How lean is too lean?

[bmgjet]

Had a search though the forum and no one mentions what AFR city turbos like or if the CVCC plays any effect in it.

Off boost it reads as 13.5-14AFR
On boost 1-8psi 11.8-12.2AFR
On boost 9-13psi 11.1-11.5
On boost 14-15psi 11.8-12
On boost 16-17psi 12.2-12.5

Is that getting to lean???

[James]

Cool to see some hard numbers on the AFRs. Be nice to get a wideband on there so we could get some exact measurements.

Those numbers look pretty good to me. 12.5:1 is probably getting a little on the lean side, 12:1 is best for power isn't it? And you usually want to be a bit richer than that on a turbo for charge cooling.

Looks like Honda sized the injectors perfectly to max out at 15psi!

Get some slightly bigger injectors in there and pull the off-boost fuel out with your adjuster, and put some extra fuel in up top.

CVCC was mean to allow leaner main charge, because of a richer secondary charge . I think it probably evened out to about normal overall ratios, but it means the spark plug is kept nice and cool (big problem in turbos), and I bet it really helps stop detonation.

[bmgjet]

That is with my wideband.
Going to get a rising rate fuel pressure reg which would size the injectors up a bit better since at 18psi they would be flowing the same as 225cc then at 20psi just about 240cc like stock honda ones.

Will run a bit richer down low but wont really be a problem till like 8psi but then it will be sweet to remove it with this field hyper-r iv been playing with, also have fuel cut defender built into it.

Would love to see what AFR completely stock T2 would be running im guessing its going to be a bit leaner then you normally have on turbo cars. 11.2-11.8

[Charles]

I had prelude injectors in an er engine at one stage. With a boost cut lifter and @ 22 psi it made 85 kw at the wheels. It was way too rich at 10:1 though. I took the injectors out and returned the stockies. They can run a bit leaner than most engines and make more power as they get leaner. I personnally would target 12.8 and pay attention to timing.

[bmgjet]

85kw is extremely low.
Thats what you should be making at 13-14psi lol.
I bet it was a dog to drive off boost if those are the 240cc prelude injectors.

Iv got my timing set to 22BTDC since im running 98 I thought another 2 degrees would be alright.

[Charles]

Don't quite agree with you. 85kw (114hp) at the wheels on 13psi is not that easy with a stock motor. That equates to roughly 148hp at the fly (more than the little mugen cars made with 22psi).

Depends on the dyno and operator there is no real point quoting one dyno off against another. Rather look at the before and after numbers on the same dyno for % improvement.

Key thing here is that I was trying to give an indication of how important a tune is. Responding on my phone probably made it a bit ambiguous.

Rich mixtures really affect power. Stocky makes about 50-60kw at the wheels, went to 85kw at the wheels @ 22psi but 10:1 and made just over 104kw at the wheels @ 26psi at 11:1. It was enough to light up the 215s in third gear when it came on boost (stock (read tall) gear ratios). These engines make a lot of torque but not very good hp numbers given their intrinsic design (small valves, small bore, long stroke, small turbo). However replacing the stock injectors and dropping the boost to around 20-22psi should see the similar numbers at 12-13:1.

Bear in mind this engine had veolia forged pistons, head studs, headwork, cam, large intercooler, vafc, garret turbo, dump, exhaust/intake etc etc.

These were the early prelude B20 injectors, from memory they flow 220cc/min from a bench test (could have been 240 (it was a long time ago)). I got 190cc min from the stock injectors on the same bench test.

I have one of these er motors in my civic at the moment. To be frank it is not my favourite motor but you need to play to it's strengths for a quick street car. Small efficient turbo, high boost, good exhaust. The stock turbo is actually a very good match for the motor. WAY better than a Garret T2 or T25. If you are upgrading a GT 17, VNT GT15 or GT17 are the ones to look at. They flow ideal numbers for the sort of hp you are looking for and the results on mini engines speak for themselves. An essential for high boost longevity is head studs. O ringing or w ringing the block really doesnt work in my experience.

It looks to me like you are making pretty good power and I agree a rising rate FPR is probably the best thing for you. I reckon you'd be pretty spot on at about 12.8 at 19-20psi as long as your fuel pump and lines are up to it.

[bmgjet]

I have a VL rb30 pump in it so it should be sweet. But still I like my AFR to be spot on since I work part time as a tuner so it would look bad if I cant even tune my own car lol.

ARP Studs/Bolts are what's next on my list. Done a lot of reading here but there seems to be some conflicting info so Im just going to take my own measurements once I tear the engine down (when the head gasket lets go which looks a long way off since compression and leak down tests are perfect 9% in the leak down and 138.139.139.138 on the compression test and there are no bubbles in the water.)

Mine made 78WKW on a rolling road on 14psi with a smoky turbo (has large front mount, 2inch intercooler piping had some ugly bends tho and 2.5inch straight pipe exhaust)
Was expecting it to make 100WKW on 20psi but I guess I should lower my expectations.
I know that dyno reads a little low from other cars iv turned there that have then gone to dobsons and made another 3-4kw with out changing anything.

Since then iv gotten a better turbo (T1 core with hyper-flowed T2 bits) and improved the inter-cooler piping (mandrel bent bends) and ported the TB slightly with a larger butterfly (would like to replace it all together but dont have the tools to do it)

Iv taken it to 20psi a few times and it was in the 13's AFR which is best for NA but really heats up turbos and would kill it afer a few seconds what so would much rather get it into the mid 11's so it lasts.

[James]

The stock turbo will be rolling off the efficiency charts after 15psi and probably quite quickly up around 20psi so you won't get the power you would expect from that pressure, because the air will be getting pretty hot, and the turbine will be really restricting the exhaust.

[bmgjet]

My hyperflowed turbo should raise the efficiency a little bit but I guess it would still be pumping out quite a bit of heat.

What turbo would be recommended for higher boost?

Also peak power is only made at 5100rpm so there must still be quite a bit of restriction in the intake or exhaust. Or its those dam small valves.

I just cant get use to these engines, Completely the opposite to all other turbo hondas iv worked with where HP was easy to get up but torque always below what was expected. But with these or at least mine torque goes up lots but only has very little effect on the HP. Im guessing thats because HP is a formula of torque * rpm divided but 5252 and we only have max power between 4800-5200 instead of being in the 7000/8000rpm range.