stu.p

hi
car seems to be pulling more clean and smooth now with rpm soleniod switch fitted and with the 4600 rpm fuel enrichment chip installed!!
got the car at approx 900 rpm tickover and cruise and idle reading approx 14.0 afr when hot..
Would like your opinions though on how lean it can go before i bring on the enrichment???.From 14.0 it richens itself when i floor it(around the late 12's) it then leans of to about 13.0-13.2 afr until at 4600 -4800rpm then enrichment kicks it rich to about 11.2 then gradually builds up to see around 12.0-12.2 at 6750 rpm..will try eventually print off graph to show yous out there but in the meantime does this seem ok????
Not had car on rollers yet but have zetronix afr gauge in car!
Rebuild majority of engine myself using arp conrod bolts and head studs
1 bar boost(peaks for split second to approx 1.05 then settle just below 1 bar)
cat bypass
standard turbo
open air filter
sc profile cams
standard valves recut for better flow
head work completed to produce approx 10-15% better flow proven on flow bench
here in the uk always run car on 97-98 RON fuel
Above is info of engine spec for opinions on afr
hope yous in the know can help?
thanks!!

nathanUK '81 930 G50

I would try a 4000 chip with your current settings.

Did you fit a modified fuel head at all?

SGOGT4

I put a 4600 in mine originally and found similar readings. You really are running too lean prior to enrichment. I think I ended up with a 4200 and am quite pleased with the AFRs.

stu.p

No just standard euro fuel head in my car nathan,,seems to have enough fuel up top i think.
might try lower chip then as you although what afr (rich) can i drop down to before it is too rich and loosing power??..say as long as it stays above 11.0 afr,is this ok??
what is the leanest at around 4k revs you can go to before it becomes unsafe,,say 12.8??.
have you a graph of your afr 930ldr?

nathanUK '81 930 G50

You should try to tweak it some more but it would appear that possibly you don't have enough fuel up top and that is why you are leaning out. Try and tweak it first though.

I would search for the data you need from quotes from porschephd or geoffrey, they are both top guys when it comes to our cars. I do have this info saved on a usb hard drive somewhere...

stu.p

cheers for help so far guys!
nathan i thought i was ok up top at max revs cause i am at approx the ideal 12.0-12.2 afr..it only is going slightly lean mid range because i am holding the enrichment signal back with this rpm soleniod switch..i have fitted and am using this switch because this stops my really rich mid range and drop in power i was having previously after i modified my wur for more fuel

stu.p

Checked my afr graph it only peaks to late 12's- 13 for a split second because of boost spike then holds about 12.7 until enrichment 4600 rpm chip kicks in then it drops to about 11.2-11.4 then gradually builds back up to 12.0-12.2 at max revs.is this now acceptable or should i richen using the co screw??
so might turn the boost down a tad as i seems to have to spike to about 1.1 bar for a split second so it holds approx 1 bar of boost on my manual boost controller although a lot of the time my boost tails of at max revs to about 0.9 bar or even lower...is this normal or is this a weak wastegate spring etc??

nathanUK '81 930 G50

12.0-12.2 is great, no problem with that.
But, I am wondering if the reason you are rich earlier in the rpm is because fuel flow through the head is maxxing out at top end rpm & the adjustment to the WUR is masking the problem.
What I am saying is that if you had 12.0 @ 4000rpm then @ 6000rpm your afr might be 13.0 which is not good.

I say leave your boost as it is and other settings. Just lower that rpm switch to 4000rpm, check afr's again and let us know.

nathanUK '81 930 G50

As for your boost tailing off I think that is due to the stock K27 being just too small. Hopefully someone else can deny or confirm this.
One of the benefits stated for the K27HFS is that it pulls all the way to the red line and laughs at 1.3bar of boost

nathanUK '81 930 G50

Ok, this says it all...

From a post of Geoffreys, thankyou Geoffrey.

Ignoring the fact that CIS is not mappable, in an ideal world (EFI), your AFR will be 14.7-15.0 in the cruise range (light throttle, no boost). As you begin to add load to the engine you need the AFRs to be richer. By 1 bar of boost, you are safe at 12.0-12.2:1. Richer than that and it is a waste. At about 12.5:1 and 1bar of boost you begin to risk melting the engine down. Obviously things like compression, cams, etc. may change the requirements.

nathanUK '81 930 G50

So, your 12.7 is too lean, change that chip to 4000rpm and see what happens.

stu.p

thanks nathan for the help
will try the 4000rpm chip to see what happens!!

SGOGT4

Nathan's comments on the K27 are spot on. I had a 7200 on my car before switching to a HFS. The old 7200 would start to die out around 5500 RPM. The HFS holds straight thru redline. And can produce way more boost than our engines should see. This I discovered when I incorrectly installed my boost controller.

Ag02M5

So if you are at 12 afr maxed out...I wonder if you could safely squeeze out some more boost, say 1.1 bar.

I also wonder what would happen with an HFS which runs strong to redline.