470 runs out of steam at 5100 rpm

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1975Scamp

1975Scamp

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Hey Moparians... I have a 470 that has 10.5:1 compression,
Heads are pro comp fully cnc'd 78cc combustion chambers they flowed 340 on intake and 290 exhaust at .600 lift. The valves are edelbrocks 2.200 intake 1.810. These heads are very similar to the Edelbrock Victor heads.
Rocker arms are Harland sharp 1.6 ratio.
Cam is Comp Cam - xe284h
Duration @ .50 is .240/.246
Cam lift with 1.6 rockers is .540/.544
Edelbrock RPM Performer dual plane intake
Holley 950HP race carb.
Mopar electronic ignition with chrome ignition module
Mopar Peformance distributor with welded plate to all in at 2200 with 14 degrees of advanced, no vacuum advance. Initial Timing is at 22 degrees, 36 degrees for Total Timing using 93 octane.
Running 3800-4000 PTC converter with 3:55 gears. 255/60/15 drag radial 27.5 inch tire.
Headers are Schumacher Tri-y's-1 5/8" tubes with 3" cutouts and full exhaust. Considering changing to TTI Step Tube headers!

The motor will run out of steam and just won't pull anymore at about 5100 rpm! Running 13.1 in a quarter, should do way better than that! Wondering if it is the headers that is choking it out or do I need to look at going to MSD or equivalent ignition? Any advise will help, Thanks!
 
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In my experience ( I have had this happen twice ) the problem is either incorrect valve springs for the cam so the valves start to float, or fuel starvation and or vapour lock caused by too small of a pickup or fuel line (or the pick up is clogged). Todays crappy ethanol filled fuels exacerbate this problem.
 
d55dave said:
In my experience ( I have had this happen twice ) the problem is either incorrect valve springs for the cam so the valves start to float, or fuel starvation and or vapour lock caused by too small of a pickup or fuel line (or the pick up is clogged). Todays crappy ethanol filled fuels exacerbate this problem.
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I have confirmed spring pressure and install height with Comp Cam! Both are at there recommendations! I have 3/8 line from fuel tank to carb, regulated to 6.5 lbs! I do not believe it is a fuel problem as I feel no stumble at all, just no more pull out of motor!
 
It sounds like a fuel problem. Check your fuel line for sharp bends (try to avoid 90 degree elbows) Is the pick up tube in the tank 3/8 as well? Double check your float level too. Seems like your car should be running at least mid 12's
 
Well the cam seems a little small to me but I ran a 241/247 hyd flat tappet in my 470 a few years back and it would pull hard to 7000 rpm so the cam is probably close enough to work. I would wager that it is valve train instability but it might be ignition related. I've seen the chrome box just give up at 5000+ rpm before. I've also seen guys who use those ignitions and make power but I've never had a lot of luck with the old Mopar Performance boxes. Maybe borrow a MSD billet distributor and 6 box from someone and see how it works. If that doesn't make any difference then it is probably the valve springs. When you use a hyd lifter in a performance application you have to get everything just right or else the lifter collapses under load and the lift goes away. You need plenty of oil pressure and the correct oil to keep the hyd lifters happy at 6000+ rpm with stiff valve springs.
 
shempthbat said:
It sounds like a fuel problem. Check your fuel line for sharp bends (try to avoid 90 degree elbows) Is the pick up tube in the tank 3/8 as well? Double check your float level too. Seems like your car should be running at least mid 12's
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There is only 1 90 degree bend from the regulator to carb.... 3/8" including tank sending unit! If it was a fuel issue, would it not stumble? There is no stumble just flattens out on power!
 
Are you running with the cut outs open ? My combo was a 451 with shu's tri-y's.373 gears and running full exhaust it ran 13o's 3600 lbs 65 Belvedere. With open tri-y's,18'' extensions, upped to 4.10's and slicks(26'') it ran 11.90's.Just for reference. 3.55's, what was the trap speed ? Just a guess, how far before you hit the stripe did you shift to high ? Last question, is it falling over at 5,100 and done or is it just not pulling as hard after 5,100 ?I know you mentioned it above,Just trying to think of things it could be. I lied,,one more question. Fuel pump ? mechanical,electric or both ?
 
It won't stumble because your using the fuel in the float bowls first, then your fuel supply can't keep up once your going.
 
Darter6 said:
Are you running with the cut outs open ? My combo was a 451 with shu's tri-y's.373 gears and running full exhaust it ran 13o's 3600 lbs 65 Belvedere. With open tri-y's,18'' extensions, upped to 4.10's and slicks(26'') it ran 11.90's.Just for reference. 3.55's, what was the trap speed ? Just a guess, how far before you hit the stripe did you shift to high ? Last question, is it falling over at 5,100 and done or is it just not pulling as hard after 5,100 ? I lied,,one more question. Fuel pump ? mechanical,electric or both ?
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Yes, just running with cutouts open! Trap speeds at 106-108 mph, shifting it in 3rd about 3/4 track! It is just not pulling after 5100, no pops, stumble or knocks, just like no more to give! Mechanical Carter high flow/high volume pump. Maybe I will try just extensions and more gear! Thanks!
 
Id like to see the time slip. 60 foot, and 1/8 mile et and mph. 106 to 108 should put you mid 12's unless you are getting a lot of tire slip on the launch throwing your mph high. How heavy is the car?
 
breakstuff said:
Id like to see the time slip. 60 foot, and 1/8 mile et and mph. 106 to 108 should put you mid 12's unless you are getting a lot of tire slip on the launch throwing your mph high. How heavy is the car?
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I stand corrected! 106-108 was my last 1/4 mile run last yr! (This was before head and cam change, I replaced old iron 546 heads with the ProComp aluminum heads.) Which was 12.6, but I have calculated my times from this yr on 1/8 mile, which was 8.4 at 83mph.
 
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Did it pull to 6 grand last year ? Before changes ?
 
Do you have jet extensions on the secondary jets? Run a temp fuel pressure gauge on the hood area to confirm fuel pressure at WOT.
I would toss the MP ignition box and put a MSD 6AL box in. Old OEM electronic distributor works fine. Make sure reluctor gap is .008
Agree headers are a choke point.
 
mderoy340 said:
Do you have jet extensions on the secondary jets? Run a temp fuel pressure gauge on the hood area to confirm fuel pressure at WOT.
I would toss the MP ignition box and put a MSD 6AL box in. Old OEM electronic distributor works fine. Make sure reluctor gap is .008
Agree headers are a choke point.
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Yes, I have jet extensions on secondaries.
 
headers (with dumps) are not choking, FAST guys are running low 10's through manifolds. A donut says your fuel delivery is suspect. 2nd guess would be ignition. ignition is easier to swap out with another box. FBO says MP boxes do a number on advance, ie. pulling timing out at higher RPM's/ I guess you could crutch that by bumping your timing up a few degrees before a test run to see if it helps any.
 
Double check all of the easy stuff before you start swapping parts. Are you 100% positive that the throttle blades are wide open? I've seen a ton of cars where the throttle linkage is not properly adjusted. A lot of people make this mistake. Have you checked your cranking compression? Leak down? Double checked your firing order and spark plugs and wires? There doesn't seem to be anything wrong with your engine design. That cam is big enough to make power, those headers are fine for your power level, those heads are bigger than you need but shouldn't be causing an issue. The compression is in the right range. So it has to be some sort of tuning issue. You are running out of fuel, or the ignition isn't working at higher speeds, or the lifters are collapsing, or you have some other little thing wrong. A poorly adjusted throttle cable can cost you 50 hp pretty easily for example.
 
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