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Discussion Starter #1
Anyone else ever feel like your car pulls harder at part throttle than full throttle? Mine sure does, at least the initial hit when it puts you back in the seat. Perhaps it's just too much air for the load/speed im going, but it's almost always felt like this.

Of course I am not talking smashing the gas and roasting the tires.
 

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Anyone else ever feel like your car pulls harder at part throttle than full throttle? Mine sure does, at least the initial hit when it puts you back in the seat. Perhaps it's just too much air for the load/speed im going, but it's almost always felt like this.

Of course I am not talking smashing the gas and roasting the tires.

Timing? Perhaps the centrifugal advance is not what it should/could be. As the engine's rpms rise, and is loosing vacuum, the vacuum advance drops off (duh :)). If there's not sufficient centrifugal advance at those rpms, a 'lag' may be noticed.

There's no adjustment, just tinkering with different springs and weights.

'Ignition 101' sticky in the ignition section may be useful.

Pete
 

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The only time I have had that problem was with a Q-jet'ed BBC and it was a lean problem. We never could figure that carb out so we put another Q-jet on the car and that lean type feeling at WOT was gone. I always suspected that the 1st carb had an obstructed fuel path in the secondary side.
 

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Discussion Starter #5
I have EFI with timing control. AFR's and Timing seem okay according to the logs. I did a lot of tuning to get the AFR's right.

I don't know if it's something with the port velocity or some sort of turbulence in the intake.

I don't have any data to go with, just a seat of the pants. Yesterday I went for a cruise and 1st gear from a slow roll and it put me back in my seat hard with about 1/2 throttle or so. Same conditions at WOT and it didn't feel as fast.
 

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Only two things come to my mind. First your are too rich and going below 12 to 1 AFR or something in your throttle is out of wack. Not being aware of your EFI can it be pushed to a point that the plates close and restrict air flow. Does it have a choke plate or is it handled electronically and if it has a plate is it closing under full throttle. I seriously doubt it is in the engine itself.
 

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Discussion Starter #7
FiTech EFI

One theory I have is that maybe because my "primary" and "secondary" butterflies open the same amount regardless of throttle position that maybe when i hit WOT it's such a large gulp of air that maybe the engine can't process it? I have tuned the fuel to have a decent AFR for that, but could that volume of air from say 2500 rpm stall out in the intake track?
 

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FiTech EFI

One theory I have is that maybe because my "primary" and "secondary" butterflies open the same amount regardless of throttle position that maybe when i hit WOT it's such a large gulp of air that maybe the engine can't process it? I have tuned the fuel to have a decent AFR for that, but could that volume of air from say 2500 rpm stall out in the intake track?
You would have a substantial bog right off the bat if that is the case. How rich does your AFR get?
 

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I've had the rich bog with the EFI. I tuned that out.

The feeling isn't a bog or stumble, it just feels slow.
You really don’t get a rich bog you lose power. My Roush 427r was making about 390rwhp at 12 pounds boost. My AF was close to 10.5 to 1 but keep in mind a boosted engine needs more fuel to keep things cool but not at that AF. It was changed to 12 AFR at full boost and my max power went to 436wrhp. Not bad for a 4.6 liter engine. Does your EFI provide a data log showing your critical specs?
 

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In this video you can see how I tuned the fuel tables and leaned it out a bunch.


I may have to do some datalogging for part throttle vs full throttle.
Were you tuning for numbers or giving the engine what it wanted?
 

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Discussion Starter #18
Were you tuning for numbers or giving the engine what it wanted?
I've been on the dyno and it liked the mid 12's AFR. Doesn't mean it couldn't be perfected, but I'd need hours on a controlled dyno setting to do it. I know for sure it hated the 10.5:1 as it bogged down hard, I was mainly tuning that out which I managed to do.
 

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dual plane
Change it to a good single plane intake and try it. No need for that with EFI, dual plane intakes just have inherent mixture distribution problems.
 

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Discussion Starter #20
Change it to a good single plane intake and try it. No need for that with EFI, dual plane intakes just have inherent mixture distribution problems.
TBI EFI's act the same way as a carb would since the fuel comes above the butterflies. Also I recall it feeling the same way with the carb too.

When it warms up I'll do some testing/data logs and see if there is anything noticeable going on.
 
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