I have the Holley 670 TB and an open element with dropbase but no spacer ring. During my 1/4 mile runs the MAP goes from 101 to 99kpa but it's a noticably steady decline all the way past 100mph. So my question is this, does this mean the motor needs a bigger TB or is this not even valid data?
I would post a screen shot of the excel chart but I'm in a computer lab right now and my computer isn't online for another week.

 

Your data is valid. How low does the MAP get? And at what RPM? A 10 Kpa drop is about 3" of Hg. For best performance that would be the max. Less would be better (< 5 Kpa).

RBob.

 

just a note of curiosity here. how rigid is the throttle cable bracket ?? might be that your throttle is slightly closing @ WOT. if you can verify that the thottle is not beng affect at WOT by either chassis movement or vacum i would look into a bigger TB.also check t ground for the map sensor as well. thing move around at high engine speeds and maybe the ground isnt solid. also you might just be running in better or worse air. you could also have a small exhuast restriction at high rpm driving up the vacum.

 

Hold the fug on a second. I try and tell people the TB is too small and all I get is a bunch of people telling me it will run out of fuel way before air. I am the only one on the airflow side and have 100 pablos on the fuel side quoting formulas. And now you dare ask this question.
Blaspheme I say. Stone the heretic!


BTW my motor did that too. There are other factors to consider *cough velocities*, but I'm told you probably don't have enough fuel. LOL :lala:

 

Like I said, it only drops a few kpa from 101 to maybe 98 by the end of the 1/4 mile (shifts at 5800). Because of the slow 0.8 fps capture rate of winaldl I was only able to see 8 frames for when I was at WOT. First frame was 101 and the last frame was 98, that's a difference of only 3kpa. It didn't matter what the engine speed was BUT just from those 8 frames you can see that the engine took longer to speed up in the different gears. I'll try and post the picture up tonight after work.
I guess this means it's a fuel and timing problem.

 

If the manifold stays close to atmospheric pressure (100 kpa) at WOT it implies there is no restriction from the TB/air cleaner/etc.

If the engine revs slower in higher gears it implies that Newton's law (F=ma) is still working .

 

If the lowest value ever was 98 Kpa then that isn't too bad. I had forgotten about the 160 baud frame rate. In that case I would just look for the lowest value and figure that it is at the highest RPM. A 3 Kpa drop is ~ 1" Hg, darn good.

As a reference point a warmed over 327 was dropping > 10 Kpa at 4800 RPM with a stock 1-11/16" 2 BBL TBI. It was dying! No fuel problems as the pressure was 30 psi with blk/org injectors.

Now with a 2" TBI it hits 6K RPM so fast I am glad it has a rev limiter.

RBob.

 

Bob, I plan on starting the lockers project but I need some questions answered. I tried to PM you but that doesn't work (I'm sure for a good reason) so do you want me to start a new thread about lockers or could you e-mail me at prevost.3@osu.edu
Anyways, I always thought the 2" bores would be plenty of air for a 350, only problem is that my cam is a mild 212 at .435" intake so it doesn't really prove too much.
If I put on a carb to play with, couldn't I keep the ecm and the map sensor to log pressure drop? Then we could see exactly what cfm the "670cfm" TBI design could be compared too. I'm guessing it's darn near 670cfm and your 327 is most likely showing that the small bore is less than 500. I'm glad too see more real world results and less BS about TBI.
I wonder if my stock coil is hurting me, this could explain a lot. It seems to not matter if I shift the car at 5000 or 5800, which must imply that after a shift the car isn't increasing in power from ~4000-5000, almost leveling off. So now I have a feeling that it's both the coil (not a good burn beyond 4000 so the o2 sensor gets false rich) AND a fuel delivery issue, which could be just about anything (injectors, fuel pump pressure with high RPM and engine load, or hopefully code). The code is free to change, everything else is expensive. I'll start first with the coil, I hope this shows improvements because it's cheap. I'm just doubtful because of the low 9.1:1 compression and mild cam.
All of this could be solved if I had the ability to afford all of the above .

 

That little MAP drop could be from the air cleaner/air inlet system itself at that high an rpm. Not an issue.

If you are running a stock coil, you should upgrade. I have to agree that the MSD coil did add quite a bit to the mid-top end.

 

I emailed ~ a week ago, I'll resend. Yes you can easily run a carb and keep the ECM to run the ignition. At the moment have a truck doing just that. Ran the 327 for about year doing that too. Just disable the O2 codes (13, 44, 45) and the high map code (33). And bring the fuel pressure down (~5 psi).

As for the power leveling out I'd bet on fuel delivery (if pump is still stock). The stock pump is not rated to a high pressure and bumping the pressure up reduces the amount of fuel able to be delivered. See if you can tape the gauge to the windshield.

The fuel delivery is one reason I went to 16 psi with BBC injectors from 30 psi and SBC injectors.

RBob.

 

Just realized you have the GMPP 212/222 .435"/.460" crate motor cam. It runs out of pulling power well before your stated shift point of 5800rpm and could cause the air starvation vac signal you see at high rpm: not enough room to get more air in with that cam vs that rpm.

If you need more oomph after 5000rpm, you will need a bigger cam. I run a 218/224 Comp XR269 with 112LS and I have to shift right around 5,500, as a comparison, to get max pull. I would suggest a HOT roller cam, or similar, if you have some scratch to get you more oomph. For less $, just go bigger with a cheapo SIS Summit/PAW 224/234 cam/lifter set. Less than a hundred bucks, installed yourself, gaskets and all.

 

I want a bigger cam. I want a roller with 218/226 and .520/.540 but that requires time, money, and the heads to be worked over. I've got a friend that's going to buy my heads and I'll just end up buying some new vortec heads already worked over for the bigger lift and then get a super vic intake. When that happens I have a good feeling that the 670 will become the bottle neck.