ozconnection Posted February 7, 2009 Share Posted February 7, 2009 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 up 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! Quote Link to comment Share on other sites More sharing options...
ozconnection Posted February 21, 2009 Author Share Posted February 21, 2009 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 far....best 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. Quote Link to comment Share on other sites More sharing options...
garvice Posted February 21, 2009 Share Posted February 21, 2009 Sounds interesting mate, you have me subscribed. Interested in the head work your doing as well and can't wait to see some photos. Brad Quote Link to comment Share on other sites More sharing options...
Daeron Posted February 23, 2009 Share Posted February 23, 2009 You might want to consider using an intake manifold with a runner diameter slightly larger than your intake valve to help keep overall velocity on the increase as the air/fuel approaches the head? Then again, I may be thinking more in an EFI realm, but I wanted to subscribe here, too, so I thought I would comment and risk foot-in-mouth. Quote Link to comment Share on other sites More sharing options...
ozconnection Posted February 23, 2009 Author Share Posted February 23, 2009 You might want to consider using an intake manifold with a runner diameter slightly larger than your intake valve to help keep overall velocity on the increase as the air/fuel approaches the head? Then again, I may be thinking more in an EFI realm, but I wanted to subscribe here, too, so I thought I would comment and risk foot-in-mouth. Port taper is what I think you might be referring to. Nice thought but that would require a custom built intake manifold. The manifold I intend to use has varying length runners so it would be impossible to do. Triple whatever manifolds lend themselves nicely to this because, even though the shape may be a little different from runner to runner, they're all the same length. L Series EFI manifolds also lend themselves to this type of runner porting as well. Not much of a taper though as the port runner walls are very thin. I believe the optimum port runner taper is about 4 degrees from a paralleled walled runner. I don't think your risking 'foot in mouth' here Daeron, come with me and enjoy the ride. It's something that has been in the back of my mind for a long time but 'convention' has it that porting involves making the hole or volume larger not smaller, generally. That 'fact' is a well worn path in automotive tradition. What I'm challanging here is convention, to see for myself if taking this path is productive for me and my application. This may not be what most of you guys seek as you're all running much lighter cars than me, hence the challange to develop an L Series engine with as much low rpm torque as I can get. I think I've beaten this line to death so I won't keep saying it. Rang the shop doing my head today. It's just needing the valve seats to be machined and I'll get it back. Then I'm going to take a 'few' pictures and share them with you all. Until then...... Quote Link to comment Share on other sites More sharing options...
Daeron Posted February 23, 2009 Share Posted February 23, 2009 Port taper is what I think you might be referring to. Nice thought but that would require a custom built intake manifold. The manifold I intend to use has varying length runners so it would be impossible to do. Triple whatever manifolds lend themselves nicely to this because, even though the shape may be a little different from runner to runner, they're all the same length. L Series EFI manifolds also lend themselves to this type of runner porting as well. Not much of a taper though as the port runner walls are very thin. I believe the optimum port runner taper is about 4 degrees from a paralleled walled runner. I don't think your risking 'foot in mouth' here Daeron, come with me and enjoy the ride. It's something that has been in the back of my mind for a long time but 'convention' has it that porting involves making the hole or volume larger not smaller, generally. That 'fact' is a well worn path in automotive tradition. What I'm challanging here is convention, to see for myself if taking this path is productive for me and my application. This may not be what most of you guys seek as you're all running much lighter cars than me, hence the challange to develop an L Series engine with as much low rpm torque as I can get. I think I've beaten this line to death so I won't keep saying it. Rang the shop doing my head today. It's just needing the valve seats to be machined and I'll get it back. Then I'm going to take a 'few' pictures and share them with you all. Until then...... Well, I just bought 1991 Honda CRX HF around Christmastime, and it has had the longblock replaced with a more standard civic 1.5, but still has the HF intake manifold, injectors, and ECU. The short version is, the intake ports on my manifold and on the stock engine are about the size of a quarter (slightly smaller) and the head on the engine now is more like the size of a 50 cent piece, so the manifold is a MAJOR bottleneck.... in one sense. Putting it another way, it is a high velocity inlet manifold with a significant anti-reversionary step at the head flange. The ECU cuts fuel at 5500 RPM anyhow, so high RPM power isn't just "not my concern," its a non-issue! The end result on my Honda is a BEAST that is most assuredly quicker than the stock powerplant, and it feels like driving a Mustang! 45mph in first gear is crazy, and 60mph in fifth at 1800 RPM in a Civic is also crazy! The car hasn't gotten registered yet, so I do not have a MPG figure to compare to the stocker's 45mpg, but I suspect I didn't lose much. If you are interested, (and I have not yet told you in another thread or something) I could send you a PM with some more of the details on my Honda; it seems our goals are largely the same regarding this build for you, and the honda for me. Quote Link to comment Share on other sites More sharing options...
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