Bones232

The attached pic shows a wide open 2nd gear run. My Grams/sec hit a wall, so to speak, at about 4900 rpm. From then on grams/sec never goes above 207.

The only thing that sticks out is my Map starts out at 100 and decreases to about 95 by the time I let off. If i'm pulling a vacuum, could i be at the limit of the intake???

What do you suppose is the bottle neck is????? Intake, Cam, heads??? Setup in sig.

Please note that on the attached graph the map, tps, rpm and gs/s are scaled to fit on the graph.

RBob

iTrader: (1)

Don't worry about the gms/sec value. In a SD system it is a calculated value, not a measured value. At the same time the airflow will steady out as the RPM increases. As the engines volumetric efficiency also drops off past peak torque.

The falling MAP at high RPM is normal. A 5 KPa drop across the TB and air cleaner isn't that bad. Converted to inches-Hg it is a little less then 1.5" Hg (same as old school vacuum value). For all out performance a value of 1" Hg would be better.

Note that this pressure drop can be from the TB unit being restrictive. Or the air intake, air cleaner assembly being restrictive. To check this can use a standard 1-bar MAP sensor and plumb it to various locations in the intake tract. Then data log it.

RBob.

Orr89RocZ

iTrader: (20)

You can try a run without the air filter to see if the filter is a restriction. Alot of the times they are undersized and could pose a small restriction. I agree with the above, its not uncommon to see alittle pressure drop at high rpm even with big throttle body and high flowing air filters

Ronny

iTrader: (1)

Is elevation a factor? I am 1200 feet. Key on I am 98. WOT ogs show 95.

305sbc

iTrader: (3)

The measured restriction will be ahead of where the MAP is being measured. 95 is not that bad, but could be improved of course.


I think it depends if you have the BARO re-calc routine turned off or not.
I think what Rbob said about hooking up another MAP to monitor that isn't affected by key-on or recalc routines is a great idea to eliminate variables and get a consistent reading for your personal reference.

Bones232

I just found it interesting as 4900-5000 is about where the engine stops pulling hard and i feel like i should be shifting. With my combo i kind of expected to pull through at least 5400-5500...

My VE table jumps off a cliff between 4800 and 5200 just to maintain my AFR setpoint which leads me to believe i've hit the airflow limit on something...

I've used two different air cleaners. An open element with a drop base and my current setup consisting of a carb hat, 3" pipe and a cone filter exiting next to my CCP canister. I really didn't feel or see any difference in performance between the two. I'm paranoid about running with no air cleaner. With my luck that would be the time i suck in a rock and waste the engine. Maybe someday...

Orr89RocZ

iTrader: (20)

The ve table is a sign of where power is being made. I'd try a simple quick run with no air cleaner just to see how much a difference a filter makes. It may not make any. The cam is not huge but it should be capable of making power in the 5000-5200 rpm range and holding to 5500

RBob

iTrader: (1)

Most likely the GMPP TBI intake is the engines bottleneck. Here is a composite pic I put together with that intake and the Performer RPM. Note the difference in runner size and shape.

I've seen the same 'falling off a cliff' with the stock L03/L05 TBI intake. And the Vortec TBI intake appears to be very similar in design.

I agree that the engine should be pulling to a higher RPM.

RBob.

Bones232

Well, I'm convinced the bottleneck is most likely the intake. Although to verify things, I will remove my air cleaner for a run to see if that makes a difference. It is simple enough to do.

Anybody know of an externally piped EGR and Vortec friendly dual plane intake that flows well?

Orr89RocZ

iTrader: (20)

What about one of the performer RPM vortec air gap intakes?

Bones232

That is exactly what i want. However, i need to figure out this EGR thing...

If my car was a couple years older i wouldn't need to worry about it....

RBob

iTrader: (1)

I understand the good intentions. However, an air gap design with a street driven TBI is not a good idea. Really need to have some heat (not a lot) in the plenum area for good fuel handling/puddling/distribution.

Although, if dumping EGR into the intake, that will add quite a bit of heat. I don't believe any of the air gap manifolds have stock EGR.

RBob.

Orr89RocZ

iTrader: (20)

YOu'd have to fab up the EGR somehow. Plumb it back into the intake at some point. I'd figure with the heatsoak, it will keep that manifold pretty warm. I dont think the air gap actually does much.

Or else, do your best to have the manifold ported,if it can be opened up without running out of room.

jim_in_dorris

Something to look at might be your injector duty cycle, if it goes static that might be the problem - easy check and nothing to change if that's not the problem

Bones232

Highest logged DC is 90%. I've used different injectors, different pressures with similar results.