390 build -What have I done wrong

[Aussie Rob]

Hi everyone, been really ill and haven't been involved for a while but good now apart from results of engine build.
 It's a .060  block 10.5 compression with the oiling mods that are recommended, Edelbrock heads and perfomer rpm intake cleaned up faced and portmatched, Harland Sharp  rollers ,FPA longtube headers, Comp hydraulic roller  232 and 237 @50 , 524 and 535 lift, 106
degree centre line and 110 separation, 780 vac sec holley. Have been on  a chassis dyno and can't produce any horse power over 4500 rpm. Torque starts at 1800 and peaks at 3400 then holds through to 4200 before starting to slide off. HP is a pretty flat curve from 3300 and  peaks at 300 rwhp at 4250 then starts to die off and it's all over by 4900. The ignition is Msd distributor 6al box ,18 initial - 37 total all in by 2800. Have played with curve and initial combinations and this works best, have also double checked degreeing of cam
Exhaust is twin 2.5'' from headers to x pipe high flow mufflers over diff to rear. I really expected this combo to produce to at least high 5's or 6000. Comp states this cam should be good till then I'm a little frustrated .Where have I gone wrong.

[jayb]

You may just need some carb tuning, its possible that your secondaries aren't opening enough, or at all.  Try tying a small tie wrap around the secondary actuator rod, coming out of the vacuum diaphram housing.  Slide it all the way up to the top against the housing, then go out and get on it a little, and come back and check it.  If the secondaries are opening it will have slid down on the rod quite a bit.

On your chassis dyno session did you get air/fuel numbers?  If so, what did they look like?

I think your peak horsepower RPM ought to be around 5500 with that combination.

[Aussie Rob]

Thanks for the reply Jay, Ihave checked the secondary opening and it's fine, af ratio 12.2 beginning at 2000rpm with it being 12.9 at peak power @4200, I thought this is probably ok. MY tach and dyno  are within 50 rpm and a seat of the pants drive gives the same result, no point going past 4900. Is it possible that it just needs more cfm in as I'm sure that exhaust is big enough for that combo.

[gtxpress]

i have pretty much the same combo except I have a 750 DP.  It starts out at around 12.7 and at WOT is around 14.7.  It pulls about 375 @ 5K and still is pulling although it is over at 5500.  I will ask about the springs.  are they correct and shimmed to the right height? 

GT

[drdano]

Fuel system details?

[Aussie Rob]

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.

[Faron]

What do you have the Rev Limiter set to ? , also try it without a limit or change it to a higher setting

[drdano]

The fuel system is standard lines with high volume holley pump

That was the same reason my 428 wouldn't run over 4500rpm at the drag strip...could be your problem.  What diameter are those standard lines?  3/8"?  5/16"?  Simple test would be to bypass the tank on the dyno, go to an external tank with larger line.  Bring a fire extinguisher...

[427Fastback]

Hey...you say its a 780 Holley so I am going to guess its a 3310.The first generation of 3310's have secondary metering blocks and after that they just have metering plates and are sold as 750's...Do you have a secondary metering block or plate..

That being said if it doesn't rev past 4900 in any gear I would suspect something else.....Cory

The rev limiter crossed my mind as well and I see two people suggested it while I was two finger typing

[Aussie Rob]

Sorry ,I probably didn't explain that properly it will continue to rev past 4900, It's just that the power drops off dramatically and you are going nowhere. The rev limiter is set at 6200( won't need that the way I'm going). Pretty sure fuel lines are 5/16. The carb is a 770 street avenger and did experiment with p/valves and jets on the dyno ,also used a 750dp and ended up with slightly lower readings all in the same rpm range. I have also made sure that msd supply is actual battery voltage and not ballasted.
                                                                                                                                                     thanks rob

[fastback 427]

My money is on the fuel system. 5/16 is marginal at best. Which holley pump? It needs a holley black minimum. Also check the fuel line pickup for clogs. What fuel filter? I put my fairlane on a chassis roll two years ago. It had 486 tq at 3000 rpm and 276 HP at 3600. It fell steadily from there. After two pulls with the same result I watched the fuel pressure gauge bounce all over hell at 3500 rpm. Took the car home and found the filter was so plugged you could hardly blow through it. Oops! I upgraded to 1/2" line and black pump, but have not had it back to the dyno yet.

[Aussie Rob]

That sure looks like something I'll have to seriously investigate. That pump is supposed to 110 gph but I don't have a pressure gauge, I just assumed that if the sight bowls showed fuel during the run then there was adequate supply.
                                                                                                                                     Thanks Rob.

[Lenz]

I'd look at installing a pressure gage to help troubleshoot the problem and it's a bonus down the road any time you hunt trouble or just need the info. 

A quick inspection of the fuel system for restrictions, dents or bad hoses seems in order also.  Since you're on a chassis dyno I'll assume the gas cap is on and locked down during your pulls, might want to make sure it's venting properly.

I'll follow up with a +1 on the lines, 5/16" can be even less at the bends or where couplers may have been installed over the years and likely isn't enough to get you where you want to be.

All the previous info you've got above is good stuff, so you have plenty to look at.  Bet these guys don't quit 'till you get it sorted out.

[Barry_R]

If those fuel lines are original look for a pinhole on the suction side of the system - between the tank and the pump.  It'll KILL flow...

[machoneman]

Replace all the rubber between the fuel lines too....although if you do have 5/16ths steel lines I agree they should be a least 3/8ths...and the requisite new rubber of course to the new lines. Be sure too that the tank is properly vented, a vented cap or on some old Fords a separate steel vent that exits under the car. Do not assume a replacement vented cap is actually venting since I've seen the gasket totally block the cap's vent hole, essentially making it non-vented!     

Cheap and easy test: remove the cap and duct tape the filler tube closed. Poke a 1/8th" hole near the top of the tape. Make a run and see what happens.

On edit: If you do replace the lines, inspect the OEM Ford sender assm. as the line that goes thought the disc is also a 5/16ths steel tube. Get a OEM sender with a 3/8ths tube or break out the old one and braze/weld in in a new 3/8ths tube. Dump as well the metal mesh OEM Ford filter sock at the end of the tube and let the engine bay side and/or carb filters handle any crud.