Ld28 Intake

[87pyro3]

Befor everyone bashes and banters     i searched 

most if not all the post and topics have insificent coverage or died.

 

where would be the optimal location of the injector bungs on the ld28 ontake, to take advantage of the longer runners?

three locations come to mind.

1. up against the flange

2. at the end of the runners below the the pelenium

3. mounted at the begining of the runners  spraying down from ontop of the second flange

 

 

 

If i missed a post that went into detail  please just point me in the right direction and remove the post

Edited March 30, 2013 by 87pyro3

[Tony D]

Yeah you missed the discussion of counter flow injection completely...

[87pyro3]

Thanks for the reply   any way you can post a link

im not afraid to read  

but finding the right keywords in the search bar is not a strong point of mine 

[roger280zx]

It depends entirely on your application.  My opinion is the lower the revs the closer to the stock injector location; i.e., option 1.  Many higher revving race cars "fog" into the velocity stack at the end of the runner, or option 3.  Both locations can be made to work well, but the latter tends to be difficult to tune at lower revs resulting in high idle and poor low rev drivability.  It does; however, shine in applications with enough head flow/cam to reach the optimal rpm.  But this is all just my opinion.

[Tony D]

The engineering facts counter the prior opinion.

 

TBI engines run exceptionally well at low rpms. They are not injecting at the back of the valve, and universally used already well developed manifold designs that had known tau characteristics.

 

It's been shown for performance, the further you position injectors from the valve, the better for mixture homogeneity and therefore consistency and power.

 

The ONLY reason for universal placement at the backs of the valve is emissions and not having to worry about tau layer transient dynamics.

 

A corollary comment is using the air box as a flame arrester is frowned upon by the legal department of all manufacturers. Their engine designs are dictated by environmental rules, not performance.

[skirkland1980]

Corkey Bell's book says to position the injector at the point of maximum velocity which would be at the intake valve in a superior designed intake manifold. I.E a manifold that has a perfect funnel shape from the runner entry to the valve.

[Tony D]

Corky says a lot of things...but didn't follow his own advice in manifolds...

Quoting his comments on turbocharged engine FI placement (contradicted by Cosworth Engineering in Turbo applications, BTW) when someone is referencing runner length (which implies N/A application) might be far of the mark.

[Tony D]

"Maximum Velocity" at a partial throttle "any rpm beyond idle" will likely be at the Throttle Plate, and not the intake valve, BTW....

Therefore reinforcing the dominant placement above the throttle plates in most engines...(F1 being best known)

 

In a turbo car, the outlet of the turbine wheel before the toroidal diffuser is highest velocity...

Edited April 1, 2013 by Tony D

[Sam280Z]

 I would say that it depends on a number of factors besides the manifold - such as the injector characteristics, the control algorithm available, and, most importantly, how you want to use the car...

 

I have just switched from sequential injection at TWM ITBs - just behind the throttle plate - to staged injection with smaller injectors spraying at the valves. I think that I was having such trouble tuning the original setup because I was using large injectors (<2ms PW at idle) that it was difficult to account for exactly when the fuel was getting to the cylinder.

 

For a street motor, I would be less concerned with "optimal" placement for power and more concerned with the ease of tuning the transients.

[Tony D]

I thought that was what I said in Post #5...

[Sam280Z]

Yes, but I thought that I'd add my personal experience and hopefully prevent someone from choosing a hard-to-tune configuration and sacrificing drivability in the quest for a few spare horsepower (unless they need that hp, of course).

 

[87pyro3]

the object being a supercharger l28 stroker  running megasquirt.

 

so im researching everyhting. to do it right the first time around. eliminating the need to buy mulitple intakes, injectors and countless hrs on a dyno to only find out to trash a setup and start again

[Sam280Z]

What HP are you looking for? How nice do you want it to idle or cruise?

 

Large injectors far away from valves make big power but don't idle or cruise well. Small injectors at valves idle and cruise well, but don't make big power. 

 

I've tried to get the best of both worlds with staged injection. See my thread here: http://forums.hybridz.org/topic/102280-ms3-w-ms3x-install-l6-turbo-sequential-injection-boost-control/

Edited April 6, 2013 by Sam280Z

[Tony D]

Bigger Question:

 

Wet or Dry Supercharger???

 

I mean, not stating that design criteria up front in the first post... C'mon!

 

A wet supercharger design pretty much alters the manifold from velocity/flow dynamics to a tau layer consistency design biased for higher flows within that design parameter.

Edited April 7, 2013 by Tony D