Rich + More Ignition, Or Lean + Less Ignition?

[foliage]

So I see mainly jap cars where they tune 10:1 and run loads of ignition, but here in Aus people tend to run more like 12:1 with less ignition timing.

What is the safer way to tune an RB motor? If you have high temps due to a small turbo running at its limits, would the more fuel + more ignition be the better method due to the richer fuel charge providing more cooling to the cylinder?

What is more likely to cause detonation, higher ignition timing? Or higher combustion temps? Is it this simple? Or are there too many other factors to simply it like this, if so what would you say the better (safer) way to tune would be?

Curious what peoples thoughts are.

Cheers

[Matt]

Just as a note they can afford to run more timing because they use 100 octane over there

[PL]

A *very* good question. And one I've grappled with myself. I've also noticed the same thing - Jap tunes tend to run a lot of fuel + a lot of timing.

Unfortunately I don't have a straight answer. I don't think there is one. I've tried tuning both ways and about the only conclusion I've reached is that you gotta give an engine what it wants. I've often found that SR's like to be leaned out - running them richer than 11.5:1 will usually cost you power. Although you're obviously always balancing AFR's with timing.

Other engines can be run crazy rich and still make good power.

I tend to run DE+T jobs (high comp) richer purely because they won't take any timing if you run them lean.

I think one big contributing factor is intercooler/turbo efficiency. If you're doing something to cause high inlet temps then you'll probably finish up having to run more fuel to help cool things down (read: keep detonation away). But if you're not pushing the turbo too hard and you have a decent intercooler (+ free flowing exhaust) then you'll get away with leaner mixtures. I run my mate's SR like this. He's put a lot of effort into optimising the combination of hardware on his engine and I tune it at 12.3:1. It loves this lean AFR and still runs a fair bit of timing - but I wouldn't dare go that lean on other engines that I don't know so well!

On average I'll tune between 11.5 and 12:1 unless I have a good reason to go richer/leaner. Often on track cars I'll try going richer to add a safety margin. I'll tune for say 11.7:1 and then towards the end of the tune I'll bump K constant up 5% and do a quick run. If there's not much difference in power then I'll leave them rich. Did an RB the other day that only lost 2kw by going down to low 11's. That's where I left it.

I read an interesting article on the Nissan Lemans cars once. They were running them crazy lean (with I assume highly optimised IGN timing figures!) - and doing it for 24 hours. A big ask. But you can do stuff like this when you have TOTAL control over everything. Fuel quality/consistency being number one. They'd also have detailed air temp compensation tables - as well as telemetry/logging so they could trim things out during the race if reqd. Not to mention being able to optimise things like combustion chamber design specifically for the tune they wanted to run!

At the other end of the scale are the drifters. You're often dealing with tired engines with suspect components controlling them - you just can't run that close to the edge. Combine this with owners who have little mechanical sympathy and don't know/care about about their engine and you need to add a big safety factor to your tuning.

OK, I'm raving now, so I'd best stop! What was the question again? Oh yeah, fuel vs timing. Give the engine what it wants is the bottom line for me. I err on the side of more fuel if in doubt - lower EGT's can't be bad.

You'll find that everyone has their own idea about what works though. I'll be very interested to hear from some of the guys who actually know stuff.

PL

[foliage]

Interesting reply Pete! It is roland here btw, always been intrigued by things like this.

Be interested to see other peoples view points.

[skylinegtrhr]

At the other end of the scale are the drifters. You're often dealing with tired engines with suspect components controlling them - you just can't run that close to the edge. Combine this with owners who have little mechanical sympathy and don't know/care about about their engine and you need to add a big safety factor to your tuning.

PL

Unfortunately this is 110% true , most of those drifter cars can't be on dyno pull more then one second before they start to overheat so ign mapping is nightmare they usually have those decorative Chinese 100$ Intercoolers kits.

[PL]

Yeah, I guess we've all seen some shockers. I don't mind doing budget blasters (in fact I quite enjoy it) but when somebody turns up with a bag of shite held together with string, then expects miracles it gets a bit much!

That RB25DE+T from the other week was a classic. R30 Skyline drift car built (by owner) on a tight budget. But done right. RB25DE from an R33 (so very cheap!) with DET injectors and some Turbonetics T3 pattern turbo he'd picked up cheap. We put an RB20DET ECU on it and wired VCT on. Simple bleed for boost. Tuned up just nice and made around the 200rwkw mark on 14psi. Good boost response too. Took it to the track over the weekend and had a ball.

Yes, both injectors and AFM were maxxed out. Yes, it was tuned rich. Still took good timing figures though. More than I expected a DE+T job on 14psi would. RB's certainly take more timing than SR's.

I'm waiting for Trent to chime in here with his tuning philosophies. Come on Trent - tear yourself away from that dyno for a minute and share your wisdom!

PL

[skylinegtrhr]

Yeah, I guess we've all seen some shockers. I don't mind doing budget blasters (in fact I quite enjoy it) but when somebody turns up with a bag of shite held together with string, then expects miracles it gets a bit much!

PL

Yes You can do things right or wrong way regardless of budget , we have customer with N15 SR20DET turbo conversion also done on tight budget with S14 AFM and injectors and my old S14 engine internals and second hand MAN truck customize intercooler (Garrett made core) and car is killing EDM EVO X in third gear .

[supersayianjim]

hey, whats wrong with with a $100 ebay intercooler???

[PL]

hey, whats wrong with with a $100 ebay intercooler???

Sometimes nothing. Sometimes everything!

I think the bottom line is if you're just upgrading a stock/mildly tuned street car then a $100 eBay 'cooler is fine. But if you're chasing the numbers then you want something that'll perform.

My brother put one on his R34 and I struggled to get 200rwkw out of it (std turbo) after 2 hours of tuning. But he wasn't bothered. It was his family car and at 5000 rpm it was still making 50rwkw more than stock.

Matt's R34 had an expensive name-brand intercooler (ARC I think...) and it made 220rwkw on the same dyno before we even started tuning.

PL

[supersayianjim]

so it's in the intercooler you say?? hmm

[PL]

No, that's just part of it....

If you have a restriction anywhere - turbo, plumbing, intercooler, exhaust then the power nazi will come to visit. "No power for you!".

PL

[supersayianjim]

i just thought all intercoolers were the same quality wise. only difference was

-bar and plate
-tube and fin

http://cgi.ebay.com/ebaymotors/Intercoo ... 3369b34f9d

this is the exact unit i have give or take an inch or 2.

[PL]

No, there are big differences in efficiency/flow. And the only way to know is to either try them or get feedback from other people who have used the exact one you're looking at.

It won't matter so much if you're not chasing big HP. eBay cores are fine for most cars.

PL

[Fusion Ed]

Made 600+bhp on an ebay core without any problems, the larger ones seem fairly generic, however I don't like the end tanks, they don't encourage efficient use of the whole core.

Agree with the above. One point about running lean on the Lemans 24hr cars is fuel stops. Running leaner can save you a huge amount of fuel over the duration of a race.

[skylinegtrhr]

I read an interesting article on the Nissan Lemans cars once. They were running them crazy lean (with I assume highly optimised IGN timing figures!) - and doing it for 24 hours. A big ask. But you can do stuff like this when you have TOTAL control over everything. Fuel quality/consistency being number one. They'd also have detailed air temp compensation tables - as well as telemetry/logging so they could trim things out during the race if reqd. Not to mention being able to optimise things like combustion chamber design specifically for the tune they wanted to run!
PL

I ask a guy which now map this car for historic race series and this is what he said:

There is some truth in it, in that the driver had quiet a lot of control over the boost and in the low boost modes the mixtures could be taken out to around the 0.98lambda area without any piston damage, but make no mistake when running in the higher boost modes they absolutely hosed fuel in, crica lambda 0.78-0.80, the cost of a DNF was just too expensive to risk.

Remember these things weren't running with closed loop anything, these early Bosch systems were very simple beast's, in order to effect a tuning tweak a new chip needed to be burnt in the pits. Now days we run this one on a Pectel T6M.

The real battle for fuel economy was in the wind tunnel, I'm told that this car in high downforce configuration was physically measured generating 8069 lbs. of downforce @ 200 mph, with just 1588 lbs. of drag. That's a lift/drag ratio of 5.08:1, and that's what really dictates how much fuel you have to burn to get the race done.

also about special fuel and MAP pressure:

Well if we talk about this specific car then for historic racing these days we tend to peg the MAP at 2750mbar absolute as we are forced to run on Sunoco TC control fuel which compared to the fuel this one ran in period is very soft indeed. In period the maximum MAP for most race tracks in the dry was around 3100mbarA with a time limited driver activated 3700mbar burst for overtaking.

In period the fuel was a very special blend indeed, highly toxic and highly controversial, in 1992 Nissan Performance Technology were hauled over the coals big time along with TRD and TWR for failing an unexpected IMSA fuel test in a rather spectacular way.

I've heard plenty of rumours from people who would know that in qualifying for important races some teams would lock the waste gates permanently closed for their strongest driver who would then do a very gentle out lap and then attempt to absolutely banzai a lap with uncontrolled boost just hoping that it lasted until he got back round to the start/finish line. I'm told that when the order to do this was given by the management a team member was simultaneously sent to the truck to fetch a fresh engine from the rack