Something's missing (SOLVED)

[chargd72]

Been tinkering around with the truck a lot lately but it feels like a lot of power is left on the table.  Here's what I'm woking with:  76 W200, 400/727 auto, Eddy 600 4bbl carb, weiand manifold, headers, 4.10 rear, 33 inch tires and the rest is stock.  The truck seems to be running great.  Engine pulls strong but tops out with low RPMs.  I can get the truck to about 60mph just under 2500 rpm.  I don't need more but it feels like it should climb a little higher.   Any ideas?

[greenpigs]

Clogged fuel filter or weak fuel pump?

Check the fuel pressure under load which should be about 5 PSI or so for a stock fuel pump.

[doctor4766]

Been tinkering around with the truck a lot lately but it feels like a lot of power is left on the table.  Here's what I'm woking with:  76 W200, 400/727 auto, Eddy 600 4bbl carb, weiand manifold, headers, 4.10 rear, 33 inch tires and the rest is stock.  The truck seems to be running great.  Engine pulls strong but tops out with low RPMs.  I can get the truck to about 60mph just under 2500 rpm.  I don't need more but it feels like it should climb a little higher.   Any ideas?

Yeah my Charger's the same.
I've heard that the big blocks should easily rev out past 5-6000rpm but my rebuilt 383 feels/sounds like it doesn't really want to go past 3000. That's with a 727/3.23 combo.
I'll be interested to see what you come up with here.
Sits on 2400 or so at 100kmh (around 60mph)

[chargd72]

Clogged fuel filter or weak fuel pump?

Check the fuel pressure under load which should be about 5 PSI or so for a stock fuel pump.

Good starting point. Brand new fuel filter so I'll check the pump. It's an electronic pump that seems fine but never been measured.

[chargd72]

Ok, installed a fuel pressure gauge. With pump running and engine off I get 5 psi.  With engine at idle I get 4 psi. With a good rev it drops to 3 psi. Is this typical? I'm using 3/8 fuel line.

[mauve66]

big block should ALWAYS be capable of 5200-5500 rpm, stock lifters will float past that though

[greenpigs]

That sounds low to me. You should have a minimum of 5 PSI throughout the rpm range,so I would try and fix that first.
What kind of pump are you running & how is it set up? Your not pulling the gas out of the tank instead of it being gravity feed I hope.

[chargd72]

It is pulling from the top of the tank because that's the stock setup. How would I make it a gravity feed without buying a new tank?

Also, is 3/8 line a good size?

[FLG]

Check your filter first, might just be clogged. (nevermind, just read that its new)  If that dosnt make a difference id check the fuel pump and the fuel pump pushrod (should be 3.25" long)

I have your address, dont buy a fuel pump...ive got a new spare one for my 400 that i no longer have so...its yours. Double check the pushrod size when you change the pump.

[chargd72]

Frank, once again I appreciate your generosity. But I think you missed that I'm running an electric fuel pump. The mechanical pump has been blocked off. Thanks for the offer though man. 

[morepower]

Your not running a regulator? If you have an adjustable regulator adjust it. You say the motor doesnt wanna go anymore? so if you floor it it just bogs down? pull out your plugs and see if they look like they've been running lean or something.

[chargd72]

Your not running a regulator? If you have an adjustable regulator adjust it. You say the motor doesnt wanna go anymore? so if you floor it it just bogs down? pull out your plugs and see if they look like they've been running lean or something.

Nope, no regulator.  It doesn't bog down when I floor it.  It has good launch but it feels like it just runs out of top end when it gets going.  It's kind of like what doctor4766.  It's just not wanting to rev higher.  If I put the truck in nuetral and hit the gas I only feel safe going to about 3500 rpm.  If I go above that, it feels like something is going to give.  Almost like that's red lining it.

[greenpigs]

I think you should get constant fuel pressure throughout the RPM range of 5 PSI as a start.

[torqueflite]

cam timeing ??

[greenpigs]

Are you sure the carb is opening 100% at the motor & also depressing the gas pedal?

This may be a strech but it is free & one less thing it could be.

[chargd72]

Are you sure the carb is opening 100% at the motor & also depressing the gas pedal?

This may be a strech but it is free & one less thing it could be.

Yessir, That was one of the first things I checked.  You said before to get my fuel pressure to a constant 5psi.  Is a 3/8 fuel line big enough to support that?

cam timeing ??

That's one thing I can't comment on.  Aside from the obvious bolt ons, I couldn't tell you about the engine's mods.

[greenpigs]

3/8 is what the 440 & HEMIS had so it should be fine for you. 

Hmm are you sure there are no kinks in the line as it is new correct?

[heyoldguy]

Your not running a regulator? If you have an adjustable regulator adjust it. You say the motor doesnt wanna go anymore? so if you floor it it just bogs down? pull out your plugs and see if they look like they've been running lean or something.

Nope, no regulator.  It doesn't bog down when I floor it.  It has good launch but it feels like it just runs out of top end when it gets going.  It's kind of like what doctor4766.  It's just not wanting to rev higher.  If I put the truck in nuetral and hit the gas I only feel safe going to about 3500 rpm.  If I go above that, it feels like something is going to give.  Almost like that's red lining it.

"it feels like something is going to give." What do you mean?

Have you done a compression test? A leakdown test? We're talking about a 35 year old 400 here. It could just be worn out.

[chargd72]

3/8 is what the 440 & HEMIS had so it should be fine for you. 

Hmm are you sure there are no kinks in the line as it is new correct?

Yep, put the new line in myself with nice smooth curves.  I think heyoldguy is on the right track.  It's most likely just a tired engine.  Did a compression test a while ago and everything was good and I don't get any color in my exhaust but like I said earlier, I have no idea what the history is behind it.  When the Charger is drivable I plan on pulling the engine anyway so as long as I can drive it around in the meantime, that's acceptable.  Thanks for the help, guys.

[FLG]

Ah missed that too lool


I think its a fuel problem...3psi is very low and I agree with gp you should se a consistent fuel pressure. I had a tired 400 that I would regurarly wind up to 5500...she didn't have much power but she went just fine

[Chryco Psycho]

the carb is definatly on the small size , you need 2 x the CI so 750 minimum .I can highly recommend a race series 750 Proform from Mancini racing [they have the lowest price I have found ]

[chargd72]

Thanks for the suggestion. I'm going to look into getting a better fuel pump first. I got to make sure I can properly feed the Carb before I can beef that up.

[heyoldguy]

Just another thought. How much slack do you have in the timing chain? Have you put a socket on the crank bolt and tried to rock the crank back and forth? If there is a lot of slack you could have slipped a tooth and the cam is now retarded some 15 degrees. Not much power under those circumstances. One indication this may have happened, is if in the recent past, you had to advance your ignition timing to get the truck to run right.

[Paul G]

If your running an electric fuel pump I would double check it's output. You could take the fuel line off the carb and run it in to a jug to see if it is putting out enough fuel, as per it's rating. I have removed Holley electric pumps on two of my cars because they went bad, and gone back to mechanical pumps. Mech pumps are quieter, more reliable, and last longer. Just something else to check.   

[chargd72]

Fuel pump it is.  Put in a new one last night that delivers a good steady 7psi and    Haven't got it on the highway yet to see what it's top end feels like but driving around town it's making much more use out of it's RPMs.  There's still room for improvement but it'll do until it's time for a full rebuild. Thanks for the help, fellas.

[idahogrumpy]

I know you said that you found the problem however, what size exhaust do you have? I have had problems with inferior ( CHEAP ) mufflers causing to much back pressure and not allowing the engine not to accelerate correctly.

Grumpy