Plenums, Do They Run Lean On Rear Cylinders?

[Redback]

Hey Guys,

I have been tossing up whether or not to bolt up a plenum to my new engine that is being built. I have been told that a few of these plenums with the throttle body mounted on the front tends to lean out the rear cyclinders. Tests using an exhaust gas temperature meter have apparently shown that the rear cyclinders are running hotter. Apparently the best design is like the APS/Atomic with the throttle body mounted in the centre. Also why did Ford not mount the throttle body to the front, rather they have also opted to mount the throttle body in the centre even as they moved forward to the FG? Can someone shed some light on this please?

[Adam]

There's another thread about this very subject. Have a search for that.

I don't think it would matter.

When a cylinder is on it's intake stroke a vacuum is created, so the higher pressure in the manifold will push into that cylinder.

Another thing to remember is that not all the cylinders are on the intake stroke at the same time, so they're not all 'competing' for the intake air.

If real world proof is more your thing then have a look at a picture of an engine from a Ferrari, Lamborghini, Mercedes Benz, Holden, a F1 car and the list goes on and on! They all have throttle bodies at one end of the chamber.

[seduced]

Also, if the thoery is that enough air can't get to the rear cylinders, wouldn't that make them run rich not lean being that the injectors will still spray equal amounts of fuel across all cylinders?

[HIRO F6]

Of all the motors ive seen destroy piston number 6, all of them had aftermarket plenums. We are now starting to see some great results from the FG intake being put onto BA / BF's. Food for thought!

[DUS12]

mine destroyed number 6 twice with stock plenum, %99 are people pushing their cars without the proper mods, tune with a safety margin, I think these cars have problems with cooling the back cylinders

[Wenier]

I thought it was the first cylinders could run lean as the pressurized air tries to go straight past them. But in saying that if it is a plenum from a reptuable maker then it should be designed in a way to avoid any leaning out.

[BarKer]

I think it is old school thoughts...

The old days when they had carbies leaning out on the furthest cylinders could be an issue and even for the early injection systems which used throttlebody injection problems could arise.. But surely multipoint injection systems made leaning out a problem of the past..

[RAP1D]

The stock fuel rail can be fingered for some lean number 6 's, though there is also a heat build up there... there's so many theories going around on this subject, believe what you like.

Front mounted TBs have been used on turbo 6s for years, RBs, 1J's ect if there were major concerns the most common plenum used on these cars would centre fed.

EA- ED falsons used a front mounted TB back in the 80s/90s, it was only the move to variable vanes/ runners in the EF that the centre fed TB came about.

I dont think anyone should jump and get all paranoid, there has to be near 1000+ XR6Ts running after market plenums, many have blown motors, but loads havnt... too many variables to point the finger at these plenums.

If your concerned about this issue and want to monitor it, set up pyro meters in each exhaust runner, ther's some cool kits to buy but they're not cheap or simple to set up.

I'd lean more towards the stock fuel rail, if your running big boost pressure its a good thing to upgrade to a twin feed rail, so that it has an even fuel pressure across each injector, they they flow/squirt the same cc into each chamber.

[icer]

all these blown motors you guys see have surge tanks with sufficient fuel pump setup?

[xcopbf]

what has me wondering you remove the top half of the intake to replace withhigh performance plenum, but your bolting it to the stock bottom half of the intake. so would it not still be restrictive. and why haven't the after market shops just build a full intake plenum like the fg one piece intake manifold. I don't see the sense in having 1 half flow really well and 1 half not.