N14 SR20 Hillclimb car
- Thread starter sunny_cullen
- Start date
Cheers. Its a pain in the arse to be honest, would have been much easier building a Nova or something! My wee brother is building a Sunny to run in the same class next year, so it won't be alone for long. Think he wants to go down the ve route though.
Nice car and mods, love the action piccys too. Spot on.
I've heard good things about them as a road tyre but they're to hard a compound for sprints and hills. I've been using part worn A048 yokos since last year and have milked every last ounce of useable rubber from them so I'm breaking out the credit card and getting some proper tyres. Managed to find 4 supersofts for less than £500 which is about the same as 2 toyo proxxes for the family a6 so it aint that bad really!
Back bumper is drilled because it acts a bit like a parachute and creates a lot of drag, drilling it out lets some of the air escape causing less drag. You can argue about how much difference this actually makes all day long but every little helps! Its fairly common among track cars and club racers.
Plans for the immediate future are Fibreglass wings, 15" rota slipstreams and kuhmo v70 supersofts which are all now purchased. For next year I'm planning a plated diff and possibly a PAR gearset depending on funds. A stand alone ecu, either emerald or dta is also on the cards for next year. Beyond that I've been collecting parts to build a high compression engine with as light as possible bottom end for about a year now but the limiting factor at the moment is traction so there is little point giving it more power until I can find more grip.
The end goal for it is 800-850kgs and approx. 200whp with the de. The time may come where there may be more to be had from the car with a vvl head but that's a long way down the line. For the moment, as long as I'm beating my previous times I know its going in the right direction.
Its an internet thing that cutting holes in the rear bumper makes it faster.
Once you are moving the air pressure build up behind the bumper doesn't allow more air to flow in.
Cutting holes means you are now giving the air a path to follow forcing it through the holes, this just creates more drag.
Simplest example, drag a bucket through some water, once the volume of water has reached its maximum the effort to pull the bucket around is minimal, now put holes in the bucket there is more resistance as you are forcing the water through the holes.
But 'i saw it once on the internet so it must be truth'
Once you are moving the air pressure build up behind the bumper doesn't allow more air to flow in.
Cutting holes means you are now giving the air a path to follow forcing it through the holes, this just creates more drag.
Simplest example, drag a bucket through some water, once the volume of water has reached its maximum the effort to pull the bucket around is minimal, now put holes in the bucket there is more resistance as you are forcing the water through the holes.
But 'i saw it once on the internet so it must be truth'
I can see the logic in what you are saying to a point.
However this practice goes back quite a bit further than the internet and has been common practice in club racing for a long long time.
Plus I have a spare bumper if the holed one is poo.
Also got a diffuser coming which should help route most of the air below the car rather than against the back bumper. That way the air volume behind the bumper should be reduced hopefully to below the maximum airflow of my holes thus it shall create less drag. At least thats the idea but I'm shit at maths and don't have a wind tunnel handy so I'll probably never know.
However this practice goes back quite a bit further than the internet and has been common practice in club racing for a long long time.
Plus I have a spare bumper if the holed one is poo.
Also got a diffuser coming which should help route most of the air below the car rather than against the back bumper. That way the air volume behind the bumper should be reduced hopefully to below the maximum airflow of my holes thus it shall create less drag. At least thats the idea but I'm shit at maths and don't have a wind tunnel handy so I'll probably never know.
Diffuser will do some good. The airflow under the car creates a revolving air bubble behind the bumper which is a high pressure zone. This prevents the incoming air from becoming trapped. It's the same with pick-up trucks. The bed area creates a separated bubble. It's better MPG to run with the tailgate up for this exact reason.
To keep them stable
I'll do my best. I actually had my mates Go pro in for one of the days at Fintray but due to being a bit special in the head managed to buger it up and take a few photos of the startline and the paddock rather than recording the runs.... I'll try and educate myself before I borrow it again.
thx for the answer, but isnt it easier to do a flat bottom (sorry i dont know the exact term in english) something like this (parts B and D)
here in trackdays the potenza re002 are being quite common and they are not too expensive. Havent tried them yet but heard good comments on them from heavier cars
More effective yes, easier no. I do plan to do this but to do it properly is not all that easy. You need to use a pretty rigid material and obviously it has to be as light as possible. Ideally it needs to cover the whole bottom of the car so you need to figure out how to let the heat from the exhaust escape. If I've time I might start experimenting with something over the winter.