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Alan L's Avatar
 
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how much turbo lag is normal.

I've never driven or been in another 930, so have little to compare to, and a board like this is probably a difficult way to accurately describe the issue - compared to trying another car.
I had my first full race day y/day in the car after months of trying to get it running good. It is slower than I expected, possibly because I am not so familiar with driving it, but one area where Iwas loosing a lot of time was getting some power down early enough in corners. It was simply bogging down, at times I had my foot nailed in 2nd gear waiting for something to happen, and hoping it did not all happen at once. Once it came on to boost, I could back off the throttle and start to drive it off the corner. But much time wasted in between waiting for something to happen. AFR's seem reasonable - at boost at least - max rpm out to 12.4, and starting around 11.8. (fiddled with WUR) Interestingly, the metering piston I manufactured seems to operate in a narrower AFR range than the original one - which went from too rich to too lean. But there has , in my view been a constant leaness issue at low throttle openings (putting early power on in corner) - around 14 AFR. I don't know how much is due to turbo lag, and how much fuel related - possibly both. But how responsive would you normally expect the beast to be below boost - mine seems fairly dead until it picks up to around 0.1 bar, then it lights up and is very throttle responsive.
Standard turbo, 0.8 boost.
Alan
Old 06-15-2008, 03:05 PM
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Mine was pretty laggy, this is why it's in pieces for upgrades

It was like, '1second 2se' then boom. My car did the 1/4 in 13.1 @ 108 so I'm pretty happy it didn't have any problems. A guy in a 996 cab thought he could lose me LOL.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
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Old 06-15-2008, 03:21 PM
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On my 79, the turbo starts kicking in @ 3.5k-3.8k and pulls hard from there. The 86 is a different beast as it spools earlier and waaaay faster. I would say it starts coming on @ 3k.
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Old 06-15-2008, 03:34 PM
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Mine seems to kick in at around 3k. Is the '86 spooling better because it is a different turbo than the '79.
Do they normally lack traction below boost? Off a standing start I get it rolling, then floor it and it sits there going nowhere, slowly, until it hits boost and the front nearly leaves the ground. Should I be getting more traction prior to the boost level? It feels like a 1000 cc shopping basket prior to that.
Alan
Old 06-15-2008, 04:18 PM
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Stock?
---OR----
Do you have mods?

Stock - YES, LOTS of lag.

Mods - Not so much.

FWIW - My '87 930 had tons of lag and didn't even hit full boost for a long time. Actually, it wasn't true but my old '85 seemed faster even though it really wasn't, I couldn't believe how the 930 felt when I first got it. It was like ah whatever. I put in a 1 bar spring and that helped but still wasn't feelin' it. So with everything stock I removed the CAT and muffler and put just a muffler (GHL) off the CAT and WOW that made a HUGE difference! So then I changed the headers out and the turbo and that made even a bigger difference. Long story short, GET THE CAT OFF OF THERE!
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Old 06-15-2008, 05:32 PM
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It is pretty much stock - turbo wise as far as I can tell. It has headers (GHL I think), we don't run a CAT in NZ. I wonder about the fuel mix at low revs - just off idle. It seems a bit stronger/responsive below boost when in warm up cycle. At race temp it is around 14 AFR. I'm not sure this is helpful in terms of getting throttle response - I suspect some leaness at this number.
I am watching the digi WUR htread with interest as I'm not sure how to dial in more fuel at this rev range without upsetting everything else - which appears about right.
I understand if I go to a K27 this would reduce some of the lag?
Alan
Old 06-15-2008, 05:47 PM
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Upgrading to a k27, headers and exhaust should reduce lag over the stock items.

Just watch out tho because the more you reduce the lag the less it feels like a kick in the pants when the boost kicks in which many of us crave.

If you are racing it around a tight circuit they do feel very sluggish (stock) and will probably be passed by the NA cars. A lot of this also has to do with the stock 4-speed tranny and it's ratios.

Just depends how far you want to go in reducing the lag and how many $$$$ you have to burn.
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Old 06-15-2008, 06:07 PM
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The circuit is reasonably tight - this I think is part of the problem - lot of time spent off- boost.
Cars I used to deal to easily in my NA car are passing me in the corners, while I have my foot nailed waiting for something to happen. I have lowered 3 &4 ratio, but am thinking I am going to spend some time in 1st gear to try and avoid these issues - unless I can tune some of the dead time out.
The straights are great - boom, and you knock them over like flies. Then they come back in the corner while your engine is asleep.
Just wondering how much of this is normal - but seems like it is pretty much so. The digi WUR may help I suspect , by firing a bit more fuel in before boost takes over.
Alan
Old 06-15-2008, 06:27 PM
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1st ? man that's gotta be some tight course,, I usually never use first after I leave the pits!
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Old 06-15-2008, 06:42 PM
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I guess this is turning into a track thread which may be better posted elsewhere - but it starts with the lag issue. I did not use 1st either except for launching, and pits. And was not expecting too. But am thinking it may be the best option to keep in the boost range. Problem is things happen exceedingly quick in 1st, on boost. Not my first option really - especially in the wet.
When we talk of turbo lag, what are we really referring to - the rev range before it kicks in?
Mine hits pretty hard at 3k, ie when I see 3k approaching I know something vicious is about to hit. The issue for me is the 500 rpm below this, it is like no body home. With 7 :0 compression, I guess it may be a bit gutless as a motor and everything really has to happen on boost. In which case I will need 1st gear on about 3/4 of the corners. Hard day at the office.
Alan
Old 06-15-2008, 07:58 PM
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This will give you some idea how they should go when boost comes on. Mine is (was) running 1.0bar and an exhaust job.

http://www.youtube.com/watch?v=9L6LGawjfMk
Old 06-16-2008, 01:17 AM
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Excellent - thank you. I want mine to go like that. I definitely have an issue in the non- boost area - I'm stuck there for about 5 secs from a start.
Alan
Old 06-16-2008, 01:47 AM
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Quote:
Originally Posted by Alan L View Post
Excellent - thank you. I want mine to go like that. I definitely have an issue in the non- boost area - I'm stuck there for about 5 secs from a start.
Alan
That shouldn't happen as the turbo should start spooling @ 3k and pull hard from 3.8k. The 86 that pulls hard from 3k+ is modded quite a bit so turbo lag is minimized. As a worst case scenario, you floor it in first and it should spool w/in a couple seconds. How's the condition of your turbo? Mileage? Maybe you have a boost leak somewhere.
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Old 06-16-2008, 03:03 AM
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OEM 930 engine has hogh boost treshold per definition and not suitable to slower courses with lot's of tight bends. I say "boost treshold" as people mistakenly mix lag with boost treshold. You can have near instant spoolup but high boost treshold and vice versa.

Lag is connected to shaft intertia, boost treshold is determined by turbo/engine sizing.

If you really want better throttle response at lower revs, I recomend using hotter cams (to smear torque curve higher up the range) and maybe a more modern turbo.

Garrett GT35 would be a perfect drop-in and it has noticeably better response than K27 variants, HF or not.

If we push issue further, you could dump the ignition before treshold to spool up the turbo quicker and adjust cams for more overlap...in most extreme case you can use anti-lag and have instant boost, but EGT's usually soar so it must be used with caution.

To round it up: there is little to be done with OEM bits and pieces. First step in my book would be to swap KKK hardware for modern Garrett pieces and run hotter cams. After that, there are plethora of more or less pricey things you can do. But you'll never make a good auto-X:er out of 930.
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Old 06-16-2008, 03:57 AM
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OEM 930 engine has hogh boost treshold per definition and not suitable to slower courses with lot's of tight bends. I say "boost treshold" as people mistakenly mix lag with boost treshold. You can have near instant spoolup but high boost treshold and vice versa.

Lag is connected to shaft intertia, boost treshold is determined by turbo/engine sizing.

If you really want better throttle response at lower revs, I recomend using hotter cams (to smear torque curve higher up the range) and maybe a more modern turbo.

Garrett GT35 would be a perfect drop-in and it has noticeably better response than K27 variants, HF or not.

If we push issue further, you could dump the ignition before treshold to spool up the turbo quicker and adjust cams for more overlap...in most extreme case you can use anti-lag and have instant boost, but EGT's usually soar so it must be used with caution.

To round it up: there is little to be done with OEM bits and pieces. First step in my book would be to swap KKK hardware for modern Garrett pieces and run hotter cams. After that, there are plethora of more or less pricey things you can do. But you'll never make a good auto-X:er out of 930.
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Old 06-16-2008, 03:57 AM
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The 964t has a mapped ignition timing rather than the mechanical dizzy that the 930 has. When I try to accelerate the timing gets retarded before boost builds. My 930 does not have boost retard, only vacuum advance. Maybe you should check out yours and confirm yours is like mine.
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1981 UK 930. G50/01 shortened, 964 3.8RS Fibreglass Body Kit, 18" Alloys 8.5" F & 10" R, 225's F & 285's R, Special Colour Metallic Blue Paint, FIA Sparco Evo's, A/C and Air Pump removed, Electronic Boost Controller, GHL Headers, Tial46 WG.
Fitting - New service kit.
Needs Fitting - Innovate XD-16 Kit, Kokeln IC. Stephen's K27 HFS, EVO Intake Assy & his Modded USA Fuel Head.

1983 UK 911 3.2 Carrera Sport Coupe. Black, Black Leather with Red Piping, Black Alloy Gear Knob, K&N Air Filter Element, Turbo Tie rods.
Needs Fitting - K&N CO Sensor, Round A/F Dial Gauge, Factory Short Shift Kit.

http://www.danasoft.com/sig/Iamnotanumber.jpg
Old 06-16-2008, 11:36 AM
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My distributor is not the standard one apparently - I only have one line going into it - vacuum from the throttle body. From an earlier discussion when I was working my way thru the car, I believe it is from an earlier model 930, and has a more aggressive curve?
The turbo is one bit I have not pulled apart - but it 'seemed' OK. Grabbing the spindle I could get no end float or axial play that I could feel - is this a useful indication?
When I floor it off the line, it really is slow to pick up revs - I suspect you could run past it until the turbo kicks in - then you are quickly looking for second, and trying to see over the front of the car.
It is shooting flames out the back on over- run into braking zone - is this indicative of anything?
Alan
Old 06-16-2008, 12:49 PM
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Quote:
Originally Posted by Alan L View Post
The turbo is one bit I have not pulled apart - but it 'seemed' OK. Grabbing the spindle I could get no end float or axial play that I could feel - is this a useful indication?
When I floor it off the line, it really is slow to pick up revs - I suspect you could run past it until the turbo kicks in - then you are quickly looking for second, and trying to see over the front of the car
Your turbo is adopted piece from a turbodiesel truck, dated early 70's. Even if perfectly healthy, it is inherently laggy old piece of iron.

Quote:
Originally Posted by Alan L View Post
.
It is shooting flames out the back on over- run into braking zone - is this indicative of anything?
Alan
Nothing more than that deccel valve doesn't do it's job (and probably nothing to worry about really). CIS doesn't cut fuel on overrun like EFIdoes, thus popping and fire on deccel.
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Old 06-16-2008, 01:01 PM
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I don't mind the flames - just that I can't see them. But everybody else seems to enjoy them.
The decel valve is the big round gold disc plumbed in the intake manifold under the intercooler - right?
A lot of EGR bits have been removed from my engine before I got it - but I think I still have the decel valve.
Alan
Old 06-16-2008, 01:13 PM
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One of the things you really need to learn AT THE TRACK is the anticipation to the apexes, in our cars we have to give WOT before the apex in such way the boost comes on at the right spot. It takes practice, but it is part of 930's; after you learn that, then the real fun begins. Be careful though because that one of the reasons people say that 930 are tail happy :-)
Old 06-16-2008, 05:25 PM
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