Holden 304 Banana Manifold

[VK_3800]

Surprised there was any measurable gain at all with the throttle body. Improving the manifold should actually make it achieve something, will be interesting.

Commodores have a bit of a gap over the radiator that can take in air from the grill/under bonnet edge, the intake will work as well as any of the OTR style units (with less noise!). Earlier Holdens don't have this space.

[brindo]

From memory I thought MACE claimed something like a 5 rwkw gain from the bigger throttle on the 304, but in hindsight I don’t know if that was an auto or manual, and at what rpm it made more power. I have read that the factory air boxes are too small as well, particularly on the earlier models. You wouldn’t know if that 5 kw gain was just from the throttle body or if it had a MACE air box or a bit more timing in the tune to get that gain. This could well be the reason why nobody sells bigger throttles for the 304.

I would not have a clue what kw gains I got. Unlikely to be as much as what MACE got. I certainly couldn’t say it had more power with the larger throttle from seat of the pants and I don’t drive it enough to really know. But it was something like 32 degs ambient when I tested it with the stock throttle, and it was around 38 degs ambient when I started the test with the 70mm throttle. And both tests were at around 7pm to 8 pm at night.

It’s interesting all the same, I’m pretty keen to learn a bit more. Worse case scenario is I have wasted a bit of time and money.

[immortality]

Really depends on which 304 they tested.

I think MACE stopped supplying those TB's as there isn't much of a market for them any more, they seem to have dropped a lot of stuff from their catalogue for that era models.

I found the stock airbox restrictive on both the VN-VS and VX (L67). With a MACE cold air intake I found it much more responsive. I did quite a bit of back to back testing between the factory stock intake on our old VS with L67 cold air intake Vs the MACE setup. The stock factory setup really suffered from heat soak and I had to pull the small plastic infill piece that seals between the radiator and cowling panel to get airflow up into the stock L67 cold air intake. VS and VT are very similar in design around the Cowling panel and bonnet and there really isn't much room to get air in there. It took me ages to get a hold of the genuine Holden VS L67 cold air intake and was most disappointed after fitting it that it made no bloody difference over just the standard VS airbox.

What I found really improved the situation was adding a air intake from the bottom of the front bar, on both my old VN and VX I used a old VN-VS intake tube, Cut a hole into the side of the MACE enclosure and fit the old intake pipe into that with it hanging just below the bottom of the front bar. Nice cool ambient air getting to the filter.

[VK_3800]

I had to pull the small plastic infill piece that seals between the radiator and cowling panel

Funnily enough one of the best factory Commodore cold air intakes was on the 4 cylinder VK, had a plastic duct that ran beside the narrower radiator. Probably more usable area than many aftermarket V8 OTR setups with the tiny filters, I guess they get away with it to an extent using a high-flow cloth filter rather than paper element.

[brindo]

The mildly ported manifold is fitted, and I have got some more data. I did have a slight hiccup with the alternator deciding it didn’t want to charge anymore. Luckily I had an old regulator as zero chance of buying one locally on the weekend.

But the results are nothing spectacular. It certainly hasn’t gone backwards, but the improvement is only slight. I also put 50 litres of fuel in before the test on the stock throttle body so it would have been a little bit heavier but there’s no excuse, the difference is really not that much. And whatever improvement is there you would probably never notice it.

The surprising thing is that it performed better with the stock throttle body, which isn’t really consistent with what the Starr manifold achieves so I must be doing something wrong. Either that or the gains that everyone claims from a Starr manifold on a stock engine are just not there - which I am more inclined to believe. What I do know from my crude flow testing is that the manifold I fitted had virtually the same size runners and was significantly less of a restriction than an un-ported one. So if there was not much gain, then the stock un-ported manifold and throttle body can’t really be a restriction and limiting performance. Which I guess is consistent with what I was thinking with the cylinder head flow rate with a stock cam being a good match to an un-ported runner.

Final Recorded Times.JPG (40.08 KiB) Viewed 745 times

One interesting thing was that the peak MAF Hz recorded with the stock manifold was always in first gear. Now with the ported manifold, it is hitting a higher value in first gear, but the max recorded is now sometimes in second gear.
Also interesting was that it was significantly hotter when I ran the stock throttle body – 37 degs C IAT – and significantly cooler again when I ran the 70mm throttle - 27 deg C IAT. And I can’t blame slower gear changes or trans slip as the larger throttle was slower from 0 to 60 kph as well.
Anyway a bit over 0.3 seconds quicker in 0 to 100kph over the stock manifold.
Bit hard to tell, but the TPS looks to be around 1% less for 60 kph comparing the stock vs ported manifold with 65mm throttle bodies. It’s not much, but perhaps a fraction more vacuum at cruising speeds. Hard to judge as 60 kph is only 3 - 4% TPS.

I don’t really know of any decent online calculators to calculate hp from 0 to 100 kph times, and their accuracy is questionable. But a bit of messing around with what I could find on google shows a theoretical gain of 8 to 10 flywheel horsepower for a 1850kg vehicle. So I guess if it is making another 10 hp just from making the manifold more efficient you could count that as a win, but there’s still no conclusive proof. Then again, you could probably spend more money than what I did porting this manifold on an underdrive pulley for an LS and have change from 10 hp as well.

Sadly all I have proved is that on a stock 304, smoothing the runners, bell mouths and neck gives a very small gain - arguably a complete waste of time and money. It’s not at any risk of blazing the rear tyres anymore now than it was before.
And nothing really to be gained with the larger throttle body, so the stock 65mm throttle must not be a restriction on a stock engine.
But unfortunately I’ll never know what the story would be if the engine had a bit more cam, compression or capacity which is what I really hoping I could do. If anyone else has a crack at porting one of these manifolds in a similar way for a worked engine, would love to see the results. Hopefully I have detailed the way to clean the runners and bell mouths up without cutting the base out with enough info for anyone else to give it a go, with or without the hydrochloric acid. I still think this porting has some potential.
These are the star flap discs I used https://www.digikey.com.au/en/products/ ... 58/3592010 If you bought 10 that would be more than enough to do one manifold.

Anyway it is what it is. The Calais was leaking a bit of oil through the cork gaskets in the valley so the manifold had to come off regardless. Not much lost and a fair bit learnt, and a couple of oil leaks fixed.
Its all back to normal now with the original CNPK memcal and original throttle body and back in place.

[immortality]

That's actually very interesting and makes me think something else is holding it back. I've never looked at the tunes in these but has me wondering about em.

On the older 304 models you went from a stock SS @ 165kw to HSV 185kw with just a slightly improved air box, better exhaust and a tune (2° more timing).

VT 304 has better heads/more comp and more cam with sees you starting off with 179kw which HSV pushed up to 195kw so there is definitely more to be found but clearly it's not the intake that is holding it back.

The more I think about it, the more I think there is something going on in the tune and as with the ecotec V6's, with the MAF, fitting a larger TB really requires a few tune adjustments to see the benefits.

[brindo]

I think the stock cams have the same profile/open area from flat tappet to the roller. But the VT 195 kw version got the Crane Compucam 2020 which has a bit more lift and duration (198 @ 0.050 and 0.432" valve lift) and a tighter lobe sep. So 16 flywheel kw for the cam, headers and tune basically. But yes the hotter intake temps make no sense at all.

And a mate has pointed out to me that there is a section on the Starr manifolds in the How to Rebuild and Hot Rod Your Holden V8 book, of which I have a copy, but wasn’t smart enough to read it earlier.
But the book claims that the Starr manifold was only good for 10 rwkw on a stock 304, which is a lot less than what I was under the impression that they make. I don’t agree with everything written in the book, but I think that figure is fairly credible so I think dispels one myth. But I recon a good part of that 10 kw would be from the better air box. So again, on a stock 304 you could leave the banana manifold as is and get the same gain just with a MACE air box. I see there is also an aftermarket replacement air box now that looks factory but has a 100mm inlet. It’s a bit expensive and doesn’t increase the air filter area, but would look factory still. The book also says with the larger neck and throttle body that air flow is now 190 cfm per runner, which I don’t think is a credible or sensible calculation as I think there is only 2 and a bit cylinders with the intake valve open at any one point in time. It’s not really as simple as just dividing everything by 8.
It also says that the runners are 43 mm diameter, whereas I measured 41.5 mm - none of the manifolds I have been involved with had 43 mm runners, but I guess I can’t discount the possibility that some manifolds may of had a slightly different casting.

Anyway, as flawed as my testing was, I’m thinking if you want to add more cam, compression or capacity, then fit a MACE air box and spend $100 porting banana manifold and I recon it will be up there with the Starr Manifold.

[immortality]

People always seemed to rave about the 2 hole mod for the stock VT style airbox, I don't think the filter size itself is the limiting factor, more everything around that filter that restricts things.

I'm still suspicious of that factory cold air snorkel personally.

I know on my VX L67, getting rid of the OEM intake for a MACE unit made a good difference, then adding my cold air intake to the MACE box improved it again.

[Dylan]

People always seemed to rave about the 2 hole mod for the stock VT style airbox, I don't think the filter size itself is the limiting factor, more everything around that filter that restricts things.

I'm still suspicious of that factory cold air snorkel personally.

I know on my VX L67, getting rid of the OEM intake for a MACE unit made a good difference, then adding my cold air intake to the MACE box improved it again.

Don't underestimate the air box OTR upgrades on these things. Definitely gains to be had.

[vlad01]

I have stuffed around a lot over the years with this kind of thing, mostly Buick but some 304 and 355 stuff.

The stock airbox is def an issue on some engines, but I think it's mostly a resonance thing than a pure restriction, that is a resonance working against the engine in a way that shows up as a physical restriction (measured as a drop in Kpa at WOT). Interestingly, this "restriction" doesn't exist on mild to moderate boosted engines, even on boosted engines that have 2-3x the power show no to little restriction with the stock airbox are heavily restricting to NA engines with 1/2 to 1/3 of the power. This has also been confirmed on the YT channel 4AGE garage with his Starlet test mule and Hilux boosted 4AGE. Boost doesn't get anywhere near as sensitive to airboxes as NA does, even when flow volumes logically would say otherwise.

I have even had this issue personally with a Mace CAI, the engine was not having it, was sucking the lid in and jamming up on the rad support, but on the dyno it never showed up as the ramp rate was not allowing this weird resonance to emerge. So I had to cut the CAI open in a way to mimic an "infinite" airbox volume.

With the 304, the intake is not the restriction and in fact, more free flowing after market manifolds make them perform much worse except in the case of something like an Edlebrock. I still have not figured out what the problem with the Holden 8 is, but they always seem to make much less power than comparable specs or setups of other engines and even on paper, the 304/355 should have a lot going for it, but it just doesn't meet the expectation. The banana manifold actually is the best thing other than the mentioned Edlebrock style manifold, I think the issue could be the heads but I am not entirely sure Possibly just a bad design with air velocity aspect of them even with decent CFM and makes sense why long runner high velocity manifold are the only ones that work decent on them. LS and Buick 6 seemed to have got this pretty good and respond great to the typical mods and upgrades, ecotec not so much, similar to the 304. Ecotec actually don't seem to gain anything meaningful at all when it comes to good headers vs the cast logs, similar to the 304 in my experience.


Ecotec and holden 8 heads have some close similarities which I feel gives some clues perhaps.

I can't comment on Chev engines, I have 0 experience with them. But I will say that the old push rod competing Ford 8s, especially the ones of the 90s are in the same boat at least stock wise as the holden 8, they seem so mediocre for their size. In my research on the mustang v6 a few years back, a basic copy of the Buick 3.8, the Ford versions were much weaker but the ford ones on paper should have been making more power, but a big difference was the head design. Ford even tried a dual runner/port design to improve flow and velocity but they still were a good 15-20hp behind Buick that predated them by years.

Things like this make you question why and what can I learn from this to make my own builds better.