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I don't know how to answer your post exactly noodle, as I'm admittedly no head expert. BUT, I know that intake and exhaust are two very different beasts especially when you sit back and consider that in one case air is rushing in under vacuum and in the other case air is being pushed out via positive pressure directly after just having a burn., and that they happen completely separated by a decent amount of time of the stroke.

 

In exhaust stroke your gases all of a sudden have a completely different molecular makeup. Different mass, density, ect.

 

I know braap would be able to explain it all much better. He seems to have a gift on the subject. Or least that decade of experience thing....

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I have a question on manifold / head port matching, exhaust and inlet,

 

Braap said in one of his posts in this thread,

 

"The intake valve opens, the piston draws the air into the cylinder, air flow is speeding up, the intake valve closes, the air still has momentum and we all know air has weight/density, the air charge compresses behind the intake valve and surges back, much like a wave hitting a wall and coming back. Then it comes back again with “almost” the same force so as the intake valve opens the air is already moving toward the valve so the piston doesn't have to draw it in"

 

my question is, if the intake manifold has a smaller diameter port than the cylinder head, thus creating a small step, and the same for the exhaust, been slightly larger, will this help with the "Helmholtz" effect or make it worse ?,

or should you just port match the head and the manifold to the same size ?

 

see picture..

 

Nigel

 

 

Nigel,

Great question.

 

What you described is basically an “anti reversion device”. Your best bet for in-depth info on anti reversion steps or devices is to do some research. I have not done any testing on the L-series with anti reversion steps or anti reversion devices so I have nothing to back up my opinions/theories on this subject with L-series.

 

 

Here is my “opinion/theory” on anti reversion devices on L-series heads.

As far as it being beneficial or not? Good question. If the engine along with its induction and exhaust system are engineered and built to take full advantage of the Helmholtz principle, then introducing an anti reversion device would seem like a step backwards, like Formula one, or NASCAR engines, (I know, not exactly L-series.) For our lowly 2 valve L-series, that anti reversion device might help bolster or band aid some weak flow or pressure surges that “may” be present, but that is purely speculation on my part. Personally, I would not try to install/induce an anti reversion step into the air stream on an L-series, especially on the intake. The liners in the round exhaust port L-heads function as anti reversion devices, but whether “that” feature of the liners is of benefit or not to producing HP is still up for debate. What we do know about the round exhaust ports with the liners intact is that they flow nicely for mild to even moderately hot L-series engines.

 

Sorry I couldn’t be of more help on that subject.

 

Paul Ruschman

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  • 4 weeks later...

While slowly reading through this thread I stumbled upon a question. I'm not done reading, so dont hit me if its already been covered!

 

If one of the limiting factors of porting the head is the wall thickness would there be a substantial gain from filling the water jacket and hogging out the ports? Or would you loose too much efficiency from the extra heat? Obviously this would only work on a track only drag engine but I'm still curious.

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While slowly reading through this thread I stumbled upon a question. I'm not done reading, so dont hit me if its already been covered!

 

If one of the limiting factors of porting the head is the wall thickness would there be a substantial gain from filling the water jacket and hogging out the ports? Or would you loose too much efficiency from the extra heat? Obviously this would only work on a track only drag engine but I'm still curious.

 

 

 

Chewie,

 

Are you talking about using something like Block filler to fill up the coolant passages in the head and then carving out the ports to something more optimum in shape and size?

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Chewie,

You are thinking in the right direction, though that route to your good idea is probably not the best way to achieve that ideal port. To fill the coolant passages and reshape the ports would work from an airflow standpoint quite well, but the engine wouldn’t last as the combustion chambers now have no place to dissipate the heat to.

 

There is another way to achieve the results you are asking about and this topic comes up once in a while in causal bench race sessions. I have seen pictures of an L-series race head, (I think it was in one of the how to modify and race your Datsun books), where the entrance for the intake ports were raised substantially. They were raised up to the valve cover rail, maybe even were raised up into the valve cover if memory serves, in an effort to straighten out the port which is less restrictive than a curved port. It was over 10 years ago the last time I saw that picture. Anyhow, in carving out the region around the ports to that extreme and rewelding in new port walls so to speak, (tubing, or just building/welding the port walls up), there “should” be no cooling issues, (other than any that currently exist). Recently, there has been talk of taking an existing head and raising the intake ports substantially as well as the exhaust, requiring extensive hacking and welding to this poor existing head. I feel that when attempting to go to this extreme, that every aspect for improvements, such as the port shape, size, taper, etc, from the valve seat to the manifold mounting surface should be taken into consideration. As you stated, this would really only benefit full tilt mega RPM race engines. Maximizing the ports as they are currently cast, (i.e. no welding or building up of new port walls), I feel will get 95% of the extreme guys approx 90% of what the two valve design will allow. Going for that extra 5-10%, would require an awful lot of hacking, welding, and machining and it is still just a 2 valve head, (not that there is anything wrong with that). wink.gif At this level, with so many 4 valve inline 6 cylinder engines readily available, (and other engine choices), you have to be really dedicated to the L-6. Though I do feel this extreme L-head should be built at least once if for no other reason than, we can!

 

Here is an example of optimizing the existing intake port entrance by essentially raising the roof without taking any material off the port floor. This custom Rusch Motorsports N-42 head has extensive valve unshrouding and extensive exhaust bowl work as well, yet no welding or building up of the ports. With a mild .465” lift cam, Ron Tylers custom intake manifold, WOLF 3d EFI and DIS, this 8.2:1 compression L-28 pulls through 7000 RPM. Now we just need to build this customer a solid bottom end with some compression to match the head, cam, and induction..

 

Here is a link to that project…

 

http://forums.hybridz.org/showthread.php?t=117607

 

 

Mis-match1Small.jpg

 

Mis-match2Medium.jpg

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Guest pc loadletter?

what would be the best way to give my stock 83zx non turbo a preformance boost so i can beat my friends integra, but still keep the longevity of my engine (i plan on keeping this car till i die). a buddy of mine is donating a 79 280z motor to me and id like some suggestions

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what would be the best way to give my stock 83zx non turbo a preformance boost so i can beat my friends integra, but still keep the longevity of my engine (i plan on keeping this car till i die). a buddy of mine is donating a 79 280z motor to me and id like some suggestions

 

PC Load Letter. This is the wrong thread for a question like that, and that is the wrong question to ask on this forum?

 

Please read the entire page linked below. Items #2, AND #3, AND #4, AND #9. in particular

 

The answer to your question is custom cylinder head work is NOT where you start to in an effort to make power to out run your girlfriends Honda.

 

http://forums.hybridz.org/announcement.php?f=65&a=2

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The P90 on my super stroker motor has welded intake ports. I made the ports to the BEST they can, and that turned into going through the water jackets. I welded up where it went through, and thus having a HIGH flow head. It is still the highest flowing L series head Ive measured. I dont do that sort of work for customers, as warranty reasons. But Ive run it like that for over three years as a daily driver with close to probably 40 thousand miles on that head and not one problem. I pressure check each of my heads with 50 PSI, to ensure no blow outs also. On race heads, you make the port optimum, then if theres holes you deal with them. You dont build the port around the water jacket, but rather the water jacket around the port. I had pictures of that head on my website, but I took them off about a year ago.

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Yes, welding the ports to allow them to be raised was a common modification. To look at the FIA L6 head, you find the ports are almost touching the valve cover gasket area---and that was a stock from Nissan casting...of course it also had water jackets that came out between the cylinders in the same area as well to prevent low-flow spots...

But yeah, raising that port will help. Filling the bottom of the port with aluminum devcon (intake only, please!) will do nice things for velocity and entrance as well...

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Yes, welding the ports to allow them to be raised was a common modification. To look at the FIA L6 head, you find the ports are almost touching the valve cover gasket area---and that was a stock from Nissan casting...of course it also had water jackets that came out between the cylinders in the same area as well to prevent low-flow spots...

But yeah, raising that port will help. Filling the bottom of the port with aluminum devcon (intake only, please!) will do nice things for velocity and entrance as well...

 

 

This is the head, I think you are talking about

 

 

Nigel

nissanl6safarihead01oi6_thumb.jpg

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Been thinking alot about what a modern 2 valve Z head would look like given all the info out there about 2 valve American engines and everything being done to them to generate big power on pump gas. So I have spent time on and off working on a 3-D CAD model of what I think it would be like for a Z-head. First, I by any means do not know what I am doing, I have only built and run 1 welded and reshaped head that is currently on my 240, and luck would have it, it runs pretty darn good. I am only doing this for fun, and really have no idea of how it will work until I finish it up, flow test it and ultimately run it. This thread has been kinda dead for a while, so hopefully this will get some more ideas going, Here some pics of the CAD File for discussion.

complete_head_1_thumb.jpg

complete_head_2_thumb.jpg

complete_head_3_thumb.jpg

complete_head_7_thumb.jpg

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This next set of pictures is of a P-90 head that has been "welded up" and roughed out with a CNC on the chambers and port bowls right of the Cad files above. The surface machining was done in a radial pattern outward from the center of the valve guide at 3 degrees and it took 8 hours of machine time. A finish pass would be 1 degree and waaay more time. Since this is just a test I figured why waste the time. There a still plenty on low spots that would need more welding and another pass, but I would probably just start over. Some details to note - angled spark plus towards the exhaust valve 15 degrees. Designed for OS valves 46 and 38. Would need the block eyebrowed I assume. Double quench pads. Streamlined leading and trailing edges on the valve guides. 54cc chamber size.

 

Jeff

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