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Have you tried AI?
This points to your stock intake being mismatched with heads and cam combo:
AI Overview
Your 351W with the Comp Cam 35-349-8, ProMaxx 9175 heads, and stock intake is experiencing a lack of power likely due to an improper intake manifold for the cam and head combination. The ProMaxx heads and Comp Cam are performance upgrades requiring an aftermarket intake that can effectively supply the increased airflow. The stock intake likely chokes the engine, preventing it from reaching its potential power.
Diagnosing the Problem
1. Intake Manifold Restriction:
Your current issue points to the stock intake being a major bottleneck. The ProMaxx 9175 heads offer significantly better airflow than stock, and the Comp Cams camshaft is designed for a broad operating range with a very rough idle, indicating it's meant to work with a performance intake.
2. Improper Match:
You have a performance cam and heads but a stock intake. This mismatch means the engine can't breathe enough to utilize the cam's potential, leading to low power.
3. Camshaft Specs:
The Comp Cam 35-349-8 is an Xtreme Energy camshaft with a significant overlap and a duration designed to work well in the 1,200-6,000 RPM range.
4. ProMaxx Heads:
The ProMaxx 9175 heads provide increased airflow and should be paired with components that allow them to operate efficiently.
Solutions
1. Upgrade the Intake:
Replace the stock intake manifold with a suitable aftermarket performance intake designed for a 351W and that also provides better air delivery for your cam and heads.
2. Ensure Proper Piston-to-Valve Clearance:
Double-check that there is adequate valve clearance, especially when using an aftermarket cam and cylinder heads.
3. Fuel and Exhaust Systems:
Consider whether your fuel delivery and exhaust systems are adequate for the increased airflow from the cam and heads.
Why you set timing to 13*?
it should be 10. Period.
Because with an aftermarket cam with different (bigger) specs to a stock cam you typically need more initial timing. A weaker vacuum signal Because of overlap can cause low idle vacuum, youbadd base timing to bring it back up. And that is just for idle, usually you can also get away with more timing through the whole curve.
But basically, with an aftermarket cam, base factory specs for anything is now wrong. Timing, MAP sensor readings, hell certain cams willneven change what a gauge will show for cranking compression.
Because with an aftermarket cam with different (bigger) specs to a stock cam you typically need more initial timing. A weaker vacuum signal Because of overlap can cause low idle vacuum, your base timing to bring it back up. And that is just for idle,
That doesn't make sense to me. That may be a work around to get the engine to idle, but at higher RPMs and with bigger loads, the computer is just now confused.
The computer thinks its at 10*, and will use all its fueling, torque, timing, load tables, etc. based on 10*, nothing else.
When I put my cam in 112 lobe seperation(not 114), sure the idle wasn't great, but that had nothing to with timing,
It had everything to do with idle air, right? its at idle, adjust the air, not the timing.
Adjusting the timing at idle sounds like a work around that fixes idle issues, and as this thread shows introduces other issues, like low power at RPM.
If it is a fuel restriction, im under the impression the larger injectors would increase fuel regardless of tune. The computer has no way of knowing the injectors are larger but between the speed density system and O2 sensors it should balance AF ratio.
The limitation with these SD computers is it only makes fueling adjustments in closed loop and that only occurs at relatively light loads and part throttle, at anything beyond that it relies on pre programmed maps that are built for the stock motor. Your engine does need bigger injectors but it doesn't need more fuel across the board it needs lots more at higher rpms and loads but almost no extra at idle, so if you were to graph it the two lines would start at the same place at idle(650rpm) and get further and further apart as they rise towards peak engine output at probably 5500rpm. So simply plugging in injectors that flow 20% more for example would make the engine pig rich everywhere except WOT.
Because with an aftermarket cam with different (bigger) specs to a stock cam you typically need more initial timing. A weaker vacuum signal Because of overlap can cause low idle vacuum, you add base timing to bring it back up.
That was the common solution back in the carb days, the increased overlap of the cam tends to make the idle mixture leaner and adding base timing will raise engine rpm and stabilize it. Adding more fuel helps too, the problem with carbs on a V8 is they don't distribute fuel perfectly even to all cylinders, the inner 4 can be slightly rich while the outer 4 are slightly lean so it'll never work as well as a multi point EFI system(1 injector per cyl), this is also the reason I would never suggest using a throttle body style EFI setup, there isn't enough benefit over just using a carb.
With a relatively mild EFI cam like this one simply adding a little more fuel at idle has the same effect, that has negative effects on emissions but that is the tradeoff.The mass air version does a better job with this even without tuning but with access to tuning it's easy to adjust idle fueling to make it stable at the factory rpm, this is especially important for auto transmissions with a factory TC as it begins to load up at as low as 800rpm which makes the vehicle want to crawl away with even a slightly higher than stock idle speed.
I had already found it. That is where I found the answer to your “which heads?” question.
Originally Posted by wwhite
That doesn't make sense to me. That may be a work around to get the engine to idle, but at higher RPMs and with bigger loads, the computer is just now confused.
The computer thinks its at 10*, and will use all its fueling, torque, timing, load tables, etc. based on 10*, nothing else.
When I put my cam in 112 lobe seperation(not 114), sure the idle wasn't great, but that had nothing to with timing,
It had everything to do with idle air, right? its at idle, adjust the air, not the timing.
Adjusting the timing at idle sounds like a work around that fixes idle issues, and as this thread shows introduces other issues, like low power at RPM.
The computer isn’t confused. It doesn’t know what the base timing is set at. There are a lot of threads in different car and truck forums about bumping the base timing from 10°.
How are you adjusting the air on your EFI engine with the stock computer without a tuner? Are you adjusting the throttle stop screw? You can’t really do that since it also changes the TPS voltages.
It doesn’t know what the base timing is set at. There are a lot of threads in different car and truck forums about bumping the base timing from 10°.
No, your right, it does not.
It calculates advance assuming base timing IS 10*, in closed loop and at part throttle.
Open loop, idle and WOT, it assumes base timing IS 10*, and uses predefined fixed data, other wise known as the 'tables'.
So, by setting base timing to 13, when your engine RPM is increased, the computer is really thinking its at 10, and wont be supplying the correct spark advance and or air/fuel that the engine needs.
Originally Posted by My4Fordtrucks
How are you adjusting the air on your EFI engine with the stock computer without a tuner?
With the factory ford part# F2PZ-9F939-A.
Ford TSB: 91-25-7
Originally Posted by My4Fordtrucks
Are you adjusting the throttle stop screw? You can’t really do that since it also changes the TPS voltages.
No, that is to set your TPS to be <1.0 volts, like 0.95v.
Also, it stops the throttle blades from being 'stuck' in the bores.
Just like with timing set at 10*, why would you or not increase the TPS to more than 1.0V........because the ECU assumes these things.
Without any tuner, those settings should be set to factory.
In any event, i'm just a diy'er that may have incorrect information, I'm not Henry.
I can see mine idle leaner, at 13*, than at 10*, it gives a more complete burn, and @ 10* A/F hangs around 11.5-12.8 A/F, and @ 13* A/F hangs around at 12.8-13.6 A/F, at red lights, now my mpg has gone from 11-12.5ish, to 13.7-14.4ish, same 7 miles and 6 red lights to work and back.
Every engine has its own personal preferences.
If no knock, stumble, or codes are present, and your temps stay in range, then that seems good for your setup.
If you had issues, like the OP has, I'd be tempted to set things to factory, and go from there.
Validating what the actual A/F is, rather than guessing is a recommended starting point.
No, your right, it does not.
It calculates advance assuming base timing IS 10*, in closed loop and at part throttle.
Open loop, idle and WOT, it assumes base timing IS 10*, and uses predefined fixed data, other wise known as the 'tables'.
So, by setting base timing to 13, when your engine RPM is increased, the computer is really thinking its at 10, and wont be supplying the correct spark advance and or air/fuel that the engine needs.
With the factory ford part# F2PZ-9F939-A.
Ford TSB: 91-25-7
No, that is to set your TPS to be <1.0 volts, like 0.95v.
Also, it stops the throttle blades from being 'stuck' in the bores.
Just like with timing set at 10*, why would you or not increase the TPS to more than 1.0V........because the ECU assumes these things.
Without any tuner, those settings should be set to factory.
In any event, i'm just a diy'er that may have incorrect information, I'm not Henry.
Even at idle the computer is constantly adjusting the timing which you can watch with a timing light. The computer adds more timing and if it is too much it backs it off so it does not use a “fixed” setting of a x rpm and load is going to be y degrees of timing. You determined air with your foot and the computer is using various sensors to add or reduce the injector duty cycle.
You introduced a new part to the equation. That kit was not designed for that purpose and would only be effective with the throttle closed.
If I remember correctly, Mustang guys used that to fix rolling idle issues.
Wrong. The only purpose of that screw is to keep the butterflies from closing too far. Nowhere in the manual does it say to adjust the stop screw
Thanks for proving my point that you cannot adjust the throttle stop screw because it changes the TPS voltage. I can and had to adjust the screw for the engine to idle but I can also recalibrate my TPS.
