No Power past 6,200 RPM?

[451Mopar]

I'm a new guy on the Drag Racing Forum, My name is Jim and here is my Problem:
I have a street/strip '71 Charger with a 451 stroker engine. When I race it seems to run best when I shift at only at 6,200 RPM?
I was expecting to shift at 6,500 RPM or above, so my question is what is holding back the engine?

The 400 engine stroked with 440 crank and rods, Ross 11:1 pistons, stage 1 ported B-1 B/S heads from Koffels. I think it may be the unported M1 single plane intake with 4150 Holley flange toped by a 1000+ cfm pro-series carb (and a 1" carb spacer). Or it may be my cam is too mild with too much emphisis on mid range torque. The cam is a Ultradyne 284R Roller cam with 251 duration @ 0.050" lift, 108 lobe center, installed about 2 to 4 degrees advanved dependind on how it is measured. The valve lift is 0.613" using my 1.6:1 ratio rockers (0.620" lift at the ideal 1.6:1 ratio) that are closer to 1.58:1 ratio.

I don't think it is the fuel system, 20-gallon fuel cell, Mallory 250 gph pump, 500 gph filter 1/2" fuel line to bypass type regulator mounted at intake (1/2" return line). Regulator to carb is AN6 braided stainless line to each bowl, fuel pressure is good at 7 to 8 psi.
The headers are 2" primary Hooker super compition headers for a 440, with 3.5" collectors. The exhaust is 3.5" to 6" Dynomax race mufflers and turn downs at the rear axle. I will probbly replace this as it is LOUD!
The ignition system is a Mallory unilite triggering a MSD6AL with 7,000 RPM limit chip. The coil is a Crane PS91, and wires are Jacobs energy core. Timing is about 32-33 total (the B-1 heads do not seem run any better with more timming.)

I know I could use more cam, but I think the M1 intake is at it's limit already?
Whay do you think?

[DartGT66]

I think it's the cam that is at least partially holding the RPM's. We've got about same kind of package with the same intake, and it has no troubles going beyond 7000, so i don't think it's the intake. Your cam resembles the Comp Cams 308R street roller we used previously, even that pulled way better in the top end and was shifted at 7000. Oh, we've got the stage VI heads and therefore the wider RB intake, I think you are using the B engine intake? Have you put the recommended fuel distribution tabs in to the manifold?

[RRunnerN9]

are your valvesprings rated for your cam? you might be floating them if there too weak!! you said your running 1/6 rockers, you have increased your lift and are putting more bind on springs.

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I have some fear if you have no fear your not going fast enough!!!

[This message has been edited by RRunnerN9 (edited September 13, 2000).]

[451Mopar]

The springs are rated for a 0.670" roller cam, and I am using the "B" intake.
The engine will rev fine past 6,200 RPM, but it dosen't make the car any faster.

The info in the info is helpful, as I have been considering getting a custom ground cam, probbly a split profile like 260/270 duration @ 0.050" and a wider lobe seperation like 112 degrees. This should really help the upper end without taking too much away from the bottom end, not to mention it would work better if I ever add Nitrous Oxide

[Dave A]

Jim,...here are a few things to check. Each of these has had me puzzled at one time. 1) confirm that the throttle cable isn't limiting your carb butterfly travel from opening fully. 2) Put in more advance, try about 35/36 degrees total, after say 3000 rpm. 3) Go back and confirm the setup (advanced/retarded) for your cam at #1 intake lobe, tdc,... this can get your lost at tuning time. 4) Are you sure that your torque converter isn't so tight that it won't spin above 6,200 or you just don't have any pull beyond that? What rpm do you launch at? Do you have a transbrake? 5) What color are your plugs after a lap, paper bag brown or darker? 6) Can you start adding/subtracting clearance on the cam (don't go beyond .004" from recommended setting in .002 increments) and see if that influences your run times? While you're at it double check your rocker/ valve stem clearance. OH, make sure that the pushrods are the correct length by the rockers be centered on the valve stem at max lift. Are you using lash caps? 7) Are you using the six pack rods? 8) I think someone else mentioned about checking your valve springs for coil bind, check to see what the seated height(length)is for the spring specs and verify you're not hitting the valve stem seals with the retainers or locks. OK, there may be something of a answer or direction to look in the above list or maybe none of it applies but don't get discouraged. Your motor should be making the most power at about 6200 as it's similar to mine. When you get this figured out the smiles will erase the anxiety you are having for the moment. Don't throw on the nitrous quite yet.

[451Mopar]

Throttle cable is adjusted correctly. For reference, I'm using the LoKar throttle cable and trans kickdown cable setup.
I tried more advance and it din't help.
I checked the installed potition of the cam and is is installed per spec on the timming card when using the intake valve opening point. The Cam card says it should now be at 102 degrees, but if I use the centerline method, I get closer to 105 to 106 degrees (because the ramps are not the same profile.)
The valve train seems fine, no problems for over a thousand miles.

I think my jetting may be slightly lean, and maybe I should use a colder spark plug. I have the C63YC champions now. I have noticed that the #1 cylinder seems to run leaner than the rest of the cylinders? There are no fuel dams in the intake, it is stock.

Like I said, the engine will run easely upto 7,000 rpm, it just dosen't make the car any faster. I am just looking for a bit more top end power.

Some things I forgot, This is a 4,150 lb street car that I race every once in awhile at Bandimere in Morrison, Colorado (6,000 Ft Altitude?) I do not have a hood scoop or fresh are intake, just the under hood air. The axle ratio is 3.91:1 and the rear tires are Mickey Thompson Street ET 11.5"x26" on 10"x15" rims.
I have a 10" Dynamic converter, but I leave at 1,500 RPM because any higher launch somkes the tires. I run 12.6's at 110 MPH pretty consistently with a best ET of 12.4.
My 60' times are pretty bad, usually 1.83 to 1.89.

[modogg360]

Whew that is one big cylinder head for the combo ,you state 11.0 to one compression , by using an aluminum head thats a loss of a compression by 1 point(heat dissapation) then running at a 6000 ft altitude, boy it could be an 8 to one engine,compression is torque and then thats one big car . even though camshaft duration affects tourque and cylinder pressure id say its to small, duration should be 270+ . but again i really beleive you need 12.5+ compression and i could bet that machine will pick up at least .5 second . i race at LACR ca(3 to 5000 ft alt)so im not an engineer but i do have some experience . lastly i hope your running at least a 4.88 gear.

[340king]

I had a friend that used the unitlite ignition in a race application. He had trouble all the time. I asked my machinist/racing buddy if he had any experience with the Uniltie distributer and an MSD setup. He said he could not make it live for any length of time.

I recommend that you try using a stock electronic distributer in conjunction with your MSD to test this. I run phased, stock distributers in a couple of engines and can rev well past 7,000 rpm with 6AL boxes. Besides, it is a pretty cheap thing to try.

One other thing to note is how fast is your trans shifting? If it is a slow shifter, you may be actuating the shift at 6,200 rpm, but the actual shift occurs at something higher like 6,500 rpm. We had this problem and actually slowed down after a trans rebuild and addition of a brake, until we increased the shift rpm to compensate for the faster shifting.