8Stack efi & manifold vacuum pressures

[Dimis]

Can anyone please tell me how their 8 Stack weber style efi system manages the following:

1) MAP pressure
2) the vacuum for the brake boost
most importantly...
3) do you know what vacuum pressure readings you're seeing at part throttle ie when cruising 0-20% throttle.

Else, I'm open to hearing about your driving experience with 8-stack efi system. TWM, Inglese, eightstack or other.

How did you find it handled cruising or street driving?
Eg: from dead stop to say 30% throttle
Or maintaining 20% throttle.

Thanks



Many thanks

[Gaz64]

Anthony,

If the intake runners are plumbed with 3/16-1/4 tubing into a common log, you can then have your map sensor and power brakes from that.

Technically the vacuum readings should be generally the same, camshaft dependant.

Rate of throttle response is linkage dependant.
You don't want throttles that open too fast off idle, or are difficult to open.

[bobcowan]

Getting usable vacuum with an Individual Runner intake is a little more involved, but certainly not overly impossible.

Wayne used to carry a manifold that had a large open plenum on the bottom. That works really well. He doesn't carry that anymore, and tells me it's no longer available. That's too bad. If you're really lucky, you might find one in the used market.

Otherwise, you'll have to make a plenum. This one was built for me by a company that's no longer around. But it's pretty simple.



For a power brake booster, I would also use a large reservoir on the firewall or underneath the fender.

The actual vacuum signal will depend on how the rest of the engine is built - particularly the cam selection. I have a huge cam and high compression, I don't get much of a vacuum signal at low rpm's.

As for driving experience - it is awesome! Crisp throttle, and power everywhere. EFI is not subject to the same low rpm problems that a carb is. Driving down the highway at 2,000 rpm's is smooth and quiet - sedate as a kitten. But mash the throttle, and it screams like a banshee and takes off like a rocket.

Be aware that any IR system can be difficult to set up and tune; just like any multi-carb intake is. The learning curve is a little bit steep. But once you get it figured out, it's relatively easy. Keep in mind that "Close Enough", isn't.

[redmt]

I just happen to have one of the VCP 8 stack manifolds for sale complete for the 351 W motor.

[Dimis]

I'm looking at an 8 stack EFI system either - Eightstack or TWM.

TWM I believe use tubing that connects all the t/bs (similar to bobs pic), but it's located above the manifold, which is housed under the center pivot of the linkage below the fuel rails, to reference for vacuum pressure.



Eightstack have developed this manifold (which isn't cheap).



Not there are 8 small holes drilled (4 of which you can see) on the underside of the manifold, inside the chamber, just beneath each of the runners.


They then seal it off by screwing in the bottom plate to create a plenum for reservoir for vacuum pressure.




What I was hoping someone could tell me is what do I need to do to ensure I can create suitable and consistent vacuum pressure for reading MAP having Brake boost, to have a street-able, and easier to tune EFI system.

Engine will be 482 cubes - mild cam, but details yet to be finalized.
Open to your thoughts, knowledge and opinions.


PS: Thanks Redmt... but I need it for an FE


Many thanks,

[Dwight]

picture of my Eight Stack for a small block Ford plenum
you can call Dale or Bob at Eight Stack and I'm sure they can help you.
Eight Stack Injection- home
Dwight

[blykins]

Power brakes? What's that?

[bobcowan]

Originally Posted by Dimis

What I was hoping someone could tell me is what do I need to do to ensure I can create suitable and consistent vacuum pressure for reading MAP having Brake boost, to have a street-able, and easier to tune EFI system.

I have the manifolds shown above, on a 427W small block. It's a large plenum with plenty of reserve. With a moderate cam, you'll get a balanced vacuum signal just like you would with a single plane carb manifold.

The deciding factor would be your camshaft. A moderate to mid level cam will create a strong signal off idle. If you have a big cam, you will probably need a reservoir for the power brakes, just as if you were using a single carb on a single plane manifold.

I also have EFI. Because my cam is gigantic, I don't get much of a vacuum signal. My primary fuel and ignition maps are based on TPS and RPM. And then I supplement those maps based on vacuum. As my vacuum drops, it adds in a bit of fuel, and takes away a bit of timing.

It's an excellent system and a real joy to drive. And the looks are just killer.

[Gaz64]

Anthony,

I'd plumb the large port from the back of the manifold plenum to a vacuum reservoir tank for your power brakes. The input to the tank should have a brake oneway valve fitted.
Your map sensor can be plumbed to one of the other smaller fittings at the rear of the manifold.

[redmt]

What are you guys using for Electronics? I'm trying to set up a Mega Squirt and I can't even figure out the hard wiring. It's possible the guy who ordered it all got the wrong stuff. MS has been no help

[Dimis]

Thanks guys that's exactly the kind of theory lesson I needed.

I'm hoping because I have a fair few cubes that it will give me a better chance for the cam to act as moderate or mild creating the vacuum pressures required for easy tuning.

If this all gets too difficult there's always a tunnel wedge with a couple of carbs.

As for electrics - I'm leaning towards motec.
Just got to find the coin to afford it.
Sorry I can't offer any advise on the Mega Squirt stuff, it's beyond my knowledge, like most things unfortunately

[Mando]

Dimis, I ran the individual vacuum lines to a common log then ran any lines I needed from there.






Regards.

[Gaz64]

Mando,

I can never stop smiling every time I see your intake,

[Mando]

Dimis, you should be able to talk with Steve Morrison on 0408 335 108 or his office on
03 97395359.

Regards.

[MOTORHEAD]

This is how the earlier 8 stack manifolds were done. Pic is my version, based on what they told me. Running webers for now.

[bobcowan]

Originally Posted by redmt

What are you guys using for Electronics? I'm trying to set up a Mega Squirt and I can't even figure out the hard wiring. It's possible the guy who ordered it all got the wrong stuff. MS has been no help

I'm using a Megasquirt MS2/Extra for fuel and ignition.

I'v never done anything like this before, so the learning curve is rather steep. But once you get it figured out, it's worth the effort. There are some really nice features available.

Winter Upgrade - Megasquirt

Megasquirt Ignition

[Luce]

Bob,

I'm glad you stuck it out and got it working to your liking. I'm legal and on the road. I'm chasing a minor glitch, but I know what it is. I had to add a trigger wheel because the dizzy doesn't give enough data points to accurately time the ignition, especially how I had it set up with the mechanical advance still working. ( I was getting tach from the VR in the dizzy and trying to add vacuum advance with MS when I started)

I need to cut a hole in the side of my cap so I can get the phasing on because near redline, it get's too far off and my MDS falls over. That and leaning out the fuel map in the cruise area some more. Run's great though and it's almost too many things to play with.

[bobcowan]

Yeah, it took me a while to get things figured out. But now that it's done, it really runs great.

I got rid of the distributor altogether. One of the reasons for a wasted spark and batch fire is that it all comes from the crank. Nothing is read from the cam or the distributor. That's more accurate at 6,000+ rpm's. It's also simpler to build, and easier to tune.

[Skuzzy]

Bob, which ignition system did you go with?

I am considering Megasquirt for my engine build as well and would like to get away from distributors while I am at it.

[Rwillia4]

I have a TWM setup and you are right the individual stacks are connected under the fuel rails with tubing to a common plenum. The MAP sensor plummed from here. I don't have vacuum assist breaks (and I don't need it for this weight) but the engine is smooth and stable at idle so I think the common plenum works well. I run an XFI with MSD and haven't had any issues. The setup was pretty easy. Get a buddy you trust in the passenger to make f/a adjustments on the fly to smooth out the response through the rpm range under load.