390 build -What have I done wrong

[jayb]

If the A/F ratio logged on the dyno still looks good at the higher engine speeds, its not going to be the fuel system.  Fuel starvation will show up as a lean condition on an A/F log.  Did the A/F numbers lean out above 4200 RPM?  If they leaned out significantly, say to 14:1 or higher, then I'd agree that the fuel system could be an issue.

[westcoastgalaxie]

Hey Barry, how would one look for a pin hole leak? What about a leak at a flared fitting? I redid mine years ago and used solid line. Problem was I had to make sections and used flared fittings. While they don't weep how could I really check them?

[drdano]

at 4250 then starts to die off and it's all over by 4900

To echo and agree with Jay above, what is the AFR doing in this range?  Still at 12-13?  If it's falling off the chart above 14 or so, I'd say you're running out of fuel.  If not, there is something else going on.

[Aussie Rob]

Thanks for the replies,the a/f ratio stays in the mid to high 12's so I don't think it's running out of fuel either, I just had a look at the plugs and not as clean as I would like to see a bit dark and this car runs perfectly ,great start up ,crisp idle, no flat spots , plenty torque and acceleration. Just hits the wall when you really want to push to the next level so I'm wondering about the rotor phasing etc. There's no scope on this dyno , so I may have to go to another.

[machoneman]

Did you check for WOT? Engine off, have a pal mat the loud pedal and check that those butterflies are straight up....at least the primary side on a vac. secondary carb. 

[Aussie Rob]

Yes mate I checked wot before the first run.

[ToddK]

Assuming your build is as per spec, I'd try changing carb, preferably to a Double pumper. I' Ve never had good luck with the street avengers.

Where are you at Rob? I'm in Perth and can help out if you need.

[Aussie Rob]

Hi Todd, I'm at the Sunshine Coast QLD mate. I tried a750 dp on one run and made 5 hp less , I bet this something so simple that I can't see the forest for the trees. A/F ratio's were simlar , no apparent leaning off. When I get a chance I will install original distributor and see if there are any variations.                 Thanks Rob.

[plovett]

If everything checks out with the fuel system, you might look at the valve springs.  Maybe something is wacky there.  Did you check installed height?   Hydraulic rollers are pretty heavy.  Combined with the FE's high rocker ratio, it could cause some float if the installed valve spring pressure is off.

Just a thought,

paulie

[ScotiaFE]

Air Filter?
Did you do the test with the filter on and off.
Some air cleaners and filters act as rev limiters.

[jayb]

Two good thoughts above.  FYI I have purchased the springs recommended by Comp for at least one FE build where they turned out to be completely inadequate for the Comp cam in the engine.  On the dyno, I can usually tell if there is a spring problem because the graph of the horsepower curve gets unstable.  I assume that this would also be visible on the chassis dyno plot.  Rob, do you have a picture of the horsepower curve from the chassis dyno that you can post?  That would answer a lot of questions, I think.

One other thing to think about is with the chassis dyno, you have the transmission and rear end involved.  Could be a problem there too...

[WConley]

Given that the A/F ratio seems good, I would suspect valve springs as well.   The spark advance curve would be the second place to look.

Best of luck!  You should be pulling hard and clean to 6K with no fuss, given your setup.

[CaptCobrajet]

Your posted spring pressures appear to be light to me.  I would be 150/350 on the mildest of hydraulic rollers.  There is more weight to control......harder to keep that heavy lifter on the cam.  Also, be sure that there was not an error during assembly of the springs......a mistake in the math could have put you a whole bunch lighter than "too light already" just by an honest mistake.

[plovett]

Springs are the comps supplied with the cam kit .I believe they are 135 seat and around 300 on the nose, they replaced the edelbrocks
According to the machine shop they are correct installed height, The fuel system is standard lines with high volume holley pump
                                                                                                                                                                 Thanks Rob.

I didn't even notice the spring pressures on my first read through of this thread.  That sounds very low if it is correct.    i would say 300 lbs open pressure is not enough.  I run over 400 lbs open pressure on my solid flat tappet cam.  Mine is not the usual flat tappet deal, but you get the idea. I'm leaning towards valve springs even more now.

JMO,

paulie

[ScotiaFE]

Might even want to put the Ed springs back on.
They show a bit more K factor.
#5792 Edelbrock #60069,#60079 Non-Rotator 145 lbs. 1.885" 355 lbs. @ .580" 1.460" 1.060" 1.130" #9734 #9612 All Performer
& RPM Cams