[PRO1]

New here today guys - so here goes...
motor is a 540, dart block, dart pro1 325 heads. Mild port work gasket match, blend and clean up. 15 cc dome Wiesco pro-tru forged pistons approx. 10:1, 4.500 bore, 4.250 stroke and 6.535 long rods.
Intake is a Holley Pro Dominator tunnel ram with (2) Holley 650 dp's. It has the 4500 top w/ 2" tall 4150 adapters. Super crisp throttle response.
2 1/8" hooker super comp headers - raced open, w/ 3" pipes slows it down .4 in the 8th.
Cam is a crane solid roller - 272/278 @ .050 w/ .708 lift on 110 lca - roughly .688 net w/ 1.7 rocker. It's street driven a little but not much and don't care about being "rowdy"- love the looks it gets. Problem is it falls flat on its face at 6200-6300. Best 60' foot is 1.38 foot braked and has turned a best of 6.41 @ 108 in the 8th. I know there is more there but can't figure out if its the cam is too small or something else.
Dont get me wrong - its one hell of a ride out of the hole w/ the front end hanging 6-8" in the air. And it pulls like a freight train form the 2000 rpm stage right to the point it falls off. I'd like it to be more "racey" to around 7000 or so and put it down in the 6.0's. So lets see what ya'll think - be nice - i'm an old fart......

 

[Tom Mobley]

probably running out of fuel. what's the fuel pressure at 6300WOT?

 

[PRO1]

I have it set at 9psi @ 2000. Its around 8 when it falls off. I tried a pair 750's recently and they ran the same once I got it off the line. Magnafuel 500 pump w/ -10 line to front of motor. 4 port regulator mntd. @ the front of the intake.
Next time I run it I'm going to try upping the needle and seat size just to see what it does.

 

[Tom Mobley]

if you have 2 carbs you have 4 N/S asemblies. that engine would live fine with a big single 4bbl with 2 N/S. That's not going to be your problem.

does it run rough or have a nasty exhaust note when it flattens out?

what about the exhaust? can you make a run with open headers to see if the exhaust is throttling it? 6 bolts, a little wire, cheap and fast way to eliminate the exhaust.

 

[jeff swisher]

raced open, w/ 3" pipes slows it down .4 in the 8th.

What do you mean by this..did you get there .4 quicker or did it take longer to get there with opened exhaust.

I have had cars that with opened headers the times suffered as did the upper rpm ..When i added 3-4 feet of tubing the cars picked up the power.

Might be some power there.
Could also be valve spring issues.

 

[PRO1]

I've been running it w/ open headers. Through the pipes chokes it down at least .4 in the 1/8. When it flattens out it has what sounds like a flutter. It doesn't pop or sound bad, it just quits pulling.

 

[jeff swisher]

I would add some jet to the carbs..could be simple as going lean on the big end.
Yes i know you tried different carbs..but that does not change the fact that it could still be lean..you just gave it the potential to pull more air...

If you know all the valve springs are good and you have tried different timing settings,, then i would step up the jet size in the secondaries.

a 396 i built a couple years ago had the new edelbrock performer 800cfm carb. .010" more jet in all 4 corners to get it closer to what it needed.

 

[overdriv]

Does your ignition box have a high speed retard???

Do you have enough timing at WOT/6300??

Go up in jet size, both carbs. If it helps, keep going till it hurts the ET/MPH.

 

[PRO1]

Ingintion box is MSD digital 6al. It has a high speed retard but I just went out and double check and its off. Timing is locked out and set at 38 deg. That's where it ran its best run so far. I've checked then plugs religiously after every pass. They look perfect, but I'll try more jet anyway just to eliminate another question. I ran into a similar problem years ago where the motor would just lay down. Wound up being the intake was too small. Put a larger single plane on and it buzzed up like it should. I'm wondering if the Holley Pro Dominator tunnel ram can flow enough air to support a 540 at full song? Any thoughts anyone. Good sugestions so far, keep them coming..

 

[overdriv]

Ingintion box is MSD digital 6al. It has a high speed retard but I just went out and double check and its off. Timing is locked out and set at 38 deg. That's where it ran its best run so far. I've checked then plugs religiously after every pass. They look perfect, but I'll try more jet anyway just to eliminate another question. I ran into a similar problem years ago where the motor would just lay down. Wound up being the intake was too small. Put a larger single plane on and it buzzed up like it should. I'm wondering if the Holley Pro Dominator tunnel ram can flow enough air to support a 540 at full song? Any thoughts anyone. Good sugestions so far, keep them coming..

The old tunnel rams of years past that I was ever around had a very small power band and usually at the higher RPMS. These manifolds lacked low end response.

When you stated the engine has "Super crisp throttle response" made me wonder if it was more of a street ram than a race intake??

The street rams would have smaller ports that would restrict flow at WOT on an engine like yours.

That is my two cents and I'm far from an expert. Hopefully someone with more knowledge of tunnel ram will key in on this part of your discusion.

Do make sure you follow up on what you do to fix your issues.