Exhaust A/R size question?

[WLD747]

Hi i need to know the advantages and disadvantages of having a smaller exhaust a/r as apposed to a bigger exhaust a/r

e/g T04E with a exhaust housing a/r of 0.69, 0.87 or 1.12.

Isnt it better to have bigger so the exhaust gases can pass out quicker?

Thanks in advance

AK

[b0neR]

To put it simply, bigger A/R = more flow and more power but at the cost of response/more lag. A smaller A/R turbine will spool a turbo quicker but at the cost of power. Matching a turbine A/R will most depend on the flow of the engine (size) and power target.

[WLD747]

On a Rb25 with a 0.87 would the spoolup will be 2 quick or is the 1.12 better so its a big laggier and more power?

[b0neR]

Im no expert but id estimate that the .87 housing would probably suit you the best...the 1.12 would be too big and .69 would strangle top end and probably come on boost to hard.

[WLD747]

I was thinking of going for the 0.87 . Would love to try a 1.12 a/r but maybe 2 laggy but would have nice power, i think :aroused: .

Im no expert but id estimate that the .87 housing would probably suit you the best...the 1.12 would be too big and .69 would strangle top end and probably come on boost to hard.

[WLD747]

Would it possible to go a small wastegate (32mm) with a large housing. Would these complement each other for perky performance?

[b0neR]

yeah, as long as the turbine is flowing most of the gas a smaller wastegate would be fine...in fact better than i bigger w/g. it does depend on some other things though.

[Guest INASNT]

If u want good power and response then piss off the 1970's TO4E and get a twin ball beaing turbo. As an example my GT30 with 0.82 a/r rear power comes on hard at around 4000rpm (1 bar).

[R31Nismoid]

On a Rb25 with a 0.87 would the spoolup will be 2 quick or is the 1.12 better so its a big laggier and more power?

Umm.. RB25? going by your sig

* RB30DET on its way

So why even think about an RB25? Or are you dreaming of the RB30?

If u want good power and response then piss off the 1970's TO4E and get a twin ball beaing turbo. As an example my GT30 with 0.82 a/r rear power comes on hard at around 4000rpm (1 bar).

:werd:

mine comes in at like 4200... pretty much the same as you Denham.

love it

[Steve]

Response and lag depend on alot of things.

Dont be too quick to think a BB turbo will outperform a bush bearing. Point in note T518Z, which can make 1 bar under 3500rpm on a 2L bottom end (SR20). Older bush bearing turbos though - just dont expect anywhere near the response as from a newer turbo.

With a GT30, I am getting 1.2bar at 4000rpm with 0.87 housing. It was not always that good, I had to sort out my exhaust and a few other bits (eg PCV valve) to get it there. I have since been told that by a Japanese mechanic and pro D1 driver, that he believes the turbo is capable of coming on boost earlier, and making more power than it does. He puts this down to tune.

Tune can make a huge difference to how a turbo comes on. Judd has bought a Jap trained mechanic over to do some tuning, and in one case, brought boost on 800 odd rpm earlier by tweaking the ecu, with a drop in detonation. Tuning can make or brake a combination, as can any other weak link in the chain.

The Jap mechanic I spoke to said he likes to tune around 11 AF ratios, and use timing to get response. This seems to be very different to what most seem to do in Aust (that I have had experience with). They tune for top power, at around 12 AF ratios.

I originally started with a 0.61 turbine AR, this was way too small for the street and resulted on boost coming in so hard that the car would step sideways at around 3000rpm even with light throttle, in 4th gear. Not good when you are travelling at 100kph in traffic.

As a result I could only use low (1 bar) boost on the street, and a tune of around 256rwkw. Now with a 0.87, it is possible to use the right foot to control boost, so I can run a tune with over 300rwkw on the street, lag is only marginally higher, and I believe it will get lower with the right tune, but still enable control with the right foot.

I am using a 40mm wastegate, and it was fine with the 0.61 housing, as it is with the 0.87.

If you are going to the 3L bottom end, I beleive the 0.87 would be too small, closer to 1.0 would be my choice.

[WLD747]

Ive bought a 1.12 housing because it would suit the 3.0L later down the track because its a project, but as its going on the rb25 very shortly and i dont want monster lag. Therefore i thought a smaller wastegate would help reduce this lag.

As for the TO4E, It was rebuilt with a 66mm compressor wheel. It needs to be balanced before put on as the previous company did a shit job. I do have the original housing of 0.69 but i think it would be 2 powerful. :wassup:

The 3L wont be ready until a couple of months because its a slow project build and money counts. The 3L is real as ive got the short block all prepared for the head and everything else. Waiting to purchase pistons so thats gona cost a bit, well thats another story.

Oh yeh tunning plays a big part of performance and response but also purchasing the correct size wastegate and manifold helps also Well im gona have a HKS To4 tunned manifold and not sure on the wastegate.

[lukits01]

Hey what's the specs for your compressor housing?

so its got a 66mm T04 compressor wheel (what trim?)

what's the A/R of the compressor housing?

is there some sort of rule to choosing a compressor housing when you've decided on the specs for turbine housing?

[WLD747]

I think the turbo has a T6 front with a T4 end.

I dont know details on the turbo as it was a dudd turbo that needs fixing so all i know is that its a 60 or 66mm compressor wheel.

Hey what's the specs for your compressor housing?

so its got a 66mm T04 compressor wheel (what trim?)

what's the A/R of the compressor housing?

is there some sort of rule to choosing a compressor housing when you've decided on the specs for turbine housing?

[DoughBoy]

If it's the T66 wheel (66mm) then it's pretty damn good - the comp map for that blade is awesome. Should be good for at least 700hp. But to flow that much you're going to need the rest of the support systems, and spec the turbine end not to be too restrictive.

[PHaT MR30]

hmm sorry to drag off topic, but my mate has a VL turbo, which has most of the good bits in it and namely a GCG hi flow turbo (T3/4 hybrid i am guessing), not long after he bought the car the turbo carked it due to a crimped oil feed line. so he ordered a new turbo from GCG, specs not exactly known.

put it on ran it at the drags and then had another problem with the car... unrelated. after fixing that problem, he decided that the exhaust a/r was too small and sent it back to GCG. after they had it a month it was sent back and told doesn't need too be done.

2 weeks ago car was dyno tuned and the best possible run was 204rwkw. now he (and i) were expecting a bit more than this. as it is not laggy at all, and boosts quite quickly

why would GCG refuse to do this?

it is getting sent back there one more time to get DONE and if they refuse, TUFF!!!

[Cubes]

204rwkw is bugger all on a vl when you consider the stocker turbo will make 180rwkw.

[R31Nismoid]

Ive bought a 1.12 housing because it would suit the 3.0L later down the track because its a project, but as its going on the rb25 very shortly and i dont want monster lag. Therefore i thought a smaller wastegate would help reduce this lag.  

nag, wastegate dont affect lag. it only opens as per the boost your running.

how well it holds boost depends on the size and how much it opens etc.

[R31Nismoid]

204rwkw is bugger all on a vl when you consider the stocker turbo will make 180rwkw.

a stocker T3 hi-flow (different wheel on comp/exhaust) makes 230rwkw on average. thats with the stock housings just machined a bit

[WLD747]

thanks R31NIsmoid. So i would be better using a 40mm wastegate instead of a 32mm so it hold boost well.

nag, wastegate dont affect lag. it only opens as per the boost your running.

how well it holds boost depends on the size and how much it opens etc.