GTi-6 - ITBs & CAMMED Track Car.. LATEST VIDEO

[Piggy]

wow. very impressed. a very composed lap.

Overtaking a 458 on the 3rd corner says it all really!!

[jammapic]

Treating the car to some paint less dent removal today... Try and get it tidied up a bit before fcs.

JP

[jammapic]

OK, so after a tough few months in storage / workshop and then a hard trip to the Nurburgring, the shell was starting to look a little tatty as people has been leaning on it, dropping tools on it etc etc.

So, had the Paintless Dent Removal guy come and knock a load of dents out, and a couple of touchups done with a little touchup pen and some wet sanding.

Have also given it a full detail today, using poorboys stuff, machine polisher, and wax.

Some up to date piccies.













Pretty much ready for FCS now! :-)

JP

[Kezzieboy]

Looking awesome buddy! How much did the paintless bodywork repair cost, if you don't mine my asking!

[jammapic]

£30 a dent.... of which there were many!!

[Kezzieboy]

Hahaha, fair one

[7057sam]

1.2's look alot better in grey than white

What time will you be on track?

[jammapic]

Not sure. Whenever I've got some spare time. As magazine staff, I'm working most of the day.

JP

---

[7057sam]

Not another car

You got too many cars

still got the jag?

[jammapic]

Nah, sold it, made some profit, bought some goodies :-)

[C.A.R.]

The Hello Kitty is a bug-bear of mine. They just look silly (I think because the Corsa boys have picked up on it!)

Nice 5 though. If you give the back edge of the headlight covers a gentle tug they will level out a bit better with the bonnet and give a better shut-line.

Loving the '6 too.

So now you have a 5 and a 6, what do you follow that up with? A 7? RX-7?!!

[jammapic]

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.

[Ruan]

Out of interest, may have been covered earlier...

Are you individually adjusting injector trim at the load sites where the banks of trumpets would be at a different harmonic resonance - or sorta leaving it as is and keeping it rich enough at those speed sites so it's enough to not toast pistons with the changes in ve??

[jammapic]

The latter. On the marelli ECU you can't adjust specific injector trims, only the lot as a whole.

It's plenty rich enough anyway, as I have a 200 cell sports cat - and we need to keep it cool.

Plus, it's like 6% difference in VE anyway, so not massive and it's not on the ragged edge of lean for power / hot.

As long as it's around 12.5-13:1 AFR under power, it's plenty rich enough not to toast something.

JP

[Dum-Dum]

That really does look like a standard GTi6 curve, just more lol

[jammapic]

Just been doing some work on articles for PFC mag, so a little bit more about trumpet lengths...

The induction stroke causes a drop in air pressure in the intake port as it draws air into the cylinder. The low pressure is essentially the same as the air being 'stretched' because gasses are elastic in nature. Behind a low pressure zone follows a high pressure zone; just as waves in the sea have peaks and troughs following each other.

Harnessing these waves in such a way as to get the positive pressure helping to fill the cylinders is what tuning is all about!!!!

Variable intake lengths do this directly, and this can be seen working in practice on various vehicles including Porsches, with the “varioram” systems. Variable valve timing does this by virtue of setting the wave off at a different point in the cycle so as to manage the positive/negative waves to best effect. Unfortunately, in the Gti-6, as with many older vehicles, we do not have any of these new fangled technologies and as such we have to do it the old school way....

In short, with the exception of reducing friction, tuning is all about harnessing pressure waves, positive ones on the intake and negative ones on the exhaust, particularly on the 'overlap phase'.

So we've all heard about longer duration camshafts, with more lift and we know they are a good thing... but why?
Well, put simply longer duration camshafts work by giving a larger 'window of opportunity' to make better use of the waves we've talked about above. This is simply because the valves are open longer and open earlier. Conversely they offer larger window of opportunity for the negative waves to hinder efficient cylinder filling and scavenging and this is what causes an engine with longer cam durations to be 'off cam' at lower revs. Or, more accurately, the fact is the engine isn't yet in a frequency range (not enough revs) to 'ride the good waves' (man).

To sum up. With short trumpets these waves have less distance to travel, so the time between them is shorter, therefore this suits high rpm better and ultimately makes more power at higher revs. With longer trumpets, the waves have further to travel so the time between them is longer, suiting lower rpm better giving us more torque, and power at lower revs.

The interesting bit here is when you see two dyno plots overlaid.



Here, you can You can see the shape of the curves are identical, but out of phase with one another and we can see the normal resonance in the torque curve that we see with most throttle body / cam conversions is also “out of phase”.
If we apply our new found knowledge of waves, and resonance in the intake we realise these peaks in our torque curve are all a product of the engine being able to make more power at the points in the rev range where the harmonics are... I.e where the waves are at their peak. As we described above, as we adjust the length of the trumpets we adjust where these peaks are in the rev range – which ultimately moves the harmonics and therefore the peaks in the torque curve.. after all, more air = more power!!!
If we had an unlimited budget, we would have started working the exhaust manifold here, to try and smooth the torque curve, but ultimately engine development costs huge amounts of money... What we are able to do though, is alter the trumpet lengths to move the torque around, as we saw above.
When we have two of the trumpets longer, and two shorter, if we find the right lengths, we can actually pick up different harmonics, or more over pick up harmonics where there are dips on the other cylinders. We effectly find a "middle ground" in the torque curve and fill out the dips.
If you see below (yes, it's a hand drawing, I told you this was the old school way!) you'll see this.



In the graph, you see inlet length (trumpet length) along the x axis, and revs (rpm) along the y axis. The curved lines on the graph show the harmonics of the inlet pulses. I haven't included the 1st harmonic, as it's so long that you'd probably need a 10 metre inlet length to catch it!

It's pretty obvious to see the relationship between harmonic and revs is relational to the length of the trumpet. The shorter the trumpet, the higher up the revs we see the harmonic.

The key point here, is the dotted line and solid line intersecting the graph. It has been oversimplified a bit here, but with trumpet length x, in my diagram we see the harmonics at 1500rpm, 3000rpm, 4500rpm and 6000rpm. With ½ X (I.e half the trumpet length) we see the harmonics at, 2250rpm, 3750rpm, 5250rpm and 6750rpm.

If we can tune these inlet lengths so that they are exactly half a harmonic out from each other (2 cylinders at one length, 2 cylinders at another length) we can effectively fill the troughs in the torque curve with power, however 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:



and a couple more piccies of the build:

[Kezzieboy]

Really is awesome stuff, cool to see all the theory I've learnt at uni works out in practice. Can't help but think you'd benefit from some CAE, though, something like Ricardo WAVE or GT Power would allow you to try out some of these iterations and create a short-list before you chuck it on the dyno, potentially saving you rather a lot of money!

[jammapic]

A lot of it I write out by hand, reference books and call upon the Wizard (Wayne Schofield)....

[Kezzieboy]

Fair enough, it just makes it easier if you want to tune cams/intake/exhaust to all work together

[jammapic]

Yeah, I can imagine.... but for me, a lot of the fun is the trial and error and learning what and by how much I need to change something.

That said, I may end up using stuff like that when it comes to tuning the exhaust manifold...

[Kezzieboy]

Yeah, I recently designed a 4-1 manifold for the R6 engine on our formula student car, it's a pretty handy tool!

[procta]

you need to do a knock hill track day.

[jammapic]

How come? Knockhill is so very far away and I'm not a massive fan if I'm being totally honest....

[lolsteve]

Becauseracecar

[martyn92]

Good read

[procta]

How come? Knockhill is so very far away and I'm not a massive fan if I'm being totally honest....

knock hill is a car killer, plus its a good challenging circuit, but if you wont do the hill, then do croft.

[jammapic]

I love Croft, done a few track days there and used to race the single seater up there.

JP

[jammapic]

So seeing as every time I go on a track, a marshall makes a snide comment about the two bonnet pins (read, spikes) sticking up out of my bonnet, though I'd better fit some recessed ones.

[jammapic]

So, it's time I updated this thread....

Lots had been going on with the car, few track days, few drives out and lots of fun.

Decided that I wanted a bit of a challenge. I've got quite in to mapping recently, so thought what better to do than buy an ECU, fit it to the car and teach myself to map it from the ground up. So that's exactly what I did:



So far, I haven't had a lot of time to actually spend mapping it. But the idle is now better than ever, light load is all mapped and there's plenty of fuelling in it to mean it can be driven around. To be honest, it's not bad. The spark timing still needs work, so when I've got some spare time I need to get back to the dyno and 'don the knock headphones and spend a little longer making sure it's running at it's optimum....

All good fun!!!

Also, in other news, I've bought a BTCC exhaust manifold, some bigger injectors and with the new ECU it will be interesting to see what numbers it pulls....

JP

[welshpug]

Don't need bigger injectors, they'll do 240 bhp.

Chris Harris's 2.5 litre E30 M3 rally car runs gti6 injectors.