sr20det tuning tips

Hi Guys,

I've been playing around with my brothers s15 lately. He's made the switch from maf based Apexi Power FC to a Haltech elite 1500. Overall this thing has been extremely easy to tune thanks to everything learned through the courses, I've been lucky to have a dyno tuned timing map to copy over from the pfc. We wrote down the timing map, used map trace and a boost gauge and recorded several runs at different points to work out the load points for speed density tuning, not the easiest process but I think it's close and I've erred on the conservative side a touch.

It would be good to get some feedback on the map if possible, i've done tons of searching but struggled to find maps for comparison. The engine is a built black top sr20det with rods, pistons, BC stage 3 272 cams, gt2876r turbo, ID1000 injectors etc.

On the fuel side one thing I'm struggling with is trying to understand why the original dyno sheet from the pfc tune shows torque dropping off after 6000rpm while the VE map is showing peak numbers between 6-7k. I'm wondering if this thing could actually take a lot more timing up top?

I've attatched the ignition map, fuel map, dyno sheet advertised for the cams and the actual dyno sheet.

Appreciate any input!

Edit: Forgot to mention have only tuned up to 1 bar on the Haltech. Dyno sheet shows high and low boost curves at 14.5 psi and 18/19 psi

VE rising with falling torque is what usually happens as a result of fuel pressure regulator flow/slope or running out of pump.

I agree with Slides, it seems like inadequate fuel supply. If the pump has't been upgraded then I would address that. You can check the logs to see if fuel pressure is dropping. If the pump has been upgraded and has adequate flow then make sure the wiring is up to par. I have run in to this issue on several S-chassis. The factory wiring is good for much more than the stock pump.

Also what fuel are you running? All of the Sr20's I've tuned have taken quite a bit more ignition timing than that. Do you have some sort of knock detection?

Good point about fuel pressure, no sensor yet but has been purchased and awaiting install. She's running on 98RON pump fuel at the moment, moving to flex fuel was the main reason for switching to the haltech but fuel system needs another upgrade first. Pump is currently a walbro 255 still with the factory wiring I believe.

Knock control is active, havn't done any testing to make sure it's working ok yet though.

On surface value it looks like the VE curve matches the advertised torque curve of the cams a little better so it's got me curious there might be a decent amount of power locked up in timing, assuming the values are legit.

Appreciate the input!

Yet another example of why VE is a BS term to use, one that can introduce problems when used like this. VE has a specific meaning, it should be ONLY used for that.

Mass Efficiency, is a more acceptable term, IMO.

Anyway, rant over - as has been said, until, and unless, you can check fuel pressure and ensure there is enough flow capacity to maintain that pressure, you're only going to be making 'best guess' diagnosis.

With the uprated camshafts, you're moving the (true) peak volumetric efficiency (actual to theoretical cylinder filling) further up the rpm range, which should both increase torque and the fuelling required for the greater mass of air in the cylinder.

It would seem you do need to increase the fuelling, as expected, but the torque isn't rising as expected. If the lambda/AFR is about as expected - which rather removed the fuel supply limitations, as such, from the current equation - then the primary suspect is the ignition timing is incorrect as, while there's a denser charge in the cylinder it isn't being ignited at the correct time for the most efficient burn. As the engine is still in one piece, I would expect it is retarded, but to be safe I'd suggest backing it off 10 degrees, or so, anyway and advancing from there - while watching EGTs. It may be knock limited, so you may reach that point first.

If there's still a problem, could you have made a change in the exhaust, so while it's getting air and fuel, it isn't able to get ride of the increased gas flow as readily?

I think I get what your saying regarding the VE and apologise if I'm using the wrong terminology, my understanding was that increasing pulsewidths at higher rpm was inline with increased air consumption assuming mixtures are on target and I was comparing it to my car where fuel tapers off at high rpm but the actual hp curve flatens out.

The main issue I have with the setup, not to rag on my brothers pride and joy, but it's how small the power band seems to be. Guys seem to be making at least the same power if not more with an extra 1000 rpm power band on the 'stage 2' cams - around the 262 mark, which doesn't totally make sense to me. I don't put too much faith in dyno figures though, car has run 12.4 @ 109.xx mph on street tyres.

Very well could be due to exhaust restriction, it has a decent setup but it's still utilising the oem manifold with 3" turbo back and a 200 cell cat.

Don't worry about my rant on the incorrect use of VE - just think of their use of it as relative air consumption. If there is a 20% increase in air mass, but they call it a 20% increase in VE, it amounts to the same increase in fuel demand.

If I read it correctly, fuelling is greatest in the 6-7k range, which makes sense, but the changes seem less than I would expect - but I may be mis-interpreting it. Another thing that will compromise the engine's breathing is camshaft timing, have you double checked that?

The OEM manifold may be contributing, some are quite efficient, some are definitely going to choke the engine - can't say what your one will do. [edit] Seems to be rather split views on that - some say the OEM is capable of up to 500hp, others say it's restrictive from around 300hp and a proper tubular one is needed. I did note that the higher power chart (Seans?) you posted specifically mentioned a tubular exhaust?

Havn't properly checked the cam timing, the engine was 'professionally' built and the vernier markings were all just set to 0 which I've only recently discovered doesn't necessarily mean they're timed. Camshafts are kind of a new thing for me lol, I got the course about dialing in cams and will check it out at some point.

We randomly tried playing with the cam timing year's ago to try and open up the power band but didn't feel anything noticeable and realised it might not be the best idea without checking clearances etc.

The example dyno sheet from Sean/Carter racing is lifted directly off the Brian Crower website as advertisement for the cams. I've tried to find other comparisons but google has turned to crap.

It'd be cool to tap the manifold and see whats actually going on with back pressure.

Bit of a dead thread, but I also had the same issue with my S15 with my cam timing set at 0 on the Vernier gears (Both @ the intake and exhaust gears) @Ders88 and had absolutely no power or boost in the mid-range. Speaking with Kelford, all of their NVCS cams are meant to be used with the VCT gear to give you the best of both worlds. (Workshop who installed the cams has failed me....)

Experimenting with cam timing on the intake end by advancing the timing by 8 degrees result in a massive gain in midrange efficiency. (Dw I know it was safe as the VCT advances the intake cam timing by 21 degrees)

I would imagine that this would yield a similar result with the BC cams if the timing has been dialed in correctly.

For reference, Alberto Big Boosts Cursed Adam LZ SR20 build had around 8 degrees of timing advance on the intake cam and 3ish on the exhaust with BC 264.

I will be slamming the VCT cam gear back in on the intake when I get some time....

Hope this helps anyone in the future.