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Small port heads.


ozconnection

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I want to know what you guys think of this idea.

 

Firstly, whenever I read peoples comments on head port development, it's often suggested that making the ports a 'little larger' will help with power output. That's fine. I can understand the idea that larger ports have the potential to flow greater volumes of mixture into and out of the engine to produce more power.

 

The idea I have, specifically for my application is to use an L28 shortblock and use a head with smaller than stock ports! If bigger ports make more power at the top end, then does it follow that smaller ports promote low engine speed torque?

 

The standard intake port on my N42 head is 34.7mm's. The intake port on my 'other' head is 30.0mm's. That's quite a reduction in cross sectional area and port volume, but surely the airspeed would be great between 2000-4000 rpm's with a big fat torque curve between these rpm's.

 

The valves are also smaller with the inlet being 38mm's and the exhaust being 33mm's! The inlet and exhaust valve would be completely unshrouded compared to larger valved unmodified heads.

 

An option would be to run a bigger cam than stock....much bigger. The smaller ports could help with minimizing reversion at low rpm's, perhaps even to the point where the idle could be somewhat smoother than expected. Would this boost low speed manifold vacuum for better carb signal strength and better functionality for the power brake booster?

 

And would the bigger cam help to restore the top end power shortage experienced by the smaller ports and valves? The power may not be spectacular but sufficient since it's low speed torque I'm after, not top end performance!

 

The final aspect that would benefit this combination is a hike in compression, from 8.3 to a calculated 10.2 to 1.

 

So, what do you all think? Are there any traps/pifalls/shortcomings that you can see? Please let me know you're thoughts.

 

Cheers! :-D

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http://mototuneusa.com/think_fast_intake_porting.htm

 

 

have a read over that. interesting theory with some results to back it up. Dont know if it would apply to our old L6s or not. worth a read tho.

 

Thanks for that Mack. The site is a bit...well...OTT, but the info IS interesting and is in similar vein to what I'm proposing.

 

I guess that the limiter with this one is finding small port heads for our engines in any volumes that would make experimentation feasable. In that sense, I guess I'm lucky!

 

What about all the engine builders out there who have played with L series engines/heads for years......what say you??? Worth it or not? Don't be shy.

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The best data on small port head performance can be found on a few oldsmobile sites that concentrate on olds 307 "y-code" engines.

 

These engines came with purposely small port heads used in an attempt by gm to get mucho torque at very low rpms......and they do just that with the side effect of running out of breath at a lower rpm than most any other gm engine.

 

Cars they came in routinely sported rear0end ratios in the 2.73 and much lower which helps all those gm full size station wagons get 20mpg on the highway.

 

Whether this applies to the l engine geometry is a completely different story.

 

It probably doesn't unless you come across such a head that nissan made for a forklift or other heavy equipment running on propane or lpg.

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Absolutely! I retrofitted an L28 block into a 1977 Fairlady Z that used the P65 L20E manifold (that curvey runner job that goes around the plenum with a two-barrel pregressive throttle plate). Using the L20ET fuel injectors, the L20 AFM, and that plenum the L28 was VERY torquey at low speed. Matter of fact, punching it in second gear at 2500 rpms would break the tires free for smoking donuts. Which the owner of the car enjoyed quite a bit. I demonstrated it for him, then let him do it several times to show 'there wsa not a special driving style' that I was using. You punched it at the rpms you mentioned (2000-4000) and that thing just WENT! The engine was 'all in' by 5500, though. No high end power to speak of, but below 4500 that thing was VERY responsive.

 

This was just that small runner manifold on a stock N42 / N42 block and head setup. The only thing I could figure was the super-small runners had such a high velocity through those runners, dumping across an anti-reversionary step into those bigger L28 N42 head ports that it didn't allow any reversion of the fuel mix at all, and just crammed fuel and air into the cylinders at the lower speeds. For a street engine, I'd do it again (like for a wife's car) in a second, if I was able to get that L20E manifold.

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interesting idea, given that alot of attention is spent on high end power output & not lower rpm mucho torque production...would want to achieve the same results out of my NA L28E...pls let me know how you make out & if you know of any other trade secrets to coax more torque out of the L28E, I've got thirsty ears ...thx for your time

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I'd like to know how many N42/N42 L28's can break traction @2.5 K in second gear! Yes, yes, that's what I want as well. Imagine the response at 60mph in top. Just floor it! Wrooooah. And how long will the engine live for at those rpm's? A day or two past forever is my guess.

 

I have seen those P65 intakes too Tony, again often snubbed because of their small runners and poor top end power potential. Shame really. In the right hands they are gold, as you will testify. (I know where I can get them...lardy da da! :ass:)

 

But more specifically, what about the L20 heads? Have you seen one of those on an L28 bottom end? And think about the compression hike, surely that's got to help with torque? I like what you said about the anti reversion step (big port/small runner scenario) but if one were to continue the runner diameter all the way to just behind the valve itself, would that be icing on the cake?

 

A workshop near me has been working on headers. They want me to experiment with a 6 into 3 into 1 setup with 'tuned' pipes, the primaries are 1.375 inches in diameter or 35mm's. So in keeping with high velocity intakes, would there be a benefit in running with something like this?

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I don't know about the small valve heads on an L28.

I think some of the effect is from that step helping prevent reversion at the lower rpms with the stock cam (what there is of it anyway).

 

The chamber design would help with compression, making the bottom end punchier as well. If the quench was set up properly it would be detonation resistant... hmmmmmm...

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I don't know about the small valve heads on an L28.

I think some of the effect is from that step helping prevent reversion at the lower rpms with the stock cam (what there is of it anyway).

 

The chamber design would help with compression, making the bottom end punchier as well. If the quench was set up properly it would be detonation resistant... hmmmmmm...

 

Oh yes, the chamber is detonation resistant alright, it's from an ET engine!

I should pop into the shed after dinner and take a few snaps of the chamber so you can see what I've got to deal with.

 

Just the valves now, might be a bit small like you said, but a larger cam could fix that, couldn't it?

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Absolutely! I retrofitted an L28 block into a 1977 Fairlady Z that used the P65 L20E manifold (that curvey runner job that goes around the plenum with a two-barrel pregressive throttle plate). Using the L20ET fuel injectors, the L20 AFM, and that plenum the L28 was VERY torquey at low speed. Matter of fact, punching it in second gear at 2500 rpms would break the tires free for smoking donuts. Which the owner of the car enjoyed quite a bit. I demonstrated it for him, then let him do it several times to show 'there wsa not a special driving style' that I was using. You punched it at the rpms you mentioned (2000-4000) and that thing just WENT! The engine was 'all in' by 5500, though. No high end power to speak of, but below 4500 that thing was VERY responsive.

 

This was just that small runner manifold on a stock N42 / N42 block and head setup. The only thing I could figure was the super-small runners had such a high velocity through those runners, dumping across an anti-reversionary step into those bigger L28 N42 head ports that it didn't allow any reversion of the fuel mix at all, and just crammed fuel and air into the cylinders at the lower speeds. For a street engine, I'd do it again (like for a wife's car) in a second, if I was able to get that L20E manifold.

 

 

 

Tony... just making sure I have these details correct here.

 

Block/head: L28, N42

Intake Manifold: L20E, ~36? 34?mm runner diameter

Injectors: L20ET (Flow rate compared to L28E? Were they the same or were they the same as L24e?)

ECU: L28E??? You didn't mention.

 

 

I ask because I'm fixing up a honda CRX for a DD.. its an HF CRX, which was an oddball, 1500 sohc 8 valve roller-rocker motor that got 62 hp but like 90 lbs of torque, and pulled about 45-50 mpg. However, my block has been replaced with a more ordinary, 1500 sohc 16v non-vtec civic motor... longblock only, still stock intake manifold (with tiny ports feeding past what I am certain is a significant anti-reversionary step into the head port) and stock injectors.

 

I haven't actually *DRIVEN* the bloody thing yet (even though I have had it for almost a month) because it took a while to get a radiator, headlights etc in and its only now coming together to a point that I will even dare an unlicensed test flight down the side street in. So I am just beginning to wonder what I might have here.....

 

In short, if you used injectors smaller than typical on a stock NA L28.. I may be okay just as-is.. but if the L20ET injectors were the same as L28E, then injectors alone might be a worthy attempt... I had previously anticipated injectors hand in hand with a manifold.

 

/threadjack

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Daeron, if the ports on an L20 engine aren't any larger than 30 mm's, its doubtful the manifold runners would be larger than the head ports! Remember, Tony said that there was a large step difference between the N42 head and the P65 manifold. My measurements of my unported N42 measure 34.7mm's. So putting that all together, I'd say the runner size of the P65 manifold would be no larger than 32mm's and probably closer to 30mm's.

 

Did you ever measure the port runner size Tony?

 

I have L20AET injectors here, but haven't ever bothered to have them flow tested to see how they compare to other injectors in the 6 cylinder family. But power figures for that engine were fairly close to an L28E so one could almost say they were the same items. Dunno for sure though.

 

Tony?

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Daeron, if the ports on an L20 engine aren't any larger than 30 mm's, its doubtful the manifold runners would be larger than the head ports! Remember, Tony said that there was a large step difference between the N42 head and the P65 manifold. My measurements of my unported N42 measure 34.7mm's. So putting that all together, I'd say the runner size of the P65 manifold would be no larger than 32mm's and probably closer to 30mm's.

 

Did you ever measure the port runner size Tony?

 

I have L20AET injectors here, but haven't ever bothered to have them flow tested to see how they compare to other injectors in the 6 cylinder family. But power figures for that engine were fairly close to an L28E so one could almost say they were the same items. Dunno for sure though.

 

Tony?

 

I know, I know, I just couldn't actually bring myself to believe in tininess of that caliber :) It was a long day yesterday, and my brains were too fuddled to think about how small the stocK 2.8L EFI ports are.

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The L20ET injectors are the same injectors as L28E injectors...same terminal horsepower and torque figures. (Green Tops?)

 

I swapped the injectors, L28 Long Block, and L20 P-Manifold into a 1977 Fairlady Z---the EFI components with the exception of the Manifold and Injectors remained unchanged. I fueld the L28 using the L20E AFM and L20E ECU that was resident in the vehicle without changing them in any way. This may be why it was so responsive down low as the L20E AFM would be like an L28 AFM with the flapper spring unwound---follow? Really sensitive to airflow changes, and goes to preprogrammed fueling well before the normal 3500 rpms in the big AFM'd cars.

 

As long as the injectors are sized properly for the engine, the pulsewidths Nissan Used in Open Loop Systems (no O2 Sensor) are remarkably consistent. Let's not even go down that road. Doing it now it would be Megasquirted!

 

As for runner measurements, nope, never did. The L20 Manifold was visibly smaller diameter than the N42 head Intake ports that were on the engine. Dinky is a good way to describe them.

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Just wanted to point out that the standard L6 head already has tiny ports. Compare it to the big port SSS L4 heads and you'll see what I mean, they're much larger, around 1.5". Going even tinier is a step in the wrong direction in my opinion unless you really just want low end grunt. Even then, there are better ways to get low end grunt, like swapping a V8.

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In Japan, for the streetlight racers I would slip the cam one tooth and give the cars back to the guys who would come back RAVING about how GREAT and POWERFUL the car was after the modification.

 

They had no clue how to drive, they just wanted a car that hunkered down and went when they mashed the pedal at 2000rpms in fourth gear...

 

Which is what the thread was about, and it's already mentioned clearly that the engine will be 'all in' by 5500rpms. Flat on it's face, just like those slipped-cam-jobs I did back in the 80's.

 

Some people don't run at 7000rpm engine. Some people don't want/need it. Some people would prefer a lower rpm bias in the torque curve.

 

And that seems to be what this thread was about, and the ways to go after that effect.

 

More compression would help as well.

 

Frankly, watching most people daily drive their Z's I'm of the opinion that I could swap a BMW Diesel or even a Golf TDI in there and nobody would be the wiser: shifting at 3000 because 'they don't want to strain the engine', shifting up at 4000 or 4500 when they are 'really going for it'...

 

I've said it before, some people are diseased. Is it the low rpm or the high rpm set? I say both, and n'er will they reconcile.

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Frankly, watching most people daily drive their Z's I'm of the opinion that I could swap a BMW Diesel or even a Golf TDI in there and nobody would be the wiser: shifting at 3000 because 'they don't want to strain the engine', shifting up at 4000 or 4500 when they are 'really going for it'...

I have a friend who fits this description perfectly. She FREAKS when I drive her Z. :lol:

 

I get the idea of the thread, I just thought maybe a dissenting opinion was in order. Choking down an L6 is in my estimation counterproductive, and as you point out, there are other ways to change the powerband without having to resort to smaller than usual ports.

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The smaller ports enhance that low end, though. And I think that is what he was going for---if you were to bump the compression, optimize cam timing, and use a stepped manifold on a fairly stock head (basically the right combination of inexpensive stock parts) you could make an engine that was very thrifty when driven in the described manner, and probably make for a nice mill in front of an (eck) automatic transmission! Even with a stick, it would be a nice driver around town.

 

Me? I'm just putting an LD28 in the damn thing with A/C and the Autobox for commuter duties...

 

I like em stump pullers, or screamers. A Man of Extremes. I don't go for a lot of this middle-of-the-road stuff! LOL

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Right. L6's generally are known for their torque. Hamstringing an L6 motor with even smaller ports just doesn't seem like the best idea to me.

 

Hypothetical: You need to cross a river to get to the other side. Would you cross at the widest part of that river or cross the river at the rapids where there is a comparatively little ground to travel? Same volume of water, yet vastly different effects. Do you see where I'm coming from?

 

Is the effect of reducing the port size the same as the river scenario above? Can we tune the ports to match the power band? I think I know what to do, at least go so far as 'giving it a try' and see what happens. I will dyno the before and after and I'll try and post the results on here.

 

Cheers.

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