my 200mph rx7 build

[Tim_B]

Good luck - very interesting project :Thumbs-up

[turbotoaster]

AS I SAID BEFORE DUDE...WILL YOUR SEALS HOLD ON AT THAT RPM???......I THINK YOU SHOULD HAVE THE ENGINE BUILT FOR THE JOB FIRST AND FOREMOST.

ALSO EXPLAIN TO ME HOW THE SIZE OF THE DOWNPIPE WILL HELP WITH THE SPOOL....IT WILL HELP WITH OVERALL POWER BUT I DONT KNOW ABOUT SPOOL.

caps lock alert!! haha

well what has been done cannot be undone, i dont have a spare 2k to take some part just to some clearancing. As long as the map if relatively safe then it should be ok, let the boost do the work instead of ignition.

One reason for a large exhaust is by lowering the outlet pressure, you increased the pressure differential, and now the exhaust gas can expand more, and do more work. That increased work pushes harder on your turbo, and it spools up faster.

kind of like letting a opening a fizzy pop bottle in space or on earth

[Big Al]

Good luck with your  project..... way over my head at the moment, but still very interesting.
Will watch further posts wit a great deal of interest.

[SiH]

The thing is though, peak power at high revs briefly is one thing, but sustained high revs at peak power, and high load, such as you will need to reach v-max, is a completely different kettle of fish. Top speed runs are so hard on cars.

I want you to succeed, i really really do, I\'ve just got a nasty feeling about this.

[turbotoaster]

When is this event? What magazine is covering it?

it will happen when the car is ready, its been covered by redline magazine as stav wants to see it as he has an fc

siH.......its all about heat, heat will kill any engine, hence the pre-water injection to battle against knock, the bigger rad to keep water temps down and the big intercooler to make sure air temps are kept to a decent level.

racing beat did 242 while being flat out for 5miles, engine held together fine, he just made sure to get heat away from the engine and that the temps were all controlled

[S3TH]

to do 100mph(gps) i need to do 4500rpm, give or take 20rpm

so to do 200mph i need to pull 9000rpm, simple maths.

There\'s a fundamental flaw in your logic. There aren\'t that many constants, values you attain at 100mph will be different from those at 200mph.

x = power at y
If y = 4500rpm, the engine will produce x, the car will travel at 100mph
If y = 9000rpm, the engine produces 2x, the car will not travel at 200mph
If y = 9000rpm, and the engine produces 4x, the car will travel at 200mph, I believe.

If you make 100mph of 200bhp @ 4500rpm, you need 800bhp @ 9000rpm to make 200mph, just to overcome drag.

That\'s just a quick example of the logic. You can find the more complicated formula online and read about it,

Pd = Fd x v = 1/2pv^3 x ACd

Of course I could be wrong, tell me what you make of it though.

[Timmy]

The car may produce 200bhp at 4500 rpm but it probably uses closer to 100bhp as you don\'t need to use wot to go that fast. So really roughly thats only 400bhp to do 200mph.

[SiH]

There\'s a fundamental flaw in your logic. There aren\'t that many constants, values you attain at 100mph will be different from those at 200mph.

x = power at y
If y = 4500rpm, the engine will produce x, the car will travel at 100mph
If y = 9000rpm, the engine produces 2x, the car will not travel at 200mph
If y = 9000rpm, and the engine produces 4x, the car will travel at 200mph, I believe.

If you make 100mph of 200bhp @ 4500rpm, you need 800bhp @ 9000rpm to make 200mph, just to overcome drag.

That\'s just a quick example of the logic. You can find the more complicated formula online and read about it,

Pd = Fd x v = 1/2pv^3 x ACd

Of course I could be wrong, tell me what you make of it though.

That\'s power though dude, not gearing. The OP was just talking about gearing when he was referencing that.

[Ed_RX7]

LOL sorry about that!!

I still think youll find its the backpressure that will help spool moreso.

Am i wrong..if so please enlighten me.

I see what your saying about the engine now tho  whats done is done!

Lets just hope it stays together for you when you attempt it.

caps lock alert!! haha

well what has been done cannot be undone, i dont have a spare 2k to take some part just to some clearancing. As long as the map if relatively safe then it should be ok, let the boost do the work instead of ignition.

One reason for a large exhaust is by lowering the outlet pressure, you increased the pressure differential, and now the exhaust gas can expand more, and do more work. That increased work pushes harder on your turbo, and it spools up faster.

kind of like letting a opening a fizzy pop bottle in space or on earth

[BlitzBoy]

LOL sorry about that!!

I still think youll find its the backpressure that will help spool moreso.

Am i wrong..if so please enlighten me.

.

Not strictly true there Ed, the only thing that will help spool is changing the actual A/R (eg decrease in Size) not decreasing the size of diameter of the exhaust. Decreasing back pressure on a turbo engine will increase top end power. To explain what will increase spool I shall quote a response from a geek I found, which explains it quite well.

"the restriction must be the turbo itself. The turbo utilizes the pressure differential between the manifold and the downpipe for its energy source. putting a restrictor infront of the turbo will reduce the pressure differential of the flow after that restrictor and the downpipe. thus actually hurting performance.

this is why turbo\'s use different turbocharger housing a/r ratios. The smaller the ratio the greater the restriction at the turbine nozzle and thus greater force applied to the turbine wheel.

If you want an every day phenomenon to impress your brain, go get your garden hose and turn it on without a nozzle.... spray a wheel of a bicycle that is upside downwheel, and see the top rpm you make. then put a nozzle on the hose and look at your new top rpm. try altering the nozzles spray pattern and thus pressure and see what changes it makes.

if you want your turbo to spool sooner you need to meet any or all of these criteria.

1. produce MORE total volume of gasses infront of the turbo, thus building higher pressures because the nozzle will only flow so much for said pressure.

2. mechanically lighten the turbo so less force is needed to move it.

3. alter the nozzle characteristics so that for the same flow a greater pressure is created and thus a greater force impacts the turbine. ***


The problem with altering the A/R to a smaller number is the restriction in the turbo gets greater. Thus you may spool the turbo faster but your total flow is more limited and thus hurting horsepower."

[arrouk]

But by increasing the size of the down pipe isn\'t that also altering the pressure differential?

What I mean is if 100 cfm is flowing through a 3" pipe it would be X pressure, if the same volume of gas is flowing through 5" pipe it would be 0.75X pressure.

As others have said above i could be wrong and welcome anyone who can correct me on this.

Matt

[BlitzBoy]

yes correct you alter the pressure differential hence helping power by increasing the diameter of the downpipe\\exhaust, it should also speed up the exhaust gasses going through the turbine wheel and in theory help spool as well. The exhaust A/R makes the biggest difference in spool though

Hope they dont have noise limits at Brunters as a 4 inch or 5 inch exhaust system will be loud!!!

[arrouk]

cool so I am thinking along the correct lines.

[Nik da Greek]

Hope they dont have noise limits at Brunters as a 4 inch or 5 inch exhaust system will be loud!!!

I was gonna mention that but I didn\'t wanna seem too negative on the dude\'s thread.... I\'m pretty sure Bruntingthorpe have rather nazi noise restrictions, and have had for a long time. Bike magazines have been testing there forever, and the number of tests that read "we never got to do a top speed run because they threw us out for being too noisy as soon as the bike fired up" are countless.....

[fil_auto]

I DON\'T CARE - I CAN\'T WAIT TO HEAR THIS BADBOY!!! WHY AM I SHOUTING! :3gears-rh:3gears-rh:3gears-rh;)

Hope they dont have noise limits at Brunters as a 4 inch or 5 inch exhaust system will be loud!!!