Stack Injection and Power Loss

[Mike]

I am a newby and have been lurking about for about 6 months. Have visited RCR twice now. Have had an Intermeccanica Speedster (911 power - was in Excellence a few years ago).

I love the look of the velocity stacks on the 2.7 RS that I had but never really could get it dialed in. Either flat spots, coughing and spitting or shooting unburned fuel out the exhaust. Kind of killed my love for the car. Ended up selling (for more than I paid - probably never happen again).

Anyway, I was thinking that stack injection on a V8 would be the way to go for a Lola, P4 or GT 40 project - the best of both worlds. I called Kieth Craft and asked them. They said that as soon as you put a filter on stack injection, significant power loss occurs (in the range of 100 hp). This is their experience with all filter solutions.

Can't run without filters.

Anyone have a solution to the problem?

I'd like to make the plunge but not willing to handle the power loss.

Thanks.
Mike

[Jac Mac]

You need to rethink the air filter Status Quo, and work towards a completely sealed plenum with large panel or cone type elements in the case of the GT40, The other two body types would require body specific design's. This would remove the elements away from the stacks. A large pod type filter used buy the turbo boy racers is the type I have in mind. In the Mk1 40 one of these could be fitted in each side of the rear clip. A bit of a clever re-design in this area would hide the filter,s and give the visual of 8 trumpets thru the rear deck plexiglass.

Jac Mac

[Jim c]

I agree you need to see the stacks.

I have studied my car MK1 and if you could seal off under the rear clip with a tray then you could make filters fit inside the intake ducts , maybe 2-3 layers off foam.
They are not a large area so they may need regular cleaning.
Unlike Jac macs suggestion you would see them.
I think if you make it look good it wont mater if you see them.
IMHO They are there for a reason you dont have to hide them.

The hard part would be the tray with a good seal.

Jim

[J. Salmon]

I have heard mixed reviews of stacked FI. I am under the impression that it is the lack of the MAF sensor that makes it problematic. I could see this as an issue when you change the flow from expected via a filter.

How is the driveablilty of Webers in comparison? Haven't heard too many folks knocking them.

[Bill Bayard]

I had a TWM 8 stack/Motec setup on my car, and dealt with the problem as shown in the first photo of the link below. There was no noticeable difference at all, with or without my home made filters. My engine never missed a beat,
and had instant throttle response from 0-6000rpms+.


http://www.gt40s.com/forum/gt40-tech...induction+hole




Bill

[Mike]

Bill -
Thanks for you link. Very cool setup - I am very impressed. Looks like the problem may be solved by a large manifold-like chamber. Maybe the guys at Kieth Craft only tried individual filters.

I think that I saw your car for sale earlier. I gave it some thought. Need to fix my storage situation first. My wife is not to keen on parking cars outside our house and the 3-car garage is full.

Thanks again. Nice to have at least one solution.
Can't bear to do a modern intake manifold setup.

Mike

[Mike]

Bill,

Who did you buy your engine from?

Mike

[Lynn]

Bill, Jim and Jac-Mac,

I have often considered not only filtering the two deck ducts, but also putting airflow meters in them so that MAF control would be a possibility with stack injection. My question is, how are you guys sealing off the the front of of this deck cavity against the firewall? It may not be quite so critical in terms of filtered air (although I wouldn't want to be out in a dusty area when it was windy without it being sealed), but it would be intolerable if your were trying to measure intake air volume for engine management.

The only workable solution I could come up with is another piece of plexy.

Lynn

[Ian Anderson]

Lynn

How about putting in a secong window actually mounted on the rear clip?

Ian

[Jac Mac]

I think if you put the MAF in each side duct of the clip you would end up with a delayed signal due to the increased plenum volume that would be created, therefore Ians suggestion could be modified to that of a clear molded plexi cover that reduced the volume to an acceptable level.

What I would really like to see is someone come up with a 'Replica IDA' that has the injectors hidden inside what was the float chamber and operates as a stand alone unit, or is that another thing I am going to have to put on my things to do list. I want this unit to look like an IDA, not a converted throttle body.

Jac Mac

[Jim c]

Bizzare Jac mac I was looking at a webber 3 days ago thinking exactly the same thing.
I love the webber look.

MAF SENSERS
All the multi throttle set ups that I have played with have been tuned on tps.
With a good ECU never seemed to have any real dramas.

Have had the pleasure off playing with cheap systems and they are a night mare.
Always have poor resolution at low TPS settings and the inability to add more load sites in areas required.
The other major factor is the injector spray patterns.
It will give off throttle problems.(large droplet size)

I understand that the MAF takes air desity into account if I remember correctly. (even on TPS a good system will have temp correction too deal with SOME of these issues). but you can get them good if detail in these areas is given.

I suppose like most things it is comprimise.

The other thing I had thought of was 8 trumpets coming into a plenum made of alloy about the volume of all the runners there abouts then putting a clear polycarbonite lid of about 15mm thick then run it all through 1 or 2 throttle bodys.
Then you could run your MAF or MAP senser.

[Lynn]

Ian & Jac Mac,

That is precisely what I meant by "another piece of plexy." Great minds think alike, I guess ;-) Jac Mac, even with the second window the transfer function of the MAFs would have to be manipulated (possibly in the circuitry 'adding' the two signals) to compensate for this along with the way the EMS adjusts the fuel map based on TPS, as well as TPS history, and RPM. e.g. if the RPMS are low and TPS is opening, the fuel map would want lead the MAF readings slightlty (modeled on a spring/damper for rates of change.)

Jim C,

What really sets the MAF controlled EMS apart from speed-density is its adaptability: you can make changes (within reason) to the intake, valve lift, air filters, etc without having to reset the fuel maps. The other thing is that it also adapts for density/altitude changes which can be very important to a performance road car and can certainly reduce set up fiddling with a race car.

Lynn

[Bill Bayard]

Originally Posted by mdw48009

Bill,

Who did you buy your engine from?

Mike

Mike,

Christian Nelson at The Engine Factory in NJ.


Lynn,

I don't know if you'd ever be able to COMPLETELY seal up the induction

area of the rear clip. That's a lot of wires, hoses, etc., let alone the firewall

to deal with. Being able to seal all that up and still be able to raise the rear

clip would be a MAJOR challenge. How about a plenum (w/MAF sensor(s)

added) surrounding the stacks, like the plexiglass filter box belonging

to a member's (I've forgotten whose) car?

Bill

[fostereast]

Hey guys,

I have not experienced stacked webers or TWM type injection, but in David Vizard's writings, he indicates that filtered stacks (with an appropriately designed filter) will result in more power than open stacks. With all the testing David Vizard does and has done, I have a hard time believing this would not be the case. (the books I have are probably from the eighties)

Any comments? I'm building an engine that I might use 58mm webers on. (With filters of course )

[Neal]

I have a 347 with 48IDAs. We lost 20hp when we put the tea strainer style filters. Pulled them off and the power came back.

[Jac Mac]

With regard to tea strainer filters, while they often show a power drop in a Dyno situation in the real world with the vehicle in motion the air pressure will (hopefully) increase in the plenum area if you have done your homework. Vizard is correct with the filter idea, With jet sprint boats we picked up power big time with K/N type filters on Hilborn type injection over straight trumpets ( no filters ) mainly because standoff was being lost etc. I watched a F5000 car without airbox here last year where the front filters were being bent back about 30 deg as it went down the front straight, you would have a job convincing me that the rear cyls were seeing the same air supply in that situation!

In our Stack setup I still feel that the trumpets need to be in their own plexi plenum ( I think a simple plexi box that seals at the base of the air horns with the MAF in between the two rows of throttle bodies from underneath- it wont be too warm after you start the motor, hold your hand on a manifold runner of a hot motor,then start it up, cools down real fast dont it!) then fit the filters in the side intakes, all your plumbing etc will be under the bottom of the plenum and wont be disturbed when you lift the rear clip. Now you have to do a real good job of sealing the rear clip even to the extent of fitting a second glass firewall as part of the rear clip.

Jac Mac

[Ross Nicol]

Jac Mac- can you explain how the filters control the reversion or standoff and aid power , I assume from the amount of gunk I have on the lower surface of my rear screen after a race that I have a fair bit of it.Is this power increase across the board or does it differ with various engines.I've been running with no filters in the belief that they are restrictive and power robbing, but from what you're saying if I fit uni filter socks to each of my trumpets I should expect a power increase, if so I want it (racers lament).This would also take care of my worry of stones into the lungs of the beast too. Of course I don't visit the kitty litter very often for this to happen, (honest!).

Ross

[Pete.]

" "Of course I don't visit the kitty litter very often"