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A new Holley for my L28

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    Hi there,

    I've just finished building a new four barrel carburettor for my next development phase on my L28.

    The Holley originally started off as a 'run of the mill' 450 cfm (list 4548) vacuum secondary four barrel. Since then, it has been extensively modified and upgraded to suit my requirements.

    Some of the features it has are:

    4 corner idle mixture adjustment

    Downleg booster venturis

    Electric choke

    Reworked metering blocks to include adjustable power valve channel restriction and idle/off idle circuits via screw in jets

    Percy's adjustable metering blocks for primary and secondary main fuel

    Centre hung fuel bowls

    Quick change secondary spring unit and

    A blended 600 cfm 4 barrel base plate.

    The next phase of engine development includes a new cylinder head where I'm concentrating on improving low engine speed torque. The head will have a much better quench around the valves and will boost my compression from 8.3 to 9.9 to one. The ports are round exhaust with liners like the P79 heads and the intake ports are smaller than the N42. (30mm's versus 34.7mm's). The intake manifold is an older candilabra single carburettor type, Nissan code E30. This manifold will be adapted to suit the Holley carburettor and it has 30mm runners, matching perfectly the Y70 head which originally came off an L20A ET engine in Japan. The head is currently at a headshop being reconditioned with guidelines not to touch the ports other than to clean the bowl region and improve the valve seat areas for better flow. A special smooth radius valve job will be tried instead of the usual 5 angle. It came with strong recommendation so I said yes to that. The head should be ready fairly soon.

    I'm very curious (and committed!) to giving this a go. I will be doing a series of dyno runs soon to establish my baseline at the moment and then gradually change over to the new parts to see their effect on performance. Remember, my aim is to improve torque at low rpms, so talk about big ports, valves and camshafts may not be what is needed, unless you can convince me otherwise! Sure, I would still like it to rev to say 5000rpm, but it is what happens when you change to the next gear higher that interests me, what happens at between say 2000 to 4000 rpm's! :) Read Torque Monster!

    Your thoughts?







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    I've installed my new Holley carb.

    Took about two hours to install, check float levels, replace a faulty needle and seat on the primaries and get the thing to idle smoothly.

    With my innovate wide band on board, I went for a few runs around the block. Tuning is so simple, it's ridiculous. Turning a couple of screws on the top of the new block sandwiched between the bowl and the original block, I had the thing tuned up in about 30 minutes of driving around, testing on flat, slight incline, heavy incline, off the mark and part/full throttle.

    The most significant thing of note is the low rpm torque! At 1500rpm in O/Drive, the thing just pulls, don't worry about shifting down, it just pulls. On the flat, it accelerated very well from this rpm.

    Impresions so throttle response/torque of any of my carbs and by far the easiest to tune. Just pull over to the side of the street, pop the hood and tweakit!!! Excellent.

    The following are a couple of quick snap shots of the booster arrangements in the carbs that I've used before compared to what I'm using now. Notice how none of the boosters fit into the mouth of the venturi, except the dogleg version. To improve the signal, I use a couple of slightly modified venturi sleeves to amplify the signal to the main fuel well even more.

    The next stop is to the dyno for another run, to compare it to my previous best. What the dyno doesn't tell you is how the car feels on part throttle and something that is quite subjective but you'll have to take it from me, it's those boosters and the ease of tuning which has impressed me most so far. :)




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    I am very eager to see the dyno results. This is a very interesting project.

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    I guess this illustrates the versatility of the L Series engine nicely. The Cedric may not be a fast car because of body weight and engine specification. The camshaft profile may limit how quickly the engine accelerates to redline but it's the same camshaft that allows this sort of towing capability to take place. Car is 1450kg X2 and a 500kg trailer. Thats nearly 7500lbs my friends!

    You should 'feel' how toey the car is now since towing that lot. Feels like a rocket ship LOL

    The L20A head has been reworked and I'll be picking it up on Monday. Some pictures to follow soon.




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    A few pictures of the Y70 L20AET head back from the shop. The injector notches were welded closed to reduce intake flow turbulance. The ports were not enlarged and remain 30mm's in diameter. The chambers have had new seats cut and the bowl area behind the intake valves were cleaned up. The short side radius on the intakes is quite large and generous which should help with airflow in this usually sluggish area. The only area that needs some work are the fresh edges created by facing the head at the edge of the combustion chambers. Shouldn't take long with fine emery cloth though. I find it interesting that this wasn't done, but then I would have to pay for it. Funny, I thought I'd paid enough already! :ermm:

    The next stage will be to put my current setup on the dyno and see what I have at the moment. Then change over the head and keep everything else the same as much as I can.

    The things that will change with the head swap are:

    Compression ratio

    Ignition timing

    Exhaust port configuration

    Intake port size and

    Cylinder head chamber shape and valve sizes.

    Typically, the idea is to change just one thing at a time but as you can see, this is virtually impossible. Things must be done with some consideration to cost. After all, this is an experiment funded totally by myself and the missus would KILL me if it got too outa hand! As it is, I'm probably spending too much but my curiosity is overwhelming! I wanna see how this thing goes!! I want to test the theory and see if it can work for me and share it all with YOU guys.


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    The next stage will be to put my current setup on the dyno and see what I have at the moment. Then change over the head and keep everything else the same as much as I can.

    The idea was to take my car to the dyno to test the engine's output. The biggest trouble I had last time I was there was the rear tyres slipping on the rollers! We even tried strapping the car down with straps but even this failed to stop wheelspin. The open centre differential wasn't helping so we gave up on it for then.

    Rather, I'm now going to be using a 'G-Tech' an accelerometer. Cleaver little tool and can be used anywhere, anytime and is a hell of a lot cheaper than running the car up on the dyno.

    I ran it the other day with a mate of mine to see how my car was performing.

    0-100km/h is 11.43 seconds

    0-400metres is 18.2 with a terminal speed of 126.7 km/h

    This was up a slight incline with half a tank of petrol and another person in the car (75kgs), so my total weight was around 1650kg's (3633 lbs).

    To put this into perspective, I looked up the timing figures on the 280ZX non turbo cars, both auto and manual trans and my figures are pretty good compared to that car in standard form. One thing for sure is the ZX is a lot lighter than my car and the heaviest one I could find weighed in at 1307 kgs, nearly 350 kg's lighter than my test weight on the day. :surprised

    But, one thing is that the auto, on full throttle, activates the kickdown solenoid so the engine revs to about 4800 rpm on the one/two shift and around 5200 rpm on the two/three shift. If you can appreciate the fact that I'm tuning my engine for maximum low speed torque, then revving the engine this far isn't exactly conducive to me producing the cars fastest or quickest times. This 'slowing' at higher revs happens twice in a run to 100km/h or a run over 400 metres!

    What I'm going to do is a run using the 'detent', almost floored but just off the kickdown switch. The car shifts early but drops the engine right back into the torque band, in fact it never actually leaves it when driving like this! ;) Knowing my gearbox and final drive ratios wheel diameters etc, the shift up points become

    1st to 2nd at 35 km/h is 3100 rpm to 1800 rpm and

    2nd to 3rd at 70 km/h is 3650 rpm to 2450 rpm.

    At 100km/h in 3rd the rpm's will be 3500 and at 127 km/h it will be the same as before at 4400 rpm.

    Can you guys see where I'm heading with this??

    I can't wait until next weekend when I'll be trying this out. Give me your thoughts, I'd like your input.


    Edited by ozconnection
    getting the figures right!

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