fasteddie313

I don't know where to ask these questions.. I can't really find any good tuning forums and my setup is kindof unique..

2.0 8 valve 4 banger at only 7.5:1 compression ratio.. Yeah, It's a dog off boost..

Some questions for tuners that have been on my mind..

How lean can I actually run in cruise between about 60-90 KPA without (probably) damaging anything? Can I run mid 15's? Run the AFR here where it just feels the best? What is "safe" at low load? How to know? As long as it's not misfiring?

Do I really need to start dropping AFR under like 150 KPA?
I mean.. This still feels like low load to me.. Throttling up to only about 100KPA is like barely accelerating up to normal road speed like a grandma.. Do I really need to be dropping AFR for this "light" acceleration?
Even cruising at like 80-90 MPH I'm in some positive boost just to hold that speed.. Do I really need to be running rich for >100KPA here? I'd rather be cruising in the high 14's for fuel mileage.. Or what can I get away with here?

What about between 150-200KPA? Are 13's good here or should I already be like into the 11s or around 12?

200-240KPA I've been trying to stay "safe", running 11.0 and even into the high 10's at higher RPM.. But OMG I can almost watch my fuel gauge dropping!! This car has turned into a gas HOG!
I see a lot of AFR maps running even 12.0 in high boost.. Is this OK?

I'd like to run leaner to get some of my fuel mileage back.. I mean, I can go out logging pulls and it seems like I can burn an 1/8th tank of gas in 5-10 miles.. I'm burning 2-3 full tanks of gas a WEEK just running around town.. (I drive the car all I can, every errand or trip, DDing)

Yeah yeah I know this isn't about fuel economy, but this is really starting to seem ridiculous..
Any advice? AFR target map examples?

These are my targets right now, and I'm tuned to them very well actually, but want to pull more fuel out where I can..



Can I keep stioch up a little higher? Like atleast to 125KPA since I have such low compression anyway?

I also have plenty of IC, up to about 210 KPA my MAT temps are nothing untill I start running out of turbo efficency.. Even at 20psi and 90F ambient I've only ever seen my MAT get to like 135F max..

My engine coolant CLT NEVER gets above about 195F, never.. No matter what.. NO heat problems whatsoever..
Running a cooler thermostat, I almost feel like it's too cold..
Even on high boost pull logs, if my thermostat is opening my CLT is going DOWN while boosting 20psi.. No problems even when its 90F ambient outside..

My ignition timing is still OEM and extremely conservative.. Looks like this..

I'm sure their is a lot more power to be had there when I get around to taking over the ignition too.. Will probably go with 4 LS coils..

What can I get away with?

JustinL

I think you are way too rich in the high boost areas. I've read that 13:1 is best for max power in n/a applications, 14.7:1 for emissions, 12:1 for boost and 16:1 for maximum lean. I'd start by dropping your 175kpa row to 12 and hold that to the 300kpa row where maybe go to 11.5 as you said you don't seem to be heating the air up too much.

I also agree that your ignition timing is super conservative. You will find some fuel economy and power in there too.

V2Rocket

light cruise you can go 16 or 17:1 if you wanted but it will be reeaallly unresponsive to throttle. also you might notice your water temps creeping up a bit when you go much leaner than stoich (14.7). BTDT.

if you are at 100kpa you're getting into the gas enough that the boost will come soon afterwards so you'll want to taper your AFRs to get ready for that. i don't think it's really possible to "cruise" at 100kpa, that is WOT on an NA car and way more than you'd see under light load.

max power is supposed to be around 13 but people tend to go 12.5-12.8 to be a little conservative. there is no reason to go below 12 unless you are running some kind of alcohol fuel which needs it. going into the 11s or even 10s is a crude anti-knock tactic from Corvairs and 930s when the dinosaurs roamed the earth. if you have to go below 12 on gasoline to avoid knock you have too much spark advance, not "not enough" fuel.

as for timing, is this a 924 turbo engine? agree with justin that you are way conservative in the low-load sections especially and you're sacrificing response and mileage there. different head and bigger bore so a rough comparison, but a 944 2.5 NA is in the 40s for advance at low load and runs in the 24-32 degrees range at WOT (100kpa).

fasteddie313

Yeah.. 924 Trubo engine, set up to run with no intercooler from the factory.. (no wonder they have a bad reliability reputation)
Most common knowledge for them is indeed dinosaur technology to keep them from exploding with their ridiculous non-intercooled intake temps.. Including the timing (but I'm still running the original ignition for now)..

Think I can take a lot of fuel out compared to their OEM tune, but it's scary ya know, though I'm getting a lot more confident in my fuel tuning and system reliability/repeatability..

I'm not on the highway very much, cruising around 85, but pretty sure I'm in and out of a little bit of boost just maintaining that..
Engine probably makes like 60hp NA on the ridiculous 7.5:1 compression ratio and darn near log manifold exhaust..

Scoots pretty good on boost though..
I think it'll take a lot with it being such a great bottom end and head clamping for a lot of boost..
Closed deck iron block with huge bearings, rods, and pins, and pretty good head studding... Known to hold atleast 450HP on EFI with a good tune and modern turbos as long as you don't spin it too fast..

Beat a Vette the other day with a 350SBC... :shrugs:

V2Rocket

thinking about it some more since it's a smaller motor it makes sense it would need more throttle opening/MAP to maintain speed than a bigger engine...like how automakers are going to small turbo engines to replace larger NA engines, pumping losses...

Thom

An AFR of 11.8 (= lambda of 0.8) is always recommended for a boosted 2V 944T engine to keep exhaust temps down, which usually go sky high because the low knock threshold resulting essentially from poor head flow prevents the ignition timing to be advanced enough. I suppose 924 heads suffer from the same design feature, and when Porsche turbocharged the 944 engine after the 924 engine, they apparently found no better thing to do than move the turbo to the other side of the engine and cool it down with coolant so that it wouldn't set the car on fire anymore when careless owners would shut down
the engine without letting it idle for a while to cool down the turbo.
The 924 block however is a closed deck iron unit and can withstand "high" amounts of boost just like its 5 cylinder big brother, but pretty much everything else needs to be upgraded.

In any case the first thing to do would be to add an intercooler, a front mount like on the 924 CGTS (and 944T) rather than the dubious top mount unit used on the 924 CGT.

fasteddie313

I think the crank and rods are good to go, but the pistons are a bit questionable if they run into detonation..

Check on the IC.. (Garage is on the slab now.. Yay!)


From everything I'm hearing, it's sounding like keeping it around 11.5 should be fine..
And that I need to invest in a knock monitoring setup..

Just changed my plugs out to a set of NGK BR9ES with 22 gaps, but they might be a bit too cold and foul.. Old plugs (8's) look great.. No signs of det.. Runs the same..

I've started this tuning starting rich and taking fuel out as I move up more boost, and it looks like I'm not done yet..
I'm about exactly 12.0 on spring only right now.. Feels pretty lame on just the spring though, like 6.5psi..

fasteddie313

[img]blob:https://rennlist.com/26eedbf8-30e8-49ca-a919-7449a0b8f38e[/img]

fasteddie313

Have a bigger AR turbine housing on the way..
Time to start thinking about sizing a compressor..

Im out of turbo at around 21-25 psi depending on ambient temp it seems..

want a 25-30 psi compressor that’ll bolt on to a stock k26 bearing housing on a stock k26/8 turbine wheel/shaft..

Any ideas?

think I need something a little bigger than a 2670 /8 compressor..

bit lower flow and higher compression than a 2.5 though..
so a bit bigger inducer to exducer ratio for higher pressure differential?

probably looking for mid 400s crank HP but I don’t really know..

compressor that’ll flow 450hp at 27.5 psi? Ish?
im really just guessing..
think I’m close?

running a pretty big FMIC.. It seems to work..