New Turbo Setup

[Harey]

He has an external gate venting to atmosphere... Don't you have an internal gate? Totally different ball game when it comes to exhaust flow

Good point, that does change things. I am just bringing up the issue of exhaust size when talking about a large turbo like a GT35. A turbo which is capable of 400rwkw on 98 fuel. The rough guide on this forum is 3" for 300rwkw, 3.5" for 350rwkw and 4" for 400rwkw.

Your right external gate venting to atmosphere wont require as large as an exhaust as an internally gated turbo. I think its just worth a thought when getting a custom exhaust made up. Wont cost much extra to be a size larger and might save you getting it all redone later.

[Room42]

I dyno tuned a 600hp na 5L v8 in my early 20's when I worked in a dyno shop. I frequently saw 500 and 600hp go through 3 inches. We tried a 4 inch exhaust on the 600hp engine and they lost about 50 hp in the midrange and made more noise. That's all.

I know that turbo cars and na cars have different requirements from their exhaust systems and I have no intention of debating this. I don't really care that much.

You are right in saying that you should go all out when you are getting work done Harey. That's the reason I got a 6boost manifold instead of an ebay job and a genuine garrett instead of an ebay job. When I get an exhaust made I will make sure its what I want.

I will be pulling the gearbox out tomorrow after work and cleaning the flywheel, pressure plate and clutch facings. Bastard better not slip after I put it back in. And I thought my gearbox removing days were over. I guess not.

Anyway I'm going to bed. Early starts are great. Up again at 4am. Thank god its Friday tomorrow.

[snozzle]

3.5" for 350rwkw? 4" for 400kw ??? Dont agree sorry, sounds like overkill. 4" seems way too big for 400kw (4" for 500kw + sounds more realistic to me..)

Im pretty confident i can make 400kw if my engine was forged and slightly more efficient in the headwork area and retain my 3" dump. I also fairly certain plenty people are making 400kw at the wheels through a 3" dump, i think SimonR32 knows who i remember this debate coming up before!

[Hanaldo]

3.5" for 350rwkw? 4" for 400kw ??? Dont agree sorry, sounds like overkill. 4" seems way too big for 400kw (4" for 500kw + sounds more realistic to me..)

Yeh, my mechanic makes 510rwkw with just a 4" exhaust, including wastegates plumbed in.

[Harey]

Yeah its a guide for plumbed in internally gated turbos.

It doesnt mean you cant make more than 399rwkw with a 3.5" exhaust or 510rwkw with a 4" exhaust, its a rough guide. So if you are aiming for over 400rwkw then you should look at a 4" exhaust if you are plumbing it back.

Yes there are people making 350rwkw on a 3" dump pipe but a lot have 3.5" catbacks.

The test is not if you can make the power but how much power you would gain from a larger exhaust, not to mention the release of back pressure and heat.

Regarding the 600hp na 5L V8, yes N/A exhausts are completely different. The turbo back exhaust looses nothing by being too big. Theoretically you want the largest exhaust you can fit. Obviously after a certain point for each power level the gains are negligible so you dont bother. But you dont loose anything from going too big.

[r33_racer]

I think the rough guide is a 4" exhaust is good for about 1000bhp. Which is probably close to about 600rwkws.

[Harey]

I did not say a 4" exhaust is only capable of 400rwkw, I am saying once you go over 400rwkw you should be looking at a 4" exhaust as you will most likely get gains.

[Crans]

Being an afm based ecu air temp correction is a built in feature. Mass of air is read dosnt matter how hot or cold it is the appropriate fuel will be injected

Map sensor based cars need air temp correction due to the fact that mass of air at the same pressure can change with air temp

[JonnoHR31]

yer thats great for fueling but and it will run through different load cells on a hot day than a cold day in the same gear. the problem is with timing, if you tune it to suit all gears on a 25 degree day then go drive on a 40 degree day, higher gears are gonna run through the same cells as lower gears on cold days. so you'll have either too much timing for a hot day or not enough for a cold day. seperate AIT timing correction is very handy but at the end of the day you only need it if you want every last bit of power.

[femno]

3.5" for 350rwkw? 4" for 400kw ??? Dont agree sorry, sounds like overkill. 4" seems way too big for 400kw (4" for 500kw + sounds more realistic to me..)

Agreed. If the trend continued then youd need a 5" for 500kw. Yeah right.

You can flow plenty through a 3 inch. Real life result: a 25 can push 360kw with a 3540 .86 on 21psi and 98ron with the gate plumbed in through a cheap 3" cat back with just a cannon muffler. Full 3 inch dump and front. It also made a bar @4000rpm. Stock unopened engine. I dont think there is much more gain to be had in that...

I dont think the 3540 is too big for street, i think its a fantastic turbo, its the best solution for that kind of power; anything bigger would be a bit frustrating. The car is still going 2 years later at around 330kw every day.

..and as for 3.5" being only a little more expensive, i think not; the mandrels are MUCH more expensive than 3" because theyre harder to make and arent as common.

[zebra]

I kind of agree there.

you can make decent power with a 3" exhaust (lets face it, 3" is a big bloody exhaust for a 2.5L engine), but what would happen if you changed it to 3.5"?

more power on the same boost is likely, not guaranteed though, so can be expensive to find out.

So when I re-do the exhaust on my car It will be Dual 3" to make sure there is no way in hell it will give me any headaches

[Room42]

When I had no exhaust or dump the turbo ran 17 psi on the gate which had a ten and a seven psi spring in it. Makes sense right?

My current exhaust is comprised of a 3inch dump, 3inch front pipe, stock cat and 3inch kakemoto cat back. When I got the dump made and the exhaust put back on the turbo ran at 14 psi.

I have a bleed valve and I have turned it up to 20 psi. The car goes fine. Its nice and quiet too. I know I can turn it up more too but due to other issues it will stay at low boost (under 20psi) for a while.

When I get a better cat I will close the bleed valve and see how many psi it makes then. Of course it will be more than previously.

The current exhaust setup killed 3 psi and the point of this post is is to show I will be losing less than 3 psi using a full 3 inch system.

I agree with zebra. What is peoples definition of decent power? My car goes better than decent in my opinion.

So when I have 1000kw does that mean I need a ten inch exhaust?

[Room42]

A little update. I went for a tuning drive today with the datalogit in use. Before I went I wound the bleed valve out so it would land around 25 psi. We made the area under boost a bit richer with the afr's to help it pick up a bit better. A big thanks to my beautiful wife for being my co-tuner.

As we got out of town I gave it some cautious wot runs in second to see what boost it was going to run and to check the knock. It ran about 25psi but to be honest I didn't have a clear look. I had wound the bleed valve 2 and a half turns up from 22 psi. Each turn is about 1 psi.

I ended up pulling 6 degrees out of load 17 to 19, 5 out of load 16, 3 out of 15 and 1 out of 14. I am now running 11, 10 and 8 degrees in load 16, 17 and 18. Winding out the bleed valve makes a fair bit of difference on when the turbo hits full boost.

The afrs are 12.0:1 from 4000rpm dropping to 11.2:1 at 7000rpm.

The highest knock level now is 11. I am pretty happy with that. I might be able to get another degree in there somewhere but that will be another day.

The car absolutely hauls ass now but I could still do with some more power. It pulls from 60 kph to 100kph almost instantly in 2nd gear. After 4500 rpm even on half throttle it will get up to 20 psi or more.

The stock coil packs were missing a bit at the higher boost level. I guess it is time to upgrade them. They work fine at 22 psi though so I'll probably wait a little while yet. I might even try adding a touch more dwell in there so get more of a spark happening.

The fuel reg line kept popping off at the higher boost so ended up cruising home. I had a look under the bonnet when I got back and most of the vacuum lines had moved along their fitting places. One of the cooler pipes was about to come off as well. It seems I will need either new lines everywhere or a bunch of little clamps or cable ties.

Funnily enough the clutch didn't slip today as I thought it would but I was a lot more gentle with the gear changes.

Soon it will be time for another round of upgrades. Brakes, clutch and wheel/tyres are next.

[DVS JEZ]

What power are u making Room?

[Room42]

What power are u making Room?

I haven't put it on a dyno yet. I can only go off similar setups that are on here. I would say conservatively 450rwhp. I'll get it on the dyno this week if I can and let you know.

[r33_racer]

I did not say a 4" exhaust is only capable of 400rwkw, I am saying once you go over 400rwkw you should be looking at a 4" exhaust as you will most likely get gains.

I wasnt saying you were incorrect. I agree with what you are saying. Im just stating for general knowledge that a 4" system is roughly good for 1000bhp before it starts to become a restriction. In saying that, you would probaby want a larger dump and then 4" from there back where the gas has hopefully cooled enough to not occupy so much space.

In reality if you spent enough time working it out you would build an exhaust system that almost constantly steps down throughout the whole length of the system to keep gas velocity at the ideal speed. So you could make a 3.5" dump or even 4" and then just run a 3" system from there back and it could support more horsepower then just a straight 3" turbo back system.

[Room42]

I did post this link in another thread to show a stock engine revving hard but since it is more related to this thread I thought I would post it here.

Just so you all know the stock tacho reads 1000rpm high in this vid. There was no clutch dumping and the 1 to 2 change was gentle.

http://www.youtube.c...h?v=ZCG9jTJozuM

[GTR260]

I did post this link in another thread to show a stock engine revving hard but since it is more related to this thread I thought I would post it here.

Just so you all know the stock tacho reads 1000rpm high in this vid. There was no clutch dumping and the 1 to 2 change was gentle.

http://www.youtube.c...h?v=ZCG9jTJozuM

What turbo u have on that?

[Hanaldo]

What turbo u have on that?

Notsureifsrs....

[zebra]

l2readthreads