hi
By installing a large cam in a speed density car the vacum signal will deminish and the ecm will think its under load correct?
Where do you start tuning in the prom? I tried doing a search but havent really come up with anything, does anyone know of any links their willing to share?
Also, whats the most powerful car out there running a 730 ecm?
can this ecm be used with a turbo or charger buy using bleader valves before the map sensor?
thanks!

 

In a round about way, yes.

First is getting the engine to idle. The main fuel and spark tables to start.

Several in the 11s, that come to mind. Though slightly modified ecms have been in the 9s.

Why not use the 749 that was used in the syclones for and ran 14 PSI in oem form?.

 

My car had a custom chip when I bought it. But it is possible to tune SD to a T, when running a big cam. Mine's the TPIS ZZ-X cam, that measures 241/241 dur. at .050 lift. The one thing I've noticed w/ my scan tool is that the chip puts in max timing from around 2300rpms -3700rpms. I think these mini-ram/big cam setups love max timing very low in the rpm band. I also know my injs. are dumping a lot of gas in at all times, which has been adjusted in the chip. I'll be tuning soon when I get the rest of the equipment. Right now I have a Pocket programmer and that's it.

 

I have a 224/234 cam @ 0.050" lift with 114 deg (maybe 118 deg...I can't remember off hand) of lobe separation. I am of the school of thought that the cam lobe separation has a lot to do with how the engine idles and therefore what vacuum signal it will produce for the MAP sensor. Large lobe separation IMO = lopey cam and crappy vacuum signal that pulses erratically. My cam, although it has a pretty good bit of duration and nearly 0.500" of lift at the valve, gives a pretty good idle. The gas mileage sux, but I drive a Jeep with a fairly large AMC V8 (using GM TBI with 1228746 ECM) under the hood, so I kinda have to live with that. Maybe I can tune the GM ECM to help out in that respect some.
Another thing you may want to consider (a lot of people don't think of this one) is how the cam selection is going to affect the operation of your torque converter (if you have one). Ask any tranny shop about selecting converters for fat cams. AFAICT, it ain't easy...there's a certain degree of art to it. YMMV. Grumpy and others here will be better able to tell you if you can tune your TCC stuff to a new cam.
HTH...good luck

 

jeepguy: you state a large LSA = crappy vacuum signal??? i thought a large LSA is desirable with a computer controlled car? 114 is the largest i see for comp cams and designed for CCC. as far a a pulsating vac signal you feel the MAP sensor will pick this up? and cause issues? I have a SD car 7747 and putting in cam maybe in 10 days. 226/232 @.05 114 LSA. i expect some issues but hope to be able to run closed loop at idle rather than force open at idle only. please comment.

 

Case in point:
My stupid sister in law just put a bigass cam in her Z71...TBI, 7747 ECM, L05 engine. She has yet to listen to reason. The MAP sensor is probably picking up the pulsating vacuum signal and the thing will idle, but it is basically dumping gas down the TB and pouring smoke out of the too-small dual exhaust she had her boyfriend try to fab up...what an idiot. I played with the TPS and showed her what was happening to the engine and she STILL won't listen to me. THEN I found the aquarium air hose they had jury rigged into the thing as a MAP vacuum hose...it got a little better, but the smoke is still there and I have a feeling the O2 sensor is black as it can ever get.
My experience comes mainly from working on carb'd engines. If you have a large LSA, it has been my experience that this leads to a lopey idle. The 114 LSA you are looking at is great. I looked at mine and it too has a 114 LSA. My cam specs are actually 214/224 @0.050" with 0.472/0.496" lift at the valves...Summit 8600 for an AMC V8. it idles really well and AFAICT, the MAP is getting a good signal. If you used a 118 LSA, I doubt it would cause THAT much of a problem (maybe someone else will chime in here) but IMO it will give a slightly rougher idle and probably send a little more of a pulsating vac signal to the MAP.
This is my experience with AMC V8's...namely the AMC 360. Mine now has GM TBI with a 1228746 ECM. It works beautifully and as soon as I get it tuned, the Rustangs had better watch out...and the Nissans
There's my $0.02...hope it helps a bit.

 

i have a cam with 240/246 duration at .050 and lope seperation of 110 the lift is .510. this is in my truck right now. i haven`t yet swaped to tpi yet. i broke a race built 700r4 some how. i have a few questions about big cams.
what is involed in tuning I.E. what tables have to be changed?
i have also heard that with a big cam the o2 sensor is useless because the big cam lets uncombusted air out the exhaust or something like that.
if that is true how do you know you have the correct air to fuel ratio?

 

proryder, if you search (or even look a few pages back) this was discussed in great detail a week ago. Valve overlap and such was very prominently mentioned in that thread with diagrams and all.

 

hi, thanks guys for your replies
The cam im using is approx. 256/264 112ls 610/630 lift solid roller in cunjunction with a pt88 turbo and a 355ci, possibly a 383 if i have to resort and buy another crank might as well up the cubes.
Form what i have noticed is that gm guys like to run speed density and the ford guys like the mass air, so my next question is why you guys like the SD vs. mass air? whats wrong with gm's mass air computer?

 

256 @ .050 and a turbo. Someone wants to shift at 7k+.

I think there is a sticky that has the MAF vs SD discussion.

A wider or higher # LSA in itself will not cause a rougher idle. As long as the total duration doesn't change, then it will idle better. Also the engine will have a wider power band and usually rev higher. It depends on how you get the wider LSA. A narrow or lower # LSA will have more overlap and therefore more reversion. Which is the big cause of the low map numbers. To get a 118 LSA you will probably need to go to a billet cam. The cast cores do not have sufficient depth of heat treating to support that much grinding to get the LSA out there. Or maybe a regrind on a GM core if they can support it.

Here is some stuff I wrote on reversion & a link to a good cam discussion with comments by an actual cam designer.
The thread was long so I quoted & linked.

Whole Thread Which was actually on intakes.

 

That cam sounds way too big for any GM computer, without serious tuning or (lots of hours and time). Most guys running turbos on a v-8 don't run that much cam at least in the mags, mainly to keep their low-mid range tq. If you're definitely going to run that cam, go with at least 383 ci. Your setup would be even more fun with at a 406+sbc.

Not all guys like SD over MAF. MAF is a lot less forgiving, but SD has a lot more depth for tuning when your making 500+ hp, which is when MAF starts to show it's weakness. Check for other posts discussing these debates. Of course some very knowlegdable guys have been banned from this site, because they were passionate about their research and beliefs.

 

That's not true. Stop spreading lies. I know that you are talking about Jesse (who I did not ban ... that decision came from above). In any case, 11sOrBust (i.e. kvu) was banned originally too ... and it wasn't for being passionate about his research and beliefs.

Tim

 

Hi
the reason I asked about speed density vs. mass air is because the ford guys are running the eec4 with no tunning except for wideband and adjustable maf sensor in the high eights low nines so makes me wounder the diff between their ecms and ours? the gm ecm's cant be that much far apart their both doing the same thing in giving the engine parameters to work with. In my opinion I thought the gm ecm's were superior to their's, they didn't even have a data stream until sometime around '93.
I hope I dont sound stupid asking about it.
thanks

 

The problem here is you are only talking about WOT. What these guys are doing in a nutshell is if they have twice the air they add twice the injector and tune the MAF so that the computer is fooled into giving the right ratio at or around that air flow. Other airflows may or may not be correct. The other part of the WOT equation is spark timing but again just set the distributor to whatever gives best performance and youe done. This also does not mean you will get the best performance to be had. Tuning the lower spark values can net gains.

You can do this to a certain extent with the GM systems. Unfortunately the MAF systems do not have larger compatable aftermarket sensors. So you will peg it. For SD systems you are stuck with the stock VE curves. You can add fuel but you will end up with a really rich low end.

The main problem with all of this is drivability. Without tuning you have to trick the computer to do what you want at 1 place in the curve and lat the rest fall out where it may. This can lead to a real dog of a car just cruising around. It can also lead to idle problems from lack of spark timing. The larger you go cam wise the more idle timing you need. If you can only crank up the distributor then all timing is moved and now you have too much at WOT. Tuning is just a way to get the best performance and make the car fun to drive with a big cam.

HTH

John

 

Can I ask why you would call someone a liar for simply stating their opinion? Geesh. What are you a communist?

Another thing I'd like to say is that by what you just posted you are implying that Jesse was banned for being passionate, like Isaid in my post, . So how the hell did I lie???

Some guys on here are way too **** about what is said on this forum. Hell, guys get banned for discussing performance cars. It's not like these guys are tell'n all you mods to go **** your mother. Geeminniefreak'nchristmas. I mean Grumpy isn't banned but he's said just is much as Ski. Oh yeah, if there's anything else I need to know I rather be pm'd than screw someones thread up like this.

Sorry,
Jester

 

How did an otherwise interesting thread go from cool to $hi+ in one post? This sucks.
So, where am I wrong about the cam LSA and the idle? I have experimented with several non-GM engines (American Motors Corp/Jeep V8 engine) and each time I went higher with the LSA, the idle went more lopey. Was it just the changes in duration @ 0.050" lift? Was it an idiosyncrasy in the engine/head design?
C'mon, guys...let's keep this one going. This is good info that anyone with GM EFI can use.

 

The lower (tighter) the LSA the greater the overlap, and the higher the manifold pressure will be at idle. All other items being equal within a cam design, a tighter LSA will have a ratty'er idle.

RBob.

 

Jeepguy, what changes in duration did you have when you switched cams. Longer duration is what makes the most difference as far as rough idle is concerned. Of course Most larger duration cams come with a tight LSA so that all of the low end is not lost from using a big dur. cam.

Once again, I apologize to you guys and to you Traxion, if I offended you. I guess I'm just bitter that Ski got banned on the boards, that guy helped me immensely with my old/new setup.

 

Hi
ok, so the tighter the lsa, the less vacum and more manifold pressure it will see at idle which brings me to what grumpy said tune the fuel spark table. Correct me if im wrong you would lean it and therefore retard the timing right or wrong?
another thing i will like to understand is this at idle open-loop, the engine is running on predetermined tables so with low manifold vacum its going to use a table to corespond with engine under load which therefore will increase idle up (surge) eg.1500rpm then the ecm see's the tps sensor reading as closed throttle, engine not underload and decrease rpm(surge down)eg. 500rpm at this point is the ecm going into limp mode to bring the idle down or is it going to use another part of the same table or not?
the deeper you get into this "stuff" the more interesting it gets.

 

Well, I have used an Edelbrock cam on an AMC 304...then I used a Crane Cam on a 360...now I have a Summit cam on another 360. There have abeen a few others too. The changes in duration were fairly radical in a few cases. I went from an RV cam in this engine to a Summit cam with a medium-high duration and 114 LSA. The idle fromthis cam, IMO, is just about perfect. It is fairly smooth at 750rpm. My MAP doesn't move that much.
honestly, I always thought the LSA was the deciding factor in idle quality. I guess you learn something everyday. Cool...