L16 intake manifold on ported head

[wayno]

Ok guys, I am wondering what issues I am going to have putting this L16 intake onto my L20b ported head, basicly, is it going to run properly with my weber on it for now?

I put an L16 exhaust manifold on the engine, and when I got the L20b intake almost off, I realized that the intake and exhaust are connected on the 1980 engine, normally I would use the dual SUs, but there is no room, as the 520 brake M/C is in the way.

I know it will choke it off at higher RPMs, but will it run correctly in normal city driving?

I also need to know for sure what one of the fittings is for, the PCV valve goes to the case vent tube, does the other big outlet go to the valve cover or does it go to the intake filter?

It looks to be a major vacuum leak to me, but if that is what it is for, let me know where it goes.

Do I use that intake insulator on the intake, or do I just transfer everything that's under the weber now?

I am taking the weber off an L20b intake, and transfering it to an L16 intake.

[DanielC]

In this picture, the fitting closest to you, with a 90 degree bend, pointing West North West is from the air pump, through a valve. It dumps a shot of fresh air into the intake manifold, for a very brief period of time when the throttle is closed. This is to prevent a momentary rich condition.

The air is controlled by a valve, that gets its signal to open from the small fitting on the number 4 intake runner, pointing straight up..

 

Keep the PCV valve. It does good things.

[wayno]

In this picture, the fitting closest to you, with a 90 degree bend, pointing West North West is from the air pump, through a valve. It dumps a shot of fresh air into the intake manifold, for a very brief period of time when the throttle is closed. This is to prevent a momentary rich condition.

The air is controlled by a valve, that gets its signal to open from the small fitting on the number 4 intake runner, pointing straight up..

 

Keep the PCV valve. It does good things.

 

So I plug that big air leak that went to the air pump?

That makes more sense to me, I just couldn't figure out how such a big hole didn't cause problems.

[Z-train]

I'm running the same manifold on my LZ-23.Low end will see an increase.Upper end will suffer some.But how offten do you plan to be north of 7000 rpm?

[Ratty260z]

anti-reversion look it up. The same will apply for the intake vs. the exhuast.

[Z-train]

anti-reversion look it up. The same will apply for the intake vs. the exhuast.

In-correct.

[albyneau]

Ok guys, I am wondering what issues I am going to have putting this L16 intake onto my L20b ported head, basicly, is it going to run properly with my weber on it for now?

I know it will choke it off at higher RPMs, but will it run correctly in normal city driving?

 

Anti-reversion is in moderation a good thing to have on the exhaust side~ it assists in inhibiting exhaust pulses travelling the wrong way. With a properly designed system this is of little concern. On the intake side it's a big NO-NO. There's no reversion pulse per-se because the intake is negative pressure. What does happen is referred to as "fallout". The increase in port size causes a dramatic reduction in port velocity~ the atomized fuel runs into itself, becoming droplets heavy enough to fall out of suspension in the airstream. This can cause your intake charge to be a bit leaner, and a wet port floor literally dripping fuel into the chamber. If you've ever seen an intake port with brown fuel stains on the port floor this is likely why. This unatomized fuel will be difficult to burn at best, and over time can wash down your top ring~ accelerating wear. Putting this all into words makes it sound more catrastrophic than it is~ but in the long term you'd see slightly reduced economy, performance, and reduced longevity, and may even be noticeable at low rpm's. You'll be fine on a temporary basis~ but best not to forget putting this on your "to-do" list of upgrades/repairs....

[Z-train]

You'll be fine on a temporary basis~ but best not to forget putting this on your "to-do" list of upgrades/repairs....

Care to expand on this?

[albyneau]

Care to expand on this?

 

Well, if you're a leadfoot, drive a clutch car, or in stop-n-go a lot~ it'll exacerbate the problem. Were I in his shoes I'd probably limit myself to 2-3 months (<5K miles)~ the sooner the better! ;)

[Z-train]

Well, if you're a leadfoot, drive a clutch car, or in stop-n-go a lot~ it'll exacerbate the problem. Were I in his shoes I'd probably limit myself to 2-3 months (<5K miles)~ the sooner the better! ;)

You're saying this without knowing what the port dimensions(intake & head) are.

[albyneau]

You're saying this without knowing what the port dimensions(intake & head) are.

 

You're right~ I don't know exactly what his ported head intake diameter is. But I've got my L16 sitting in front of me, and it doesnt take a huge amount of porting on the L20B heads to double the volume (not the diameter). Double the volume equals half the velocity to move the same amount of air/fuel.....

 

Peace~

Scott

[Z-train]

You're right~ I don't know exactly what his ported head intake diameter is. But I've got my L16 sitting in front of me, and it doesnt take a huge amount of porting on the L20B heads to double the volume (not the diameter). Double the volume equals half the velocity to move the same amount of air/fuel.....

 

Peace~

Scott

Granted,if you are trying to feed a "55-gallon drum" head port with a "firehose" intake port,there'll be issues.BUT,as the two sizes "shrink towards a uniform diameter"all issues go away ( at a certain point)and in fact benefits are had long before the I.D's match.

[Ratty260z]

having the step from the intake will help because if you run a large cam with a lot of overlap the air that passes the intake valve while the piston rises will be disrupted by the step preventing the turbulence in the carb which will keep the mixture and airstream more uniform and smooth.

[Z-train]

having the step from the intake will help because if you run a large cam with a lot of overlap the air that passes the intake valve while the piston rises will be disrupted by the step preventing the turbulence in the carb which will keep the mixture and airstream more uniform and smooth.

I think you got that back wards.The intake will have the smaller I.D.,thus there will be no "step" for the mixture to"see".

 

Scott,what's the I.D. of the runner port on that L-16 manifold?

[datzenmike]

[Ratty260z]

I think you got that back wards.The intake will have the smaller I.D.,thus there will be no "step" for the mixture to"see".

 

Scott,what's the I.D. of the runner port on that L-16 manifold?

 

I meant what I said by having the intake manifold port smaller then the head port you create a small wall that disrupts air flowing past the intake valve when you have a large cam with lots of overlap.

[Z-train]

I meant what I said by having the intake manifold port smaller then the head port you create a small wall that disrupts air flowing past the intake valve when you have a large cam with lots of overlap.

O.K.,now that it's clear,you are in-correct.

[Z-train]

Mike-Lemme guess,the head ports are about 35mm and the intakes are 31mm?(assuming stock dimensions)

[wayno]

I guess I was a little vague, my head has been ported to match the dual SU type manifold, but the brake M/C is in the way, so I put a stock L16 intake manifold on the engine that was the size of the head before I had it ported, little intake manifold holes, large head intake holes.

I suppose I could have started hunting around for something that I am not sure exists, which is a stock 2 barrel intake manifold with 1 1/2 inch runner holes.

This W53 head(closed chamber) doesn't have the big valves in it, it has stock valves with a RV cam.

So it will run normally till I can find another larger intake manifold for the weber that will breathe better?

BTW, the only way that this engine could ever rev to 7000rpms, is if I floor it in neutral.

I spend all my time between 2500 and 4200 rpms.

It's been put together except for the heater core hoses, i'll put some fuel in the tank tomarrow and see if it will start.

I had to fab a cable linkage pull out of 3 differant carbs to get this setup.

[Z-train]

Wayno-do you have the head port I.D. measurements?

[banzai510(hainz)]

what I did is use a Felpro intake gasket and put it up to the L16 intake manifold then hoggeed it out close to the 1.375 size.

Like in Datzenmikes photo youll see it getting hogged out.

 

I put mine on a l20 1.375 head and smooth the corners inside the weber tall plenum tyep carb adapeter

 

seems fine on my L16/18s

 

also depends if you have a water passage on the head if you want to run a heater line or not

[wayno]

Wayno-do you have the head port I.D. measurements?

 

I don't know what this question means, as I don't know what measurements you are asking for, are you talking about the measurement at the intake manifold mounting surface, are you talking about the measurement 1 inch inside the port, are you talking about valve size, I don't understand the question.

What I have done to these heads is have the intake ports on the head ported to match the dual SU intake manifold which is 1 1/2 inch, at the same time I usually have 280Z valves installed in the head, but this head I decided to save money and leave the stock valves, and use a RV cam, foolishly thinking that the cam would make up the differance of having smaller valves.

The problem with that thinking is it doesn't take into account other things, like how cams actually work.

So now I have a head that has less torque than I have with a completely stock head, and on the hiway where the cam kicks in, I am choking it with small valves, as it is sitting on a stock L20b block, which I have never found any usefull power above 4500rpms.

I am having another head built at this moment to replace the head that is on the engine now.

Now I need to be educated on a single carb sidedraft, do they have the same power as dual 38mm SUs with 1 1/2" runners, what is the best brand?

[wayno]

 

 

Hey there datzenmike, I didn't really notice that your photo was of a modified intake till hainz mentioned it was being hogged out, so will it make a differance with a L16 intake manifold?

It's hard to tell if the L20b manifold and the L16 manifold have the same runner size back closer to the carb, or if the L16 is smaller, as the L16 manifold has a water jacket for warming the manifold, when the L20b manifold does not, as it is warmed using the exhaust manifold.

Another reason is I don't want to remove the L16 manifold now, as I just mounted it with a new gasket.

Are the intake runners the same size inside?

[Z-train]

I don't know what this question means, as I don't know what measurements you are asking for,

The port opening where the manifold mounts to the head.

[wayno]

The port opening where the manifold mounts to the head.

 

 

The head is ported out 1 1/2 inches, same as the dual SU type manifolds, at least the ones I have.