New FMIC & Low on Vac

I just installed quite a bit of modz and am looking for some ideas as what to look for:

FMIC, Steg Heads & Big Cam profile, 1.73 rockers. I am looking to see if with all this, when I cruise about 50 or 60 on the highway and let off the gas, the most VAC I get is about 10. I'm used to 20-23 or so prior to changing everything over.... Could have to do with tuning? Or may there be a leak somewhere? I couldn't see it leaking because everything seems to be installed fine.

Or could it even be the Cam Sensor position? I used the tool to set it, but my degrees may not be set to 26* after top dead center... Could that be it?

Or is it my imagination & this thing really should idle strong, have a dead spot at the start of the throttle & low vac when off the throttle.

Thanks,
Anthony

What exactly is a "BIG" cam profile? I put a cam with these specs in an SC:

Intake 589 lift, 238 duration
exhaust 605 lift, 248 duration

Idles at about 5 inches of vacuum, and on a decel it gets a good 15 inches of vacuum when the RPMs are up above 2000. Be advised, this cam profile has 80 degrees of overlap, making it quite a "leaker" when it comes to idle, but it can still hold 5 inches of vacuum. The power in the car comes on at about 3400RPM, and dies off around 6800RPM.

Chris

Anthony,

If that is Stegimeir's latest cam, then it sounds about right. The specs are nearly the same as what is in my engine, and I'm getting 10 inches of vac at 1100 rpm idle and about 7 or 8 in gear at 800 rpms. But I am getting 20 something inches of vac when lifting the throttle above 3000 rpms, so I don't know why your only showing 10. Are you sure the hose to the gauge isn't leaking where it plugs onto the intake manifold adaptor ?

I also have a little bit of a dead spot just off idle...but it only seems to be a problem when the engine gets over 180 degrees.

So how does it run ??

David

Anthony....I just installed the same upgrades as you and got the car running a week or so ago and also have no more than about 8 in of vacuum at idle.
I too have a dead spot off idle with my cam.
I don't think you have too much to worry about. Mine put up some real impressive numbers on the dyno but the driveability has suffered a little as expected with a drastic cam change.

2 words guys, "EEC Tuner"

I got the car we just put that radical cam in purring like a kitten. When we started it up on a stock tune, it ran, but horribly. Now it runs awesome with the correct tuning. BTW, on a stock tune, with the 50LB injectors, it was so rich at WOT, we were probably losing 50 HP at least just because of that. Can't beat an EEC tuner if you have big injectors and a big cam.

Chris

Yep, it's his latest. And this thing cams pretty hard.. I am cool with the vacuum issue. Now I have another problem. As Chris said~ The dam tuning issue. .. I have the 90 mafs & it seems to run like crap. I know Brian can compensate on a dyno tune. But I tried a few things and check this out.

I took the chip out Brian sent me (this burn isn't the right one) and figured screw it and unplugged the maf. Let me tell ya, it ran full rich, but with the exception of the roughness at idle and the dead spot just after idle, while driving it hauled. The check engine was on as expected, but after idle it sure ran awesome. Got hot of course, but ran nice. I think I need a good maf. My buddy that built it with me said that he has a pro-m 75 bullit (however ya spell it) calibrated for 42lb'ers & supercharged. He said that with no chip & that maf it should fix all my problems.

Can anyone negate this?
Anthony

Here's a shot prior to completion & clean up, but you get the idea. And Fellas, this thing is Violently Nasty. I can't wait to get it to run right. This is going to be something else. Once it runs right, I have a few more things to add. Dave, like you Mrs., I'm starting to be accused of have an endless obsession at this point. When I got home the other night (in front of her) I put my paycheck on the hood and said "Her Hunny, Now Get yourself something nice!" I don't think I'll ever hear the end of that one..

Fix all your problems, certainly not, but it will be a start. With 50 LB injectors, and a MAF calibrated for 50 LB injectors, the car still didn't run great, but it was certainly driveable. Starting the car was a bitch because the fuel pulse width at crank is a fixed number, that doesn't change with the MAF you put in. You can imagine, 50LB injectors spray quite a bit more fuel at 7MS pulse width than 30LB injectors. It was flooding it out at start up. With the EEC tuner, I simply changed those numbers, now you reach in the window, turn the key, and 1/2 a second later it's running. That's just one example of what your MAF and injector combination will not solve. However, you're only using 42LB injectors, so you probably won't notice that problem as much as we did with the 50LBs. (BTW, you should be using 50s with your setup)

Not having an EEC tuner is like leaving your stock carburator on a car after doing all kinds of engine work. Of course the computer compensates better than a carburator, but it's a close analogy.

As a side note, awesome job on that intercooler. You have the right idea there. Nothing is better than square footage where the cooling area is concerned. Much better than those double wide intercoolers.

Chris

Chris,

Tony, Anthony and I all have custom chips from Apten Performance in our cars...my car and Tony's were tuned on the dyno. The dead spot coming off idle didn't happen on mine until switching to the Pro-M 87mm Bullet MAF. It's more of a rough spot than a dead one..but it shouldn't be there.

I've had something like a dozen EEC tuner files, and 28 chip reburns...believe me I'm aware of the importance of a good tune. Did you tune yours on a dyno with wide band o2, or by seat of the pants ? If you haven't already done so...get your car on the dyno and check your A/F ratio. I agree about the 50# injectors...that's what I have.

Anthony, your going to have to get that car on the dyno for a proper tune...you have too much invested to risk screwing it up. Brian is flying to Carlisle PA for dyno tuning....I would suggest getting your car there.

David

Dave,

Didn't tune it on a dyno yet. Car just got running 2 weeks ago. However, I also didn't tune it "seat of my pants" because I have all the proper equipment to measure sensor outputs on the car. Even have a seperate Stoich guage on the car to see live data from the O2 sensors at all times. (nice guage BTW). A dyno date is scheduled for the near future though. Not easy to find a place in my area (Long Island). There are also some serious mods scheduled for this engine in the near future too (M112 blower, air to water intercooler, new intake to support new blower/intercooler setup), above and beyond the internal engine work we've already done, so I don't want to get too crazy tuning just to do it all over again in a few months.

Sounds like the MAF Transfer function is different on that new MAF sensor. You know what has to be done.

Chris

Chris~ That sounds like a fun setup. Should be pretty fun to fab up. Seems like everything needs fabbing, so why not go all out!

Dave~ I'm already set to meet with Brian and get the SC dyno-tuned. However, I may be looking to get it done with a different mafs. I'm looking into the pro-m87. First I want to see if I can get it in time. But, I'm looking to test and see if I get it calibrated for 42's & Sc'ed engine, I am thinking it will run good enough to get to Carlisle without a problem. Because with the current chip/setup I don't think it will be good to drive out there. It's about 3 hours, but running pig rich. And I think it's the 90mafs screwing up the works.

We'll see,
Anthony

Anthony,

When it's complete, you'll be able to go to Paul at Blue Tongue Motorsports to get yourself a kit. We're working with him to get it completed. Unfortunately it will mean the addition of a 3" raised center hood because of the fact that the intercooler will be mounted directly below the blower, but it's worth it to get rid of the obvious thing holding us back at this point, the M90 blower. He's working on a direct replacement kit also, so you can use the factory intake, intercooler, tubes, etc, just replace your M90 with the M112.

You can contact Paul at http://www.bluetonguemotorsports.com if you have any questions or interest.

Chris

welcome to the world of fast SC's

If you have the high lift cam I am thinking of, it will never idle or have low range throttle response as good as some of the mild setups out there. That's just the price you pay for power!!!

I still think the 90MM LMAF is the best setup to use, but your setup definatly is going to need tuning. Just 7 more days...

LoL.. Yeah I hear ya Brian. For every action there's a reaction.. If you think we will be fine tuning the 90mafs, I will leave it for you to optimize. As for Idle, this thing rivals some 60's muscle cars. To me it sounds pretty damn nasty.

Hey, do you think it would be advised to change my O2's before the tune? Or doesn't matter? I don't think there is anything wrong, just figured I'd do it in chance of any issues later. Also, will the rear gearing matter? I have the 327's now, but will be changing to 373's. Should I do that prior to the tune as well? Or does that not matter as well?

Anthony

as long as the O2's work, there's no need to change them. Also for the gearing we won't need to change the tune since it's an AOD.


Brian

Hey, this sucks!!!!! I want my car fast too.....

Well, gotta get my car to the dyno and get some numbers. Calling Gary tonight and getting the payment to him. Hell, my car is nothing compared to you guys!!!!!!!!!!!!!!


Anyway, Anthony, the cam WILL not let it idle more than 7-8 inches of vacuum. It should pull around 12-14 inches off throttle (letting off), and more when high in the RPM.


Nice to see these cars moving!!!!!!!!!!!


See you guys there.

Hey Chris.....It's Don, how's the car?????

Talk to Dave lately??? His car is almost done.


Don

Didn't tune it on a dyno yet. Car just got running 2 weeks ago. However, I also didn't tune it "seat of my pants" because I have all the proper equipment to measure sensor outputs on the car. Even have a seperate Stoich guage on the car to see live data from the O2 sensors at all times. (nice guage BTW).

Click to expand...

Chris,

I'm not trying to sound like a know it all, but I don't want you to damage your engine. Unless you have special wide band o2 sensors installed specifically for monitoring air fuel ratios. your not seeing all info you need.

The data your stock sensors provide won't be good enough to properly tune the car, because the range of the o2 sensors are way to narrow to tell what mixture your getting at WOT. It may say full rich on your gauge, but still be dangerously lean. I've seen it first hand on at least three other SCs.

If in doubt, tune it rich until you can get it on the dyno.

David