304 Power Curve

[vlad01]

Don't the banana bits in them act like runners? I would of thought cutting and adding a box on top would mess with the flow characteristics making them worse in some aspects

[vlad01]

people have tried lots of things .bigger necks welded on and 90mm TB's ,TB straight on the front no elbow,runners cut to above fuel rails and boxed,2 plenums one on each bank,cut the bottom out and shorten runners and weld the bottom back in creating a bigger plenum are and shorter runners,group A style cut and weld jobs.most end up back at the point of bolting on a 4barrel manifold setup.ive seen one in nz with 8 TB trumpet manifold at powercruise went pretty hard until a conrod ended up on the ground LOL.

we have one of those manifolds laying around somewhere here.

[Holden202T]

yeah thats exactly the problem, you shorten the runners and they are crap down low in the revs, pretty much where you want more

i've seen a 304 rebuilt, 286 cam all the usual shit, cut the bananas off at the fuel rail level, added a box and twin TB's on the front .... 150hp at the wheels or something, put the stock setup back on, 200hp at the wheels, same dyno lol!

[Grim304]

yes, the length of runners is very important.
Not difficult to do, just a matter of careful and correct physics applied.
Trumpets inside the box give the length and they can cross each other, it would end up being close to the original length

[immortality]

I've seen really good gains with a torque power dual plane with a 4 barrel throttle body on it! only real issue with it was the heat from the engine into the filter above, I've never seen the results from a c.o.m.e manifold with the TB on the front but it looks the goods!

The COME manifold is way to big and it has distribution problems running lean to rich front to rear. Only really any good for a 383 or 396 strokers or engines that rev to high heaven. Much better manifolds around. The TP manifolds is where it's at I think.

COME now do a low rise single plain manifold much like the Harrop and TP single but with a lower carby base for bonnet clearance, seen one used on a engine that made good power with a little porting to the manifold. Probably not bad manifold if you have bonnet clearance issues.

[immortality]

yeah thats exactly the problem, you shorten the runners and they are crap down low in the revs, pretty much where you want more

i've seen a 304 rebuilt, 286 cam all the usual shit, cut the bananas off at the fuel rail level, added a box and twin TB's on the front .... 150hp at the wheels or something, put the stock setup back on, 200hp at the wheels, same dyno lol!

That would be the Walker manifold. Seems it is a total failure. I don't think there made any more.

[immortality]

people have tried lots of things .bigger necks welded on and 90mm TB's ,TB straight on the front no elbow,runners cut to above fuel rails and boxed,2 plenums one on each bank,cut the bottom out and shorten runners and weld the bottom back in creating a bigger plenum are and shorter runners,group A style cut and weld jobs.most end up back at the point of bolting on a 4barrel manifold setup.

There was a thread on the SC forum about ported standard banana manifolds that flowed as well as the Star 90mm TB item. It was ported using the liquid like stuff (I forget what it's called) with only a standard 65mm TB, I figure it would flow better again with a bigger TB on it.

No matter what you do though, you still end up with a manifold that has the plenum at the bottom which is great if you're making a hair dryer but fairly much a POS for making good power.

I'm thinking I'm gonna try some HPC type coatings on mine along with maybe some port matching and a 75mm LS1 TB as I want to keep the Senator stock looking but failing that I may just go to a TP dual. I'm picking up a spare bananas manifold to play with this weekend, once I have that I'll have the LS1 TB and adaptor on it's way.

I still think that the VL/VN Grp A manifolds are one of the best for a Holden engine but unfortunately they just cost to god damn much.

[Grim304]

The plenum is only on the bottom if you use it.

[delcowizzid]

todays ebay find LOL quad webber manifold http://www.ebay.com.au/itm/Holden-Vn-Vp ... 27d77f584e

[Grim304]

Very similar to the type of stuff we used to make in the 70's for cars which never had any aftermarket manifolds available.

My idea was to try and remove some of the heat and to include cross overs and trumpets to add virtual length and speed into the runners, unsure of a final design but I would make up my mind as I made it, likely a twin Throttle body with either 1 per bank or 1 per quad front/rear.

It's only an idea at this stage and I have no actual requirement yet as busy enough with other projects