Jason Moyle Racing

oh-oh , sounds ominous!

I will pop something up in due cause.

Nice work. What calculations did you do around Plenum volume. What runner length did you go for in the end? Might be in the earlier posts but I didn't spot it.

A short evaluation of the manifold.

I have used a new rolling road this time to get it calibrated, therefore,  it is not wise or even fair to compare the figures, especially considering that there was a large difference in the peak values from previous best results.

I was expecting, if tested on the same rolling road the inlet plenum would lose me maybe around 10bhp peak (complete guess but a figure i would be happy with looking at OEM plemums, the hope would be this plenum flows better at the higher rpm) from the best my ITBs had given me in the past and I would be happy with that. What it has potentially lost me in BHP may only be realised if I return the original rolling road.

Therefore to draw any comparisons about my manifold, to my ITB setup, I'm using track times and seat dyno.

Things to note, the last time my car was running the ITBs on the same rolling road/cal/engine it was down on power last year by around 20bhp, from 187bhp to 166bhp, I have still have not worked out what the reason could have been... the crank sensor timing was only a couple of degrees out measured at around 25 degrees before TDC (at moderate revs) it was a new trigger wheel and timing was at the time suggested as the cause.

Anyway, the last result the ITBs made around 166bhp flywheel on the old dyno and with that tune I went to Goodwood and Curby. I then went back to both tracks with the plenum and took timings.

So, at Goodwood peak top speed with new plenum was 119mph, the old ITB setup was slightly lower than this. The plenum felt every bit as fast and reduced the induction noise. Happy with that because reducing noise was my primary aim whilst maintaining as much go (as possible) as the ITBs had.

At two separate Curby events with the ITBs my car did a 29:60 and 29:44. (same settings but different temperature days). Fairly close.

With the new plenum at Curby my car did a 29:17.

The seat dyno after Curby said it felt faster on the short track, at Curby it was much easier to break traction with the plenum when getting on the power. It required a much more controlled driver compared to the ITBs. (this took some getting used too on cold tyres).

Inbetween all these events all I changed (including geo to tyres etc ) was the plenum and I removed 7kg from changing my bonnet to a GRP item.

Overall I feel the engine is more grunty than the 166bhp ITB setup and the Curby time and Goodwood speeds confirms it for me (I also surprised a few other drivers who noted the golf goes well). The plenum does pull the car around a track better than the ITBs in their last state of tune.

The figures from the new rolling road are 'only 136bhp est at the wheels (162 est fly) but this figure has pulled the car around tracks faster than the 166bhp from the other rolling road.

Peak BHP/torque from ITB plot and Plenum plot on different rolling roads is, I feel, about all that could usefully be compared. It shows that the plenum was breathing well and not being restrictive at the higher RPM range when compared to the ITBs, which is a good thing and goes some way to say the plenum could flow well and could handle more BHP if the rest of the engine was built to breath.

ITB peak BHP 6900rpm LBFT 5000rpm ATflywheel
plenum peak BHP 7000rpm LBFT 4500rpm ATW (at 5000rpm there was a slight dip in the curve which may be able to be mapped out.)

In the future I am hoping to test the plenum in a different way to gauge where its potential performance might become restrictive.

One thing I have learnt from this exercise is that I will only ever use rolling roads that give out wheel horse power figures.

Difficult comparing results from different days, but if the trend is consistent then it should be right that the new setup is quicker in the real world.

I struggle to believe it's only got 136 bhp at the flywheel, as that's less than a stock engine. Did you mean at the wheels? Having said that, the peak torque does look a bit low for a 16v. Is it still running on std cams and head?

I made an error, it should have been 136bhp at the wheels not the flywheel, est flywheel 162bhp.  You were dead right to question it, I'm not that interested in the Dyno figures, unless they are completed on the same Dyno , hence my move toward track timess, and I was impressed with the times it pulled : ) so whatever the figures were I was still happy, makes more sense that it was wheel hp because that comes closer to what the times suggest.

Agreed about the torque, it's not dropping of at 4500rpm it just does not get any higher, the ITBs it did keep rising, it does hold on until much higher rpm like the ITBs did.

I will pop a picture of the plot up to illustrate the profiles.

After my last track day I noticed a very slight crack in the paint on runner one. All the others were fine, when pushing down hard on the manifold with the engine running no extra air was was being let in because the revs did not rise. After parking the car up for the winter I set about stripping the manifold off to investigate further a develop the design.



The crack was along the join between the flange and the runners, it must be a combination of leverage, harmonics and the fact I gound the welds down weakening them. To put it right I firstly cut a 1mm groove into the manifold across the join and then I welded with a thick filler rod and plenty go heat. This time I will leave the weld alone and not grind it flat.





Secondly I welded in 3mm plate along the runners length.



I did something similar to the plenum end with 3mm plate.





Finally I will add a brace from the block to the manifold to triangulate the structure.