Holden 304 Banana Manifold

[immortality]

The only thing wrong with a stock 304 is a small cam and poor compression which the banana manifold was designed to work with. Put on a larger after market manifold on a stock 304 and the shorter/larger runners will kill intake velocity, cylinder fill ....power.

Add a mild cam (depending on your definition of mild), some compression and a stock Harrop dual plane manifold port matched to the stock "as cast" 304 heads and you'll make over 400 hp.

I think you'll find the same with the ecotec, someone did the math and the stock manifold on paper is ideal, runner length and plenum volume and yet....

[vlad01]

Yeah I've done this tuning with a decently large cam on a 355, the COME manifold was a step backward in every way compared to the banana, even though logic said it should have performed better, at least at the top end. But it gained nothing there and lost everywhere else significantly.

Iirc, it was about 235@ 50 on the duration, somewhere mid to high 500 lift and 10 ish odd comp. It made the same power as Gareth's ecotec with arguably a lot more mods, but on a smaller 228@ cam and 540 lift cam and at lower rpm too. But interestingly the eco ran banana manifold and good heads, alloy ones with extensive re-work done here locally (as cast they were pretty bad, lots of mistakes). Both made around the 210 rwKw, the v8 was at I think 5600 rpm the eco was at 5000 rpm. Torque was higher on the eco iirc hence the same sort of power but at a lower rpm. The comp was crazy high though on e85 but not anywhere enough to account for the difference in nearly 2L and making it at a lower rpm and a smaller cam.

Also it's worth pointing out that the holden 8 has a notably larger cam per specific output than most engines used in our cars, which tells me that the heads are most likely the issue. It's also odd that the intake lobe is larger than the exhaust which tells me there could have been some band aiding done to try to improve some deficiencies.

[immortality]

I've not heard many good reports on the COME manifold except for boost or n/a if used with twin carbs on top in a tunnel ram type configuration. Most reports say it has a major air distribution issue and maybe your test results confirm that. It's way to big for a 304 and even a 355. Interestingly, my mate has a low comp 355 with a smallish cam and that COME manifold and it goes reasonably well for the tiny cam.

Here in NZ the NZV8 touring series mandated stock as cast 304 heads, control cam which was a small solid cam 234°/234°, port matched Harrop dual intake manifold and I believe about 10.5:1 CR and they made 400-420hp with that configuration using a carb. There was also a control exhaust and it had to run on BP98 fuel.

TK did always say the 304 heads had very good exhaust ports.

[vlad01]

That's interesting they get 400hp from that cam spec, not something I have seen much of without full all out porting and larger cams than that, but I don't know if they are stoked or not, it was a long time ago when I was seeing people trying to get 400hp from a 304 with the factory iron heads and it seemed to be as far as they could achieve. It almost sounds like having it 304 instead of 355 might actually make more power maybe? I have seen cases of this when the intake ports are the main limiting factor and stroking said engines would actually reduce hp potential at the gain of low rpm torque increase.

The Buick v6 is such an engine and I have also seen people de-stroke barras as a means of increasing hp. Buick Indy did this as well. This is when the heads end up liming the hp potential for a given displacement, so destroking the engine allows you to turn the engine faster for the same airflow and cam and making more efficient use of the displacement.


I know of a few examples back in the day when people tried to stroke the V6 and kind of got nowhere and some went backwards in terms of peak hp. And I confirmed this in dynosim with all the correct headflow specs and I found that at 6800 rpm, no matter how big the cam and everything else optimal, the hp sort of peaked and would not increase much. Adding a stroker, the hp and rpm went backwards, even if I put an even bigger cam. This tells me, that the heads with all potential eeked out of them are only good for about 100hp/L and will peak at 6800 rpm at the stock stroke, destroking suggests that the rpm can be increased well past 7500 rpm and hp can start to increase further but the gains were probably not worth the cost and reliability of the valve train and such high rpm for a engine of this design.


Man this has gone way off track, sorry everyone

[VK_3800]

Yep, horses for courses. Testing the manifold in isolation is a good approach but it doesn't tell you much if the factory intake isn't really a restriction on a standard engine. Do the same test where it is a restriction (higher compression, a decent cam and exhaust and/or stroked) then I imagine you'll see a bigger improvement. The numbers may be a little underwhelming as-is but they do seem to show that more can be had from the stock manifold, which I believe is the point.

The intake air temp drop is also interesting, I'd suggest that might work well in combination with an HSV style tune to get a little more from ignition timing and maybe fuel adjustments.

[brindo]

Probably should clarify the intake temps. The VT has no air temperature sensor in the manifold, it’s taken from the air cleaner lid. So all those temps are taken upstream of the throttle body.
So the difference is the difference in ambient temps. I tried to do the testing at night as its cooler and no traffic, but on the night I tested the stock throttle body it was still pretty hot. We’ve had some rain and hail storms pass nearby us, so the temps dropped quite a bit which is why it was so much cooler for the 70mm throttle, not that it helped.

Looking at the before and after of a bell mouth, logic says it has to be better.
And I guess also to put it into perspective, you could easily say this ported manifold would be 0.5 second quicker over the quarter mile, and that would be a decent gain from just cleaning up the manifold. I ran my old VT 5.0 station wagon at a test n tune once – heavier vehicle but a stock 5.0 auto. Don’t remember the speed, but was 10.42 seconds for the 1/8 mile. If you knocked half a second of a 16 second quarter mile you’d be happy.

Bell Mouths Before and After.JPG (52.37 KiB) Viewed 981 times

[immortality]

Those really are weird results. It shows more air flow from the MAF, lower ambient temp (which might explain more airflow as it's more dense for a given volume) and yet went slower. Still makes me think it's in the tune. Seen similar stuff with the V6's. Added a smaller pulley on the L67 and now it doesn't light up the rear tires like it did with the stock pulley. Weird considering it's making more boost and getting more air.

The MAF based tunes really don't like the bigger TB without some tuning changes.

Does your VT stock TB have the extra material behind the TB blade on the one side like the ecotec?

Ideally we'd need to have data logs for the various runs and see what the fuel and timing are doing which might explain the results a bit better.

[brindo]

Yes it does. I don't have a photo of it, but there is a large raised lump just after the throttle blade. When they bore it out, this obviously gets machined out as well. I have read this lump was to help off idle throttle changes, but wondering if once its removed contributes to the problems with throttle blade sticking/not returning back to closed.

[immortality]

(I believe) that lump is to give a smoother transition from idle and it also (conveniently) reduces throttle response. They did the same on the ecotec V6's. You might find that you'll get a lean spot on throttle application with the bored out unit as you'll get a lot more air Vs TPS %age change.

On the early V6 models the throttle was like an on/off switch, great for enthusiastic drivers but not so much for your average granny.

I've not had issues with a sticking throttle with the 69mm V6 TB's.

[vlad01]

I've never heard of the sticking throttle thing. Is that a 304 only issue?

I love the earlier V6 with their touchiness I find them much easier to drive than cars that have a delay from the throttle, they always cause me to surge and hop, this is especially a problem with cars that have a lazy DBW and I find them almost undriveable no matter how much I try to get used to them.

DBW is getting a lot better programming in some newer cars these days which is good to see and have a almost cable like response.