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Discussion Starter · #1 ·
I'm having an issue where my engine under load wot won't spin over 4400rpm. It's done this with two different cams. (The first cam had some lobes that were starting to go flat ) I've messed with the carb and ignition timing with no change. I'm running a efi converted to carb 460 (not ideal but it's what I had), .030 over, 9.3:1 cr, high volume ford racing oil pump, comp cam 34-235-4 w/ matching springs, comp roller rockers, minor port and Polish on heads, intake has been opened up, holley 750 w/ vac secondaries, and full msd setup( 6a box, billet diz w/ vac adv, large rotor cap, and plug wires). Not sure where to look next. Any ideas would be greatly appreciated.
 

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That combo should pull like a freight train to 5K rpm.

Spring number?
Installed height?

Total ignition timing?

Fuel pump type?




S
 

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Discussion Starter · #3 ·
It was the springs for the cam and installed to specs. Holley red fuel pump. Timing was at 16 base with 37 total at 3500. Now at 12 base with 33 total at 2800 (did the same thing at both settings). I'm at about 12:1 a/f ratio at wot.
 

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Are you sure the secondaries are opening? Sounds like you're going flat because your primaries are done by 4,500 rpm.
 

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Discussion Starter · #5 ·
I put a softer spring in and could feel a secondary bog when they opened. Also my a/f guage is letting me know they are. Could it be ignition? What gap on the plugs is recommended? They're at .050 now. Could it be the pickup in the diz? Manifold vac drops to 0 at wot. Low idle, 700 rpm is at 9" and high idle, 850 rpm is at 13". Cruise at 1500 rpm is 16" and at 2500 is 9". Not sure if the vac readings help. They don't seem right to me.
 

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Get in a right place, duplicate the conditions where the engine falls off, and immediately shut the engine and fuel pump off. Then see if there is gas in the float bowls.
 

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I had this problem when I ran an Edelbrock 750 on mine, as did my dad on his 429. It wouldn't pull over 4500RPM no matter what. I put a Holley 750 Double Pumper on there, never had a problem since. Maybe that carb is choking it?
 

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I put a softer spring in and could feel a secondary bog when they opened. Also my a/f guage is letting me know they are. Could it be ignition? What gap on the plugs is recommended? They're at .050 now. Could it be the pickup in the diz? Manifold vac drops to 0 at wot. Low idle, 700 rpm is at 9" and high idle, 850 rpm is at 13". Cruise at 1500 rpm is 16" and at 2500 is 9". Not sure if the vac readings help. They don't seem right to me.
That cam should be making a lot more vacuum than 9" at idle. Did you degree the cam when you installed it?

Have you verified TDC on the balancer?

Check for vacuum leaks?
 

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Discussion Starter · #9 ·
I have a holley 750 on the engine. I could try the other holley 750 that I have. Maybe there is a problem with my carb.
I did degree the cam and the balancer is brand new and dead on zero at TDC. I agree the vac at idle is low but haven't found any vac leaks. I haven't checked my pcv valve. I know that wouldn't cause my issue but might explain my low vac at idle. I'll be working on it today.
 

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Which EFI intake adapter are you using?

Price Motorsports has their 4 hole 1 5/8" throttle bore unit which I found caused our EFI crate engines to pull too much WOT vacuum during dyno pulls.

I designed a HP adapter that eliminates that issue. 1.75" bores on the deep side of the intake and a large oval on the shallow side for an equalizing effect. PCM makes it for me.


Find out what valve springs you have and what the installed height is.

Check and double check everything.

Color of spring in secondary dashpot?
Fuel pressure at WOT


Yes I noted your 12.0 AF at WOT and no vacuum at WOT. There is ALWAYS VACUUM at WOT. 1.5" or less is preferable. Most of our stuff runs 1.2 to 1.3"



S
 

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Discussion Starter · #11 ·
The adapter was one that I made. It's an open style and I'm running a 1" hvh super sucker carb spacer. The same setup I have been using for years before the rebuild.

I checked the springs twice when I installed them but I will check them again.

The secondary spring is the stiffer of the 2 yellow springs. I had the purple spring in before with the same issue.

I haven't checked the fuel pressure at wot yet. I had this problem before I installed the holley pump. My fuel pressure Reg is about 7 years old and it did sit for a few years when I was rebuilding everything.
 

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The adapter was one that I made. It's an open style and I'm running a 1" hvh super sucker carb spacer. The same setup I have been using for years before the rebuild.

I checked the springs twice when I installed them but I will check them again.

The secondary spring is the stiffer of the 2 yellow springs. I had the purple spring in before with the same issue.

I haven't checked the fuel pressure at wot yet. I had this problem before I installed the holley pump. My fuel pressure Reg is about 7 years old and it did sit for a few years when I was rebuilding everything.

Is your fuel pressure regulator a dead head style or bypass?

Dead head units can sometime be restrictive.



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Discussion Starter · #13 ·
It's a holley and a dead head style. It's coming out. The holley red pumps are internally regulated at 7 psi. So I'm going to run without it and see what happens.
 

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Discussion Starter · #14 ·
I found some passages in the metering blocks that were causing my vac problem and some cruise issues. My issue is more noticeable and starts earlier in the rpm but it will turn past 4400 rpm now. It's making a popping or cackling noise out of the exhaust from 4200 rpm and up and gets really bad around 4400 rpm and up.
 

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It is not a surprise that the additional regulator was the culprit.

Do you have a known good carburetor to switch out?



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Discussion Starter · #16 ·
It was the metering block that was causing some of it. Just check my spring installed height and I have a few that are at 1.9" and the springs should be at 1.8". Is this enough to cause valve float?
 

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It was the metering block that was causing some of it. Just check my spring installed height and I have a few that are at 1.9" and the springs should be at 1.8". Is this enough to cause valve float?
Yup especially on the intake side. Loss of valve train control and loss of power comes on long before audible valve float / bounce or lifter pump up.



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Discussion Starter · #18 ·
Ok I'm ordering shims tonight. I don't know how I missed that. I'm kinda glad this happened. I found a few other issues that I may not have noticed otherwise. Thank you for all your help.
 
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