. Stick with a street style Holley and modify it, that's fine for street work, spirited highway and occasional drag use.

PARTS LIST
I consider the inlet or intake manifold a fundamental performance part, it will determine how your engine responds and what modifications to make to your Holley to get the best from it.

There are several L Series six cylinder intake manifolds and I've used them all,

Clifford 6=8
Arizona Z
Cartech 4 bbl adapter for twin SU manifold
Modified stock 2 barrel intake P45,P53 E30,P30
Genuine factory 4 barrel intake E32 (Yes it exists and I have one!)

Engine performance will vary depending on the manifold selection. The best for torque is the Arizona, the best for power is the Clifford. These claims have been dyno verified by me on my L28. Manifold selection depends on how you drive and what you want your machine to do. If you’re happy with your top speed and you wish to improve your torque, I'd go for the Arizona manifold, it'll get you to your top speed seconds faster. If you want to go faster and you’re looking for more top end power, the Clifford manifold will do that for you. The other manifolds fall somewhere in between.

The aftermarket manifolds that I have I all got from ebay. I think the Arizona manifold is still available from Arizona Z Car and the Clifford is sold by Motorsport Auto (MSA).

Quick tune

Each manifold will require the carburetor to be tuned differently. A carb tuned up for an Arizona manifold cannot be directly fitted to a Clifford manifold. The design of the manifolds and there induction pulsing are so different, it just won't work. This is what some people fail to realize and give up on this style of induction altogether. Like I said, they take for granted the subtle differences and get frustrated when their setup falls way short of their expectations.

The cheapest way to go is to modify your existing two barrel factory manifold. It requires two adapter plates that mount onto the existing Nissan manifold. The internal passageways can be ground with a rotary burr to smooth things out (with the manifold off the engine), but you don't have to do this. Grinding may improve flow through the manifold into the ports of the engine. I used to matchport all my intake runners to the head. I don't do this anymore as I believe the step is important as an anti-reversion barrier. The factory did this so I figure we don't have to change this aspect with our adaptions.


Throttle.

I'm using, with great success, a cable throttle. It was too hard to adapt the existing throttle linkages to the Holley carburetor throttle arrangement so I went back to the pedal in the cabin and started from there. What I can get here in Australia and what you can get there is probably different. I can take photos of what I have and make a few drawings of everything. That might be the best way to show you and then you can gather similar parts locally to do your adaption. Or you might look at what I've done and think of something yourself. Overall I'm really happy with my throttle arrangement, its never failed me so far!

Fuel line and pump.

I installed an Autometer fuel pressure guage to my car very early on to assess my fuel delivery. The pressure reading on the guage would fall to almost zero with hard driving. The standard pump and fuel lines were considered too small to maintain adequate fuel flow to the engine. I upgraded to a Carter fuel pump and enlarged the fuel supply line from 1/4 inch to 5/16's inch. The return line to the fuel tank was unaltered. The 5/16 fuel line was made from proper fuel line tube, appropriately bent like the old one which I used as a template after I first removed it from under the car. On my most recent car, I went to 3/8 inch fuel line but used a 5 meter roll of EFI hose instead of the hard line. This was much easier to do and I used plastic electrical conduit as a covering over the fuel hose to protect it from stones etc.
The fuel outlet from the tank is only 1/4 inch. If the car was fuel injected by you, it may be a problem point. With a carby car running a Holley, whenever you step off the throttle, the carb will fill up again so if you're going to tow a trailer up a long hill with your foot to the floor, I might suggest you'll need to modify this outlet.

Air filters.

I run K&N 14X3 inch round filter with a flat base or a snorkel type with a K&N style pod filter at the end. Just don’t run anything that's too small in diameter or too close to the mouth of the carburetor height wise. Make sure you never run on the street without a filter of some kind. Tuning in the garage without one is ok.

Carb spacers

I have run a 2 inch spacer but there is really no need to. A one inch spacer is tall enough to keep manifold heat away from the carburetor. There are open and 4 hole types of phenolic spacers. What you use depends on the manifold you use on your engine. On the Clifford manifold you can use either spacer but on the Arizona I use just the 4 hole spacer. I don't use aluminium type spacers because they conduct heat too easily. We want to keep the carb and fuel cool at all times. A heat shield is an option and I have one installed on one of my cars made from a bent sheet of aluminium which limits radiated heat from the exhaust and rocker cover.

Manifold heating.

I used to run this all the time. The advantage was that the engine warmed up quickly, reducing choke on time and erratic cold weather/cold engine running. There is a place for this in terms of consistent running but I found that in our climate that rarely drops below 5 degrees in winter and my car isn’t a daily driver, I could disable it. There is some more power to be had with it disconnected but only slightly so, hardly noticeable really

Carburetor selection.

I have used:
Square bore vacuum secondary 450, 465 and 600cfm.
Square bore mechanical secondary 390cfm
Spread bore vacuum secondary 650cfm

The carbs with the smallest primary venturis have the best throttle response. The 650 was a surprise with its small primary venturis. They are smaller than the ones in the 600cfm carb.
The carb I found to be best is the 465cfm carb List 1848. I use an electric choke on all my carbs but manual choke is acceptable. I use a K&N stub stack to improve airflow into the mouth of the carb but this is optional. A 350 2 barrel is smaller in cfm rating than the four barrels but the size of the venturis on the 350 are actually larger than all of the four barrels.

The carb you choose will then need to have some modifications made. The accelerator pump and the power valve channel restriction are the two most important areas that need work. Without these modifications, there will be over fueling with flat spots and stumbling. There's a lot of detail here so I won’t go into it now. That’s a separate article in itself.

The secondary spring that controls the secondary venturis opening is another tuning tool. Too early and there is a stumble but too late and there is power left on the table.

Conclusion.

They are great conversions, I just took my Cedric coupe for a run today and it performs really, really well with the Clifford and 465 Holley carburetor on it. As you can see, it’s more than one weekends worth of work but for me and maybe you, the results are worth it.

Mark Avramovic
Sydney, Australia.

_________________
1971 240C P230 coupe L28 10.5:1 comp. N/A Haltech Elite 750. ITB's, tuned exhaust, 6 speed manual trans 4.625 LSD

'Nissantiques - Join the Club'


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PostPosted: Thu Sep 14, 2017 4:56 pm 
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Joined: Tue Feb 05, 2013 11:50 am
Posts: 21
Location: North West Victoria, Australia
Hi Mark,

Thanks for posting that piece, it is very informative :)
I actually have a couple of those carbs you mention, but I am more interested in making the original Hitachi on my L24 work as it should. Do you have any idea who I could get to service my original carb?
I have a '77 240k sedan :) I also have some issues with the carb, I put a rebuild kit through it a couple of years back hoping to eliminate an issue it had but ended up creating different issues and have been chasing them ever since. One of them turned out to be the leather plunger that required extra stretching and oiling to make it work properly, but the most annoying one is that after shutting the car off, it dumps all the fuel in the carb into the cylinders, making it hard to restart and choked up. (Float bowl level in the glass is half way up during running and is empty after being switched off and sitting for a while).
Left overnight, the engine always starts immediately on the choke and runs fine until warm.
Another issue is part throttle stumbling.....almost feels like an intermittent electrical gremlin. There's also full throttle stumbling until the secondaries kick in :( It actually accelerates more cleanly just off full throttle.
Too many issues for my head to get around, which is why I'd love to speak to or organise to visit someone that actually knows what they are doing with these original Hitachi's!!!

H.


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