All this talk of building turbo L's

[Guest xero]

what about the N/A L's?

 

I read ALL of the porting the P90 head thread, but does ANY of that theory have to do with normally aspirated cars? like the intake port being big and shrinking down to a smaller size, or the various combustion chamber designs with the ridge between the intkae and exhaust ports

 

All I really want to know is because no body specifies if they are tuning for a turbo or N/A, I can't tell if people's theories and designs will work for both or are turbo specific,

[SleeperZ]

I can't think of any theoretical differences between forced induction and naturally aspirated flow goals. All of the same parameters are considered: volume of flow, pressure drop, velocity of flow. Forced induction is more forgiving of intake flow restrictions as it can compensate by raising boost pressure (within reason).

 

Another difference, and I'm not sure how it plays out, is the exhaust flow design. Scavenging can be desireable n/a, but I don't know if it applies to exhaust flow into a turbine.

[Guest xero]

that's what I thought, but there's always alot of differences between turbo engines and N/A engines as far as design goes, I figured that seeing as you have a turbo in the way, you could port out the exhaust plenty and not worry about not enough back pressure, and then it'd help turbo spool up and what-not, but if you make the exhaust not restrictive enough, then you lose ALOT of torque and risk hurting the engine more than helping it,

[johnc]

The exhaust side of the L6 head is where people should focus their efforts on. Especially cylinders 3 and 4. When you can get all 6 exhaust ports to flow within 5 cfm of each other (regardless of the ulitmate flow number) you've accomplished a lot.

[Guest xero]

but at what point is too much porting? I know there's no such thing as too much in a turbo engine (with-in reason) but when it comes to N/A, too much will hurt performance and hurt your engine, is there a certain amount of that should flow through the exhaust side for optimimum HP and torque? like even a rough number will be fine.

 

or is it just port the hell out of it, you can't hurt it, kind of thing?

[johnc]

but at what point is too much porting?

 

That's basically an unanswerable question. What's the intended use? What's the budget? What rules is the head being built to? What cam? What valve sizes? What valve springs? What rockers? What intake manifold? What fuel delivery system? What ignition system? What exhaust header? What exhaust system? How much does the car weight? What gearing?...

[JMortensen]

There is a 75% rule, exhaust should flow 75% of what intake flows, at least for N/A's. The reason why everyone says to be careful is that you can screw up and make the head flow worse, or very unevenly. You can cut right into the water jacket too. Then the port has to be welded.

 

I had a friend with a SSS 510 head with the huge 1.5" ports. He hogged it out to 1 7/8". The thing runs fine...above 5000 rpm. That's actually OK for him, because it is a roadrace/autox car that spins 8K (I still think its a little much and he would be better off with a little more midrange power). But on a street car, if you make the ports too much bigger, the intake velocity drops, and you need that velocity to make power, at least that is what JohnC is always saying.

 

Since the Z has tiny ports compared to the L4 SSS heads, I can't help but think that you can go MUCH bigger without causing too many problems, but you need to know what you're doing, where to take metal from, and where not to take metal from, and you need a flowbench to make sure that everything is even when you're done. If you just want to clean up the castings and make the port walls smooth, and port match, I don't think you can really do too much damage. I've seen pros do it though, and I don't have the time/patience/expertise to really hog out a head. You've gotta be a special kind of anal for that sort of work.

 

Jon

[Guest xero]

so for a street car, doing everything that a race car would do in moderation (heavy moderation) could prove promising?

 

Problem is, (ready for some long drawn out history?) I don't have a Z, I just love cars. I want to know everything about them, and pretty much own them all at one point in my life. I'm not happy with my 240sx right now, so I'm thinking of getting a Z, but because there's so many choices, I jump around. At one point I want a Z, a couple weeks ago I wanted a Type-3 VW Squareback. Being a poor college student doesn't help any. So for right now, I'm on a mission to learn as much as possible, amassing knowledge to use in the future. I have ideas of what I want, but they all tend to be way overboard, and what many people wouldn't run on the street, and what many people call me stupid for wanting to do.

 

If I was to build this hypothetical Z, I'm currently thinking 3.1L stroker, 11:1 compression and 50mm Webers. So we'll just use that as an example, that all right? (also, you can assume I already know alot about cars, I've been in the game for 3 years, and specifically Nissans, I'm a moderator for Northwest Nissans up here in the NW [go figure])

 

thanks guys and sorry for the long drawn out explanation of myself and the questions I ask

[johnc]

As an example, the ports (including valves at the proper lift) on my NA 3L L6 head flow at least 10 more CFM then any other L6 head Jim Thompson has ever tested, including some of the Electromotive ones from the 80s. Interestingly though, the ports match up to a stock Nissan head gasket - no grinding of the gaskets needed. That should tell you that the flow numbers are produced through velocity and proper port shaped as opposed to making the ports bigger.