HELP! Our Homecoming trip could be in danger!

:confused:

The Spence car is on track to make a debut at Homecoming this year with one, significant glaring exception that is placing our trip somewhat in jeopardy - the car is undrivable.

We are running an Accel DFI fuel injection system and the motor is only developing 7" - 12" of vacuum (idle to run) which is driving the MAP sensor nuts. I can re-scale the entire fuel strategy to match the low vacuum, but this really does not seem right for the motor. I'm looking for any advice or suggestions that the group may have on why my vacuum may be so far off. Here's what we know to date:

1. 351W, 0.030 over, 9.1 compression
2. 224/232 at 0.50 cam with .555/.565 lift on 1.6 rockers. 108 intake centerline with 112 degree separation. Both Comp Cams and Cam Motion have validated the grind for the combination. Comp indicates 13" of vacuum is normal for the cam, everyone else in the world I have talked to says no way, cam should pull at least 18"
3. Auto trans with 2500 stall
4. Cranking compression is 155# or 160# for 6 holes, other 2 holes are at 150# and 152.5#
5. Valve covers are not pulling vacuum, propane tests suggest no vacuum leaks
6. Vacuum readings on the MAP have been validated by a gauge
7. Only vacuum pulling off the plenum is for the MAP and fuel regulator, everything else is sealed up
8. I think I recall degreeing the cam, and definitely remember installing it straight up and even getting a second opinion to ensure the cam was installed on the right tooth. I haven't gone back to validate this yet because I am trying to avoid yanking off the timing cover.
9. I have taken the car from 20 degrees to 45 degrees of initial timing to see if there was a serious retard issue. (A serious issue with the timing that is. We know there is a serious retard issue with the mechanic. :))

I'm at my wit's end and looking for some help. If you have any advice or know anyone I can call please let me know!

(Funny story - I did get the car around the block a few times with a seriously modified fueling strategy...I got into the throttle a little farther than planned and outside of my adjusted fuel map. The EFI dumped a bunch a gas into the motor and the backfire in the manifold launched one of the breather covers over the top of the car. Once I cleaned my pants and determined nothing was hurt as a result my neighbors and I all had a good laugh!)

Brian, you might want to post your data on the FFR forum. It seems most of those guys run fuel injected engines and I see posts regarding FI configuration all the time. Collectively, they seem to have an awful lot of experience.

Some of the smartest tuning people I've seen are here. http://www.innovatemotorsports.com/forums/

You can also contact Accel and get a referal to a local tuner.

Double check your rocker nuts.

+1 on Patrick's suggestion. Did it run fairly smooth, even with lo vacuum? I assume hydraulic lifters - and also assume you went only 1/2 turn on the nut after the pushrods were snugged up between the lifter and rocker arm. While you can go more, there's not really any advantage to do so.

Head/manifold gaskets were glued on? - and manifold bolts are tight? Gaskets are in, between stacks and manifold? Any block-off plugs missing?

A slow easy surveillance of the whole upper tract might give rise to something.




-Roger

Rocker nuts? You mean like overtightening the nuts on a hydraulic lifter and holding the valve open? Check, in good shape. My rocker specs suggested 0.030 preload which corresponds to 60% of a turn based on my thread pitch. (How's that for anal?)

Head gaskets on with copper adhesive. Intake gaskets on with sealant. Everything is tight.

Only block off plugs on our intake are right in the center on the plenum, and all are closed up.

The prevailing theory is that the cam timing is off and that the cam is either mismarked or installed one-tooth-off. Looks like the timing cover is coming off. Yuck.

Brian it sounds like a cam issue to me. When you built the engine perhaps there was an inadvertant crank advance, one tooth will make a big difference?

Ralph

Ralph,
Cam issue seems to be the concensus. Timing cover is coming off tomorrow night, should be able to get the degree wheel on the front of the motor. I really think I installed the cam right but am beginning to doubt myself!

Where's Brent when you need him?

Alan

Good Luck Brian!

Ralph

Yes Brian, good luck! I hope you find the source of the problem quickly.

Actually I called Brent this morning...I have a plan of attack for this weekend. I have a couple things to try before pulling the front of the motor off...I looked at that last night and just dread the thought of doing that!

Brian, Hope Brent has the solution. I've done the remove the front of the engine thing before with the engine in the car. Yuk!! I am getting ready however to do it again. I am planning on changing out my camshaft for a milder version that has some torque in the RPM range I drive most of the time. Currently I have removed the entire 3rd member, which makes it easier to put in a new battery tray on the shelf above the gas tank, (which is also out), and it makes it easier to install the handbrake calipers. The reason for the removal is that I am planning on putting Trigos on. So I will be selling my 16" Compomotives with rubber.

I'm sure you'll tell us how it went!!

Happy Easter!!

Ralph

Well crap-ola. Yesterday morning I cursed Ford for running the water pump through the timing cover and proceeded to pull the front of the motor off. I finally got to the cam and verified that I did install it correctly. (Yeah for me, bad for my problem!)

Then I pulled out the degree wheel and verified the intake centerline - it came in at 106.5 versus the 108 spec. I verified the lift and duration of the intake lobe as well. I have a couple more checks but it looks like the cam is correct for both grind and installation.

Brian,

Is is possible that the lower vacuum readings are a result of the individual runner manifold? I'm not an expert by any means but have heard that there are special cam requirements when using Weber IDA setups. I wonder if the same is true for individual runner EFI?

Patrick,
It's possible, and I'm beginning to wonder. The 8 individual runners all have a small port to a central plenum which is where the vacuum pulls from. Brent is UPSing me a manometer which will allow me to measure vacuum at each stack, independent of the plenum. If I am pulling vacuum at the stack, but not at the EFI MAP sensor I can recalibrate the EFI to run on the reduced vacuum without any issue. I just didn't want to go that route without trying to fix what appears to be some other vacuum issue!

I will be researching weber cam and manifold setups and will be making a call to inglese tomorrow.

I think we have found the answer. Patrick was on the money with the individual runner manifold diagnosis. I have never played around with this type of manifold so was a bit out of my league in terms of expertise, but the short answer is that individual runners will not build vacuum like a plane manifold due to the pulses of vacuum and reversion that will balance themselves out to something less than actual cam vacuum.

Bottom line, I need to tune my EFI system to run on 10" of vacuum. So, i'll bolt the motor back together and get tuning so we can make the Alabama run!

Congrats Brian on figuring out the problem! Thanks to you and Patrick for educating us!

Ralph

Brian,

I'm glad you got that sorted. Does the DFI setup have an Alpha-N mode as opposed to Speed Density? Alpha-N is a function in the FAST XFI EFI setup that is designed for individual runner EFI manifolds producing less than 10" of vacuum. You may not need it if you have balance tubes connecting each runner to a MAP sensor.

Quote:

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Originally Posted by pbrown

Brian,

I'm glad you got that sorted. Does the DFI setup have an Alpha-N mode as opposed to Speed Density? Alpha-N is a function in the FAST XFI EFI setup that is designed for individual runner EFI manifolds producing less than 10" of vacuum. You may not need it if you have balance tubes connecting each runner to a MAP sensor.

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Alpha-n , XFI, EFI, Speed what?,:confused::confused: man I'm glad I just have carberators. :)

Quote:

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Originally Posted by RJacobsen

Alpha-n , XFI, EFI, Speed what?,:confused::confused: man I'm glad I just have carberators. :)

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I heard that, Rod.

Brian, glad you are making headway. All this talk has really been keeping us in su-Spence about wether or not you'd make it down. However, we knew that you would work it out, as the EFI is really just a fuel di-Spence-ing system. Looking forward to seeing y'all, now that you have a di-Spence-ation to fix the engine problem. The tough part is all the ex-Spence-s that you have had in getting to this point. I feel for you...

That said, I certainly hope that you don't have any trouble with the su-Spence-ion, front or rear, as that could cause you to di-Spence with the trip altogether.

In any event, I'm sure that, once you get all the bugs worked out, the car will become indi-Spence-able to you.

On your trip south, if you get bored with the drive you could just hum a little tune... sing a song of sixSpence, a pocket full of rye...:confused:

OK, OK... enough of this nonSpence:eek:!

Accel DFI does not have Alpha-N or a TPS/MAP blend like the MoTec or Redline EFI controllers. I have considered running the TPS input into the MAP sensor since both are linear 5-volt controllers. That is totally uncharted territory and I rather not tread there if I don't have to.

I have been spending lots of time on the GT-40 websites, there are a lot of guys there with stack EFI systems. Most of my conversations have been with guys in Australia and the UK. The Spence car has gone international!

I was lucky to find another guy who is running an Accel on an ITB system and he posted a ECU control file specifically for this type of manifold. As soon as I get the motor screwed together I will give that a try as well.

We should be able to make Homecoming, although the car may not be tuned perfectly. I'll bring an extra set of plugs (or two) in case we foul them and hope for the best!

Some days a carb is a good thing, but once we get this system dialed in there won't be a carb that can compete!

How is it going with the EFI tuning? Is it running yet?

Patrick,
The car is back together and running, but the tune is not perfect. We have a revised fuel map from Accel that matches our setup and the low rpm running is much better. Unfortunately the mid and high rpm running is not good and overall the car is not very drivable. After much research and discussion we are renting a dyno and an Accel tuning tech for a day to help us get the car set up. It's a tight schedule between now and homecoming!

We welcome show cars as well as go cars to the open house.

Alan