spt2002

Re: L28 injected manifold



Posted by Stephen Taranto on May 19, 19102 at 01:30In Australia

In Reply to: Re: L28 injected manifold posted by jason on May 15, 19102 at 19:26:00:

: G'day

: I was trying to get this setup to work just a few weeks ago. Unfortunatly, it s not as simple as it looks. The plenum chamber is not parallel to the engine so the front two intake runners are longer than the rear two, Another problem is that there is a water jacket running under-neath the plenum chamber (rather difficult to get in and re-join it). One option is to cut the flanges off the runners so that you have the injector mounts etc and then custom make a manifold from ali tubing, I suppose it depends on how talented you are as to the final product (as there is a bit of science to the manifold design) It still might be worth trying to cut and weld the manifold just to see what happens.

: cheers
: jason



Hi Jason

I have been working on exactly this for some time. I'm no scientist or mathematician (or speller). But as I understand it and I may be wrong, there are some calculations to be done.

1. Swept volume/capacity of engine versus volume of plenum chamber including volume of ruuners (I think)This I believe should be 1/1.
On the L28 this is approx 2.8/3.0 (a very ruogh estimate)It's near enuogh to being ok.

2 Total cross sectional area of all inlet ports versus total cross sectional area of throttle body choke(s). This I believe should also be 1/1.
On an L28 this is approx 680 sq.mm./315 sq.mm.(the area of the opening on the plenum chamber's flange for mounting the throttle body).This is half of what might be ideal. It will certainly creat negatve pressure in the plenum wigch would speed up the airflow through each runner. That may be detramental at high engine speed.

3 Length of runners (torque characteristics are derived from this). On the L28 they are approx 175mm which is going to give good low down torque characteristics. Not good for top end power.

4 Position of injecters. On the L28 they are vertually in the head and aimed nicely at the intake valves. This is good for the torque factor too. Not too good for the high end power as I understand it. Note that racing cars quite often have their injectors either just behind the throttle body chokes or even directed at the throttle body chokes on the inlet side of the chokes all be it on extremely short runners.

All in all it was a great set up for a streetable car with a good deal of weight to drag around, not for a high performance sports car(which it quite clearly wasn't).

Now to make it work better for better power/performance you need to rework a couple of things for either 4 or 6 cylinders.

1. A new plenum grafted on to the manifold, keeping the linkage mountings would be the way to go. You could then open out the runners a little(there is not much meat in them)and match them to the inlet ports as they are way out on the L28.

2. The new plenum would then allow for a new throttle or two which would better match the area of the inlet port openings. You may want to have them facing the runners which would work well with the linkage towers too or you have them at each end of the new plenum or side by side at one end. They're not like carby's. They dont have keep the fuel suspended in the air flow. They just have to control airflow. It should just be a volumetric thing, what ever adds up.

3. Runner length would stay about the same and that would be quite ok considering you are going to up the airflow and the fuel flow.

4. Use higher flow injectors of your choosing and may be then include secondery injectors idealy at the other end of the runners (somewhere up stream in the runners) or located in the plenum or just behind the throttle body chokes. This will help at high engine speed. I would start without the secondaries and play with different primaries first.

5. You will obviously need to make the injector cutouts in the L20 head too.

6. All the necasary sensors will be required and a good ecu to make it run.

It's a long post, I know. And I would love for somebody out there to correct me if I'm wrong because I'm about ready to build mine up roughly along those lines for my 280 flat top in my 74 260 Z coupe.










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: : G'day

: : I was trying to get this setup to work just a few weeks ago. Unfortunatly, it s not as simple as it looks. The plenum chamber is not parallel to the engine so the front two intake runners are longer than the rear two, Another problem is that there is a water jacket running under-neath the plenum chamber (rather difficult to get in and re-join it). One option is to cut the flanges off the runners so that you have the injector mounts etc and then custom make a manifold from ali tubing, I suppose it depends on how talented you are as to the final product (as there is a bit of science to the manifold design) It still might be worth trying to cut and weld the manifold just to see what happens.

: : cheers
: : jason

: I have been working on exactly this for some time. I'm no scientist or mathematician (or speller). But as I understand it and I may be wrong, there are some calculations to be done.

: 1. Swept volume/capacity of engine versus volume of plenum chamber including volume of ruuners (I think)This I believe should be 1/1.
: On the L28 this is approx 2.8/3.0 (a very ruogh estimate)It's near enuogh to being ok.

: 2 Total cross sectional area of all inlet ports versus total cross sectional area of throttle body choke(s). This I believe should also be 1/1.
: On an L28 this is approx 680 sq.mm./315 sq.mm.(the area of the opening on the plenum chamber's flange for mounting the throttle body).This is half of what might be ideal. It will certainly creat negatve pressure in the plenum wigch would speed up the airflow through each runner. That may be detramental at high engine speed.

: 3 Length of runners (torque characteristics are derived from this). On the L28 they are approx 175mm which is going to give good low down torque characteristics. Not good for top end power.

: 4 Position of injecters. On the L28 they are vertually in the head and aimed nicely at the intake valves. This is good for the torque factor too. Not too good for the high end power as I understand it. Note that racing cars quite often have their injectors either just behind the throttle body chokes or even directed at the throttle body chokes on the inlet side of the chokes all be it on extremely short runners.

: All in all it was a great set up for a streetable car with a good deal of weight to drag around, not for a high performance sports car(which it quite clearly wasn't).

: Now to make it work better for better power/performance you need to rework a couple of things for either 4 or 6 cylinders.

: 1. A new plenum grafted on to the manifold, keeping the linkage mountings would be the way to go. You could then open out the runners a little(there is not much meat in them)and match them to the inlet ports as they are way out on the L28.

: 2. The new plenum would then allow for a new throttle or two which would better match the area of the inlet port openings. You may want to have them facing the runners which would work well with the linkage towers too or you have them at each end of the new plenum or side by side at one end. They're not like carby's. They dont have keep the fuel suspended in the air flow. They just have to control airflow. It should just be a volumetric thing, what ever adds up.

: 3. Runner length would stay about the same and that would be quite ok considering you are going to up the airflow and the fuel flow.

: 4. Use higher flow injectors of your choosing and may be then include secondery injectors idealy at the other end of the runners (somewhere up stream in the runners) or located in the plenum or just behind the throttle body chokes. This will help at high engine speed. I would start without the secondaries and play with different primaries first.

: 5. You will obviously need to make the injector cutouts in the L20 head too.

: 6. All the necasary sensors will be required and a good ecu to make it run.

: It's a long post, I know. And I would love for somebody out there to correct me if I'm wrong because I'm about ready to build mine up roughly along those lines for my 280 flat top in my 74 260 Z coupe.