mos90

hello everyone.. im in the process of tuning my 91 l98 corvette and heard you guys know your ****.

here is my deal.

my setup..

91 l98 350 ci.
miniram
dart pro1 200 cc heads. flow 270 at .550
tpis zz-x cam 241/241@.050 lift .598/.598
11/1 comp ratio
tpis headers
6 speed with 3.33 gears.
msd ignition

tpis did a stage 6 chip for me and have no luck getting it to run well in closed loop. it was backfiring through the intake and very sluggish off idle. the blm's were at 108 at idle and 112 at cruise.
i didnt even get to do any wideband wot runs at this point.

so initially my idle was at 850 and i was only pulling 7 in of vacuum. tpis said to bump the idle up to 1100 to pull 12 in. and that worked well. i did this in the chip setting using tunerpro. so doing that i put the vacuum guage back on and it was holding steady.

i turned the tps sensor voltage up to .62

base timing is set to 10* now. was at 6* and didnt run as well.

so the next thing i needed to is start fooling with the ve tables. my initial goal was to work on low rpms. so now figuring my idle map is around 65 kpa i started pulling fuel from the lower ve table to aceive a 128 blm at idle and part thottle. no matter what i did the problem would not go away..

so the next thing i did was make a few phone calls to good tuners. most of them said that with a cam that size in a 350 ci motor and my computer i would need to run in open loop all the time. and fine tune my ve tables with a wideband, this is not a problem for me, i have an innovate..

so with this new info i tried it and i disable closed loop and it seemed to elimiate 99% of of the backfiring and 90% of my thottle lag. believe me it still is not tuned 100% right yet but is running much better now..

the main reason for this post is to see if you guy think this is the correct was to tune my car. considering nothing else has worked so far.

would a tuning issue cause a backfire though the intake, or am i looking at another problem?

let me tell you what ive checked so far.

new plugs,cap,rotor, coil.
cant find any vacuum leaks.
timing was checked 3 times with esd disconnected.
the only thing not rechecked yet is valve adjustment.

any input would be greatly appeciated..

let me know what i may have left out..

thanks,
steve

funstick

yes on running open loop.
yes thats a big cam in a 350
yes those are big heads for a 350 ( 7500rpm )
yes its going to be fun
yes TPIS stole your money good luck getting it back
yes youve got to spend some time tunning.

Welcome to the club. put up your email addy ive got some timming curves that should get you going in the right direction.

loose the miniram intake and get a stealth ram. the TQ is so much smoother.

mos90

email is mos90@twcny.rr.com

it was my choice to pick the cam. i took out the zz409. should have left it alone.

the least tpis couldve done was tell me the tuning issues with this cam upfront.. i had one there chip in before and it worked well so they only got me for $100.00.. no biggie.

as far as the backifiring.. could that be tuning or another issue?

funstick

backfires are most likely tunning issues or could be vacum leak related. TPIS chips are almost all stock fueling with some small mods to timing. there a joke. ill get together a whole bunch of bin's ive done on miniram engines and email them to you tommorow. if i dont email me a reminder ive got alot going on lately so im pretty busy and i tend to forget to do things.

mos90

thanks, any thing will help at this point.

with my base timing at 10 or 11* and the total timing at 29* in the chip, i feel that is to much timing at wot.. around 40* . i usually dont like to go over 36* total.

it gonna be hard to get accuate a/f readings at idle with this cam.
is there any tricks? im mounting my wide band o2 in the pass side header..

i wouldve chosen the steath ram but to fit under the hood of my car i need a custom plenum.

92Z

iTrader: (1)

Funstick,

Could you e-mail me those Miniram bin's also? (kbond3@kc.rr.com)

My set-up runs pretty good with my own DIY-PROM, just wanted to compare to some others.

My set-up:

383
Miniram
AFR 195's
Comp Extreme ( 236/242 .520 .540 110 lsa)
11:1
1 3/4 headers
700r4 2600 stall
3.73 gear

Thanks

mos90

did you get it to run ok in closed loop?

mine just wont..

92Z

iTrader: (1)

mos90,


Yeah, it runs pretty good in closed loop, it runs rich at idle because of all of the overlap. Although this cam is large i also have 33 more cubic inches. I used this cam hoping to bleed off some cylinder pressue down low to deal with the 92 octane gas here in Kansas. I also had to play with the Acceleration Enrichment MAP and TPS tables to get rid of and off-idle stumble. Also, the idle BLM's will be 108 unless you change the Force BLM Idle Cell CCP % D.C. Threshold :

https://www.thirdgen.org/techbb2/sho...threadid=90791


Also VEMaster is very useful.

Hope this helps

funstick

no iv had to run most cams over 480 lift 230@50 with lda tighter then 110 in open loop. espcially with long tube headers and no cats with really free flowing exhuast. your motor will most likely never run in open loop without somebody add a table tot he ecm to dictate o2 voltage vs rpm. for the toggle value. i havent gotten out to the shop for the last few days so i havent been able to get to the tune library ive got. im heading out there in about an hr. ill grab a floppy and save a few bin for you.

TRAXION

My car ran beautifully in CLOSED loop with a mid 230 duration cam .... lift close to 600 ... and an LSA lower than 110. Piece of cake actually. MiniRam, long tubes, etc.

Tim

funstick

well i find that completely amazing. as every car ive seen with cam's bigger then that just throw to much oxygen in the exhuast to get a good reliable o2 reading. and then with the mixture distrobution issue with the miniram its gets even worse. now with a stealth rams ive been able to run a closed loop ide but ive had to play with all the o2 sensor pid params to get it there. so care to enlighten us on how you performed this feat ?

i typed something else but i felt out of charecter typing it. care to list the full combo ?

Grim Reaper

Ditto. I've successfully tuned a solid roller with 248/256 @ .050 & 110 LSA to run very nicely in closed loop. Miniram also btw.

zz17iroc

iTrader: (4)

I agree. No problem tuning with my MiniRam. I installed GM's 847 cam 234/242 @ 112 lsa in a 350 with no problem running in closed loop.

funstick

put a 5 gas in the pipe and come back with the same attiude.

i figure maybe i should elaborate on this a bit more. when your tunning on cams with some foritude youll find that even the narow band 02 and the wideband also start telling some lies. youll see and engine that indicates a 14.7:1 a/f etc etc etc but its actual gonna be closer to 11:1 . im not saying its actually gonna be 11:1 but it often drift extremly rich just to get it to a reading close to stioch. so if you have a way to change the 02 tables to work at a swing voltage of 150millivollts with a low limit of 0 and a high limit of 300 and these are examples of just idle and low throttle then you running around running to rich. this is where doing idle plug cuts become extremly useful.so yes running a closed loop idle might idle well its often far to rich in the chamber just wasting fuel and youd never know. that where a 5gas become useful. you can go ahead and tune for the lowest hc at idle without becoming unstable and thats not including the other gas data,. but for most cars running cams bigge then i mentioned it also become a game of cylinder heads. i should have added 190cc pluis runners to that.

anesthes

iTrader: (12)

What was the centerline (intake) and overlap ?

So far I've driven my car around the lot enough to say "holy ****, this steering absolutely sucks!", but yeah. It moved a little in closed loop. Bunch of lean pops.

cam specs: 230/245 @.050, 533/540 lift, 114lsa, 112 centerline (9.5 overlap)

mos90

here is the specs on my cam. ive got it running ok, but it is still rich at idle and part thottle..

closed loop is a big no so far fo me.. and my afr readings on my wideband at idle may not be to close either. 13/1

lobe sep. 112
valve overlap. 16.6*
intake valve open 12.4*btdc
intake centerline 108
intake duration 240.6
intake valve close 48.2*abdc
exhaust valve open 56.3*bbcd
exhaust centerline 116
exhaust valve close 4.3*atdc
exhaust duration 240.6

89gta383

iTrader: (5)

Maybe we need to start a big cam tuning club.

I'm having problems with my 242-254 .555-.585 110lsa cam in my 383, miniram car. Always runs rich at idle and my vacuum is like 7 inches at idle at 1000 rpm. Initial timing from 6* to 16* doesn't help any. I need some timing tables to reference with mine. Brake pedal is still hard even with a vacuum canister. Still don't have a wideband, so I guess I'm in the dark without one.

At this point I'm about to give up and change cams to something smaller with a 112-114 lsa.

Any chance I can also get those bins emailed to me so I can take a look at trying something new if I see something?

I'm running 6E, but I think the principles would apply to both maf and sd cars.

micdoctr@yahoo.com

Grim Reaper

The cam is Comp Cams XR286R.

Go here --> http://www.compcams.com/Technical/Se...umber=12-772-8

for the cam specs.

89gta383

iTrader: (5)

Glenn, any secrets you can share on tuning that cam?

batchfire

my car runs very good close to 128 everywhere with a 240 duration cam and a 7730 long tube headers ect...

Grim Reaper

Secrets? Time, patience, and attention to detail.

Some people would like others to think there is a "great mystery" to all this stuff, but there is not. And, despite what others would have you believe, you DON'T need access to a ton of specialized equipment to properly tune an engine.

I have been tuning engines since the 60s when I was a kid. I was always able to get the "most" out of my own engine and I had VERY LITTLE in the way of tuning aids. (A good set of ears and pulling the plugs were my primary tuning aids).

Also, fuel is NOT as important and spark. Only if your fuel is GROSSLY OUT does it greatly affect power. I have found that 12.8-13.0 on a naturally aspirated engine tend to yields the most power on a NA engine. But even if you are a little richer (or a little leaner), that the effects on power are not that great.

Spark is another story. Just a couple of degrees can make a significant difference (compared to fuel).

FYI, you would be amazed how "out of tune" most cars are right from the factory (if that gives you any hint).

anesthes

iTrader: (12)

Is trying to cruise under the cam's powerband just stupid?

In overdrive, if I cruise around 60mph, which is around 1900-2000rpm, it will go ok for a few seconds, surge, backfire, rattle the torque converter, etc.

I've tried pulling fuel, adding advance. Not sure where to go.

If i'm above say 2400 or so, no matter how little the TPS the car is fine.
But holding it in drive on the highway doesn't do wonders for fuel economy, AND it keeps the water temp up.

Engine is a 10:1 358, trickflow alum heads, and a cc-306 cam.

Here is the cam specs:

http://www.compcams.com/Technical/Se...umber=08-306-8

-- Joe

junkcltr

iTrader: (1)

You have too much cam (upper rpm) for what you are trying to do. You need to be in the cam range to have it run properly. You have probably seen running out of cam at high RPM with smaller cams, now you have it with too much cam at low RPM. Ever jun a two-stroke below the pipe? You have the same thing here.

It seems you are happy with the HP, but don't like the low RPM characteristics & fuel mileage. I had the same problem a few years ago. Boost is the best answer to the problem. You could run a small cam with good low RPM characteristics, good fuel MPG, good emissions, and the same or more HP as you have now. The other solution is to rev it up more and deal with the MPG.

You probably won't like hearing this, but I would remove the cam and install something with less than 220* @ .050. Then either supercharge or turbocharge it. You could sell the heads to recover some of the SC/TC cost. You really don't need them with SC/TC for the HP you have now. With fuel prices they way there are, the SC/TC will pay for itself...and you will make more HP than you have now.

anesthes

iTrader: (12)

I used to run a supercharged setup. Was nice but has quirks too. I ran the '749 for a lot of years and it worked fairly well, car went quick. But I wanted to try this NA.

Tim ran about as much cam as me with a miniram, and a 700R4. I'm curious how his setup ran in the low rpm areas.

-- Joe

87_TA

It really depend alot on total overlap - not just at .050! Some people still don't understand that.. Thats why it helps to run a solid roller due to less total overlap needed to obtain the same at .050..
My had an old hyd 230/230 @ 110 that was impossible to run closed loop, no matter how much timing you run, or little it would creat to much exhaust heat due to fuel burning in headers - the only way I could stop it was lock blm's or disable closed loop - just to much oxygen in exhaust stream..

I then switched to a 242/242 solid, with 8* less "total" overlap and could run closed no problem.. Now run a 248/252 also in closed - when i had guys on here telling me "I ran a big came with no problems, its your tuning" None of those people knew the total overlap of their cam..
Dropping the 02 bias table helped, but no where near enough..
I was able to get the car to run beautiful in open loop, and using o2 readings after 2000 rpm.. Some cams you just have to!! know the shape of the lobe.. But I do think the zz409 would run in closed loop being tpis designed it - but then again, don't trust anything they make!

anesthes

iTrader: (12)

What was the total overlap of the cam you got to run in closed loop, and the one that wouldn't?

Mine has 74.5 degrees total overlap.. (290/307 hyd roller).

Another thing is.. Are you running MAP or MAF? I've always liked MAP better, but man. with this cam it's rough. (pardon the pun). I idle between 75-80kpa, wot is between 95-100kpa, 'cruise' is around 87-90kpa. Throttle off
coast is about 23kpa.

-- Joe

JP86SS

iTrader: (1)

Trying to cruise below that cam operating range is not going to be pretty.
Might look into advancing it a bit (4 *) to bring the bottom end down slightly.
I did that to increase my DCR because of my 9.3 static CR being so low.
It will cost you some top end but might make the bottom drivability worth it.

anesthes

iTrader: (12)

I think I have the cruise figured it. It's a lean condition.

Come to find out, my cruise is pretty much 1900-2200rpm, which although is low in the power band, the cam should still make more power down there than a stock L98 does at 4500rpm. So I'd think it should pull a relatively light car with a decently geared rear end. Looking at the log, 02s drop to the double digits and it pops (lean miss?).

At this point, i'm more concerned with learning some of the trucks of getting it to work with closed loop. I read through a bunch of old threads about adjusting the 02 swing points. 87, based on some other posts, appears to have got a cam with about 84 degrees of overlap to run closed loop. I'd love to hear how. I'd also love to hear more about his map readings, share a log, etc.

-- Joe

devilfish

x2

I experince the same thing. Couching/bucking, rattel in the tranny below 1800rpm. Abow super smooth. And I use the hotcam.
Whery close to give up.

anesthes

iTrader: (12)

Well. Heres what I have done:

1) Forced open loop
2) Lots of spark advance. Like 25+ degrees idle, 29 degrees cruise, 36 wot, and
41 degrees decel (high vac)
3) Cut a TON of fuel out. Almost all of the surging, bucking, rattle below 2k
was a rich condition. Leaned it out and it's great now. I think I need more fuel up top (above 4k), but i'll have to do some track testing for that.

This is a 10:1 350, bored .040 over with a cc-306 cam, trickflow heads milled to 55cc, long tube headers, true dual exhaust with H-pipe and dual bullet cats.
The car passed Massachusetts emissions on Monday 7/9/2007 on the emissions dyno.

-- Joe

JP86SS

iTrader: (1)

Cool!

Camaroz29

iTrader: (3)

Good job, that is the biggest cam I've ever seen pass a sniffer.

Matt87GTA

I'm just getting back after my GTA after it sitting for the last about two years... (tour in Iraq, etc.)

I think I am going to lock it into open loop and go from there. I just ran it a little and just like I remembered, it ran very rich at idle and hesitates here and there on tip in only in certain spots down low. It pulls pretty well at WOT and any of the higher RPMs really, but it just didn't feel all that strong to me.

So I pulled the plugs and they were WET with fuel... That was pulling them after a cold start and short idle period but you can smell the fuel at idle even at operating temp.

This is a 10.7:1 383, Brodix CNC 215cc heads, TPIS ZZX cam, Miniram, Long tubes, 3-wire heated O2.

When I tuned it way back when, I knew it wasn't perfect, but I got it to go pretty decent and wanted to run it on the dyno and did and got the WOT stuff pretty good and it pulled good numbers so I left it alone. Well I am sick of it hesitating and sucking down fuel like it is so it is time to get after the tune again.

Anywho.... I have to dig out my equipment for tuning but now I have my very own Innovate to play with so I hope that with that, a partner in the car to watch the Innovate, and locking it into Open Loop, I can get it in line again. I am just glad to see that some others have had good luck with this and I might be asking you guys for help shortly .

devilfish

So you using open loop all the time, or just for the emissions tests?

anesthes

iTrader: (12)

All the time. my emissions tune is my normal tune.

-- Joe

Grim Reaper

Congrats on making it pass emissions.

Out of curiosity, is it an IM240 dyno type and are the number similar to California's (for that vintage)?

anesthes

iTrader: (12)

Hey!

Thanks, and Yep, IM240 or 242 something like that.

HC limit is 02.00 grams per mile. Mine was 01.75. Which is 'close' but still great
for a 306 degree cam with 72 degrees overlap

CO limit is 030.00 grams per mile, mine was 001.40, WAY under
NOx limit is 03.00 grams per mile, mine was 00.54. Again way under.

Some folks would not agree with my logic, but I thought that the cam with a lot of overlap would help the fact that I don't have an EGR (miniram), would have slightly higher-than-normal HC, but still be ok emissions wise. It's a BEAR to tune, not a lot of resolution but I think I finally have it right.

I used to have a wideband, but they are very useless on a cam with this much overlap. Perhaps better than narrowband for reporting 'whats in the exhaust', but doesn't tell you squat about burn mixture when both valves are open for as much time as they are.

And again, this is open loop only.

-- Joe

91L98Z28

What methods have you used to do the VE table tuning when NB and WB are useless?

My 71 is running a 406 and the cam is a 240/248 (advertised 294/302) solid roller, 110* LSA, and needless to say it has a bit of overlap and the NB/WB would probably be useless or close to it. It's presently carb'd, but this problem (no ability to measure AFR) is one of the nags that keeps me from taking the plunge to EFI.

anesthes

iTrader: (12)

Mainly plug readings and by ear, smell and just trying things. Bogs, pops, smells, etc than it's a fuel problem. Rich bog, lean pops, rich backfires. Keep going one way until it's worse, than go the other way. Kinda like a carb.

-- Joe

Camaroz29

iTrader: (3)

I'm starting to think that with large cams if your catalytic converters are present and functioning properly and your car is in a good state of tune the car should pass.

89gta383

iTrader: (5)

I'm running closed loop just fine. 383, miniram, 10.5:1 comp, 230 .600 107lsa cam. Still hard to get rid of the gassy smell when it is running in the garage though....

Matt87GTA

Well, I would venture a guess that the "gassy smell" is becuase it is idling rich which is precisely what mine does and I cannot stand and is not good for the engine at all. It does uncool things like fouls plugs, uses up excessive amounts of fuel, STINKS, burns your eyes, etc. etc.

The problem is the huge amounts of unburnt fuel and raw air (ie lots of O2) that go straight through the engine at low RPM/light load. They completely baffle especially a NB O2 sensor and will cause the ECM to trim the fuel upward due to the high levels of O2 and make an either well or rich running engine run even richer....

funstick2

funny how i siad that 2 yrs ago in this very thread. I guess someone finally found out on there own.

Congrat on passing the IM240 its a tough test.

Funstick