383/496 stroker bogging on highway

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Matt DeCicco

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Ok so here's the deal,
I have a newly built 496 stroker. Has aluminium head, hydraulic roller, mp performance ignition, 11.5:1, Holley blue pump set to 6.5psi, holley 750 mechanical. The car is a 4 speed. Timing set to about 13°, about 8 HG vac, floats adjusted, acc pump adjusted, 6.5 PV (have smaller coming).

The car goes like hell 1,2,3 shift right up to 5,500. Once I hit 4 it starts to bog/ cut out like it's running out of fuel. If I cruise up to 4th on highway, as soon as I get over 3,000 rpm it does it again. When it happens I have to put the clutch in and feather it to get it back to normal, it takes a few seconds and backfires through exhaust a little bit, sometimes it stalls.

I had the car running decent and this issue was not present, but I noticed the throttle cable wasn't opening fully so I adjusted it and got a lot more power but now have this issue! I'm not sure if it's timing related, maybe need to adjust vac advance or spring in distributor? It's strange that it's only in 4th over 3k. Thanks for the help!
 
You think carb itself? Or to the carb? I have 6.5 psi to the carb. What's strange is it's only an issue in 4th. My gauge is under the hood so not sure what the pressure is driving.
 
Just a from personal experience note...
On my stroker 1 to 2 on the streets was a beast.
On the 1/4 mile running flat out my carb ran out of fuel by the 1/8 mile.
By the time I hit the return lane it would jump back to life.
Mine is very thirsty
 
The vacuum seems low for a 496 with a hydraulic roller and that static compression. What are the cam specs?
It may be a volume-note-due-to-the-pump issue. The owner of the 496 I did has a much larger carb and automatic, it makes about 580hp, and it's being fed by a stock appearing Carter mechanical pump but using a 3/8 line and sender.
Some things to look at: from tank sender to carb needs to be 3/8" diameter (or -10); the MP ignition has the right centrifugal curve and that the module is grounded well; and if it's an orange module I'd toss it in favor of a Standard Ignition LX-101or the MP chrome box.
Lastly - you really need a larger carb. There is a problem with "too small" of a carb and that is they get very hard to tune well because you're using it outside the expected performance window of the manufacturer. It's not that it won't work, but it needs a lot of adjustment that may or may not be easily done (air bleeds, etc). So I'd suggest you get a carb on there that will work better. That 496 I mentioned gained about 25hp with a larger carb on the chassis dyno, and gets 13mpg on the highway.
 
Fuel system is 3/8 from tank to blue pump mounted on frame connector under passenger floor, canister type filter under the hood with 6 micron filter. Cam is lunati .565 in, .570 ex, 251/255 duration. Line has 3-90°, 2-45°, and a distribution block where the gauge is that makes a 90.
 
Last edited:
Matt DeCicco said:
Fuel system is 3/8 from tank to blue pump mounted on frame connector under passenger floor, canister type filter under the hood with 6 micron filter. Cam is lunati .565 in, .570 ex, 251/255 duration. The fuel system has 3-90°, 2-45, and a distribution block at the pressure gauge that makes a 90.
Click to expand...
 
Not the best but should be adequate, carb is a bit small but will still work fine, I think the initial timing is a little low, where is the timing at full advance?
 
have tried running the car up until it cuts out, kill the motor and roll to a stop in neutral and see if you have fuel in the bowls?
 
Matt DeCicco said:
Gonna give that a shot, didn't think of that.
Click to expand...
Did you figure out your issue with the bogging?..Mine did that and my fuel pump was bad even though my gauge said it was putting out the right amount of fuel.After replacing the old fuel pump it stop bogging.
 
Matt DeCicco said:
Ok so here's the deal,
I have a newly built 496 stroker. Has aluminium head, hydraulic roller, mp performance ignition, 11.5:1, Holley blue pump set to 6.5psi, holley 750 mechanical. The car is a 4 speed. Timing set to about 13°, about 8 HG vac, floats adjusted, acc pump adjusted, 6.5 PV (have smaller coming).

The car goes like hell 1,2,3 shift right up to 5,500. Once I hit 4 it starts to bog/ cut out like it's running out of fuel. If I cruise up to 4th on highway, as soon as I get over 3,000 rpm it does it again. When it happens I have to put the clutch in and feather it to get it back to normal, it takes a few seconds and backfires through exhaust a little bit, sometimes it stalls.

I had the car running decent and this issue was not present, but I noticed the throttle cable wasn't opening fully so I adjusted it and got a lot more power but now have this issue! I'm not sure if it's timing related, maybe need to adjust vac advance or spring in distributor? It's strange that it's only in 4th over 3k. Thanks for the help!
Click to expand...


FWIW (I realize this is a fairly old thread) do not set power valve opening by looking at idle vacuum. You need to set PV opening by cruise vacuum. Whatever cruise vacuum is, go 2 points lower. I have about 8 inches of vacuum at idle and I run a 10.5 PV. That's because I have about 14-15 inches of vacuum at a cruise.


If you do it correctly, you can size the t slot much smaller and not have tip in issues.
 
yellow rose said:
FWIW (I realize this is a fairly old thread) do not set power valve opening by looking at idle vacuum. You need to set PV opening by cruise vacuum. Whatever cruise vacuum is, go 2 points lower. I have about 8 inches of vacuum at idle and I run a 10.5 PV. That's because I have about 14-15 inches of vacuum at a cruise.


If you do it correctly, you can size the t slot much smaller and not have tip in issues.
Click to expand...
Okay that is good info to know..I run a 1050 Dominator and blocked off where my power valve .
 
13 initial is the first issue IMO.

A 6 micron filter, that's tight for a fuel system. Most don't run anything less than a 10. I'd bet the filter may be a restriction.
 
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