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 1028 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.