my observance is that i cannot verify A/F with my WB02 when at 1400 rpms cruising. the A/F is errattic. i tried adding more fuel in those cells to no avail. i am thinking car cannot tolerate a load at low rpm's 1400-1500. 21-25 ded spark adv from the best of my recollection in that rpm/map cell. the cam manufacturer rates cam 1800-5800 for efi. at 1600 rpms issue goes away and can pull the gear. it is clear that cam wont allow a 1400 4th(of 5)gear pull.

what is happening as far as cylinder filling at that point in time?

i understand there is some self EGR'ing occurring and exhaust gas is bleeding into the cylinder diluting the mix? am i correct on that? is vacuum diminishing at same time not allowing intake charge to come streaming in. like dead on arrival. if i had a vac gauge in intake would i see vac drop to like zero at 1400 vs good vac at 1600 rpms? i guess i could log map as well and i believe it did see that. i typically do not log that kind of event. is this what is happening? 3.07 gears are no help. some day 3.55 coming.

ps this cam has much diff running characteristics than old

 

Take a look at various gains and pay attention to the proportional gain stuff.

Rbob gave me a hand with some stuff and just for an example on the $8D code the f-body version has a whole lot wider swing point than any y-body .(havent tested further as I'm lakcing a running $8D car at home)

Might be something u want to look at.

Rauschers paper on proportional gains and TBI code is linked in the tuning guide up top under the sticky

later
Jeremy

 

You just might be *below the cam*.
Using a higher operating range cam, means you're going to sacrifice at the lower range.

If making fueling changes, makes no difference, try moving the timing.

What is the narrow band doing at this point?.

 

I run a very similar cam in my 305 to the one in your sig, the old L82 stick. It pulls well down to 1,200 RPM in OD (5,300 lbs & 3.73 gears). I can mash the gas lightly and it just smoothly pulls away. My typical 20% TPS acceleration will knock the vacuum down to below 5 in/hg until the tach hits about 2,000 or so. It does pull better when you keep the tach above 2,000 though.

It helped alot when I changed my % TPS for WOT table to lower numbers at low RPMS. A cam this large likes a slightly richer air fuel mixture at low RPMs. Under about 1,500 RPM I could run NO MORE than about 20% TPS without getting into the same buck/surge that you have. I also run an open loop idle in mine.

Try pulling the timing back to about 15* at that MAP and load. I run 6* of base timing and climb in both directions as MAP decreases and RPM increases.

 

Grump: what is NB doing? i am open loop now. when i was in CL A/F would swing dramatically form say 15/1 to 20/1 and unstable at idle and same when i depress pedal and load engine in high gear. OL stable today at 15/1. when i try to load engine in high gear it show some AE event then goes lean. i generally just drop down a gear to allow the car to accellerate. when over 1500 rpms the WB logs appear normal as far as A/F and AE event. again OL WB logs look much better on generall sane driving event.


i guess i am confirming the cam wont allow a pull down that low. no big deal just adjust driving style. gears may be in future(2006).

Fast: i ran 15 deg as well as 21 deg and i believe car ran better with 21. 15 certainly was not good. next season i will play with spark a bit for improving drivability. where i live it is quite hilly and makes for interesting tuning. TPS/PE is aboput 30% last i checked. car in barn tomorrow so need to tune the sleds(hurley or bust) now. hurley silver street is beckoning my presence.

 

edited: Because I can't delete my post

 

JP: thanks for the help. will reapproach tuning after long winter is over.

 

What I was getting to, was if your WB is reading ~15:1, and the NB is at 200mv, or 600mv, then you might have *missed the tune*. Timing can have a tremendous influence on AFRs, especially at low speeds.

One other thing for the batch fire mode guys to think about is that the injector fires at the DRP. Change the cam timing, and the DRP to cam event synch goes to dodo.

 

The DRP with repect to injector squirt caught my interest. I installed my 216 I/E degree @ .050 duration, .454" I/E lift @ .050, 110 degree seperation cam straight up because I figured the inject time might make a difference.

How does fueling overlap change under boost? I installed the cam with the specs above before going with boost. Everyone says that the 110 degrees and single pattern is bad in boost applications. I wonder how much horsepower I would gain with a "boost" camshaft compared to the one that I have already.
I sure wish cams where easier to change.

J

 

The smaller the cam, the more overlap it can take in a turbo app.
One formula I found was @.050 (Int dur + exh dur)/4 - LSA.
And shoot for between -10 and + 2 or so. Your at -2, and I've seen guys make 850rwhp with that number on an HR.
The tiny amount of info I was able to get out of Dutweiler was to use a 112 LSA on a 216-218 cam.
Best I can tell is don't get too hung up on cam specs and cam it for whatever rpm you want. HP will follow boost.
Oh, and don't use chambered mufflers.

edit- I said that a little stupid. The smaller the cam, the tighter the LSA can be and still not hurt power.
At some point the combo will have a small enough turbine housing the backpressure will become even more of an issue and a tight lsa could start to hurt you.

 

Grump: that may have gone over my head. are you refering to the mv the 02 sensor is switching over to command stoich in CL? in my tunercat program it is set at 14.5/1. TC said dont expect it to be changed much from what the factory designed the 02 sensor to do. are you suggestintg if i want idle A/F at 14.00/1 i need to change the switch points in constants(TC)? again i am OL and it was suggested by some i should attempt to run CL and enjoy the benefits. been back and forth on that and the WB A/F i see in OL is rock solid rather that all over the place per my logs. same with idle. this AM at 73 mph was reading 16/1 and never budged. 55 mph was like 15/1 and solid. came off xway and read 14.0/1 and idle was smooth 1000 and not asynch. 900 i believe goes asynch. air temps were like 50 F and low humidity. today was one of the best days in ran ever! as a point of interest i have my CL blms running at 123-124 at above air temp but OL. driving around town i see A/F on WB from 13.00/1 to about 15.00/1. running a bit rich may "crutch" my AE and maybe that is a good thing. AE has never been better but still that bog when i load engine and accellerate were slowly. thinking that is spark and will approach less of SA in those areas where this happens. if i dont drive like a grandma AE seems very good. in barn 601 pm tonigh so last day to drive. hurley, wi beckons. silver street awaits.

CC efi cam. installed straight up

 

That is some great info. Thanks. Sorry for getting off topic here. I think the cam worked great before the boost was added and that is why I stuck with it (and I didn't want to buy a new one cause this was was new sitting in the box.). In general, wouldn't overlap be OK under boost if the AFR is a little on the rich side (11.5:1 AFR). The exhaust pressure would be holding the "fresh" intake charge from the exhaust sucking it out. I have heard that usually the exhaust pressure is fairly high in boosted apps with bad manifolds/headers.

 

See my previous for edit

An excellent turbo exh will still see around 1.5x boost at the exh valve I've read. And a good number to shoot for is 2x for a street app. The low rpm stuff with quick 1800-2k spool will usually be higher still. Not so simple physics. The exh can't be less than the intake and be making boost. So in reality, the chamber won't reach the MAP till around 7-10 deg ATDC.
I did a calc once but can't remember the exact number. Thinking about that a while will give you a headache.

Ronny, lowering Stoich will cause other problems.
I think Bruce meant to lower the window settings.
See Rbob fueling paper.
Or here's an 8D equivalent thread. https://www.thirdgen.org/techbb2/sho...hreadid=311190
What it does is lower the avg afr because the sensor will spend more time below 450mv. I think there's a discussion in the 8D section of the stickies.

 

That got me thinking as well.
Not sure on how much is there but I imagine you could get to the point of still firing the injector with the intake open during some overlap.

What would be your best guess as to # of degrees the inject (max PW +adders) must finish before the valve begins to open?

I'm contemplating the exact advance/retard for my install and would like to consider the whole picture of overlap and events before I decide. Hope this doesn't go too far off topic.

 

The DRP can be moved too.
I didn't think you were running a big enough cam to have to worry much about it.

 

Only by moving the distributor.

I dunno, I got one of em big 206/206 @ .050, and I can make quite a difference by changing the injector timing (148 SEFI).

 

Unless you're running sequential, SOME cylinder will have SOME injection on an open valve with batch fire.

A hefty cam needs the timing due to slower burn when down low with lots of trapped exhaust, low dynamic comression, etc.. How much timing is a matter of...

 

well this is the start of a good discussion!

unfortunately i had to put car in hibernation so wont be able to experiment with my timing tables till next year. last nigh i put car under load 1400 rpms with high gear and it wasnt very pretty. A/F was bouncing around 20/1 and higher with bucking and surging. i believe in those cells were 21 deg A. again once at 1500 better and 1600 rpms is clearded out nicely and went to 16/1 on WB. again my blms are around 124 in those cells when CL. ran OL last night.

other than that car never ran better(OL) lately.

hurley or bust. silver street beckons! vette in barn and Poo sitting in its place. race on!

 

I am installing a 224/230 @112 LSA roller and was contemplating running it 2-4 degrees advanced. So my interest is peaked on this one.

 

would say that advanced might not be bad. gonna need more spark advance on the bottom end though.

 

Obviously you haven't tried to run an OLD GEN 1 SBC with that much cam. Keep in mind, mine is an old hydraulic cam but still features 224/224* @ .050, 291/288 advertised, 115* lobe center and will idle at 6* timing advance when the EST connector is disconnected.

I am with Jon, lots of us are still tuning TBIs and doing darn well at it.

 

I edited this post.

Has several interesting thoughts in it.

Lets keep it clean and continue without bickering, you know who you are.

later
Jeremy

 

Again, THIS WAS A NICE AND INFORMATIVE POST


JON, LET IT GO

SEAN, LET IT GO

BRUCE, LET IT GO

REDNG, LET IT GO

NOW