Downpipe sizing for a GT4088r

[PhilMorrison]

My downpipe consists of a 45* bend, to 70cm straight section and another 45* section. I was planning on keeping this section all 3" (72.5mm I.D), and then tapering out to 4" after this section.. Is this going to be adequate, or should it become 4" much sooner?

 

See the setup here:

 

http://media.driftworks.com/S15/NewTurbo1.jpg

 

 

http://media.driftworks.com/S15/NewTurbo2.jpg

[Mike B]

if it's not 4" at the start don't bother making it 4" later. the ex gases will have cooled and it won't make any difference aside making your head ring.

 

If it is 4" at the start you can move it to 3 " but not the other way around.

 

Many people use 3" systems on here and I can't see any significant difference in spool.. so don't worry about it.

 

looks like a good install!! well done for doing something different, keep us up to date!

[b_have]

Great build! That has to be the shortest ic pipework ever, are you using a pull fan under the ic?

[Mike B]

also, if that's a 4088r, it looks like you are using the .96 divided housing.

 

If so then you want the .81 housing. I have tried a .68, .81 and the original .96 on mine and the .96 and .68 are hopeless on the 2jz, the .81 is the only one to go for.

 

it makes a massive difference to power and response.

[Ric]

i hope you never have to take those cam covers off, lol

[PhilMorrison]

if it's not 4" at the start don't bother making it 4" later. the ex gases will have cooled and it won't make any difference aside making your head ring.

 

 

If it is 4" at the start you can move it to 3 " but not the other way around.

 

You've really confused me know. Everything I've heard says that the exhaust needs to get progressivly bigger. A massive step to 4" from an turbo exhaust port that measures 66mm (don't you just love the metric/imperial clash in the UK ) would create turbulance.

I've also heard that the longer an exhaust is, the bigger diameter it has to be as it gets further back, as hot gasses flow alot quicker than cooler gases, so even small bends in the pipe create restrictions.

 

looks like a good install!! well done for doing something different, keep us up to date!

 

Thanks .

 

 

Great build! That has to be the shortest ic pipework ever' date=' are you using a pull fan under the ic?[/quote']

 

Push fans, but it's a V mount setup, so will have devided flow between the radiator and the IC that exits through a huge vent in the bonnet .

 

also, if that's a 4088r, it looks like you are using the .96 divided housing.

 

If so then you want the .81 housing. I have tried a .68, .81 and the original .96 on mine and the .96 and .68 are hopeless on the 2jz, the .81 is the only one to go for.

 

it makes a massive difference to power and response.

 

It's a 1.06 huzzah .. I'm pretty good with the tripple carbon clutch, but I'm not sure if it's going to be just too laggy myself.. We'll see eh!

 

i hope you never have to take those cam covers off, lol

 

They come off with 3mm to clear . Alot of thought went into working on the engine when it's in situe.

[Mike B]

I spoke to the guys who made my exhausts; been preparing high end rally cars for 20 years, and he said that when the gasses are closer to the engine they are hotter and take up far more room as they are expanded, as they progress down the pipe they cool and shrink.. so it's far more important to have size at the beginning not the end... Just what I was told by one of the old boys. He may be wrong, but it makes sense. Anything 3" is plenty big enough anyway.. there are other things you can do that will have more effect.

 

otherise, if you have the constriction at the engine end then a big fat pipe after that you just have a big trumpet.. and sore ears... lol

 

1.06, better you than me buddy. Set your alarm for when that spools; really the .96 was undrivable, I was really dissapointed. I also recon that the .81 makes more power... is spools and bites so much faster. By the time the 1.06 had bitten the .81 would be two gears further down the road, at the same HP, unless you are running 7.5-9.5k

 

If you want a cheap .96 let me know and it's yours!!

[PhilMorrison]

Cheers . I'll see how I get on with the 1.06. The final drive is going to be 3.6, and the limiter at 8k, so it may be okay .

I'm a bit of a power whore at the moment. What power have you got out of the 0.81 version?

[Mike B]

to be honest I don't know.. I managed 580 at the fly with the .68 and it felt wrong... infact pretty dull and wet... if more reactive than the .96 but just slightly down on power and asthmatic, the power curve was nearly linear.

 

The .81 feels ballistic by comparison, not just in power (although it is clearly the fastest setup on the bum dyno), but in engine spool and response. I have not been on the dyno with it yet but it feels like an extra 100+, and ferociously instant. I use an uprated diff and 295's at the moment and struggle for straight line grip, until I get 5th (130+). Summer would be a different matter though.

 

I'd be interested to see what you thought of the 1.06, but you'd have to try the others as a benchmark to know. Power is all well and good but you need to be able to use it effectively.... dyno printouts can be pretty misleading until you get the car on the road.

[paul mac]

i agree with everything Mike B has said, one of the only things i remember about my HNC was gas flow, exhausts can get smaller as they progress due to the cooler gas contracting, a good example is big diesel stacks or boilers they are big at the base and get smaller at the outlet, the one caviat i would make is if you are going to lag the exhaust you will (theoretically) prevent it from cooling and the velocity may benefit from keeping it the same size or slightly bigger, i think a lot of the exhaust manufacturers with 90mm pipe etc use it as a gimmick, bigger is not allways better even with a turbo a huge exhaust will also reduce low down torque

[PhilMorrison]

Okay thanks guys .

 

I'm going to try it out with a short 3" downpipe, and if that appears to be a restriction, we'll sort something bigger. I'd like to see between 650-700@the fly, but I don't know if I'm kidding myself there.

[Ryan.G]

Nice work Phil!

 

Are you going to be fitting some sort of heat sheild on the exhaust housing of the turbo to stop it heat soaking that intercooler.

[PhilMorrison]

Yeah of course . The downpipe will be ceramic coated inside, and wrapped outside, and the exhaust housing will possibly be ceramic coated if we can find someone to do it, or just bagged, and a 2 layer ally insulation board between them as well.

Heat is a massive killer of drift cars with the amount of time we stay full load full throttle, so everythings been taken into account in that department

[Mike B]

really interested to see how it goes in the end. What ecu are you planning to use, and what is the car, nissan or rx7? 'm a rubbish engine bay spotter!