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Crazy idea? Seeking opinions on this intake


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Short and large diameter runner are for HP and small, long runners for torque I believe. These are long and large runners, so best of both worlds?

 

Still, the flange doesn't fit the head.....

 

What If you cut it off behind the flange and weld a  EFI flange on it with the injector bosses and port it to match the diesel runners, would this be a good low down torque manifold?

I'm asking because I have a L28 in my heavy Nissan Patrol which could use more low down torque. I'm going turbo with it and want as much torque as possible (already have a P90 head, RB20 turbocharger, flat top pistons)

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^ I was just thinking along the same lines as JP.

 

1: First the current injector position has to go. It is just wrong . You can buy weld on universal injector bungs and easily position the injectors in the right position on the manifold. Factory EFI designs and angles are a good starting point. You want the spray pattern to hit the backside of the intake valve . Right in the center of the valve is a good starting point. 

 

2: Cut the  " J " turn out of the manifold. Leave as much of a straight leg as you can on the flange side and the plenum side. Then weld the two sections together. Basically you should now have shorter runners with a larger diameter ( than the Factory NA EFI runners )  that allows a straight shot into the cylinder head. Win Win. Of couirse Plenum is now rotated 90 degrees, so you may have to reposition the TB flange, if it not a symmetrical square flange. 

 

With these modifications, particularly the injector boss re-location,  you will have something interesting to test that will at least work. 

 

Look around the internet and you will find successful and proven high performance Plenum manifold designs that all have similar characteristics. Key points are:

 

A: Injector placement as close to intake valve as possible. 

 

B: Proper plenum design. This can be very tricky, especially on Turbo engines. What looks right can be terrible from an actual distribution of air flow. There are some basics to follow, but using a pre-made factory or Custom plenum is a not a bad idea. Unless you have $100,000 or so of CFD computers and air flow testing equipment sitting in your basement

 

C: Runners as straight as possible. No unnecessary bends to slow down airflow. Velocity is important even in a dry manifold. Some gentle bends may be seen in some of these manifolds, but that is only to facilitate port entry angle and hood clearance.

 

 

Here are some pictures  picture of proven designs for Audi/VW 1.8 5  Turbo engines. NA version is virtually identical. A good design for a NA engine will also be good for a Turbo engine, and vica versa.

 

SEM manifold:

 

phpU8c2WQ.full.jpg

 

034 Motorsports manifold

 

2z8cmt3.jpg

Edited by Chickenman
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These should give OP some basics as to good overall designs. Pay attention to injector placement and plenum design. You don't need the flashy CF and anodized finish to make something decent. 

 

Here is a picture of an SEM manifold next to the stock VW/Audi manifold. Runner sizing on VW/Audi engines is more than large enough stock ( We have 5 valve per cylinder engines ). Most of the improvements come on the Plenum side. Plenum is too small on the stock manifold. Stock manifolds does not have a very well  balanced airflow to cylinders either. 

 

 

post-44147-0-35783000-1488531595_thumb.jpg

 

Custom Plenums produce some of the finest aftermarket manifold in the world. Very highly regarded in the Motorsport world. Check out the 2JZ-GTE manifold on their FB page for some design ideas for the L28. Yes thye do supply L28 manifolds as well. These are $$$$$:

 

https://www.facebook.com/customplenumcreations 

 

 

16806974_1583004888393828_86913013682021

 

 

SRDE20 Manifold

 

17015701_1590633714297612_13967986498567

Edited by Chickenman
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Short and large diameter runner are for HP and small, long runners for torque I believe. These are long and large runners, so best of both worlds?

 

Still, the flange doesn't fit the head.....

 

What If you cut it off behind the flange and weld a  EFI flange on it with the injector bosses and port it to match the diesel runners, would this be a good low down torque manifold?

I'm asking because I have a L28 in my heavy Nissan Patrol which could use more low down torque. I'm going turbo with it and want as much torque as possible (already have a P90 head, RB20 turbocharger, flat top pistons)

 

the main/easy correlation is with length - short runners for high rpm performance, long runners for low rpm performance. this has to do with benefits from tuning for pressure waves as much as actual flow. diameter has to do with velocity and so is more of a dependent variable based on other design factors.

 

i like the idea of this manifold for a mild/street turbo application though. long runners for good low rpm response and boost for high rpm. i think the runners are still a bit long for that though, so i think you're idea of welding a plenum to the lower section is great.

 

but whats teh point of any of this if the flange doesnt fit?

 

 

 

^ I was just thinking along the same lines as JP.

 

1: First the current injector position has to go. It is just wrong . You can buy weld on universal injector bungs and easily position the injectors in the right position on the manifold. Factory EFI designs and angles are a good starting point. You want the spray pattern to hit the backside of the intake valve . Right in the center of the valve is a good starting point. 

 

2: Cut the  " J " turn out of the manifold. Leave as much of a straight leg as you can on the flange side and the plenum side. Then weld the two sections together. Basically you should now have shorter runners with a larger diameter ( than the Factory NA EFI runners )  that allows a straight shot into the cylinder head. Win Win. Of couirse Plenum is now rotated 90 degrees, so you may have to reposition the TB flange, if it not a symmetrical square flange. 

 

With these modifications, particularly the injector boss re-location,  you will have something interesting to test that will at least work. 

 

Look around the internet and you will find successful and proven high performance Plenum manifold designs that all have similar characteristics. Key points are:

 

A: Injector placement as close to intake valve as possible. 

 

B: Proper plenum design. This can be very tricky, especially on Turbo engines. What looks right can be terrible from an actual distribution of air flow. There are some basics to follow, but using a pre-made factory or Custom plenum is a not a bad idea. Unless you have $100,000 or so of CFD computers and air flow testing equipment sitting in your basement

 

C: Runners as straight as possible. No unnecessary bends to slow down airflow. Velocity is important even in a dry manifold. Some gentle bends may be seen in some of these manifolds, but that is only to facilitate port entry angle and hood clearance.

 

 

Here are some pictures  picture of proven designs for Audi/VW 1.8 5  Turbo engines. NA version is virtually identical. A good design for a NA engine will also be good for a Turbo engine, and vica versa.

 

SEM manifold:

 

phpU8c2WQ.full.jpg

 

034 Motorsports manifold

 

2z8cmt3.jpg

 

 

i agree but a few pesky clarifications :) aftermarket manifolds are entirely built for high boost/high rpm - thats why they look like they do. doesnt mean they should be used as a guide for intake manifold design and doesnt mean they are right for everyone. for instance, factory RB manifolds look a lot like the diesel manifold being criticised here (pictures below)

 

also i entirely agree that the injector placement in the proposed manifold is... far from ideal. seems to be a convenience factor based on where the original flange was. but FYI the common practice of injector placement at the head is actually primarily to help with emissions (esp cold start) but the goal is just getting a well homogenized/atomized mixture in the chamber and there are other alternatives.

 

34gsjex.jpg

 

rmi99v.jpg

Edited by ol doc gully
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