Welshpug, do some reading into volumetic efficiency. We can work out exactly what the AFR is on each cylinder by looking at the power curves with different trumpet setups. We can then ensure the "mean" AFR coming out the tailpipe is rich enough to keep the cat cool, and also rich enough across all the cylinders to not cause issues.



That's exactly what it's doing dcc, NOT working in balance, and thus giving me a totally smooth torque curve, removing the resonance you get with different trumpet lengths.



I can only go off what the dyno told me. It said that stock, and just with a K&N and sports cat / exhaust system, I made 177hp and now, on the same dyno with all the mods, 227hp.

As I keep saying, I think the dyno is a touch optimistic... that said, I can't get away from the fact it's shown a 50hp gain, and the way the car feels I'd say that's right.

Why would Wayne Schofield of Chip Wizards lie?



Varied trumpets have been around for years. Look at the old Mclaren Can Am cars for example:



Multiple lengths gives you a better spread of torque and smoothed out resonance. Plain and simple. Read organ pipe tuning, volumetic efficiency, velocity stacking and then realise what a power run on a dyno ACTUALLY shows you (volumetic efficiency). From this, we can work out the dips and the troughs and use the AFR out the tailpipe to calculate exactly what lengths we need.

Once we've staggered the lengths, we can make sure we get the fuelling right and rich enough not to give us hot spots in the rev range.

JP

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HDI Engine Tuning / Remapping Services - https://www.facebook.com/dervtech

306 GTi-6 Track Car - 200+ hp all N/A!
306 DTurbo Track beasty - 209.9hp - RIP

Build it properly? Absolutely no resonance in the torque curve whatsoever and smoother than any throttle bodied 306 I've ever been in? Hmmm.

Also, on the trip to the Nurburgring, I averaged 1mpg less than a totally stock GTi6. Doesn't seem to use too much fuel to me.

JP

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HDI Engine Tuning / Remapping Services - https://www.facebook.com/dervtech

306 GTi-6 Track Car - 200+ hp all N/A!
306 DTurbo Track beasty - 209.9hp - RIP

Maybe in your opinion. Of the ones I've been in, running all 4 trumpets the same length, aftermarket management etc, on Omex, DTA and Emerald, mine is smoother. I doubt the management has much to do with it, at the end of the day, they all have a VE table to do fuelling, and timing maps. It's more likely the trumpet lengths smoothing out the peaks, and filling up the troughs.

To be fair, it made more torque with all 4 trumpets longer, but soon after the peak, there was a dip, which made less. The staggered lengths smoothed that out.

I'm happy with it, it goes like the clappers and it seems to be working well.

The whole point of this thread was to show we don't all have to be sheep, and things can be done differently. I'd say I have proved that, stock management, staggered trumpets and certainly over 215hp on a stock motor. If people don't believe the numbers, fair enough, I'm not bothered, I have a feeling the dyno was a little enthusiastic... but when was the last time you saw one on stock management, with staggered trumpets etc run on the dyno? ;-)

JP

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HDI Engine Tuning / Remapping Services - https://www.facebook.com/dervtech

306 GTi-6 Track Car - 200+ hp all N/A!
306 DTurbo Track beasty - 209.9hp - RIP

I think Stef205 ran one on stock management also.

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Senior Test Automation Engineer for the 306GTi6 Owners Club Forum

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You missed an important bit out that I said welshpug, the staggered trumpets.

I remember reading he did that on stock management, but with a bit of a botch to get it running with a map sensor still in place. Also, didn't he ditch the setup as it didn't work right in the end or bad fuel consumption or something?

JP

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HDI Engine Tuning / Remapping Services - https://www.facebook.com/dervtech

306 GTi-6 Track Car - 200+ hp all N/A!
306 DTurbo Track beasty - 209.9hp - RIP

Yes, I read it back to check I wasn't wrong and noticed a spelling mistake. I'm sure the admin would be happy to confirm I didn't change any of the detail.

Jeez, you lot are pedantic.

JP

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HDI Engine Tuning / Remapping Services - https://www.facebook.com/dervtech

306 GTi-6 Track Car - 200+ hp all N/A!
306 DTurbo Track beasty - 209.9hp - RIP

There is nothing fundamentally wrong with a staggered trumpet setup, it's been used on more engines than I have digits to count on.

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- Bespoke rollcages/additions/adjustments. Half cages right up to complete custom spaceframes - MSA/FIA spec, CDS, ROPT, T45, etc - PM me
Email me!
Custom-made polybushes available - need an odd size or fitment? - anything from batch work to one-off pieces.

There is a company that make adjustable length ones. Would of made your life much easier.

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230 hp 2.1 16v XU 205 rallye on jenveys Project thread here
309 3dr K20 Type R

Yeah, I probably would tbh. It's noticeably slower if you gun it after it's been sat running a while, as it pulls in all the hot air - then gets going after a few seconds.

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HDI Engine Tuning / Remapping Services - https://www.facebook.com/dervtech

306 GTi-6 Track Car - 200+ hp all N/A!
306 DTurbo Track beasty - 209.9hp - RIP

Yeah, I saw those... but got the others free from Jenvey for testing!

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HDI Engine Tuning / Remapping Services - https://www.facebook.com/dervtech

306 GTi-6 Track Car - 200+ hp all N/A!
306 DTurbo Track beasty - 209.9hp - RIP

Looks spot on mate but that number plate gets me everytime

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"Police arrested two kids yesterday, one was drinking battery acid, the other was eating fireworks. They charged one and let the other one off."

OK, so backtrack a tad...

I talked about using staggered trumpets to move harmonics in the torque curve, and make for a smoother power band and more area under the curve.

But, they say the proof of the pudding is in the eating, so here it is.



Here, you can see two dyno plots overlaid. The one which makes peak power at slightly higher RPM is with the shorter trumpets, and the one with power at lower RPM are the longer trumpets.

You can see the shape of the curves are identical, but higher and lower RPM peak power. This is normal for longer and shorter trumpets. This is the key here.

When we have two of the trumpets long, and two short, we effectly find a "middle ground" in the curves. This is helpful as we fill the troughs with power, but we do also lose our peaks - hence the peak power is marginally lower.

What's important though, is area under the curve. Clearly, the more the better, and by filling the troughs we make the car smoother and more drivable.

Below is the outcome of the staggered trumpets:



We actually did find a little more power with some more ignition advance and leaning the mixture out a touch, but the shape of the graph remained largely the same.

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HDI Engine Tuning / Remapping Services - https://www.facebook.com/dervtech

306 GTi-6 Track Car - 200+ hp all N/A!
306 DTurbo Track beasty - 209.9hp - RIP