1497 replies to this topic

[The Batman]

good news that its up and running whats the rev limit?

[NickB787]

Just got home I was getting used to it also noted as the temps dropped it felt stronger, there are a few things which need adjusting one is a lag between lifting off and revs dropping from full throttle( changing gear) Rev is set to 7500 but peak power is about 7000, I don't think running a smaller pulley will actually be an issue with driving, they changes the map and pulley at the same time so I think once they continue with the mapping software adjustments it should allow a smaller pulley setup 2.8 should be ok Just glad to have her back

[NickB787]

Safe and drivable for the national and le mans then

lemans yes National no I had to cancel some time ago as I couldn't guaranty being ready in time.

[techieboy]

Glad you're back and things are sounding vaguely positive for a change. I guess you did pick the hottest day of the year to stick it on the dyno.

[Mangham54]

Just wait a place will come up with your name on it, if you are willing to strike

[alanoo]

there are a few things which need adjusting one is a lag between lifting off and revs dropping from full throttle( changing gear)

Hum...

What is your DBW throttle body exactly ?
(sounds very very much like a DBW PID algorithm issue, which can be VERY dangerous)

[NickB787]

It's a porsch 996TB , Approx 70mm wonder if oem turbo is worth a try to see if it goes?, anyone with a spare I only have a saab tb laying around or is there a larger tb which works ok on turbos?

Edited by NickB777, 28 June 2012 - 08:38 PM.

[Nev]

Hi Nick, I would imagine that a 70mm TB would be fine for approx 350 to 400 BHP - perhaps a very mild bottle neck, but nothing major. Why is it that you are trying to replace you current one? Is it simply cos you think it's causing a restriction or cos of some other loom/wiring/mapping issue?

[NickB787]

What TB are you using Nev?. I reason I was going to give another TB a try was just to see if the slight problem with lag when lifting off is partly due to the Porsche TB itself or as alanoo had mentioned about a possible "DBW PID algorithm issue"

[Nev]

My current TB is an Z20LET OEM one that has been bored out from 56mm to 62mm. I know an engineer might be able to increase this to approx 68mm on the OEM unit. However, if he does this the TB will lose the green rubber seal, leaving approx only 3 mm of material on the outside circumerance to hermitically mate with the top hat and inlet manifold. You'd have to make some sort of self made seal to replace the OEM one which might leak boost if not done right. TBH I think a 62mm TB would be ok for your sort of power level. After all Im making 500 BHP with just 21 PSI of boost with a 62mm TB, so it can't be that bad of a restriction. Though you really need an engineer like WinStar to model your pressure drop across it, which I have only a basic idea of how to do, hence my recommendations are just based on my experience rather than any sort of engineering

Edited by Nev, 30 June 2012 - 08:20 AM.

[Winstar]

You need to remember that the TB on the SC is pre compression so needs to be much larger than on a turbo car as the volume flow rate is much higher

[Nev]

Oh golly, I had completely forgotton that. So yes, pre-boost TBs need to be a lot larger. As background info, If you are making 370 BHP, you will need approx 550 cubic feet of air per minute. Thus, if you're TB was 70 mm internally then the airflow through it would be 245 KPH.... it doesn't take much to realise that that would be an inefficiency, so moving up in diameter would almost certainly reduce resistances in my estimation.

[alanoo]

What TB are you using Nev?. I reason I was going to give another TB a try was just to see if the slight problem with lag when lifting off is partly due to the Porsche TB itself or as alanoo had mentioned about a possible "DBW PID algorithm issue"

Are you 100% sure both OE and your TB are from the same brand ? (I think it's Bosch or Siemens on the Z20LET ?)

[VX-GT]

gas velocity 200-280 ft/s is good thats 219-307 kph standard lsj tb flows @675cfm (standard day) perfect for upto 420bhp

[The Batman]

Porsche tb is bosch

[JimmyJamJerusalem]

I really struggle to keep up in this thread!!! How are you getting on then Nick, was the dyno kinder to you than it was to me....? I was well low, but thanks again for the dyno time!!!!!

[NickB787]

No Jimmy not at all, I need a big TB then 70mm min would be nice how big is the LSJ one?

[techieboy]

68mm

[oakmere]

Nick from speaking to the lads at CS when I was there they know exactly what the issues are with your car and it is nothing to do with your TB. It is to do with the way the ECU controls engine speed for turbo cars above 80% loadings. I was told at this point the LET ECU controls engine speed via boost control not TB opening but it can not do this with the charger as it is mechanically driven. ThInk that is right anyway?

[NickB787]

Yep I am fully aware of this