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Gordo

Gordo takes over the Peter Mac Build.

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Thanks. It's just windows movie maker. He shot the short videos on a digital camera, then down loaded on lap to and put it together.

I'm quite impressed with what he can do. Cheers.

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Had a run at PI on the weekend. Some in car video shows me battling with a Porsche . He had more power and good brakes, but I was all over him in the fast corners. I was getting frustrated (lol). And tried to out brake him going into Honda corner. Got onto the dirty line and locked them up. Bugger. I finally got him but I think he was worried about his car, because I was clearly not! Haha.

Click on the link.

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Great video Gordo. I love watching your laps.

How'd the flat bottom go, did it feel any different. Maybe without the extra weight you could have got him on the straight. ;) hehe

Cheers

Mick

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Those Porsche Caymans have lots of top end power.

Great drives and looks like you have plenty of grips.

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So , how did the flat bottom go at PI ?

Well lets see, from what I could feel, first up was slight under steer. So the rear defuser gave a little more down force.

Dialled the under steer out with more front neg camber.

RPM on the main straight was the same. So NO aero or drag benefit !

I PB this car one second faster, but I wouldn't credit the flat bottom for that.

The track temp was 50deg which helped my wide tires get near there operating temps. That's we're the one second improvement came from.

To be honest , I think I'm fighting with these old tires and aren't getting the grip I need.

So next year will try some new ones. And will really be hoping that will get the job done.

So if your thinking of doing a flat bottom, don't waste your time. But a rear defuser would help.

One option I have now is to take the wing off and run a standard type bob tail with the defuser. Would reduce the drag!

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Do you think that could be to do with the fact you aren't venting enough air over the top of the car from the engine bay? I looked back at your other pics and cant tell if the wheel arches are open to the engine bay compartment.

Maybe it is still dumping the same amount of dirty air under the car, which the diffuser is sorting out at the back from your now there are some streaks to smoother it out.

 

I know doing a slant forward radiator like this might be a bit of a stretch, but if you run thermos on the front of the radiator you might be able to fit a duct that works in the same way. Maybe try removing the inspection lids and see if that make any small gain, particularly at high speed. Looking at the aero data i linked earlier, a lot of this aero stuff (besides adding massive front splitter and rear wing) only seems to net small gains, but they do add up if you do enough.

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d3 does have a point, what could be happening now is that air from the engine bay is moving rearwards and down between the body and the new full undertray and exiting above the diffuser. I tried an easy experiment with mine, drive somewhere safe with the bonnet unlatched and see at what speed it starts to lift up. This indicates how much pressure is building up in the engine bay, a lot is not good for aero (drag) or cooling. Much bigger bonnet vents on mine helped both.

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The air that enters via the radiator support panel, needs to have greater volume to disperse, lose its pressure, and then be sucked out, using front nder tray with reverse angled slits aided by flaps from front crossmember back to gearbx bell aids the vacuum extraction f the air.

Two tiny little bonnet vents, at rear of bonnet, where it top f bonnet, near cowl, s a negative pressure zone, will nt extract all the air that flows in through front panel openings.

A full flat bottom will concentrate airflow back into floorpan tunnel around gearbox, creating a "wall" of slow mving air.

 

Rear diffuser extended past rear bumper, and wrapped up forward f the tank area, and at sides continues up into rear wheel arch inners, will be effective in cleaning air under car and getting it out.

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All good points guys. Food for thought. But you can not stop all the air going down the tunnel . We need an air flow to help cool the diff and gearbox.

And as Jason says the under bonnet pressure has to be reduced. I've tried to make the opening smaller buy extending the lip on the bonnet. So it's just air through the radiator and 120mm side hole for carby air. Also added more bonnet vents

Having said that I think we are only talking tenths of a second here. Any more mods will only make very small gains.

The best gain should be new tires. These slicks are 4 to 5 years old. To hard.

Like under steer out of Honda corner at PI with hot tires, 300mm wide and not on the power. Like really ? Not good.

But thanks guys for your input. Does make me think about different possibilities. Cheers.

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Agree Gordo, I missed the obvious extra bonnet vents you have done, duh. Really it's impossible to have too much engine bay venting although as you say there must be some airflow under to keep the components there cool. But providing there is a clear air exit path component cooling should look after itself.

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Hi Gordo,

 

Just re-read this in anticipation of the next chapter this weekend - hope it goes well

 

My (very light) bonnet flexes heaps the front straight at PI, gives bonus 3+ cm venting on the rear edge (maybe not ideal)

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The area where the cowl panel meets the windscreen is a big stall area, so it probably does SFA. In the wind tunnel testing i linked earlier, they popped the bonnet up and it had no effect.

For effective pressure venting I think you would need to run the vents further down the bonnet like the Scuderia race car pictured below:

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No, no, no, those Scuderia vents are wrong. They are in the right place but should be facing to the back to allow air out from under the bonnet. If more air in was required then opening the grill area a bit would have done the trick but for a NA L6 engine that part looks about right.

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I think if you look closely, the metal is folded up at the front of the vent to promote a low pressure zone to help suck the air OUT of the vent.

Radiator opening only needs to be 25% of radiator area from memory.

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Pics aren't very clear but the second one seems to show a front facing open vent, the black part. Anyway, we are agreed that the idea is to get air out there in that low pressure area, not in.

 

Blocking off part of the S30's too large grille opening looks good in the first pic.

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Had a run down at the Island at the weekend. Hung Do was there testing his new Brake master cylinder system . All went well in his 240z SC car. All ready for the PI Historics. Good luck mate.

The weather was perfect for fast times , so I bettered my best time with a 1.46.4. I have to say all the aero mods make it faster in the corners. But much slower down the main straight. 600rpm down on the red zed. I think now that I've layer down a good time, I might take off some of the aero to reduce the drag and try and find a happy medium with grip and speed.

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